Nondestructive Evaluation: Buried Pipe NDE Reference Guide—Revision 2

1025220

EPRI Project Manager

S. Kenefick

ELECTRIC POWER RESEARCH INSTITUTE

3420 Hillview Avenue, Palo Alto, California 94304-1338 • PO Box 10412, Palo Alto, California 94303-0813 • USA 800.313.3774 • 650.855.2121 • askepri@epri.com • www.epri.com

This document does NOT meet the requirements of 10CFR50 Appendix B, 10CFR Part 21,

ANSI N45.2-1977 and/or the intent of ISO-9001 (1994)

Nondestructive Evaluation: Buried Pipe NDE Reference Guide—Revision 2

1025220

Technical Update, December 2012

DISCLAIMER OF WARRANTIES AND LIMITATION OF LIABILITIES

THIS DOCUMENT WAS PREPARED BY THE ORGANIZATION NAMED BELOW AS AN ACCOUNT OF WORK SPONSORED OR COSPONSORED BY THE ELECTRIC POWER RESEARCH INSTITUTE, INC. (EPRI). NEITHER EPRI, ANY MEMBER OF EPRI, ANY COSPONSOR, THE ORGANIZATION BELOW, NOR ANY PERSON ACTING ON BEHALF OF ANY OF THEM:

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This is an EPRI Technical Update report. A Technical Update report is intended as an informal report of continuing research, a meeting, or a topical study. It is not a final EPRI technical report.

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This publication is a corporate document that should be cited in the literature in the following manner:

Nondestructive Evaluation: Buried Pipe NDE Reference Guide—Revision 2. EPRI, Palo Alto, CA: 2012. 1025220.

ACKNOWLEDGMENTS The following organization prepared this report:

Electric Power Research Institute (EPRI) 1300 West W.T. Harris Blvd. Charlotte, NC 28262

Principal Investigator S. Kenefick

This report describes research sponsored by EPRI.

The following EPRI staff members contributed to or reviewed portions of this report:

Mike Blanchard Tim Eckert Bob Grizzi Kenji Krzywosz Pedro Lara Nathan Muthu Mike Quarry David Smith Jack Spanner Steve Swilley

EPRI thanks the following companies for providing pictures, information, or recommendations for this report:

AGR Group Field Operations, Inc. A. Hak Industrial Services Applied Research Associates Applus RTD USA Diakont Elite Pipeline Services General Electric Company Inspector Systems iTRobotics Inline Devices Mears Group, Inc. Olympus NDT Pure Technologies, Ltd. Quest Integrity Rosen Inspection Russell NDE Systems, Inc. TesTex, Inc. TSC Inspection Systems WesDyne International

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ABSTRACT The infrastructure of today’s fleet of nuclear power plants has been in place for several decades. Aging mechanisms have had time to potentially challenge the structural and leakage integrity of systems, structures, and components, such as buried piping and tanks. Instances of inadvertent release of fluid containing small amounts of radioactive effluents into the surrounding soil have resulted. Although it is not threatening public health and safety or compromising environmental protection, it has affected public confidence in the safe operation of nuclear power plants.

To address this, the Nuclear Strategic Issues Advisory Committee (NSIAC) issued Underground Piping and Tanks Integrity Initiative in August 2010. The goal of this initiative was to “provide reasonable assurance of structural and leakage integrity of in-scope underground piping and tanks, with special emphasis on piping and tanks that contains licensed materials.” Industry guidance on implementing this initiative is provided in Nuclear Energy Institute (NEI) document NEI 09-14, Guideline for the Management of Underground Piping and Tank Integrity. An overview of these requirements and industry references is included in this report.

Nondestructive evaluation (NDE) plays a significant role in meeting the initiative requirements. Although the nuclear power industry has successfully implemented NDE programs for decades to maintain safe and economic operations, it has limited experience in examining buried pipes. NSIAC recognized the need for development of buried pipe inspection technology and assigned the Electric Power Research Institute (EPRI) the responsibility of managing the research necessary to improve such technology. High-level EPRI advisors identified the need for buried pipe NDE information and directed EPRI to develop this report.

This report includes an overview of several commercially available NDE technologies that can be used to detect and characterize wall-loss damage in underground pipe. This includes basic theory of each of the NDE technologies, as well as an overview of the techniques, equipment, capabilities, and applications. Factors such as pipe access and cleanliness requirements, degradation mechanism, material type, and examination extent that must be considered in selecting the appropriate NDE technology are provided. Because delivery of NDE sensors is a major factor in examining buried pipe, a section on available remote delivery technology is provided.

This is the second revision of the report, and it replaces EPRI reports 1021626 and 1022930. Future revisions are planned to capture results of EPRI research, new information on NDE technology, and resolutions to NDE gaps as they are filled.

Keywords Buried pipe Electromagnetic remote field testing (RFT) Guided wave In-line inspection (ILI) Nondestructive examination (NDE) Nuclear Energy Institute (NEI) 09-14 Underground Piping and Tanks Integrity Initiative

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CONTENTS 1 INTRODUCTION .................................................................................................................... 1-1

1.1 Conversion Factors ........................................................................................................ 1-4 1.2 Abbreviations and Acronyms ......................................................................................... 1-4

2 BURIED PIPE ASSESSMENT OVERVIEW ........................................................................... 2-1 2.1 Initiative Implementation Schedule ................................................................................ 2-1 2.2 Procedures and Oversight ............................................................................................. 2-4 2.3 Risk Ranking and Prioritization ...................................................................................... 2-4 2.4 Inspection Plan............................................................................................................... 2-8

3 NDE OVERVIEW AND SELECTION ...................................................................................... 3-1 3.1 Buried Pipe Discontinuities ............................................................................................ 3-1

3.1.1 Corrosion ............................................................................................................... 3-4 3.1.2 Erosion .................................................................................................................. 3-5 3.1.3 Internal Loads ....................................................................................................... 3-5 3.1.4 External Loads ...................................................................................................... 3-5 3.1.5 Mechanical or Design Defects .............................................................................. 3-6 3.1.6 Occlusion .............................................................................................................. 3-6 3.1.7 Failure Mechanisms .............................................................................................. 3-6

3.2 NDE Technology Overview ............................................................................................ 3-7 3.2.1 Ultrasonic Examination Overview ......................................................................... 3-7 3.2.2 Guided Wave Overview ........................................................................................ 3-7 3.2.3 Remote Field Testing Overview ............................................................................ 3-7 3.2.4 Magnetic Flux Leakage Overview ......................................................................... 3-8 3.2.5 Electromagnetic Technology Overview ................................................................. 3-8 3.2.6 Radiography Overview .......................................................................................... 3-8 3.2.7 Visual Testing Overview ........................................................................................ 3-8 3.2.8 Laser Profilometry Overview ................................................................................. 3-9 3.2.9 Leak Detection Overview ...................................................................................... 3-9 3.2.10 Other NDE Technologies .................................................................................... 3-9

3.3 NDE Selection Guidance ............................................................................................. 3-10 3.4 Additional Resources ................................................................................................... 3-14

4 ULTRASONIC TECHNOLOGY .............................................................................................. 4-1 4.1 Ultrasonic Wall Thickness Capability Summary ............................................................. 4-1 4.2 Ultrasonic Thickness Measurement Techniques ........................................................... 4-3

4.2.1 Ultrasonic Piezoelectric Contact Technique .......................................................... 4-3 4.2.2 Ultrasonic EMAT Technique ................................................................................. 4-4

4.3 Signal Displays and Calibration ..................................................................................... 4-5 4.3.1 Thickness Measurement Considerations .............................................................. 4-9

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4.4 Piezoelectric Ultrasonic Transducers ........................................................................... 4-10 4.4.1 Contact Transducers ........................................................................................... 4-12 4.4.2 Delay Line Transducers ...................................................................................... 4-12 4.4.3 Immersion Transducers ...................................................................................... 4-12 4.4.4 Dual-Element Transducers ................................................................................. 4-12

4.5 Electromagnetic Acoustic Transducers ........................................................................ 4-13 4.6 Linear Phased Array .................................................................................................... 4-16 4.7 Ultrasonic ILI Tools ...................................................................................................... 4-23

4.7.1 Flow-Through In-Line Ultrasonic Array ............................................................... 4-23 4.7.2 Flow-Through In-Line Rotating Ultrasonic Transducer........................................ 4-26 4.7.3 Robotic Driven In-Line Rotating Ultrasonic Transducer ...................................... 4-27 4.7.4 Robotically Driven In-Line Rotating EMATS Ultrasonic Probe ............................ 4-28 4.7.5 Roboticaly Driven In-Line Circumferential Lamb Wave ....................................... 4-30

4.8 Ultrasonic Monitoring Technology ................................................................................ 4-34 4.9 Other Zero-Degree Piping Applications ....................................................................... 4-35

5 GUIDED WAVE ULTRASONIC TESTING ............................................................................. 5-1 5.1 Guided Wave Wall Thickness Capability Summary ....................................................... 5-2 5.2 Principles of Guided Wave Ultrasonic Testing ............................................................... 5-4

5.2.1 Guided Wave Sensors .......................................................................................... 5-6 5.3 Data Analysis ............................................................................................................... 5-10 5.4 Project Management .................................................................................................... 5-14 5.5 Deployment Outside the Pipe ...................................................................................... 5-14 5.6 Deployment for Monitoring ........................................................................................... 5-17

6 REMOTE FIELD TESTING ..................................................................................................... 6-1 6.1 Remote Field Wall Thickness Capability Summary ....................................................... 6-2 6.2 Instrumentation for RFT ................................................................................................. 6-4 6.3 Pipe Threats Examined with RFT .................................................................................. 6-5 6.4 Advantages, Disadvantages, and Limitations of RFT .................................................... 6-5 6.5 Deployment Outside the Pipe ........................................................................................ 6-6 6.6 Deployment Inside the Pipe ........................................................................................... 6-6 6.7 Signal Analysis for In-Line Operations ........................................................................... 6-7

6.7.1 RFT of Prestressed Concrete Pipe for Wire Failures ............................................ 6-8

7 MFL TECHNOLOGY .............................................................................................................. 7-1 7.1 MFL Wall Thickness Capability Summary ...................................................................... 7-2 7.2 High-Resolution MFL ..................................................................................................... 7-4 7.3 MFL Sensors and Calibration ......................................................................................... 7-7 7.4 Data Analysis ................................................................................................................. 7-7

7.4.1 Nonrelevant Signals Caused by Magnetic Permeability or Stress Changes ......... 7-9 7.4.2 Thin Crack-Like Defects ...................................................................................... 7-10

7.5 Deployment Outside the Pipe ...................................................................................... 7-10 7.6 Deployment Inside the Pipe ......................................................................................... 7-11

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8 ELECTROMAGNETIC TECHNOLOGY (FERROMAGNETIC) .............................................. 8-1 8.1 Pulsed Eddy Current Technology .................................................................................. 8-1

8.1.1 Pulsed Eddy Current Wall Thickness Capability Summary ................................... 8-2 8.1.2 Pulsed Eddy Current Overview ............................................................................. 8-4 8.1.3 Broadband Electromagnetic Method ..................................................................... 8-7

8.2 LFET, E-PIT, and SLOFEC Wall Thickness Capability Summary ................................. 8-8 8.3 The E-PIT Tool ............................................................................................................. 8-10

8.3.1 Through-Transmission Array Probe .................................................................... 8-12 8.4 LFET ............................................................................................................................ 8-14 8.5 SLOFEC Testing .......................................................................................................... 8-17

8.5.1 Applications of SLOFEC ..................................................................................... 8-19 8.6 Alternating Current Field Measurement ....................................................................... 8-22 8.7 Magnetic Tomography Method .................................................................................... 8-25 8.8 Concentric Magnetic Field ............................................................................................ 8-25 8.9 Meandering Wire Magnetometer .................................................................................. 8-26

9 RADIOGRAPHIC TESTING TECHNOLOGY ......................................................................... 9-1 9.1 Radiography Wall Thickness Capability Summary ........................................................ 9-2 9.2 Radiation Sources .......................................................................................................... 9-4 9.3 Formation of a Radiographic Image ............................................................................... 9-6

9.3.1 Film-Based Radiography ....................................................................................... 9-6 9.3.2 Digital Radiography ............................................................................................... 9-6 9.3.3 Comparison of Digital and Conventional Radiography.......................................... 9-9

9.4 Radiographic Examination Techniques ........................................................................ 9-10 9.5 Pipeline Examination Using Radiography .................................................................... 9-10

9.5.1 Radiographic Detection of Thinning .................................................................... 9-12 9.5.2 Radiography of Welds ......................................................................................... 9-15

10 VISUAL TESTING TECHNOLOGY .................................................................................... 10-1 10.1 Optical Aids Used for Visual Examination .................................................................. 10-1 10.2 Application and Use of Visual Testing ........................................................................ 10-1 10.3 Factors Affecting Visual Testing ................................................................................. 10-2

10.3.1 Cleanliness ........................................................................................................ 10-2 10.3.2 Luminescence and Surface Conditions ............................................................. 10-2 10.3.3 Test Object Effects ............................................................................................ 10-3

10.4 Deployment Outside the Pipe .................................................................................... 10-3 10.4.1 Pit Gauging ....................................................................................................... 10-3

10.5 Deployment Inside the Pipe ....................................................................................... 10-5 10.5.1 Rigid Borescopes .............................................................................................. 10-5 10.5.2 Fiber-Optic Borescopes .................................................................................... 10-6 10.5.3 Special-Purpose Borescopes ............................................................................ 10-6

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10.5.4 Video Borescopes ............................................................................................. 10-7 10.5.5 Remote Positioning and Transport Systems ..................................................... 10-7

10.6 Deployment Above the Pipe ....................................................................................... 10-9 10.7 Deployment for Monitoring ......................................................................................... 10-9

11 LASER PROFILOMETRY TECHNOLOGY ........................................................................ 11-1 11.1 Laser Profilometry Wall Thickness Capability Summary ............................................ 11-1 11.2 Principles of Laser Profilometry ................................................................................. 11-3 11.3 Laser Profilometry Capabilities .................................................................................. 11-4

11.3.1 Limitations of Laser Profilometry ....................................................................... 11-4 11.4 Pipeline Corrosion ...................................................................................................... 11-5 11.5 Deployment Inside the Pipe ....................................................................................... 11-6

12 LEAK DETECTION TECHNOLOGY .................................................................................. 12-1 12.1 Deployment Outside the Pipe .................................................................................... 12-2 12.2 Deployment Inside the Pipe ....................................................................................... 12-2 12.3 Deployment Above the Pipe ....................................................................................... 12-3 12.4 Deployment for Monitoring ......................................................................................... 12-3

13 ILI TECHNOLOGY ............................................................................................................. 13-1 13.1 Flow-Conveyed (Free-Swimming) Tools .................................................................... 13-2 13.2 Cable-Pulled or Tethered Vehicles ............................................................................ 13-6 13.3 Guide-Wire-Propelled Tools ....................................................................................... 13-7 13.4 Robotically Driven or Tractor Tools ............................................................................ 13-9

13.4.1 Manned Vehicles for Large-Bore Pipes .......................................................... 13-12 13.5 Access Considerations ............................................................................................. 13-13 13.6 Cleaning ................................................................................................................... 13-14

14 CONCLUSIONS ................................................................................................................. 14-1

15 REFERENCES ................................................................................................................... 15-1 15.1 In-Text Citations ......................................................................................................... 15-1 15.2 Recommended Reading—General NDE Concepts and Guidelines .......................... 15-2 15.3 Recommended Reading—MFL .................................................................................. 15-4 15.4 Recommended Reading—Eddy Current Testing ....................................................... 15-5 15.5 Recommended Reading—Pulsed Eddy Current Testing ........................................... 15-6 15.6 Recommended Reading—Conventional Radiographic Testing ................................. 15-7 15.7 Recommended Reading—Digital Radiographic Testing ............................................ 15-8 15.8 Recommended Reading—Visual Examination .......................................................... 15-9 15.9 Recommended Reading—Laser Profilometry .......................................................... 15-10 15.10 Recommended Reading—Magnetic Particle Testing ............................................ 15-11 15.11 Recommended Reading—ACFM ........................................................................... 15-12 15.12 Recommended Reading—ILI Tools ....................................................................... 15-13 15.13 Recommended Reading—RFT .............................................................................. 15-13 15.14 Recommended Reading—Liquid Penetrant Examination ...................................... 15-14

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LIST OF FIGURES Figure 3-1 Three classifications for pitting corrosion of carbon steel pipe ................................. 3-2 Figure 3-2 External metal loss resulting from corrosion observed on steel pipe ....................... 3-3 Figure 3-3 Internal pipe corrosion .............................................................................................. 3-3 Figure 4-1 Application of ultrasonic straight beam examination ................................................ 4-3 Figure 4-2 Ultrasonic immersion technique ............................................................................... 4-4 Figure 4-3 An EMAT used to measure wall thickness on a coated pipe .................................... 4-5 Figure 4-4 Detection of an internal flaw with straight-beam ultrasonics ..................................... 4-6 Figure 4-5 Step wedge calibration block .................................................................................... 4-7 Figure 4-6 Examples of B-scan, C-scan, and D-scan displays .................................................. 4-8 Figure 4-7 Wall thinning picture and corresponding C-scan image ........................................... 4-9 Figure 4-8 Components of an ultrasonic straight-beam sensor ............................................... 4-11 Figure 4-9 Graphical representation of an ultrasonic beam ..................................................... 4-12 Figure 4-10 Basic configuration of an EMAT ........................................................................... 4-13 Figure 4-11 An EMAT .............................................................................................................. 4-14 Figure 4-12 An EMAT system .................................................................................................. 4-14 Figure 4-13 An EMAT signal .................................................................................................... 4-15 Figure 4-14 Generation of 100% coverage with an ultrasonic phased array ........................... 4-16 Figure 4-15 Phased array Sonatest WheelProbe .................................................................... 4-17 Figure 4-16 The closely spaced holes, and the resulting C-scan image of the holes

obtained with the wheel probe .............................................................................................. 4-18 Figure 4-17 Ultrasonic side view images of closely spaced holes obtained with the

WheelProbe .......................................................................................................................... 4-18 Figure 4-18 A field-removed corroded pipe and C-scan image obtained with the

WheelProbe in the vacinity of the picture .............................................................................. 4-19 Figure 4-19 Phased array Olympus HydroFORM .................................................................... 4-20 Figure 4-20 Phased array Olympus HydroFORM with pipe scanner ....................................... 4-20 Figure 4-21 An example of internal corrosion image obtained with the HydroFORM

phased array probe ............................................................................................................... 4-21 Figure 4-22 Photograph of external corrossion in a field-removed pipe and resulting

images obtained with the HydroFORM probe ....................................................................... 4-22 Figure 4-23 A fixed transducer array ILI tool ............................................................................ 4-23 Figure 4-24 EPRI 60-ft mockup ............................................................................................... 4-24 Figure 4-25 Localized thinning in EPRI mockup ...................................................................... 4-25 Figure 4-26 A dent and the resulting C-scan ........................................................................... 4-25 Figure 4-27 A. Hak Industrial Services flow-conveyed tool using a rotating mirror .................. 4-26 Figure 4-28 A. Hak Industrial Services small-diameter, flow-conveyed tool using a

rotating mirror ........................................................................................................................ 4-26 Figure 4-29 Applus RTD pipeline inspection tool ..................................................................... 4-27 Figure 4-30 Applus rotating ultrasonic probe head .................................................................. 4-28 Figure 4-31 Diakont EMAT in-line pipe robotic crawler ........................................................... 4-29 Figure 4-32 Diakont EMAT data acquisition analysis screen ................................................... 4-30 Figure 4-33 Illustration of Lamb wave generation .................................................................... 4-31 Figure 4-34 WesDyne Lamb wave robotic crawler system ...................................................... 4-31 Figure 4-35 WesDyne Lamb wave data analysis display ........................................................ 4-33 Figure 4-36 An Innerspec Lamb wave scanner ....................................................................... 4-33 Figure 4-37 Applus RTD PermaFlex sensors installed on an acid regeneration column ......... 4-34 Figure 5-1 Schematic of a guided wave inspection concept ...................................................... 5-5 Figure 5-2 Teletest guided wave piping probe collar ................................................................. 5-6

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Figure 5-3 Guided Ultrasonics Ltd. guided wave piping probe collar ......................................... 5-7 Figure 5-4 Teletest torsional and longitudinal transducers module ........................................... 5-8 Figure 5-5 Guided Ultrasonics Ltd. torsional transducers .......................................................... 5-8 Figure 5-6 Magnetostrictive sensor guided wave probe ............................................................ 5-9 Figure 5-7 Different size defects having the same percent CSA ............................................. 5-11 Figure 5-8 Schematic of guided wave piping mockup ............................................................. 5-13 Figure 5-9 Guided wave data obtained from the piping mockup ............................................. 5-13 Figure 5-10 Excavated buried piping ....................................................................................... 5-15 Figure 5-11 A pipe penetrating a basement wall ..................................................................... 5-16 Figure 5-12 Removal of buried piping coating ......................................................................... 5-16 Figure 5-13 Permanently installed guided wave collar ............................................................ 5-18 Figure 6-1 Basic principle of remote field eddy current probe ................................................... 6-1 Figure 6-2 A tethered RFT tool .................................................................................................. 6-6 Figure 6-3 Deployment of a 3-in.-diameter RFT tool ................................................................. 6-7 Figure 6-4 RFT local wall loss indication ................................................................................... 6-8 Figure 6-5 Pure Technologies’ remote field eddy current/transformer coupling tool for

assessment of prestressed concrete piping ............................................................................ 6-9 Figure 7-1 Illustration of the MFL concept ................................................................................. 7-1 Figure 7-2 Illustration of a three-axis MFL ................................................................................. 7-5 Figure 7-3 Example of 3-D signal displays from a high-resolution three-axis MFL-type

system ..................................................................................................................................... 7-6 Figure 7-4 Example of 2-D signal displays for a high-resolution three-axis MFL-type

system for discontinuities of various depths ............................................................................ 7-6 Figure 7-5 MFL data analysis output provided with Inline Devices InSight data analysis

software, Example 1 ............................................................................................................... 7-8 Figure 7-6 MFL data analysis output provided with Inline Devices InSight data analysis

software, Example 2 ............................................................................................................... 7-8 Figure 7-7 MFL inspection on outside surface ......................................................................... 7-10 Figure 7-8 Inline Devices MFL ILI tool designed to go through elbows ................................... 7-11 Figure 7-9 Pure Technology expandable MFL ILI tool ............................................................. 7-12 Figure 8-1 Pulsed eddy current examples and uses .................................................................. 8-2 Figure 8-2 Principles of pulsed eddy current technique ............................................................. 8-5 Figure 8-3 Schematic showing decay of eddy current ............................................................... 8-6 Figure 8-4 BEM being manually applied inside a pipe ............................................................... 8-7 Figure 8-5 BEM inline device ..................................................................................................... 8-8 Figure 8-6 E-PIT sensor ........................................................................................................... 8-11 Figure 8-7 Sample data from a 4-in. E-PIT sensor .................................................................. 8-11 Figure 8-8 Through-transmission array probe for inspecting carbon steel pipe from the OD .. 8-12 Figure 8-9 No lift-off: 0.990-in.-diameter, 100% hole, 119 mV, 95° ......................................... 8-13 Figure 8-10 0.375-in. lift-off: 0.990-in.-diameter, 100% hole, 34 mV, 99° ................................ 8-13 Figure 8-11 LFET function schematic ...................................................................................... 8-15 Figure 8-12 Examples of LFET scanners ................................................................................ 8-16 Figure 8-13 LFET calibration waveform ................................................................................... 8-16 Figure 8-14 LFET waveform, showing two

flaws measuring 50% and 70% wall loss .............................................................................. 8-17 Figure 8-15 Principles of SLOFEC testing ............................................................................... 8-18 Figure 8-16 Comparison of relative detection capability of MFL and SLOFEC testing at

different wall thicknesses ...................................................................................................... 8-19 Figure 8-17 General Electric SLOFEC robot in the calibration tray ......................................... 8-20 Figure 8-18 End view of the General Electric SLOFEC robot .................................................. 8-20 Figure 8-19 SLOFEC sensor ................................................................................................... 8-21

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Figure 8-20 SLOFEC robot being inserted into a 24-in. pipe through a 20-in.-long opening ... 8-21 Figure 8-21 EPRI 24-in.-diameter mockups ............................................................................. 8-22 Figure 8-22 Induction coils above a metallic plate ................................................................... 8-23 Figure 8-23 Eddy currents flowing around a fatigue crack ....................................................... 8-23 Figure 8-24 Types of AC field measurement probes ............................................................... 8-24 Figure 8-25 Meandering wire magnetometer array and details of the loops embedded

within the array ...................................................................................................................... 8-26 Figure 9-1 Schematic of basic principle of industrial radiography .............................................. 9-2 Figure 9-2 Isotope source being deployed ................................................................................. 9-5 Figure 9-3 Electronic source exposure arrangement ................................................................. 9-5 Figure 9-4 Digital radiography .................................................................................................... 9-8 Figure 9-5 Uses of industrial radiography for pipeline inspection ............................................ 9-11 Figure 9-6 Graphic representation of tangential and double-wall exposure, single-wall

viewing techniques ................................................................................................................ 9-13 Figure 9-7 Radiographic image of tangential technique on insulated piping ........................... 9-14 Figure 9-8 Double-wall technique on insulated pipe ................................................................ 9-15 Figure 9-9 Radiographic image of double-wall-exposure, single-wall viewing ......................... 9-15 Figure 10-1 Location grid (0.5-in. grid) marked on pipe with external corrosion during

direct examination ................................................................................................................. 10-4 Figure 10-2 Deployment of digital pit gauge on metal surface ................................................. 10-4 Figure 10-3 Borescope fundamentals ...................................................................................... 10-5 Figure 10-4 Pipeline crawler .................................................................................................... 10-9 Figure 11-1 Laser profiler scanning a pipe surface .................................................................. 11-1 Figure 11-2 Schematic of laser triangulation method .............................................................. 11-4 Figure 11-3 A corrosion map generated by laser profilometry ................................................. 11-5 Figure 11-4 Video and laser inspection, tractor-conveyed ILI vehicle ..................................... 11-6 Figure 13-1 Design elements of an ILI tool .............................................................................. 13-2 Figure 13-2 A flow-conveyed ILI tool ....................................................................................... 13-3 Figure 13-3 A typical, permanent pig launcher–receiver configuration .................................... 13-3 Figure 13-4 A temporary launcher for a flow-conveyed ILI tool ............................................... 13-4 Figure 13-5 A bidirectional, flow-conveyed ILI tool .................................................................. 13-4 Figure 13-6 Gauging pig .......................................................................................................... 13-5 Figure 13-7 Flow-conveyed ILI tool inside a temporary launcher with a fiber-optic data

cable ..................................................................................................................................... 13-6 Figure 13-8 A cable-pulled vehicle ........................................................................................... 13-7 Figure 13-9 Guide-wire propulsion used in the EPRI concept vehicle ..................................... 13-8 Figure 13-10 Multiple-drive-wheel, robotically conveyed ILI tool ............................................. 13-9 Figure 13-11 Deployment of a robotically conveyed ILI tool into a buried pipe ..................... 13-10 Figure 13-12 Pipe system examined with a robotically driven ILI tool ................................... 13-10 Figure 13-13 Robotically driven ultrasonic ILI tool for large-diameter pipe ............................ 13-11 Figure 13-14 The EPRI large-bore, instrumented vehicle ...................................................... 13-12 Figure 13-15 Foam-core cleaning pigs .................................................................................. 13-15

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LIST OF TABLES Table 1-1 Conversion factors ..................................................................................................... 1-4 Table 2-1 NEI 09-14 buried pipe implementation schedule ....................................................... 2-2 Table 2-2 NEI 09-14 underground piping and tanks integrity initiative implementation

schedule ................................................................................................................................. 2-3 Table 2-3 Risk ranking matrix .................................................................................................... 2-5 Table 3-1 Codes for variables and conditions .......................................................................... 3-10 Table 3-2 Selection of NDE technology for metal loss ............................................................. 3-12 Table 4-1 Ultrasonics: function .................................................................................................. 4-1 Table 4-2 Ultrasonics: deployment options ................................................................................ 4-2 Table 4-3 Ultrasonics: impact of surface and coating on results ............................................... 4-2 Table 4-4 Ultrasonics: applicable pipe materials ....................................................................... 4-2 Table 4-5 Ultrasonics: capability variables ................................................................................. 4-3 Table 5-1 Guided wave: function ............................................................................................... 5-2 Table 5-2 Guided wave: deployment options ............................................................................. 5-2 Table 5-3 Guided wave: impact of surface and coating on results ............................................ 5-3 Table 5-4 Guided wave: applicable pipe materials .................................................................... 5-3 Table 5-5 Guided wave: capability variables ............................................................................. 5-4 Table 5-6 Guided wave mode types .......................................................................................... 5-5 Table 5-7 Capabilities and limitations of guided waves ........................................................... 5-10 Table 6-1 Remote field: function ................................................................................................ 6-3 Table 6-2 Remote field: deployment options ............................................................................. 6-3 Table 6-3 Remote field: impact of surface and coating on results ............................................. 6-3 Table 6-4 Remote field: applicable pipe materials ..................................................................... 6-4 Table 6-5 Remote field: capability variables .............................................................................. 6-4 Table 7-1 MFL: function ............................................................................................................. 7-3 Table 7-2 MFL: deployment options .......................................................................................... 7-3 Table 7-3 MFL: impact of surface and coating on results .......................................................... 7-3 Table 7-4 MFL: applicable pipe materials .................................................................................. 7-4 Table 7-5 MFL: capability variables ........................................................................................... 7-4 Table 8-1 Pulsed eddy current: function .................................................................................... 8-3 Table 8-2 Pulsed eddy current: deployment options .................................................................. 8-3 Table 8-3 Pulsed eddy current: impact of surface and coating on results ................................. 8-3 Table 8-4 Pulsed eddy current: applicable pipe materials ......................................................... 8-4 Table 8-5 Pulsed eddy current: capability variables .................................................................. 8-4 Table 8-6 LFET, E-PIT, and SLOFEC: function ......................................................................... 8-9 Table 8-7 LFET, E-PIT, and SLOFEC: deployment options ...................................................... 8-9 Table 8-8 LFET, E-PIT, and SLOFEC: impact of surface and coating on results ...................... 8-9 Table 8-9 LFET, E-PIT, and SLOFEC: applicable pipe materials ............................................ 8-10 Table 8-10 LFET, E-PIT, and SLOFEC: capability variables ................................................... 8-10 Table 9-1 Radiography: function ................................................................................................ 9-3 Table 9-2 Radiography: deployment options ............................................................................. 9-3 Table 9-3 Radiography: impact of surface and coating on results ............................................. 9-3 Table 9-4 Radiography: applicable pipe materials ..................................................................... 9-4 Table 9-5 Radiography: capability variables .............................................................................. 9-4 Table 11-1 Laser profilometry: function ................................................................................... 11-2 Table 11-2 Laser profilometry: deployment options ................................................................. 11-2 Table 11-3 Laser profilometry: impact of surface and coating on results ................................ 11-2

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Table 11-4 Laser profilometry: applicable pipe materials ........................................................ 11-3 Table 11-5 Laser profilometry: capability variables .................................................................. 11-3 Table 12-1 Leak test limits of detection ................................................................................... 12-1

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1 INTRODUCTION The infrastructure of today’s fleet of nuclear power plants has been in place for several decades. Aging mechanisms have had time to potentially challenge the structural and leakage integrity of systems, structures, and components, such as buried piping and tanks. This has resulted in instances of inadvertent release of fluid containing small amounts of radioactive effluents into the surrounding soil. Although it is not threatening public health and safety or compromising environmental protection, it has affected public confidence in the safe operation of nuclear power plants.

To address this, the Nuclear Strategic Issues Advisory Committee (NSIAC), composed of the chief nuclear officers of all U.S. utilities, issued two initiatives to establish the nuclear industry expectations for buried piping. The first is the Industry Ground Water Protection Initiative, issued in 2007, which has a goal of preventing radioactive materials from migrating off-site [1]. The second initiative is the Guideline for the Management of Buried Piping Integrity, issued in November 2009 [2]. This initiative was revised to incorporate industry operating experience and was reissued as the Underground Piping and Tanks Integrity Initiative in August 2010 [3]. The goal of this initiative is to “provide reasonable assurance of structural and leakage integrity of in-scope underground piping and tanks, with special emphasis on components that contain licensed materials.”

These initiatives are high-level documents that establish the intent, roles and responsibilities, definitions, and implementation schedules of the program elements. The primary difference between them is that the Industry Ground Water Protection Initiative focuses on monitoring for and managing inadvertent radiological releases, and the Underground Piping and Tanks Integrity Initiative focuses on providing reasonable assurance of continued structural and leakage integrity [1, 3]. Because the Underground Piping and Tanks Integrity Initiative focuses on assessing component integrity, it has a significant nondestructive evaluation (NDE) component; therefore, this report focuses on it. Guidance on implementing the initiatives is provided in the following Nuclear Energy Institute (NEI) documents:

NEI 07-07, Industry Ground Water Protection Initiative—Final Guidance Document [1]

NEI 09-14, Guideline for the Management of Underground Piping and Tank Integrity [2]

NEI 09-14 was prepared by NEI, working in conjunction with the NEI Buried Pipe Integrity Task Force. The Buried Pipe Integrity Task Force is composed of buried pipe subject matter experts from several utilities, the Electric Power Research Institute (EPRI), and the Institute of Nuclear Power Operations. The task force reports to the Buried Pipe Integrity Working Group, which is led by an executive from the NSIAC. In addition to preparing NEI 09-14, the task force is responsible for addressing questions on NEI 09-14, preparing and reviewing reports to the NSIAC, and addressing initiative deviations. The roles and responsibilities for utilities, EPRI, the Institute of Nuclear Power Operations, Authorized Nuclear Inspectors, and the NEI are provided in NEI 09-14 and described in Section 2, Buried Pipe Assessment Overview. One of EPRI’s responsibilities is to manage the research necessary to improve inspection technology for underground piping and tanks.

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Although the nuclear power industry has successfully implemented NDE programs for decades to assess safety-related and non-safety-related components to maintain safe and economic nuclear power plant operations, it has limited experience in examining buried pipes. Many NDE processes that the industry uses are applied to examining pipe; however, it is impractical to apply them to buried pipe due to the lack of access to the pipe surface and the sheer volume of piping. Although the nuclear industry is at the initial stages of buried pipe assessment programs, other industries, such as the pipeline transmission, petrochemical, and water industries, have experienced issues with buried piping and, therefore, have more experience examining them. Although buried pipe in these industries certainly differs, there are enough similarities that the nuclear industry can gain from their experiences.

However, there are solutions. For instance, effective NDE can be conducted with internal inspection devices using conventional technologies such as ultrasonics, as well as nonconventional electromagnetic techniques. Remote NDE methods, such as guided wave technology, can be used to examine buried pipe sections from areas where the pipe is accessible. When buried piping is exposed, NDE techniques are available that can be used to examine large surface areas and through coatings. Also, specialized NDE techniques are available to detect pitting corrosion that might not be detectable with conventional methods.

EPRI advisors identified the lack of readily available information on buried pipe NDE information as an industry gap. To rectify this, the Nuclear Power Council requested that EPRI generate a report to provide an overview of available buried pipe NDE technologies that could potentially be used to meet the NSIAC initiative. EPRI worked closely with the NDE and the Balance of Plant Corrosion integration committees to develop a scope. Because of a very tight schedule, EPRI contracted the development of the initial draft of the report to a firm experienced in examining buried piping in other industries. The original version of this report was revised in 2011to make the report more nuclear power industry-specific and to capture new buried pipe NDE information. Future revisions are planned to capture results of EPRI research, new information on NDE technology, and resolutions to NDE gaps as they are filled. Much has happened with regard to buried pipe in the nuclear industry since the initial revision of this report. The NSIAC revised Guideline for the Management of Buried Piping Integrity to become Underground Piping and Tanks Integrity Initiative [3]. NEI 09-14 was revised to incorporate these changes as well as several other additions. With EPRI report 1021175, EPRI revised Recommendations for an Effective Program to Control the Degradation of Buried and Underground Piping and Tanks (1016456, Revision 1) [4]. NEI issued Industry Guidance for the Development of Inspection Plans for Buried Piping [5], which provides a technically based approach for development of inspection plans that establish reasonable assurance of structural and/or leakage integrity of buried piping through applying the results of indirect inspections and direct examinations. This information provides the basis for a nuclear power-specific buried pipe integrity assessment program. NEI plans to incorporate this into the next revision of NEI 09-14, which is scheduled for 2012.

An overview of NEI 09-14 requirements, an overview of the EPRI report 1021175, Recommendations for an Effective Program to Control the Degradation of Buried and Underground Piping and Tanks (1016456, Revision 1) [4], and information on an assessment program are provided in Section 2, Buried Pipe Assessment Overview.

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A significant revision of the initial report was published in 2011 that included replacing information from other industries with the new nuclear power industry information that had become available. Also, information pertaining to crack detection was removed because it was incomplete in the context of nuclear power applications. Significant new information pertaining to buried pipe NDE technology, capabilities, and industry experience was added to Sections 4 through 12. Further information pertaining to selecting NDE methods, along with a general overview of NDE technology, was developed and included in Section 3. Section 13, In-Line Inspection Technology, on NDE tool launching and retrieving options, was added.

This revision adds new information on NDE, industry developments, and experience throughout the report. For instance, new information on in-line magnetic flux leakage (MFL) technology that can be used in piping containing elbows, which make its use more viable in nuclear power industry, has been added to Section 7, MFL Technology. Another example is in-line robotic electromagnetic acoustic transducer (EMAT) ultrasonic technology, which has recently become available and is now scheduled to be used in a nuclear power plant in 2012. Technology using Lamb wave ultrasonics to examine from a fixed axial position around a circumference of a pipe has become available. Both of these technologies have been added to Section 4, Ultrasonic Technology. These are only a few of the technologies that have been added.

EPRI published report 1025219, Nondestructive Evaluation: Buried Pipe NDE Technology Assessment and Development Interim Report, in 2012. This report provides detection and characterization results of an assessment conducted to benchmark buried pipe NDE technologies. NDE data were collected in a controlled fashion on various EPRI mockups. The NDE results were then compared to the mockup truth. A statistical assessment of the performance was made for the following criteria:

Overall detection results

Detection by depth

Detection by discontinuity type

Detection by minimum extent

Detection false calls (number of nondegraded areas identified as degraded)

Depth sizing (along pipe axis)

Length sizing (along pipe circumference)

Axial discontinuity location

Circumferential discontinuity location

Detection and sizing repeatability

The project also supports technology implementations, provides resources for vendors to improve technologies and procedures, acquires and constructs mockups to assess and develop NDE technology, and supports the nuclear power industry in implementing buried pipe NDE technology.

EPRI will publish report 1025215, Inspection Methods for Tanks and Containment Liners, in 2012, which will be similar to this one except that it will provide information on NDE technology that can be used to examine tanks.

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Another good resource is EPRI report 1021470, Balance of Plant Corrosion —The Buried Pipe Reference Guide. This report provides additional information on topics such as pipe degradation, cathodic protection, coatings, linings, locating buried pipe, water and soil analysis, coating surveys, concrete pipe inspection, excavation, fitness for service, repair, replacement, prevention, and mitigation. Because these technologies cover most of the commercially available options, the report focuses on providing examples of these technologies. EPRI is not endorsing these vendors, only providing information learned in the process.

The information contained in this report is intended to provide an overview of some currently available buried pipe NDE technologies and is by no means exhaustive. Pictures and descriptions of certain equipment and process applications are for illustrative purposes only. EPRI does not endorse any product or services of the referenced suppliers.

1.1 Conversion Factors

Table 1-1 lists the measurements used in this report, along with conversion factors to convert them between U.S. measurements and International System of Units measurements.

Table 1-1 Conversion factors

Measurement Conversion

Distance

1 in. = 25.4 mm

1 ft = 0.3048 m

1 mm = 0.039 in.

1 km = 0.621 mi

1 mil = 25.4 μm

Flow 1 gpm = 3.785 L/m

Pressure 1 psi = 6.89 kPa

1 atm = 0.101 MPa

Speed 1 mph = 1.609 km/hour

Temperature °C = (°F - 32) × 5/9

°F = (°C × 9/5) + 32

1.2 Abbreviations and Acronyms

The following abbreviations and acronyms are used in this report:

ACFM alternating current field measurement

ANSI American National Standards Institute

ASNT American Society for Nondestructive Testing

API American Petroleum Institute

ASME American Society of Mechanical Engineers

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BEM broadband electromagnetic method

CSA cross-sectional area

EMAT electromagnetic acoustic transducer

E-PIT external pipeline integrity tool

EPRI Electric Power Research Institute

ID inside diameter

ILI in-line inspection

LFET low-frequency electromagnetic technique

MFL magnetic flux leakage

MIC microbiologically influenced corrosion

NACE National Association of Corrosion Engineers

NDE nondestructive evaluation

NEI Nuclear Energy Institute

NPS nominal pipe size

NSIAC Nuclear Strategic Issues Advisory Committee

OD outside diameter

RFT remote field testing

SLOFEC saturation low-frequency eddy current

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2 BURIED PIPE ASSESSMENT OVERVIEW This section provides a summary of the Underground Piping and Tanks Integrity Initiative and the associated NEI implementation guidance, NEI 09-14 [2, 3]. The stated goal of the initiative and NEI 09-14 is to “provide reasonable assurance of structural and leakage integrity of in-scope underground piping and tanks … [with] special emphasis on components that contain licensed materials” [2]. The Underground Piping and Tanks Integrity Initiative will accomplish the following:

Drive proactive assessment and management of the condition of piping and tanks that fall within the scope of the initiative

Ensure sharing of industry experience

Drive technology development to improve available techniques for inspecting and analyzing underground piping and tanks

Improve regulatory and public confidence in the industry’s management of the material condition of its underground tanks and piping systems

2.1 Initiative Implementation Schedule

The Underground Piping and Tanks Integrity Initiative contains the major elements, key attributes, and milestones that make up the U.S. nuclear power industry’s approach to underground piping and tank integrity [3]. Table 2-1 provides the major milestones, associated tasks, and due dates for the original buried pipe initiative elements. Table 2-2 provides the same information for the underground piping and tank initiative elements. The U.S. fleet had completed the first three milestones of the buried pipe portion of the initiative at the time this report was prepared.

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Table 2-1 NEI 09-14 buried pipe implementation schedule [2]

1. Procedures and Oversight—By June, 30, 2010:

Ensure clear roles and responsibilities including senior level accountability for the Buried Pipe Integrity Program.

Develop a Buried Pipe Integrity Program document and implementing procedures.

2. Risk Ranking—Risk rank buried piping segments by December 31, 2010. Risk Ranking shall incorporate the following attributes:

Pipe function

Pipe locations and layout

Pipe materials and design

Health of cathodic protection systems, if applicable

Based on the preceding data and other information, determine:

— The likelihood of failure of each piping segment

— The consequences of failure of each piping segment

A means to update the risk ranking as necessary

A database to track key program data, inspection results, and trends

3. Inspection Plan—By June 30, 2011, develop an inspection plan to provide reasonable assurance of integrity of buried piping. This plan shall include the following key attributes:

Identification of piping segments to be inspected

Potential inspection techniques

Inspection schedule for buried piping segments based on risk ranking

Assessment of cathodic protection, if applicable

4. Plan Implementation—Implementation of the Inspection Plan shall start no later than June 30, 2012. The condition assessment of buried piping containing radioactive material shall be completed by June 30, 2013.

5. Asset Management Plan—Inspection results shall be used as input to the development of an asset management plan for buried piping. This plan shall receive a high level of review and approval and will be in place by December 31, 2013.

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Table 2-2 NEI 09-14 underground piping and tanks integrity initiative implementation schedule [2]

1. Procedures and Oversight—By December 31, 2011

Identify the plant programs or measures that manage the material condition of components within the scope of the Underground Piping and Tanks Integrity Initiative.

Establish the necessary controls and implementing process to coordinate the applicable programs and measures and ensure that they meet the intent of the Initiative.

Establish clear roles and responsibilities including senior level accountability for implementation of the Underground Piping and Tanks Integrity Initiative.

2. Prioritization—Prioritize underground piping and tanks by June 30, 2012. Prioritization shall consider the following attributes:

Function

Locations and layout

Materials and design

Process fluid

Health of cathodic protection systems, if applicable

Based on the preceding data and other information, determine:

— The likelihood of failure of each component

— The consequences of failure of each component

A means to update the prioritization scheme as necessary

Process(es) to allow retrieval of key program data

3. Condition Assessment Plan(s)—By December 31, 2012 develop or identify existing condition assessment plans that will provide reasonable assurance of integrity of components within the additional scope of the Underground Piping and Tanks Integrity Initiative. These plans shall include the following key attributes:

Identification of underground piping and tanks to be assessed

Potential assessment techniques

Assessment schedules that take into account the relative priority of components. This schedule should be coordinated with the schedule developed for the original Buried Piping Integrity Initiative to ensure that the components with the highest overall priority are addressed first.

Assessment of cathodic protection, if applicable

4. Plan Implementation—Implementation of the Condition Assessment Plan for underground piping and tanks shall start no later than June 30, 2013. The condition assessment of underground piping and tanks containing radioactive material shall be completed by June 30, 2014.

5. Asset Management Plan—Inspection results shall be used as input to the development of asset management plans for components within the scope of the Underground Piping and Tanks Integrity Initiative. These plans shall receive a high level of review and approval and will be in place by December 31, 2014.

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2.2 Procedures and Oversight

Buried pipe programs, procedures, and the oversight necessary to implement a successful program are now in place at all U.S. plants. EPRI report 1021175, Recommendations for an Effective Program to Control the Degradation of Buried and Underground Piping and Tanks (1016456, Revision 1), identified key elements of such a program, including management’s objectives, financial commitment, interface with other key programs, process development, definition of roles and responsibilities, qualification and training requirements, and reporting and trending results [4]. Refer to the report for details.

2.3 Risk Ranking and Prioritization

The second buried pipe milestone entails the completion of a risk ranking for all in-scope buried piping. Nuclear industry piping systems carry a variety of fluids, including water, gases, and oils, and are typically designed and constructed in accordance with codes and standards (American Society of Mechanical Engineers [ASME], American National Standards Institute, American Water Works Association, and so on) providing a margin of safety, principally with respect to release of product due to leakage. Many nuclear plant piping systems include buried piping, which can amount to miles of in-scope piping. Buried pipe can be buried close to the surface or more than 40 ft deep. It can be buried in hard-to-reach areas such as under buildings, parking lots, or other plant structures, and in some cases, it is encased in concrete.

Although some of these piping systems transport water and gas that contain radioactive effluents such as tritium or are nuclear safety-related, most do not contain sensitive materials and are not safety related. The failure consequence of a noncritical pipe that does not contain radioactive effluents or environmentally sensitive material might be insignificant. Random or low-value excavations and inspections of buried pipe can damage other buried commodities and create more consequential hazards. Inspection of pipe beneath or near buildings can impact safe plant operations and maintenance. Therefore, it is pertinent to risk rank the piping to determine which areas should be further assessed.

Risk ranking is a method to assess the likelihood and consequence of a postulated failure [6]. The risk ranking process for the Buried Piping Integrity Initiative should meet the intent of EPRI report1021175, Recommendations for an Effective Program to Control the Degradation of Buried and Underground Piping and Tanks (1016456, Revision 1) [4]. Risk ranking is recognized as an acceptable practice in ASME Code Case N-560-2 for selecting ASME class 1 piping welds for examination. This process considers probability and consequences of failure, focusing on elements in the highest risk group—probability considers relevant degradation mechanisms, and consequence considers break size and operating mode with the highest impact on plant safety. The output of a risk ranking could fall into the categories shown in Table 2-3.

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Table 2-3 Risk ranking matrix

Risk Groups

High—Cat 1, 2, 3

Medium—Cat 4, 5

Low—Cat 6, 7

Consequence Category

None Low Medium High

Failu

re Po

tential

High Cat 7 Cat 5 Cat 3 Cat 1

Medium Cat 7 Cat 6 Cat 5 Cat 2

Low Cat 7 Cat 7 Cat 6 Cat 4

Software can be used to risk rank buried piping systems. One such software that has been used to risk rank buried pipe is the EPRI BPWORKS1 program. Material, design, and operations variables for a piping segment are input to the software. The BPWORKS program calculates both the likelihood and the consequence of a failure based on the data provided, using a points-based approach.

A susceptibility model considers each degradation mechanism based on the relevant variables (such as temperature, material, and chemistry). For each segment, the inside surface susceptibilities are combined (microbiologically influenced corrosion [MIC], pitting, stress corrosion cracking, and so on), as are the outside surface susceptibilities. These susceptibilities are adjusted based on any leak history and any wall thickness inspection data. The resulting number of points is used to determine the individual likelihood (low, medium, or high) of failure. The likelihood models consider such variables as the following:

Inside diameter (ID) leak (degradation initiated from the fluid side)

— Microbiologically influenced corrosion

— Stress corrosion cracking

— Non-MIC pitting

ID break

— Microbiologically influenced corrosion

— Stress corrosion cracking

— Non-MIC pitting

— Water hammer

— Cavitation

1 BPWORKS is a registered trademark of EPRI.

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ID occlusion

— Tuberculation

— Bivalve attachment

Outside diameter (OD) leak (degradation initiated from the soil side)

— Microbiologically influenced corrosion

— Stress corrosion cracking

— Non-MIC pitting

OD break

— Microbiologically influenced corrosion

— Stress corrosion cracking

— Non-MIC pitting

— Ground settlement

— Building settlement

— Unmitigated heavy surface loads

Likelihood data input include such variables as the following:

Design information

— Operating pressure and temperature

— Pipe diameter and wall thickness

— Required pipe wall thickness

— Installation date

Fabrication data

— Pipe material

— Joint type, including use of backing rings

— Post-weld heat treatment

Linings and coatings

— Types of lining and coatings used

— Lining or coatings survey or inspection data

Fluid information

— Line content and water treatments

— Flow velocity

— pH, sulfides, chlorides, and so on

Soil and burial conditions

— Soil resistivity and redox potential (summer and winter)

— Soil moisture, pH, chlorides, sulfides (summer and winter)

— Depth and trench fill material

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Cathodic protection

— Type of cathodic protection used

— Cathodic protection operational history (operating within National Association of Corrosion Engineers [NACE] limits)

— Cathodic protection system surveys or inspection interval

System or line history

— Results of previous inspections (external or internal)

— Leak, break or repair history

— Water hammer or cavitation events

Ground or building settlement

For consequence, points are assigned to each of the following considerations:

Safety class

Failure effect on safe shutdown or core damage frequency

Failure result in radioactive ground contamination

Failure result in nonradioactive ground contamination

Failure result in airborne emissions

Failure can effect worker safety

Leak or break flow can be made up

Line has leak detection system

Line service >1 unit

Cost of repair

Failure can cause collateral damage

Failure will result in lost generation

Failure requires operator workaround or long-term modification

The points are summed for each segment, and the total number of points is used to determine the level of consequence (none, low, medium, or high).

Although risk ranking is a good tool, it is only one of a variety of inputs that are used in developing an inspection plan. The risk ranking process does not provide a specific list but does highlight areas of significant susceptibility and consequence. Other tools or inputs that can be used include the following:

Pipe-to-soil potential measurements of the cathodic protection system show a location to be outside NACE-recommended criteria

Over-the-line surveys (such as DC voltage gradient or AC current attenuation) identify a location that might have significant degradation to the coating

Plant experiences (internal and external)

Trending of past inspection results

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Areas that industry experience has found to be of higher risk (such as locations where the pipe enters or exits the soil)

Results of guided wave ultrasonic examinations

Results of ID visual examinations (crawlers and borescopes—for cases where ID degradation is a significant concern)

2.4 Inspection Plan

The purpose of the inspection plan is to support an assessment to provide reasonable assurance of the integrity of buried piping. The key phrase here is provide reasonable assurance, because it is difficult to define such a process. A subset of the NEI Buried Pipe Integrity Task Force was tasked with the responsibility of providing industry guidance on how this might be accomplished. The result was the publication of the NEI Buried Pipe Integrity Task Force document Industry Guidance for the Development of Inspection Plans for Buried Piping [5]. This document will be published in the 2012 revision of NEI 09-14. An excerpt from this document addresses reasonable assurance:

Reasonable assurance is an industry methodology used to achieve increased confidence in the capability of a structure, system or component (SSC) to perform its intended function. Reasonable assurance does not equate to absolute assurance or confidence. Rather, reasonable assurance collects appropriate data/insights/information to support the establishment of increased confidence. Situations may occur where sufficient data cannot be easily collected; in these cases, the available data may be supplemented with additional insights to bolster a technical foundation of reasonable assurance. If available information (even with supplemental insights) is insufficient to support a conclusion of reasonable assurance, then additional actions must be taken to achieve reasonable assurance. Ultimately, the establishment of reasonable assurance is the obligation of the owner. This guideline provides insights to achieve consistency among industry users to identify what actions are generally necessary to establish reasonable assurance for structural and/or leakage integrity for buried piping.

The stated purpose of this document is:

[T]o provide a technically based approach for development of inspection plans that establish reasonable assurance of structural and/or leakage integrity of buried piping through the application of the results of both indirect inspections and direct examinations. The approach is programmatically founded in the precepts established in the “Recommendations for an Effective Program to Control the Degradation of Buried and Underground Piping and Tanks (EPRI 1016456, Revision 1)” and utility site specific program documents. This document is intended to establish reasonable assurance for scoped buried piping systems; optimizing the inspection scope, while not requiring 100% inspection.

The purpose refers to indirect inspections and direct examinations, which have totally different implications and definitions. The significant difference in this document is that a direct examination is given much more credit in achieving reasonable assurance than an indirect inspection is given. Essentially, an indirect inspection is used to identify where a direct inspection should be conducted. A direct examination is used to assess the extent of corrosion

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activity identified by indirect inspections and confirm the effectiveness of the indirect results. Although it is not necessary to conduct indirect inspections, they can be used to reduce the number of direct examinations required. The definitions provided in Industry Guidance for the Development of Inspection Plans for Buried Piping are the following [5]:

Direct examination—An NDE examination where the NDE sensor(s) is in immediate contact with or in close proximity to the section of the component being examined. Results provide some degree of quantitative measurement of wall thickness or discontinuity size. Direct examinations can be performed from the interior or exterior surface. Detection and characterization capabilities vary by NDE method as well as by specific NDE technique. Examples of NDE methods include ultrasonics, eddy current, radiography, visual and various electromagnetic techniques. Visual examinations need to be supplemented with NDE or engineering judgment that addresses the condition of the pipe wall.

Indirect inspection—Survey techniques used to assess the likelihood of degradation without having direct access to the section of the component being examined. These inspections typically measure surrounding conditions that may be indicative of corrosion or damage. Results are typically qualitative and less accurate than direct examinations. Examples of indirect inspection methods include over-the-line surveys and for the purpose of this document, long range guided wave.

Under the guidance of this document, the risk ranking developed in the second milestone, and the generation of line groupings-based process fluid, an inspection plan is developed. The purpose of generating line groupings is to extrapolate inspection results from one or more examinations in the group to limit the number of inspections. Further separations of lines with similar physical attributes (such as material, coatings, line depths, soil, age, use of cathodic protection, operating condition and frequency, and pipe joining method) are considered. The methods of applying indirect inspections and using these results are described in detail. A detailed methodology for selecting the number of direct examinations and their locations is also presented.

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3 NDE OVERVIEW AND SELECTION This section provides an introduction to commercially available NDE technologies that can be used to examine piping for wall degradation. The nuclear industry has successfully applied NDE to many nuclear power applications, such as examination of welds in piping and vessel, turbine components, heat exchanger tubing, bolting, vessel internals, and so on. This includes using NDE to assess the integrity of piping systems for metal loss. For instance, the industry has, for more than two decades, relied on ultrasonics to identify and characterize flow-accelerated corrosion in piping. Although the NDE techniques used for this application have been successful, they cannot be applied to buried pipe due to a lack of access to the pipe wall surface and differing damage mechanisms.

NDE technique selection is often a compromise of component access, examination speed, detection capabilities and limitations, component preparation, and cost. Not all technologies will work in all applications. Capabilities vary by method and even by application. Proper method selection is based on the damage mechanism, desired sensitivity, and access to the pipe. Technology application will be limited by piping access and what defects must be detected. This section provides an overview of applicable NDE technologies and some guidance on technology selection. Because buried piping might be unearthed for other purposes such as coating inspections or might be otherwise accessible, the technologies presented in this report also include those that require access to the outside surface.

The shape and size of a discontinuity is an important variable in determining the NDE technology to use. For instance, if detection of a wide area of general corrosion is necessary, an ultrasonic process, similar to what is used for examinations for flow-accelerated corrosion, in which the pipe is gridded and readings are taken at grid points, would be in order. However, electromagnetic techniques that look for relative changes within an area might not be effective. Conversely, a gridded ultrasonic approach might not be as effective in detecting isolated pitting, whereas the electromagnetic approach looking for relative change would. Further, although a general ultrasonic approach might not detect isolated pitting, other ultrasonic approaches using specific transducer types or phased array-type probes might work well. Therefore, it is critical to select not only the correct technology but also the proper technology application.

3.1 Buried Pipe Discontinuities

The length and width of corrosion features are important factors related to the probability of detection performance for NDE technologies. The length and width of corrosion pits in steel can be characterized as narrow/deep (pinholes), elliptical, and shallow/wide (see Figure 3-1). Often, an external metal loss population due to corrosion might exhibit all three categories for depth-to-length aspect as pitting progresses from initiation to coalescence. The aspect ratio (depth to length or width) for corrosion pits can be affected by pipe metallurgy as well as the corrosion mechanism.

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Figure 3-1 Three classifications for pitting corrosion of carbon steel pipe

Understanding the damage pattern of a flaw mechanism is important not only for selecting an NDE technology but also for the method in which the technology is applied. For instance, examination techniques that could be used to detect and characterize the general corrosion shown in Figure 3-2 would be different from that for the smaller-diameter corrosion pits shown in Figure 3-3. The NDE sections that follow will provide information that can be used to help select the appropriate NDE technologies and techniques.

Narrow Deep

Elliptical

Shallow Wide

L or W

D

L or W

D

D

L or W

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Figure 3-2 External metal loss resulting from corrosion observed on steel pipe

Figure 3-3 Internal pipe corrosion

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EPRI report 1021175, Recommendations for an Effective Program to Control the Degradation of Buried and Underground Piping and Tanks (1016456, Revision 1), describes potential corrosion, erosion, loading, mechanical, and design damage mechanisms that could be encountered in buried pipe [4]. Because understanding flaw mechanisms is important in selecting and implementing NDE technology, the damage categories and descriptions are repeated in the following sections. Refer to the report for additional information.

3.1.1 Corrosion

Corrosion includes the following:

General corrosion is the most common form of corrosion. It is caused by the loss of electrons from an anode to a cathode in the presence of an electrolyte (such as water or moist soil). The locations of anodes and cathodes on the metal surface are constantly changing, leading to a relatively uniform and slow loss of wall thickness. Rust of mild steel in salt water is a common example. General corrosion rarely leads to leaks or failures on its own.

Localized corrosion, including pitting, underdeposit corrosion, and crevice corrosion, occurs when the anodes and cathodes are relatively stationary, leading to a localized but more aggressive wall loss. Localized corrosion can cause leaks, but it rarely causes loss of overall structural integrity.

Galvanic corrosion occurs when two dissimilar metals or different portions of the structure at different potentials are in contact in the presence of an electrolyte.

Selective leaching/dealloying results from one of the alloying elements selectively dissolving, leaving behind a porous and weakened structure. Graphitization of gray cast iron and dezincification of brass alloys are two common examples. Dealloying can degrade the structural integrity of the component.

Microbiologically influenced corrosion is not a separate form of corrosion but one in which the standard forms of localized corrosion (pitting, underdeposit corrosion, crevice corrosion, and so on) are accelerated by the presence of microbes. MIC can be initiated from either the fluid side or the soil side.

Stray current corrosion can occur at locations where there is an externally induced electrical current that is following a path other than the intended circuit. Accelerated corrosion will result at locations where the current is discharged.

Environmentally assisted cracking can result from an interaction of tensile stress, a susceptible material, the environment, and time. Environmentally assisted cracking can degrade the structural integrity of the component.

Embrittlement is a form of corrosion that mostly affects high-strength steels. Cathodic protection, galvanic corrosion, welding, and other processes can create conditions in which hydrogen atoms diffuse into the metal matrix and then recombine to form molecular hydrogen. The resulting pressure can cause loss of ductility, a reduction in tensile strength, and cracking.

3-5

3.1.2 Erosion

Erosion includes the following:

Cavitation is an erosive mechanism that occurs when a flowing fluid experiences a drop in pressure followed by a pressure recovery. If the local pressure falls below the vapor pressure, small bubbles are formed. As the pressure recovers, the bubbles collapse and create high local water jet velocities, which can cause metal removal.

Solid particle erosion occurs when abrasive particles (such as sand or volcanic ash) transported by the fluid strike a component surface at a sufficiently high velocity and cause metal removal.

Flashing. Although it is uncommon in buried and underground piping and tanks, flashing can occur in liquid-filled lines at locations where the pressure drop is large enough to generate vapor, which impacts the surface at a high velocity and erodes the surface.

Liquid droplet impingement. Although it is quite uncommon in buried and underground piping and tanks, liquid droplet impingement can occur in a flowing, two-phase fluid (such as wet steam) when high-velocity water droplets impact a component surface and cause metal removal.

3.1.3 Internal Loads

Internal loads include the following:

Internal pressure can create one of the conditions that cause environmentally assisted cracking to occur.

Severe pressure transients such as water hammer can cause a pipe burst.

3.1.4 External Loads

External loads include the following:

Earthquake. Seismic events can result in soil or building settlement and wave passage (soil strain). These loads can create overstress in piping and tank components.

Soil and building settlement. Improperly compacted soil can settle, and improperly designed foundations can result in building settlement, potentially resulting in significant stresses on buried piping and tanks.

Heavy surface loads. Unmitigated, heavy surface loads can cause large stresses on piping and tanks that are buried at relatively shallow levels.

Soil overburden. Overburden caused by improper design of thin-walled or deeply buried piping systems and tanks can result in high compressive stresses.

Frost heave. Lines can experience significant stresses where they pass through the frost line.

Nearby construction activities. Activities that change the soil compaction around buried piping and tanks or near the trenches, tunnels, or vaults supporting underground piping can cause significant stresses in the piping and tanks.

3-6

3.1.5 Mechanical or Design Defects

Mechanical or design defects include the following:

Improper handling. Buried piping and tanks can be damaged during construction or during excavation activities (for example, gouging from a backhoe).

Inadequate thrust restraint on piping can result in a premature leak or failure.

Lack of proper pipe support can result in overstress or buckling.

Improper support or anchoring of buried tanks can lead to tank movement, resulting in overstress of nozzle connections.

3.1.6 Occlusion

Occlusion (such as loss of flow area) can be caused by events such as the following:

Tuberculation. Tubercles (corrosion nodules) can be formed by general corrosion acting alone or with the participation of microbes.

Bivalves. Bivalve larvae, including zebra mussels and Asiatic clams, can attach to pipe, grow and multiply, and obstruct flow.

Sedimentation. Sedimentation, including sand and organic debris, can deposit in low- flow areas.

Debris. Ingested organic and inorganic floating and suspended matter that passes the traveling screens and filters can deposit in low-flow areas and/or heat exchanger inlets.

3.1.7 Failure Mechanisms

Failure mechanisms are also described in the EPRI report Recommendations for an Effective Program to Control the Degradation of Buried and Underground Piping and Tanks [4] and include the following:

Leak. A leak is caused by a pinhole puncture or a tight crack, without burst or fracture. Leak can be also caused by opening of bell and spigot joints, improper installation or failure of harnessed joints or fittings, or cracking and circumferential tearing of pipe due to differential settlement or inadequate thrust restraint.

Break. A break can consist of a burst, a guillotine break or a brittle fracture. A burst is a rupture caused by over-pressure, either by a steady pressure rise or by a sudden pressure transient (water hammer), with or without corrosion. A guillotine break in a buried pipe can be due to soil movement. A brittle fracture can be due to overload of a pipe made of brittle material, such as cast iron, or a material susceptible to selective leaching, such as cast iron or brass alloys. In prestressed concrete cylinder pipe, a break can occur due to loss of prestress resulting from a breakage of prestressing wires caused by corrosion or hydrogen embrittlement.

Occlusion. This failure mode groups the mechanisms that cause a reduction in flow area from the growth of macro- or micro-fouling or deposition of debris, as well as damage caused by loosened deposits carried downstream. Occlusion can also be caused by debris generated by a failed lining in the pipe or connected tank.

3-7

3.2 NDE Technology Overview Several commercially available NDE technologies are available to detect and characterize damage such as corrosion and cracking in piping system. The following sections provide an overview of these NDE technologies. Further information on basic theory, equipment, technique advantages, limitations, access requirements, and application is provided in Sections 4 through 12. These sections are limited to a general overview. Additional resources can be found in the Recommended Reading sections of Section 15.

3.2.1 Ultrasonic Examination Overview Ultrasonic testing is a volumetric NDE method that is well suited for examining piping for the detection and characterization of corrosion and cracks. Specialized ultrasonic technologies based on straight-beam methods are used to measure wall thickness of piping systems, whereas angle-beam methods are used to identify cracks but can also be used to detect wall thinning. Ultrasonic methods can be used to identify and accurately characterize corrosion depth and extent. Detailed corrosion map images can be generated when appropriate equipment is used. Examinations, if conducted from the outside surface, can generally be conducted while the system is in operation. The technology can be applied manually or with mechanical delivery tools from either inside or outside the pipe. Ultrasonic monitoring methods can be used to monitor piping systems. More information on ultrasonic technology is presented in Section 4.

3.2.2 Guided Wave Overview Guided wave technology uses low-frequency ultrasonic waves to volumetrically examine piping for the detection of changes in wall thickness. Although the technology can also be applied to detect cracking, it is not addressed in this report. The technology offers the advantage that a large volume of material can be examined from a single access position. Inaccessible locations including buried, insulated, coated, or obstructed areas of piping can be inspected without having to expose the entire pipe surface, making it a cost-effective inspection technology. Guided wave inspection of buried pipe is a relatively new, complex application that is still evolving. More information on guided wave technology is presented in Section 5.

3.2.3 Remote Field Testing Overview Remote-field testing (RFT) uses low-frequency AC and through-wall transmission to volumetrically examine piping. The basic RFT probe consists of an exciter (transmitter) that sends a signal to the detector (receiver coil). The field travels outward from the exciter, through the pipe wall, and along the pipe. The receiver coil detects the magnetic field that has traveled back through the pipe wall. In areas of metal loss, the field arrives at the detector with a change in phase and greater signal strength (amplitude) due to the reduced path through the steel. The through-wall nature of the technique allows for the detection of external and internal defects with approximately equal sensitivity. RFT often requires minimal cleaning and is tolerant, to some extent, of deposits, coatings, and liners. The technology is essentially limited to application inside the pipe. More information on RFT is presented in Section 6.

3-8

3.2.4 Magnetic Flux Leakage Overview MFL testing senses magnetic flux leakeage caused by material discontinuities. Although it is primarily used to detect, locate, and characterize corrosion, it can also be used to detect mechanical damage and some surface-breaking cracks, depending on crack orientation. Material is magnetized with either permanent magnets or electromagnets, causing a magnetic field to be set up in the material. The flow of magnetism will go around, over, or under local voids in the material to maintain its relative path from one magnet to another—similar to the flow of water around a rock in a stream. Sensors detect these changes in the flow of the magnetic field in three directions (axial, radial, and circumferential) to characterize the anomaly. The sensor signals are processed for data analysis. MFL tools can be deployed both inside and outside a pipe. More information on MFL technology is presented in Section 7.

3.2.5 Electromagnetic Technology Overview A variety of NDE techniques and technologies use an extension of conventional eddy current and RFT technologies. They are sometimes characterized by proprietary approaches, making technologies offered by specific equipment vendors unique. Several technologies such as alternating current field measurement (ACFM), pulsed eddy current, and the broadband electromagnetic method (BEM) use such electromagnetic principles. The magnetic tomography method and concentric magnetic field are two relatively new electromagnetic technologies that can be used from above the pipe. These technologies are presented in Section 8.

3.2.6 Radiography Overview Radiography is a mature NDE technology that is widely used to detect discontinuities embedded in a material or located on the surface of piping. In general, radiography can detect features that have an appreciable thickness change in the direction parallel to the radiation beam. Both traditional film and digital radiography techniques are available. Although radiography is an effective tool for identifying corrosion, it is limited to accessible pipes. When pipes are accessible, radiography can be used to examine pipe without removing the protective coatings. More information on radiography technology is presented in Section 9.

3.2.7 Visual Testing Overview Visual inspection applications range from using simple laws of geometrical optics to more complex optical techniques that assess light properties. The basic process involves illuminating the test specimen with light, usually in the visible region. The specimen is then examined by human eyes or light-sensitive devices. The surface of the specimen should be adequately cleaned before being inspected. For many types of piping systems, visual testing can be used to determine the quantity, size, shape, surface finish, reflectivity, color characteristics, fit, functional characteristics, and presence of surface anomalies and discontinuities. Visual inspection can be performed inside and outside the pipe. Cameras placed on crawlers or borescope equipment can be used to gain internal access. When combined with direct measurement devices such as pit gauges, visual testing provides data for detailed assessment of fitness for purpose. More information on visual inspection is presented in Section 10.

3-9

3.2.8 Laser Profilometry Overview Laser profilometry is a relatively new inspection technology that enables precise measurement of surface imperfections. This technology entails traversing an area of interest with a laser sensor. The sensor captures two-dimensional (2-D) surface profiles of the interest area. These profiles are recorded with respect to time or distance traveled. Laser profilometry sensors use optical triangulation to determine the distance between the sensor and the target surface. Optical triangulation requires a light source, imaging optics, and a photodetector. The light source and focusing optics generate a collimated, or focused, beam of light and channel it onto a photodetector. The profiles generated are compiled into a three-dimensional (3-D) surface topography that can be analyzed by visualization software to enable precise measurement of surface imperfections. More information on laser profilometry technology is presented in Section 11.

3.2.9 Leak Detection Overview Low-pressure leak testing is used to detect through-wall perforations, small pinholes, and loose connections. Leak detection can be performed on a variety of materials, including steel, cast iron, plastic, and concrete. Above-the-pipe applications are also available for deployment. These inject tracers into the fluid, and leaks are discovered if the tracer makes its way outside the pipe. Advances in leak detection technology, such as those using acoustic leak detection systems, allow for deployment within pipes. More information on leak detection technology is presented in Section 12.

3.2.10 Other NDE Technologies The following NDE technologies are principally used for crack detection, so no further information is provided in this report. However, Section 15 provides recommended reading resources to learn more about these technologies.

Eddy current inspection is based on the principles of electromagnetic induction and is used to identify or differentiate among a wide variety of physical, structural, and metallurgical conditions in electrically conductive metals. Eddy current inspection can be used to measure or identify conditions and properties such as electrical conductivity, magnetic permeability, grain size, heat-treatment condition, hardness, and physical dimensions. This allows it to be used to detect and characterize discontinuities in piping and tubing materials, such as seams, laps, cracks, voids, and inclusions. It can also be used to sort metals and detect differences in their composition, microstructure, and other properties. Nonconductive or nonmagnetic metal coating on a magnetic metal can be measured. Because eddy currents are created using an electromagnetic induction technique, inspection methods do not require direct electrical contact with the part being examined.

Magnetic particle inspection is a mature NDE technology commonly used to detect surface and slightly subsurface discontinuities, such as cracks in ferromagnetic materials. It is not used to detect corrosion. It is relatively fast and typically requires minimal surface preparation. The magnetic particle examination is based on the principle that magnetic flux in a magnetized object is locally distorted by the presence of a discontinuity. This distortion causes some of the magnetic field to exit and re-enter the test object at the discontinuity. Fine ferromagnetic particles are applied to the material. These particles arrange themselves along the magnetic flow lines, thereby forming an outline or indication of the discontinuity.

3-10

Liquid penetrant inspection is a mature NDE method used to detect discontinuities that are open to the surface of essentially nonporous materials. This technique is not typically used to identify corrosion, unless it is used to detect small-diameter pitting-type discontinuities. Liquid penetrant fluids are applied to an adequately prepared surface, where they will seep into the surface opening by capillary action. Excess penetrant is removed from the surface when the established dwell time is reached. A developer is then typically applied to draw out the penetrant and create sufficient contrast. Liquid penetrant examinations can be performed without special equipment except for an ultraviolet (black) light when fluorescent penetrants are used.

Hydrostatic proof testing is used either to ensure that piping systems retain safety factors prescribed from the original construction design codes or to ensure that safety factors are maintained for corroded pipe. Using established failure criteria for corroded pipe, a survivable defect size can be determined for a hydrostatic test, and a re-inspection interval can be predicted based on an assumed future corrosion growth rate. There are limitations associated with such testing when it is applied after the pipeline has been in service for a number of years. First, it provides no information regarding the depth or location of subcritical flaws. Second, it requires the pipeline to be taken off line for the testing. Third, it can be difficult or nearly impossible to remove fluids from the pipeline after a pressure test. More information on hydrostatic testing is presented in Section 13.

3.3 NDE Selection Guidance Table 3-2 provides a method of viewing some of the capabilities of the listed NDE technologies for application to detecting metal loss in piping. It considers variables such as pipe size, material, and access, as well as damage mechanism. The table provides a reference to the applicable section in the report where additional information can be found on that NDE technology. Although the table provides references to applicable NDE technology, it cannot consider all potential variables. Therefore, good engineering judgment is still required to assess whether the technology can be effectively applied. The NDE technologies are categorized by the following:

Outside pipe

Inside pipe

Above pipe—outside the pipe and not in contact with the pipe

Monitoring—technology capable of monitoring pipe condition

The NDE technology’s capability to detect and discriminate for the listed variables and conditions are coded as shown in Table 3-1.

Table 3-1 Codes for variables and conditions

APP The NDE technology is applicable.

SC The NDE technology might be applicable. See the applicable section of this report.

X The NDE technology is not applicable.

3-11

Most nuclear power plant owners have NDE experts on staff to provide guidance on applying NDE technology. It is highly recommended that these individuals be engaged in the buried pipe NDE process because they can provide support and guidance in selecting and applying NDE technology. NDE personnel must go through rigorous training and qualification programs to become certified to conduct NDE. Certification levels of I, II, and III are used for each NDE method, with Level III being the highest level. Even if a utility Level III does not have experience in the applicable NDE method, he or she can provide overall guidance based on experience from the other methods. Further support can also be obtained from the NDE staff at EPRI as they have experienced staff with expertise in most utility NDE applications.

3-12

Table 3-2 Selection of NDE technology for metal loss

Nom. Pipe Diameter Pipe Material OD Inspection Access ID Inspection Access ID Bore Metal Loss Discrimination

Performance Ground Cover

Surface Condition

Tec

hnol

ogy

Ca

teg

ory

Com

pen

diu

m S

ectio

n

NDE Technology < 3

NP

S

3-6

NP

S

> 6

NP

S

Ste

el

Pla

stic

Cas

t Iro

n

Re-

enfo

rce

d C

onc

rete

Ful

l Exc

avat

ion

Par

tial E

xcav

atio

n

No

Exc

avat

ion

Pip

e in

Pip

e

Insu

late

d w

/ non

-ma

gne

tic c

lad

Ext

erna

l Co

atin

g P

rese

nt D

urin

g In

spec

tion

No

Ext

erna

l Coa

ting

Laun

ch R

ece

ive

Tra

ps

Shu

t D

own

Re

mov

e F

lan

ges

No

ID a

cces

s po

ssib

le

ID C

oatin

g P

rese

nt D

urin

g In

spec

tion

Mon

o B

ore

No

Be

nds

or T

ees

In-li

ne v

alv

es te

es o

r be

nds

< 1

.5D

ML

De

pth

ML

Len

gth

ML

Wid

th

ML

Pos

ition

Re-

enfo

rce

d C

onc

rete

Asp

halt

Soi

l

Out

side

Pip

e

4 UT Thickness APP APP APP APP X X X APP APP X X X X APP APP APP APP APP APP APP <20% APP APP APP X X X

5 GWUT APP APP APP APP X X X APP APP X X X APP APP APP APP APP APP APP X <50% X APP APP X X X

7 VT MFL (MPI) APP APP APP APP APP APP APP APP APP X X X X APP APP APP APP X APP APP X X X X X X X

7 MFL Scanner APP APP APP APP X X X APP APP X X X X SC APP APP APP APP APP X <20% APP APP APP X X X

8 E-Pit APP APP APP APP X APP X APP APP X X X APP APP APP APP APP APP APP APP <50% APP SC APP X X X

8 Low-frequency electromagnetic APP APP APP APP X APP X APP APP X X X APP APP APP APP APP APP APP APP <50% APP SC APP X X X

8 SLOFEC APP APP APP APP X APP X APP APP X X X APP APP APP APP APP APP APP APP <50% APP SC APP X X X

8 Pulsed Eddy Current APP APP APP APP X APP X APP APP X X APP APP APP APP APP APP APP APP APP <20% SC SC SC X X X

4 EMAT APP APP APP APP X APP X APP APP X X APP APP APP APP APP APP APP APP APP <20% SC SC SC X X X

8 ACFM APP APP APP APP X APP X APP APP X X X APP APP APP APP APP APP APP APP SC SC SC SC X X X

8 Broadband Electromagnetic APP APP APP APP X APP X APP APP APP X X APP APP APP APP APP APP APP APP <50% APP SC APP X X X

9 Radiography APP APP APP APP APP APP APP APP APP X SC SC APP APP APP APP APP APP APP APP SC SC SC SC X X X

10 VT Camera APP APP APP APP APP APP APP APP APP X X X X APP APP APP APP X APP APP SC SC SC APP X X X

10 VT Pit Gauge APP APP APP APP APP APP APP APP APP X X X X APP APP APP APP X APP APP <20% APP APP APP X X X

11 VT Laser APP APP APP APP APP APP APP APP APP X X X X APP APP APP APP X APP APP <20% APP APP APP X X X

Insi

de P

ipe

4 IRIS APP X X APP X X X APP APP APP APP APP APP APP APP SC X SC APP SC <20% APP APP APP X X X

6 RFEC-Tethered X APP APP APP X X X APP APP APP APP APP APP APP X SC X SC APP SC <20% APP APP APP X X X

6 RFEC/TC X APP APP APP X X APP APP APP APP APP APP APP APP X SC X SC APP SC X X X X X X X

7 MFL- Flow Conveyed SC APP APP APP X X X APP APP APP APP APP APP APP APP SC X SC APP SC <20% APP APP APP X X X

10 VT- Internal APP APP APP APP APP APP APP APP APP APP APP APP APP APP APP APP X APP APP APP X X X X X X X

11 VT- Tractor Conveyed X APP APP APP X X X APP APP APP APP APP APP APP X SC X SC APP SC SC SC SC APP X X X

12 Leak Test APP APP APP APP APP APP APP APP APP APP APP APP APP APP APP APP APP APP APP APP X X X X X X X

14 UT- Flow Conveyed X APP APP APP X X X APP APP APP APP APP APP APP APP SC X SC APP SC <20% APP APP APP X X X

14 UT-Tractor Conveyed X APP APP APP X X X APP APP APP APP APP APP APP X SC X SC APP SC <20% APP APP APP X X X

Note: NPS = nominal pipe size

3-13

Table 3-2 (continued) Selection of NDE technology for metal loss

Nom. Pipe Diameter Pipe Material OD Inspection Access ID Inspection Access ID Bore Metal Loss Discrimination

Performance Ground Cover

Surface Condition

Tec

hnol

ogy

Ca

teg

ory

Com

pen

diu

m S

ectio

n

NDE Technology < 3

NP

S

3-6

NP

S

> 6

NP

S

Ste

el

Pla

stic

Cas

t Iro

n

Re-

enfo

rce

d C

onc

rete

Ful

l Exc

avat

ion

Par

tial E

xcav

atio

n

No

Exc

avat

ion

Pip

e in

Pip

e

Insu

late

d w

/ non

-ma

gne

tic c

lad

Ext

erna

l Co

atin

g P

rese

nt D

urin

g In

spec

tion

No

Ext

erna

l Coa

ting

Laun

ch R

ece

ive

Tra

ps

Shu

t D

own

Re

mov

e F

lan

ges

No

ID a

cces

s po

ssib

le

ID C

oatin

g P

rese

nt D

urin

g In

spec

tion

Mon

o B

ore

No

Be

nds

or T

ees

In-li

ne v

alv

es te

es o

r be

nds

< 1

.5D

ML

De

pth

ML

Len

gth

ML

Wid

th

ML

Pos

ition

Re-

enfo

rce

d C

onc

rete

Asp

halt

Soi

l

Abo

ve

Pip

e

8 Magnetic Tomography Method APP APP APP APP X X X APP APP APP X APP APP APP APP APP APP APP APP APP SC X X X X X X

8 No-Pig APP APP APP APP X X X APP APP APP X APP APP APP APP APP APP APP APP APP SC X X X X X X

Mon

itori

ng

4 Wall Thickness-Perm. Mount UT APP APP APP APP X X X APP APP X X APP APP APP APP APP APP APP APP APP <20% SC SC SC X X X

5 Wall Thickness- GWUT APP APP APP APP X X X APP APP X X X APP APP APP APP APP APP APP X <50% X APP APP X X X

12 Leak Monitoring APP APP APP APP APP APP APP APP APP APP APP APP APP APP APP APP APP APP APP APP X X X X X X X

Note: NPS = nominal pipe size

3-14

3.4 Additional Resources

Other available resources for conducting successful in-line inspection (ILI) include the following:

NACE SP0102-2010 – In-Line Inspection of Pipelines. This document provides recommendations for ILI service providers and pipeline operators to plan, organize, and execute an ILI project.

API 1163 – In-Line Inspection Systems Qualification Standard. This document provides performance-based requirements for ILI systems, procedures, personnel, equipment, and associated software.

ANSI/ASNT ILI-PQ – In-Line Inspection Personnel Qualification and Certification. This document provides qualification and certification requirements for ILI personnel.

4-1

4 ULTRASONIC TECHNOLOGY Ultrasonic examination technology is commonly used in the nuclear industry, as well as in many other industries, to assess newly manufactured and in-service materials such as metals, plastics, composites, fiberglass, ceramics, and glass. It is commonly used to identify and characterize discontinuities in piping, plates, tubing, vessels, and turbines, as well as several other product forms. Ultrasonics is routinely used to accurately measure material wall thicknesses or to identify imperfections such as cracks in piping components. This section focuses on ultrasonic fundamentals applied when examining piping components for the presence of thinning.

4.1 Ultrasonic Wall Thickness Capability Summary

This section provides an overview of application variables associated with using ultrasonic technology to examine piping for wall degradation. Typical or expected results are presented in five tables. Although these results are accurate in most instances, it is important to understand that, like most technology applications, there are exceptions. To keep the information concise, the tables do not fully address all potential variations. This being said, the results shown in the tables are accurate in most situations. Table 4-1 summarizes the technology function. Table 4-2 summarizes how the technology can be deployed. Table 4-3 addresses how surface condition, coatings, and other conditions affect the technology application. Table 4-4 provides some of the piping materials that the technology can be used to examine. Table 4-5 captures capabilities for a number of variables. To provide a consistent review format, these tables are presented in each technology section.

Table 4-1 Ultrasonics: function

Function Comments

Thickness Yes. Can measure small changes in thickness

Can be used to profile surface(s) Transducer-side surface—Yes (for immersion techniques)

Back side—Yes

Can detect internal and external surface metal loss

Yes

Can detect axial and circumferential metal loss

Yes

Can discriminate between internal and external metal loss

Yes

Crack detection Yes

Embedded discontinuities Yes; some inclusions can produce signals that are similar to wall thickness signals; other ultrasonic techniques or NDE methods can be used to assess results

4-2

Table 4-2 Ultrasonics: deployment options

Table 4-3 Ultrasonics: impact of surface and coating on results [7]

Table 4-4 Ultrasonics: applicable pipe materials

Deployment Comments/Considerations

Manual deployment Yes (inside and outside pipe)

In-line deployment Can be deployed with free-swimming, tethered, and crawler tools

Automated outside surface Yes

Monitoring Yes

Examination Surface Expected Outcome (Most Situations)

Bare and smooth Yes (optimal)

Bare and rough Depends on how rough and the technique; as roughness increases, energy transmission decreases; immersion techniques are more forgiving

Painted Yes (most cases)

Coated Piezoelectric—Possibly when relatively smooth, thin, hard, and well bonded

EMATs—Yes, but limited by coating thickness*

Lined Piezoelectric—No

EMATs—Yes, but limited by lining thickness*

Silt, Tubercles, and Similar Debris Piezoelectric—No

EMATs—Yes, but limited by thickness*

Materials Comments

Carbon steel Yes

Stainless steel Yes for most; does not work on some cast stainless steels.

Aluminum Yes

Cast iron Situation-dependent based on grain structure

High-density polyethylene Yes

Fiberglass Yes (in some situations)

4-3

Table 4-5 Ultrasonics: capability variables

Variable Yes No Comments

Single-sided access for volumetric examination

X

Capable of examining when piping is in service

X

Capable of noncontact examination * * * Piezoelectric—no; EMATs—yes

Capable of examining significant axial pipe volume away from sensor

X

No couplant required * * * Piezoelectric—no; EMATs—yes

Capable of producing an image showing size and shape of discontinuity

X

No radiological concerns X

4.2 Ultrasonic Thickness Measurement Techniques

4.2.1 Ultrasonic Piezoelectric Contact Technique

Zero-degree piezoelectric contact transducers are commonly used for manual thickness examinations. Ultrasonic energy is generated by exciting a piezoelectric crystal with an electrical pulse, causing it to vibrate at a predetermined frequency. Ultrasonic energy is transmitted into the material through a couplant, as shown in Figure 4-1. The energy travels in the pipe until it is reflected, refracted, or attenuated. Energy received back to the transducer deforms the piezoelectric crystal, resulting in voltage that is processed and displayed as a signal on the ultrasonic instrument.

Figure 4-1 Application of ultrasonic straight beam examination

4-4

Ultrasonic immersion techniques are routinely used on ILI devices and can be used on the exterior surface, such as is described in Section 4.6, Linear Phased Array. As with contact ultrasonic techniques, ultrasonic energy is generated with a piezoelectric transducer. However, rather than generating ultrasonic energy directly into the material, it is generated into a fluid that is in contact with the pipe surface. Thus, the ultrasonic energy travels through the fluid and then into the pipe material, as illustrated in Figure 4-2. This results in ultrasonic energy reflecting off the water-to-pipe interface, as well as the pipe backwall surface. Accurate material thickness is determined by measuring the transit time between the two signals and multiplying it by material velocity. Additional thickness confirmation can be made by measuring the time separation between multiple signals.

Figure 4-2 Ultrasonic immersion technique

For ILI devices, immersion techniques can also be used to measure the fluid distance between the transducer and the inside pipe surface. This can be used to profile the inner pipe surface and to discriminate between internal and external surface corrosion because the fluid distance will increase for metal loss, as illustrated in Figure 4-2. In addition, interior and exterior dents can be identified because fluid distance will decrease for external dents or increase for internal dents.

4.2.2 Ultrasonic EMAT Technique

Alternatively, ultrasonic energy can be transmitted and received by a less commonly used EMAT. The energy propagation, reflection, and defect characterization are the same as for a piezoelectric transducer. An EMAT induces ultrasonic waves into a test object with two interacting magnetic fields. A relatively high-frequency field generated by electrical coils interacts with a low-frequency or static field generated by magnets to create the wave in the surface of the material being tested. Various types of ultrasonic waves can be generated using different radio frequency coil designs and orientation to the low-frequency field. An example of an EMAT measuring wall thickness through a coated pipe is shown in Figure 4-3.

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Figure 4-3 An EMAT used to measure wall thickness on a coated pipe

4.3 Signal Displays and Calibration

The most common instrument displays are the A-scan presentation and digital thickness readout. An A-scan presents time on the horizontal axis and signal amplitude on the vertical axis, as illustrated in Figure 4-4.

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Figure 4-4 Detection of an internal flaw with straight-beam ultrasonics

This illustration shows ultrasonic energy reflecting off an internal flaw and the backwall surface. The bottom image illustrates what the A-scan would look like for this configuration. The signals in red represent the flaw signal, and the ones in green represent the backwall signals. Because the reflected energy from the flaw travels less distance than that from the backwall, the signal is to the left of the backwall signal. For thickness examinations, the A-scan can be calibrated to represent thickness, allowing thickness to be read directly off the A-scan display. Other points of interest in the A-scan (see Figure 4-4) are the following:

There are two flaw indication signals and two backwall signals. This is the result of ultrasonic energy traveling back and forth between these reflectors multiple times. These signals are typically called multiples. Highly accurate wall thickness measurements can be made by measuring the time difference between the corresponding multiple signals. This measurement is especially useful for taking measurements on thin-wall materials.

The initial pulse (far left signal) can interfere with measuring thin-wall materials using single-element, contact-type transducers. The larger the initial pulse, the more disruptive it is on the measurement. The size of the initial pulse is dependent on transducer and pulser variables. This can be overcome by using other types of contact transducers or an immersion technique.

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Instruments with digital readouts can be used to accurately measure wall thickness by measuring the ultrasonic energy transit time in the material and multiplying it by the material’s velocity. It is strongly recommended when using a digital display for wall thickness measurements that an instrument that also has an A-scan display be used to confirm the validity of the digital readout. This recommendation is based on the A-scan’s ability to display thinning with a small footprint that might not be detected with a digital readout. An A-scan can also help in distinguishing an internal inclusion from a change in thickness that might otherwise be interpreted as thinning. Many digital display instruments are available with A-scan capabilities.

Although material velocity can be input to many ultrasonic instruments, it is important to properly calibrate ultrasonic instruments to get accurate thickness measurements. This calibration is accomplished by using step-wedge calibration blocks of like material (see Figure 4-5).

Figure 4-5 Step wedge calibration block

In addition to A-scans and digital readouts, B-scan, C-scan, and D-scan images (see Figure 4-6) can be generated to provide more comprehensive methods of data analysis. These views are typically used when encoded data are acquired, such as with phased array probes, mechanized external crawlers, and ILI devices. The C-scan is essentially a plot view of the data, with pipe circumference on one axis and pipe length on the other. The color pallet can be set to represent many variables, but it is usually set to thickness, time of flight, or signal amplitude, all of which are useful in identifying wall degradation. The B-scan can be set to display a side view of the wall degradation, and the D-scan can display an end view.

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Figure 4-6 Examples of B-scan, C-scan, and D-scan displays

Figure 4-7 shows how a C-scan image can be used to provide a good illustration of thinning within a pipe. The picture shows exterior corrosion in a pipe, occurring along the outline of an attached beam. The corresponding thinning damage can be readily seen in the C-scan. Further analysis of the C-scan could be done by zooming in on the thinning damage or by adjusting the color plot to represent a specific thickness range. For instance, the color pallet could be set to display thickness only below minimum wall, if desired.

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Figure 4-7 Wall thinning picture and corresponding C-scan image Used with permission from Quest integrity

4.3.1 Thickness Measurement Considerations

Although highly accurate thickness measurements can be made with ultrasonic examination using zero-degree techniques, it is important to understand the application and associated limitations, some of which are provided in this section.

Accurate measurements can be made only on isotropic materials. Isotropic materials have constant material velocity. Most piping materials used in the nuclear power industry have isotropic properties; however, some materials, such as some cast stainless materials, are not isotropic.

Only the material region within the transducer’s ultrasonic beam is examined for material thickness. For zero-degree examination, this would essentially be the region directly below the transducer. This can be overcome by taking multiple thickness measurements or by scanning the surface and monitoring the signals for changes in thickness. This can be conducted to identify the

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thinness area or to map out a prescribed thickness range. Another method is to grid a pipe and take thickness measurements at the grid intersections. A variation of this is to scan within the grid and report the thinnest thickness or range of thicknesses. Grid size should be in line with the purpose of the examination.

Ultrasonic thickness measurement accuracy is limited by the wavelength of the ultrasound used in the measurement. Theoretically, thickness accuracy is equal to half the wavelength. However, this is generally achievable only in ideal conditions.

The amount of energy reflected from a discontinuity is dependent on size and orientation to the sound beam. The signal of a reflector within the sound beam decreases as it gets smaller than the transducer’s sound beam. In addition, signal strength decreases as the angle of a reflector decreases from being perpendicular to the sound beam. At some point, for both size and orientation, the reflector becomes undetectable. Focused beam and phased array techniques can be used to overcome some of these limitations. Therefore, it is paramount that proper equipment and techniques be used to identify such indications as pitting corrosion. Alternatively, other examination techniques such as radiography might be necessary. Even with general backwall corrosion, care must be taken to identify the actual thinnest reading.

Ultrasonic thickness techniques can also detect internal inclusions such as laminations or voids, as illustrated in Figure 4-2. If indications from such reflectors are not correctly dispositioned, an incorrect conclusion can be reached that the pipe is thinned, whereas, in reality, it contains only a nondetrimental inclusion. Alternative ultrasonic techniques, such as angle beam, or other NDE methods, such as radiography, can be used to further assess such conditions. Some components, such as castings, are more likely to contain such inclusions.

Temperature has various effects on ultrasonic examination. Transducers have a temperature range in which they can be effectively used. High-temperature transducers can be obtained that can perform in high-temperature applications. An additional temperature consideration is that the metal temperature can affect material velocity. Therefore, calibration should be performed on calibration blocks that are in the same temperature range as the material to be tested.

4.4 Piezoelectric Ultrasonic Transducers

Although ultrasound can be generated in a pipe in a variety of ways, the piezoelectric transducer is the most common method. The main components of a piezoelectric ultrasonic contact-type transducer are shown in Figure 4-8.

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Figure 4-8 Components of an ultrasonic straight-beam sensor

A multitude of transducers are commercially available, made for many different purposes. Even for measuring thickness, there is a large selection of transducers available having specific advantages. Transducer frequency and shape affect transducer capabilities. For instance, higher-frequency transducers have shorter wavelengths, making them more sensitive to smaller reflectors. However, they also have less penetration power. Thus, a frequency that works well on fine-grain carbon steel might not be effective for a coarse-grain stainless steel due to lack of penetration. Further, a low-frequency transducer that has good penetration might not be adequate for detecting isolated pitting. Other factors, such as transducer crystal size and shape or ultrasonic instrument settings, can have similar effects. Although it is beyond the scope of this report to go into specifics, the following transducer generalities are typical for metal examination:

Normally used transducer frequency range is 0.5–25 MHz. The most common frequencies are in the 2.25–5 MHz range.

Round or square piezoelectric elements are most common.

Transducer sizes between 0.25 in. and 1.0 in. are common.

Higher frequencies are desired for wall thickness measurements, when possible.

Highly dampened transducers with short ring times are preferred for thickness measurements.

In transducer selection, it is important to understand an ultrasonic beam and how it can affect results. Figure 4-9 is a simulation of an ultrasonic beam, showing the near field and far field. In the near field, it can be seen that there are variations in the beam intensity. Such variations can have a significant impact on a transducer’s capability of detecting a reflector. In general, a transducer should be used only in its far field region to avoid this issue. The intensity in the far field, along the axial distance, varies inversely with the square of the distance. The greatest concentration of ultrasonic energy is in the center (axis) of the beam; however, the beam does spread, as can be seen in the simulation. Although it is not shown in this simulation, another significant factor is the dead zone of a sound field. This is the region in which the transducer is

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transmitting and, therefore, cannot receive reflected ultrasonic energy. This is a factor of the instrumentation. All these effects must be considered when selecting a transducer for a specific application, and they should be addressed in the procedure. The following sections provide an overview of typical transducers.

Figure 4-9 Graphical representation of an ultrasonic beam

4.4.1 Contact Transducers

A contact transducer has only a thin wear plate between the piezoelectric crystal and the test surface. Measurements are often the simplest to implement. Near field and dead zone effects must be considered when using this type of transducer. Generally, it is not a good selection for thickness measurements in thin materials.

4.4.2 Delay Line Transducers

A delay line transducer incorporates a piece of material such as Lucite or Rexolite in the face of the piezoelectric element. The purpose of the delay line is to contain the dead zone and near field of the transducer so that thin wall measurements can be made. It can also be effective for high-temperature applications, because it can be a thermal insulator between a hot surface and the actual transducer. Delay lines can also be shaped or contoured to improve ultrasonic coupling for curved surfaces.

4.4.3 Immersion Transducers

An immersion transducer is used in a fluid; ultrasonic energy is transmitted from the transducer through the fluid into the part. This type of transducer is typically used on ILI tools and can be used in many fluids, such as water, diesel, and many petroleum products. The dead zone and near field of the transducer are typically confined to the fluid path, thereby allowing for thin wall measurements. They are generally more forgiving of rough surfaces.

4.4.4 Dual-Element Transducers

A dual-element transducer incorporates individual transmit and receive piezoelectric elements. This results in the elimination of the dead zone. The elements on these transducers are typically slightly tilted toward the middle of the transducer and have some wedge delay. These transducers provide better performance in corrosion survey applications than do their single-element counterparts.

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4.5 Electromagnetic Acoustic Transducers

The principle of EMATs is illustrated in Figure 4-10. A permanent magnet or electromagnet produces a steady magnetic field, and a coil of wire carries a radio-frequency current. The radio frequency induces eddy currents in the surface of the specimen, which interacts with the magnetic field to produce Lorentz forces that cause the specimen surface to vibrate in response to the applied radio frequency. When receiving ultrasonic energy, the vibrating specimen can be regarded as a moving conductor or a magnetic field that generates currents in the coil. The clearance between the transducer and the metal surface affects the magnetic field strength and the strength of the eddy currents generated, and the ultrasonic intensity falls off rapidly with increasing gap. Precautions must be observed for keeping the gap relatively constant for a specific inspection application.

Figure 4-10 Basic configuration of an EMAT

A picture of an EMAT coil is shown in the upper left picture of Figure 4-11. The upper right picture of Figure 4-11 shows the coil attached to the probe, and the bottom picture shows a protective cover placed over the transducer. Figure 4-12 shows an example of an EMAT system.

N SCoil

Horizontal Magnetic FieldUltrasonic

Compressional Wave

Magnet

N SS Coil

Vertical Magnetic Field

Ultrasonic Shear Wave

Magnet

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Figure 4-11 An EMAT

Figure 4-12 An EMAT system

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The principal advantage of EMATs compared with piezoelectric transducers is that EMATs need not be in direct contact with the test surface, allowing for the following benefits:

Couplant is not needed.

EMATS can examine piping through coatings and linings.

Surface preparation is reduced.

EMATS can be used in gas piping.

EMATS can be used in high-temperature environments.

The principal disadvantages of EMATs compared to piezoelectric transducers are the following:

There is lesser resolution, as shown in the EMAT A-scan provided in Figure 4-13.

There is lower signal-to-noise ratio.

Transducers generally have a larger footprint.

Figure 4-13 An EMAT signal

More information on using EMATs to measure wall thickness through coatings can be obtained in EPRI report 1025228, Nondestructive Evaluation: Buried Pipe Direct Examinations Through Coatings. The cost of realizing these advantages is relatively low operating efficiency. However, this can be overcome by using high transmitter current, low-noise receivers, and careful electrical matching. In ferromagnetic materials, the magnetization or magnetostrictive mechanisms of coupling can often be used to enhance signal levels.

The principal disadvantages of EMATs compared with piezoelectric transducers is that EMATs have a larger footprint (1–2 in. diameter) and, therefore, have less resolution and sensitivity to small pits.

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4.6 Linear Phased Array

Ultrasonic phased array has become increasingly used in the nuclear industry for such applications as examination of welds. Recently, linear phased array search units have become available that can be used to examine piping for wall loss. Phased array wall thickness examinations have the potential to provide significant benefits over conventional ultrasonic techniques, especially contact techniques. A phased array search unit generates a beam with multiple small elements, as is illustrated in Figure 4-14. Such a beam can be generated to provide 100% coverage at a relatively fast data acquisition speed.

Figure 4-14 Generation of 100% coverage with an ultrasonic phased array

The use of phased array probes significantly improves the capability of detecting much smaller reflectors such as pitting than is possible with conventional, larger-diameter zero-degree contact transducers. This is significant because corrosion can result in small pits or voids, some of which might not be detectable with larger-diameter transducers. Also, these phased array search units typically use encoders, allowing for the generation of color-coded C-scan or B-scan images of the thickness condition. Using these images enhances the probability of detecting small reflectors, such as pits. Because both the ultrasonic and the positional data are electronically stored, additional data analysts can review the data. The data can also be used at future inspections to compare with new data to identify wastage rates.

An example of one of these phased array probes is the Sonatest corrosion WheelProbe (see Figure 4-15). A 64-element linear array is located inside a flexible rubber wheel that conforms to the scan surface. The wheel is filled with a fluid that couples the array to the tire. Ultrasound energy is transmitted through the fluid and the tire into the piping material by misting the piping surface with water, eliminating the need for ultrasonic couplant. Because the tire is conformable to the surface to some degree, coupling can be achieved on a rougher surface than might not be easily achievable with a contact transducer. The 64-element linear phased array is 2 in. wide and has a data of resolution of 0.031 in. The wheel probe is encoded as it is rolled around the circumference or axis of the pipe.

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Figure 4-15 Phased array Sonatest WheelProbe

Ultrasonic data were collected with the wheel probe by EPRI staff on a variety of mockups to assess the capabilities of the phased array technology. One of the more challenging sets of discontinuities is a series of 12 0.1888-in. diameter holes that have a 0.1875-in. ligament between them. A picture of the holes is shown in Figure 4-16. Each of the three rows contains different hole depths of approximately 25%, 50%, and 75% through wall, as illustrated in the top left image of Figure 4-17. Ultrasonic data were collected on the face of the pipe opposite the holes and processed. The image on the right side in Figure 4-16 is a C-scan image of the area that not only shows the holes but also clearly shows the ligaments between the holes. Two side view images of the holes that reveal the hole depths are shown in Figure 4-17. The top right image represents a slice of data taken through the row of holes showing the different depths of the holes. The bottom image shows a slice of data taken through the row of 75% deep holes. Also evident in the side view images are the ligaments. The capability of detecting, resolving, and characterizing such small discontinuities can be an important component in an integrity assessment of a pipe.

EPRI report 1025219, Nondestructive Evaluation: Buried Pipe NDE Technology Assessment and Development Interim Report, contains the results of a comprehensive assessment of the technology as well as a technical basis for using the phased array technology.

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Figure 4-16 The closely spaced holes, left, and the resulting C-scan image of the holes obtained with the wheel probe, right

Figure 4-17 Ultrasonic side view images of closely spaced holes obtained with the WheelProbe (The top image represents a slice of data taken through the holes of different depths; the bottom image shows a slice of data taken of the deeper holes.)

Further data were collected with the wheel probe on a field-removed corroded pipe that contained significant internal corrosion, which is shown in the top image in Figure 4-18. The lower image shows the resulting C-scan image of an area in the vicinity of the area of the photograph. A dimpling-type corrosion can be seen in the photograph. This can also be seen in the C-scan image. Although not shown, side view images can also be generated that would show a cross section of the pipe. Additional information on this, as well as results obtained through coated piping, can be found in EPRI report1025228, Nondestructive Evaluation: Buried Pipe Direct Examinations Through Coatings.

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Figure 4-18 A field-removed corroded pipe (top) and C-scan image (bottom) obtained with the WheelProbe in the vacinity of the picture

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Another approach to phased array zero-degree probes is the Olympus HydroFORM2 corrosion array (see Figure 4-19). This phased array device uses a gasket that holds a column of water between the array and the piping surface. The 2.36-in.-wide array contains 64 elements, creating a 0.039-in. pitch. The claimed near-surface resolution is 0.063 in., and scan speed is 4 in. per second. The array also uses four elements together to obtain a better response to nonparallel reflectors, such as pits. Because the device is immersed, it can scan over rougher surfaces than can be achieved with surface probes. It can also be attached to a scanner, as shown in Figure 4-20, allowing for encoding in the axial pipe direction.

Figure 4-19 Phased array Olympus HydroFORM

Figure 4-20 Phased array Olympus HydroFORM with pipe scanner

2 HydroFORM is a registered trademark of Olympus Corp.

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Data were collected with the ultrasonic phased array HydroFORM probe on EPRI mockups. Data were collected on the field-removed specimen pictured in Figure 4-21. This sample is similar to the one described previously and shown in Figure 4-18. The imaged results of the ultrasonic data are shown in Figure 4-21. The top right is a traditional A-scan that can be used to very accurately measure the wall thickness. The right image is a side view, showing the corrosion depth in that particular slice of data. The lower image is the C-scan image showing corrosion that exceeds an adjustable threshold.

Figure 4-21 An example of internal corrosion image obtained with the HydroFORM phased array probe

Phased array data were taken with the HydroFORM probe from the outside surface of a 6-in. diameter field-removed pipe containing significant inside and outside surface corrosion. Figure 4-22 is a photograph (top) of a deep exterior pit (circled) that was scanned. The results are presented in Figure 4-22 (lower), which shows a side view cutting through the deep corrosion in the upper right and a C-scan (top view) showing wall loss at a set depth threshold (adjustable). In the side view, it appears as if the deep portion of the exterior pipe wall is inside of the pipe. This is due to the velocity of water being approximately one-fourth the velocity of steel. Because it takes longer for the energy to travel through the water path that is longer to reach the bottom of the pit as compared with the pipe wall, the pit bottom is imaged further in time. The thickness of this thinned area is easily determined in the A-scan by measuring the distance between the two peaks. It can also be measured in the side view by adjusting cursors to the inside and outside wall.

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Such an immersion probe provides a unique capability when compared with a contact probe, and the data collection time was a matter of seconds. The rough surface, especially the deep pit, would make it very challenging to collect data with contact probes. At best, special small-diameter probes would be required to collect data in the pitted areas, and then the surface may be inadequate to make adequate contact to obtain adequate signals. In addition, data imaging, such as what is presented, would not be possible. Also, additional surface preparation would likely be required to make the surface smooth enough to transmit the ultrasonic energy into the material. In either case, the surface still needs to be adequately free of debris. With the immersion probe, data were collected in the as-found condition in a matter of seconds.

Figure 4-22 Photograph of external corrossion in a field-removed pipe (top) and resulting images (bottom) obtained with the HydroFORM probe

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4.7 Ultrasonic ILI Tools

Several ultrasonic ILI technologies are commercially available for measuring wall thickness, detecting and characterizing wall loss on both the interior and exterior surfaces, and identifying dents initiated from both the interior and exterior surfaces. Although not yet routinely used in the nuclear power industry, this type of technology is used in other industries, such as the petroleum industry. Although immersion techniques are typically used, other methods are available and addressed in this section. This allows for an examination without having the pipe full of water. Ultrasonic technology can be installed on flow-conveyed, robotically driven, or tethered devices. They can be installed in in-service or out-of-service piping segments. A variety of methods are used for generating ultrasonic energy in the pipe, including an array of fixed transducers, a fixed transducer with a rotating mirror, EMATS, contact transducers, and rotating transducers.

EPRI has assessed two ultrasonic technologies—a flow-conveyed array technology and a robotically driven technology using rotating transducers. Results of these assesments can be found in EPRI report 1025219, Nondestructive Evaluation: Buried Pipe NDE Technology Assessment and Development Interim Report. In addition, EPRI observed the deployment of a flow-conveyed, fixed-transducer, rotating mirror technology at Arkansas Nuclear One, which is covered in this section.

4.7.1 Flow-Through In-Line Ultrasonic Array

Quest Integrity’s technology uses an array of transducers distributed around the circumference of their flow-conveyed ILI tools. The number of transducers is dependent on the diameter of the tool, but it can vary from as few as 48 on a small-diameter tool to 366 or more on a larger-diameter tool. The tool contains the onboard electronics necessary to acquire and store ultrasonic data, such as pulsers, receivers, and digitizers. The transducers are electronically pulsed at high rates to ensure coverage. The tool incorporates centering devices along its length, which are also used to propel the tool along the length of the pipe. Data are downloaded through a universal serial bus port to a laptop upon conclusion of the examination and then verified immediately to ensure data quality. An illustration of a smaller-diameter tool maneuvering around a 180°, short-radius bend is provided on the left in Figure 4-23. On the right is another ilistration of a fixed array tool.

Figure 4-23 A fixed transducer array ILI tool Used with permission from Quest Integrity

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The tool consists of multiple modules and is designed to negotiate multiple short-radius, 180°, 1-diameter bends, while traveling at speeds up to 24 in. per second. The ILI tool was demonstrated to EPRI on an 8-in.-diameter, 60-ft-long EPRI mockup that contained six elbows, as illustrated in Figure 4-24. Two of the elbows were back-to-back, and one was a 1-diameter bend elbow, confirming that the tool could negotiate such a bend. This is important because many ILI tools are limited to 1.5-diameter bends. The Quest Integrity ILI tool flowed through the entire 60-ft mockup, acquiring data throughout, in less than 1 minute. To further test the capability of the ILI tool, it was flowed back and forth for a total of three trips through the mockup, without incident. Depending on the application, the technology could also be tethered through a piping system.

Figure 4-24 EPRI 60-ft mockup

The results were analyzed with data analysis software to identify and characterize wall thinning. The software was capable of displaying traditional 2-D images, such as C-scans and B-scans, as well as 3-D graphics. An example of a 3-D view is provided in Figure 4-25 for a section of localized thinning at a depth of 0.10 in. in the EPRI mockup.

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Figure 4-25 Localized thinning in EPRI mockup

Dents can also be readily detected with internal ultrasonic tools. An example of a dent and the resulting C-scan image are presented in Figure 4-26.

Figure 4-26 A dent and the resulting C-scan

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4.7.2 Flow-Through In-Line Rotating Ultrasonic Transducer

The in-line application at ANO used a flow-conveyed, fixed transducer with a rotating-mirror ILI tool from A. Hak Industrial Services. The ILI uses a rotating mirror to direct the ultrasonic beam at a 90° angle to the pipe wall. As the tool is propelled, the spinning motion of the mirror results in a helical path of inspection, scanning down the length of the pipe. The tool used at ANO is shown in Figure 4-27. The right side of the tool contains the transducer and rotating mirror. Wheel encoders can also be seen in the tool that allow for tracking of the tool within the pipe. The short configuration of the tool allowed it to be conveyed through many elbows contained in the ANO pipe. The tool maneuvered more than 2000 ft of service water pipe at ANO in less than 2 hours, without incident.

Figure 4-27 A. Hak Industrial Services flow-conveyed tool using a rotating mirror

The tool contains onboard the necessary electronics to acquire and digitize the signal; however, in lieu of storing data onboard, data are transferred through an optical cable out the back end of the tool. This creates the advantage of monitoring data quality and inspection speeds in real time. For instance, if inspection speed is too fast, flow conditions can be changed to slow the tool. An example of a small-diameter ILI tool from A. Hak Industrial Services is provided in Figure 4-28.

Figure 4-28 A. Hak Industrial Services small-diameter, flow-conveyed tool using a rotating mirror

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Although the data can be monitored in real time, A. Hak has data analysis software that is used to detect and characterize wall thinning after the data are collected.

Depending on the application, the technology could also be tethered through a piping system.

4.7.3 Robotic Driven In-Line Rotating Ultrasonic Transducer

Applus RTD has an 8-in.-diameter robotically driven pipe inspection tool at EPRI. A photograph of the tool is provided in Figure 4-29.

Figure 4-29 Applus RTD pipeline inspection tool

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The tool uses a rotating probe head (see Figure 4-30) holding two transducers, 180° apart from each other. The transducers are positioned approximately 2.17 in. away from the inner pipe surface. The head is rotated 360° for each 0.79 in. of travel and acquires 128 measurement revolutions to obtain complete coverage. Travel speed is 1.57 in. per second. The system is controlled by an exterior computer through a high-strength 4101-ft umbilical cord that is wrapped on an electrically controlled winch. The winch and umbilical cord are designed to pull the tool out of a pipe if needed. The umbilical cord contains a fiber-optic cable for data transmission, a power cord, and an air line to expand the drive wheels to contact the pipe. The analysis system provides capabilities of viewing large sections of data with C-scan displays.

Figure 4-30 Applus rotating ultrasonic probe head

4.7.4 Robotically Driven In-Line Rotating EMATS Ultrasonic Probe

An EMAT robotic inline inspection crawler technology that can generate zero-degree and angle beam into the pipe was demonstrated at EPRI by Diakont Advanced Technologies. Because the ultrasonic energy is produced with EMATS, couplant is not required. The system also has onboard video cameras that can be used to assess the internal surfaces as well as monitor the EMAT probes. A photograph of a Diakont crawler is provided in Figure 4-31. This system has two EMAT sensors, each of which is attached to the telescoping arms shown in Figure 4-31. The telescoping arms are attached to a device that is rotated. The crawler has three tracks that are expanded to the inside surface of the pipe in order to center the rotating device within the pipe. The telescoping arms are expanded so that the sensors are in near contact with the inside surface of the pipe. There is a wheel mechanism at the end of the telescope arms that positions the sensor at a fixed distance from the inside pipe surface.

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Figure 4-31 Diakont EMAT in-line pipe robotic crawler [8]

The crawler is driven through the pipe length with the three-track drive system. The system is controlled with an exterior computer connected through a high-strength umbilical cord containing data transmission and power lines. Data are collected by rotating the sensors over the circumference of the pipe with the crawler in a fixed axial position. Data are transmitted through the umbilical cord to an external data collection system where it can be analzed in real time to determine data integrity. Figure 4-32 shows an example of the data acquisition analysis screen, which shows the EMAT A-scan as well as the video images. The tool is then indexed axially in the pipe, and the head is again rotated in the pipe to collect additional data. This continues until the desired examination volume is completed. The tool is capable of providing full coverage in straight runs of pipe. If complete coverage is not desired, the system can be manipulated to obtain whatever coverage is desired. Coverage in components such as elbows may be limited.

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Figure 4-32 Diakont EMAT data acquisition analysis screen [8]

4.7.5 Roboticaly Driven In-Line Circumferential Lamb Wave

WesDyne offers a Lamb wave technique that is deployed with a robotically driven crawler that uses two piezoelectric transducers to direct Lamb wave energy around the circumference of a pipe, as illustrated in Figure 4-33. These transducers are moved axially along the pipe to produce full coverage of the pipe with the crawler, as shown in the photograph of the WesDyne crawler in Figure 4-34. One of the advantages of this technique is that only two strips slightly wider than the transducers need to be cleaned rather than the entire pipe surface. Couplant is fed to the transducers from the tanks, shown on the left side of Figure 4-34, to transmit ultrasonic energy into the pipe. The crawler is driven through the pipe with a track drive system, as shown in Figure 4-34.

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Figure 4-33 Illustration of Lamb wave generation

Figure 4-34 WesDyne Lamb wave robotic crawler system

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Lamb waves are a type of guided wave in a plate that fills the volume between the inside and outside surfaces with ultrasonic energy and can propagate much longer distances than conventional ultrasonic bulk waves. Lamb waves have two components of displacement, one in the direction of propagation and one in the direction out of the plane of the wall thickness. Although Lamb waves only occur in flat plates, similar Lamb-type guided waves can propagate around a curved plate, such as the circumference of a pipe. These can be referred to as Lamb-type circumferential guided waves. One way to generate this type of guided wave is with a piezoelectric transducer mounted on a wedge material. These waves can travel around the full circumference of a pipe. A typical detection threshold is approximately a 5% change of the cross-sectional area that the wave fills. Because this process uses relatively small transducers, the cross-sectional area is approximately 1-in. wide times the pipe wall thickness. Therefore, the theoretical detection capability in a 0.375-in.-thick pipe wall would equal a 0.25-in.-wide 20% through-wall reflector.

As with any guided wave method, the optimum operating modes (A0, A1, S0, S1, and so forth) are selected prior to the inspection. Optimum modes are those that have minimal particle motion at the inner and outer surfaces to minimize attenuation from coatings, water, and so forth. These modes are generated by selecting appropriate frequencies and wedge angle based on material properties and pipe wall thickness. The system uses conventional broadband pulser and receiver to generate multiple lamb wave modes. All modes are recorded in the radio-frequency data, and signal processing is used to extract the mode of interest during analysis.

Both the wraparound signal and the weld crown signal are at a known physical distance from the transducers. The time of flight to these known signals is used to identify the group velocity of the mode that has propagated around the circumference of the pipe. If multiple modes propagate the full circumference, synthetic aperture focusing technique is used to isolate them.

After the mode(s) that have propagated have been identified, a fast Fourier transformation is performed to identify the frequency of that mode, which is then used as a parameter in a cross correlation filter to isolate the particular frequency. Synthetic aperture focusing technique processing is then performed to isolate the unique group velocity to generate a single mode in the data. If multiple modes are present, this process is repeated for the other modes. An example of the generated image is shown in Figure 4-35. The signals shown in the image were generated from the following:

A: 20% through wall by 0.25-in. notch

B: 40% through wall by 0.25-in. notch

C: 60% through wall by 0.25-in. notch

D: 80% through wall by 0.25-in. notch

E: Cluster of eight 1/8-in. diameter 50% through-wall holes

F: 0.5-in. diameter 50% through-wall hole.

G: Grind area 0.5-in. diameter ~30% TW at deepest

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Figure 4-35 WesDyne Lamb wave data analysis display

Innerspec has a Lamb wave technology similar to the technology described previously; however, instead of generating Lamb waves with piezoelectric crystals, the Innerspec system generates the Lamb waves with EMATs around the circumference of the pipe. EMATs offer the benefits presented in the EMAT section of the report including not having to use couplant and reduced surface condition requirements. Although the technology is generally operated on the exterior of the pipe, it could be operated on the inside of the pipe. A photograph of the device being used on the outside of the pipe is shown in Figure 4-36. The data analysis software is unique to the system and different from that described previously.

Figure 4-36 An Innerspec Lamb wave scanner

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4.8 Ultrasonic Monitoring Technology

Several approaches using ultrasonic-based concepts are available for permanent installation and monitoring of local wall thickness. Piezoelectric probes designed to be mounted to the outside pipe surface by adhesive compounds are available. The adhesive provides coupling between the piezoelectric and the pipe, and it is resistant to degradation caused by moisture and soil stress. A communication cable connects the transducer to an aboveground location, such as a test post. This allows periodic measurements to be made by connecting a compatible ultrasonic test unit to the test post.

Recently, new approaches to ultrasonic transducers include the proprietary sol-gel ultrasonic transducer deployment, in which an adhesive is applied to the pipe surface that forms the piezoelectric element, without the need for a separate transducer. This technology has similar performance characteristics to conventional probes but with the potential for a larger inspection footprint area than is economically viable with conventional probes. Applus RTD has developed this online, permanent inspection monitoring system for high-temperature applications. Sensors can be mounted directly onto piping (see Figure 4-37) or mounted on a metallic foil and then glued onto the structure.

°F = (°C x 9/5) + 32

Figure 4-37 Applus RTD PermaFlex sensors installed on an acid regeneration column

Top electrode: 15mm x 15mm

Top electrode: 7mm diameter

12 dB stronger

6 ConnectorsFFA.00.250.CTA27

6 FUT

200°C Cable

8 Pin Connector(Two Ground)

Steel PipeOD: 100 mm

Thickness: 4.5 mm

6 ConnectorsFFA.00.250.CTA27

6 FUT200°C Cable

8 Pin Male(Two Ground)

8 Pin Female(Two Ground)

Worst Corrosion Area

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The GE Rightrax system of online monitoring has been in use for several years. The basic components of the Rightrax monitoring system are the sensor and the data logger. The sensor is a multi-element, flexible, self-adhesive ultrasonic transducer array that is permanently bonded to a pipe at locations to monitor wall thickness. A calibration sensor, an identification chip, and a temperature sensor are built into the sensor unit, and the individual ultrasonic transducers are each accessed by means of an integrated control module. A self-adhesive tape provides ultrasonic coupling, and after it is installed, the sensor can be coated with any conventional insulating or proofing material that is used to protect the pipe or plant.

4.9 Other Zero-Degree Piping Applications

In addition to accurate wall thickness measurement, ultrasonic zero-degree techniques can be used to accomplish the following:

Identify and measure liquid levels.

Identify blockages and deposits.

Identify and measure hydrogen embrittlement.

Identify and measure internal discontinuities, such as laminations, porosity, cracks, slag inclusions, and voids.

5-1

5 GUIDED WAVE ULTRASONIC TESTING The common structures of pipes, tubes, plates, and rods that serve many engineering purposes are also natural waveguides. Electrical or mechanical energy can follow the boundaries of these waveguides to propagate long distances. Just as light energy can propagate down a fiber-optic cable, acoustic energy can propagate in the wall of a pipe. Acoustic waves that propagate in a pipe or other structure in which the wavelength is larger than the thickness of the structure are known as ultrasonic guided waves. Such waves can be used for NDE of materials to detect flaw mechanisms such as corrosion in buried pipe.

Guided waves offer many desirable benefits for examination of buried pipe. A 100% volume inspection of a large area can be conducted efficiently from a single access position. Inaccessible locations, including buried, insulated, coated, or obstructed areas, can be inspected without expensive measures to gain access to the pipe or structure. It requires only limited excavation and cleaning of the local pipe surface. These attributes make it a cost-effective technology for performing inspections that would otherwise be cost prohibitive.

Although guided wave technology is desirable for economical examination of buried pipe, it is a complex technology that has many variables and limitations. An understanding of its capabilities and limitations is essential for conducting an effective buried pipe guided wave inspection. The technology has detection and application limitations that must be considered when planning for inspection and assessing the results. Variables such as pipe geometry, coating type, coating thickness, soil loading, backfill material, burial depth, and pipe content have a substantial effect on guided wave propagation, sensitivity, and coverage capabilities. In many cases, these variables are not known until the examination is performed. For this reason, the effectiveness of the examination, in many cases, is not known until the examination is performed. However, the better these variables are understood before the examination, the better the chance of success.

The EPRI report Buried Pipe Guided Wave Examination Reference Document (1019115) was prepared specifically for guided wave examination of buried pipes in nuclear power plants [9]. The report provides information necessary for establishing a guided wave examination program and identifying variables and limitations that must be considered when using guided wave technology to examine buried pipe. Basic information on guided wave theory, data acquisition, data analysis, and a literature study are provided. In addition, a section identifying key tasks for a strategy to manage such a project is included. Equally important, inspection limitations are outlined to help ensure that capabilities are not overstated. By using the information in the report, a utility can implement successful guided wave inspections.

It is highly recommended that utilities obtain and use the EPRI report Buried Pipe Guided Wave Examination Reference Document (1019115) when examining buried pipes with guided wave technology [9]. This section contains excerpts from that report to provide a general overview of the guided wave technology. It is not intended to be a complete explanation of the technology or an application guide.

5-2

5.1 Guided Wave Wall Thickness Capability Summary

This section provides an overview of application variables associated with using guided wave technology to examine piping for wall degradation. Typical or expected results are presented in five tables. Although these results are accurate in most instances, it is important to understand that, like most technology applications, there are exceptions. To keep the information concise, the tables do not fully address all potential variations. This being said, the results shown in the tables are accurate in most situations. Table 5-1 summarizes technology function. Table 5-2 summarizes how the technology can be deployed. Table 5-3 addresses how surface condition, coatings, and other conditions affect technology application. Table 5-4 describes some of the piping materials that the technology can be used to examine. Table 5-5 captures capabilities for a number of variables. To provide a consistent review format, these tables are presented in each technology section.

Table 5-1 Guided wave: function

Table 5-2 Guided wave: deployment options

Function Comments

Thickness Cannot be used to provide accurate thickness

Can be used to profile surfaces No

Can detect internal and external surface metal loss

Yes

Can detect axial and circumferential metal loss Yes

Can discriminate between internal and external metal loss

No

Crack detection If sufficiently large

Embedded discontinuities Can easily detect embedded discontinuities if sufficiently large

Deployment Comments/Considerations

Manual deployment Yes

In-line deployment No

Automated outside surface No

Monitoring Yes

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Table 5-3 Guided wave: impact of surface and coating on results

Table 5-4 Guided wave: applicable pipe materials

Examination Surface Expected Outcome (Most Situations)

Smooth surface Yes

Rough surface Yes to a degree; increased surface roughness will decrease effective examination distance from sensor

Painted Typically, yes

Insulated Typically, yes

Vaulted or sleeved Typically, yes

Coated Coatings will shorten effective examination distance from sensor; thicker, softer coatings will more drastically shorten the distance

Lined Lining will shorten effective examination distance from sensor

Silt, tubercles, and similar debris Can shorten effective examination distance from sensor

Pipe in soil Soil or backfill will shorten effective examination distance from sensor

Embedded in concrete Typically no, unless concrete is disbonded from the pipe surface

Materials Comments

Carbon steel Yes

Stainless steel Yes, in most cases

Aluminum Yes

Cast iron Yes, in most cases

High-density polyethylene Unknown

Fiberglass Unknown

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Table 5-5 Guided wave: capability variables

Variable Yes No Comments

Single-sided access for volumetric examination

X

Capable of examining when piping is in service

X

Capable of noncontact examination X

Capable of examining significant axial pipe volume away from sensor

X

No couplant required X

Capable of producing an image showing size and shape of discontinuity

X Unrolled pipe display produces an image, but not highly accurate quantitatively

No radiological concerns X

5.2 Principles of Guided Wave Ultrasonic Testing

When sound is created from a source in a material, it naturally expands in all directions, just as ripples do when a pebble is dropped into a pool of water. However, when an object has boundaries, the boundaries prevent the wave front from naturally expanding in all directions. If the dimension between the boundaries is less than the wavelength of the sound, the reflections from the boundaries interfere with one another, rather than separating from each other as distinguishable pulses. Any reflections from the boundaries will superimpose on one another. When these multiple reflections interfere constructively, a guided wave mode will be formed. This occurs only at certain frequency and phase velocity components in the longitudinal axial direction.

Recently, guided waves have been used to inspect buried piping for the nuclear power industry. A guided wave inspection requires access to the surface at a particular location, either by accessing the pipe where it comes out of the ground or by digging an access hole. The surface is cleaned of any coating, dirt, or scale. A device composed of rings of either piezoelectric or magnetostrictive transducers is placed around the circumference of the pipe. The transducers are pulsed to generate a mechanical vibration in the pipe that travels down the pipe in both directions. The guided wave fills the entire cross section to achieve a 100% volume inspection.

Guided wave energy is reflected by variations in structure, such as an increase (weld crown) or decrease (thinning) in wall thickness, and by variations in component configurations, such as welded attachments, tees, or flanges. The extent of the reflection depends on the difference in acoustic impedance at the location—the higher the difference, the more energy reflected. Reflected energy with sufficient energy is sensed by the probe, and the instrument generates and records signals that can be evaluated. A rectified radio-frequency waveform is collected on a display, which shows the amplitude of the received signals as a function of distance. The waveform is similar to the amplitude (A-scan) that is typically used in conventional bulk wave ultrasonic inspections. A schematic of an A-scan is shown in Figure 5-1. The transducer ring

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generates a guided wave mode that propagates down the pipe. The ring then listens for returning echoes. The reflected echoes are detected at the ring, with their arrival time indicating their positions. Processing of the data enables nonaxisymmetric indications such as flaws to be discerned from axisymmetric reflectors such as welds.

Figure 5-1 Schematic of a guided wave inspection concept

There are three basic types of guided wave modes in a pipe: longitudinal, torsional, and flexural. Longitudinal and torsional waves can be axisymmetric, which means that the power distribution is uniform around the circumference of the pipe. Longitudinal modes contain radial and axial components of displacement. Torsional modes have only a circumferential component. Flexural modes are inherently nonaxisymmetric and possess all three components of displacement. Table 5-6 shows the different types and their characteristics.

Table 5-6 Guided wave mode types

Mode Type Symmetry Displacements Notation Generated By

Longitudinal Axisymmetric Axial and radial L(0,1), L(0,2), L(0,3), . . .

Axisymmetric transducers with an axial or radial displacement excitation

Torsional Axisymmetric Circumferential T(0,1), T(0,2), T(0,3), . . .

Axisymmetric transducers with a circumferential displacement excitation

Flexural Nonaxisymmetric Axial, radial, and circumferential

F(1,1), F(2,1), . . . , F(1,2), F(2,2), . . . F(n,m)

Reflections from flaws and nonaxisymmetric transducers

5-6

Flexural modes are more complicated but quite useful because reflections from flaws will have flexural modes, because the flaw is nonaxisymmetric. This concept can be used to determine whether a reflection is a weld or a flaw. This can be accomplished by using a transducer that is segmented around the circumference to detect the nonaxisymmetric distribution of the reflection. Flexural modes are currently being studied as a possibility to improve the sizing and classification of guided wave inspection techniques.

5.2.1 Guided Wave Sensors

5.2.1.1 Piezoelectric

Guided waves can be generated with piezoelectric transducers similar to those used in conventional ultrasonics. Guided wave energy is generated in the material by positioning the transducer in contact with the material and pulsing it with an electrical charge to generate a mechanical vibration into the pipe. Returned energy encountered by the piezoelectric transducer is converted from mechanical energy to an electric voltage, proportional to the magnitude of the mechanical force, which is recorded or presented on an instrument display.

Long-range guided wave pipe probes typically contain many piezoelectric transducers assembled into an array that is wrapped around and attached to a pipe. A photo of a Teletest probe containing more than 100 transducers is shown in Figure 5-2, and a picture of a Guided Ultrasonics Ltd. probe attached to a pipe is provided in Figure 5-3.

Figure 5-2 Teletest guided wave piping probe collar

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Figure 5-3 Guided Ultrasonics Ltd. guided wave piping probe collar

The collars are typically made for specific pipe diameters and allow for insertion of individual test modules into the rings. Probe collar sizes vary by the guided wave technique, equipment manufacturer, and pipe size.

Individual transducer modules are inserted into the probe collars to make up the probe. Each module contains several transducers that will make up the rings of transducers that go around the pipe. The number of transducer rings to be placed around the pipe is a factor of the desired guided wave type and the method of generating the wave type. The Teletest ring (see Figure 5-2) has five rings and is capable of generating torsional and longitudinal waves in a pipe. Three rings are used to produce the longitudinal waves, and two are used to produce the torsional wave.

Figure 5-4 shows a picture of the transducer module containing five transducers. The outer and middle transducers are used to generate longitudinal waves, and the other two transducers are used to generate torsional waves. The properties of all five transducers are the same. The difference between the longitudinal transducers and the torsional transducers is their orientation within the array. The axis of the torsional transducers is in the circumferential direction, and the orientation of the longitudinal transducers is in the axial direction of the pipe.

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Figure 5-4 Teletest torsional and longitudinal transducers module

An example of the Guided Ultrasonics Ltd. system module is shown in Figure 5-5. The module contains two rows of transducers that can be used to generate only a torsional wave. An array of this type of module can be used to generate only torsional waves.

Figure 5-5 Guided Ultrasonics Ltd. torsional transducers

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5.2.1.2 Magnetostrictive

A magnetostrictive sensor generates and detects guided waves based on the magnetostrictive effect, a phenomenon whereby variations in magnetization cause a physical dimension change in ferromagnetic materials. Mechanical waves are generated by supplying a time-varying electrical current to a coil placed adjacent to a ferromagnetic material. This causes a change in the magnetic fields within the material near the coil. The material changes its length locally, in a direction parallel to the applied field. This abrupt change (magnetostrictive effect) results in the generation of the guided wave in the material. When a mechanical wave (such as reflected energy) is encountered by the coil, it generates a changing magnetic flux in the coil, resulting in an electric voltage proportional to the magnitude of the mechanical wave. A magnetostrictive sensor setup typically consists of bonding or dry-coupling a thin ferromagnetic strip (such as iron-cobalt material) onto the component and placing coils over the strip. An example of a magnetostrictive sensor probe used on a pipe is shown in Figure 5-6.

Figure 5-6 Magnetostrictive sensor guided wave probe

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5.3 Data Analysis

Guided wave capabilities depend on several factors. It is important to understand these variables when planning for examinations and when applying subsequent results, because they do impact capabilities. Although guided wave technology can provide some quantitative information, it is primarily a qualitative screening tool. Table 5-7 provides a general overview of guided wave capabilities and limitations for examination of buried pipe.

Table 5-7 Capabilities and limitations of guided waves

Capabilities Limitations

Can provide a rapid method of screening relatively long runs of pipe

Cannot determine actual remaining wall thickness

Can detect inside and outside surface wall loss as well as circumferential cracks

Cannot differentiate between inside and outside wall loss

Can examine an inaccessible area of a component from a remote location

Cannot inspect past a flange or detect isolated small pits

Can be used to examine a pipe containing a product

Cannot precisely characterize reflector shape and size

The original intent of axisymmetric guided wave inspection was for assessment of general pipe condition, mainly in terms of wall thinning and corrosion detection. Because these are typically volumetric conditions, they have a projected area onto the pipe wall when looking axially down the pipe toward the defect. Therefore, the measure of detection capability adapted for guided wave is called percent cross-sectional area (percent CSA). It is the ratio of projected defect area to the total projected pipe wall area, times 100%.

The percent CSA can be misleading when assessing fitness for service because several shapes can exhibit the same percent CSA and, therefore, produce similar signal responses. For instance, the top and middle images in Figure 5-7 have the same percent CSA; however, the middle image has twice the surface area of wall loss. This is because the axial length of the indication in the middle image is twice as long as that of the top image. Similarly, the middle and bottom images have the same percent CSA, even though the depth of the middle image is twice as deep as that of the bottom image. This is the case because the circumferential extent of the lower image is twice that of the middle image. An additional scenario could be if the circumferential extent of the middle image were half that shown, the resulting depth of the same percent CSA would be through wall.

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Figure 5-7 Different size defects having the same percent CSA

Reflectors in a pipe can affect capabilities of detecting additional flaws further down the pipe. If the initial reflector is sufficiently large, it can mask those further down the pipe. A large reflector can reduce the penetration power and lead to significant mode conversions or distortion beyond it. If the reflector is smaller, however, defects greater than 2 ft apart in an axial direction can usually be found.

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Guided wave sensitivity levels depend on both pipe diameter and thickness. For a specific sensitivity level, the minimum detectable reflector size increases as pipe wall and diameter increase. If wall loss is confined to one area and a sufficiently small CSA, it is possible for a through-wall discontinuity to be undetectable. The size of an undetectable area is larger for thicker and larger-diameter pipe. Therefore, it is important to consider the flaw mechanism and the desired sensitivity level when using or considering the use of guided waves. Additional research is needed to further refine detection capabilities.

Guided wave techniques are still generally considered primarily screening techniques, providing indications of where to look further with local techniques for the verification and sizing of flaws. Reflections from flaws can be used to provide some qualitative information, whereas quantitative information is often difficult to obtain with high accuracy. One indication can often be determined to be more or less severe than another, based on the amplitude, pulse shape, and circumferential distribution of the received echo.

Flaws can be distinguished from axisymmetric features such as welds. This is done by using a segmented transducer around the circumference. If the reflection is fairly uniform for each segment, the indication is some type of axisymmetric reflector. When one or two segments receive most of the reflection, the reflector is nonaxisymmetric and likely a flaw. The circumferential location, and to some degree the extent, can be determined by the receiving transducer segments. Focusing can also be used to identify the circumferential location of the indication. Axial depth of an indication is currently not conducted. In general, it is not possible to determine whether a reflector is located on the interior or exterior surface of a pipe. Additional research is needed for more accurate flaw characterization.

Axial locations are calculated based on the guided wave velocity. The actual wave velocity pertaining to a particular structure can be different from the theoretical standard for that material. Because of this, calibrations for each structure based on known reflectors such as welds, backwalls, and flanges, can help correct the axial locations. Plus or minus 2 ft is usually possible. Calibrations are also required for improving inspection repeatability, because some factors such as temperatures and loaded fluids can change properties of pipes and coatings.

False call rates can increase when low signal-to-noise ratios are used in identifying flaws. Techniques such as using multiple wave modes and acquiring data at multiple locations can potentially reduce false calls. Focusing technique can also be used to reduce false call rates by increasing signal-to-noise ratios. Studies must be conducted to quantify probability of detection and false call rates.

The mockup (see Figure 5-8) consists of a 40-ft-long section of pipe (two 20-ft-long sections welded together) welded to an elbow, which in turn is welded to another 20-ft section of pipe. The pipe is 24-in. in diameter. Various wall thinning simulated reflectors are in the mockup, in the locations shown in Figure 5-8. Data were collected with the sensor placed on the end of the 40-ft section.

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Figure 5-8 Schematic of guided wave piping mockup

The collected data are displayed in A-scan format (see Figure 5-9), with time on the horizontal axis and signal strength on the vertical axis. Time 0 represents the sensor location. Several signals represent the various reflectors within the mockup.

Figure 5-9 Guided wave data obtained from the piping mockup

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5.4 Project Management

Good project management and communication are essential elements to a successful guided wave examination. Both the licensee and the inspection organization (vendor) must effectively understand and implement certain responsibilities. The licensee should establish an examination plan to document and communicate the objectives, expectations, and conditions of the inspection to the vendor. Effective and timely communication is necessary because, in many cases, component variables and, therefore, inspection capabilities, are not known until after the inspection is in process. A communication plan should be put in place between the licensee and the vendor to establish key contacts and to control the distribution of information. Guided wave procedures should be used in performing the examinations. Accurate reporting of results and limitations must be conducted. A bid specification establishing the licensee’s criteria for the guided wave examination should be prepared so that the licensee can assess the prospective vendors’ capabilities.

The purpose of the examination plan is to document the scope, purpose, expectations, resources, and variables for each inspection location. The licensee should prepare the examination plan in advance of the examinations with the best information available. The vendor should use the plan to prepare for the inspection and review it to determine whether additional information is needed and to assess whether the requirements can be met. When performing the examination, the vendor should use the plan as the source of utility requirements. The plan should be used for the pre-job meeting and daily meetings. The vendor should use the examination plan to document the work that was completed, and the licensee should use the plan to verify that requirements were met.

The examination plan will likely need to be modified during the project as additional information is identified. In many cases, variables are unknown until the pipe is uncovered, and therefore, inspection capabilities are unknown until examination is performed. Inspection results or limited capabilities can necessitate additional inspection locations. The licensee key contact should be responsible for keeping the examination plan up to date and distributed to the proper people.

5.5 Deployment Outside the Pipe

It is important that the locations of the bell holes be so that the access to the pipes is properly selected to maximize examination effectiveness. The guided wave probe should be placed in strategic locations in relation to piping features such as welds and piping geometry to ensure maximum coverage and to minimize undesired signal responses. Placement of the guided wave probes in relation to components such as elbows and tees is important because they affect transmission of guided wave ultrasonic energy.

In addition, adequate access must be obtained for probe placement and surface preparation. Access requirements depend on the probe type and manufacturer. The guided wave inspection vendor or equipment vendor should be contacted for specific information on access requirements. When possible, it is beneficial to excavate an area in which several lines can be examined from a single bell hole (see Figure 5-10). To do this, it is important to have accurate drawings of pipe locations or a method of accurately locating the pipe.

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Figure 5-10 Excavated buried piping

Inspection from two directions is advisable. If that is not achievable, it is beneficial to collect data from at least two different, adjacent points to obtain redundancy. Data from two locations can be used to confirm an indication location. Further, it helps to identify nonrelevant signals that could be bouncing back and forth between reflectors such as welds or other landmarks.

Access can also be gained to the pipe before it goes underground, such as at a pipe penetrating a basement wall (see Figure 5-11) or going into the ground. Examining a pipe in this way is cost effective; however, potential complications exist, such as the concrete-to-pipe interface as well as anchors or supports contained within a penetration.

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Figure 5-11 A pipe penetrating a basement wall

After the pipe is exposed, it must be properly prepared. Thick protective coating must be removed before the probe is placed onto the pipe. Depending on the coating, it can be difficult to remove, and in some cases, it requires scraping (see Figure 5-12). An additional complication is that some coatings have been found to contain asbestos.

Figure 5-12 Removal of buried piping coating

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The pipe surface will likely require additional surface preparation after the coating has been removed to ensure adequate coupling between the pipe surface and the probe. Piezoelectric guided wave probes typically do not use couplant but rather rely on probe surface–to–pipe surface contact. Magnetostrictive probes also require intimate contact to transmit guided wave energy. Improper surface conditions will, to some degree, inhibit the generation of guided waves into the pipe. Surface preparation can be difficult in some instances because clearance between the pipe and surroundings can be relatively tight. General guidance on surface condition includes the following:

Dirt and other foreign matter, such as scale and rust, should be removed.

Paint is allowable if it is in good condition, tightly adhering, and relatively thin.

Coatings thicker than 0.04 in. will likely require removal.

Corrosion or pitting can inhibit transmission of guided wave energy.

5.6 Deployment for Monitoring

Most guided wave inspections currently being performed use portable transducer collars that are strapped around the pipe at any given location. This requires a hole to be dug each time the guided wave tests are conducted. Excavation is an expensive process that also adds the risk of damaging the pipe in the process. However, guided wave transducers exist that can be permanently installed on buried piping systems. These permanently installed systems can significantly reduce the need for repeated excavations and add the benefits of improved sensitivity and reliability of data interpretation by trending the guided wave responses.

The system consists of a low-profile, flexible circuit transducer that is glued and clamped around the exposed pipe surface. It is sealed with a polyurethane jacket to protect it during backfill as well as from the elements and to help ensure its lifetime. The unit has a height of 0.39 in. from the pipe surface. A cable extends from the transducer to a desired location above the ground, where a weatherproof electrical connection box is set up. Initial tests are done to verify that the transducer is installed adequately. Further tests are then done after backfill. Future tests can be performed by simply bringing the instrumentation to the site of the connection box and plugging in the cable.

Figure 5-13 illustrates an example of a transducer collar that has been permanently mounted on a pipe, where the threat of corrosion has been validated and long-term monitoring is required. The sensor is located beneath the red polymer weather-protection coating, and the electrical connection box is the yellow box on the right side of the figure.

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Figure 5-13 Permanently installed guided wave collar

This approach also enables trending of guided wave data. Manufacturers have observed sensitivity to cross-sectional changes of <1% of the total cross section. They have seen virtually no difference in data quality from the portable transducers that have been more commonly used. Since 2006, these systems have been installed on oil terminals and in some subsea applications. Technical specifications for operating temperatures give the range of -4°F to 194°F.

As with other guided wave approaches, permanently mounted guided wave transducer collars do not measure and report pipe wall metal loss directly; instead, they characterize metal loss reflectors on the basis of area of circumferential metal loss (estimated cross-sectional loss). Flaw depth and volumetric loss cannot be accurately measured; consequently, guided wave currently does not enable determination of structural or leakage integrity. Therefore, excavation and direct examination is the recommended response for characterizing indications of a guided wave screening tool.

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6 REMOTE FIELD TESTING Piping and tubing can be internally inspected using the RFT concept. RFT is an NDE technique that uses low-frequency AC and through-wall transmission to inspect pipes and piping systems. The through-wall nature of the technique allows external and internal defects to be detected with approximately equal sensitivity. This characteristic is especially valuable for the testing of thick-walled ferromagnetic pipeline and piping systems. RFT often does not require cleaning of the pipe and is not sensitive to internal coatings or linings.

RFT is not sensitive to the presence of nonmetallic materials. Therefore, the technique can be applied to piping without cleaning the internal surface and is not sensitive to external or internal coatings or linings. However, some internal pipe cleaning might be required to ensure proper sensor access and to reduce lift-off effects.

RFT, like other electromagnetic techniques, is sensitive to nonrelevant indications that result from magnetic permeability variations. Accordingly, significant effort is expended during data analysis to discriminate between relevant and nonrelevant indications to minimize false calls.

Remote-field eddy current measurement consists of an exciter coil and one or more receiver elements. The exciter coil has typically a ring shape with a diameter that approximates the pipe’s internal diameter. The sensing elements are placed at a sufficient distance from the exciter coil so that eddy current direct magnetic field is not significant and the remaining so-called remote magnetic effectively saturates the pipe.

In the basic RFT system (see Figure 6-1), there is one exciter coil and one detector coil. In this basic configuration, both coils are wound coaxially with respect to the tested pipeline or piping system and separated by a distance greater than twice the pipe diameter. This axial distance is characteristic of RFT. If the exciter and detector were to be placed close together, the detector would measure only the field generated by the exciter in its vicinity.

Figure 6-1 Basic principle of remote field eddy current probe

Driver or Exciter Coil Pickup or DetectorCoil

External Field

Remote Field

Indirect Coupling Path

Direct Field

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The single detector coil, called the bobbin arrangement, exhibits limited pitting resolution, providing wall loss information that is proportional to the pipe cross-sectional change. RFT pitting resolution can be improved by using multiple coils arranged circumferentially, each of them resolving the wall loss changes in their vicinity. This latter arrangement is called RFT detector array.

Anomalies are detected when they interfere with the preferred eddy current paths and magnetic fields. The use of separate exciter and sensor elements means that the RFT probe operates naturally in a driver-pickup mode instead of the impedance-measuring mode of traditional eddy current testing probes. The following three conditions must be met to make the probe work:

The exciter and sensor must be spaced relatively far apart (greater than twice the pipe diameter) along the pipe axis.

An extremely weak signal at the sensor must be amplified with minimum noise generation or coupling to other signals. Exciter and sensing coils can consist of several hundred turns of wire to maximize the signal strength.

The correct frequency must be used. The inspection frequency is generally so that the standard depth of penetration (skin depth) is the same order of magnitude as the wall thickness (typically one to three wall thicknesses).

When these conditions are met, changes in the phase of the sensor signal with respect to the exciter are directly proportional to the sum of the wall thicknesses at the exciter and sensor.

6.1 Remote Field Wall Thickness Capability Summary

This section provides an overview of application variables associated with using RFT technology to examine piping for wall degradation. Typical or expected results are presented in five tables. Although these results are accurate in most instances, it is important to understand that, like most technology applications, there are exceptions. To keep the information concise, the tables do not fully address all potential variations. This being said, the results shown in the tables are accurate in most situations. Table 6-1 summarizes technology function. Table 6-2 summarizes how the technology can be deployed. Table 6-3 addresses how surface condition, coatings, and other conditions affect technology application. Table 6-4 provides some of the piping materials the technology can be used to examine. Table 6-5 captures capabilities for a number of variables. To provide a consistent review format, these tables are presented in each technology section.

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Table 6-1 Remote field: function

Table 6-2 Remote field: deployment options

Table 6-3 Remote field: impact of surface and coating on results

Function Comments

Thickness

Yes, but not as accurate as ultrasonics. Accuracy is affected by material properties and requires calibration with piping of similar metallurgic properties. RFT assessments should be verified with ultrasonics, if practical.

Can be used to profile surface No.

Can detect internal and external surface metal loss

Yes.

Can detect axial and circumferential wall loss Yes.

Can discriminate between internal and external metal loss

No.

Crack Detection No.

Embedded Discontinuities Yes, if volumetric and sufficiently large.

Deployment Comments/Considerations

Manual deployment No

In-line deployment Can be deployed with free-swimming, tethered, and crawler tools

Automated outside surface No

Monitoring No

Examination Surface Expected Outcome (Most Situations)

Bare and smooth Yes

Bare and rough Yes

Painted Yes

Coated Yes

Lined Yes

Silt, tubercles, and similar debris Yes

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Table 6-4 Remote field: applicable pipe materials

Table 6-5 Remote field: capability variables

Variable Yes No Comments

Single-sided access for volumetric examination

X

Capable of examining when piping is in service

X

Capable of noncontact examination X

Capable of examining significant axial pipe volume away from sensor

X

No couplant required X

Capable of producing an image showing size and shape of discontinuity

X

No radiological concerns X

6.2 Instrumentation for RFT

Instrumentation includes a recording device, a signal generator, an amplifier (because the exciter signal is of much greater power than that typically used in eddy current testing), and a detector. The detector can be used to determine exciter/sensor phase lag or can generate an impedance-plane-type of output such as that obtained with conventional driver-pickup eddy current testing instruments.

Instrumentation developed specifically for use with RFT probes is commercially available. Conventional eddy current instruments capable of operating in the driver-pickup mode and at low frequencies can also be used. In the latter case, an external amplifier is usually provided at the output of the eddy current instrument to increase the drive voltage. The amplifier can be an audio amplifier designed to drive loudspeakers, if the exciter impedance is not too high.

Materials Comments

Carbon steel Yes

Stainless steel Yes, but requires custom instrumentation

Aluminum Yes, but requires custom instrumentation

Cast iron Yes

High-density polyethylene No

Fiberglass No

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6.3 Pipe Threats Examined with RFT

Signals from pipes and piping systems can be categorized as follows:

Internal corrosion

— General wall loss caused by flow-accelerated corrosion

— Localized pit damage caused by microbial-induced corrosion

External corrosion

— General wall loss for pipe systems without coating or with extensive coating degradation and no cathodic protection

— Localized pit damage for coated pipe systems

RFT is generally used for detection of wall loss in carbon steel piping. Localized pitting can be detected using detector arrays, as described previously. Pitting resolution depends on the detector array arrangement and the deployment mechanics.

An advantage of RFT is its ability to measure wall thickness through scale, coatings, and liners, with approximately equal sensitivity to outer and internal wall loss. RFT can be used to examine cast iron, ductile iron, and steel pipes through as much as 0.98 in. of scale or tubercles, which is common in many raw water piping systems. This is significant because it reduces the need for cleaning. Piping systems can be inspected without removal of oil, sand, and wax. RFT has also been used to inspect through high-density polyethylene-lined steel piping for metal loss condition.

6.4 Advantages, Disadvantages, and Limitations of RFT

Advantages of RFT include the following:

There is noncontact measurement, resulting in minimal friction with pipe wall.

There is ability to measure wall thickness through scale, coatings, and liners.

Typically requires less cleaning than other ILI tools.

There is approximately equal sensitivity to internal and external wall loss.

A couplant is not required.

RFT can be used to detect internal and external metal loss.

RFT is sensitive to axial and circumferential orientated metal loss.

Disadvantages and limitations of RFT include the following:

Inspection speed is generally less than that of other ILI NDE methods.

RFT cannot discriminate between internal and external metal loss.

ILI tool sensors are specific to pipe size and material characteristics.

External metallic conditions such as clamps can affect RFT signal.

RFT Cannot examine components such as elbows or the adjacent piping within two pipe diameters.

It exhibits reduced pitting spatial resolution when compared to MFL. For in-line deployments, a 1-in.-diameter pitting resolution is achievable at 1-in. lift-off when using detector arrays.

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6.5 Deployment Outside the Pipe

RFT technology, in its true sense, is not deployed outside the pipe. Variations of RFT principles are used outside the pipe; they are addressed in Section 8, Electromagnetic Technology (Ferromagnetic).

6.6 Deployment Inside the Pipe

RFT ILI tools are commercially available that can be used to examine a relatively wide range of pipe sizes made of various ferromagnetic materials. However, an individual RFT ILI tool might be limited to a range of piping sizes and material properties. If an ILI tool is not available for a specific diameter or material, one can generally be designed and constructed for the specific application needs. Equipment and inspection vendors can provide specific information on ILI tool availability and, if necessary, lead times and cost to build specific ILI tools.

Some available RFT ILI tools are self contained, including electronics, batteries, memory, sensors, and odometer. Tools are designed to traverse bends and operate at pressures up to 700 psig. The self-contained tools can be used in free-swimming operations or carried on crawlers. Free-swimming ILI tools require two access points and special facilities for launching and receiving, and they have limitations for passing through pipe branches, tees, and valves. Some RFT tools are available with the instrumentation separated from the sensor head and placed outside the pipe. These tools are deployed using a tethered configuration. The tethered tools have the advantage that a single point of access is required, but the tool range is limited by the number elbows that it can traverse, with three elbows generally being considered the limiting number. Figure 6-2 illustrates a tethered RFT tool configuration. This tool uses a beads-on-a-string configuration, which gives it the flexibility to negotiate 90° elbows. The diameter of the tool is smaller than the ID of the pipe to allow for protrusions, lining, and scale.

Centralizers maintain a uniform annulus between the tool and the pipe, and a wire line tether runs over an odometer sheave to measure the distance travel of the tool. A picture of a 3-in.-diameter RFT tool before deployment is shown in Figure 6-3.

Figure 6-2 A tethered RFT tool

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Figure 6-3 Deployment of a 3-in.-diameter RFT tool

To overcome the elbow number limitations, two other delivery systems have recently been developed: wheel-propelled and guide-wire-propelled systems (see Section 16, ILI Technology).

6.7 Signal Analysis for In-Line Operations

Wall thickness estimations are performed by calibrating the phase change of the sensor signal. Calibrations are typically performed using a long pipe section of similar material properties to the pipe of interest and machining defects of the size and shape of interest. Although defects affect both the amplitude and the phase of the signal, the amplitude is also sensitive to changes in the material permeability and/or lift-off. Therefore, phase analysis is the primary method of evaluation, with amplitude analysis providing supporting evidence for false call discrimination.

The signal analysis technique for the basic bobbin coil arrangement is well documented. Bobbin coil signals are tolerant of lift-off. Polar plots are used to measure the pipe cross-sectional changes and to discriminate between relevant and nonrelevant indications.

The signal analysis techniques for the detector array require sophisticated analysis software to identify wall loss locations. Detector array signals are sensitive to lift-off variations. Because in in-line operations, the detector coils are likely to move up and down, depending on the internal pipe environment and the mechanics of the delivery tooling, discrimination between relevant and nonrelevant signals requires the use of filters. Filter software is generally vendor proprietary, but it is based on standard signal processing methods, such as low pass, high pass, median, and harmonic. Use of filters requires the vendor to be highly qualified in their application because the filters can actually mask relevant defect information.

In addition, significant improvement in the signal-to-noise ratio is achieved by maintaining the detector array centralized during the examination. Performance of a vendor delivery system’s centralization mechanics is not well documented. Figure 6-4 shows an example of a local wall loss indication at the bottom of the pipe.

6-8

Figure 6-4 Remote field testing local wall loss indication

6.7.1 RFT of Prestressed Concrete Pipe for Wire Failures

The remote field eddy current measurement process has been adapted for assessing the wire condition in prestressed concrete piping [10].

Prestressed concrete piping is widely used in water mains and has also been applied at some power plants for service and cooling water applications. The pipes are typically of large bore, and their wall cross section includes a relatively thin carbon steel liner that is reinforced externally with carbon steel wire, all this embedded in concrete to provide environmental protection.

Failure of these systems occurs when the wires break due to corrosion. When enough wire failures accumulate on a pipe section, the liner is no longer capable of holding the operating pressure, and the pipe bursts catastrophically.

The remote field eddy current process was adapted to estimating the number of wire breaks by a technique called remote field eddy current/transformer coupling (RFEC/TC).

When the wires are in good condition, the combination of the wires and the liner act as a transformer, amplifying the magnetic field that is sensed remotely. The failure of wires directly decreases this amplification, thereby providing a measure of wire breaks after calibration. The process is tolerant of lift-off.

Deployment is typically done with the pipes drained. A cart, driven by an individual, runs through the pipe with the exciter at the front and a spinning detector on the back that collects data as it travels (see Figure 6-5).

6-9

Figure 6-5 Pure Technologies’ remote field eddy current/transformer coupling tool for assessment of prestressed concrete piping

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7 MFL TECHNOLOGY MFL is an electromagnetic examination technique that induces a magnetic field into a ferromagnetic metal to essentially create a magnetic circuit within the material. This is conducted with high-strength U-shaped permanent magnets or electromagnets of sufficient strength to magnetically saturate the material. Permanent magnets are more widely used because they do not require an electrical power supply. Although electromagnets are not as widely used because they require power, they do permit adjusting the magnetization level to the application, and they can be turned off during installation of the device into the pipe. Brushes are often used between the magnets and the piping surface to complete the circuit. Magnetic lines of flux flow between the magnetic poles and are monitored with various magnetic sensors placed between the magnet poles. Areas of corrosion or cracking interrupt this flow and, if of sufficient strength, will be detected by the sensors. Mechanical damage, such as dents and gouges as well as inclusions, can cause a diversion in the magnetic field and therefore can also be detected. The output of the sensors is recorded as the tool travels and is subsequently analyzed to identify and characterize damage. The concept is illustrated in Figure 7-1.

Figure 7-1 Illustration of the MFL concept

7-2

MFLs generally achieve high spatial resolution of discontinuities, which is especially beneficial for detection of pitting-type flaws. The degree of detection is dependent on the MFL technology used, which is generally divided into low-resolution and high-resolution categories. The low-resolution tools typically measure one component of the magnetic field and provide corrosion detection information with coarse pit-depth grading. High-resolution devices measure two or three components of the magnetic field, improving both detection and characterization capabilities. These high-resolution tools are becoming more prevalent because of their higher performance in detecting and characterizing corrosion-type defects.

Historically, MFL internal inspection devices have been limited to use in long piping systems that have sweeping bends. This is because of the large size and limited flexibility of the delivery system because it houses relatively large permanent magnets. However, advancements in the technology and the delivery systems have led to MFL systems that can now be used in piping containing elbows with 1.5-radius bends. Prior to conducting an MFL examination, it is critical to assess piping conditions to determine whether the delivery system will be adequate. Considerations such as pipe branches, tees, valves, and diameter changes must be evaluated. The condition of the inside surface must also be considered because coatings, linings, and debris impact performance capabilities. The degree to which these considerations can be tolerated is system dependent.

MFL data acquisition can be conducted at a relatively fast rate because 360° coverage is achieved by placing MFL sensors around the entire circumference of the tool. Inspection speeds on the order of 7 mph can be achieved.

7.1 MFL Wall Thickness Capability Summary

This section provides an overview of application variables associated with using MFL technology to examine piping for wall degradation. Typical or expected results are presented in five tables. Although these results are accurate in most instances, it is important to understand that, like most technology applications, there are exceptions. To keep the information concise, the tables do not fully address all potential variations. This being said, the results shown in the tables are accurate in most situations. Table 7-1 summarizes technology function. Table 7-2 summarizes how the technology can be deployed. Table 7-3 addresses how surface condition, coatings, and other conditions affect technology application. Table 7-4 provides some of the piping materials the technology can be used to examine. Table 7-5 captures capabilities for a number of variables. To provide a consistent review format, these tables are presented in each technology section.

7-3

Table 7-1 MFL: function

Table 7-2 MFL: deployment options

Table 7-3 MFL: impact of surface and coating on results

Function Comments

Thickness Not direct thickness. MFL tools estimate wall loss using proprietary models whose accuracy is vendor dependent. It is customary to group the estimates into a few wall loss bands.

Can be used to profile surface Yes. The method can achieve high spatial pitting resolution.

Can detect internal and external metal surface loss

Will detect both inside and outside surface connected pitting. However, there is a maximum wall thickness for detection of opposite side metal loss that is system dependent.

Detection of gradual wall thickness change is limited and can require special processes.

Can detect axial and circumferential wall loss

No. The method exhibits directional sensitivity and might not detect long axial defects.

Can discriminate between internal and external metal loss

System dependent.

Crack detection Yes.

Embedded discontinuities Yes.

Deployment Comments/Considerations

Manual deployment Yes

In-line deployment Yes

Automated outside surface Yes

Monitoring No

Examination Surface Expected Outcome (Most Situations)

Bare and smooth Yes

Bare and rough Yes

Painted Yes

Coated System dependent. Most systems can tolerate thin coating, and some can tolerate thick coatings.

Lined Generally, no, but some systems can tolerate linings.

Silt, tubercles, and similar debris

No. Up-and-down movement of the magnets caused by the debris will affect the magnetic saturation circuit and technique performance. Also, because the magnets run close to the pipe wall, debris accumulation ahead of the tool risks the tool getting lodged.

7-4

Table 7-4 MFL: applicable pipe materials

Table 7-5 MFL: capability variables

Variable Yes No Comments

Single-sided access for volumetric examination

X

Capable of examining when piping is in service

X

Capable of noncontact examination X

Capable of examining significant axial pipe volume away from sensor

X

No couplant required X

Capable of producing an image showing size and shape of discontinuity

X

No radiological concerns X

7.2 High-Resolution MFL

High-resolution MFL systems measure flux leakage in the axial, radial, and circumferential directions, as illustrated in Figure 7-2, by mounting the magnetic sensors in strategic orientations. This information can be processed to produce unique signatures for each of the orientations collected. Examples of this for metal loss are displayed in Figures 7-3 and 7-4. The displays in Figure 7-3 show the 3-D displays for each of the orientations for a discontinuity. As can be seen, the signals are different for each orientation. Figure 7-4 shows a 2-D display for of the three orientations for 25%, 40%, 50%, 60%, and 75% through-wall discontinuities. The figure also shows that the magnitude of change in the signal increases as discontinuity depth increases.

Each signature provides unique information that an analyst can use to detect discontinuities as well as length-, width-, and depth-size them. This combined three-axis approach provides a more complete assessment and, therefore, more accurate sizing results than can be obtained with single-axis low-resolution MFL tools that only measure the axial component. In addition to the

Materials Comments

Carbon steel Yes

Stainless steel Only ferromagnetic stainless steels

Aluminum No

Cast iron Yes

High-density polyethylene No

Fiberglass No

7-5

characterization advantages, the three-axis approach provides multiple signals that can be compared with each other to minimize false call. However, the pit wall loss estimation from the three-axis information requires a more complex calculation model. These models are proprietary, and their estimation accuracy is vendor dependent.

Figure 7-2 Illustration of a three-axis MFL

7-6

Figure 7-3 Example of 3-D signal displays from a high-resolution three-axis MFL-type system

Figure 7-4 Example of 2-D signal displays for a high-resolution three-axis MFL-type system for discontinuities of various depths

7-7

7.3 MFL Sensors and Calibration

The most common sensors used in an MFL system are Hall effect devices and coils. They are placed around the circumference of the tool between the magnet poles with the spacing between the sensors so that complete coverage of the pipe surface is achieved.

The coil responds to changes in the magnetic field and can be arranged with its faces parallel or perpendicular to the inspected surface. The signals induced in single coils as they pass through leakage fields depend on the distance from the coil face to the surface, as well as the orientation, area, and number of turns of the coil. The coil is also rugged and has well-characterized performance. Because the coil signal responds to the magnetic field change, MFL tools instrumented with coils perform best when travelling at constant speed.

The Hall sensor is a solid-state device that measures magnetic field intensity. Because it can be made with a smaller active area, it typically provides higher flaw resolution. The Hall sensor can also be placed at various orientations allowing for measurement of flux leakage at multiple orientations, as shown in Figure 7-2. This capability allows for three-axis MFL technology. Tools instrumented with Hall sensors are tolerant of speed changes during the scan.

MFL systems require calibration because signal response is dependent on material properties such as permeability and wall thickness. As such, calibration should be done on like materials. In addition, the shape and size of calibration discontinuities must be considered because they affect signal response. Discontinuity shape and size versus signal response is a relatively complex subject and beyond the scope of this report. The MFL service provider, as well as other resources, should be consulted.

7.4 Data Analysis

MFL data are typically recorded electronically during data acquisition and subsequently analyzed by a skilled MFL data analyst using sophisticated data analysis software. Examples of data analysis software output are provided in Figures 7-5 and 7-6, which were obtained with Inline Devices InSight3 software.

3 InSight is a registered trademark of Inline Devices.

7-8

Figure 7-5 MFL data analysis output provided with Inline Devices InSight data analysis software, Example 1

Figure 7-6 MFL data analysis output provided with Inline Devices InSight data analysis software, Example 2

7-9

Detection capabilities are affected by the discontinuity’s orientation to the magnet poles of the MFL system as the flux lines travel between the magnet’s poles. Specifically, detection capabilities are best when discontinuities are transverse to the flux lines and least when parallel to them to the point of not being detectable. This is especially the case for narrow discontinuities, such as cracks. In addition, detection is not only dependent on the strength of the MFL signal received from a discontinuity but also the strength of that signal compared with the associated noise signals, known as signal-to-noise ratio. Signal-to noise ratios are affected by several factors, including system design, sensor type, cleanliness, surface condition, impurities, scanning speed, and desired discontinuity size. MFL signals are generally low in amplitude and require amplification. In addition, they typically require filtering to remove unwanted noise signals.

MFL estimates the pit wall loss by modeling the leakage responses using proprietary techniques as opposed to ultrasonics time-of-flight measurements. It is customary to group the estimates into a few wall loss bands to improve the confidence of the results.

Complementary techniques might be needed to determine whether wall loss is on the inside or outside pipe surface. This can be done by placing a high-frequency eddy current transmitter-receiver in the inspection probe that exhibits detection sensitivity to inside pipe surface defects only. Because phase discriminators are typically not used in MFL techniques, this indication characterization is based on amplitude response.

7.4.1 Nonrelevant Signals Caused by Magnetic Permeability or Stress Changes

Stress and magnetic permeability variation affect the flux-carrying capability of magnetic materials. A local decrease in flux-carrying capability will generally cause a signal similar to a metal loss signal. In addition, a local increase in flux-carrying capability will cause a decrease in signal amplitude. This signal can result in false calls when performing wall loss assessments.

Stress changes can also lead to signals detectable by the MFL process. In the case of axial stress, the change in flux-carrying capability is larger than the length of magnetizer, causing the amount of flux in the pipe to be altered. For tensile stresses, the overall flux levels in the pipe will increase, and, for compressive stresses, the flux level will decrease.

7-10

7.4.2 Thin, Crack-Like Defects

Thin, crack-like defects set up a local dipole. The strength of this dipole is proportional to the field of each pole times the separation of the poles. For tight cracks, such as stress corrosion cracking, the separation is small; therefore, the dipole is weak. The leakage from the dipole can be detected as long as the sensor is close to the defect. Detection of cracks using ILI works best for cracks that are open to the internal surface. For cracks on the external surface, the crack must be deep, so that the dipole is close to the internal surface, and wide, so that the dipole is strong. From an inspection perspective, the following features of crack-like defects are important:

Crack detectability improves as the crack width increases. Stress corrosion cracking and stitched electric resistance-welded welds are quite tight, making their detection and sizing difficult.

Proximity of adjacent defects and pipeline features affect detectability. Stress corrosion cracking often occurs in colonies, confusing the inspection signals and making data interpretation difficult. Seam weld defects, by definition, occur near seam welds, which often introduce a geometric discontinuity. This discontinuity also makes signal interpretation difficult.

7.5 Deployment Outside the Pipe

MFL devices are available for application from the external surface of a pipe to detect and characterize internal wall loss. An example of such a system is provided in Figure 7-7. The detection and sizing performance for outside-the-pipe MFL scanners can vary widely, depending on the design and intended application. Scanners can be used for general condition screening or can provide high-level detection and sizing performance such as that found in tools used to inspect coil tubing for the energy industry. The equipment manufacturer should be consulted for detailed performance specifications.

Figure 7-7 MFL inspection on outside surface

7-11

7.6 Deployment Inside the Pipe

MFL-based ILI tools are widely and effectively used in industries such as the pipeline transmission industry. They can be used to detect and characterize cracks, pitting, corrosion, and erosion in piping systems. Extensive testing is performed before the tool enters an operational pipeline; using a known collection of measured defects, tools can be trained and tested to accurately interpret the various defect signals. MFL inspection tools are suited for inspection of exposed, bare, painted, or thinly coated ferromagnetic components.

Unfortunately, the designs of many of these tools are for long relatively straight runs of pipe and not piping containing components such as elbows that are common to many nuclear power piping applications. Fortunately, MFL ILI tooling has become available and is capable of maneuvering through piping systems containing elbows. The photograph in Figure 7-8 shows an Inline Devices MFL ILI tool designed to go through piping with elbows. This particular tool is a flow-through-type device that is moved through the pipe with product flow. Another example of an inline tool that can be maneuvered through a pipe with elbows is the Pure Technologies tool shown in Figure 7-9. This large-diameter tool is expandable/collapsible and can be manually moved through a pipe.

Figure 7-8 Inline Devices MFL ILI tool designed to go through elbows

7-12

Figure 7-9 Pure Technology expandable MFL ILI tool

Some of the free-swimming ILI tools can also be attached to a tethered wire line and pulled through piping configurations. The length of pipe that can be inspected is limited by the wire line pull capacity relative to the number of bends that will be encountered.

Depending on the requirements of the examination, an MFL ILI tool can consist of a single body, as shown in Figure 7-9, or multiple segment tool, as shown in Figure 7-8. In any case, the device must house the magnetizing section, MFL sensors, power supply (typically a battery), and a data acquisition and storage device, either in one segment or multiple segments. The size of the power supply is dependent on the length of the pipe; long runs can require multiple segments. Additional functions, such as calipers to measure the interior of the pipe for abnormalities such as dents, encoders for positional information as well as measuring tool speed, and inertial mapping devices for mapping piping location and configuration, can also be used.

Differences in performance for individual technologies are principally due to the number of sensors used in the tool designs relating to measurement of the characteristic magnetic field vectors (axial, circumferential, and radial). Some ILI MFL tool designs use triaxial magnetic field measurement, and others characterize defects based on one- or two-axis field vectors. The level of technology selection depends on the level of defect assessment to be supported (Code Case N-513-2, Level I, II, or III, ASME B31G, and so on) and the expected frequency and severity of the corrosion [11, 12].

Pipe wall deformations are an indication of mechanical damage and are most commonly a result of outside force causing dents or ovality. MFL sensor technology cannot directly detect and measure pipe wall deformation; therefore, ILI tools generally use additional mechanical calipers,

7-13

which generally consist of fingers or arms that directly contact the pipe wall, translating displacement of the arms into a measurement of deformation relative to the center of the ILI tool. An example of calipers is shown in the left segment of the Inline Device MFL ILI tool shown in Figure 7-8. Although mechanical damage may not provide a significant threat to low-pressure piping typical of nuclear buried piping, it can be useful for identifying and locating exterior coating damage caused by exterior deformation.

Internal pipe surface cleanliness is an issue for flow-conveyed, free-swimming ILI tools. For MFL ILI tools, a thin layer of oxide or debris can be tolerated for sensor performance, but the presence of debris can adversely affect the differential pressure capability of the drive cups for all flow-conveyed ILI tools, regardless of the NDE technology. Internal cleaning of pipe systems can be accomplished by pumping a cleaning pig or chemical cleaning. A variety of cleaning pig designs are available on the market.

8-1

8 ELECTROMAGNETIC TECHNOLOGY (FERROMAGNETIC) A variety of NDE technologies have been developed that are extensions of conventional eddy current or RFT technologies. They are sometimes characterized by proprietary approaches, making technologies offered by specific equipment vendors unique. This section describes the following electromagnetic technologies that are applicable to piping:

Inside or outside the pipe

— Pulsed eddy current

— Low-frequency electromagnetic technique (LFET)

— Saturation low-frequency eddy current (SLOFEC)

Outside the pipe

— External pipeline integrity tool (E-PIT4)

— ACFM

— Meandering wire magnetometer array

Above the pipe

— Magnetic tomography method

— Concentric magnetic field method

8.1 Pulsed Eddy Current Technology

Pulsed eddy current is suitable for detection of area corrosion in ferromagnetic objects with various wall thicknesses. It can be used to examine through insulation, meaning that insulation material can be left in place. Examples of pulsed eddy current applications are shown in Figure 8-1.

4 E-PIT is a registered trademark of Russell NDE Systems, Inc.

8-2

Figure 8-1 Pulsed eddy current examples and uses

8.1.1 Pulsed Eddy Current Wall Thickness Capability Summary

This section provides an overview of application variables associated with using pulsed eddy current technology to examine piping for wall degradation. Typical or expected results are presented in five tables. Although these results are accurate in most instances, it is important to understand that, like most technology applications, there are exceptions. To keep the information concise, the tables do not fully address all potential variations. This being said, the results shown in the tables are accurate in most situations. Table 8-1 summarizes the technology function. Table 8-2 summarizes how the technology can be deployed. Table 8-3 addresses how surface condition, coatings, and other conditions affect technology application. Table 8-4 provides some of the piping materials the technology can be used to examine. Table 8-5 captures capabilities for a number of variables. To provide a consistent review format, these tables are presented in each technology section.

App

licat

ion

on C

oncr

ete

Cove

red

Pipe

Str

uctu

re

Inspection for Corrosion Under Insulation

8-3

Table 8-1 Pulsed eddy current: function

Table 8-2 Pulsed eddy current: deployment options

Table 8-3 Pulsed eddy current: impact of surface and coating on results

* Wall thickness can be measured through nonconductive materials, such as insulation, coatings, paint, concrete, bitumen, dirt, and sludge. It can also be measured through aluminum and stainless weather sheeting.

Function Comments

Thickness An averaged thickness

Can be used to profile surface No

Can detect internal and external metal surface loss

Yes

Can detect axial and circumferential wall loss Yes

Can discriminate between internal and external metal loss

No

Crack detection No

Embedded discontinuities Typically, no

Deployment Comments/Considerations

Manual deployment Yes

In-line deployment No

Automated outside surface No

Monitoring No

Examination Surface Expected Outcome (Most Situations)

Bare and smooth Yes

Bare and rough Yes

Painted Yes*

Coated Yes*

Lined Yes*

Silt, tubercles, and similar debris Possibly*

8-4

Table 8-4 Pulsed eddy current: applicable pipe materials

Table 8-5 Pulsed eddy current: capability variables

Variable Yes No Comments

Single-sided access for volumetric examination

X

Capable of examining when piping is in service

X

Capable of noncontact examination X

Capable of examining significant axial pipe volume away from sensor

X

No couplant required X

Capable of producing an image showing size and shape of discontinuity

X

No radiological concerns X

8.1.2 Pulsed Eddy Current Overview

Conventional eddy current techniques use single-frequency, sinusoidal excitation and measure the defect response as impedance or voltage changes on an impedance plane display. To detect the defects, the magnitude and phase changes are interpreted. However, the pulsed eddy current method uses a step function voltage to excite the probe. The advantage of using a step function voltage is that it contains a continuum of frequencies. As a result, the electromagnetic response to several different frequencies can be measured with just a single step. Because the depths can be obtained all at once, if measurements are made in time domain (that is, by considering the signal strength as a function of time), indications produced by flaws or other features near the inspection coils will be seen first and more distant features will be seen later in time.

Materials Comments

Carbon steel Yes

Stainless steel No

Aluminum No

Cast iron No

High-density polyethylene No

Fiberglass No

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To improve the strength and ease of interpretation of the signal, a reference signal is usually collected, to which all other signals are compared. Flaws, conductivity, and dimensional changes produce a change in the signal, and a difference between the reference signal and measurement signal is displayed. The distance of the flaw and other features relative to the probe will cause the signal to shift in time. Therefore, time gating techniques (as in ultrasonic inspection) can be used to gain information about the depth of a feature of interest.

The geometry of the test object should be simple, such as straight sections of pipe work. Wall thickness readings can be affected by nearby nozzles, welds, internals, and support structures. A clearance of 2 in. is typically needed. It is not possible to inspect under stream tracing, near supports, or in sharp bends. The limitation in geometry is relevant when inspecting for corrosion beneath insulation.

The applied operating principle of pulsed eddy current can vary from system to system. To obtain a quantitative reading of wall thickness, different equipment uses different algorithms that relate the diffusive behavior in time to the material properties and the wall thickness.

The principle of operation is illustrated in Figure 8-2. A pulsed magnetic field is sent by the probe (transmitter) coil. This penetrates through any nonmagnetic material between the probe and the object under inspection (such as insulation material). The varying magnetic field induces eddy currents on the surface of the object. The diffusive behavior of these eddy currents is related to the material properties and wall thickness of the object.

Figure 8-2 Principles of pulsed eddy current technique

Insulation

Steel Wall

Eddy Current

Sheeting

SensorCoils

Magnetic Field

Transmitter Current

ReceiverAmplifier

Analysis of Eddy Current Signal

Wall ThicknessMeasurements

Transmitter

Receiver

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The detected eddy current signal is processed and compared to a reference signal. The material properties are eliminated, and a reading for the average wall thickness within the magnetic field area results. One reading takes a few seconds. The signal is logged and can be retrieved for later comparison in a monitoring approach (see Figure 8-3). Pulsed eddy current wall thickness readings are relative values, showing variations in wall thickness on the object being inspected.

Although this is sufficient in many applications, absolute readings can be obtained by a wall thickness calibration at one point of the object. This is dependent on having consistent electromagnetic properties throughout the material because variations will affect the wall thickness readings.

Figure 8-3 Schematic showing decay of eddy current (shorter signal on corroded area)

The area over which a measurement is taken is referred to as the footprint. Probe design is so that the magnetic field focuses on an area on the surface of the object. The result of the measurement is a reading of the average wall thickness over the footprint area. The size of this area depends on the insulation thickness, the object thickness, and the probe design. Roughly, the footprint can be considered to be in the order of the insulation thickness. Due to the averaging effects, the detection of highly localized defect types such as pitting is not reliable with this technique. Additional information on pulsed eddy current can be found in EPRI report 1019558, Field Evaluation of Pulsed Eddy Current. This report provides considerably more information on how pulsed eddy current works, specifically on the Applus RTD-INCOTEST

5 pulsed eddy current

technology. In addition, the report provides the results of a comparison between pulsed eddy current and ultrasonic technology on in-service components containing flow-accelerated corrosion and mockups containing simulated thinning. When reviewing these results, it is important to assess whether your target flaw mechanism size and shape are comparable to those in the report.

5 RTD-INCOTEST is a registered trademark of Applus RTD.

Wall LossSignal

WallLoss

8-7

8.1.3 Broadband Electromagnetic Method

BEM is a pulsed eddy current technology that has been used to assess buried pipe in the nuclear industry [13]. It has been used by manually applying the sensor to the pipe surface, as shown in Figure 8-4. In addition, an inline tool (see Figure 8-5) has been used that incorporates multiple sensors on a device that is maneuvered through the pipe.

Figure 8-4 BEM being manually applied inside a pipe

8-8

Figure 8-5 BEM inline device

8.2 LFET, E-PIT, and SLOFEC Wall Thickness Capability Summary

This section provides an overview of application variables associated with using LFET (see Section 8.4), E-PIT (see Section 8.3), and SLOFEC (see Section 8.5) technologies to examine piping for wall degradation. Typical or expected results are presented in five tables. Although these results are accurate in most instances, it is important to understand that, like most technology applications, there are exceptions. To keep the information concise, the tables do not fully address all potential variations. This being said, the results shown in the tables are accurate in most situations. Table 8-6 summarizes the technology function. Table 8-7 summarizes how the technology can be deployed. Table 8-8 addresses how surface condition, coatings, and other conditions affect technology application. Table 8-9 provides some of the piping materials the technology can be used to examine. Table 8-10 captures capabilities for a number of variables. To provide a consistent review format, these tables are presented in each technology section.

8-9

Table 8-6 LFET, E-PIT, and SLOFEC: function

Table 8-7 LFET, E-PIT, and SLOFEC: deployment options

Table 8-8 LFET, E-PIT, and SLOFEC: impact of surface and coating on results

Function Comments

Thickness A general estimate of thickness

Can be used to profile surface No

Can detect internal and external metal surface loss

Yes

Can detect axial and circumferential wall loss Yes

Can discriminate between internal and external metal loss

Yes

Crack detection Yes

Embedded discontinuities Typically, no

Deployment Comments/Considerations

Manual deployment Yes

In-line deployment SLOFEC

Automated outside surface SLOFEC, LFET

Monitoring No

Examination Surface Expected Outcome (Most Situations)

Bare and smooth Yes

Bare and rough Yes

Painted Yes

Coated Yes

Lined Yes

Silt, tubercles, and similar debris May in some applications

8-10

Table 8-9 LFET, E-PIT, and SLOFEC: applicable pipe materials

Table 8-10 LFET, E-PIT, and SLOFEC: capability variables

Variable Yes No Comments

Single-sided access for volumetric examination

X

Capable of examining when piping is in service

X

Capable of noncontact examination X

Capable of examining significant axial pipe volume away from sensor

X

No couplant required X

Capable of producing an image showing size and shape of discontinuity

X

No radiological concerns X

8.3 The E-PIT Tool

External pipe scanners are available that use an electromagnetic field sensor technology that has similarities to RFT. Figure 8-6 shows the Russell NDE Systems E-PIT tool, which is used from the pipe’s outside surface. The device is manually moved along the longitudinal axis of pipe and can be used when the pipe is in service. This sensor is capable of detecting internal or external flaws. Standard sensors are available for pipe sizes ranging from 1.125 to 12 in. NPS. Larger pipe diameters have been inspected with customized sensors. The E-PIT scanner can test through nonmagnetic external coatings with a maximum thickness of 0.197 in. To provide reliable and repeatable results, the exterior surface must be bare or have a uniform coating or painting thickness to avoid variable lift-off. For better wall loss estimates, it is desirable to know the nominal coating thickness. When scanning, it is important that the sensors are positioned evenly on the inspection surface.

Materials Comments

Carbon steel Yes

Stainless steel No

Aluminum No

Cast iron No

High-density polyethylene No

Fiberglass No

8-11

Figure 8-6 E-PIT sensor

The bottom of the sensor conforms to the outside pipe surface and is used to couple to the pipe wall during examination. The unit scans a pie-shaped subsection of the pipe; multiple axial scans are used to capture the entire pipe circumference. The distance is recorded, using an odometer encoder that is attached to one of the wheels. Figure 8-7 displays a screen capture with data from a 4-in. E-PIT probe. The highlighted areas indicate localized internal pitting. The unit can be used as a quick screening tool or as a measuring tool if used in conjunction with a calibration pipe.

Figure 8-7 Sample data from a 4-in. E-PIT sensor

8-12

8.3.1 Through-Transmission Array Probe

As a complementary tool to E-PIT, Russell NDE Systems has provided another probe to allow inspection of accessible piping, carbon steel, or gray cast iron from the outside for detection and characterization of inside- and outside-initiating damage forms. Unlike the traditional RFT of testing ferromagnetic components, this probe operates in the near-field zone at extremely low operating frequencies. Basically, eight pairs of differentially connected receiver coils are placed between the pair of driver coils. Figure 8-8 shows the probe configuration when mounted on the pipe for manual inspection. In general, for a given probe configuration, it would take two axial scans by rotating the probe assembly to complete the 360° pipe coverage.

Figure 8-8 Through-transmission array probe for inspecting carbon steel pipe from the OD

EPRI conducted a conducted an assessment of the probe on 10-in. pipe mockups with simulated coating thickness of up to 0.357 in. Figures 8-9 and 8-10 show the general configurations of the 16-channel array coil outputs from a 0.990-in.-diameter through-wall hole with no lift-off (no coating) to 0.375-in. lift-off of simulated coating. Signal responses at 16 Hz were obtained from the 10-in. diameter, schedule 40, ductile iron pipe with nominal wall thickness of 0.370 in. Figure 8-9 shows the through-wall signals with no lift-off. Figure 8-10 shows the through-wall signal outputs with 0.375-in. lift-off. The expected decrease in the amplitude accompanied by slight phase angle rotation was noted.

8-13

Figure 8-9 No lift-off: 0.990-in.-diameter, 100% hole, 119 mV, 95°

Figure 8-10 0.375-in. lift-off: 0.990-in.-diameter, 100% hole, 34 mV, 99°

8-14

Figures 8-9 and 8-10 present the following features:

Strip chart 1 displays 8 of 16 absolute channels; only odd channels are displayed here. In contrast, strip chart 3 displays 8 axially differentiating pairs of coil outputs (that is, coil 1–coil 2, coil 3–coil 4, and so on).

Pipe views 2 and 4 display amplitude signals of interest (absolute odd channel signal outputs on pipe view 2 and differential coil outputs on pipe view 4.)

Both absolute and differential Lissajous outputs are shown, along with expanded strip charts for the differential Lissajous pattern with associated phase angle and amplitude information.

Signal outputs show the same hole twice—during pushing and retraction of the probe assembly.

The following observations were made from the mockup inspection:

Phase angle–based calibration can be used to estimate percent wall losses.

A 0.500-in.-diameter pit that is 50% deep can be detected at up to 0.250-in.-thick simulated coating thickness.

Lift-off (coating) does affect phase angles; the same flaw depth can result in different phase angles.

This sensor will provide complementary output to the E-PITsensor technology.

The entire pipe circumference can be inspected generally in two scans, at up to 6 in. per second.

Using phase angle orientation, inside/outside surface–connected flaw discrimination is possible.

It is less accurate than traditional ultrasonic wall thickness measurements.

8.4 LFET

The TesTex LFET uses an electromagnetic driver and coil arrangement to create magnetic lines of flux through the volume of pipe wall. Metal loss due to corrosion changes the nominal conditions of the field. Signals produced by these changes are received by a pickup coil, measuring magnetic flux amplitude and phase. Similar to MFL in its sensor arrangement and usage, it offers electronic phase analysis and data interpretation.

The LFET is an NDE tool that can be used to examine ferrous and nonferrous piping to detect general wall loss and pitting. Although RFT is normally used to examine the pipe from inside a pipe, the LFET is generally applied from the outside surface. However, LFET can be used to examine larger pipes from the inside, using handheld scanners. The LFET can be used to examine painted, coated, and tape-wrapped piping; however, it is not a through-insulation inspection. The technology can be applied to any size piping with a thickness up to 0.75 in. cumulative, including any coatings. LFET is able to provide a quick scan of the test piece to provide wall thickness measurements. LFET is quantitative when proper calibration standards are employed. LFET can also be used as a rapid screening tool, and then followed up with ultrasonics.

LFET functions by injecting an electromagnetic signal into the test piece, rather than using magnets, making it a dry, noncontact method. The process is illustrated in Figure 8-11.

8-15

Figure 8-11 LFET function schematic

The return signal strength is measured and stored for reference. Any changes in the signal are noted, and the distorted signals are compared with the reference signal to create a delta. The delta is then compared with a calibration table to determine the amount of wall loss.

LFET identifies and quantifies inside and outside surface–connected discontinuities, such as pitting, general wall losses, caustic and phosphate gouging, corrosion cells, hydrogen damage, MIC attack, flow-accelerated corrosion, cracking, erosion, and manufacturing defects, through nonmagnetic coatings of up to 0.25 in.

During a LFET inspection, a scanner is moved along the test piece at a constant speed of approximately 4 in. per second. While one technician is moving the scanner, a second technician is watching the computer as the data are acquired. Any suspicious signals are rescanned. If the signal repeats, the location is marked for further investigation. The LFET signal is analyzed, and the flaw is sized using calibration standards. LFET scanners (see Figure 8-12) use up to 64 pickup sensors, depending on the application and design.

8-16

Figure 8-12 Examples of LFET scanners

In general, the LFET system collects 1200 samples per second, which makes scanning time quite rapid when compared with RFT scans. This technique works by pushing a scanner along the outside of the pipe. The system is lightweight and modular, and it uses digital signal processing electronics while being operated with a laptop computer. The results are displayed in real time with high-resolution color graphics and 3-D display, as shown in Figure 8-13. It shows the LFET signals obtained from 0.375-in.-diameter pits with 20%, 40%, and 60% wall loss on a 2.5 × 0.203 in. wall thickness. The waveform was collected with a 2.5-in. OD LFET scanner that contains eight sensors.

Figure 8-13 LFET calibration waveform

3-D Display

8-17

Figure 8-14 shows an image of in-service damage found in a pipe.

Figure 8-14 LFET waveform, showing two flaws measuring 50% and 70% wall loss

Additional information on LFET can be found in the EPRI report Nondestructive Evaluation: Remote Field Technology Assessment for Piping Inspection Including Buried and Limited Access Components (1021153) [14].

8.5 SLOFEC Testing

SLOFEC is an electromagnetic technique that detects loss-of-material discontinuities and cracks, similar to the MFL technique. However, instead of detecting the flux leakage with a passive coil or Hall effect sensor, the SLOFEC uses eddy current sensors.

When applied on ferromagnetic steels, the depth of penetration of the eddy currents is quite small. The flow of eddy currents in a thin layer close to the surface of the component is disturbed by defects in one of two ways: loss-of-material defects on the far surface alter the magnetic flux in the component, which in turn alters the eddy currents, or defects on the near surface directly interrupt the flow of eddy currents. These two responses can be discriminated by measurement of phase angle of the eddy current. The SLOFEC technique is able to inspect a greater wall thickness and also able to cope with thicker nonmagnetic coatings than MFL inspection systems can. Moreover, SLOFEC is able to differentiate between front surface and backwall discontinuities. This inspection technique is applicable to a variety of materials and components. Figure 8-15 illustrates the principle of the SLOFEC technology.

50% 70%

50% 70%

8-18

Figure 8-15 Principles of SLOFEC testing

As shown in Figure 8-15, SLOFEC testing uses a combination of eddy current and magnetic field. By using superimposed DC magnetism, the depth of penetration of the eddy current field lines in the ferromagnetic materials is increased. When a defect is present, the magnetic lines have a higher density in the remaining wall thickness, consequently changing the relative permeability in the area, which changes the eddy current field lines.

Eddy currents in steel have a small penetration depth due to the high relative magnetic permeability. This limits penetration of the eddy currents to the outer surface. This effect, called the skin effect, is strongly reduced by magnetic saturation of the test piece wall, causing a low relative permeability. This allows the eddy current to penetrate deeper (magnetic saturation not only creates a low permeability and uniform flux but also suppresses the usual local permeability variations within the material), eliminating a source of noise. Figure 8-16 shows the relative sensitivity curves for MFL and SLOFEC technologies. These curves are typical for inspection results on thick plates. Defect detection is achieved in combination with special electronics and fast, online signal processing. The phase information is obtained and can be correlated to discriminate the defect location (external versus internal wall).

8-19

Figure 8-16 Comparison of relative detection capability of MFL and SLOFEC testing at different wall thicknesses

8.5.1 Applications of SLOFEC

In-line SLOFEC technology is commercially available. Photographs of a self-propelled robotic inspection tool offered by General Electric are shown in Figures 8-17 and 8-18. The SLOFEC sensors are located on the right side of robotic device, as pictured in Figure 8-17. A closer image of the sensor section is provided in Figure 8-19. The tool contains the onboard electronics necessary to operate the SLOFEC sensors.

The system is controlled with an exterior computer through a high-strength umbilical cord containing a data transmission and power line. The tool is driven through the pipe by the black drive wheels shown in Figure 8-17. Figure 8-20 shows a picture of the tool being inserted into a 24-in. pipe through a 20-in. opening created by removing a valve. Data are taken by rotating the sensor head over the entire circumference of the pipe with the device held steady in the axial direction. Data are transmitted through the umbilical cord to an external data collection system where they can be analzed in real time to determine data integrity. The tool is then indexed axially in the pipe, and the head is again rotated in the pipe to collect additional data. This continues until the desired examination volume is completed. The tool is capable of providing full coverage in straight runs of pipe. If complete coverage is not desired, the system can be manipulated to obtain whatever coverage is desired. Coverage in components such as elbows can be limited.

Magnetic Flux Leakage

Saturated Low FrequencyEddy Current

Rel

ativ

e D

etec

tion

Sen

sitiv

ity

Wall Thickness (mm)

8-20

Figure 8-17 General Electric SLOFEC robot in the calibration tray

Figure 8-18 End view of the General Electric SLOFEC robot

8-21

Figure 8-19 SLOFEC sensor

Figure 8-20 SLOFEC robot being inserted into a 24-in. pipe through a 20-in.-long opening

8-22

An assessment of this SLOFEC technology was performed at EPRI in 2012 on three 24-in.-diameter, schedule 40 mockups containing various discontinuities of various depths, widths, and lengths. Two of the mockups are 40-ft-long, straight, coated pipes, and the third is a 60-ft-long, uncoated pipe containing an elbow. The mockups were masked during data acquisition and analysis to conceal the extent and location of the discontinuities. A general view of the mockup configuration is shown in Figure 8-21. The results of the assessment can be found in EPRI report 1025219, Nondestructive Evaluation: Buried Pipe NDE Technology Assessment and Development Interim Report.

Figure 8-21 EPRI 24-in.-diameter mockups

8.6 Alternating Current Field Measurement

The ACFM technique is an electromagnetic technique that uses induced uniform currents and magnetizes flux density sensors to detect and size surface-breaking discontinuities without calibration. The term uniform means that, at least in the area beneath the probe, current lines in the absence of a discontinuity are parallel, unidirectional, and equally spaced. ACFM is most often used for assessing the condition of welds. The technique works through coatings and paint and requires minimum cleaning.

The basis of the ACFM technique is AC that is induced to flow in a thin skin near the surface of any conductor. By introducing a remote, uniform current into an area of the component under test, when there are no defects present, the electrical current is undisturbed. If a crack is present, the uniform current is disturbed, and current flows around the ends and down the faces of the crack. Because the current is AC, it flows in a thin skin, close to the surface, and is unaffected by overall geometry of the component. An illustration of the current flow is provided in Figure 8-22.

8-23

Figure 8-22 Induction coils above a metallic plate

The eddy currents flow across the surface of the plate, until they encounter a surface-breaking defect, as shown in Figure 8-23. The eddy currents are forced to flow around or beneath the defect. The eddy currents in the middle of the defect are forced downward, away from the surface. This causes a drop in the magnetic field, shown in blue. The eddy currents near the ends of the defect are forced to flow around the ends. This causes an increase in the current density near the start and end of the defect; this can be used to locate the ends. The strength of the magnetic field gathered from sensor coils is used to calculate the location, length, and depth of the surface-breaking defect.

Figure 8-23 Eddy currents flowing around a fatigue crack

A conventional ACFM probe contains a field inducer and one pair of sensors. In its simplest form, an ACFM array probe contains multiple sensor pairs operating with a single (larger) field inducer. The probes can be built as arrays, allowing for increased scan coverage.

8-24

With a single field, the inspection is limited to a particular orientation of defects (predominantly oriented along the direction of scan). To overcome this limitation, it is possible to incorporate other field inducers in the array probe to allow a field to be introduced within the sample in other orientations. This is particularly useful in situations in which the crack orientation could be unknown or variable. Examples of ACFM probes are shown in Figure 8-24.

(a) Weld scan probe (b) Pencil probe

(c) Compliant array probe, dry application

Figure 8-24 Types of AC field measurement probes

The unidirectional currents used in ACFM are most strongly perturbed by planar discontinuities. However, surface corrosion pitting also perturbs current flow to some extent and can also be detected. The degree of current perturbation is much lower than for a crack of the same depth and length, so on an initial scan, a corrosion pit looks like a shallow crack. However, the distinguishing feature of a pit is that, unlike a crack, it will produce the same signal regardless of the orientation of the interrogating current.

8-25

8.7 Magnetic Tomography Method

The noncontact, magnetic tomography method inspection technology for ferrous buried, submerged, or aboveground pipe and pipelines was made available to the pipeline industry in 2002. This technology assesses metal loss and crack defects based on relative changes of the stress-strain state of pipe, not the physical size of defects. A noncontact magnetometer is passed over the pipe and overburden, recording fluctuations in magnetic field strength along the pipeline. Flaws are located by relating the magnetic permeability of the pipeline to stress raisers, and they are defined by analyzing the interconnection of stress concentration with a change in the polarity of the components of the earth’s natural magnetic field.

The magnetometer data are subsequently analyzed and a risk-prioritized report of likely locations with pipe wall damage (metal loss, deformations, or cracks) is prepared. Excavations, direct examinations, and defect assessment are subsequently conducted based on the magnetic tomography method report.

8.8 Concentric Magnetic Field

A proprietary technology called No-Pig uses concentric magnetic fields. It is covered by U.S. and European patents [15–17]. In this technology, AC is induced in a pipe between two contact points, generating concentric magnetic fields associated with the inside and outside pipe surfaces. Due to skin effect and the stray magnetic flux, the surrounding magnetic field is frequency dependent; in the case of no metal loss defects, the surrounding magnetic field is circular. Any deviation from a concentric circular shape, such as that associated with inner or outer surface wall thinning, affects the center point of the magnetic field lines, causing a deviation in center point for inner and outer magnetic fields. An array antenna is passed over the surface of the ground, above the buried pipe. The magnetic fields are analyzed and, where the centers of the magnetic fields diverge, a location for wall loss or thinning is reported.

The nominal pipe diameters are 3–16 in., with a maximum wall thickness of 0.393 in. The maximum burial depth is 6 ft. The maximum inspection length of pipe between two contacting points is 3280 ft. Inspection speed, depending on surface conditions, is reported to be a maximum of 2296 ft per day.

Field demonstrations of this technology have been limited to bare ground surface cover. Future developments and application research is planned to be conducted in North America, and the effect of concrete (reinforced and nonreinforced) as flexible pavements will be investigated. This technology claims a probability of detection of 96% for 50% wall thickness metal loss, with minimum length and width of 1.97 × 1.97 in.

8-26

8.9 Meandering Wire Magnetometer

The meandering wire magnetometer array represents a recent development in eddy current–based inspection technology. This concept uses coils embedded and arranged within a flexible film array. The flexible film is moved over the surface of the pipe, as shown in Figure 8-25.

Figure 8-25 Meandering wire magnetometer array and details of the loops embedded within the array

The newest development of the meandering wire magnetometer array can detect and size metal loss, with software providing the capability to permanently record the inspection data. The preferred deployment is on bare, blasted pipe surface, but it has been reported to perform through nominal pipe coating thickness. The meandering wire magnetometer array has also been reported to detect and size crack length and width distributions.

9-1

9 RADIOGRAPHIC TESTING TECHNOLOGY Radiographic testing is used to detect the features of a component or assembly that exhibit a difference in thickness or physical density as compared to surrounding material. Large differences are more easily detected than small ones. In general, radiography can detect only those features that have an appreciable thickness in a direction parallel to the radiation beam. This means that the ability of the process to detect planar discontinuities such as cracks depends on proper orientation of the test piece during inspection. Discontinuities such as voids and inclusion, which have measureable thickness in all directions, can be detected if they are not too small in relation to section thickness. In general, features that exhibit a 1% or more difference in absorption compared to the surrounding material can be detected.

Industrial radiography is versatile because it can be used to examine miniature electronic parts to large structural components. In addition, it can be used on most known material and in many manufactured forms, such as castings, weldments, and assemblies.

Radiography can provide an effective NDE technique for locating and evaluating anomalies that can adversely affect the integrity of an operating piping system. Unfortunately, it is hindered by the restrictions associated with a radioactive source and the use of chemicals in developing film. However, digital methods are available that eliminate the need for such chemicals and also reduce the radioactive source strength needed. Digital images can be processed, viewed, and acted on in real time in the field, and image enhancement software can also be used determine pipeline condition.

Three basic elements of radiography are a radiation source, the test piece, and a sensing material, which are shown schematically in Figure 9-1. The test piece is a plate of uniform thickness, containing an internal flaw having absorption characteristics different from those in the surrounding material. Radiation is absorbed by the test piece as the radiation passes through it at a different rate from the flaw and surrounding material. Therefore, the radiation intensity impinging on the sensing material in the area beneath the flaw is different from that which impinges on adjacent areas. This produces an image, or shadow, of the flaw on the sensing material. Often, a penetrameter is placed on the component during the exposure and evaluated in the radiograph to determine the minimal amount of material change (sensitivity) and definition that can be deciphered from the radiograph.

9-2

Figure 9-1 Schematic of basic principle of industrial radiography

9.1 Radiography Wall Thickness Capability Summary

This section provides an overview of application variables associated with using radiography to examine piping for wall degradation. Typical or expected results are presented in five tables. Although these results are accurate in most instances, it is important to understand that, like most technology applications, there are exceptions. To keep the information concise, the tables do not fully address all potential variations. This being said, the results shown in the tables are accurate in most situations. Table 9-1 summarizes the technology function. Table 9-2 summarizes how the technology can be deployed. Table 9-3 addresses how surface condition, coatings, and other conditions affect technology application. Table 9-4 provides some of the piping materials the technology can be used to examine. Table 9-5 captures capabilities for a number of variables. To provide a consistent review format, these tables are presented in each technology section.

9-3

Table 9-1 Radiography: function

Table 9-2 Radiography: deployment options

Table 9-3 Radiography: impact of surface and coating on results

Function Comments

Thickness Process results in a qualitative image that can be used to identify changes in wall thickness. Techniques are available to provide some level of quantitative thickness results.

Can be used to profile surfaces Provides a superimposed image of both examination and backwall surface.

Can detect internal and external surface metal loss

Yes.

Can detect axial and circumferential metal loss

Yes.

Can discriminate between internal and external metal loss

With special techniques.

Crack detection Cracks can be readily detected.

Embedded discontinuities

Embedded discontinuities with adequate volume parallel to the radiation beam, such as inclusions, can be readily detected. Discontinuities perpendicular to the radiation beam such as laminations are not detectable.

Deployment Comments/Considerations

Manual deployment Yes. A typical application would have the radiation source and detector on the outside of the pipe. However, one could be on the inside of the pipe.

In-line deployment No.

Automated outside surface Tools are available.

Monitoring Generally not.

Examination Surface Expected Outcome (Most Situations)

Bare and smooth Yes

Bare and rough Yes

Painted Yes

Coated Yes

Lined Yes, unless liner is excessively thick

Silt, tubercles, and similar debris Yes

9-4

Table 9-4 Radiography: applicable pipe materials

Table 9-5 Radiography: capability variables

Variable Yes No Comments

Single-sided access for volumetric examination

X

Capable of examining when piping is in service

X

Capable of noncontact examination X

Capable of examining significant axial pipe volume away from sensor

X

No couplant required X

Capable of producing an image showing size and shape of discontinuity

X

No radiological concerns X

9.2 Radiation Sources

Two types of electromagnetic radiation are used in industrial radiography: x-rays and γ-rays. X-rays and γ-rays differ from other types of electromagnetic radiation (such as visible light, microwaves, and radio waves) only in their wavelengths, although there is not always a distinct transition from one type of electromagnetic radiation to another. Only x-rays and γ-rays, because of their relatively short wavelengths (high energies), can penetrate opaque materials to reveal internal flaws.

X-rays and γ-rays are physically indistinguishable; they differ only in the manner in which they are produced. X-rays result from the interaction between a rapidly moving stream of electrons and atoms in a solid target material, whereas γ-rays are emitted during the radioactive decay of unstable atomic nuclei. Photographs of isotope and electronic source exposure arrangements are shown in Figures 9-2 and 9-3, respectively.

Materials Comments

Carbon steel Yes

Stainless steel Yes

Aluminum Yes

Cast iron Yes

High-density polyethylene Yes

Fiberglass Yes

9-5

Figure 9-2 Isotope source being deployed

Figure 9-3 Electronic source exposure arrangement

9-6

9.3 Formation of a Radiographic Image

The most important process in radiography is the conversion of radiation into a form suitable for observation or further processing. The conversion is accomplished with either a recording medium (usually film) or a real-time imaging medium (such as fluorescent screens or scintillation crystals). The imaging process can also be assisted with intensifying or filtration screens, which intensify the conversion process or filter out scattered radiation. Image quality is governed by image contrast and resolution. These two factors are interrelated in a complex way and are affected by several factors.

Radiographic sensitivity, which should be distinguished from image quality, generally refers to the size of the smallest detail that can be seen on a radiograph or the ease with which the images of small details can be detected. Radiographic sensitivity refers more to detail resolvability, which should be distinguished from spatial resolution and contrast resolution. For example, if the density of an object is quite different from the density of the surrounding region, the flaw might be resolved because of the large contrast, even if the flaw is smaller than the spatial resolution of the system. On the other hand, when the contrast is small, the area must be large to achieve resolvability.

9.3.1 Film-Based Radiography

In a film-based radiographic system, film is enclosed in a light-proof container, a component is placed in front of it, and it is exposed with an x-ray source or isotope, such as Iridium-192. The film then goes through processing, in the dark, with a number of chemical baths. The chemicals are then washed off, and the film is dried so that its latent image may be seen. The result is a 2-D image that can be viewed with a light box viewing station. After viewing, the film must be carefully stored within a specified temperature and humidity range if it is to be used in the future.

9.3.2 Digital Radiography

Digital radiography is finding an increasing role for in-service NDE, as a diagnostic tool in the manufacturing process, for online production line testing, and as a maintenance tool in the field of industrial NDE. Digital radiographic detectors are also being used as handheld devices for pipeline inspections, as film replacement devices, and in industrial computed tomography systems. The digital method, by its nature, provides numerical results important for metrology and thickness measurements.

In the field of industrial digital radiography, there is really no single, standard x-ray system to address all applications. Economics, speed, quality, and the impact of the overall manufacturing or service process are keys in designing and building digital radiographic systems. A large aspect of that design is the consideration of the digital x-ray detection device, itself. For this selection, there are almost as many choices of detectors as there are ways to configure the overall test system.

New digital detectors have the potential to replace the radiographic film. Flat panels, imaging plates, and solid-state sensors allow fast processing of radiographs with higher dynamics than film applications. Many of the principles for x-ray or γ-ray detection are similar, particularly when digital-based cameras such as charge-coupled device cameras are used. Digital systems use discrete sensors, with the data from each detection pixel being read out into a file structure to form the pixels of the digital image. Parallel to the development of digital detectors, improved line cameras open new ways for mobile application in industrial radiography.

9-7

High-quality radiographs can be obtained, even from media-filled pipelines. The analysis of scattered radiation and energy dispersion techniques provide additional information about the chemical composition and structure. Dual-energy applications lead to contrast enhancement for multicomponent systems, as well as filled pipelines and other containers.

Digital or computed industrial radiography, by use of reusable storage phosphor screens, offers a convenient and reliable way to replace film. Some exceptions to discrete sensor-based systems are the photostimulable phosphor system that forms a latent image (similar to film) on a storage phosphor imaging plate. The screen is then read electronically, using special laser scanners. The pixelization in this case is based not on the x-ray or γ-ray sensitive phosphor, but in the laser scanning process. This can reduce the cost of consumables as well as reducing exposure, processing, and archival times. Intangible savings include improved environmental safety and longer usability of isotopes.

More and more applications can be covered by improving the image quality of digital radiography systems. Digital images offer many advantages in terms of image manipulation and workflow. Film scanning, computed radiography, and direct radiography, by using different kinds of flat-panel detectors, all have their specific application fields.

Following are some industrial digital radiography techniques and methods that are commonly used for piping examinations. Figure 9-4 gives an example, showing ease of setup and possibilities of checking for exposure coverage.

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Figure 9-4 Digital radiography (exposure setup and radiograph)

9.3.2.1 Radiographic Film Digitization

Radiographs are produced in a conventional manner on an industrial radiographic film, by following the normal way of processing—test setup, radiation exposure, processing, drying, film quality assessment, interpretation, reporting, filing, and archiving. The film is then placed in a reader, and the image is read and digitized for viewing and archiving on a software-based system. This digitization will help in extracting more information from film, which is not normally possible with human eye visualization. Digitization will also assist in long-term archiving, which also allows for remote analysis through networking.

9.3.2.2 Direct Digital Radiography

The radiographic image is directly captured on the flat plate and transmitted directly to the computer. Amorphous silicon digital x-ray detector systems, capable of high-resolution, real-time radiography, and amorphous selenium detector systems, for high-resolution, off-line

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interpretation and evaluation, are used extensively. Direct digital radiography does not require any intermediate steps or additional processes to capture images. The process provides a direct feed from panel to imaging system or workstation. Direct digital radiography is suitable in industrial applications in which medium and finer grain films are being used.

9.3.2.3 Computed Radiography

In place of using a conventional radiographic film to capture images, computed radiography uses an imaging plate. This plate contains photosensitive storage phosphors that retain the latent image. When the imaging plate is scanned with a laser beam in the digitizer, the latent image information is released as a visible light. This light is captured and converted into a digital stream for computing a digital image.

A major consideration in using flexible phosphor-imaging computed radiography system plates is that any source that can be used with conventional x-ray or γ-ray application can also be used with this filmless technology. More importantly, the phosphor imaging plates can be directly substituted for radiographic film. They can be used in the same film holders and cassettes as those used for film, they can be used in applications requiring inspection of curved test objects, and bending is not an issue.

9.3.2.4 Computed Tomography

Computed tomography is an imaging technique that generates an image of a cross-sectional slice of a test object. Computed tomography differs from other radiography techniques in that the radiation beam and the detector lie in the same plane as the surface being imaged. Moreover, because the plane of a computed tomography image is parallel with the energy beam and detector scan path, computed tomography systems require a computing procedure to calculate, locate, and display the point-by-point relative attenuation of the energy beam passing through the structures within the cross-sectional slices of the test object.

High-resolution detector lines and time-delayed integrating lines speed up the data acquisition and lead to an image quality that is sufficient for weld inspection and casting production monitoring. Computed tomography applications also allow the determination of the flaw depths and shapes, which is not possible with conventional radiography. In addition, dual-energy applications lead to contrast enhancement for multicomponent systems as well as inspection of filled pipelines and other containers.

9.3.3 Comparison of Digital and Conventional Radiography

Digital radiography has advantages compared to conventional film radiography for certain applications in terms of image quality, exposure times, and enhanced detection capabilities, as follows:

Increased dynamic range, providing good image contrast over a wide range of exposure. Makes it possible to investigate and evaluate more complex-shaped parts with wider thickness ranges, which reduces the need for multiple exposures for different thickness sections.

A high tolerance for varying exposure conditions and greater freedom in the selection of exposure doses, which drastically reduces the need for retakes.

Additional data analysis capabilities.

Darkroom or chemical processing is not needed.

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Exposure times and requirements are reduced.

Phosphor flexible plates can be reused.

Electronic archival, storage, and communication capabilities.

Eliminates the need for darkrooms and chemical processes, which helps protect the environment from hazardous chemical disposition and associated costs.

9.4 Radiographic Examination Techniques

Various techniques are used to examine piping. The choice is based on examination purpose, geometry, size, sensitivity requirements, in situ space availability, and so on. Pipeline and piping system radiographic techniques that are frequently used include the following:

Single-wall, single-image technique. The source is kept outside and the film inside, or vice versa, and the weld is exposed section by section. Panoramic exposures can be taken when the source is placed inside the pipe, film is wrapped around the circumference of the pipe, and the film is exposed at one time.

Double-wall penetration techniques. These techniques are used when the inside of the surface is not accessible. The source of radiation and the film are kept outside, and the radiation penetrates both the walls of a pipe. Some of the double-wall penetration techniques are double-wall, single-image; double-wall, double-image; and superimposing techniques.

Latitude technique. There is a limit on specimen thickness range that can be inspected satisfactorily in a single radiograph. One method of extending this thickness range, thereby reducing the number of exposures required for a particular specimen, involves the simultaneous exposure of two films of different speeds. When two films of different speeds are used to image the same subject in one exposure, the latitudes of the films are summed to expand the total latitude for the exposure.

Special techniques. In a complex part, it is often necessary to consider certain areas individually and prepare a separate technique for each area. Some pipelines are designed to have the configurations of core pipe and a casing to meet the intended purposes. Double envelope welds can be tested by using multiwall penetration techniques.

Many factors other than good radiographic techniques influence radiographic contrast. For pipeline radiography, radiation energy is probably the most important. The absorption of radiation by steel decreases with increasing energy; the absorption coefficient at 150 kV is about three times that at 700 kV. For optimum detection of small changes in thickness, the absorption should be as high as possible, so that large differences in exposure, consistent with a reasonable amount of energy being transmitted, can provide a realistic overall exposure.

9.5 Pipeline Examination Using Radiography

In the utility, nuclear, and petrochemical industries, there is a variety of applications of penetrating radiation and radiographic testing. Most of the radiographic requirements come about during fabrication and construction of boilers, pressure vessels, nuclear power plant components, and piping systems. However, some of these same requirements come into effect when repairs, replacements, or additions are made to the facilities. Radiography also has become a valuable

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tool for assessing deterioration caused by corrosion and erosion in many pipes, vessels, and other components that are part of today’s complex plants. Penetrating radiation has seen many applications in detecting and measuring fluids and their movements, leak detection gauges, liquid level gauges, and other important monitoring instrumentation.

Radiographic testing requires access from both sides of a test piece (source side and film side); therefore, a single category cannot be assigned to this method. There are configurations in which both source and imaging medium are placed outside the pipe, with complete circumferential accessibility (as shown in bottom left insert of Figure 9-5).

Figure 9-5 Uses of industrial radiography for pipeline inspection

For defects deeply seated within the volume of the material, radiographic examination is one of the methods recommended for all metals and alloys, both ferrous and nonferrous. The range of capabilities offered by the variety of sources and equipment makes radiography a valuable examination method. One of the most important advantages of radiography is that limited surface preparation is necessary.

Radiography can easily be selected to detect and size the following types of discontinuities:

Cracks (parallel to the radiation beam)

Volumetric defects, such as slag inclusions or voids

Blockages or deposits inside the pipeline and piping systems

Material thickness and the presence of erosion and corrosion

Foreign material inside a component

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In petrochemical structures, oil and gas processing plants, pipelines, and power stations, the digital industrial radiography has many applications.

9.5.1 Radiographic Detection of Thinning

Radiography can be used to detect and, in some cases, measure metal loss in piping systems with the following characteristics:

With a wide range of component thicknesses

That are insulated, coated, or lined

Contain internal fluids

While the line is in service

Made of large- or small-diameter and thick- or thin-walled pipes

Containing corrosion hidden under components such as pipe supports

Presence of wall loss through scales or scabs

Radiography is especially effective for detecting localized corrosion such as pitting or MIC when compared to other NDE techniques. Film density or projection measurements, with the help of suitable software, can easily be correlated with wall thicknesses or the presence of corrosion or erosion.

The two radiographic techniques most commonly used for determining wall thickness and detecting thinning are the tangential technique and the double-wall-exposure single-wall-viewing technique (through-wall) shown in Figure 9-6. Both techniques can be used to examine piping through insulation.

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Figure 9-6 Graphic representation of tangential and double-wall exposure, single-wall viewing techniques

9.5.1.1 Tangential Radiographic Technique

A popular technique for detection of wall thinning is the tangential radiography technique. In tangential radiography, a view of the pipe cross section, including a view of the pipe wall, is projected on the film (sensor elements), enabling direct measurement of the remaining pipe wall thickness. The extremities of the pipe wall cross section projected onto the film can be defined by a line drawn from the source to the sensor through a tangent point on the outside pipe surface and from the source to the sensor through a tangent point on the inside pipe surface. The thickest portion of the pipe through which the radiation passes is, therefore, a chord that is bisected by the internal tangent point. The cross section of the pipe wall that appears in the image is approximately perpendicular to the center of the chord (see Figure 9-7).

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Figure 9-7 Radiographic image of tangential technique on insulated piping

9.5.1.2 Double-Wall Radiographic Technique

Another useful radiographic technique for the detection of wall thinning is the double-wall-exposure single-wall-viewing technique, in which the radiation beam penetrates both walls of a pipe, but only the wall closest to the recording medium is analyzed. An object of known thickness and of the same material (usually a step wedge) is placed on or near the pipe in the area of interest. This allows for direct measurement of the pipe wall thickness from the image. Wall thickness can be determined from the film density using a common radiation attenuation formula. The distortion in the image due to pipe curvature can also be corrected to provide accurate measurements. A photograph of a double-wall-exposure arrangement through insulation is shown in Figure 9-8, and a typical double-wall-exposure image is shown in Figure 9-9.

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Figure 9-8 Double-wall technique on insulated pipe

Figure 9-9 Radiographic image of double-wall-exposure, single-wall viewing

9.5.2 Radiography of Welds

Characteristic discontinuities in pipeline welds are slag, elongated piping in the root, scattered piping and porosity, burn-through in the root, incomplete root penetration, incomplete sidewall fusion, and cracks, which often break the inner surface in the heat-affected zone. Except for cracks and incomplete sidewall fusion, these discontinuities are amenable to detection by radiography. Open cracks can be detected, but tighter cracks, even though favorably oriented, are detectable only by optimum practice. Some cracks might not be revealed at all.

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10 VISUAL TESTING TECHNOLOGY Visual inspection applications range from using simple laws of geometrical optics to more complex optical techniques that assess light properties. The basic process involves illuminating the test specimen with light, usually in the visible region. The specimen is then examined with the eye or by light-sensitive devices. The equipment required for visual inspection is extremely simple, but adequate illumination is essential. The surface of the specimen should be adequately cleaned before being inspected.

Visual inspection can be performed outside the pipe as well as inside the pipe, using cameras or borescope equipment. When combined with direct measurement devices such as pit gauges, visual testing provides data for detailed assessment of fitness for purpose. For many types of pipeline and piping systems, visual testing can be used to determine quantity, size, shape, surface finish, reflectivity, color characteristics, fit, functional characteristics, and the presence of surface anomalies and discontinuities.

Visual testing is a great help in assessing the coating condition for pipelines and piping systems. It can be great tool, as a first step, for sorting, prioritizing, and ranking risks and for following up with more elaborate volumetric examinations.

10.1 Optical Aids Used for Visual Examination

An optical microscope with a combination of lenses can be used to magnify object images. Such aids as binoculars and telescopes can be used to examine a component from a considerable distance. Optical aids in visual examination are beneficial and recommended to magnify defects that cannot be detected by the unaided eye, and to permit visual checks of areas not accessible to the unaided eye. In performing visual or optical checks, it is of utmost importance to know the types of defects that can develop and to recognize the areas in which such failures can occur. Magnifying devices and lighting aids should be used wherever appropriate.

10.2 Application and Use of Visual Testing

Important details can be collected during visual examination that would be useful for future analysis and also to decide on the type of NDE to be used for further analysis. Visual inspection should be carried out as a complementary method to other NDE methods. Inaccessible areas can be inspected by means of borescopes and fiber-optic techniques. Depending on the severity of the service defect and the component in use, decisions will be made whether to salvage the component. If the product is found unacceptable during visual examination, further NDE need not be conducted, thus saving the time and cost of inspection.

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Visual examination of plant system components by an experienced inspector can reveal the following information:

General condition of the component

Presence of a leak and other abnormal operation conditions

Presence or absence of surface deposits (such as oxide films or corrosive product on the surface), scaling, corrosion, erosion, discoloration, and oxidation bulging

Presence or absence of cracks, orientation of cracks, and position of cracks relative to the various zones in the case of welds

Surface porosity, unfilled craters, contour of the weld beads, and the probable orientation of the interface between the fused weld bead and the adjoining parent metal

Potential sources of mechanical weakness, such as sharp notches or misalignment

Missing parts, dimensional conformances, gross defects visible on the surface, and distortion during fabrication and in service

10.3 Factors Affecting Visual Testing

Lighting is the most important factor affecting visual examination. Often, emphasis is placed on equipment variables such as borescope view angle or degree of magnification, but if the lighting is incorrect, no magnification is going to improve the image. Other working conditions are also important, including factors that cause operator discomfort and fatigue.

10.3.1 Cleanliness

Vision depends on the amount of light reaching the eye or the light-sensitive device. In visual tests, the amount of light can be affected by distance, reflectance, brightness, and contrast, or the cleanliness, texture, size, and shape of the test object.

Cleanliness is a basic requirement for a good visual test. It is impossible to gather visual data through layers of opaque dirt unless cleanliness itself is being examined. In addition to obstructing vision, dirt on the test surface can mask actual discontinuities with false indications. Cleaning typically can be done by mechanical or chemical means or both. Cleaning avoids the hazards of undetected discontinuities and improves customer product satisfaction.

10.3.2 Luminescence and Surface Conditions

Vision depends on reflected light entering the eye. The easiest way to ensure adequate lighting is to place the light source and the eye as close to the test surface as the focal distance allows. Similarly, a magnifier should be held as close to the eye as possible, ensuring that the maximum amount of light from the target area reaches the eye.

Reflectance and surface texture are related characteristics. It is important for lighting to enhance a target area, but glare should not be allowed to mask the test surface. A highly reflective surface or a roughly textured surface might require special lighting to illuminate without masking. Supplementary lighting must be shielded to prevent glare from interfering with the inspector’s views.

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The amount of light required for a visual examination depends on several factors, including the type of test, the importance of speed or accuracy, reflections from backgrounds, and inspector variables. For visual and other NDE applications, a ratio of 3:1 between the test object and darker background is recommended.

10.3.3 Test Object Effects

The test object determines the specifications for the instrument used during examination and the required illumination. Objective distance, object size, discontinuity size, reflectivity, entry port size, object depth, and direction of view are all critical aspects of the test object that affect the visual test.

Objective distance is important in determining the illumination source and the required objective focal distance for the maximum power and magnification. Object size, combined with distance, determines what lens angle or field of view is required to observe an entire test surface. Discontinuity size determines the magnification and resolution required for visual testing. Reflectivity is another factor affecting illumination. Dark surfaces such as those coated with carbon deposits require higher levels of illumination than light surfaces do. The entry port size determines the maximum diameter of the instrument that can be used for visual examination. Object depth affects focusing. If portions of the object are in different planes, the instrument for visual examination must possess sufficient focus adjustments of depth of field to visualize these different planes sharply.

10.4 Deployment Outside the Pipe

10.4.1 Pit Gauging

Mechanical pit gauging and mapping of external corrosion is often overlooked as a specific NDE task, but it often represents an important element of direct examination required to fully discover the condition of corroded pipe to determine fitness for purpose.

A direct examination of external corrosion, using pit gauging to determine depth of metal loss, often begins with linear location measurements from reference points such as girth welds, fittings, and the top center of a pipe. Figure 10-1 shows the application of a 0.5 × 0.5 in. grid drawn over a local area of corroded pipe. Metal loss depth is measured and recorded at each grid position.

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Figure 10-1 Location grid (0.5-in. grid) marked on pipe with external corrosion during direct examination

Several designs for pit gauges are available, but the most widely used pit gauge used for assessing external corrosion of pipelines is a dial indicator fixed to a bridging bar. Figure 10-2 shows the application of a typical bridging bar to measure metal loss depth.

Figure 10-2 Deployment of digital pit gauge on metal surface

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The reliability of metal loss depth measurements using a pit gauge is significantly affected by locating the deepest location of metal loss within the individual pit or grid location. Actual corrosion rarely has a uniform, smooth, cross-sectional profile.

10.5 Deployment Inside the Pipe

Visual examination uses probing energy from the visible portion of the electromagnetic spectrum. Changes in the light’s properties after contact with the test object are detected by a human eye or machine vision. Detection is enhanced and made possible by mirrors, magnifiers, borescopes, videoscopes, or other vision-enhancing accessories.

10.5.1 Rigid Borescopes

The rigid borescope was invented to inspect a bore. It was a thin telescope, with a small lamp at the top for illumination. Most rigid borescopes now use a fiber-optic light guide system as an illumination source.

The image is brought to the eyepiece by an optical train consisting of an objective lens, sometimes a prism, relay lenses, and an eyepiece lens. The image is not a real image but an aerial image—it is formed in the air between lenses. This means that it is possible to both provide diopter correction for the observer and control the objective focus with a single adjustment to the focusing ring at the eyepiece.

The focus control in rigid borescopes greatly expands the depth of field over nonfocusing or fixed-focus designs. At the same time, focusing can help compensate for the wide variation in eyesight among visual inspectors. Figure 10-3 illustrates the principles of borescopes.

Figure 10-3 Borescope fundamentals

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10.5.2 Fiber-Optic Borescopes

The industrial fiber-optic borescope is a flexible, layered sheath, protecting two fiber-optic bundles, each composed of thousands of glass fibers. One bundle serves as an image guide, and the other bundle helps to illuminate the test object. Light travels only in straight lines, but optical glass fibers bend light by internal reflection and, therefore, can carry light around corners.

A single fiber transmits little light, but thousands of fibers can be bundled for transmission of light and images. To prevent the light from diffusing, each fiber consists of a central core of high-quality optical glass coated with a thin layer of another glass with a different refractive index. This cladding acts as a mirror—all light entering the end of the fiber is reflected internally as it travels and cannot escape by passing through the sides to an adjacent fiber in the bundle.

Although the light is effectively trapped within each fiber, not all of it emerges from the opposite end. Some of the light is absorbed by the fiber itself, and the amount of absorption depends on the length of the fiber and its optical quality. For example, plastic fiber can transmit light and is less expensive to produce than optical glass, but plastic is less efficient in its transmission and is unsuitable for use in fiber-optic borescopes.

10.5.3 Special-Purpose Borescopes

Angulated borescopes are available with forward oblique, right-angle, or retrospective visual systems. These instruments usually consist of an objective section with provision for attaching an eyepiece at right angles to the objective section’s axis. This permits inspection of shoulders or recesses in areas not accessible with standard borescopes. Special-purpose borescopes include the following:

Calibrated borescopes are designed to meet specific visual examination requirements. The external tubes of these instruments can be calibrated to indicate the depth of insertion during a test. Borescopes with calibrated reticles are used to determine angles or sizes of objects in the field when held at a predetermined working distance.

Panoramic borescopes are built with special optical systems to permit rapid panoramic scanning of internal cylindrical surfaces of tubes or pipes.

Wide-field borescopes have rotating objective prisms to provide fields of view up to 120°.

Ultraviolet borescopes are used during fluorescent magnetic particle and fluorescent penetrant tests. These borescopes are equipped with ultraviolet lamps, filters, and special transformers to provide necessary wavelengths.

Waterproof and vapor proof borescopes are used for internal tests of liquid, gas, or vapor environments. They are completely sealed and impervious to water or other types of liquid.

Water-cooled or gas-cooled borescopes are used for tests of furnace cavities and for other high-temperature applications.

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10.5.4 Video Borescopes

The coupling of video and borescope technologies has solved some of the longstanding problems experienced by operators of conventional borescopes. In some cases, video equipment has simply been adapted to an existing borescope, transmitting images to a monitor as they appear in the eyepiece. More sophisticated systems transmit images to a monitor electronically, by means of a tiny camera located at the distal tip of the borescope. This camera is typically a solid-state silicon chip or light sensor known as a charge-coupled device.

Video borescopes transmit images in the following way:

1. Light is sent to the test area by fiber-optic light guides or light-emitting diodes.

2. When the light reaches the test area, a fixed-focus lens in the tip of the probe gathers reflected light and directs it to the surface of the charge-coupled device.

3. On the chip charge-coupled device, the pixels convert light into analog electrical signals.

4. The signals travel down the length of the probe through a series of amplifiers and filters.

Video borescopes eliminate the problems of fatigue and discomfort related to eyestrain with standard borescopes and improve the ability of inspectors to interpret images correctly. They also allow multiple views of the same object, making evaluations more reliable and facilitating training. A given image can be transmitted simultaneously to any number of monitors at the site or remote location.

In comparison with standard borescopes, the depth of field (range of distance in focus) with video borescopes is so expanded that focusing becomes unnecessary. By eliminating the time-consuming task of refocusing, video borescope make remote visual testing more efficient and less fatiguing.

Video borescopes are well suited to applications requiring several viewings of inside surfaces and can provide high image quality in terms of magnification, resolution, and color accuracy, as well as accurate measurement for situations in which critical assessment is required.

10.5.5 Remote Positioning and Transport Systems

Several types of remote positioning and transport systems are currently in use. Regardless of their specific form and function, the systems share a common element—the controlled manipulation of a video camera for remote visual examination of system components.

Integrating video camera technology with the latest in positioning and transport systems results in new inspection tools that can be used to safely complete the testing process in situations in which radiation, heat, or chemicals present serious health hazards to the visual inspector or in which physical configurations prevent inspector access.

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The term positioning and transport systems refers to any apparatus that puts a video camera and lightning in proper spatial relationship to visually test a component so that the camera can detect discontinuities. This definition is general to include as many configurations as possible.

The category that is interesting for buried pipeline and piping system’s visual inspection (from inside or from outside) is the automated system category. Automated systems can be fully autonomous or semiautonomous.

10.5.5.1 Robotic Visual Examination Systems

A fully autonomous (robotic) system will transport a camera to a given location without operator intervention. These systems have closed-loop control logic and respond to the environment in which they operate. Such systems can transport a camera between two points, negotiating all obstacles encountered en route. Consequently, they require highly developed sensors and sophisticated feedback processing.

Research has continued on systems of this type. However, unless the visual test requires simple pattern recognition, a visual examiner must evaluate the visual data. This requires operator remote control over vehicle movement, and it opens the vehicle control logic loop, destroying the system’s fully autonomous character. Because the vehicle must perform in a semiautonomous manner at the inspection location, most automated vehicles are constructed as semiautonomous vehicles from the onset, chiefly for economic reasons.

10.5.5.2 Semiautonomous Visual Examination Systems

Semiautonomous positioning and transport systems operate on open-loop control logic. These systems respond to input from an outside source, typically an operator, rather than from acquired sensory input and internally processed feedback. A good example of this type of device is a stepping pipe crawler. The feet of a stepping pipe crawler extend to and withdraw from the pipe wall as the vehicle body expands and contracts, respectively. This design provides the vehicle with the ability to climb within vertical piping, Each step involves a series of cylinder pressurizations and depressurizations. An operator oversees the overall motion (that is, forward, reverse, stop, and scan) and the computer determines the proper cylinder sequencing to produce the motion. The operator–computer relationship is necessary, particularly in vertical piping, where the computer ensures leg engagement. This prevents an operator from erroneously disengaging the fixture and letting it fall. In turn, the operator prevents the vehicle from walking into thermowells or flow orifices. Figure 10-4 shows an example of a pipeline crawler.

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Figure 10-4 Pipeline crawler

10.5.5.3 Selecting a Transport System

A great variety of transport vehicles are available, ranging from submersible vehicles to remotely controlled crawlers, with all manner of walking and rolling vehicles in between. With no shortage of vehicles to choose from, the difficulty arises in finding an appropriate transport vehicle for a given task.

The most effective method for the selection of transport systems is sistering—that is, networking between similar industrial facilities to obtain the most current information regarding vehicle application to specific tasks. The aim of this communication is to locate a vehicle that will most closely meet the operator’s immediate needs. Many companies use personnel whose sole function is to network in this fashion and maintain current files for a variety of applications. Vehicles located by this method might not meet the operator’s specific needs; however, it is most likely that reasonable modifications can be made to the available vehicle to fit inspection requirements.

10.6 Deployment Above the Pipe

No above-the-pipe deployment technologies currently exist for visual testing. Visual inspections require direct contact with the inner or outer pipe surfaces.

10.7 Deployment for Monitoring

No monitoring deployment technologies currently exist for visual testing technology.

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11 LASER PROFILOMETRY TECHNOLOGY With miniaturized optics, electronics for rapid signal processing, and computer-aided visualization, laser profilometry is becoming an effective NDE method. This technology entails traversing an area of interest with a laser sensor. The sensor captures a 2-D surface profile in the area of interest, and profiles are recorded with respect to time or distance traveled. Furthermore, these profiles are compiled into a 3-D surface topography that can be analyzed by visualization software to enable precise measurement of surface imperfections.

A laser profilometry inspection system can acquire substantial quantities of inspection data in a short time. With a properly configured automated laser profilometry system, a 49-ft-long pipe surface can be inspected in approximately 3 minutes, while acquiring well over 1 million radius readings. Figure 11-1 shows an example of a handheld laser profiler.

Figure 11-1 Laser profiler scanning a pipe surface

11.1 Laser Profilometry Wall Thickness Capability Summary

This section provides an overview of application variables associated with using laser profilometry technology to examine piping for wall degradation. Typical or expected results are presented in five tables. Although these results are accurate in most instances, it is important to understand that, like most technology applications, there are exceptions. To keep the information concise, the tables do not fully address all potential variations. Table 11-1 summarizes the technology function. Table 11-2 summarizes how the technology can be deployed. Table 11-3 addresses how surface condition, coatings, and other conditions affect technology application. Table 11-4 provides some of the piping materials the technology can be used to examine. Table 11-5 captures capabilities for a number of variables. To provide a consistent review format, these tables are presented in each technology section.

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Table 11-1 Laser profilometry: function

Table 11-2 Laser profilometry: deployment options

Table 11-3 Laser profilometry: impact of surface and coating on results

Function Comments

Thickness No

Can be used to profile surface Yes (for data collection surface)

Can detect internal and external metal surface loss

Yes (for data collection surface)

Can detect axial and circumferential wall loss Yes (for data collection surface)

Can discriminate between internal and external metal loss

Yes (for data collection surface)

Crack detection Yes (for data collection surface)

Embedded discontinuities No

Deployment Comments/Considerations

Manual deployment Yes

In-line deployment Yes

Automated outside surface Yes

Monitoring No

Examination Surface Expected Outcome (Most Situations)

Bare and smooth Yes

Bare and rough Yes

Painted No

Coated No

Lined No

Silt, tubercles, and similar debris No

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Table 11-4 Laser profilometry: applicable pipe materials

Table 11-5 Laser profilometry: capability variables

Variable Yes No Comments

Single-sided access for volumetric examination

X

Capable of examining when piping is in service

X External surface only

Capable of noncontact examination X

Capable of examining significant axial pipe volume away from sensor

X

No couplant required X

Capable of producing an image showing size and shape of discontinuity

X Only the surface to which it is applied

No radiological concerns X

11.2 Principles of Laser Profilometry

Laser profilometry sensors use optical triangulation to determine the distance between the sensor and the target surface. Optical triangulation requires a light source, imaging optics, and the photodetector. The light source and focusing optics generate a collimated or focused beam of light and focus it onto a photodetector. The photodetector can be either a lateral-effect detector for high-speed measurement or a charge-coupled device.

A diagram of a general point triangulation optical sensor is shown in Figure 11-2. As the distance between the sensor and the surface changes, the incident light, scattered by the surface and imaged in parallax by a lens, creates a focused spot of light that moves across a spatially sensitive photodetector. Processing electronics convert the detector output into an absolute range signal. The optical source can be an incandescent bulb, a light-emitting diode, or a laser diode. The viewing optics can be as simple as a pinhole but are usually a single-lens or multielement optical lens system. The detector can be bi-cell, a lateral-effect photodiode, or a charge-coupled device array.

Materials Comments

Carbon steel Yes

Stainless steel Yes

Aluminum Yes

Cast iron Yes

High-density polyethylene Yes

Fiberglass Yes

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Figure 11-2 Schematic of laser triangulation method

11.3 Laser Profilometry Capabilities

Laser profilometry from inside and outside a pipeline and piping systems can reveal the following information:

Presence of open cracks, both internally and externally

Presence or absence of surface deposits (such as oxide films or corrosive product on the surface), scaling, corrosion, erosion, discoloration, and oxidation bulging

Presence or absence of pitting and surface porosity, both internally and externally

Potential sources of mechanical weakness, such as sharp notches or misalignment

Missing parts, dimensional conformances, and gross defects visible on the surface, and distortion during fabrication and in service

A key advantage of using laser profilometry for the location and measurement of internal pitting is that piping can be scanned quickly to obtain detailed dimensional information without the negative influence of external features such as changes in the metallurgical content.

11.3.1 Limitations of Laser Profilometry

Disadvantages of laser profilometry include the following:

The pipe surface must be clean of debris, coatings, and moisture.

Surfaces to be inspected must be shaded from sources of bright, direct light sources (such as sunlight).

Specific deployment technologies have restrictions for distance from the inspection surface and incident angle.

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11.4 Pipeline Corrosion

Pipelines are examined to locate corrosion damage sites from outside, using crawlers or handheld scanners. Insulation, cladding, and external coatings must be removed, and general requirements are for a NACE No. 2 blasted finish. If corrosion is discovered, the area must be analyzed to determine whether the corroded pipe requires a repair. In case of external corrosion detected from inside a pipe, the areas of suspected corrosion can be excavated to allow for a detailed inspection of the pipeline surface. Accurate surface inspection can be essential to accurately calculating remaining life and deciding on a course of action. A laser profilometry scanning tool can provide an accurate contour map of the structural surface corrosion.

It is also important that the software that controls and visualizes the inspection data be able to distinguish between normal pipeline or piping system features, such as welds (seam and circular), and determine the depth and severity of the corrosion. An example of a corrosion map generated by an automated laser scanning tool is shown in Figure 11-3.

Figure 11-3 A corrosion map generated by laser profilometry

Corrosion can result in complex flaw configurations that are difficult to quantitatively assess using convention NDE. By scanning the internal surface using a high-speed, rotating laser profilometer, high-resolution maps of a pipe’s internal surface can be generated. A cross-sectional display can allow the operator to view the surface pits in both cross-sectional and axial perspectives. With interactive software, a cursor can be used to measure the depth of a pit at any location.

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11.5 Deployment Inside the Pipe

Tractor-conveyed ILI vehicles have been used to internally deploy laser profilometry for the purpose of deformation measurement. Figure 11-4 shows a laser sensor head that is deployed on an ILI vehicle. The vehicle is equipped with a rotating head for laser-based measurements of the pipe wall deformation or bore restriction, as well as a pan-and-tilt camera head for visual inspection. Tractor-conveyed deployment of laser profilometry is possible only in dry gas or dry empty pipe because laser energy cannot be transmitted through liquid. There are no flow-conveyed ILI deployments available for laser profilometry technology.

Figure 11-4 Video and laser inspection, tractor-conveyed ILI vehicle

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12 LEAK DETECTION TECHNOLOGY Leak testing at low pressures (approximately 1 atm) is an accepted method for demonstrating the tightness of connections and detecting through-wall perforations in pipe systems. Leak testing is particularly useful for detecting small pinholes that cannot be detected by other NDE concepts. Leak tests do not detect the defects in pipe wall or connections directly, but they detect the rate of leak as a measure of severity. Leak detection methods with their leak limits of detection are shown in Table 12-1.

Table 12-1 Leak test limits of detection

Method Leak Limit of Detection

(Mbar-Liter/Second)

Bubble test, water 0.01

Bubble test, soap 0.0001

Pressure decay 0.001

Acoustic 0.001

Vacuum decay 0.001

Halogen sniffer 0.00001

Helium sniffer 0.000001

Halogen detector 0.000001

Mass spectrometer 1 × 10-11

The allowed leak rate for chemical process equipment varies from 0.1 to 1 mbar-liter/second, depending on the specific application [18]. Lower limits of detection and allowable leak rate are used for more critical safety applications or to ensure long-term leak integrity.

A variety of commercially available leak detector sniffers for tracer gas applications can be deployed above the pipe, above grade. Pressure drop or decay tests are routine, and equipment and contractors are widely available in North America. New acoustic leak detection devices can be deployed inside the pipe.

Acoustic leak detection systems have proven to be an effective means for identifying leaks in water pipelines. Currently, three predominant acoustic leak detection systems are used: acoustic listening devices, leak noise correlators, and tethered hydrophone systems.

Low-pressure leak testing will not detect metal loss, so it is of limited use in demonstrating the future integrity of buried pipe when corrosion cannot be fully mitigated. In addition, low-pressure leak testing cannot demonstrate the pressure-carrying capability of corroded pipe.

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12.1 Deployment Outside the Pipe

Acoustic sensors (typically accelerometers or hydrophones) can be placed on the pipe or connections at convenient access points; for example, at locations of aboveground taps or valves. The aim is to determine the position of the leak, which in this case is the distance from sensor 1 to the leak. This distance is related to other variables by the following:

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tcdd

Where:

d is the distance between the two sensors.

c is the speed at which the leak noise propagates through the pipe.

Δt is the difference in arrival times of the noise at the two sensors.

Thus, to accurately determine the leak, these three variables must be known. The distance between the sensors, d, can be measured reasonably accurately using a variety of methods, such as a global positioning system. The wave speed, c, is difficult to measure and remains an area for further research. To estimate Δt, the cross-correlation of the signals from the sensors is generally used. However, the quality of this estimate depends on the type and positioning of the sensors and the processing of the signals.

12.2 Deployment Inside the Pipe

The newest leak detection technologies are deployed from inside the pipe. Tethered in-line acoustic leak-detection transducers have been used to inspect buried water distribution pipelines. Acoustic leak detection depends on the principle that leaks in pressurized pipes >30 psi will exhibit a characteristic sound amplitude and frequency range, with leak severity producing changes in sound amplitude that is proportional to water pressure. The Sahara water pipeline inspection system reportedly can detect water leaks in pressurized pipelines as small as 0.004 gpm while the pipeline is in service, introducing the sensor with a cable through a stuffing box fitted to a valve. Leak locations can be located to an accuracy of 18 in. and can be used to detect leaks in steel, cast iron, plastic, or concrete pipe systems with a minimum reported diameter of 10 NPS.

A free-swimming (nontethered) internal acoustic leak detection device was developed by Pure Technologies in 2004. This technology contains acoustic sensors, power, and recording capability in a spherical aluminum body that is encased within a foam covering. This ball assembly is inserted through a valve connection, and the ball rolls along the pipe with flow, recording both distance and acoustic signature. The ball is retrieved at the end of the inspection run by inserting a catch net through another valve and extracting the ball. The insertion and extraction can be performed while the pipe is under pressure. The claimed leak detection capability for the ball is 0.10 gpm, and it can inspect pipe ≥10 NPS. This technology is applicable to steel pipe, cast iron, plastic, and concrete pipe.

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12.3 Deployment Above the Pipe

A variety of gas detection equipment is available that can be deployed above grade to survey for leaks. Generally, a tracer gas is added to facilitate detection. The individual equipment vendors should be consulted for complete performance specifications.

12.4 Deployment for Monitoring

Current on-pipe or above-pipe leak detection acoustic technologies can easily be used to continuously monitor for leaks.

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13 ILI TECHNOLOGY ILI tools provide a means of delivering proficient NDE technologies within the pipe to detect and characterize wall degradation without the expense and risk associated with excavation. Such tools can be equipped with ultrasonic, RFT, MFL, and electromagnetic NDE sensors, some of which are routinely used from the outside surface. For instance, an internal ultrasonic examination can provide similar results to those conducted from the outside and, in some cases, provide more detail. Although many available ILI tools are designed for straight transmission pipelines and not usable in plant pipe configurations, effective ILI tools are commercially available for plant piping applications.

The Buried Pipe Integrity Task Force report Industry Guidance for the Development of Inspection Plans for Buried Piping [5] specifies the number of direct examinations necessary to achieve reasonable assurance. The number of direct examinations required per line depends on many factors, but it can be as many as three. Additional direct examinations might be required if damage is found. At the time of publication, it was common practice to excavate a 10-ft section of pipe to conduct such a direct examination.

Although conducting a direct examination of an excavated pipe section is an effective method of assessing pipe condition, it is typically quite expensive and disruptive, and it puts other assets at risk. In addition, it is limited to the particular section of pipe. For example, piping that is close to a building or equipment such as transformers might require structural analysis and result in the need for shoring. Pipe running under buildings, in vaults, or encased in concrete might not be accessible without significant cost and effort. Excavating a pipe that is beneath other pipes or cables puts those assets at risk, not only during the excavation process but also during the burial process.

Direct examinations can be obtained with an ILI tool, thereby eliminating excavations if a tool can be inserted into and operated within the pipe. Not only can ILI tools be used to eliminate excavations but also they can be used to increase reasonable assurance levels. After an ILI tool is placed into a pipe, it can be used to examine whatever length of pipe can be accessed with marginal additional expense. Even if 100% coverage is not achievable within a pipe, it will typically be more than what is achieved with a 10-ft excavation. If multiple direct examinations are required in a line, the potential exists that an ILI tool could satisfy each of them, thereby eliminating multiple excavations. Further, trending can be established because most ILI tools electronically record NDE data.

Although ILI tools can provide significant benefit, their use can be complicated by a variety of factors. Unfortunately, today’s nuclear power fleet was not designed for the use of ILI tools as transmission pipelines were, with launching and receiving stations built into the system. Thus, access must be gained to insert ILI tools. This can require piping modifications to install ILI launching and receiving stations or installing a hot tap, items that are routinely used in other

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industries for ILI tool access. Alternatively, the ILI tool can be inserted and retracted through an accessible pipe end, such as end of a diesel fuel fill line or pipe within a tank. Some tools can be inserted through a disassembled component such as a valve or possibly a strainer. ILI service providers are knowledgeable and should be consulted for potential solutions.

The limited availability of ILI tools to navigate piping bends, vertical runs, and other such challenges is principally due to the historic lack of demand for such tools. Whereas the transmission pipeline industry has mature inspection technology to examine long, straight runs of pipe due to high demand for such technology because of piping failures and regulation. Increased demand for ILI tools that can effectively maneuver though bends and other challenges from not only the nuclear industry but also the refining, chemical, gas, and water industries will spur development of new and more adaptive ILI technologies. Even the transmission pipeline industry is driving such developments due to increased regulations. Technology advancements such as more space-efficient sensor, data, and power packages are facilitating such developments.

The following sections provide an overview of the ILI concepts, as well as other key information in applying ILI tools. This section does not specifically address the NDE concepts because they are presented in prior sections. These sections should be consulted for capabilities and cleanliness requirements.

13.1 Flow-Conveyed (Free-Swimming) Tools

A flow-conveyed (free-swimming) ILI tool is typically self contained and is moved through a piping system with product flow. Such ILI tools typically contain an arrangement of conforming cups that allow the ILI tool to be conveyed by gas or liquid product within the pipe. The cups are designed to open against the pipe wall when under flow pressure to provide tool stabilization. An illustration of a modular-type, flow-conveyed ILI tool is provided in Figure 13-1, and a more rigid tool is illustrated in Figure 13-2. Both devices are capable of flowing through piping containing bends; the modular tool, because it is flexible, and the rigid tool, because it is short in length. As is typical, both tools contain the NDE sensors, power supply, positioning devices, and necessary NDE electronics.

Figure 13-1 Design elements of an ILI tool

Optional Data TetherPower and Data Modules

Odometer WheelsSecondarySensors

PrimarySensors Drive Cups

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Figure 13-2 A flow-conveyed ILI tool

A flow-conveyed ILI tool is inserted and extracted from piping systems with launchers and receivers. These devices can be either permanently installed into a piping system or temporarily attached. Figure 13-3 illustrates the configuration of a typical launcher, providing a trap that can be isolated from the pipe contents. A receiver is similarly configured.

Figure 13-3 A typical, permanent pig launcher–receiver configuration

When piping can be taken out of service for inspection, the design of a temporary launcher for flow-conveyed ILI tools becomes simpler. For out-of-service lines, there is no need to provide an operational bypass for the main line. A trap barrel can be fitted to the piping by means of a flange connection or weld; isolation might not be needed between the trap barrel and the piping, if the line to be inspected is depressurized while it is out of service before inspection. A kicker

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fitting for pressurizing the trap barrel with liquid or gas provides drive for the ILI tool. The drive fluid must be compatible with the ILI tool sensor technology (MFL or ultrasonic). Figure 13-4 illustrates a temporary launcher connected to a line that is removed from service during inspection.

Figure 13-4 A temporary launcher for a flow-conveyed ILI tool

Some flow-conveyed ILI tools can be launched and retrieved from a single launcher/receiver; they are referred to as being bidirectional. Bidirectional capability is generally provided by fitting an ILI tool with drive cups that can effectively seal and provide drive due to differential pressure from either direction. An example of a bidirectional ILI tool is provided in Figure 13-5.

Figure 13-5 A bidirectional, flow-conveyed ILI tool

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Before launching an ILI tool, it is important to understand any restrictions that might limit tool flow. One method of accomplishing this is to survey the line with a gauge pig. A gauge pig is a short-length pig that contains an aluminum gauge plate of the same diameter as the minimum bore diameter placed between drive cups (see Figure 13-6). Deformation of the gauge plate indicates the presence of a bore restriction that might restrict the flow of the tool and, therefore, must be rectified before the inspection tool is run to prevent it from becoming stuck.

Figure 13-6 Gauging pig

Onboard data storage is a standard feature for flow-conveyed ultrasonic ILI tools; however, a fiber-optic cable deployed between the tool and a data module that remains in the launcher barrel during the course of the inspection can also be used (Figure 13-7). For ILI tools with full onboard data storage, the results of the inspection (run quality and pipe condition) are not available until after the ILI tool is received and the data are downloaded and analyzed. By using the fiber-optic data cable, real-time data are received. This allows for the ability to know and control the rate of movement of the ILI tool within the pipe. Tool speed is an important factor, especially for ultrasonics. If the speed is known, flow adjustments can be made to maximize NDE performance. In addition, data quality can be assessed in real time. Figure 13-7 shows an example of a flow-conveyed ILI tool within a launcher and its fiber-optic data cable being prepared for connection before launching.

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Figure 13-7 Flow-conveyed ILI tool inside a temporary launcher with a fiber-optic data cable

13.2 Cable-Pulled or Tethered Vehicles

Cable-pulled or tethered vehicles use a single entry point, typically a flange, to enter the pipe [10]. Tethered vehicles house the sensors in the vehicle body, and the acquisition electronics reside on the surface. The exciter power and detector signals are transmitted by a cable. In one commonly used procedure, the tool is introduced into the pipe and pumped, normally with water, to a target location. The tool is then pulled back to the access point, examining the pipe as it is pulled (see Figure 13-8).

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Figure 13-8 A cable-pulled vehicle

The pump and cable-pull operation is facilitated by a fixture that is mounted at the flange. This fixture provides a water-tight, sealed connection, enabling the passage of the cable while the vehicle is being pumped or retrieved. Cable-pulled vehicles have the advantage that access logistics are simplified by requiring only a single point of entry.

Cable-pulled vehicles, on the other hand, have their range of inspection limited by the number of elbows (typically three). The vehicle is pumped until three elbows are included in the segment and then pulled back. Exceeding this limit puts the tool at risk of becoming stuck. In addition, tethered vehicles have a relatively loose fit inside the pipe, which may cause the sensor to move up and down with travel, affecting sensitivity.

13.3 Guide-Wire-Propelled Tools

One way to overcome the number-of-elbows limitation of the tethered tools while handling the motion difficulties of the pigs through branches, tees, and valves is to use guide-wire propulsion [10].

The guide-wire propulsion, a concept currently being developed under EPRI funding, requires an entry and an exit point. The exit point can, in principle, be a pipe other than the one being inspected—for example, a larger-diameter pipe. The entry into the new host pipe, however, must include a rounded corner, or the tool could get stuck.

The deployment includes two steps. In the first step, a thin wire is laid out along the route. The method for laying the wire depends on the obstacles; methods include crawlers, push rods with halfway catch baskets, and vacuum-and-feather techniques. These methods are used by other industries to lay down cables in conduits. After the wire has been placed, the vehicle follows, using the stationary cable to propel itself along the route (see Figure 13-9).

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Figure 13-9 Guide-wire propulsion used in the EPRI concept vehicle

A guide-wire-propelled vehicle has no limits on the number of elbows that it can traverse. In addition, because the route is preset by the wire, the vehicle can pass through branches, tees, and valves. Finally, because the vehicle is not pressed against the pipe, the risk of becoming stuck is reduced. In the event of a mechanical malfunction, the wire can be used to pull the vehicle out by winch action.

The disadvantages of the guide-wire vehicles include erratic lateral motion inside the pipe because of the loose fit. To minimize the lateral motion effect on data quality, the guide-wire tool should include sensor position stabilization through servo-mechanical systems.

The advantages of guide-wire propulsion include the following:

There is no limit to the number of elbows being traversed.

Tools can travel through elbows, tees, and valves.

Loose pipe fit motion minimizes the risk of getting stuck.

The disadvantages include the following:

Deployment must be preceded by guide-wire installation.

Passage from a smaller-diameter into a larger-diameter pipe must include a rounded corner, or the tool could become stuck.

Sensor position must be stabilized to isolate it from vehicle motion.

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13.4 Robotically Driven or Tractor Tools

The term robotically driven in this report refers to deployment of NDE sensors inside the pipe with a vehicle propelled under its own traction by wheels or tracks. A robotically driven ILI tool and ultrasonic sensor deployment are shown in Figure 13-10. It can be tethered or nontethered, with the primary use of the tether to deploy power, control the tool, and transmit NDE data. A variety of tether designs are available, with lengths of up to 10.5 miles. NDE deployable technology include ultrasonics, some electromagnetic, and visual. The magnets of MFL tools typically have too much drag to be used.

(a) A robotically driven tool (b) Ultrasonic sensor deployment

Figure 13-10 Multiple-drive-wheel, robotically conveyed ILI tool

The tool is introduced through a pipe end, which can be created by removing a spool piece or a valve. Figure 13-11 shows a tool being guided into an 8-in.-diameter pipe with a tray. A spool piece was removed for this deployment. Figure 13-12 shows a schematic of the piping configuration navigated during an actual inspection.

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Figure 13-11 Deployment of a robotically conveyed ILI tool into a buried pipe

Figure 13-12 Pipe system examined with a robotically driven ILI tool

Figure 13-13 shows an example of a large-diameter (16- to 60-in.), robotically driven ILI tool, illustrating a different approach to the use of drive wheels, with the ultrasonic sensors located in the center of the tool. The figure shows the overall view of the inspection vehicle and the sensor ring where ultrasonic sensors are positioned.

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Figure 13-13 Robotically driven ultrasonic ILI tool for large-diameter pipe

Robotically driven ILI tools have several advantages:

Low-flow or no-flow conditions can be inspected.

Tools are capable of navigating many piping features such as elbows and bends.

Real-time NDE data are available, allowing increased scrutiny of suspect areas.

The ILI tool is less sensitive to surface deposits or the presence of bore restrictions.

Internal pipe condition is relevant mainly to the NDE sensor performance; tractor conveyance is less sensitive to debris compared to flow-conveyed ILI.

A tether minimizes risk of losing the tool.

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Although a robotically driven ILI tool has advantages, it also has drawbacks:

Piping systems must be removed from service.

The number and severity of bends that an ILI tool can transverse is limited by the drag of the tether.

The height of vertical runs is a limiting factor.

Although robotically driven ILI tools are available for pipe diameters from 3 in. to as large as 60 in., the overall pipe segment geometries must be evaluated for the presence of bends, bend types, bend number, and pipe slopes to be negotiated. This means that individual pipe segment geometries and, ideally, pipe isometric drawings must be supplied to the ILI vendors for consideration before any robotically driven tool can be deemed applicable for a particular assessment. Inspection vendors might be able to custom-build solutions to accommodate the physical pipe characteristics.

13.4.1 Manned Vehicles for Large-Bore Pipes

For large-bore pipes, it becomes quite costly to perform a full 360° examination in one pass. However, a person can enter large-bore pipes, so tools can be designed to scan the pipe in several passes while being controlled by an operator. Vehicles for large-bore pipes are typically custom-made for the particular application.

EPRI has developed an instrumented vehicle for delivering remote field and deep penetration eddy current sensors inside large-bore pipe for the detection of pipe wall corrosion and weld corrosion, respectively (see Figure 13-14).

Figure 13-14 The EPRI large-bore, instrumented vehicle

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These NDE technologies permit examination though coatings, cement liners, and mud up to 1 in. thick [19]. Other NDE techniques, such as ultrasonics and EMATs, require a different position relative to the pipe surface and currently cannot be delivered.

This tool set requires that an operator assist the vehicle to complete its tasks. The delivery mechanics include sensor spatial stabilization to isolate the sensor position from the cart’s motion and any effect this motion might have on data quality. The vehicle is currently not designed to climb through vertical pipe sections.

One feature of the EPRI vehicle is that all the components are modularly designed to fit through a 24-in. manhole. Thus, the vehicle assembly and disassembly is performed inside the pipe.

Advantages of the EPRI instrumented vehicle for large-bore pipes include the following:

Tolerance of coating, cement liner, and mud up to 1 in. thick.

Dual tool set to examine for wall loss and weld corrosion.

Instrumentation stabilized to isolate vehicle side motion from sensor position.

Modular component design permits entry through a 24-in. manhole.

The disadvantages of the vehicle include the following:

Pipe must be drained.

Cannot climb vertical pipe sections.

13.5 Access Considerations

Pipe access considerations and pipe configuration determine the type of vehicle that can be deployed [4]. From a user’s viewpoint, it is imperative that the pipe configuration and any obstructions be clearly identified in advance and that the information be transmitted to the service provider during the planning stage of the inspection. When planning a buried pipe inspection, the following steps are recommended:

1. Plan a meeting of all involved (facilities, contractors, and so on).

2. Gather relevant pipeline configuration information.

3. Establish whether the pipe can be drained and whether it is necessary to do so.

4. Establish pipe access requirements.

5. Establish internal pipe cleaning requirements.

6. Establish debris disposition logistics.

7. Establish instrumented vehicle traveling requirements.

8. Establish on-site facility support requirements.

9. Determine vendor detection capability (smallest detectable defect).

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The vendor typically requests detailed information about the pipe configuration to ensure that the tool can be pulled out safely. A typical vendor questionnaire includes the following:

Diameter, nominal wall thickness, material specifications

Length of pipe

Whether the pipe must be drained

Number of elbows

Elbow curvature (1D, 1.5D, or 2D)

Description of valves

Description of tees

Locations and type of branches

Access description

Power available

Pipe internal condition (mud or debris thickness)

13.6 Cleaning

The degree of internal pipe surface cleanliness is a function of both NDE sensor requirements and the ILI tool. Ultrasonics (non-EMAT) and MFL require relatively clean surfaces, whereas RFT and other electromagnetic techniques can tolerate some level of debris. The specific NDE sensor section should be referenced for further information on surface requirements. The operations of ILI tools can also be influenced by internal debris if significant enough. For instance, debris can adversely affect differential pressure capability of the drive cups for flow-conveyed ILI tools. The equipment or inspection service vendor should be consulted for the degree of cleanliness required.

Pipe cleaning can be accomplished by a number of methods such as pumping a cleaning pig through the pipe, chemical cleaning, or water or gas blasting. A variety of cleaning pig designs are commercially available. Examples of foam-body cleaning pigs with abrasive strips are shown in Figure 13-15. Such foam pigs provide flexibility in negotiating pipes with bends and bore restrictions. Rigid-body cleaning pigs are available that have various configurations for scrappers and debris magnets, depending on the type of internal deposits.

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Figure 13-15 Foam-core cleaning pigs

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14 CONCLUSIONS This report of NDE technology describes a number of tools that can be deployed outside, inside, and above the pipe to understand the integrity of nuclear power plant buried pipe with respect to metal loss due to corrosion. Buried pipe integrity management plans must consider the capability of NDE tools to detect and discriminate metal loss, considering that metal loss can be present in a variety of morphologies, ranging from pinholes to general wall thinning. This report will be updated periodically as new technologies emerge and operating experience is captured.

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15 REFERENCES

15.1 In-Text Citations

1. NEI 07-07. Industry Ground Water Protection Initiative—Final Guidance Document. Nuclear Energy Institute, Washington, DC: 2007.

2. NEI 09-14. Guideline for the Management of Buried and Underground Piping Integrity. Nuclear Energy Institute, Washington, DC: 2009.

3. Underground Piping and Tanks Integrity Initiative. U.S. Nuclear Regulatory Commission, Washington, D.C. 2010. Available from http://pbadupws.nrc.gov/docs/ML1034/ ML103410507.pdf.

4. Recommendations for an Effective Program to Control the Degradation of Buried and Underground Piping and Tanks (1016456, Revision 1). EPRI, Palo Alto, CA: 2010. 1021175.

5. Buried Pipe Integrity Task Force. Industry Guidance for the Development of Inspection Plans for Buried Piping. April 2011. Available from http://pbadupws.nrc.gov/docs/ ML1119/ML111950018.pdf.

6. Chris Burton and David Smith. “Risk Ranking for Buried Pipe and EPRI BPWORKS Software,” presented at the Industry/NRC Meeting on Buried Pipe, White Flint, MD (September 21, 2010).

7. Nondestructive Evaluation: Buried Pipe Direct Examinations Through Coatings. EPRI, Palo Alto, CA: 2012. 1025228.

8. Edward Petit de Mange Diakont, “Demonstrated Use of EMAT UT Technology for Assessment of Nuclear Plant Buried Piping.” Paper presented at the EPRI Buried Piping Integrity Group Meeting, Memphis,Tennessee (July 2012).

9. Buried Pipe Guided Wave Examination Reference Document. EPRI, Palo Alto, CA: 2009. 1019115.

10. John Tiratsoo, ed. Pipeline Pigging & Integrity Technology, Third Edition. Clarion Technical Publishers, Houston, TX. 2010.

11. ASME Code Case N-513-2. “Evaluation Criteria for Temporary Acceptance of Flaws in Moderate Energy Class 2 or 3 Piping.” ASME, New York: 2007.

12. ASME B31G. “Manual for Determining the Remaining Strength of Corroded Pipelines: Supplement to B31 Code for Pressure Piping.” ASME, New York: 2009.

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13. Jim Melchionna and Jim Shrode, “Inspection of Service Water Piping 24” SW Carbon Steel Thru Wall Spools & 30” Non-Safety Related Header to Turbine Loads Using BEM Technology and Confirmatory UT at the Salem Nuclear Generating Station During April 2011 2R18 RFO.” Paper given at the EPRI Buried Piping Integrity Group Meeting, Memphis, Tennessee (July 2012).

14. Nondestructive Evaluation: Remote Field Technology Assessment for Piping Inspection Including Buried and Limited Access Components. EPRI, Palo Alto, CA: 2010. 1021153.

15. Guennadi Krivoi, Martin Klinger, and Johann Hinken. “Procedure and Device for Detecting Nonuniformities in the Wall Thickness of Inaccessible Metal Pipes.” U.S. Patent 6,501,266 B1, filed April 27, 1999, and issued December 31, 2002.

16. Guennadi Krivoi and Johannes Peter Kallmeyer. “Test Method and Apparatus for Noncontact and Nondestructive Recognition of Irregularities in the Wall Thickness of Ferromagnetic Pipes.” U.S. Patent 6,727,695 B2, filed October 9, 2002, and issued April 27, 2004.

17. Johann Hinken, Martin Klinger, and Guennadi Krivoi. “Method and Device for Detecting Irregularities in the Thickness of the Walls of Inaccessible Metal Pipes.” European Patent EP1075658, filed April 27, 1999, and published June 30, 2004.

18. Inspection Manual: Federal Equipment Leak Regulations for Chemical Manufacturing Industry, Volume III: Petroleum Refining Industry Regulations. United States Environmental Protection Agency, Washington, D.C. 1998. EPA/305/B-98-011. Available from http://epa.gov/oecaerth/resources/publications/assistance/sectors/insmanvol3.pdf

19. Catawba Field Trial of EPRI’s Large-Diameter Buried Pipe Instrumented Vehicle. EPRI, Palo Alto, CA: 2008. 1016676.

15.2 Recommended Reading—General NDE Concepts and Guidelines

A Guideline Framework for Integrity Assessment of Offshore Pipelines. DNV Technical Report No. 44811520, Rev 2, 2006.

Allgaier, M. W., S. Ness, P. McIntire, P., and P. O. Moore. Nondestructive Testing Handbook, 3rd Edition. Vol. 8, Visual and Optical Testing. Columbus, OH: American Society for Nondestructive Testing. 1993.

ASM Handbook, 9th Edition. Vol. 17, Nondestructive Evaluation and Quality Control. Materials Park, OH: ASM International. 2000.

ASTM Book of Standards Volume 03.03: Metals Test Methods and Analytical Procedures: Nondestructive Testing. American Society for Testing and Materials International. 2009.

Bossi, R. H., F. A. Iddings, G. C. Wheeler, and P. O. Moore. Nondestructive Testing Handbook, 3rd ed. Vol. 4, Radiographic Testing. Columbus, OH: American Society for Nondestructive Testing. 2002.

Bray, D. E. and D. McBride, eds. Nondestructive Testing Techniques. New York: John Wiley & Sons. 1992.

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Bray, D. E. and R. K. Stanley. Nondestructive Evaluation: A Tool in Design, Manufacturing, and Service. New York: McGraw Hill. 1989.

Cartz, L. Nondestructive Testing: Radiography, Ultrasonics, Liquid Penetrant, Magnetic Particle, Eddy Current. Materials Park, OH: ASM International. 1995.

Daley, Beth. “Leaks Imperil Nuclear Industry.” Boston Globe, January 31, 2010.

Halmshaw, R. Introduction to the Nondestructive Testing of Welded Joints. Cambridge, United Kingdom: Abington Publishing. 1988.

Hlamshaw, R. Nondestructive Testing, 2nd ed. London, United Kingdom: Edward Arnold. 1991.

Hull, B. and V. John. Nondestructive Testing. Basingstoke, United Kingdom: McMillan. 1988.

Jackson, C. N., N. Charles, C. N. Sherlock, and P. O. Moore. Nondestructive Testing Handbook, 3rd ed. Vol. 1, Leak Testing. Columbus, OH: American Society for Nondestructive Testing. 1997.

McMaster, R. C., ed. Nondestructive Testing Handbook, 1st ed. Columbus, OH: American Society for Nondestructive Testing. 1959.

Miller, R. K., E. Hill, and P. O. Moore. Nondestructive Testing Handbook, 3rd ed. Vol. 6, Acoustic Emission Testing. Columbus, OH: American Society for Nondestructive Testing. 2005.

Moore, D. G. and P. O. Moore. Nondestructive Testing Handbook, 3rd ed. Vol. 8, Magnetic Testing. Columbus, OH: American Society for Nondestructive Testing. 2008.

Nondestructive Testing Methods. TO33B-1-1 (NAVAIR 01-1A-16) TM43-0103. Washington DC: Department of Defense, United States Air Force. June 1984.

Recommendations for an Effective Program to Control the Degradation of Buried and Underground Piping and Tanks (1016456, Revision 1). EPRI, Palo Alto, CA: 2010. 1021175.

Service Water Piping Guideline. EPRI, Palo Alto, CA: 2005. 1010059.

Stanley, R. K., P. O. Moore, and P. McIntire. Nondestructive Testing Handbook, 3rd ed. Vol. 9, Special Nondestructive Testing. Columbus, OH: American Society for Nondestructive Testing. 1995.

Tracy, N. and P. O. Moore. Nondestructive Testing Handbook, 3rd ed. Vol. 2, Liquid Penetrant Tests. Columbus, OH: American Society for Nondestructive Testing. 1999.

U. S. Department of Transportation. “Serious Pipeline Incidents.” PHMSA Stakeholder Communications. Available from http://primis.phmsa.dot.gov/comm/reports/safety/serpsi.html. Accessed August 2010.

U. S. Nuclear Regulatory Commission. “Buried Piping Activities.” Available from http://www.nrc.gov/reactors/operating/ops-experience/buried-piping-activities.html. Updated April 2010. Accessed August 2010.

Udpa, S. S. and P. O. Moore. Nondestructive Testing Handbook, 3rd ed. Vol. 5, Electromagnetic Testing. Columbus, OH: American Society for Nondestructive Testing. 2004.

15-4

Wenk, S. A. and R. C. McMaster. Choosing NDT: Applications, Costs and Benefits of Nondestructive Testing in Your Quality Assurance Program. Columbus, OH: American Society for Nondestructive Testing. 1987.

Workman, G. L., D. Kishoni, and P. O. Moore. Nondestructive Testing Handbook, 3rd ed. Vol. 7, Ultrasonic Testing. Columbus, OH: American Society for Nondestructive Testing. 2007.

15.3 Recommended Reading—MFL

ASTM E-1316, Terminologies of Nondestructive Examination.

ASTM E-570, Practice for Flux Leakage Examination of Ferromagnetic Steel Tubular Products.

Atherton, D. L. “Effects of Line Pressure on the Performance of Magnetic Inspection Tools.” Oil & Gas Journal, 1986.

Atherton, D. L. et al. “Stress Induced Magnetization Changes of Steel Pipes—Laboratory Tests,” IEEE Transactions on Magnetics, Vol. MAG-19, No. 4, 1983.

Blitz, J. Magnetic Methods. Electrical and Magnetic Methods of Nondestructive Testing. New York: Adam Hilger. 1991.

Bubenik, T. A., D. R. Stephens, B. N. Leis, and R. J. Eiber. Stress Corrosion Cracks in Pipelines: Characteristics and Detection Considerations. Battelle, Report No. GRI-95/2007, The Gas Research Institute. 1995.

Bubenik, T.A. et al. In-Line Inspection Technologies for Mechanical Damage and SCC in Pipelines—Final Report. Report No. DTRS56-96-C-0010, U.S. Department of Transportation. 2000.

Crouch, A.E. “Using MFL Corrosion Signals to Measure Pipe Wall Stress.” The Pipeline Pigging and Repair Conference. Clarion Technical Conference. 2003.

Jiles, D. Introduction to Magnetism and Magnetic Materials. London, UK: Chapman and Hall. 1991.

McMaster, R. C., ed. Nondestructive Testing Handbook, 1st ed. Columbus, OH: American Society for Nondestructive Testing. 1959.

Moore, D. G. and P. O. Moore. Nondestructive Testing Handbook, 3rd ed. Vol. 8, Magnetic Testing. Columbus, OH: American Society for Nondestructive Testing. 2008.

Nestleroth, J. B. Evaluation of Circumferential Magnetic Flux for In-Line Detection of Stress Corrosion Cracks and Selective Seam Weld Corrosion, PRCI Report L51811 199.

Nestleroth, J. B. and A. E. Crouch. Variation of Magnetic Properties in Pipeline Steels. Report No. DTRS56-96-C-0010, Subtask 1.1, U.S. Department of Transportation. 1998.

Nestleroth, J. B. and T. A. Bubenik. Magnetic Flux Leakage Technology for Natural Gas Pipeline Inspection. Battelle, Report No. GRI-00/01800, The Gas Research Institute. 1999.

Recommendations for an Effective Program to Control the Degradation of Buried and Underground Piping and Tanks (1016456, Revision 1). EPRI, Palo Alto, CA: 2010. 1021175.

15-5

Stanley, R. K., P. O. Moore, and P. McIntire. Nondestructive Testing Handbook, 3rd ed. Vol. 9, Special Nondestructive Testing. Columbus, OH: American Society for Nondestructive Testing. 1995.

15.4 Recommended Reading—Eddy Current Testing

ASTM E-1312, Practice for Electromagnetic (Eddy Current) Examination of Ferromagnetic Cylindrical Bar.

ASTM E-243, Practice for Electromagnetic (Eddy Current) Examination of Copper and Copper Alloy Tubes.

ASTM E-309, Practice for Eddy Current Examination of Steel Tubular Products Using Magnetic Saturation.

ASTM E-326, Practice for Electromagnetic (Eddy Current) Examination of Seamless and Welded Tubular Products, Austenitic Stainless Steel and Similar Alloys.

ASTM E-376, Practice for Measuring Coating Thickness by Magnetic Field or Eddy Current Examination Method.

ASTM E-566, Practice for Electromagnetic (Eddy Current) Sorting of Ferrous Metals.

ASTM E-571, Practice for Electromagnetic (Eddy Current) Examination of Nickel and Nickel Alloy Tubular Products.

Atherton, D. L. and S. Sullivan. “Electromagnetic Technique for Pressure Tubes.” Materials Evaluation, Vol. 44. 1986.

Bubenik, T. A., D. R. Stephens, B. N. Leis, and R. J. Eiber. Stress Corrosion Cracks in Pipelines: Characteristics and Detection Considerations. Battelle, Report No. GRI-95/2007, The Gas Research Institute. 1995.

Bubenik, T.A. et al. In-Line Inspection Technologies for Mechanical Damage and SCC in Pipelines—Final Report. Report No. DTRS56-96-C-0010, U.S. Department of Transportation. 2000.

Burrows, M. L. A Theory of Eddy Current Flaw Detection. University MicroFilms, Inc., 1964.

Dodd, C. V., W. E. Deeds, and W. G. Spoeri. “Optimizing Defect Detection in Eddy Current Testing,” Material Evaluation. 1971.

Fisher, J. L., S. T. Chain, and R. E. Beissner. “Remote Field Eddy Current Model,” in Proceedings of the 16th Symposium on Nondestructive Evaluation. 1987.

Kilgore, R. J. and S. Ramchandran. “NDT Solution: Remote Field Eddy Current Testing of Small Diameter Carbon Steel Tubes.” Material Evaluation, Vol. 47. 1989.

Lord, W., Y. S. Sun, and S. S. Udpa. “Physics of the Remote Field Eddy Current Effect,” in Reviews of Progress in Quantitative NDE. 1987.

15-6

McMaster, R. C., ed. Nondestructive Testing Handbook, 1st ed. Columbus, OH: American Society for Nondestructive Testing. 1959.

Moore, D. G., and P. O. Moore. Nondestructive Testing Handbook, 3rd ed. Vol. 8, Magnetic Testing. Columbus, OH: American Society for Nondestructive Testing. 2008.

Muthu. Engineers Guide I—Electromagnetic NDE Guide for Utility Engineers. TM-114284.

Nestloerth, J. B. and T. A. Bubenik. Magnetic Flux Leakage Technology for Natural Gas Pipeline Inspection. Battelle, Report No. GRI-00/01800, The Gas Research Institute. 1999.

Recommendations for an Effective Program to Control the Degradation of Buried and Underground Piping and Tanks (1016456, Revision 1). EPRI, Palo Alto, CA: 2010. 1021175.

Schmidt, T. R. “The Remote Field Eddy Current Inspection Techniques.” Materials Evaluation, Vol. 42. 1984.

Stanley, R. K., P. O. Moore, and P. McIntire. Nondestructive Testing Handbook, 3rd ed. Vol. 9, Special Nondestructive Testing. Columbus, OH: American Society for Nondestructive Testing. 1995.

15.5 Recommended Reading—Pulsed Eddy Current Testing

Bubenik, T. A., D. R. Stephens, B. N. Leis, and R. J. Eiber. Stress Corrosion Cracks in Pipelines: Characteristics and Detection Considerations. Battelle, Report No. GRI-95/2007, The Gas Research Institute. 1995.

Cohn, M. J., Y. S. Garud, and J. de Raad. “Software and Pulsed Eddy Current Analysis Enhance Detection of Flow Accelerated Corrosion.” Power Engineering, Vol. 103, No. 11, 1999.

Collins, R., D. H. Michael, and K. B. Ranger. “The AC Field Around a Plane Semi Elliptical Crack in a Metal Plate.” in Proceedings of the 13th Symposium on Nondestructive Evaluation, Nondestructive Testing Information Center, San Antonio, Texas. 1981.

De Haan, V. O., P. de Jong, and J. Wolters. “Systeembeschrijving INCOTEST.” Röntgen Technische Dienst BV, Rotterdam, The Netherlands, 1998.

Fontana, M. G. Corrosion Engineering. McGraw Hill Book Company. 1986.

Hussein, K., A. Shaukat, and F. Hassan. “Corrosion Cracking of Gas Carrying Pipelines.” Material Performance, Vol. 28, No. 2, 1989.

Lugg, M. C., A. M. Lewis, D. H. Michael, and R. Collins. “The Non-Coating ACFM Technique. Electromagnetic Inspection IOP Short Meetings—12,” Institute of Physics, UK. 1988.

McMaster, R. C., ed. Nondestructive Testing Handbook, 1st ed. Columbus, OH: American Society for Nondestructive Testing. 1959.

Moore, D. G. and P. O. Moore. Nondestructive Testing Handbook, 3rd ed. Vol. 8, Magnetic Testing. Columbus, OH: American Society for Nondestructive Testing. 2008.

15-7

Recommendations for an Effective Program to Control the Degradation of Buried and Underground Piping and Tanks (1016456, Revision 1). EPRI, Palo Alto, CA: 2010. 1021175.

Robers, M. A. and R. Scottini. “Pulsed Eddy Current in Corrosion Detection,” 8th ECNDT Barcelona. 2002.

Röntgen Technische Dienst BV, “Wevelstroom I (Training Manual),” Röntgen Technische Dienst BV, Rotterdam, The Netherlands, 2001.

Scottini, R. and J. Klootwijk. “RTD-INCOTEST, Pulsed Eddy Current (Training Manual),” Röntgen Technische Dienst BV, Rotterdam, The Netherlands, 2001.

Scottini, R. Chevron Symposium on TOL Corrosion, Bangkok, Thailand. 2006.

Scottini, R. “Inspection of Steel Sheet Piling,” ALWC 2005, Liverpool. 2005.

Stanley, R. K., P. O. Moore, and P. McIntire. Nondestructive Testing Handbook, 3rd ed. Vol. 9, Special Nondestructive Testing. Columbus, OH: American Society for Nondestructive Testing. 1995.

Vogel, B., J. Wolters, and F. J. Postema. “Pulsed Eddy Current Measurements on Steel Sheet Pilings,” 9th International Conference on Structural Faults and Repair, Engineering Technics Press, 2001.

15.6 Recommended Reading—Conventional Radiographic Testing

ASNT CP-IRRSP-1A, Industrial Radiography Radiation Safety Personnel. American Society for Nondestructive Testing. 2001.

ASTM E-1030, Test Method for Radiographic Examination of Metallic Casting.

ASTM E-1032, Test Method for Radiographic Examination of Weldments.

ASTM E-1742, Practice for Radiographic Examination.

ASTM E-746, Practice for Determining Relative Image Quality Response of Industrial Radiographic Imaging Systems.

ASTM E-94, Guide for Radiographic Examination.

Bossi, R. H., F. A. Iddings, C. G. Wheeler, and P. O. Moore. Nondestructive Testing Handbook, Radiographic Testing. 3rd ed., Vol. 4. American Society for Nondestructive Testing, Columbus, OH: 2002.

Bubenik, T. A., D. R. Stephens, B. N. Leis, and R. J. Eiber. Stress Corrosion Cracks in Pipelines: Characteristics and Detection Considerations. Battelle, Report No. GRI-95/2007, The Gas Research Institute. 1995.

EPRI. Materials Reliability Program: Primary System Piping Butt Weld Inspection and Evaluation Guideline (MRP-139, Revision 1). Palo Alto, CA: 2008. 1015009.

EPRI. Nondestructive Evaluation: Evaluation of Filmless Radiography. Palo Alto, CA: 2008: 1016656.

15-8

EPRI. Nondestructive Evaluation: Evaluation of Filmless Radiography. Palo Alto, CA: 2010. 1021154.

EPRI. Nondestructive Evaluation: Evaluation of Filmless Radiography. Palo Alto, CA: 2011. 1022933.

EPRI. Nondestructive Evaluation: Status of Digital Radiography. Palo Alto, CA: 2007. 1015141.

McMaster, R. C., ed. Nondestructive Testing Handbook, 1st ed. Columbus, OH: American Society for Nondestructive Testing. 1959.

Quinn, R. A. and C. C. Sigl. Radiography in Modern Industry. 4th ed. Eastman Kodak Company 1980.

Stanley, R. K., P. O. Moore, and P. McIntire. Nondestructive Testing Handbook, 3rd ed. Vol. 9, Special Nondestructive Testing. Columbus, OH: American Society for Nondestructive Testing. 1995.

15.7 Recommended Reading—Digital Radiographic Testing

ASME Section V, Article II, Digital Imaging.

ASNT CP-IRRSP-1A, Industrial Radiography Radiation Safety Personnel. American Society for Nondestructive Testing, OH: 2001.

ASTM E-1030, Test Method for Radiographic Examination of Metallic Casting.

ASTM E-1032, Test Method for Radiographic Examination of Weldments.

ASTM E-1475, Guide for Data Fields for Computerized Transfer of Digital Radiological Examination Data.

ASTM E-1742, Practice for Radiographic Examination.

ASTM E-2597, Practice for Manufacturing Characterization of Digital Detector Arrays.

ASTM E-746, Practice for Determining Relative Image Quality Response of Industrial Radiographic Imaging Systems.

ASTM E-94, Guide for Radiographic Examination.

Barber, G. “Digital Imaging Techniques/Solutions.” 10th APCNDT. 2001.

Blakeley, B. “Digital Radiography—is it for you?” BINDT Insight, Vol. 46, No. 7, 2004.

Bossi, R. H., F. A. Iddings, C. G. Wheeler, and P. O. Moore. Nondestructive Testing Handbook, Radiographic Testing. 3rd ed., Vol. 4. American Society for Nondestructive Testing, Columbus, OH: 2002.

Bubenik, T. A., D. R. Stephens, B. N. Leis, and R. J. Eiber. Stress Corrosion Cracks in Pipelines: Characteristics and Detection Considerations. Battelle, Report No. GRI-95/2007, The Gas Research Institute. 1995.

15-9

EN 14784-1 and -2, Nondestructive Testing—Industrial Computed Radiography with Storage Phosphor Imaging Plates—Parts 1 and 2.

Giakos, G. C. et al. “Detective Quantum Efficiency of CZT Semiconductor Detectors for Digital Radiography.” Instrumentation and Measurement, IEEE Transactions, Vol. 53, No. 6, 2004.

Ingold, B. J. “Radiography Testing,” The AMMTIAC Quarterly, Vol. 2, No. 2.

McMaster, R. C., ed. Nondestructive Testing Handbook, 1st ed. Columbus, OH: American Society for Nondestructive Testing. 1959.

Mohr, G. A. and C. Beuno. “A Si Flat Panel Detector in Industrial Digital Radiography.” BINDT Insight, Vol. 44, No. 10, 2002.

Morro, F. A. “Computed Radiography: The Future of Radiographic Inspection.” 15th WCNDT. 2000.

Pardikar, R. J. “Real Time Radioscopy and Digital Image Processing Techniques for On Line Inspection of Welds in Boiler Tubes.” Journal of Nondestructive Evaluation, Vol. 20, No. 3, 2000.

Quinn, R. A. and C. C. Sigl. Radiography in Modern Industry. 4th ed. Eastman Kodak Company, 1980.

Ravindran, V. R. “Digital Radiography using Flat Panel Detector the Nondestructive Evaluation of Space Vehicle Components.” Journal of Nondestructive Testing and Evaluation, Vol. 4, No. 2, 2005.

Stanley, R. K., Moore, P. O., and McIntire, P. Nondestructive Testing Handbook, 3rd ed. Vol. 9, Special Nondestructive Testing. Columbus, OH: American Society for Nondestructive Testing. 1995.

Vaidya, P. R. and R. Narayanan. “Performance of Evaluation of the Imaging Plates for Industrial Radiography Applications.” Journal of Nondestructive Evaluation, Vol. 20, No. 3, 2000.

Vaidya, P. R. “Flat Panel Detectors in Industrial Radiography,” International Workshop on Imaging NDE-2007, India, 2007.

15.8 Recommended Reading—Visual Examination

A Guideline Framework for Integrity Assessment of Offshore Pipelines, DNV Technical Report No. 44811520, Rev 2, 2006.

Allgaier, M. W., S. Ness, P. McIntire, and P. O. Moore. Nondestructive Testing Handbook, 3rd ed. Vol. 8, Visual and Optical Testing. Columbus, OH: American Society for Nondestructive Testing. 1993.

ASM Handbook, 9th ed. Vol. 17, Nondestructive Evaluation and Quality Control. Materials Park, OH: ASM International. 2000.

Cheu, F. U. “Automatic Crack Detection with Computer Vision and Pattern Recognition of Magnetic Particle Indications.” Materials Evaluation, Vol. 42, No. 12, 1984.

15-10

Cope, A. D. and A. Rose. “X-Ray Noise Observation Using a Photoconductive Pickup Tube.” Journal of Applied Physics, Vol. 25, 1954.

Flory, L. E. “The Television Microscope.” Cold Spring Harbor Symposia for Quantitative Biology, Vol. 16. Cold Spring Harbor, NY: 1951.

Jackson, C. N., N. Charles, C. N. Sherlock, and P. O. Moore. Nondestructive Testing Handbook, 3rd ed. Vol. 1, Leak Testing. Columbus, OH: American Society for Nondestructive Testing. 1997.

Kaufman, J. E., and J. F. Christensen. IES Lighting Handbook. 5th ed. New York: Illuminating Engineering Society. 1972.

McMaster, R. C., ed. Nondestructive Testing Handbook, 1st ed. Columbus, OH: American Society for Nondestructive Testing. 1959.

Moore, D. G. and P. O. Moore. Nondestructive Testing Handbook, 3rd ed. Vol. 8, Magnetic Testing. Columbus, OH: American Society for Nondestructive Testing. 2008.

Nondestructive Testing Methods. TO33B-1-1 (NAVAIR 01-1A-16) TM43-0103. Washington DC: Department of Defense United States Air Force, June 1984.

Service Water Piping Guideline. EPRI, Palo Alto, CA: 2005.1010059.

Stanley, R. K., P. O. Moore, and P. McIntire. Nondestructive Testing Handbook, 3rd ed. Vol. 9, Special Nondestructive Testing. Columbus, OH: American Society for Nondestructive Testing. 1995.

Tracy, N. and P. O. Moore. Nondestructive Testing Handbook, 3rd ed. Vol. 2, Liquid Penetrant Tests. Columbus, OH: American Society for Nondestructive Testing. 1999.

Weimer, P. K., S. V. Forgue, and R. R. Goodrich. “The Vidicon Photoconductive Camera Tube.” Electronics, Vol. 23, No. 5. 1950.

Wenk, S. A. and R. C. McMaster. Choosing NDT: Applications, Costs and Benefits of Nondestructive Testing in Your Quality Assurance Program. Columbus, OH: American Society for Nondestructive Testing. 1987.

Workman, G. L., D. Kishoni, and P. O. Moore. Nondestructive Testing Handbook, 3rd ed. Vol. 7, Ultrasonic Testing. Columbus, OH: American Society for Nondestructive Testing 2007.

15.9 Recommended Reading—Laser Profilometry

A Guideline Framework for Integrity Assessment of Offshore Pipelines, DNV Technical Report No. 44811520, Rev 2, 2006.

Allgaier, M. W., S. Ness, P. McIntire, and P. O. Moore. Nondestructive Testing Handbook, 3rd ed. Vol. 8, Visual and Optical Testing. Columbus, OH: American Society for Nondestructive Testing 1993.

ASM Handbook, 9th ed. Vol. 17, Nondestructive Evaluation and Quality Control. Material Park, OH: ASM International 2000.

15-11

Bennet, J. M. and L. Mattsson. Introduction to Surface Roughness and Scattering. Optical Society of America, Washington, D.C.

Cheu, F. U. “Automatic Crack Detection with Computer Vision and Pattern Recognition of Magnetic Particle Indications.” Materials Evaluation, Vol. 42, No. 12, 1984.

Cope, A. D. and A. Rose. “X-Ray Noise Observation Using a Photoconductive Pickup Tube.” Journal of Applied Physics, Vol. 25, 1954.

Jackson, C. N., N. Charles, C. N. Sherlock, and P. O. Moore. Nondestructive Testing Handbook, 3rd ed. Vol. 1, Leak Testing. Columbus, OH: American Society for Nondestructive Testing. 1997.

Kaufman, J. E., and J. F. Christensen. IES Lighting Handbook. 5th ed. New York: Illuminating Engineering Society. 1972.

McMaster, R. C., ed. Nondestructive Testing Handbook, 1st ed. Columbus, OH: American Society for Nondestructive Testing. 1959.

Moore, D. G. and P. O. Moore. Nondestructive Testing Handbook, 3rd ed. Vol. 8, Magnetic Testing. Columbus, OH: American Society for Nondestructive Testing. 2008.

Owen, R. B. and M. I. Awcock. “One and Two Dimensional Position Sensitive Photodetectors.” IEEE Transactions on Electron Devices. Vol. ED-21, No. 3, 1968.

Program on Technology Innovation: 3D Profilometry Acquisition Scanning System (3D PASS). EPRI, Palo Alto, CA: 2010. 1020637.

Stanley, R. K., P. O. Moore, and P. McIntire. Nondestructive Testing Handbook, 3rd ed. Vol. 9, Special Nondestructive Testing. Columbus, OH: American Society for Nondestructive Testing. 1995.

Stout, K. J. and L. Blunt. Three Dimensional Surface Topography, 2nd ed. Penton Press. 2000.

Weimer, P. K., S. V. Forgue, and R. R. Goodrich. “The Vidicon Photoconductive Camera Tube.” Electronics, Vol. 23, No. 5, 1950.

15.10 Recommended Reading—Magnetic Particle Testing

ASM Handbook, 9th edition: Vol. 17, Nondestructive Evaluation and Quality Control. Material Park, OH: ASM International. 2000.

ASME Boiler and Pressure Vessel Code, Section V, “Nondestructive Examination,” Article 7, “Magnetic Particle Examination.” New York: ASME.

ASTM E-125. Standard Reference Photographs for Magnetic Particle Indications on Ferrous Castings.

ASTM E-1444, Practice for Magnetic Particle Examination.

ASTM E-269, Definition of Terms Relating to Magnetic Particle Inspection.

ASTM E-709, Guide for Magnetic Particle Examination.

15-12

Blitz, J. Magnetic Methods. Electrical and Magnetic Methods of Nondestructive Testing. New York: Adam Hilger. 1991.

ISO 17638, Nondestructive Testing of Welds—Magnetic Particle Testing.

ISO 17638, Nondestructive Testing of Welds—Magnetic Particle Testing Welds— Acceptance Levels.

ISO 3059, Nondestructive Testing—Penetrant Testing and Magnetic Particle Testing— Viewing Conditions.

ISO 9934-1, Nondestructive Testing—Magnetic Particle Testing—Part 1: General Principles.

ISO 9934-2, Nondestructive Testing—Magnetic Particle Testing—Part 2: Detection Media.

ISO 9934-3, Nondestructive Testing—Magnetic Particle Testing—Part 3: Equipment.

Jiles, D. Introduction to Magnetism and Magnetic Materials. London, UK: Chapman and Hall 1991.

McMaster, R. C., ed. Nondestructive Testing Handbook, 1st ed. Columbus, OH: American Society for Nondestructive Testing. 1959.

Moore, D. G., and P. O. Moore. Nondestructive Testing Handbook, 3rd ed. Vol. 8, Magnetic Testing. Columbus, OH: American Society for Nondestructive Testing. 2008.

Stanley, R. K., P. O. Moore, and P. McIntire. Nondestructive Testing Handbook, 3rd ed. Vol. 9, Special Nondestructive Testing. Columbus, OH: American Society for Nondestructive Testing. 1995.

15.11 Recommended Reading—ACFM

Bubenik, T. A., D. R. Stephens, B. N. Leis, B. N., and R. J. Eiber. Stress Corrosion Cracks in Pipelines: Characteristics and Detection Considerations. Battelle, Report No. GRI-95/2007, The Gas Research Institute. 1995.

Carroll, L. B. and C. D. Monaghan. “Detection and Classification of Crack Colonies Using ACFM Technology—Phase I.” NDE Performance Demonstration, Planning and Research. PVP, Vol. 353, NDE, Vol. 16, New York, ASME International.

Collins, R., D. H. Michael, and K. B. Ranger. “The AC Field Around a Plane Semi Elliptical Crack in a Metal Plate,” in Proceedings of the 13th Symposium on Nondestructive Evaluation, Nondestructive Testing Information Center, San Antonio, Texas. 1981.

Lugg, M. C., A. M. Lewis, D. H. Michael, and R. Collins. “The Non-Coating ACFM Technique.” Electromagnetic Inspection IOP Short Meetings—12, Institute of Physics, UK. 1988.

McKurdy, D. M. and A. M. Lewis. “ACFM Above a Hemispherical Pit in an Aluminum Block.” Review of Progress in Quantitative Nondestructive Evaluation, Vol. 12A, 1993.

15-13

McMaster, R. C., ed. Nondestructive Testing Handbook, 1st ed. Columbus, OH: American Society for Nondestructive Testing. 1959.

Moore, D. G., and P. O. Moore. Nondestructive Testing Handbook, 3rd ed. Vol. 8, Magnetic Testing. Columbus, OH: American Society for Nondestructive Testing. 2008.

Raine, G. A. and C. Laenan. “Additional Applications with the ACFM Technique.” Insight, Vol. 40, No. 12, Northampton, UK. 1988.

Stanley, R. K., P. O. Moore, and P. McIntire. Nondestructive Testing Handbook, 3rd ed. Vol. 9, Special Nondestructive Testing. Columbus, OH: American Society for Nondestructive Testing. 1995.

15.12 Recommended Reading—ILI Tools

NUREG/CR-6876, BNL-NUREG-74000-2005. Risk-Informed Assessment of Degraded Piping Systems in Nuclear Power Plants. Brookhaven National Laboratory, Upton, NY. 2005.

Shie, T. Unpiggable Pipelines, Phase 1, Literature Review and Definition. PRCI Report Project No. 82290831, 2009.

Training for Buried Pipe Program Owners, Session 23: In-Line Inspection. EPRI, Palo Alto, CA: 2010. BP101.

15.13 Recommended Reading—RFT

Atherton, D. L. and S. Sullivan. “Electromagnetic Technique for Pressure Tubes.” Materials Evaluation, Vol. 44. 1986.

Atherton, D. L. “Effects of Line Pressure on the Performance of Magnetic Inspection Tools.” Oil & Gas Journal, 1986.

Atherton, D. L. et al. “Stress Induced Magnetization Changes of Steel Pipes—Laboratory Tests.” IEEE Transactions on Magnetics, Vol. MAG-19, No. 4, 1983.

Bubenik, T. A., D. R. Stephens, B. N. Leis, and R. J. Eiber. Stress Corrosion Cracks in Pipelines: Characteristics and Detection Considerations. Battelle, Report No. GRI-95/2007, The Gas Research Institute. 1995.

Bubenik, T.A. et al. In-Line Inspection Technologies for Mechanical Damage and SCC in Pipelines—Final Report. Report No. DTRS56-96-C-0010, U.S. Department of Transportation. 2000.

Fisher, J. L., S. T. Chain, and R. E. Beissner. “Remote Field Eddy Current Model,” in Proceedings of the 16th Symposium on Nondestructive Evaluation. 1987.

Kilgore, R. J. and S. Ramchandran. “NDT Solution: Remote Field Eddy Current Testing of Small Diameter Carbon Steel Tubes.” Material Evaluation, Vol. 47. 1989.

Lord, W., Y. S. Sun, and S. S. Udpa. “Physics of the Remote Field Eddy Current Effect,” Reviews of Progress in Quantitative NDE. 1987.

15-14

McMaster, R. C., ed. Nondestructive Testing Handbook, 1st ed. Columbus, OH: American Society for Nondestructive Testing. 1959.

Moore, D. G. and P. O. Moore. Nondestructive Testing Handbook, 3rd ed. Vol. 8, Magnetic Testing. Columbus, OH: American Society for Nondestructive Testing 2008.

Mergelas, B., J. Spanner, and R. Fongemie, “New NDE Technique for Inspection of Prestressed Concrete Pipe,” presented at the EPRI Piping and Bolting Conference, San Antonio, 1999.

Nestleroth, J. B. and A. E. Crouch. Variation of Magnetic Properties in Pipeline Steels. Report No. DTRS56-96-C-0010, Subtask 1.1, U.S. Department of Transportation. 1998.

Nestleroth, J. B. and T. A. Bubenik. Magnetic Flux Leakage Technology for Natural Gas Pipeline Inspection. Battelle, Report No. GRI-00/01800, The Gas Research Institute. 1999.

Schmidt, T. R. “The Remote Field Eddy Current Inspection Techniques.” Materials Evaluation, Vol. 42, 1984.

Stanley, R. K., P. O. Moore, and P. McIntire. Nondestructive Testing Handbook, 3rd ed. Vol. 9, Special Nondestructive Testing. Columbus, OH: American Society for Nondestructive Testing. 1995.

15.14 Recommended Reading—Liquid Penetrant Examination

ASM Handbook, 9th Edition: Vol. 17, Nondestructive Evaluation and Quality Control. Material Park, OH: ASM International. 2000.

ASTM E-1208, Test Method for Fluorescent Liquid Penetrant Examination Using the Lipophilic Post-Emulsification Process.

ASTM E-1209, Test Method for Fluorescent Liquid Penetrant Examination Using the Water-Washable Process.

ASTM E-1210, Test Method for Fluorescent Liquid Penetrant Examination Using the Hydrophilic Post-Emulsification Process.

ASTM E-1219, Test Method for Fluorescent Liquid Penetrant Examination Using the Solvent-Removable Process.

ASTM E-1220, Test Method for Visible Penetrant Examination Using Solvent-Removable Process.

ASTM E-1417, Practice for Liquid Penetrant Testing.

ASTM E-1418, Test Method for Visible Penetrant Examination Using the Water-Washable Process.

ASTM E-165, Practice for Liquid Penetrant Examination for General Industry.

ASTM E-2297, Guide for Use of UV-A and Visible Light Sources and Meters used in the Liquid Penetrant and Magnetic Particle Methods.

ASTM E-433, Reference Photographs for Liquid Penetrant Inspection.

15-15

Jackson, C. N., N. Charles, C. N. Sherlock, and P. O. Moore. Nondestructive Testing Handbook, 3rd ed. Vol. 1, Leak Testing. Columbus, OH: American Society for Nondestructive Testing. 1997.

McMaster, R. C., ed. Nondestructive Testing Handbook, 1st ed. Columbus, OH: American Society for Nondestructive Testing. 1959.

Nondestructive Testing Methods. TO33B-1-1 (NAVAIR 01-1A-16) TM43-0103. Washington DC: Department of Defense, United States Air Force, June 1984.

Tracy, N. and P. O. Moore. Nondestructive Testing Handbook, 3rd ed. Vol. 2, Liquid Penetrant Tests. Columbus, OH: American Society for Nondestructive Testing. 1999.

Wenk, S. A. and R. C. McMaster. Choosing NDT: Applications, Costs and Benefits of Nondestructive Testing in Your Quality Assurance Program. Columbus, OH: American Society for Nondestructive Testing. 1987.

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