AC 2009-488: NONDESTRUCTIVE TESTING (NDT) COURSE RENOVATION FORTHE POWER ENGINEERING TECHNOLOGY PROGRAM

Alex Fang, Texas A&M UniversityDr. Alex Fang is an Assistant Professor in the Department of Engineering Technology andIndustrial Distribution at Texas A&M University. He received the BS degree in aerospaceengineering (1976) from Tamkang University in Taiwan, the MS degree in aerospace engineering(1987) and the Ph.D. degree in mechanical engineering (1996) from Texas A&M University. Hejoined the Manufacturing and Mechanical Engineering Technology faculty at Texas A&M in2007. He teaches courses in the area of nondestructive testing (NDT), nonmetallic materials, andstrength of materials. Dr Fang’s research interests are in the areas of ceramic grinding, lapping,and polishing, NDT, acoustics, genetic algorithm, and multi-objective optimization.

Wei Zhan, Texas A&M UniversityDr. Wei Zhan is an Assistant Professor of Electronics Engineering Technology at Texas A&MUniversity. Dr. Zhan earned his D.Sc. in Systems Science from Washington University in 1991.From 1991 to 1995 he worked at University of California, San Diego and Wayne StateUniversity. From 1995 to 2006, he worked in the automotive industry as a system engineer. In2006 he joined the Electronics Engineering Technology faculty at Texas A&M. His researchactivities include control system theory and applications to industry, system engineering, robustdesign, modeling, simulation, quality control, and optimization.

© American Society for Engineering Education, 2009

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Nondestructive Testing (NDT) Course Renovation for the Power

Engineering Technology Program

Abstract

Nuclear power has now been recognized as one of the best alternative energy sources due to its zero carbon footage and relative low cost per kilo-watt hour compared to other alternatives. In Texas alone, 6 new nuclear power plants are expected to be built in the near future, which will require approximately two thousand qualified personnel to operate and maintain. In response to this urgent need, the Department of Engineering Technology & Industrial Distribution (ETID) at Texas A&M University has started a 4-year Power Engineering Technology (PET) degree program in the Fall Semester of 2008 which is dedicated for the nuclear power industry. One of the junior courses in the curriculum is Inspection Methods consisting mainly of the nondestructive testing methods which include liquid penetrant, magnetic particle, ultrasonic, eddy current, radiography, and others. NDT has long been widely utilized for various flaw detections (crack, void, corrosion, and delamination, etc.) during manufacturing as well as maintenance by many industries to ensure the quality or safety of a component or system. It is an indispensible group of technologies mandated by the regulatory agency for the safe and reliable operation of nuclear power plants. A separate program within the ETID department, the Manufacturing and Mechanical Engineering Technology (MMET) program, has already offered an Inspection Methods course to introduce NDT in general but not specifically tailored for the nuclear power industry. To have better use of resources, a course renovation is under way which aims to address the needs for both the MMET and PET programs. This course renovation is based on the information collected through the interactions with the NDT service providers and nuclear power plant operators. In this paper, the course development experiences in the two key areas, i.e., the state-of-the-art NDT technologies - phased array ultrasound (PA) and computed radiography (CR), will be presented. Discussions will also be given regarding the roles of PA and CR in the current and future NDT inspection of nuclear power plants. Introduction

Through the recognition of global warming by the world community, the formation of the Kyoto Protocol in 1997 and effective date of February 2005 point to the importance and necessity of having energy sources with low carbon emission. With the support for expansion by the current US National Energy Policy1, nuclear energy is arguably the best alternative energy source due to its high capacity and the lower production cost per kilowatt compared to other alternative energy sources such as wind power and solar power. Twenty-two applications have been submitted to the NRC for new reactors thus far and 11 more are expected by the end of 20092. The urgent issue facing the building boom for nuclear power plants is the training of a new workforce for these new plants as well as the replacement of aging workers in existing plants. In respond to these needs, the Department of Engineering Technology and Industrial Distribution (ETID) at Texas A&M University has started a new Power Engineering Technology (PET) program in the

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Fall of 2008. One of the courses in the PET curriculum is ENTC 402 Inspection Methods2, which includes liquid penetrant (PT), magnetic particle (MT), ultrasound (UT), radiography (RT), and eddy current (ET) technologies. This is an existing course designed to give a general introduction of commonly used industrial nondestructive testing (NDT) methods to our students in another ABET credited MMET program. This course has been taught without targeting any specific industry. The goal of the MMET program is to train our students for industries that need engineers with knowledge in the mechanical and/or manufacturing disciplines. The nuclear power industry has never been one of the intended targets; thus, the course contents of ENTC 402 mention nothing related to the nuclear power industry. To accommodate the students from the PET program, the course has to be renovated to add things relevant to the nuclear power industry but also useful to the students in the MMET program. In the meantime, the IAC (Industrial Advisory Committee) of the MMET program has been recommending shifting the focus of the NDT class toward the latest technologies - namely phased array ultrasonic testing (PA UT) and digital radiography (i.e., computed radiography (CR)) which have been gaining enormous popularity from the petrochemical and nuclear power industries recently. Since the technology trend was so obvious based on the information collected from various sources, a decision was made to renovate the ENTC 402 class by adding PA UT and CR equipment to our lab, having their theories and principles taught in class, and getting input from the NDT experts working in the nuclear power industry. This paper will give a concise presentation of the two technologies and discuss the differences and technological advantages of PA UT and CR compared to their conventional counterparts (single-element UT and film based RT). A very critical NDT inspection, which uses the phased array technology, related to the structural integrity of the nuclear reactor head will be presented in this paper and used in the class lecture as well. Information regarding hand-held phased array ultrasonic flaw detectors and opinions from industrial leaders about phased array technology are also presented in this paper. The NDT practices and procedures that are unique to the nuclear power industry will also be discussed. Phased Array Ultrasonic Technology

The conventional ultrasonic testing method is based on the pulse-echo configuration as shown in Figure 1 where a piezoelectric transducer sends a high frequency sound wave typically between 0.5 MHz and 15 MHz to the test object. The echoes from the backside of the test object and the flaw, if any, will be displayed on the screen of the instrument in terms of waveform signals called A-scan as displayed in Figure 1. The horizontal axis of the screen display indicates the time of flight or the travel distance of the sound wave which allows the operator to determine the location of the flaw from the incident point of the sound beam. The vertical axis of the screen display indicates the amplitude or strength of the signal which can be used for the sizing of the flaw. This conventional UT method has been used for more than 50 years without major changes until the battery-powered portable phased array UT equipment became available in June 20024 which started a rapid spread of acceptance of the phased array technology for flaw detection in recent years. In fact, the phased array ultrasonic technology has been used in cardiac and obstetrics applications since the late 70s and early 80s, respectively, while its use in NDT applications didn’t

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start until mid-19905,6. The late adoption of the phased array technology in NDT is partly due to the fact that the sound speed in metals is typically three times faster than in water or human tissues, requiring faster electronic circuits for this technology. The early phased array ultrasonic NDT equipment was very expensive, non-portable, and designed only for specific applications, and was thus little known to the NDT professions. The battery-powered portable phased array UT equipment relies heavily on the computing power of today’s advanced computer hardware and software technologies.

Figure 1. Illustration of Conventional Ultrasonic Testing3

Phased array ultrasonic equipment uses a transducer which comprises an array of piezoelectric elements ranging mostly from 16 to 128 compared to the single-element transducer used for the conventional ultrasonic flaw detector. Each of these elements is individually controlled and pulsed by the instrument. The most simple and common phased array transducers are linear array transducers composed of a series of linearly arranged and tightly spaced elements as shown in Figure 2, although probes of various shapes and configurations such as circular and matrix (2-dimensional) arrays are also available.

Figure 2. Linear Flexible Phased Array Transducer (bent in concave view)7

Linear Array of

Piezoelectric Elements

A-Scan

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Figure 3. Principle of Phased Array; Delay Laws Calculated to Focus at a Given Depth and

Angle8 The same fundamental principle, acoustic interference, applies to both the conventional and phased array ultrasonic transducers for the forming of their sound beams. To apply wave interference to a conventional transducer with a single element, the element can be viewed as composing of a multitude of point sound sources according to Huygens’ Principle. However, these imaginary point sources are all pulsed at the same time which produces a slightly divergent beam consisting of near and far fields. On the other hand, phased array transducers are composed of multiple physical elements which can be pulsed individually and follow a given timing pattern (called focal or delay law) for part or all of the elements at any moment to form a beam with a particular direction and focusing distance. Figure 3 shows how a resultant wave front is formed by the interference of waves from a linear array transducer for a given focal law and it also shows the ability to focus and steer by guiding the beam to a specific focusing depth and angle. Figure 4 provides more detailed illustrations for the three types of operations unique to the phased array transducers. Figure 4(a) shows how the electronic scanning is carried out. By alternately or incrementally firing a subset of the elements in the array, the beam can be electronically translated. This electronic scanning provides much faster inspection speed without the need to move the transducer and can also be used to produce a top-view (C-scan) image of a large area by moving a transducer doing raster scanning. Figure 4(b) depicts the focusing operation. The focal law attached to each diagram tells the pulsing time delay for each element. It can be seen that different focusing depth corresponds to a different focal law. Figure 4(c) illustrates the steering operation which allows a single transducer to scan multiple angles compared to the single angle solution for the conventional ultrasonic technology. More importantly, the capability of steering the beam for reaching limited-access regions within a component is extremely valuable for the inspection of parts with complex geometry such as the dovetail root of a steam turbine blade. As with focusing, different steering angles correspond to different focal laws as well. These three operations can be utilized individually or combined in various fashions for different applications. For example, a typical sectorial scan (S-scan) can be produced by performing a steering operation alone as shown in Figure 5. In this case, a plastic

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angle wedge is also used to increase (or rotate) the steering angle by adding an angle of refraction to cover the region of interest, which could not be reached otherwise due to limitations on beam steering angle.

Figure 4. Three Unique Operations of Phased Array Technology

(a) Electronic Scanning, (b) Electronic Focusing, (c) Electronic Steering9

Focal or Delay Laws

Sound Beams

(b)

(c)

Linear Array of Piezoelectric Elements

(a)

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The real time 2-dimensional S-scan image in Figure 5 is certainly much more intuitive than the 1-dimensional A-scan signals (displayed to the left of the S-scan image), which makes the interpretation of test results much easier and more reliable. Notice that the A-scan signals correspond only to one specific beam angle - the blue line marked on the S-scan image.

Figure 5. Sectorial Scan Image of a specimen with 3 side-drilled holes

A Critical Application of Phased Array Ultrasonic Technology in Nuclear Power Plants (an

example developed for class lecture)

The most critical component of a nuclear power plant is the nuclear reactor in which a tremendous amount of heat is generated through a controlled fission chain reaction of highly enriched nuclear fuel (uranium dioxide). Figure 6 shows the most common type of power producing nuclear reactor, a pressurized water reactor (PWR), which is normally housed in a thick concrete containment structure. The high heat carried by the pressurized water is transferred through a heat exchanger to a steam generator to drive the turbine electric power generator. Figure 7 gives a close-up view of the upper head of the reactor pressure vessel along with a detailed view of a penetration nozzle welded on the head. The 7” thick exterior wall of the reactor pressure vessel is made of low alloy steel lined with 3/8” type 308 stainless steel interior cladding. The upper head has through-wall penetration nozzles for control rod drive mechanisms and instrumentation systems made from nickel-based alloy (e.g., alloy 600 or Inconel) and related weld metals (e.g., alloy 182). In early 2002, the Davis-Besse Nuclear Power Station, located in Oak Harbor, Ohio, discovered a large cavity at one nozzle during a refueling outage

A-Scan

Sectorial

Scan

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inspection. The steel portion of the wall thickness was totally lost due to corrosion which was attributed to the leakage of boric acid contained in the pressurized water through small cracks on the J-groove weld. The boric acid contained in the pressurized water is used to regulate the rate of fissions taking place in the reactor by the absorption of fission causing neutrons. This incidence prompted the development of a new NDT inspection procedure utilizing the phase array technology for the inspection of surrounding areas at and around the j-groove weld of the penetration nozzles. This inspection is conducted from the outside of the reactor head (base metal side) and is a typical example of a dissimilar metal weld inspection. That means to detect cracks on the nickel-based weld or stainless steel cladding the sound beam has to be able to travel through the base material (steel) and reach the surfaces of the cladding and weld, which could not be done with conventional ultrasonic technology.

Figure 6. Typical Pressurized Water Reactor10

PWR Nuclear Reactor

Reactor Vessel

Upper Head

(detailed view

in Fig. 7)

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Figure 7. Close-up View of Reactor Pressure Vessel Upper Head10

Figure 8. Reference Standard Used for the Calibration of Phased Array Flaw Detector

The inspection of dissimilar metal welds involving austenitic (stainless steel) or nickel-based metals has long presented big challenges for ultrasonic NDT due to the large, attenuating, and skewing grains. The phased array technology is the only proven ultrasonic technology for this type of inspection11. The South Texas Project (STP) nuclear power plant developed the inspection procedure with a Harfang X-32 phased array flaw detector and was approved by the Nuclear Regulatory Commission (NRC) in 200312 about a year after the David-Besse incidence. One of the key components for the development of this inspection procedure is the fabrication of a reference standard (mock-up) for the calibration of the instrument before any inspection. For the consistency and quality of inspections, a reference standard with one or several artificially induced flaws of known size is always required for any ultrasonic inspection and has to be made

Penetration

Nozzle

Base Metal (Steel) Stainless Steel

Cladding Penetration Nozzle (Alloy 600)

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with the same materials and geometry as the part to be inspected. Figure 8 shows the reference standard used by the STP nuclear power plant. Equipment Manufacturers of Phased Array Ultrasonic Flaw Detector

Table 1 lists the major equipment manufacturers of hand-held battery-powered portable phased array ultrasonic NDT flaw detectors. Figure 9 shows their designs. In the US, Olympus and GE Inspection Technologies are the main players in this market. They both provide 50% academic discounts to educational institutions for their phased array ultrasonic systems.

Table 1. Equipment Manufacturers of Portable Phased Array Ultrasonic Flaw Detector

Manufacturer Model Price

Range

Website

GE Inspection Technologies

Phasor XS, Phasor 16/16 Weld

$20K-30K http://www.geinspectiontechnologies.com/

Olympus Inspection & Maintenance

Systems

Epoch 1000, OmniScan PA, OmniScan M,

TomoScan Focus LT

$20K-50K http://www.olympus-ims.com/en/ndt-products/

Russell NDE Systems, Inc

Harfang X-32 http://www.russelltech.com/UT/HarfangX32.html

AGR Field Operations

TD Handy-Scan, TD Focus-Scan

http://www.technologydesign.co.uk/d/index.php?pageId=0

Figure 9. Major Hand-Held Phased Array Ultrasonic Flaw Detectors

GE Inspection Technologies Phasor XS

AGR Field Operations TD Handy-Scan Olympus OmniScan

Russell NDE Systems Inc Harfang X-32

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Comments and Opinions Made by Industrial Leaders Regarding Phased Array Technology

The following are the comments made by leaders in the NDT equipment industry, end users, and owners of NDT service providers: Michael Moles13 (Industry Manager for Petrochemical, Welding, and In-service inspection at Olympus NDT) says "Yes and no, just like TV did (and did not) replace radio. Yes, it will replace conventional ultrasonics for some applications much of the time, for example weld inspections and maybe corrosion mapping." He also notes that, "Phased arrays will also move into areas that were not addressed (well) before. However, there will always be some areas that conventional UT will be retained, where convenience, cost or simplicity are key."

Francois Mainguy13 (Vice President -Technology, and Founder of Harfang Microtechniques) says, "I think that in five years from now, at least 50 percent of flaw detection will be done by phased arrays because of obvious productivity and reliability benefits for cheap investment." He further adds that, "Thickness gauges and low-cost mono-element digital flaw detectors will keep the other 50 percent and they will be used for very simple applications and the choice of the technology really depends on the application."

Dave Jankowski13 (General Manager-Ultrasonic and Eddy Current Products at GE Inspection Technologies) says that, "Phased array technology is slowly gaining acceptance; companies have pinpointed specific applications in which phased array imaging would benefit the inspection." He is of the opinion that over the next ten years, phased array imaging will probably displace 80 percent of conventional ultrasonic flaw inspections. Dave also notes that, "you need to go application by application and phased array imaging is more suitable especially in applications where you have to inspect from multiple locations and with multiple beam angles covering large volumes". He further concludes, "Of course it cannot replace conventional ultrasonics entirely, but phased array imaging definitely complements some of the traditional ultrasonics applications."

The cofounders of Advanced Inspection Technologies (AIT), Michael Beard and Jim Halley, who are also members of Industrial Advisory Committee for the MMET program of the ETID Department have been strong advocates for phased array technology and computed radiography. They envision the industrial trend and advantages of this new technology based on their more than 40 years of combined experience in the NDT of nuclear and petrochemical industries. As a matter of fact, AIT has become a NDT service provider with their ultrasonic inspection business based totally on phased array technology.

Computed Radiography (CR) Technology

In a nut shell, computed radiography (CR) is very much the same as conventional film-based radiography with the exception that the silver halide emulsion coating on the polyester film substrate is replaced with a layer of photostimulable phosphor material, a mixture of three different barium fluorohalides doped with europium as an activator14: BaFI:Eu2+, BaFCl:Eu2+, and BaFBr:Eu2+. This new type of radiation sensitive material on a thin plastic substrate used for CR is called a phosphor imaging plate or simply imaging plate (IP) which looks and feels just like

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the conventional film. CR has been labeled as filmless radiography since chemical film developing is no longer needed. All radiographic principles and inspection procedures remain the same for both conventional films and phosphor imaging plates. When exposed to X-ray or gamma ray radiation, the europium atoms in the imaging plate are ionized (converted from 2+ to 3+), liberating an electron to the high energy conduction band. The number of liberated electrons is proportional to the amount of radiation absorbed locally. These free electrons will soon settle in nearby crystalline defects (halogen vacancies) where electrons possess energy slightly below the conduction band. These settled electrons constitute the latent image. Unlike conventional film in which a permanent image is produced directly on the film after exposure, the latent image stored in the phosphor material is transient and waiting to be read. The laser beam from a laser scanner is then used to extract the latent image from the phosphor material by stimulating the electrons up to the conduction band again. These born-again free electrons will quickly fall back to their original birth places, the lower energy valence band around the europium ions. This laser stimulus process transforms europium from the 3+ back to the +2 state and the energy drop from the conduction to valence band is released in terms of visible light. The emitted light is collected using a light guide as shown in Figure 10 and is fed to a photomultiplier tube where the light is converted to an electrical signal and digitized into a digital image. The gray scale value of each pixel on the image is determined according to the amount of light emitted from the corresponding dot on the imaging plate. Because the images are captured digitally, images can be easily enhanced with today’s powerful image processing software. An image can be erased by simply exposing the plate to a room-level fluorescent light. Most laser scanners automatically erase the image plate after laser scanning is complete. The imaging plate can then be re-used. A complete CR system consists of imaging plates of various sizes, a laser scanner, a computer workstation with CR system software, and a high resolution monitor as shown in Figure 11.

Figure 10. Illustration of the readout stage involved in generating a computed radiography

image15

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Figure 11. Components of a CR System

Interestingly enough, like phased array ultrasonic technology, CR was also originally developed for medical applications as a replacement for film-based radiography. In 1975, Kodak patented the first scanned storage phosphor system16, whereas Fuji was the first to actually commercialize a complete CR system in 1983. The medical community started the acceptance of these systems in the late 1980s. However, this technology was not developed for industrial NDT applications until around 1997. The STP nuclear power plant in Wadsworth, Texas adopted CR for their NDT application only a couple of years ago17. The first CR system was extremely bulky as shown in Figure 12. Today’s CR laser scanner can be made portable and as small as a printer due to the advancement of computer and electronic technologies.

(a) (b) Figure 12. (a) First Commercial Model of CR System for Medical Applications18

(b) Today’s Portable Laser Scanner (printer size) Advantages of CR Technology over Conventional Film-based Radiography With imaging plates, CR technology has the following advantages over the film-based radiography:

≠ As with conventional film, imaging plates are flexible and can be used wherever film is used; however, imaging plates are reusable for about a thousand exposures if handled properly.

≠ It is an environmentally friendly technology as no chemical processing is ever needed. ≠ CR produces digital images which can be easily duplicated, shared, archived, and

retrieved. ≠ Because imaging plates are far more sensitive to radiation than conventional film, CR

requires up to 20 times less exposure to produce acceptable images19. In many instances, this means an isotope of lower strength and dose can be used as the radiation source along with a shorter exposure time which results in improved productivity and safer working environment for NDT technicians. For example, a much stronger cobalt 60 (1.17-1.33 MeV) can be replaced with iridium 192 (0.3-0.6 MeV) for CR imaging. A relatively

Imaging Plate Laser Scanner Workstation + Software + Monitor

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weak radioactive isotope selenium 75 (0.09-0.4 MeV) was unknown to NDT professions in the past, but it became a favored radiation source recently for many CR NDT applications20,21. For nuclear power plants, using a source of lower strength and dose implies a smaller radiation exclusion zone which will allow other maintenance works to proceed in the area which would otherwise be classified as an exclusion zone if conventional film were used. This may result in big savings if the outage maintenance can be cut shorter as a plant outage costs about one million dollars per day17. It is quite clear that the overall benefits and savings distantly outweigh the higher acquisition cost of a CR system.

≠ Imaging plates have about 10 times the dynamic range (or exposure latitude) of film, which drastically reduces the risk of an overexposure or underexposure problem commonly associated with conventional film. A large dynamic range also means it is possible with CR to produce acceptable images for parts with a large range of varying thicknesses which would otherwise need to shoot multiple images with conventional film. Figure 13(a) compares the dynamic range between the imaging plate and conventional film with images taken from an identical step wedge. Figure 13(b) shows the clear advantage of an image produced with a medium having a wide dynamic range in which all varying thicknesses possess acceptable image densities (darkness). Figure 14 shows a CR image of a high pressure steam pipe used in nuclear power plants. It can be seen that the pipe was wrapped with a thick layer of thermal insulation material which is typical for steam pipes. The main goal for this pipe CR inspection is to monitor and detect the flow-accelerated corrosion on the pipe walls. Flow-accelerated corrosion has been a major engineering and maintenance issue for the nuclear power plant which can be effectively detected with CR without the need to remove the insulation.

≠ With today’s amazingly powerful image processing software as an integral part of the CR system, CR users can easily change the image density, enhance the contrast, zoom a selected region, invert the image color, make an embossing view, etc. to improve the probability of detection which cannot be done with conventional film.

≠ With CR, images can be viewed in about one minute after exposure compared to at least two and a half minutes for conventional film using an automatic processing system. Manual processing of conventional films will take at least 7 minutes.

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Figure 13. Demonstration of CR’s Dynamic Range (a) Dynamic Range Comparison between Imaging Plate and Conventional Film22 (b) CR Image of a Part with a Large Range of Varying Thicknesses18

Figure 14. CR Image of an Insulated Steam Pipe23

Disadvantages of CR Technology

≠ Imaging plates are extremely sensitive to back and internal scatters, although this can be reduced to a certain degree with a thin lead screen.

≠ Imaging plates are relatively expensive. It costs around $500 to $600 for a 14”x17” IP.

(a) (b)

Imaging

Plate Film

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Discussions

The NDT inspection procedures developed for nuclear power plants are all referenced from the ASME Boiler and Pressure Vessel Code. For example, code Sections V (Nondestructive Examination) and XI (Rules for Inservice Inspection of Nuclear Power Plant Components) need to be referred to for the development of inspection procedures for the in-service NDT inspection of nuclear power plant components. Additionally, any procedure developed in-house even by an NDT level III personnel has to get the approval of the NRC12 (Nuclear Regulatory Commission) by passing a performance test of the procedure on a reference standard (mock-up) before it can be implemented. For other industries, approval by an NDT level III personnel is all that is required to implement a new procedure. The NDT inspections conducted in nuclear power plants are mainly for the inspection of welds and corrosions using either ultrasonic or radiographic method, or both. This is similar to the inspections conducted for the petrochemical industry, but it is drastically different from those for the aircraft maintenance industry. In 5 years of working for an airline as an NDT technician/director, the lead author did not once use either ultrasonic or radiographic method for inspecting welds. During this course renovation effort, the author has not only learned a lot about the latest NDT technologies, but also gained some knowledge about the different NDT focuses, challenges, and practices occurring in different industries, which certainly will benefit the students. To acquire some knowledge about CR, the lead author attended the 3rd VMI (Virtual Media Integration) Annual CR User Group Conference held in St. Augustine, Florida from June 9-12, 2008 and watched all presentations given by people from various nuclear power plants and NDT service providers. The impression the lead author received was that all the attendees were very enthusiastic about exchanging experiences, and they all seemed very happy with the CR technology. Some of the NDT service providers in the conference had done contract work for nuclear power plants. They all relied on CR for radiographic jobs for the reasons mentioned in the previous section, Advantages of CR Technology over Conventional Film-based Radiography. The only complaint was the lack of qualified technicians and the difficulty in making the transition with existing crew who were not familiar with the operation of the computers and software. The industrial trend was quite obvious, everyone going for CR for nuclear power plant NDT, which validated our decision to add CR to the ENTC 402 course.

Induction of the New NDT Technologies to the Classroom and Lab

Time Allocations and Teaching Contents for Phased Array and Computed Radiography

ENTC 402 is a three credit hour course consisting of two one-hour class lectures and one two-hour lab session per week. An adjustment has been made to the syllabus starting this semester (Spring 2009) for the induction of the two latest NDT technologies, phased array ultrasound and computed radiography, into ENTC 402. The revised time allocations for the lectures and labs for each of the five NDT methods are listed in Table 2. The set of guidelines for the training of level II technician published by the American Society for Nondestructive Testing (ASNT), Recommended Practice No. SNT-TC-1A, is also listed in the table for reference. It has never been our intention to follow the ASNT guidelines since our teaching goal is not to

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train level II technicians. Nevertheless, the time allocation to each method in our ENTC 402 class is about half of those recommended by ASNT guidelines except for the eddy current method.

Table 2. Time Allocation for ENTC 402 Course

Test Method Level II Training Hours Recommended

by ASNT

ENTC 402 Class Lecture

Hours

ENTC 402 Lab Sessions

ENTC 402 Combined Lecture

and Lab Hours

Liquid Penetrant 8 2 1 4

Magnetic Particle 8 2 1 4

Ultrasound 40 10 (2)* 5 (1)* 20 (4)*

Radiography 40 10 (2)+ 3 (3) + 16 (8) +

Eddy Current 16 3 1 5

Total hours 112 27 11 49

* - the numbers in parentheses are the portion of time allocated for phased array technology + - the numbers in parentheses are the portion of time allocated for computed radiography The two lecture hours allocated to phased array technology will cover the basic principles and present the example of its application in nuclear power plants as described previously. The one lab session allocated to the phased array will be the last one for the ultrasonic method after students become familiar with the conventional method through practices during the previous four lab sessions. A flawed weld sample that has been used for testing with the conventional method will be used to demonstrate the difference between phased array technology and the conventional method. The two lecture hours allocated to computed radiography will cover its basic principles and issues associated with the inspection of components in nuclear power plants. The lab sessions will be completely devoted to computed radiography and no film-based radiograph will be produced as we don’t have a darkroom facility for the development of conventional films. As such, the discussion of conventional film characteristics and the film developing process will be cut back, and the exposure calculations associated with conventional film (for change in film type or film density) will be totally eliminated to leave room for the introduction of computed radiography and the imaging plate. Additionally, the same flawed samples that students used for their ultrasonic testing will be used again for the CR testing to learn the differences between the two methods. Lab Equipment for Phased Array Ultrasound (shown in Figure 15) Flaw Detector: Phasor XS made by GE Inspection Technologies with an active aperture size of

16 elements and maximum probe size of 64 elements Transducers: linear array type of probes with 16, 32, and 64 elements Wedges: 36 degree for 16 and 32 element probes, and 30 degree for 64 element probe Test samples: flawed weld coupons made by Flaw Tech Technology25, which have all flaws

certified and documented by the manufacturer Demonstration Block: steel block with 3 visible flaws which is one of the option items for Phasor;

useful for class or lab demonstration

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(a) (b)

Figure 15. (a) GE Phasor XS Phased Array Flaw Detector and Probes (b) Test Samples with Known Flaws

Lab Equipment for Computed Radiography

X-ray tube: LORAD LPX-160 with a peak voltage of 160 KV Control Unit: 100% duty cycle, fan cooled, maximum tube current of 5 mA Lead Shielded Cabinet: 56”x41”x41” and weigh 2200 lbs, circuit interlocking with the X-ray

control unit CR System: Including VMI 5100 MS CR Digitizer, a workstation with Starrview software, a 3-

mega pixel high resolution LCD display, and imaging plates Among the equipment used for computed radiography, the X-ray tube and cabinet as shown in Figure 16 are just about to be moved into our NDT lab. They were donated by TEAM Industrial Services of Alvin, Texas. The CR system is donated by the VMI of Pensacola, Florida and will be delivered in late March.

Figure 16. LORAD X-ray System and Lead Shielded Cabinet

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Bibliography

1. “National Energy Policy,” Report of the National Energy Policy Development Group, May 2001, US

Government Printing Office, ISBN 0-16-050814-2 2. Porter, Jay, Zhan, Wei, Alvarado, Jorge, and Morgan Joseph, “Power Engineering Technology: A New Program

Targeted at the Nuclear Power Industry,” ASEE Annual Conference 2008, AC 2008-614. 3. http://www.ndt-ed.org/EducationResources/CommunityCollege/Ultrasonics/Introduction/description.htm 4. http://www.rfsales.com.au/others/sub_category/products/index.php?ID=SONATEST+HARFANG+X32 5. Woo, Joseph, “A summary of the early development of Ultrasonics prior to the 1950s leading to medical

applications,” http://www.ob-ultrasound.net/ultrasonics_history.html 6. http://www.bercli.net/products/IMASONIC.htm

7. http://www.sonatest-plc.com/faq/phasedarray.html

8. http://www.bercli.net/images/principles_phased_array.png 9. http://www.imasonic.fr/Industry/PAprinciple.php 10. http://www.nrc.gov/reactors/operating/ops-experience/vessel-head-degradation/images.html 11. Halley, Jim and Moles, Michael, “Advances in the NDT of Dissimilar Metal Welds,” Material Evaluation,

December 2008, p1241-1245 12. Private communication with Lyle Spiess, Corporate NDT Level III, STP Nuclear Power Plant in Wadsworth,

Texas 13. Vidyasankar, S., “Phased Array Ultrasonics: Is it the Future of Ultrasonic Nondestructive Testing (NDT)? - Part

3”, Dec. 5, 2006, http://www.frost.com/prod/servlet/market-insight-top.pag?docid=88875665

14. http://www.medcyclopaedia.com/library/topics/volume_i/p/photostimulable_phosphor_plate.aspx 15. http://en.wikibooks.org/wiki/Basic_Physics_of_Nuclear_Medicine/Dual-Energy_Absorptiometry 16. Kodak document, “Kodak Continues Its Computed Radiography Innovation,” August 2005 17. Private communication with David Stuhler at STP Nuclear Power Plant in Wadsworth, Texas 18. Morro, Fred of Fujifilm NDT Systems, “Computed Radiography – Evolutions to Revolutions,” NDTMA 2007

Annual Conference 19. http://www.fujindt.com/pr_jan15.html 20. Prince, David, “CR Applications in China” VMI 3rd Annual CR Users Group Conference, June 2008 21. Simpson, Matt, “CR at Wolf Creek Generating Station,” VMI 3rd Annual CR Users Group Conference, June

2008 22. Zscherpel, Uwe and Ewert, Uwe of BAM Berlin, Division VIII.3, “Computed Radiography,” INDE 2007,

Kalpakkam, India, April 2007 23. May, Clyde, “Successful Applications of Computed Radiography,” VMI 2nd Annual CR Users Group

Conference, June 2007 24. ASNT Recommended Practice No. SNT-TC-1A, American Society for Nondestructive Testing (ASNT) 25. http://www.flawtech.com/

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