improving nuclear plant reliability by developing an eddy

1 Copyright © 2014 by ASME

IMPROVING NUCLEAR PLANT RELIABILITY BY DEVELOPING AN EDDY CURRENT TEST STRATEGY

TO IDENTIFY UNCOMMON CONDENSER TUBE DEFECTS

James A. Kocher Director of Emerging Technologies

Conco Services Corp. 530 Jones Street Verona, PA 15147

[email protected]

Robert Frazee System and Thermal Performance Engineer

STP Nuclear Operating Company PO Box 289, Wadsworth, TX 77483

[email protected]

Matthew Wolf Eddyfi

Senior Applications Specialist 2800 Louis-Lumière, Suite 100

Québec, Québec G1P 0A4 CANADA

[email protected]

ABSTRACT Eddy Current Testing (ECT) of condenser tubes is essential

to maintaining good plant reliability and availability. Early

identification of defects can allow for adequate remedial action

and prevent forced outages caused by condenser tube leaks.

The well-known catastrophic failure in the nuclear industry in

Japan has not only raised concern in Japan over aging nuclear

power plants, but has also raised concern over safe operations

in the United States and around the world. Ongoing reliability

and instability issues due to reported leaks in condensers have

also been the topic for nuclear watchdogs. This focus on the

nuclear plant condenser has brought to light the various levels

of sophistication and capability in ECT.

In ECT, the type of defect present in a condenser tube is

determined by the characteristics it presents under test. The

tubes must be adequately cleaned prior to testing and some

awareness or evidence of the type of defect to be uncovered

should be available to the testing team. In cases where defects

are discovered that are inconsistent with prior awareness further

exploratory testing is common. Exploratory testing can proceed

to test areas of suspected defects in the tubing, and it may result

in a complete redefinition of the test procedure, inclusive of

instruments, probe types and other key ECT criteria. A

comprehensive knowledge of testing options and their practical

application is necessary to redefine a test that will yield

meaningful results and achieve the intended objective; to

identify the type and extent of defect and take remedial action

therefore preventing failure.

This paper addresses such a case at the South Texas Project

(STP) Nuclear Power Plant where peculiar defects were

undeterminable under standard ECT procedures. The defects

continued to negatively impact reliability and stability at the

plant until a new ECT process and test procedure were

developed, demonstrated and deployed. The result achieved

was accurate defect detectability and improved nuclear plant

reliability.

INTRODUCTION With the catastrophe at Fukushima in Japan and a climate

of heightened concern over nuclear safety and reliability,

watchdogs have been holding nuclear power plants accountable

for providing adequate and frequent maintenance and inspection

programs to their plants to assure reliability. In the United

States, groups like the Citizen’s Awareness Network have asked

Proceedings of the ASME 2014 Power Conference POWER2014

July 28-31, 2014, Baltimore, Maryland, USA

POWER2014-32274


the Nuclear Regulatory Commission, or NRC, to investigate

plants like the FitzPatrick plant, of Entergy Nuclear Operations,

for untreated condenser problems. In the case of the FitzPatrick

plant, fouling and leaks dramatically decreased the efficiency

and reliability of the nuclear plant, which lead to instability,

catching the attention of nuclear watchdogs. (Citizens

Awareness Network, 2013) The detrimental long-term effects

of leaving the damage caused by fouling and leaks in

FitzPatrick’s condenser tubes’ unattended has been the source of

numerous avoidable unplanned outages and the sole reason that

Entergy has now completed a condenser replacement. (Alliance

for a Green Economy, 2013) Similarly, at the Vermont Yankee

nuclear power plant, nuclear watchdogs from the New England

Coalition wanted the plant closed as a result of wasteful

emissions as a result of condenser tube leakage. The untreated

leaks had allowed cooling water from the Connecticut River to

contaminate the condensate. Watchdogs know that a problem

like this could cause more inefficiency and unreliability through

secondary damages caused by foreign elements or objects

traveling in the steam. (Dillon, 2012)

Addressing the issue of condenser tube leaks and tube

condition is an important topic for a nuclear plant in achieving

reliability and stability in a climate where there is so much

concern. South Texas Project aims to keep their condenser

clean and reliable, maintaining availability long into the future.

Condenser Description

South Texas Project (STP) Nuclear Power Plant was

commissioned for operation in 1988. A picture of the plant is in

Figure 1. There are two units, Unit 1 and Unit 2, similar in

design and capacity. The condensers are single pass, multi-

stage with three compartments of 32,078 tubes each making the

total number of tubes per unit 96,234. The tube material is

titanium grade 2, size ¾” O.D. by 22 BWG approximately 54’

9’’ long. The units are base loaded and produce 1,250

megawatts of power each. Figure 2 shows the typical STP

waterbox.

Makeup water for the Circulating Water System is pumped

from the nearby Colorado River and sent to the facility’s 7,000

acre, 18 foot deep, holding reservoir adjacent to the plant. Two

traveling screen systems remove debris from the cooling water,

one for the water which is pumped from the river and the other

for the water from the reservoir to the condensers.

Eddy Current Testing

Eddy current testing is a well-established form of

nondestructive testing used to examine non-ferritic tubing in

condensers and heat exchangers. The eddy current method is a

volumetric testing process that uses an electromagnetic field to

identify defects in the tubing. An electron flow (eddy current)

is induced in electrically conductive material and an

electromagnetic field is generated. Any anomaly in the material

will disrupt the magnetic field or eddy current and the anomaly

can therefore be identified. Depending on the number of

frequencies and channels used, including both differential and

absolute channels, defects with unique characteristics such as

pitting, tube wall thinning, cracking, grooving or denting on the

inner diameter (ID), as well as the outer diameter (OD) of the

tubing can be found. The characteristics of the defects are often

the key to identifying the predominant failure or corrosion

mechanism present. The results are analyzed and anomalies can

be categorized and reported by defect type and depth. This

provides management with an accurate assessment of unit

condition and remaining useful life. Additionally, precautionary

steps can be taken to plug or avoid any potential failures

reducing costly condenser tube leaks and preventing forced

outages. (Droesch, D., et al.)

While Eddy Current testing is performed on non-ferritic

tubing material, ferritic materials are typically tested with

Remote Field Technology (RFT). Condenser and heat

exchanger tubing such as austenitic stainless steel, titanium,

brass and copper nickel are often tested with Eddy Current

methodology.

The applicable codes and procedures for performing Eddy

Current Testing for the balance of plant components at a nuclear

facility may include but are not limited to: the American Society

of Nondestructive Testing, Inc.’s (ASNT) SNT-TC-1A,

ANSI/ASNT CP 189 guidelines, ANSI E690 and E571, ASME

BPVC, Section V, Article 8 and ASNT Standard for

Qualification and Certification of Nondestructive Testing

Personnel.

PROJECT BACKGROUND

Condenser Tubes Heavily Scaled with Calcium Carbonate

In September, 2006, an inspection of the tubes in Unit 1 at

STP showed a scale deposit inside the tubes that proved on

analysis to be a very tenacious form of calcium carbonate, or

calcite (CaCO3). While tube fouling itself is detrimental to

plant performance and turbine backpressure, it usually consists

at STP as a result of varying degrees of particulate

sedimentation and biologic growth, from algae to bryozoa,

clams and mussels, the removal of which is not extraordinarily

difficult. Calcium carbonate scale, however, poses a serious

problem with limited remedial solutions. It is a crystalline

compound found in such materials as limestone and marble. At

STP, several tubes were tested for thickness of the CaCO3.

Thickness of twenty samples tested ranged from .007” to .031”,

with an average of .019”. It was concluded that the Unit 1

condenser performance was continuing to deteriorate due to the

increasing scale on the ID of the tubes and debris clogging the

tubes. STP Plan of Action was prepared.

The problem statement in STP’s Plan of Action cited that

scaling and fouling of the tubes resulted in degraded

performance of the condensers; the plan also noted that erosion

of the outlet tube sheets had been observed. Further, if these

processes were to continue there would be a serious operational

impact not only in performance but the continuing threat of

leaks could impact reliability and availability.

A comprehensive review of available technology for

removing calcium carbonate scale was conducted. It was


determined that the best cleaning procedure was going to be one

pass per tube with undersized standard metal-bladed cleaners,

followed by multiple passes of various sized calcium carbonate

cutting cleaners (incorporating scale cutting wheels) stepped in

seven sizes to satisfy a range of scale thickness. After the scale

had been fractured by the calcium carbonate cutting cleaners, a

final pass was made in each tube by the appropriately sized

standard all-purpose metal-bladed mechanical cleaner to

remove the fractured scale. The tube cleaners are shown in

Figure 3.

The initial cleaning project was successful and over 5,000

pounds of scale, was removed from the 96,234 condenser tubes

in Unit 1. In a subsequent outage, the Unit 2 condensers were

also cleaned with the same process used for Unit 1. Over 4

cubic yards of calcium carbonate, weighing more than 3,000

pounds, was removed from Unit 2. It is believed that the tubes

in Unit 2 were less fouled because they had been cleaned with

metal-bladed mechanical tube cleaners in a prior outage, while

the tubes in Unit 1 had been cleaned with nylon brushes that left

ridges inside the tubes, promoting faster build-up of debris and

scale.

The tube cleaning exercises were successful and as a result

of the removal of the calcium carbonate scale, South Texas

Project Nuclear Power Station reported a significant increase of

approximately 3 megawatts of power from the two units.

(Saxon, Jr. and Moye 2007)

The plant continued operation and performed regular

cleaning during overhauls during the next few refueling cycles.

Since the initial cleaning, the plant experienced improved

performance but had also experienced some condenser tube

leaks. The number and timing of leaks is shown as a graph in

Figure 4. The same information is listed in Table 1 below, Tube

Leaks.

Unit 1 Unit 2

No. Date When

Discovered No. Date

When

Discovered

3 Oct. –

06’ Outage 12

Feb. -

07’ Outage

3 Nov. –

06’ In Operation 1

Feb.

– 10’ In Operation

1 Sept. –


Apr. -

10 Outage

1 Dec. -


Mar.

– 12’ Outage

1 Oct. -


July


3 Mar. –

11’ Outage 1

June


2 Apr. -

11’ In Operation

1 June –

13’ In Operation

1 Aug. –

13’ In Operation

2 Sept. –

13’ In Operation

Table 1, Tube Leak Frequency

From October 2006 to September 2013 Units 1 and 2

experienced 18 and 22 tube leaks respectively, 25 of which

were discovered and adequately resolved during outages and 15

of which occurred during operating cycles over the seven year

period, for an average of approximately two leaks per year over

the two condensers. For the three year period from November

2006 to September 2009, the Unit 1 condenser operated

successfully without any leaks at all, as did Unit 2 from

February 2007 to February 2010. As indicated in Figure 4 there

were a number of causes for the tube leaks.

Concern about what appeared to be scratches and grooving

in the tubes was raised after the 2011 cleaning and outage. The

scratches and grooves were discovered during a boroscopic

examination conducted while examining a tube failure that had

occurred during the outage. Tubes were extracted, a root cause

investigation was initiated and a tube failure analysis

performed.

In discussion with plant personnel the primary concern was

through wall damage not seen in the sample provided, generated

from; a.) The force of operators pushing scale cutters that were

stuck in the tubes from deposit build up or obstructed tubes, and

b.) The grooves would give rise to fatigue cracking given the

vibration and stresses of operational cycles experienced at the

plant and in the condenser. For these reasons it was essential to

determine the extent and magnitude of the defects and access

the overall tube condition in the condensers. From sampling,

only a handful of tubes had been thoroughly inspected. To

mitigate the risk of additional tube failures, rather than only

testing the tubes known to have generated difficulty or have

blockages in the cleaning process, all 96,234 tubes in each

condenser were to be tested.

Tube samples were provided to a number of nondestructive

testing firms to develop a test plan. Figure 5 shows the tube

condition of one of the tube samples observed. The close up is

of the tube as found from the Inlet, 12N lower waterbox of the

unit 1 condenser, the area of interest in the particular tube

sample, the image shows some scratches and grooves

approximately ½” to 1” long. Figure 5 also shows an

unexpected observation of which appears to be a pit. The

following Figures 6 and 7 show the same defects at 15X and

60X magnification. In particular, Figure 7 shows three

markings that would typically all have a similar signal under a

traditional Eddy Current inspection, if any, yet the difference in

shape and size these markings would suggest different causes.

Figure 8, shows additional undefined irregularities on the tube

surface. Finally, Figure 9, is a cross section, a groove of

concern at 100X magnification, this groove being measured at

approximately 7% of tube wall loss is a channel and wide

groove of a much different radius than the tube ID and of a

different shape than any cleaning device would suggest. Other,

scratches on the internal surface were measured at 2% of tube

wall loss.

Given all of the above, there was motivation for a more

thorough investigation and modification of testing parameters.


TESTING PLAN

Concerns about the potential of widespread damage

sparked further investigation and the involvement of EPRI to

assist with detection and sizing techniques for the specific

concern. Custom calibration standards were also developed to

mimic the defects found in failed tubes.

Eddy Current Approach

Titanium tubing used in steam surface condenser

applications is typically not affected by corrosion and is

normally subject only to mechanical damage. This includes

physical damage from loose parts, vibration wear, steam

impingement and high cycle fatigue. Since titanium is not

susceptible to the normal corrosion mechanisms found in

condensers conventional Eddy Current techniques are sufficient

for detection, sizing and characterization of the defects

expected. In the case of the suspected grooving at STP a more

detailed signature of the defects was necessary. The use of

conventional bobbin coil probes could not accurately identify

the presence or magnitude of the grooving, and therefore it was

necessary to modify the test plan and incorporate a more

suitable probe.

Development of Exploratory Testing

The Electric Power Research Institute (EPRI) NDE center

was solicited for assistance with an Eddy Current inspection

technique to help determine the extent, orientation, and if the

defects had multiple circumferential instances at a given

location. Calibration standards were developed to mimic the

defect confirmed from a failed tube that was pulled from the

condenser and dissected at a metallurgical laboratory. The

grooves also gave rise to consider the potential for stress

cracking. The focus by EPRI was to ensure detection of the

grooving and associated cracking. The goal also was to

determine if there were single occurrences or multiple

occurrences at a given location in the tube. For this, EPRI

recommended a narrow groove, segmented bobbin coil which

can divide the circumference of a tube into four parts with each

coil focused on only 90 degrees of the tube instead of 360

degrees of coverage by a standard bobbin coil. The narrow

groove segmented bobbin was able to provide information as to

whether or not there was a single instance or multiple grooves at

a given location. Narrow groove segmented bobbins were also

suggested for follow up and confirmatory examination to

determine the damage mechanism found with the conventional

bobbin coil.

With the intent to mitigate risk and assure reliability and

availability, STP developed plans for 100% inspection of unit 1

and unit 2 condenser tubes to obtain a full condition assessment

and to avoid further mid-cycle failures. STP knew it was

necessary to gain full understanding of what type of defects

existed and how many tubes were effected to minimize the

potential for premature failure. Those with a high risk needed

to be removed from service or plugged to prevent any chance of

a mid-cycle leak that would cause a reduction in power

production.

Unit 1 Inspection

The initial 100% inspection performed on the unit 1

condenser incorporated the EPRI recommended narrow groove

segmented bobbin probe. The probe provides conventional

bobbin data and is sensitive to the axial indications

encountered. The segmented bobbin coil arrangement can

determine the flaw distribution within the same circumferential

location and did provide information by dividing the tube

circumference into 90o segments but was deemed limited on

providing any further detail on flaw characterization. Further

discussion with EPRI determined that a conventional bobbin

coil was as efficient detecting the suspected grooving.

Unit 2 Inspection

The initial 100% inspection performed on STP’s unit 2

condenser incorporated the use of a conventional bobbin probe

to provide initial Eddy Current data on all the tubes. All tubes

that had defects exceeding 40% of wall loss were re-inspected

using the narrow groove segmented bobbin for flaw

confirmation and characterization. The expectation was to save

plugging tubes with less critical flaws which were not axial or

crack-like. Unfortunately, the narrow groove segmented bobbin

probe was not able to provide enough additional flaw data to

support a sound decision to avoid plugging certain defects. The

inspection was completed using only the conventional bobbin

probes without following up with the narrow groove probe.

The Need for an Alternative Plan

In both unit 1 and unit 2 condensers at STP, there was no

previous inspection data on record that could be referenced to

determine if defects noted during the 100% inspection were pre-

existing, or if they were more recent developments. In the

absence of historical data on these units, the determination of

what mechanism was present: grooving, cracking, or a

volumetric indication, was impossible. With much uncertainty

present and the concern that flaws could lead to premature tube

failure, the plugging criterion for the flaws noted remained at a

conservative 40% of wall loss. The result was hundreds of tubes

being removed from service. STP is continuing the pursuit for

more detailed results in order to plan any necessary remedial

action. Testing continues using state-of-the-art Eddy Current

applications tailored to their unique flaws. Considerations for

additional exploration have included Rotating Pancake Coil

(RPC) technology and the current focus is on the use of Array

technology.

Rotating Pancake Coil (RPC) technology

One method of acquiring detailed signatures of indications

found with a conventional bobbin coil is by use of a Rotating

Pancake Coil (RPC) technique. The RPC technique is one that

uses a small, sensitive pancake coil affixed to a device that can

deliver the coil inside of an installed condenser tube and rotate


the coil to scan the entire circumference of the tube ID.

Compared to a bobbin coil which interrogates the entire

circumference of a tube at the same time, the pancake coil is

smaller, more sensitive and can detect all types of degradation.

Though a pancake coil is capable of providing the level of

detail sought after, the technique has some undesirable traits.

The probes are fairly expensive and are somewhat delicate.

They normally do not perform well physically in environments

where the tube condition is not optimum and where spots of

scale and deposits may be present. Probe usage can be

excessive and costly. Additionally, the scanning speed is very

slow compared to a bobbin coil. The RPC probe traverses at

.2” to .5” per second compared to 36” to 60” per second with a

bobbin coil.

Figure 10 shows how a conventional bobbin coil

interrogates the entire tube circumference at the same time

limiting our ability to determine if a flaw is isolated or multiple

in a given instance. The RPC probe, Figure 11, can pinpoint

areas in the tube to provide more detailed flaw characteristics.

Array Technology

Array probes are the perfect blend of pancake coil

sensitivity with the convenience of full circumferential tube

coverage and a higher inspection speed. Much like the basic

pancake coil, Array coils are sensitive to all types of defects and

provide the same level of detail as the pancake and, in many

cases, even more detailed results. Coupled with an enhanced

digital display, the latest Array technologies provide

unsurpassed eddy current analysis.

Where the RPC technique is a single coil that has to be

rotated inside the tube to provide complete coverage, Array

techniques are an assembly of multiple pancake coils, as many

as 24 to 36, affixed to the probe body and can be pulled straight

through the tube without rotation. The illustration, Figure 12,

also shows the disadvantages of single coil scanning versus

multiple coil Array technology. The scanning speed using the

multiple array coils is much faster and insures complete

coverage. The real advantage can be seen in the display of the

data obtained from advanced Array coil technology (Figure 13).

The standard RPC display is a connection of scans

displayed on a grid to provide a view of the entire tube

circumference. Advanced Array coil displays connect the data

of each coil and displays it on a color gradient scan that is

voltage sensitive providing an easy to read image outlining the

defect’s signature. This once high cost technology, often out of

budget range for the balance of plant applications, has been

recently offered at a price that is affordable to the common

marketplace. For this particular Eddy Current inspection

application, the EddyFi DEFHI Array probe was selected for an

investigative inspection.

Figure 14, shows the finite detail of the multiple array coil

technology provided by EddyFi in their DEFHI Array coil

probe. The probe coupled with EddyFi’s Magnify software

allows for display of the data points seamlessly and shows

greater detail over the standard RPC technology.

In addition to the Array coils, the DEFHI probe

incorporates a conventional bobbin coil that provides for a

simultaneous standardized examination. The typical inspection

process requires a scan of the tubes with a bobbin coil followed

by a scan of the tube with a RPC or other specialized technique

to obtain information on defects of interest. This is an enormous

time savings, especially for tube inspections, where known

conditions exist that require the use of both techniques for

detection and sizing. Figure 15, shows an Array of an axial

crack in a calibration standard in the AXIAL F1 channel. The

Circumferential channel CIRC F1 has no response as expected,

it is only sensitive to circumferential damage.

Figure 16 shows 4 X 20% flat bottom OD holes in the

ASME standard. One can clearly see they are separated 90°

degrees apart and are volumetric since they are equally

responsive in both the CIRC and AXIAL channels.

When the STP samples were viewed with the EddyFi Array

technology the original assumption of the defects being caused

by the wheels of the scale cutters being forced through the tubes

may not have been correct due to the steep front and rear entry

and exit points of the defect. The defects if generated by the

wheels in the cleaning device would have shown a gradual entry

and exit to the flaw. Additionally, absent of the Eddy Fi

technology the unique defects in Figures 6 and 8 would have

appeared as a simple elongated groove under traditional Eddy

Current testing. In as much, EddyFi is leading to a more

thorough inspection and investigative result.

With the use of the Array technology, defects found in

condenser tubes can be further quantified into categories of

damage type, not just depth of wall loss. Various damage

mechanisms may require different plugging strategies. Tubes

with general pitting and volumetric flaws may be left in service

with deeper degradation than a crack-like indication. Having

more detailed defect characteristics can help avoid excessive

and sometimes unnecessary plugging. The EddyFi Array probe

was deployed on a trial basis to gather data from the STP

condenser tubes.

CONCLUSION

Eddy Current examination is used effectively for

determining defects in condenser tubing. However when the

defect characteristics are uncommon, variation in the testing

approach is necessary. In this case Eddy Current testing with

standard bobbin coil probes could not identify the unique

characteristics of the defects. Experimentation with narrow

groove probes and rotating pancake coil probes was required

before concluding that the most accurate testing results would

be achievable through application of Array technology.

Accuracy is essential for Eddy Current testing to be a viable

solution in risk mitigation and improving the reliability and

availability of the condensers in nuclear plants, keeping nuclear

watchdogs at bay as the nuclear power plants age. In the case

of STP a testing method has been developed and identified that

will help to assess the current condition and remaining useful


life of the condenser tubes. Following the assessment any

remedial action plan can be effectively implemented.

REFERENCES Alliance for a Green Economy. (2013, August 1). “FitzPatrick

Nuclear Reactor Sees Skyrocketing Condenser Problems”.

Alliance for a Green Economy. Retrieved January 27, 2014,

from

http://www.allianceforagreeneconomy.org/content/fitzpatrick-

nuclear-reactor-sees-skyrocketing-condenser-problems

Citizens Awareness Netowrk. (2013, March 18). “Watchdogs

say Entergy not qualified to operate reactors”. VTDigger.

Retrieved January 27, 2014, from

http://vtdigger.org/2013/03/21/watchdogs-say-entergy-not-

qualified-to-operate-reactors/

Dillon, J. (2012, April 11). VPR: “Condenser Leaks Plague

Vermont Yankee Plant.” Vermont Public Radio. Retrieved

January 27, 2014, from

http://www.vpr.net/news_detail/94113/condenser-leaks-plague-

vermont-yankee-plant/

Droesch, D., et al., (2006), “The Advantages of Using Multiple

Frequencies for Eddy Current Examination of Condenser

Tubing,” Proceedings of ASME Power 2006, Atlanta, GA, May

4-6, pg. 2

The American Society for Nondestructive Testing, Inc., (2007),

“Recommended Practice No. SNT-TC-1A 2006”, Columbus,

OH.

American Society of Mechanical Engineers, 2007, “ASME

Boiler and Pressure Vessel Code, Section V, Nondestructive

Examination, Article 8, Nondestructive Examination of Tubular

Products, NY, NY.

The American Society for Nondestructive Testing, Inc., (2007),

“ASNT Standard for Qualification and Certification of

Nondestructive Testing Personnel, 2006 Edition, Columbus,

OH.

Saxon, Jr., G. and Moye, W. (2007), “South Texas Nuclear

Power Plant Unit 1 Condenser; Scale Deposit Removal from

96,234 Condenser Tubes,” Proceedings of ASME Power 2007,

San Antonio, TX, July 17-19, pg. 3.

ACKNOWLEDGMENTS The authors acknowledge Conco Services Corp., STP

Nuclear Operating Company and Eddyfi for their support and

encouragement in producing this paper.

Figure 1, South Texas Project Nuclear Power Plant (STP)

Figure 2, One of Six Waterboxes of STP’s Unit 1 Condenser

Figure 3,Calcium Carbonate Tube Cleaner and Standard C4S

Type Tube Cleaner and CaCO3 Scale


Figure 4, Number and Timing of Condenser Tube leaks

Figure 5, Tube Interior Close-Up

Figure 6, Internal Surface. [Mag = 15X]


Figure 7, Internal Tube Surface. [Mag = 60X]

Figure 8, Irregular internal markings. [Mag = 60X]

Figure 9, Cross-section through groove, ~7% of wall thickness

lost. [Mag = 100X]

Figure 10, Standard Bobbin Coil Probe, Olympus

Figure 11, Top, Rotating Pancake Coil (RPC) and Standard

Bobbin Coil, Bottom.

Figure 12, Illustration of single coil scanning versus multiple coil

Array technology, Absolute NDT.


Figure 13, The Magnify display with multiple responses from an

EddyFi Array probe

Figure 14, Finite detail of the multiple Array coil technology

provided by EddyFi in their DEFHI Array coil probe.

Figure 15, Shows an Array from an Axial crack in a Standard.

Figure 16, 4 X 20% flat bottom OD holes in the ASME standard.

improving nuclear plant reliability by developing an eddy

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