Results of the Program for the 

Inspection of Nickel Alloy 

Components

Office of Nuclear Regulatory Research 

NUREG/CR-7019 

PNNL-18713, Rev. 1

Results of the Program for the 

Inspection of Nickel Alloy 

Components 

Manuscript Completed: April 2010 

Date Published: August 2010 

Prepared by 

S.E. Cumblidge, S.R. Doctor, P.G. Heasler, and T.T. Taylor 

Pacific Norhwest National Laboratory 

P.O. Box 999 

Richland, WA 99352 

I. Prokofiev, NRC Project Manager 

NRC Job Code N6593

Office of Nuclear Regulatory Research 

NUREG/CR-7019 

PNNL-18713, Rev. 1 

iii

Abstract

The U.S. Nuclear Regulatory Commission (NRC) executed agreements with organizations in 

Japan, Sweden, South Korea, Finland, and the United States to establish the Program for the 

Inspection of Nickel Alloy Components (PINC). A series of round-robin tests was conducted by 

teams from Europe, Japan, Korea, and the United States. The teams examined a series of test 

blocks designed to simulate cracked piping dissimilar metal welds and bottom-mounted 

instrumentation tube penetrations. The round-robin tests were carried out to determine the 

effectiveness of a variety of nondestructive testing techniques for the detection of simulated 

stress corrosion cracking. These round robin tests were conducted using nickel-based alloys, 

such as Alloy 600. In these tests, 22 test blocks, 19 containing simulated primary water stress 

corrosion cracking and 3 blanks, were used. The teams used techniques ranging from 

conventional ultrasonic techniques to experimental potential drop methods. The results were 

then scored to allow for comparisons between the techniques. The conclusions and 

recommendations presented in this report are based on the probability of detection, false call 

probability, and sizing statistics measured in the round robin studies. 

The highest-performing technique for detection and length sizing, for both dissimilar metal welds 

and bottom-mounted instrumentation nozzles, was the use of eddy current testing on the 

cracked surface. Ultrasonic testing showed that it could be used effectively for detection and 

length and depth sizing. The effective detection of flaws in bottom-mounted instrumentation 

nozzles by eddy current and ultrasound shows that it may be possible to reliably inspect these 

components in the field. The high variability in the team performances suggested that the skill 

of the team conducting the test is a very important factor in the quality of the examination. This 

suggests that some form of strict inspector qualification, such as a performance demonstration 

program, is required to ensure that the inspections are effective. This evaluation also shows 

that it may be beneficial to tie the inspection interval length to the crack growth rates in the 

materials of interest. Materials with very high crack growth rates may require inspections at 

every outage to provide a sufficient improvement factor. 

This body of work suggests that several NDE techniques need to be used in tandem to ensure

adequate flaw detection and sizing from the noncracked surfaces. Eddy current provided the 

highest performance for flaw detection from the cracked surface. The round-robin results from 

this effort showed that a combination of conventional and phased array ultrasound provided the 

highest performance for accurate depth sizing in dissimilar metal piping welds. It is worth noting 

that eddy current is not universally applicable for dissimilar metal welds, as many welds are in 

locations that do not allow for inner diameter inspections. If access to the flawed surface is not 

possible, a combination of phased array ultrasound and conventional ultrasound appears to be 

the most effective alternative. 
iv
v

Foreword

Between November 2000 and March 2001, leaks were discovered in Alloy 600 control rod drive

mechanism (CRDM) nozzles and associated Alloy 182 J-groove attachment welds in several 

pressurized-water reactors (PWRs). Destructive examination of several CRDMs showed that 

the leaks were the result of primary water stress corrosion cracking (PWSCC). By mid-2002, 

over 30 leaking CRDM nozzles had been reported in the United States. Moreover, during this 

same time, a circumferential hairline crack was detected in the first weld between the reactor 

vessel nozzle and the A loop hot leg piping at another PWR that was subsequently determined 

to be PWSCC. Such events, both domestic and international, made it apparent that additional 

research was necessary to address the problem of stress corrosion cracking (SCC) in nickelbased alloys in PWR components. 

The U.S. Nuclear Regulatory Commission (NRC) executed agreements with organizations in 

Japan, Sweden, South Korea, Finland, and the United States to establish the Program for the 

Inspection of Nickel Alloy Components (PINC). The Pacific Northwest National Laboratory 

(PNNL) assisted NRC with the coordination of PINC with two primary objectives:

1. Compile a knowledge base on cracking in Alloy 600 and similar nickel-based alloys in 

nuclear power plants (NPPs) including the crack morphology and non-destructive 

examination (NDE) responses.

2. Identify and quantitatively assess capabilities of current and emerging NDE techniques to 

detect, size, and characterize tight cracks using NDE mock-ups with PWSCC simulations.

The PINC participants identified, ranked, and determined which component configurations 

should be considered for the study. A series of test blocks with cracks were then designed and 

fabricated to simulate the selected component configurations. This report describes the results 

of the round robin tests that were performed to assess the NDE effectiveness and reliability. 

The first primary objective of the study was to produce an electronic resource on PWSCC in 

nickel-based alloys. This included documenting the material generated in support of an 

improved understanding of (1) PWSCC morphology, (2) NDE responses to PWSCC, and (3) the 

capability of NDE to reliably detect and accurately size PWSCC. This information should prove 

to be a valuable resource for the problem of SCC in nickel-based alloys in NPP components.

With regard to the second primary objective (i.e., investigate the capability of various NDE 

methods to detect and size the through-wall extent of PWSCC), the report describes the efforts 

of the PINC participants to detect and measure the lengths of cracks. The surface conditions, 

access to both sides of the weld, and inspection conditions for the PINC specimens provided 

the inspectors with less challenging conditions than would be expected in field inspections of 

PWR components. Although the inspection conditions were less challenging, team 

performance was highly variable. This supports performance demonstration efforts in the 

nuclear industry to ensure adequate qualification of inspectors. The variability in team 

performance should be factored in the decisionmaking process when applying the results of this 

study.
vi

Nonetheless, some firm conclusions could be made. For example, eddy current inspection from 

the cracked surface demonstrated the highest probability of detection for the examination of the 

dissimilar metal weld specimens. None of the NDE techniques in this round robin study 

demonstrated the capability to accurately measure the depths of flaws in dissimilar metal welds 

to ASME Section XI Code requirements. The study suggests that, in certain situations, 

examinations would be improved through the use of several NDE techniques to ensure 

adequate flaw detection and sizing.
vii

Contents

Abstract...................................................................................................................................... iii

Foreword.....................................................................................................................................v

Executive Summary .................................................................................................................xvii

Acknowledgments...................................................................................................................xxiii

Acronyms and Abbreviations..................................................................................................xxvii

1.0 Introduction.......................................................................................................................1.1

1.1 PINC Steering Committee .........................................................................................1.2

1.2 Task Group on NDE..................................................................................................1.3

1.3 Task Group on PINC Atlas ........................................................................................1.3

1.4 Data Analysis Group .................................................................................................1.4

2.0 Test Block Descriptions ....................................................................................................2.1

2.1 Dissimilar Metal Weld Round-Robin Test Blocks.......................................................2.1

2.1.1 Available Mid-Thickness Dissimilar Metal Weld Test Blocks............................2.1

2.1.2 Schematic Drawings for Mid-Thickness Dissimilar Metal Welds ......................2.6

2.1.3 Coordinate Systems for Mid-Thickness Dissimilar Metal Welds.......................2.8

2.2 Bottom-Mounted Instrumentation Round-Robin Test Blocks ...................................2.11

2.2.1 Schematic Drawings for BMI Test Blocks ......................................................2.19

2.2.2 Coordinate Systems for BMI Round Robin ....................................................2.27

2.3 Description of Fabrication Techniques Used in Developing PINC Test Blocks ........2.32

2.3.1 Flaw Fabrication in Test Blocks 5.1–5.3 ........................................................2.32

2.3.2 Flaw Fabrication in Test Blocks 2.9, 2.10 and 5.6..........................................2.34

2.3.3 Flaw Fabrication in Test Block 5.7 .................................................................2.34

2.3.4 Flaw Fabrication in Test Block 5.8 .................................................................2.35

2.3.5 Flaw Fabrication in Test Blocks 5.9 and 5.10.................................................2.36

2.3.6 Test Blocks 5.11 and 5.12 .............................................................................2.37

2.3.7 Flaw Fabrication in Test Blocks 2.1–2.6 and 5.13–5.16.................................2.37

2.4 Description of True States for the Test Blocks.........................................................2.40

2.4.1 Description of the True State Used for Dissimilar Metal Weld RoundRobin Test Blocks..........................................................................................2.40

2.4.2 Description of the True State Used for Bottom-Mounted Instrumentation 

Round-Robin Test Blocks ..............................................................................2.40

3.0 Techniques and Procedures Descriptions.........................................................................3.1

3.1 Ultrasonic Techniques...............................................................................................3.1

3.1.1 Conventional Ultrasound .................................................................................3.1
viii

3.1.2 Phased Array Ultrasound.................................................................................3.2

3.1.3 Adaptive Phased Array Ultrasound..................................................................3.3

3.1.4 Time-of-Flight Diffraction .................................................................................3.3

3.2 Electromagnetic Techniques .....................................................................................3.4

3.2.1 Eddy Current ...................................................................................................3.4

3.2.2 Potential-Drop Techniques ..............................................................................3.5

4.0 Analysis of Performance...................................................................................................4.1

4.1 Scoring Procedure Used for PINC Round Robins .....................................................4.1

4.1.1 Definitions of False Call Probability and Probability of Detection .....................4.4

4.1.2 Calculation of FCP...........................................................................................4.5

4.1.3 Logistic Regression model for POD.................................................................4.5

4.1.4 Scoring Example for Single Flaws ...................................................................4.6

4.1.5 Scoring Process for Multiple Closely Spaced Cracks.......................................4.8

4.2 Evaluation of Detection Capability for the PINC Round Robin .................................4.10

4.2.1 Probability of Detection Results for the PINC DMW Round Robin .................4.10

4.2.2 Probability of Detection Results for the BMI Round Robin .............................4.22

4.3 Sizing Results as Measured by the PINC Round Robin Exercises ..........................4.32

4.3.1 Sizing Results from the PINC DMW Round Robin.........................................4.32

4.3.2 Flaw Length Sizing in Dissimilar Metal Welds................................................4.39

4.3.3 Sizing Results from the PINC BMI Round Robin............................................4.53

5.0 Impact of PWSCC Detection and Sizing Performance with Respect to Component 

Integrity.............................................................................................................................5.1

6.0 Field Experience with PWSCC .........................................................................................6.1

6.1 Swedish Experience..................................................................................................6.2

6.1.1 Development of Inspection Qualification for PWSCC in Sweden .....................6.3

6.1.2 Simulated PWSCC Cracks ..............................................................................6.4

6.1.3 Comparison of the Signal Response from the UT and EC Inspection in 

the Plants and the Response from the Inspections of the Simulated 

Cracks .............................................................................................................6.4

6.2 United States Experience..........................................................................................6.5

6.3 Japanese Experience................................................................................................6.7

6.3.1 DMW ...............................................................................................................6.7

6.3.2 CRDM ...........................................................................................................6.12

6.3.3 BMI................................................................................................................6.13

7.0 Parametric Studies – NDE Responses and Flaw Morphology (NA2 and Simulated 

Flaws)...............................................................................................................................7.1

7.1 Manufactured Flaw Nondestructive Testing Responses ............................................7.1
ix

7.2 North Anna 2 Flaw Responses..................................................................................7.7

7.3 Comparison of Eddy Current Response of Manufactured Flaws and for 

PWSCC in North Anna 2 ...........................................................................................7.8

8.0 Conclusions and Recommendations from PINC Round Robins........................................8.1

8.1 Probability of Detection Performance ........................................................................8.1

8.1.1 Dissimilar Metal Weld Pipe Specimen Round Robin Probability of 

Detection Performance....................................................................................8.1

8.1.2 Bottom-Mounted Instrumentation Round Robin Probability of Detection 

Performance....................................................................................................8.2

8.2 Sizing Performance...................................................................................................8.3

8.2.1 Dissimilar Metal Weld Pipe Specimen Sizing Performance..............................8.3

8.2.2 Bottom-Mounted Instrumentation Weld Sizing Performance............................8.3

8.3 General Conclusions.................................................................................................8.4

9.0 References .......................................................................................................................9.1

Appendix A – Destructive Data Analysis for Dissimilar Metal Weld Pipe Specimens............... A.1

Appendix B – Destructive Analysis of Bottom Mounted Instrumentation Tube Samples .......... B.1

Appendix C – Inspection Plots for Dissimilar Metal Weld Samples.......................................... C.1

Appendix D – Block Hitograms for Dissimilar Metal Weld Samples......................................... D.1

Appendix E – Inspection Plots for Bottom-Mounted Instrumentation Samples ........................ E.1

Appendix F – Block Hitograms for Bottom-Mounted Instrumentation Tube Samples................F.1

Appendix G – PINC Data Compilation.....................................................................................G.1

Appendix H – U.S. Plant Field Experience with Alloy 600 Cracking......................................... H.1
x

Figures

1.1 Organization Chart for Steering Committee and Task Groups .......................................1.1

2.1 PINC Block 2.1 from Japan Nuclear Energy Safety Organization – Pressurizer 

Surge Line to Safe-End Dissimilar Metal Weld...............................................................2.2

2.2 PINC Block 2.2 from JNES – PZR Surge Line to Safe-End Dissimilar Metal Weld.........2.3

2.3 PINC Block 2.3 from JNES – PZR Surge Line to Safe-End Dissimilar Metal Weld.........2.3

2.4 PINC Block 2.4 from JNES – PZR Surge Line to Safe-End Dissimilar Metal Weld.........2.4

2.5 PINC Block 2.5 from JNES – PZR Surge Line to Safe-End Dissimilar Metal Weld.........2.4

2.6 PINC Block 2.6 from JNES – PZR Surge Line to Safe-End Dissimilar Metal Weld.........2.5

2.7 PINC Block 2.9 from Swedish Qualification Center ........................................................2.5

2.8 PINC Block 2.10 from SQC............................................................................................2.6

2.9 PINC Test Blocks 2.1 through 2.3 – PZR Surge Line to Safe-End Dissimilar Metal 

Weld Test Blocks ...........................................................................................................2.6

2.10 PINC Test Blocks 2.4 through 2.6 Test Blocks – PZR Surge Line to Safe-End 

Dissimilar Metal Weld Test Blocks .................................................................................2.7

2.11 PINC Block 2.9 from Swedish Radiation Safety Authority ..............................................2.7

2.12 PINC Block 2.10 from SSM............................................................................................2.8

2.13 Coordinate System for PINC Test Blocks 2.1, 2.2, and 2.3 ............................................2.9

2.14 Coordinate System for PINC Test Blocks 2.4, 2.5, and 2.6 ............................................2.9

2.15 Coordinate System for PINC Test Block 2.9 from SSM/SQC .......................................2.10

2.16 Coordinate System for PINC Test Block 2.10 from SSM/SQC .....................................2.10

2.17 PINC 5.7 from PNNL – WNP-1 BMI Nozzle Penetration 1 ...........................................2.11

2.18 PINC 5.8 from PNNL – WNP-1 BMI Nozzle Penetration 2 ...........................................2.12

2.19 PINC 5.9 from PNNL – WNP-1 BMI Nozzle Penetration 3 ...........................................2.12

2.20 PINC 5.10 from PNNL – WNP-1 BMI Nozzle Penetration 4 .........................................2.13

2.21 PINC 5.11 from PNNL – WNP-1 BMI Nozzle Penetration 5 .........................................2.13

2.22 PINC 5.12 from PNNL – WNP-1 BMI Nozzle Penetration 6 .........................................2.14

2.23 PINC 5.13 from JNES – BMI Nozzle Test Block No. 1 .................................................2.15

2.24 PINC 5.14 from JNES – BMI Nozzle Test Block No. 2 .................................................2.16

2.25 PINC 5.15 from JNES – BMI Nozzle Test Block No. 3 .................................................2.16

2.26 PINC 5.16 from JNES – BMI Nozzle Test Block No. 4 .................................................2.17

2.27 PINC 5.1 from KINS – BMI Nozzle Test Block .............................................................2.17

2.28 PINC 5.2 from KINS – BMI Nozzle Test Block .............................................................2.18

2.29 PINC 5.3 from KINS – BMI Nozzle Test Block .............................................................2.18

2.30 Extra Block from KINS – BMI Nozzle Test Block..........................................................2.19

2.31 PINC 5.1 from KINS.....................................................................................................2.20
xi

2.32 PINC 5.2 from KINS.....................................................................................................2.21

2.33 PINC 5.3 from KINS.....................................................................................................2.22

2.34 PINC 5.6 from SSM/SQC.............................................................................................2.23

2.35 PINC 5.7 from NRC/PNNL...........................................................................................2.23

2.36 PINC 5.8 from NRC/PNNL...........................................................................................2.24

2.37 PINC 5.9 from NRC/PNNL...........................................................................................2.24

2.38 PINC 5.10 from NRC/PNNL .........................................................................................2.25

2.39 PINC 5.11 from NRC/PNNL .........................................................................................2.25

2.40 PINC 5.12 from NRC/PNNL .........................................................................................2.26

2.41 Test Blocks PINC 5.13 through 5.16 from JNES..........................................................2.26

2.42 Seal Weld Configuration for PINC 5.13 through 5.16 from JNES .................................2.27

2.43 Coordinate System for PINC 5.1 through 5.3 from KINS..............................................2.27

2.44 Z Dimension for BMI Blocks.........................................................................................2.28

2.45 Coordinate System for PINC 5.1–5.3 ...........................................................................2.29

2.46 Coordinate System for PINC 5.6 – SSM/SQC F3.537.2...............................................2.30

2.47 Coordinate System for Test Blocks PINC 5.7–5.12......................................................2.30

2.48 Circumferential Coordinate System for Test Blocks PINC 5.13–5.16 ...........................2.31

2.49 Axial Coordinate System for Test Blocks PINC 5.13–5.16 ...........................................2.31

2.50 Example Flaw Coupon as Used for Test Blocks 5.1–5.3..............................................2.32

2.51 Example Weld Undercut Flaw as Used in Test Blocks 5.1–5.3 ....................................2.33

2.52 Flaw Placement in Test Block 5.3 ..................................................................................2.33

2.53 Weld Solidification Crack in Test Block 5.6 at 45 Degrees ...........................................2.35

2.54 Thermal Fatigue Cracks in Test Block 5.7....................................................................2.35

2.55 Penetrant Testing Results for Test Block 5.10 .............................................................2.36

2.56 BMI Test Blocks for Preparing SCC .............................................................................2.37

2.57 Procedure for Preparing Laboratory SCC in a Sample Piping Specimen .....................2.38

2.58 Example of Laboratory-Induced SCC in BMI Test Block (parallel to the weld)..............2.39

2.59 Example of Laboratory-Induced SCC in BMI Test Block (perpendicular to the 

weld)............................................................................................................................2.39

3.1 Conventional Ultrasonic Testing.....................................................................................3.2

3.2 Use of Delays to Steer and Focus Ultrasonic Beams in Phased Array Transducers ......3.2

3.3 Time-of-Flight Diffraction Technique ..............................................................................3.4

3.4 Eddy Current Diagram ...................................................................................................3.5

3.5 Four-Probe Potential-Drop Measurement ......................................................................3.6

4.1 Scoring Procedure for PINC Round Robins ...................................................................4.1
xii

4.2 Probability of Detection versus Scoring Tolerance for Teams and Flaws for DMW 

Round Robin..................................................................................................................4.3

4.3 Probability of Detection versus Scoring Tolerance for All Teams and Flaws in BMI 

Round Robin..................................................................................................................4.4

4.4 Scoring Inspection Results of Test Block 2.9 with 10-mm Tolerance .............................4.7

4.5 Methodology for Determining Singularity or Multiplicity of Linear Surface Flaws ............4.9

4.6 Test Block 5.1 –Individual Flaws ..................................................................................4.10

4.7 Test Block 5.1 – Individual Flaws Combined Under Rules of IWA-3400.......................4.10

4.8 DMW Probability of Detection and False Call Rates in DMW Test Blocks for the 

Inspection Techniques Showing Qualifications ............................................................4.13

4.9 Probability of Detection Plotted versus the Crack Depth in DMW Test Blocks..............4.18

4.10 Probability of Detection Curves for Detection Procedures in DMW Test Blocks ...........4.19

4.11 Probability of Detection Curves for Flaw Orientation in DMW Test Blocks ...................4.21

4.12 Probability of Detection Regression for Examinations of the Penetration Tube 

Interiors in BMI Test Blocks .........................................................................................4.25

4.13 Probability of Detection Regressions for Cross-Coil Eddy-Current Techniques with 

95% Confidence Intervals in BMI Test Blocks ..............................................................4.27

4.14 Probability of Detection Regressions in BMI Test Blocks for Array Eddy-Current 

Techniques ..................................................................................................................4.28

4.15 Probability of Detection Regressions in BMI Test Blocks for Potential-Drop 

Techniques ..................................................................................................................4.28

4.16 Probability of Detection Regression in BMI Test Blocks for Adaptive Phased Array 

Technique....................................................................................................................4.29

4.17 BMI Flaw Probability of Detection versus Flaw Length for Each Flaw Fabrication 

Technique....................................................................................................................4.31

4.18 BMI Flaw Probability of Detection versus Flaw Depth for Each Flaw Fabrication 

Technique....................................................................................................................4.31

4.19 Depth Sizing Regression in DMW Test Blocks.............................................................4.34

4.20 Dissimilar Metal Weld Depth Sizing Results for Team 38.............................................4.39

4.21 Results of Length Sizing on Circumferential Flaws in DMW Test Blocks......................4.42

4.22 Results of Length Sizing on Axial Flaws in DMW Test Blocks......................................4.48

4.23 Depth Sizing Results for BMI Surfaces ........................................................................4.55

4.24 Length-Sizing Results for Cross-Coil Eddy-Current Probes in BMI Test Blocks ...........4.56

4.25 Length Sizing Results for Array Eddy-Current Probes in BMI Test Blocks ...................4.57

4.26 Length Sizing Results for Potential-Drop Techniques in BMI Test Blocks ....................4.57

4.27 Length-Sizing Results for Adaptive Phased Array Ultrasound Techniques in BMI 

Test Blocks ..................................................................................................................4.58

5.1 Probability of Detection Curves from Round Robin and Curves Used for 

Probabilistic Fracture Mechanics Evaluations ................................................................5.2
xiii

6.1 DMW Failures of Pressurizer Nozzles in Tsuruga 2 .......................................................6.9

6.2 DMW Failure of Steam Generator Nozzle in Mihama 2................................................6.10

6.3 DMW Failure of Reactor Vessel Outlet Nozzle in Ohi 3................................................6.12

6.4 Failure of CRDM J-Groove Weld in Ohi 3 ....................................................................6.13

6.5 Spurious ECT Indication Found in BMI of Takahama...................................................6.14

7.1 Three Cracked Weld Metal Coupons with Thermal Fatigue Crack on the Left, 

Weld Solidification Crack on the Right, and Laboratory Stress Corrosion Crack at 

Center............................................................................................................................7.2

7.2 Artificially Grown Stress-Corrosion Crack in Coupon of Alloy 182 Weld Metal ...............7.2

7.3 Eddy Current Response from Laboratory-Grown Stress Corrosion Crack in Alloy 

182 Weld Metal..............................................................................................................7.4

7.4 Signal-to-Noise Analysis of Eddy Current Response from Laboratory-Grown 

Stress Corrosion Crack in Alloy 182 Weld Metal ............................................................7.4

7.5 Eddy Current Response from Thermal Fatigue Crack in Alloy 182 Weld Metal ..............7.5

7.6 Signal-to-Noise Analysis of Eddy Current Response from Thermal Fatigue Crack 

in Alloy 182 Weld Metal .................................................................................................7.5

7.7 Eddy Current Response from Weld Solidification Crack in Alloy 182 Weld Metal...........7.6

7.8 Signal-to-Noise Analysis of Eddy Current Response from Weld Solidification 

Crack in Alloy 182 Weld Metal .......................................................................................7.6

7.9 Eddy Current Response Distributions for 13 Crack Indications in North Anna 2 

Nozzle 31, 3 Manufactured Cracks, and 9 Electro-Discharge Machined Notches ..........7.9
xiv

Tables

2.1 Test Block Categories....................................................................................................2.1

2.2 Index of Photographs, Drawings, and Coordinate Systems for PINC Test Blocks in 

Mid-Thickness Dissimilar Metal Weld Round-Robin Test ...............................................2.1

2.3 Dissimilar Metal Weld Test Block Dimensions................................................................2.2

2.4 Test Blocks for BMI Round Robin ................................................................................2.11

2.5 Available Cracks in the PINC Mid-Thickness Dissimilar Metal Weld Test Blocks as 

Provided by JNES and SQC ........................................................................................2.41

2.6 Round-Robin Test Blocks for Mid-Thickness Dissimilar Metal Weld.............................2.42

2.7 Flaws Used for Surface Inspections in BMI Test Blocks...............................................2.42

2.8 Flaws Used for Penetration Tube Inspections in BMI Test Blocks................................2.43

4.1 Test Block PINC 2.9 Inspection Results.........................................................................4.6

4.2 Detection Results for Sample Inspection of PINC Test Block 2.9...................................4.8

4.3 DMW POD by Teams with 10-mm Tolerance in DMW Test Blocks..............................4.12

4.4 Probability of Detection by Flaws in DMW Test Blocks ................................................4.14

4.5 Summary of False Calls in DMW Test Blocks ..............................................................4.14

4.6 Individual Team PODs Listed versus DMW Flaw Depth Sorted by Team Number.......4.16

4.7 Individual Team PODs Listed versus DMW Flaw Depth Sorted by ID Technique.........4.16

4.8 Individual Team PODs Listed versus DMW Flaw Depth Sorted by OD Technique.......4.16

4.9 Probability of Detection Summary for Procedures in DMW Test Blocks .......................4.17

4.10 Probability of Detection for Circumferential Flaws as a Function of Depth in DMW 

Test Blocks ..................................................................................................................4.20

4.11 Probability of Detection for Axial Flaws as a Function of Depth in DMW Test 

Blocks..........................................................................................................................4.21

4.12 Probability of Detection for Each Test Block in BMI Test Blocks ..................................4.23

4.13 Number of Baseline and Challenging Flaw Observations for Each Team in BMI 

Test Blocks ..................................................................................................................4.23

4.14 Probability of Detection Scores for Tube Examinations in BMI Test Blocks..................4.24

4.15 Probability of Detection Scores for Tube Examinations for Flaws Combined Using 

ASME Rules in BMI Test Blocks ..................................................................................4.24

4.16 Probability of Detection and False Call Rates for Each Team Using a 10-mm 

Tolerance Box in BMI Test Blocks ...............................................................................4.25

4.17 Probability of Detection Results in BMI Test Blocks for Baseline and Challenging 

Flaws with Upper and Lower 95% Confidence Levels..................................................4.26

4.18 Probability of Detection Regression Results for 5-, 10-, and 15-mm Flaws in BMI 

Test Blocks ..................................................................................................................4.26

4.19 BMI Flaw Probability of Detection and Important Parameters ......................................4.30
xv

4.20 Summary of Depth Sizing Results on All Flaws in DMW Test Blocks...........................4.33

4.21 Dissimilar Metal Weld Depth Sizing Results for Team 16.............................................4.39

4.22 Summary of Length Sizing Results for Circumferential Flaws in DMW Test Blocks......4.40

4.23 Summary of Length Sizing Results for Axial Flaws in DMW Test Blocks......................4.41

4.24 Dissimilar Metal Weld Length Sizing Results for Team 16 ...........................................4.41

4.25 Length-Sizing Results for BMI Penetration Tube Examinations....................................4.54

4.26 Summary of Depth Sizing Results for BMI Surfaces ....................................................4.54

4.27 Length-Sizing Results for Surface Examinations in BMI Test Blocks ...........................4.56

5.1 Probabilistic Fracture Mechanics Results for Individual Team PODs from PINC for 

DMW..............................................................................................................................5.3

6.1 Risk-Damage Matrix ......................................................................................................6.2

6.2 Defect Characteristics Found Significant for Ultrasonic Testing .....................................6.5

6.3 Defect Characteristics Found Significant for Eddy Current Testing ................................6.5

6.4 SG Nozzle DMW Inspection Results............................................................................6.11

7.1 North Anna 2 Eddy Current Responses and Destructive Validation ...............................7.7

xvii

Executive Summary

The U.S. Nuclear Regulatory Commission (NRC) executed agreements with organizations in 

Japan, Sweden, South Korea, Finland, and the United States to establish the Program for the 

Inspection of Nickel Alloy Components (PINC). The objectives of the PINC program participants 

are:

• To join together for cooperative research.

• To address the problem of primary water stress corrosion cracking (PWSCC), a form of 

degradation observed in some pressurized water reactor pressure boundary components. 

Specifically, the research was designed primarily to understand the morphology of PWSCC 

cracks, to assess nondestructive evaluation (NDE) techniques for detecting and 

characterizing cracks with such morphology, and to distinguish them from other types of 

flaws or other innocuous weld conditions. This program provided data that enabled a 

quantitative assessment of available NDE techniques to detect and size PWSCC in nickelbased alloys.

The PINC participants identified and ranked all PWSCC and component configurations for 

consideration for study in the PINC framework. The three areas that were ranked highest were 

bottom-mounted instrumentation (BMIs), dissimilar metal welds (DMWs), and control rod drive 

mechanisms (CRDMs). The BMIs were identified as top priority because it is not easy to 

replace a reactor pressure vessel bottom head and repairs are challenging, as was learned at 

the South Texas Project. The issue of dissimilar metal welds was considered to also be very 

important based on the cracking that had been experienced at V.C. Summer and Ringhals. The

CRDM issue was also assigned a high priority because of the number of plants world wide that 

have experienced cracking and the Davis-Besse event. However, the low availability of CRDM 

assemblies and the need to complete the PINC round robin in a timely fashion made it possible 

to address only the dissimilar metal welds and the bottom-mounted instrumentation nozzles. 

Dissimilar metal piping weld assemblies were available immediately so this round-robin study 

was able to start first.

The PINC was focused on studying two aspects of PWSCC. One was to document the crack 

morphology and NDE responses of PWSCC and compare these data with methods to simulate 

PWSCC for NDE capability studies. The other was to study the capability of various NDE 

methods to detect and size the through-wall extent of PWSCC. The studies involving NDE 

capability were carried out as international round robins with PINC participants. The results are,

in some cases, discussed with reference to the requirements of ASME Code, Section XI, 

Appendix VIII. It should be noted that the round robin study was not designed to constitute an 

Appendix VIII compliant demonstration.

This report describes the efforts of the PINC participants to assess the capability of NDE 

techniques to detect and characterize the through-wall depth and length of PWSCC in dissimilar 

metal welds and in bottom-mounted instrumentation penetration tubes and J-groove welds. 

Based upon the information that was developed from conducting round-robin exercises on 

DMW samples and BMI nozzles, this study provided the following conclusions and 

recommendations. The conclusions and recommendations presented in this report are based 
xviii

on the probability of detection, false call probability, and sizing statistics measured in the round 

robin studies. 

Probability of Detection Performance

Dissimilar Metal Weld Pipe Specimen Round Robin Probability of Detection Performance

The conclusions that may be inferred from the experimental results for the dissimilar metal 

welds pipe specimens are as follows:

1. Conclusion: Eddy current inspection from the cracked surface demonstrated the highest 

probability of detection (POD) for all flaws in the DMW round robin.

• PINC Recommendation: The results of this study show that eddy current inspection 

are the preferred detection technique for dissimilar metal welds, where conditions 

allow access to the same surface from which the crack originates and where the 

surface conditions allow for ECT testing.

2. Conclusion: The POD results for the DMW round robin show significant variability in POD 

performance based upon technique, procedure, and team.

• PINC Recommendation: The results illustrate the usefulness of performance 

demonstration as a means to help ensure the reliability of DMW inspections.

3. Conclusion: The potential-drop techniques that were used in the DMW round robin 

demonstrated the lowest POD performance.

• PINC Recommendation: The potential-drop techniques used in the DMW round robin 

need further development before use as detection techniques in inservice inspection 

programs.

Bottom-Mounted Instrumentation Round Robin Probability of Detection Performance

The conclusions that may be inferred from the experimental results for the bottom mounted 

instrumentation tube specimens are as follows

1. Conclusion: Inspections using a single cross-coil eddy-current probe achieved a high POD 

and a low false call rate. These examinations were performed with multiple frequencies, 

with the highest frequency used being 300–400 kHz.

• PINC Recommendation: The results of this study suggest that single cross-coil 

probe eddy current using frequencies of 300–400 kHz are the preferred method for 

finding surface-breaking flaws in BMI J-groove welds.

2. Conclusion: Inspections using adaptive phased array ultrasound were able to detect all 

baseline difficulty flaws and none of the challenging flaws (baseline and challenging flaws 

are defined in Section 4.2.2).
xix

• PINC Recommendation: While adaptive phased array ultrasound was slightly less 

effective than eddy current testing, the results of this study suggest that adaptive 

phased array ultrasound can be effectively used to find flaws in BMI welds.

3. Conclusion: The inspections using array eddy-current techniques used in this BMI round 

robin study had a reduced POD and a much higher false call rate compared to the higher 

frequency cross-coil ECT examinations.

• PINC Recommendation: The results of the BMI round-robin study show that the 

procedures using array ECT probes operating at 100–200 kHz used in this round 

robin test require further development for detection in inservice inspection programs.

4. Conclusion: The closely coupled potential-drop technique was able to detect thermal 

fatigue flaws and SCC flaws with a POD of 50%. For weld solidification flaws, the POD was 

0%. No false calls were made by the inspectors using this technique. 

• PINC Recommendation: The results of the BMI round-robin study show that the 

closely coupled potential-drop technique requires further development before it can 

be used for detection of flaws in inservice inspection programs.

5. Conclusion: Induced-current potential drop was used on only one baseline difficulty test 

block and two challenging test blocks, possibly skewing the results. There are not enough 

inspections on baseline difficulty test blocks to draw meaningful conclusions on the POD 

performance on these test blocks.

• PINC Recommendation: Further testing needs to be performed to determine if ICPD 

can be used for inservice inspection.

Sizing Performance

Dissimilar Metal Weld Pipe Specimen Sizing Performance

The conclusions that may be inferred from the experimental results indicate the following:

1. Conclusion: None of the NDE techniques in this round robin study demonstrated the 

capability to accurately depth size flaws in dissimilar metal welds to ASME Section XI code 

standards. The average depth sizing for all techniques tended to slightly undersize the 

flaws and had standard deviations and RMSE errors of approximately 7 mm. Two 

techniques came close to meeting ASME Section XI standards.

• PINC Recommendation: The depth sizing of flaws should be improved. The use of 

phased array UT and conventional ultrasound together showed the most promise.

2. Conclusion: Eight teams length-sized flaws with an RMSE within the ASME Section XI 

standard of 0.75 inch (19 mm). Teams that used phased array UT and eddy current 

achieved higher accuracy than teams that used conventional UT and potential-drop 

techniques.
xx

• PINC Recommendation: Phased array UT or a combination of eddy-current 

techniques and conventional UT are the preferred method for length sizing.

Bottom-Mounted Instrumentation Weld Sizing Performance

The conclusions that may be inferred from the experimental results indicate the following:

1. Conclusion: Cross-coil eddy current, adaptive phased array ultrasound, and closely 

coupled probe potential-drop techniques were able to accurately length-size the flaws in the 

J-groove welds (RMSE of 2.45–4.70 mm). 

• PINC Recommendation: These techniques can be used to length-size flaws in BMI 

J-groove welds.

2. Conclusion: The test block geometry made depth-sizing using ultrasound difficult, and not 

enough data was collected in this round-robin test to accurately determine the effectiveness 

of the depth-sizing techniques.

• PINC Recommendation: More work should be performed to determine the depthsizing capabilities of the various techniques.

Based on the round-robin tests, including detection and length-sizing capabilities, several 

techniques need to be used in tandem for flaw detection and sizing in dissimilar metal welds 

comparable to ASME Section XI. Eddy current testing had the highest POD performance, and a 

combination of conventional and phased array ultrasound was the only technique that provided 

RMSE depth-sizing capabilities close to Section XI requirements. It is worth noting that eddy 

current is not universally applicable for dissimilar metal welds, as many welds are in locations or 

have surface conditions that do not allow for ID inspections. If ID access is not possible, a 

combination of phased array ultrasound and conventional ultrasound appears to be the most 

accurate alternative. 

General Conclusions

1. Conclusion: The surface conditions, access to both sides of the weld, and inspection 

conditions for the PINC specimens provided the inspectors with less challenging conditions 

than would be expected in field inspections of nuclear power plant components.

• PINC Recommendations: The probability of detection and sizing results should be 

considered an upper bound for the inspection techniques. 

2. Conclusion: Inspection procedures and teams with formal NDE qualifications tended to 

have a higher POD and lower false call rate than teams and procedures with no formal 

qualifications.

• PINC Recommendation: As NDE inspections are carried out by qualified inspectors, 

the probability of detection and length sizing results for the qualified teams and 

procedures should be considered the most representative of field inspections. 
xxi

3. Conclusion: An analysis of the POD curves generated by the PINC round robin testing 

showed that the procedures improved safety by factors of 1.1 to 1.5 for a 10 year interval 

and by factors of 1.3 to 2.1 for a four year interval. (These safety factors use the crack 

growth rates for stress corrosion cracks in stainless steel welds.)

• PINC Recommendation: Effective NDE techniques may need to be combined with 

inspection intervals selected based on the crack growth rates. The analysis should 

be refined using PWSCC crack growth rates in nickel-based alloys.
xxii
xxiii

Acknowledgments

There have been significant contributions made by a number of people and organizations to 

accomplish this study. The authors acknowledge special appreciation to Deborah Jackson and 

Carol Moyer of the NRC for their leadership in helping organize and start the PINC and Iouri 

Prokofiev for his leadership. George Schuster (retired) of Pacific Northwest National Laboratory 

(PNNL) was the initial leader and chairman of the Data Analysis Group and the Atlas Information Tool task group. The authors also acknowledge the hard work and effort of the round-robin 

invigilators who reviewed inspection procedures and monitored the work of inspection teams, 

and they thank members of the Data Analysis Group who worked diligently to ensure that the 

very large set of data was correct and suggested the analysis that was performed. 

The following companies participated in the PINC dissimilar metal weld round robin and should 

be acknowledged for their significant contributions:

• European Inspection Teams

a. FORCE Institute

b. Wesdyne TRC (two teams)

c. Tecnatom

d. VTT (two teams)

• Korean Inspection Teams

a. Korea Plant Service and Engineering Company

b. Doosan Heavy Industries

c. Sean-UMI-ANSCO

d. Seoul National University

e. Korea Hydro & Nuclear Power Company

• Japanese Inspection Teams

a. Tohoku University – Three Teams

− Fracture and Reliability Research Institute

− Institute of Fluid Science

− Department of Nanomechanics

b. Mitsubishi Heavy Industries, Ltd., Takasago Research & Development Center – Two 

Teams

− Ultrasonic testing team

− Eddy-current testing team

The following companies participated in the PINC BMI weld round robin and are acknowledged 

for their significant contributions:

• European Inspection Team

– Wesdyne TRC
xxiv

• Korean Inspection Team

– Korea Plant Service and Engineering Company

• Japanese Inspection Teams

a. Tohoku University – Three Teams 

− Fracture and Reliability Research Institute

− Institute of Fluid Science

− Department of Nanomechanics

b. Mitsubishi Heavy Industries, Ltd, Takasago Research & Development Center – Two 

Teams

− Ultrasonic testing team

− Eddy-current testing team

• United States Inspection Team

– The Electric Power Research Institute

The authors acknowledge the following organizations who have participated in the PINC.

Organizations from Japan

• Japan Nuclear Energy Safety Organization (JNES)

• Japan Power Engineering and Inspection Corporation (JAPEIC)

• Tohoku University

• Mitsubishi Heavy Industries, Ltd (MHI)

• KANSAI Electric Power Company

Organizations from Europe

• Swedish Radiation Safety Authority (SSM)

• Swedish Qualification Centre (SQC)

• Wesdyne TRC, Sweden

• VTT, Finland

• Force Institute, Denmark

• Wesdyne TRC, Sweden

• Tecnatom, Spain

• Helsinki University of Technology
xxv

Organizations from South Korea

• Korea Institute of Nuclear Safety (KINS)

• Korea Atomic Energy Research Institute (KAERI)

• Korea Plant Services & Engineering Co. Ltd. (KPS)

• Sungkunkwan University

• Korea Electric Power Research Institute (KEPRI)

Organization from the United States

• Electric Power Research Institute

Finally, the authors thank Ms. Kay Hass for typing and editing the seemingly endless versions 

and revisions of this document.
xxvi
xxvii

Acronyms and Abbreviations

AC alternating current

ACPD alternating current potential drop method

ASME American Society of Mechanical Engineers

BMI bottom-mounted instrumentation

BWR boiling water reactor

CCPPD closely coupled probe potential drop method

Circ circumferential

COD crack-opening displacement

conv.ut conventional ultrasonic testing

CRDM control rod drive mechanism

DAG Data Analysis Task Group

DC direct current

DCPD direct current potential drop method

DE destructive evaluation

DMW dissimilar metal welds

ec eddy current testing

ECT eddy current testing

EdF Électricité de France

EDM electro-discharge machining

em electromagnetic inspection techniques

EPRI Electric Power Research Institute

FCP false call probability

ICPD induced-current potential-drop method

ID inner diameter

IDSCC interdendritic stress corrosion cracking

ISI inservice inspection

JAPEIC Japan Power Engineering and Inspection Corporation

JNES Japan Nuclear Energy Safety Organization

KAERI Korea Atomic Energy Research Institute

KEPRI Korea Electric Power Research Institute

KINS Korea Institute of Nuclear Safety

KPS Korea Plant Services & Engineering Co. Ltd.

Len length

LOCA loss-of-coolant accident

Meas measured

MHI Mitsubishi Heavy Industries, Ltd
xxviii

NA2 North Anna Unit 2

NDE nondestructive evaluation

No. number

NRC Nuclear Regulatory Commission

OD outer diameter

PD potential drop method

PINC Program for the Inspection of Nickel Alloy Components

PNNL Pacific Northwest National Laboratory

POD probability of detection

PWR pressurized water reactor

PWSCC primary water stress corrosion cracking

PZR pressurizer

RMSE root mean square error

RPV reactor pressure vessel

RVHP reactor vessel head penetration

SB surface-breaking

SCC stress corrosion cracking

SKI Swedish Nuclear Power Inspectorate

SQC Swedish Qualification Center

SSM Swedish Radiation Safety Authority

std dev standard deviation

TFC thermal fatigue cracks

TG Task Group

TOFD time-of-flight diffraction

Tol tolerance

UE Uddcomb Engineering

USP ultrasonic shot peening

UT ultrasonic testing

WJP water jet peening

WSC weld solidification cracks
1.1

1.0 Introduction

Stress corrosion cracking in nickel alloy materials has occurred world-wide in a number of 

nuclear power plants and is seen as a serious issue affecting the reliable and safe operation of 

nuclear power plants. Stress corrosion cracking in dissimilar metal welds is often referred to as 

primary water stress corrosion cracking (PWSCC) or interdendritic stress corrosion cracking 

(IDSCC). For this report the term primary water stress corrosion cracking (PWSCC) will be 

used. PWSCC degradation has resulted in breaches of the pressure boundary and caused

leakage in several dissimilar metal welds (Bamford 2000; Bamford et al. 2002; Jenssen et al. 

2002a; Jenssen et al. 2002b), control rod drive mechanism nozzle penetration weldments (Frye 

et al. 2002; Lang 2003), and bottom-mounted instrumentation nozzle penetration weldments 

(Halpin 2003). Reliable detection of PWSCC is challenging because the geometries, materials, 

and configurations are not conducive to reliable nondestructive evaluation (NDE) and the 

service-induced cracking exhibits very tight and very complex branching in the nickel-based 

welds.

The U.S. Nuclear Regulatory Commission (NRC) executed agreements with organizations in 

Japan, Sweden, South Korea, the United States, and Finland to establish the Program for the 

Inspection of Nickel Alloy Components (PINC). The objectives of the PINC program participants 

are:

• To join together for cooperative research.

• To address the problem of PWSCC. Specifically, the research was designed primarily to 

understand the morphology of PWSCC cracks, to assess NDE techniques for detecting and 

characterizing cracks with such morphology, and to distinguish them from other types of 

flaws or other innocuous weld conditions. This program provided data that enabled a 

quantitative assessment of available NDE techniques to detect and size PWSCC in 

dissimilar metal welds. 

PINC program participants organized the project into a Steering Committee, two task groups, 

and the Data Analysis Group, as illustrated in the following organizational chart (Figure 1.1).

PINC Steering 

Committee

Dr. Iouri ProkofievChairman

Task Group on 

NDE

Dr. Steven DoctorChairman

Data Analysis

Group

Dr. Stephen CumblidgeChairman

Task Group on 

PINC Atlas

Dr. Robert HarrisChairman

Figure 1.1 Organization Chart for Steering Committee and Task Groups
1.2

1.1 PINC Steering Committee

Steering Committee Members

Deborah Jackson was the original Chairman from the NRC, in 2004 she was replaced by 

Carol Moyer, and in 2007 Carol Moyer was replaced by Iouri Prokofiev 

Katsumi Kono

Suck-Chull Kang was the initial representative from KINS. In May 2007 he was replaced 

by Myungho Song and in May 2008 he was replaced by Haedong Chung

Pentti Kauppinen

Peter Merck

Naoki Chigusa was the initial representative from Kansai Electric Power Company. He 

was replaced by Mr. Hiraoka.

Masanobu Iwasaki was the substitute for Dr. Chigusa. In June 2008, he was replaced 

by Mr. Taniguchi.

Tetsuo Shoji

Jack Spanner

Esa Leskelä

Rob Harris

Non-Voting Members

Steven Doctor

Stephen Cumblidge

The Steering Committee of the Program provides guidance for the project and its 

implementation and:

• Advises the Task Groups on program implementation and recommends related actions.

• Monitors the program progress, collects, coordinates, and assimilates the results of projects 

(Task Groups) addressing specific aspects of the problem, and promotes practical 

implementation of program results at the national level.

• Provides a forum for exchanging information among group members on related work 

underway and planned activities. The Steering Committee develops strategies to deal with 

matters requiring coordination with members. 

• Assures that the efforts of the Task Groups and of the program as a whole remain focused 

on specific technical issues that have been agreed to by PINC members as well as ensuring 

that the work is progressing to an agreed upon time schedule.

• Provides a final report documenting the results of this program and providing specific 

recommendations for inspection of PWSCC.
1.3

1.2 Task Group on NDE

Task Group (TG) NDE Members

Steven Doctor – Chairman

Ichiro Komura

Katsumi Kono

Kwangsik Yoon

Kyungcho Kim

Sung Sik Kang

Pentti Kauppinen

Peter Merck

Tommy Zettervall

Shuji Tanioka

Jack Spanner

This Task Group (TG)-NDE has the following objectives:

• Develop designs of round-robin studies that need to be conducted in order to quantify the 

effectiveness of NDE for the detection and characterization of PWSCC.

• Review and assess methods to simulate the NDE responses from implanted flaws that will 

mimic the NDE response from service-induced PWSCC for use in round-robin studies.

• Review available mockups for use in the round-robin studies and, if new assemblies are 

needed, ensure that they are developed.

• Develop a test plan for each intended round-robin study.

• Coordinate the PINC inspection teams so that a schedule can be developed for circulating 

the assemblies and ensure it is followed.

• Use invigilators to oversee the round-robin inspections in each country and to ensure 

uniformity of guidance for each team.

• Coordinate receipt of inspection results.

1.3 Task Group on PINC Atlas

Task Group Atlas Members

Robert Harris – Chairman

Seiji Asada 

Joo Youl Hong

Tae Hyun Lee

Iouri Prokofiev

Brian Rassler

Myung Ho Song

Boyd Taylor
1.4

Kwangsik Yoon

Masanobu Iwasaki

Kyungcho Kim

Sung Sik Kang

Tetsuo Shoji

Shuji Tanioka

Hännu Hanninen

Karen Gott

The objective of the TG-Atlas technical subgroup is to produce a final product of the PINC 

program that is an electronic resource of information on PWSCC in nickel-based alloys used in 

nuclear power plant applications. This will include documenting the material that has been 

generated in support of an improved understanding of (1) the morphology of PWSCC, (2) NDE 

responses to PWSCC, and (3) the capability of NDE to reliably detect and accurately size 

PWSCC.

• The TG-Atlas group is taking the following as input:

– Results of the activities of the other task groups

– Presentations of PINC members

– Submissions from PINC members

– Available open literature

• The TG-Atlas will produce an Atlas in electronic form as output that will be provided to all 

PINC participants.

• The Atlas will be user-friendly and permit additions by users.

• The Atlas will document the following:

– PWSCC morphology

– PWSCC NDE results from real PWSCC and simulated PWSCC

– Round-robin test results

– To the extent practicable, contrasting morphology and NDE results from other types of 

cracking and noise sources that are likely to be confused with PWSCC

– References and links to the open literature.

1.4 Data Analysis Group

Data Analysis Group Members

Stephen Cumblidge – Chairman 

Steven Doctor, Invigilator U.S.

Pat Heasler 

Peter Merck

Tommy Zetterwall, Invigilator Europe
1.5

Ichiro Komura, Invigilator Japan

Kazunobu Sakamoto

Kyung-Cho Kim, Invigilator Korea

Myung Ho Song

Yongsik Kim

Sung Sik Kang

Pentti Kauppinen

Jack Spanner

Anders Brunn

This group is responsible for:

• Coordinating the analysis of the data that was generated during the round-robin trials 

conducted under TG-NDE

• Coordinating the need for oversight of destructive testing

• Assembling the data and information for inclusion into the Atlas

• Developing a final report on the round-robin trials for submitting to the Steering Committee.

The PINC surveyed the program participants to identify and rank all PWSCC and component 

configurations for consideration to be studied in the PINC framework. The three areas that were 

ranked highest were the bottom-mounted instrumentation, dissimilar metal piping welds, and 

control rod drive mechanisms. The bottom-mounted instrumentation (BMI) areas were identified 

as top priority because it is not easy to replace a reactor pressure vessel bottom head and 

repairs are challenging, as learned at the South Texas Project nuclear power plant. The issue

of dissimilar metal welds (DMWs) was considered to also be very important, based on the 

cracking experienced at the V.C. Summer and Ringhals plants. The control rod drive 

mechanism (CRDM) issue was also ranked high because of the Davis-Besse event and the 

number of plants worldwide that have experienced cracking. However, the limited availability of 

CRDM assemblies and the need to complete the PINC round robin in a timely fashion made it 

possible to address only the DMWs and the BMI nozzles. It was also thought that the NDE 

techniques used for BMIs would be used on CRDMs and, as a result, would be addressing the 

CRDM inspection issues. DMW assemblies were available immediately, so this round-robin 

study was able to start first. 

The PINC program focused on studying two aspects of PWSCC: (1) document the crack 

morphology of PWSCC and (2) study the capability of various NDE methods to detect and size 

the through-wall extent of PWSCC. The studies involving NDE capability were carried out as 

international round robins with PINC program participants. 

This report documents the study of NDE inspection capability to detect and measure the length

and through-wall extent of PWSCC in DMWs. The report is organized as follows.
1.6

Section 1 provides introductory material and explains the organization of the PINC program. 

Section 2 describes the test blocks used by the PINC program, including photographs of the test 

blocks, schematic drawings of product forms, and dimensions of the test blocks. Section 2 also 

gives the coordinate system used in the round-robin test. Section 3 describes the nondestructive testing techniques used to examine the test blocks in the round-robin trials. Section 4

describes the scoring procedure used for the analysis in this report, the information on 

probability of detection (POD) results, and the sizing performance for the NDE techniques/ 

procedures used. Section 5 provides a discussion on how the POD results relate to the integrity 

of the systems. Section 6 contains the experiences in the international community with cracking 

in nickel-based components in reactors. Section 7 compares the eddy current responses found 

for the various flaw types with PWSCC found in the North Anna 2 reactor pressure vessel head. 

Section 8 discusses the results and highlights the conclusions and recommendations that can 

be drawn.
2.1

2.0 Test Block Descriptions

This section of the report describes the test blocks used for conducting the PINC round-robin 

tests. Section 2.1 describes the test blocks used for the dissimilar metal weld tests. The test 

blocks used in the bottom-mounted instrumentation tube tests are described in Section 2.2. 

Section 2.3 describes the flaw implantation procedures used to produce the test blocks.

Section 2.4 describes the flaw locations in the test blocks.

2.1 Dissimilar Metal Weld Round-Robin Test Blocks

Participants in the PINC have offered more than 30 test blocks for use in round-robin tests of 

NDE effectiveness. The test blocks used in the PINC round robin tests have 68 cracks in 

nickel-base weld metal that are intended to simulate PWSCC in a variety of component 

geometries. The test blocks were divided into two categories that were circulated, inspected, 

and analyzed separately. These two categories are described in Table 2.1.

Table 2.1 Test Block Categories

Typical Component Thickness/Tube Inner Diameter (ID)

Mid-thickness dissimilar metal weld Wall thickness range 4.1 to 4.7 cm

Bottom-mounted instrumentation Tube ID < 2.8 cm

2.1.1 Available Mid-Thickness Dissimilar Metal Weld Test Blocks

Table 2.2 cross-references the photographs, drawings, and coordinate systems provided in this 

section for the dissimilar metal weld test blocks.

Table 2.2 Index of Photographs, Drawings, and Coordinate Systems for PINC Test 

Blocks in Mid-Thickness Dissimilar Metal Weld Round-Robin Test

PINC 

Reference No. Photograph Drawing

Coordinate

System

PINC 2.1 Figure 2.1 Figure 2.9 Figure 2.13

PINC 2.2 Figure 2.2 Figure 2.9 Figure 2.13

PINC 2.3 Figure 2.3 Figure 2.9 Figure 2.13

PINC 2.4 Figure 2.4 Figure 2.10 Figure 2.14

PINC 2.5 Figure 2.5 Figure 2.10 Figure 2.14

PINC 2.6 Figure 2.6 Figure 2.10 Figure 2.14

PINC 2.9 Figure 2.7 Figure 2.11 Figure 2.15

PINC 2.10 Figure 2.8 Figure 2.12 Figure 2.16
2.2

Table 2.3 presents the block dimensions used in the PINC dissimilar metal weld round robin. 

Each block is described as a cylindrical shell, even the nozzle blocks PINC 2.9 and 2.10. The x, 

y, and z dimensions describe the volume that could be inspected. For those inspections in 

which an inspection volume was not recorded, the volumes listed in Table 2.3 were used.

Table 2.3 Dissimilar Metal Weld Test Block Dimensions

Test 

Block

Thickness 

of Weld 

Butter, mm

Inner 

Radius, 

mm

Outer 

Radius 

Axial, 

mm

Axial 

Dimension, 

mm

Circumferential

Dimension, 

degrees

Inspection Volume

X1, 

mm

X2, 

mm

Y1, 

mm

Y2, 

mm

Zl, 

mm

Z2, 

mm

PINC 2.1 5 149 195 400 70.0 -119.1 119.1 -40 40 0 46

PINC 2.2 5 149 195 400 70.0 -119.1 119.1 -40 40 0 46

PINC 2.3 5 149 195 400 70.0 -119.1 119.1 -40 40 0 46

PINC 2.4 5 149 195 130 120.0 -204.2 204.2 -65 65 0 46

PINC 2.5 5 149 195 130 120.0 -204.2 204.2 -65 65 0 46

PINC 2.6 5 149 195 130 120.0 -204.2 204.2 -65 65 0 46

PINC 2.9 5 151 193 550 360.0 -1212.6 1212.6 -40 40 0 42

PINC 2.10 5 151 193 220 360.0 -1212.6 1212.6 -40 40 0 42

All available photographs for mid-thickness DMW test blocks are shown in this section.

Figure 2.1 PINC Block 2.1 from Japan Nuclear Energy Safety Organization (JNES) –

Pressurizer (PZR) Surge Line to Safe-End Dissimilar Metal Weld
2.3

Figure 2.2 PINC Block 2.2 from JNES – PZR Surge Line to Safe-End Dissimilar Metal 

Weld

Figure 2.3 PINC Block 2.3 from JNES – PZR Surge Line to Safe-End Dissimilar Metal 

Weld
2.4

Figure 2.4 PINC Block 2.4 from JNES – PZR Surge Line to Safe-End Dissimilar Metal 

Weld

Figure 2.5 PINC Block 2.5 from JNES – PZR Surge Line to Safe-End Dissimilar Metal 

Weld
2.5

Figure 2.6 PINC Block 2.6 from JNES – PZR Surge Line to Safe-End Dissimilar Metal 

Weld

Figure 2.7 PINC Block 2.9 from Swedish Qualification Center (SQC)
2.6

Figure 2.8 PINC Block 2.10 from SQC

2.1.2 Schematic Drawings for Mid-Thickness Dissimilar Metal Welds

Schematic drawings are provided to give product form configuration and dimensions for the test 

blocks. The three test blocks PINC 2.1, 2.2, and 2.3 have similar configurations, as shown in

Figure 2.9. The three test blocks PINC 2.4, 2.5, and 2.6 are likewise similar to each other, as 

shown in Figure 2.10. The dimensions of the SQC test block from the Swedish Radiation Safety 

Authority (SSM) are shown in Figure 2.11 and Figure 2.12. All units are in millimeters for 

Figures 2.9–2.12.

Figure 2.9 PINC Test Blocks 2.1 through 2.3 (JNES No. SH1 to SH3) – PZR Surge Line to 

Safe-End Dissimilar Metal Weld Test Blocks
2.7

Figure 2.10 PINC Test Blocks 2.4 through 2.6 Test Blocks (JNES No. ST1 to ST3) – PZR

Surge Line to Safe-End Dissimilar Metal Weld Test Blocks

Figure 2.11 PINC Block 2.9 from Swedish Radiation Safety Authority (SSM)
2.8

Figure 2.12 PINC Block 2.10 from SSM

2.1.3 Coordinate Systems for Mid-Thickness Dissimilar Metal Welds

This section documents the coordinate system for use in the mid-thickness dissimilar metal weld 

round-robin test. The reader should pay careful attention to the documented coordinate system 
2.9

for each test block. The convention for increasing X (always along the weld) and Y (always 

across the weld) varies from test block to test block.

Figure 2.13 shows the coordinate system for test blocks PINC 2.1, 2.2, and 2.3. The x-axis

increases clockwise when viewed from the stainless steel side and starts at the midpoint of the 

weld length. The y-axis increases toward the carbon steel side and starts at the weld centerline. 

The z-axis starts at the outside surface and increases into the part. Figure 2.14 shows the 

coordinate system for test blocks PINC 2.4, 2.5, and 2.6. This coordinate system uses the 

same convention as that shown in Figure 2.13.

For PINC 2.9, the x-axis increases counterclockwise around the part when viewed from the 

stainless steel side and starts at a scribe line on the part, as shown in Figure 2.15. The y-axis

starts at the DMW centerline and increases toward the stainless steel side. For PINC 2.10, the 

x-axis increases counterclockwise around the part when viewed from the stainless steel side 

and starts at a set of punch marks on the part, as shown in Figure 2.16.

Figure 2.13 Coordinate System for PINC Test Blocks 2.1, 2.2, and 2.3

Figure 2.14 Coordinate System for PINC Test Blocks 2.4, 2.5, and 2.6
2.10

Figure 2.15 Coordinate System for PINC Test Block 2.9 from SSM/SQC

Figure 2.16 Coordinate System for PINC Test Block 2.10 from SSM/SQC
2.11

2.2 Bottom-Mounted Instrumentation Round-Robin Test Blocks

Fourteen test blocks were selected for the round-robin test on NDE effectiveness for 

degradation in BMI nozzle penetration seal welds. Table 2.4 references the photographs and 

drawings for the test blocks. Test blocks 5.4 and 5.5 did not contain cracks in the weld metal 

and were not used in the round-robin test studies. An extra test block was provided by KINS, 

and was not in the original test design. Although the test block was optional, all teams were 

encouraged to try to include this test block in their inspection schedule. The extra test block is 

shown in Figure 2.30.

Table 2.4 Test Blocks for BMI Round Robin

ID Provider Test Block Photograph Drawing

PINC 5.1 KINS Penetration W17 Figure 2.27 Figure 2.31

PINC 5.2 KINS Penetration W22 Figure 2.28 Figure 2.32

PINC 5.3 KINS Penetration W46 Figure 2.29 Figure 2.33

PINC 5.6 SSM/SQC F3.537.2 No Photograph Figure 2.34

PINC 5.7 NRC/PNNL WNP1.BMI.1 Figure 2.17 Figure 2.35

PINC 5.8 NRC/PNNL WNP1.BMI.2 Figure 2.18 Figure 2.36

PINC 5.9 NRC/PNNL WNP1.BMI.3 Figure 2.19 Figure 2.37

PINC 5.10 NRC/PNNL WNP1.BMI.4 Figure 2.20 Figure 2.38

PINC 5.11 NRC/PNNL WNP1.BMI.5 Figure 2.21 Figure 2.39

PINC 5.12 NRC/PNNL WNP1.BMI.6 Figure 2.22 Figure 2.40

PINC 5.13 JNES BMI No 1 Figure 2.23 Figures 2.41 & 2.42

PINC 5.14 JNES BMI No 2 Figure 2.24 Figures 2.41& 2.42

PINC 5.15 JNES BMI No 3 Figure 2.25 Figures 2.41 & 2.42

PINC 5.16 JNES BMI No 4 Figure 2.26 Figures 2.41 & 2.42

Figure 2.17 PINC 5.7 from PNNL – WNP-1 BMI Nozzle Penetration 1
2.12

Figure 2.18 PINC 5.8 from PNNL – WNP-1 BMI Nozzle Penetration 2

Figure 2.19 PINC 5.9 from PNNL – WNP-1 BMI Nozzle Penetration 3
2.13

Figure 2.20 PINC 5.10 from PNNL – WNP-1 BMI Nozzle Penetration 4

Figure 2.21 PINC 5.11 from PNNL – WNP-1 BMI Nozzle Penetration 5
2.14

Figure 2.22 PINC 5.12 from PNNL – WNP-1 BMI Nozzle Penetration 6
2.15

Figure 2.23 PINC 5.13 from JNES – BMI Nozzle Test Block No. 1
2.16

Figure 2.24 PINC 5.14 from JNES – BMI Nozzle Test Block No. 2

Figure 2.25 PINC 5.15 from JNES – BMI Nozzle Test Block No. 3
2.17

Figure 2.26 PINC 5.16 from JNES – BMI Nozzle Test Block No. 4

Figure 2.27 PINC 5.1 from KINS – BMI Nozzle Test Block
2.18

Figure 2.28 PINC 5.2 from KINS – BMI Nozzle Test Block

Figure 2.29 PINC 5.3 from KINS – BMI Nozzle Test Block
2.19

Figure 2.30 Extra Block from KINS – BMI Nozzle Test Block

2.2.1 Schematic Drawings for BMI Test Blocks

Schematic drawings are provided to give product form configuration and dimensions for the test 

blocks. The first three test blocks from KINS have the configurations shown in Figures 2.31, 

2.32, and 2.33. The outside diameter of the BMI penetration tubes is 38 mm, and the inside 

diameter is 15.5 mm. PINC 5.6 has the configuration shown in Figure 2.34. The outside 

diameter of the tube is 47 mm; the inside diameter is 25 mm. The six test blocks PINC 5.7

through PINC 5.12 are similar to each other and, as shown in Figures 2.35 through 2.40, the 

outside diameter of the tube is 44 mm and the inside diameter is 15.9 mm. The four test blocks 

from JNES have a tube outside diameter of 38.1 mm and an inside diameter of 9.5 mm. Their 

configuration is shown in Figures 2.41 and 2.42. The units in Figures 2.31–2.33 are in inches, 

and the units in Figures 2.34–2.42 are in millimeters.
2.20

Figure 2.31 PINC 5.1 from KINS
2.21

Figure 2.32 PINC 5.2 from KINS
2.22

Figure 2.33 PINC 5.3 from KINS
2.23

Figure 2.34 PINC 5.6 from SSM/SQC

Figure 2.35 PINC 5.7 from NRC/PNNL
2.24

Figure 2.36 PINC 5.8 from NRC/PNNL

Figure 2.37 PINC 5.9 from NRC/PNNL
2.25

Figure 2.38 PINC 5.10 from NRC/PNNL

Figure 2.39 PINC 5.11 from NRC/PNNL
2.26

Figure 2.40 PINC 5.12 from NRC/PNNL

Figure 2.41 Test Blocks PINC 5.13 through 5.16 from JNES
2.27

Figure 2.42 Seal Weld Configuration for PINC 5.13 through 5.16 from JNES

2.2.2 Coordinate Systems for BMI Round Robin

This section documents the coordinate system for use in the bottom-mounted instrumentation 

nozzle penetration seal weld round-robin test. Figure 2.43 shows the coordinate system for the

first three test blocks, PINC 5.1 through 5.3. The circumferential axis increases clockwise when 

viewed from the top of the test block and starts at the 0-degree mark on the part. The radial 

axis starts at the center of the tube. The Z dimension for PINC 5.1 through 5.3 is measured 

from one of two areas as follows.

Figure 2.43 Coordinate System for PINC 5.1 through 5.3 from KINS
2.28

Figure 2.44 Z Dimension for BMI Blocks

For measuring defects in the J-groove weld, the Z dimension should be measured from the top 

(surface that is facing the reactor core) wetted surface that is clad, has a J-groove weld, and may 

or may not have buttering. The surface is curved; therefore, the Z dimension is reported relative 

to the angular location around the specimen. Figure 2.44 is an illustration of the Z dimension.

For measuring defects within the BMI tube, the Z dimension should be measured from the top of 

the tube down, as shown in Figure 2.45. 

Figure 2.46 shows the coordinate system for the fourth test block, PINC 5.6. The circumferential axis increases counterclockwise when viewed from the top of the test block and starts at 

the 0-degree mark on the part. The radial axis starts at the center of the tube.

For PINC test blocks 5.7–5.12, the zero Θ is defined by a hole drilled into the cladding, with Θ

going clockwise when looking down on the specimen, as shown in Figure 2.47. The radial axis 

starts at the center of the tube. For PINC text blocks 5.7–5.12, when defects in the J-groove 

weld are measured, the Z dimension should be measured from the top (the surface facing the 

reactor core) wetted surface that is clad, J-groove, and has buttering. The surface is curved; 

therefore, the Z dimension is reported relative to the angular location around the specimen.

For PINC test blocks 5.13–5.16, the circumferential axis increases clockwise around the part 

when viewed from the top of the test block and starts at the 0° punch mark direction on the side 

surface of the test block, as shown in Figure 2.48. The radial axis starts at the center of the tube.

For the axial coordinate system of PINC 5.13–5.16, the Y = 0 position is the top of the test block. 

The length for "Y+" is measured along the surface of the test block, as shown in Figure 2.49.

For PINC test blocks 5.13–5.16, when defects in the J-groove weld are measured, the Z 

dimension should be measured from the top (the surface facing the reactor core) wetted surface 

that is clad, J-groove, and has buttering. The surface is curved; therefore, the Z dimension is 

reported relative to the angular location around the specimen.
2.29

Figure 2.45 Coordinate System for PINC 5.1–5.3
2.30

Figure 2.46 Coordinate System for PINC 5.6 – SSM/SQC F3.537.2

Figure 2.47 Coordinate System for Test Blocks PINC 5.7–5.12
2.31

Figure 2.48 Circumferential Coordinate System for Test Blocks PINC 5.13–5.16

Figure 2.49 Axial Coordinate System for Test Blocks PINC 5.13–5.16
2.32

2.3 Description of Fabrication Techniques Used in Developing PINC 

Test Blocks

This section describes how the flaws were introduced into the various PINC test specimens. 

The implantation techniques are important because one of the goals of the PINC is to understand what makes the flaws easier or more challenging to detect. Each flaw manufacturing 

technique produces flaws with a different morphology. The variety of flaw manufacturing 

techniques used in the PINC BMI test blocks allows for an analysis of the difficulty in detecting 

the different types of cracks.

2.3.1 Flaw Fabrication in Test Blocks 5.1–5.3

Most of the cracks used in test blocks 5.1, 5.2, and 5.3 were produced by first creating the flaws 

in coupons and then welding the coupons containing the flaws into the welds. One example of 

a crack that was fabricated into a weld is shown in Figure 2.50.

Figure 2.50 Example Flaw Coupon as Used for Test Blocks 5.1–5.3

Other flaw types such as porosity and lack of fusion were introduced into the weld using the 

same technique. Flaw types such as weld undercut were cut directly into the penetration tube. 

The undercut flaw is shown in Figure 2.51.

This method of crack fabrication is commonly used and is well understood. The use of coupons 

does pose one possible issue—the effects of the additional welding on the ultrasonic and 

electrical properties at the weld–sample interface.
2.33

Figure 2.51 Example Weld Undercut Flaw as Used in Test Blocks 5.1–5.3

These flaws were implanted in the penetration tubes and welds of the BMI samples. 

Additionally, weld flaws can be introduced into the samples during the welding process. Sample 

5.3 has implanted cracks, undercut, and a lack of fusion weld flaw. The placement of these 

flaws is shown in Figure 2.52. 

Implanted

Cracks

Undercut

Welding Defect

(Lack of Fusion)

Penetration Tube

J-Groove Weld

Buttering

Figure 2.52 Flaw Placement in Test Block 5.3
2.34

2.3.2 Flaw Fabrication in Test Blocks 2.9, 2.10 and 5.6

The flaws in test blocks 2.9, 2.10, and 5.6 were fabricated via a weld-solidification process. The 

region where the crack was fabricated was excised and then filled in with “poisoned” weld metal 

that is designed to crack on cooling. The cracks in these test blocks were designed to simulate 

the eddy current responses found for cracks in the 182 weld metal in the Ringhals 4 reactor 

(SQC 2003). The eddy current responses for the fabricated cracks were checked to ensure 

they were similar to the responses in real stress corrosion cracks (SCC) that occurred in nickel 

alloy material.

Possible issues with this style of crack fabrication are similar to those for the fabricated flaws 

used in test blocks 5.1–5.3—the weld fabrication zone can possibly be detected in an eddy 

current or a visual examination. A visual examination of the cracked areas showed no 

disturbance of the surface caused by the implantation process and that the weld solidification 

cracks were surface-breaking. The flaws in Block 5.6 at 45, 180, 225, 255, and 315 degrees 

were clearly detected in photographs, and the flaw at 135 degrees had a possible crack-like 

indication. A sample weld solidification crack in test block 5.6 is shown in Figure 2.53.

2.3.3 Flaw Fabrication in Test Block 5.7

The flaws in test block 5.7 were fabricated using an in situ thermal fatigue process. This 

process is able to introduce flaws into the material without the weld fabrication problems 

associated with the coupon insertion or weld-solidification cracking. It is also possible to control 

crack properties such as crack opening displacement (COD) and crack depth with a high level 

of precision. The thermal fatigue cracks are very expensive, however, so only two such flaws 

were ordered. Because of an accident during the fabrication of one of the flaws, three flaws are 

present in test block 5.7. Only two have the proper pedigree involving length and depth, 

however. All three flaws in test block 5.7 were confirmed as surface-breaking using visual 

examination. Photography of the flaws showed that the flaws at 15 degrees and 300 degrees 

consisted of multiple small cracks spaced closely together. The flaw at 15 degrees is shown in 

Figure 2.54.
2.35

mm

1

2

3

Figure 2.53 Weld Solidification Crack in Test Block 5.6 at 45 Degrees

Figure 2.54 Thermal Fatigue Cracks in Test Block 5.7

2.3.4 Flaw Fabrication in Test Block 5.8

Test block 5.8 had a weld repair, but no crack or other flaws, fabricated into the weld. This test 

block is designed to control for the issues caused by the flaws fabricated via welding flawed

coupons into the test blocks and the weld-solidification cracks. The inspection of test block 5.8 

provides important insight to determine if the inspectors are finding the fabrication regions and 

not the cracks themselves.
2.36

2.3.5 Flaw Fabrication in Test Blocks 5.9 and 5.10

The flaws in test blocks 5.9 and 5.10 were fabricated using a weld-solidification cracking 

process similar to the process used in test block 5.6. The difference between test block 5.6 and 

test blocks 5.9 and 5.10 is that the flaws in test blocks 5.9 and 5.10 were tailored to be more 

challenging to detect. These flaws are designed to mimic difficult-to-detect indications such as 

those found in the North Anna 2 nozzle 31. It is worth noting that the indications with 

challenging to detect NDE responses in North Anna 2 were later found to be less than 8 mm 

deep.

A careful visual examination using high-resolution macro photography found no evidence of 

surface-breaking flaws in test blocks 5.9 or 5.10. This is in contrast to the weld solidification 

flaws in test block 5.6, where flaws were visible on the surface. Test blocks 5.9 and 5.10 were 

then examined using fluorescent dye penetrant testing. The penetrant testing of test block 5.9 

showed no indications of any surface-breaking flaws. The penetrant testing of test block 5.10 

found no linear indications, but two small spots of penetrant appeared at locations consistent 

with the crack implantation regions of 255 and 315 degrees. During the destructive examination 

of sample 5.10 the crack was revealed to have a limited surface-breaking component, and it is 

now believed that the PT indication near 315 degrees may have come from a welding defect 

such as porosity. The results of the penetrant testing are shown in Figure 2.55. 

Figure 2.55 Penetrant Testing Results for Test Block 5.10
2.37 

2.3.6 Test Blocks 5.11 and 5.12 

No flaws were present in test blocks 5.11 or 5.12. These test blocks were included in the study 

to provide blank BMI specimens to help discern the false call rate for the inspectors. 

2.3.7 Flaw Fabrication in Test Blocks 2.1–2.6 and 5.13–5.16 

For the test blocks 2.1–2.6 and 5.13–5.16, the flaws were fabricated using laboratory-grown 

stress corrosion cracking (SCC). The geometry of the test blocks before preparing the SCC is 

shown in Figure 2.56. In the case of BMI test blocks, the penetration tubes were cut off before 

preparing the SCC, and the tubes were re-welded after preparing the SCC. Figure 2.57 shows 

the procedure for preparing laboratory SCC in a piping sample. Figure 2.58 and Figure 2.59 

show typical examples of laboratory-induced SCC in the case of these BMI test blocks. 

SCC 

Tub

SCC 

Tube

Figure 2.56 BMI Test Blocks for Preparing SCC 
2.38 

Partial remove of weld

metal

Re‐weld of SCC

susceptible weld metal

Sensitization heat

treatment

Periodic confirmation of

SCC growth

Remove the starter notch

Preparing thestarter

notch

Loading by3‐point or 4‐

point bending

Polishing the surface of

weld

Fabrication of test blocks

Local soakof polythionic

acid using reserve box

Starternotch

reservebox polythionicacid

loading loading

Figure 2.57 Procedure for Preparing Laboratory SCC in a Sample Piping Specimen 
2.39

Figure 2.58 Example of Laboratory-Induced SCC in BMI Test Block (parallel to the weld)

Figure 2.59 Example of Laboratory-Induced SCC in BMI Test Block (perpendicular to the 

weld)
2.40

2.4 Description of True States for the Test Blocks

The flaws in each test block were documented during the construction of each block, and this 

documentation was used to provide the locations, lengths, and depths of each flaw. Test 

blocks 2.1–2.6, 5.2, and 5.13–5.16 were destructively examined to validate these parameters, 

and the true-state information reflects the destructive test results. Test block 5.10 received a 

limited destructive validation to determine the crack characteristics such as COD and depth. 

The destructive testing results for test blocks 2.1–2.6 are contained in Appendix A; the 

destructive results for test blocks 5.2, 5.10 and 5.13–5.16 are contained in Appendix B.

2.4.1 Description of the True State Used for Dissimilar Metal Weld RoundRobin Test Blocks

Drawings and photographs of the test blocks were provided to the participating teams of 

inspectors. Information on the actual test specimens is limited to drawings and schematics that 

were useful for inspection planning. Table 2.5 lists some of the important parameters of the 

round-robin test of mid-thickness (40–50 mm) dissimilar metal welds. Table 2.6 details how 

many of each sample were used in the study. It is important to note that test block 2.9 had two 

flaws that did not have appropriate documentation. These flaws, named F9.13 and F9.14, were 

left in the test block from a previous set of tests. As the exact position, depth, and sizes are not 

known, they are not used for POD or sizing regressions.

2.4.2 Description of the True State Used for Bottom-Mounted Instrumentation

Round-Robin Test Blocks

The objectives of the round-robin test include simulating the NDE responses from PWSCC by 

selecting manufactured cracks with appropriate NDE responses. This includes both peak 

response and indication length. The degradation initiation sites associated with through-wall 

leaks from observed PWSCC show cracks as short as 4 mm. Therefore, fabricated cracks in 

the test blocks have a range of crack lengths, including some short cracks to simulate this 

condition. Some unexpected fabrication flaws were expected to be present in the test blocks,

and PNNL fingerprinted the blocks, locating the cracks to separate them from the unexpected 

fabrication flaws. Inspection teams were instructed to expect fabrication flaws and a range of 

crack properties in the test blocks.

The test assemblies from Sweden, Japan, and the United States all have the cracks located in 

the J-groove weld or buttering. Three of the Korean assemblies have cracks in the penetration 

tubes and at the interface between the penetration tube and the J-groove weld. In one 

additional assembly provided by Korea, the location of the cracks is unknown. For sample 5.10, 

flaw 3 was identified as being smaller than was specified in the true state documentation, and 

was less than one millimeter in depth. Flaw 6 appeared to be mostly embedded, with a small

section breaking the surface. 

Table 2.7 and Table 2.8 show the test blocks and cracks used in the BMI study.
2.41

Table 2.5 Available Cracks in the PINC Mid-Thickness Dissimilar Metal Weld Test Blocks as Provided by JNES and SQC

Flaw 

Number

PINC 

Reference 

Number X1 X2 Y1 Y2 Z1 Z2

Flaw 

Orientation

Depth, 

mm

Length, 

mm Tilt

SHCC1 PINC 2.1 −17.0 10.5 0.6 3.1 41.2 46 C 5.8 21.0 0

SHCC2 PINC 2.2 −26.2 28.8 0.3 4.6 34.3 46 C 13.5 42.0 0

SHCC3 PINC 2.3 −53.7 59.5 0.3 4.2 30.0 46 C 17.8 86.5 0

STCC1 PINC 2.4 −1.7 −0.7 7.0 24.0 41.1 46 A 4.9 17.0 0

STCC2 PINC 2.5 −1.3 2.2 −7.0 31.0 33.7 46 A 13.3 38.0 0

STCC3 PINC 2.6 −7.3 2.6 −6.0 36.0 24.5 46 A 23.2 42.0 0

F9.1 PINC 2.9 57.3 95.6 −5.0 1.2 7.0 42 C 35.0 30.0 −10

F9.2 PINC 2.9 518.7 544.3 −4.0 −2.4 24.0 42 C 18.0 20.0 −5

F9.3 PINC 2.9 707.4 745.7 −13.2 −7.0 19.0 42 C 23.0 30.0 15

F9.4 PINC 2.9 875.8 898.8 −3.0 −1.4 33.0 42 C 9.0 18.0 −10

F9.5 PINC 2.9 990.3 1009.5 −3.1 −2.0 36.0 42 C 6.0 15.0 10

F9.6 PINC 2.9 1128.4 1154.0 −3.1 0.4 32.6 42 C 9.4 20.0 −20

F9.7 PINC 2.9 168.4 194.0 −18.7 −17.0 35.8 42 C 6.2 20.0 15

F9.8 PINC 2.9 360.4 386.0 −18.0 −16.3 35.8 42 C 6.2 20.0 −15

F9.9 PINC 2.9 613.1 638.6 −19.0 −15.0 36.0 42 C 6.0 20.0 10

F9.10 PINC 2.9 1054.3 1079.9 −18.0 −18.0 36.0 42 C 6.0 20.0 0

F9.11 PINC 2.9 791.6 814.6 −16.0 −16.0 30.0 42 C 12.0 18.0 0

F9.12 PINC 2.9 1199.2 1224.7 −14.0 −9.5 16.6 42 C 25.4 20.0 −10

F9.13* PINC 2.9 417 435 0 24 NA NA NA NA NA NA

F9.14* PINC 2.9 293 317 −21 −11 NA NA NA NA NA NA

F10.1 PINC 2.10 151.6 151.6 −20.0 0.0 22.0 42 A 20.0 20.0 0

F10.2 PINC 2.10 252.6 254.9 −20.0 0.0 32.0 42 A 10.0 20.0 10

F10.3 PINC 2.10 350.3 350.3 −12.0 0.0 36.0 42 A 6.0 12.0 0

F10.4 PINC 2.10 448.0 454.8 −20.0 0.0 12.0 42 A 30.0 20.0 10

F10.5 PINC 2.10 805.1 805.1 −16.0 −7.0 30.0 42 A 12.0 12.0 0

F10.6 PINC 2.10 902.1 906.1 −20.0 0.0 24.0 42 A 18.0 20.0 −10

F10.7 PINC 2.10 1003.8 1003.8 −20.0 0.0 17.0 42 A 25.0 20.0 0

C = circumferential, A = axial.

*Not used for POD or sizing (see page 2.39)
2.42

Table 2.6 Round-Robin Test Blocks for Mid-Thickness (40–50 mm) Dissimilar Metal Weld

Number of SSM test blocks 2

Number of JNES test blocks 6

Total length of weld to be inspected 4 meters

Table 2.7 Flaws Used for Surface Inspections in BMI Test Blocks

Test 

Block Flaw Θ1, ° Θ2, ° r1, mm r2, mm Z1, mm Z2, mm SB* Orient

5.1 Surf5.1.5 268 304 20 23.6 1 10 no Circ.

5.2 Surf5.2.3 148 155 19.3 27.3 0 14.1 yes Axial

5.3 Surf5.3.3 130 160 19.1 27.7 0 8 yes Circ.

5.3 Surf5.3.6 338 338 19.1 30 0 10 yes Axial

5.6 Surf5.6.1 45 45 24 28 0 2 yes Axial

5.6 Surf5.6.2 131 139 34 34 0 2 yes Circ.

5.6 Surf5.6.3 225 225 55 60 0 2 yes Axial

5.6 Surf5.6.4 310 320 58 58 0 5 yes Circ.

5.6 Surf5.6.5 245 265 30 30 0 5 yes Circ.

5.6 Surf5.6.6 180 180 35 41 0 1.5 yes Axial

5.7 Surf5.7.1 162 168 42 42 0 2 yes Circ.

5.7 Surf5.7.2 15 15 34 37 0 3 yes Axial

5.7 Surf5.7.3 300 300 32 40 0 NA Yes Axial

5.8 No Flaw NA NA NA NA NA NA NA NA

5.9 Surf5.9.1 15 15 43 47 0 1 yes Axial

5.9 Surf5.9.2 75 75 33 36 0 6 yes Axial

5.9 Surf5.9.3 193 197 44 44 0 3 yes Circ.

5.9 Surf5.9.4 345 345 45 49 0 7 yes Axial

5.10 Surf5.10.1 39 51 33 33 0 9 yes Circ.

5.10 Surf5.10.2 72 78 45 45 0 7 yes Circ.

5.10 Surf5.10.3† 225 225 39 41 0 0.4 yes Axial

5.10 Surf5.10.4 251 259 46 46 0 2 yes Circ.

5.10 Surf5.10.5 285 285 36 40 0 2 yes Axial

5.10 Surf5.10.6† 315 315 46 48 0 4.5 yes Axial

5.11 No Flaw NA NA NA NA NA NA NA NA

5.12 No Flaw NA NA NA NA NA NA NA NA

5.13 Surf5.13.1 349 7.8 34.7 36.9 0 2.2 yes Circ.

5.13 Surf5.13.2 175 188 33.3 36.1 0 2.4 yes Circ.

5.14 Surf5.14.1 340.1 22.5 29.8 36.6 0 10.5 yes Circ.

5.14 Surf5.14.2 166.9 194.8 29 31.4 0 2.1 yes Circ.

5.15 Surf5.15.1 87.7 91.1 25.1 36.4 0 3.5 yes Axial

5.15 Surf5.15.2 265.3 270.8 25 35.2 0 3.3 yes Axial

5.16 Surf5.16.1 88.9 95.5 22.4 38.8 0 10.9 yes Axial

5.16 Surf5.16.2 268.9 275.9 23.2 36.6 0 5.8 yes Axial

*SB = surface-breaking, † Determined by destructive evaluation to be too small for use in scoring
2.43

Table 2.8 Flaws Used for Penetration Tube Inspections in BMI Test Blocks

Test 

Block Flaw Θ1, ° Θ2, ° r1, mm r2, mm Z1, mm Z2, mm SB Orient

5.1 Tube5.1.1 8 44 19.1 21.7 299.1 306.4 no Circ.

5.1 Tube5.1.2 68 112 10.3 19.1 304.8 304.8 no Circ.

5.1 Tube5.1.3 202 202 7.5 12.2 310.7 338.6 yes Axial

5.1 Tube5.1.4 209 245 15 19.1 309.1 315.7 no Circ.

5.1 Tube5.1.5 268 304 19.8 23.6 303 303 no Circ.

5.1 Tube5.1.6 303 339 14.7 19.1 299.9 299.9 no Circ.

5.2 Tube5.2.1 15 70 17.4 23.7 294.1 307.9 no Circ.

5.2 Tube5.2.2 90 93 18.6 21.1 305.2 352.7 no Axial

5.2 Tube5.2.3 100 107 7.5 10.7 296 321.6 yes Axial

5.2 Tube5.2.4 148 155 19.3 27.3 327.1 341.2 no Axial

5.2 Tube5.2.5 220 290 7.5 19.1 304.5 317 yes Circ.

5.2 Tube5.2.6 305 350 14.4 19.7 290.4 297.6 no Circ.

5.3 Tube5.3.1 13 43 16.3 19.1 293.5 293.5 no Circ.

5.3 Tube5.3.2 86 116 21.6 27.7 307.2 313.3 no Circ.

5.3 Tube5.3.3 130 160 19.1 27.7 315.2 322.8 no Circ.

5.3 Tube5.3.4 191 227 7.5 21.7 315.9 315.9 yes Circ.

5.3 Tube5.3.5 269 313 19.1 29.6 300.2 310.4 no Circ.

5.3 Tube5.3.6 338 338 19.1 29.9 293 303.8 no Axial

*SB = surface-breaking
2.44
3.1

3.0 Techniques and Procedures Descriptions

The teams conducting the examinations used a wide mix of nondestructive techniques, ranging 

from standard methods such as conventional ultrasonic inspection to experimental techniques 

such as potential drop. Because there was a wide variety in techniques and the application of 

those techniques, comparing the effectiveness of the individual techniques would result in a 

very complex matrix. PNNL has divided the different techniques used in the DMW and BMI 

round-robin tests into two broad categories—ultrasonic and electromagnetic. 

Within the ultrasonic category, the following methods were used:

• conventional ultrasound

• conventional phased array

• adaptive phased array 

• time-of-flight diffraction (TOFD).

Within the electromagnetic category, the following methods were used:

• eddy current 

• potential-drop methods, including both direct current (DC) and alternating current (AC)

methods, and modified variations of these techniques.

3.1 Ultrasonic Techniques

Ultrasonic techniques use beams of high-frequency sound to interrogate the materials. 

Ultrasonic techniques are capable of inspecting a volume of material to determine the location, 

size, and depth of flaws. During inservice inspection (ISI) outages at nuclear power plants, 

ultrasonic methods are used in the examination of piping welds; hence, their use in the PINC 

DMW round robin. Most ultrasonic inspections of piping welds are performed from the outside 

of the pipe, looking for cracks initiating in the inner pipe surface. Some ultrasonic inspections 

are conducted from the inner diameter of a pipe, and from the wetted surface of J-groove welds 

and the inner diameter of penetration tubes.

3.1.1 Conventional Ultrasound

Conventional ultrasonic techniques use a transducer mounted on a wedge to produce an 

ultrasonic beam with a specific fixed angle in the material. Typical angles used for ultrasonic 

inspection of nuclear components include 30-, 45-, and 60-degree beams that use both 

longitudinal and shear wave modes of propagation. The ultrasonic transducers can be used to 

manually scan a test object, or the search unit may be designed to fit in a mechanized scanning 

fixture and the data collected electronically. A conventional ultrasonic transducer examining a 

specimen from the outer diameter (OD) is shown in Figure 3.1.
3.2

Transducer

Flaw

Specimen

Wedge

Transmitted

Beam

Reflected

Beam

Figure 3.1 Conventional Ultrasonic Testing

Conventional ultrasound is one of the most common and time-tested techniques used to 

examine reactor components. Inspectors and regulating agencies have a great deal of 

experience with the capabilities and limitations of conventional ultrasound. The disadvantages 

of conventional ultrasonic techniques are that they can be time-consuming to apply because a 

detailed inspection may require many separate examinations using different angles and different 

frequencies.

3.1.2 Phased Array Ultrasound

Phased array ultrasound is a newer ultrasonic technique that is achieving greater acceptance 

for performing ISI at nuclear power plants. Unlike a conventional ultrasonic transducer, a 

phased array ultrasonic transducer consists of several individual elements. These elements are 

excited to transmit individually at specific time delays, allowing one transducer to emit a beam at 

many angles and focused at several depths. Phased array beam forming is shown 

schematically in Figure 3.2. 

Delay

Straight Beam Depth Focusing Steering

Figure 3.2 Use of Delays to Steer and Focus Ultrasonic Beams in Phased Array 

Transducers
3.3

Phased array ultrasound offers several advantages over conventional ultrasound because a 

single phased array transducer can be used to emit many angles almost simultaneously. This 

versatility allows the inspector to examine a sample much more quickly. Because phased array 

ultrasound requires sophisticated electronics to control the individual elements, it also provides 

electronic data-recording capabilities. The main disadvantages of phased array ultrasound are 

the increased expense of transducers and sophisticated electronics over conventional ultrasonic 

probes and the relative newness of, and lack of experience with, the technique. As with 

conventional ultrasound, phased array UT is normally used from the outer diameter of a pipe. 

Phased array ultrasound can be used from the wetted surface of a J-groove weld or the inner 

diameter of a penetration tube. 

3.1.3 Adaptive Phased Array Ultrasound

Adaptive phased array ultrasound uses the versatility of phased array technology to allow for 

detailed inspections of samples with irregular surfaces. The system first measures the surface 

profile using an initial scan and then corrects the delay laws used to focus the beam through the 

irregular surface. The adaptive phased array technique offers the additional benefit of working 

on a variety of sample configurations, unlike conventional ultrasonic testing (UT) that would 

require a custom probe and/or wedge for each surface profile. Adaptive phased array UT 

testing is normally performed from the cracked surface.

3.1.4 Time-of-Flight Diffraction

Time-of-flight diffraction is a well-established ultrasonic technique that is very useful in crack 

detection and sizing. The TOFD technique uses two transducers that face each other to detect 

cracks in the material. When arranged properly, a surface lateral wave travels between the two 

transducers and a back-wall signal is produced by the beam bouncing off of the far side of the 

sample. If a surface-breaking flaw is present between the two transducers, it will interrupt either 

the lateral wave or the back-wall wave, and the tip of the flaw will produce a secondary signal, 

which is also detectable. The TOFD setup is a very powerful technique for detection and length 

and depth sizing of flaws. TOFD can be used from the ID or OD of a pipe or other component. 

A diagram of the TOFD technique is given in Figure 3.3.

TOFD has some disadvantages, however. The TOFD arrangement has a large footprint and is 

not useful for inspections that have limited access to a component. For TOFD to work properly, 

the transducers generally need to be on a level and relatively flat surface. The region of interest 

for most reactor inspections is at or near a weld; if the weld has not been machined flat, the 

weld crown and other geometrical features associated with welds may make TOFD unusable. 

Also, TOFD is less sensitive to flaws that are parallel to the plane of the transducers.
3.4

Figure 3.3 Time-of-Flight Diffraction Technique

3.2 Electromagnetic Techniques

Electromagnetic techniques detect flaws by inducing electromagnetic currents in the sample 

and measuring how the flaws affect the induced current. Electromagnetic techniques are often 

very useful at detecting surface-breaking flaws but are not typically used to depth-size flaws.

3.2.1 Eddy Current

Eddy current inspection uses a coil or coils held very close to a surface. An AC current is 

passed through the coil. The AC current creates a cyclical magnetic field around the coil. 

When this magnetic field intersects with a conducting material, such as steel or stainless steel, 

electrical currents are induced in the materials. These currents make their own magnetic fields, 

which interact with the magnetic field generated by the coil. The changes in resistance and 

inductive reactance in the coil allow one to measure the electrical properties of the material. 

Breaks in the surface, such as cracks, affect the eddy currents in the materials and can be 

measured using the eddy current system. An eddy current test setup is shown schematically in 

Figure 3.4. 
3.5

AC

Voltmeter

Induced 

Currents

Induced 

Currents

Flaw

Figure 3.4 Eddy Current Diagram

Eddy current testing (ECT) is very effective at detecting surface-breaking flaws, but usually only 

from the same surface at which the flaw originates. For piping welds ID inspections are 

required. Using eddy current inspection for through-wall examinations is possible only with thin 

materials such as steam generator tubes and is not possible for most reactor piping. ECT is 

one of the most common techniques used to inspect samples where the possible cracked 

surface is accessible to inspectors. The main weakness of eddy current inspection is that it is a 

surface and near-surface examination only and cannot be performed through more than a few 

millimeters of metal. The technique is not capable of characterizing the through-wall size of 

cracks more than a few millimeters in depth.

3.2.2 Potential-Drop Techniques

Although there are several implementations of potential-drop techniques, they all function by 

passing a current (AC or DC, depending on the technique) through the specimen and use 

several probes to measure the electrically induced voltage of the material (see Figure 3.5). 

Flaws in the material affect the electrical voltage and current, and this effect can be measured. 

Some potential-drop measurements need to be made from the surface broken by the crack, but 

some implementations can be used through the entire thickness of a pipe. Potential-drop 

techniques are not commonly used in reactor inspections. The potential drop technique has 

many variations, some of which are used from the ID and some from either side of a pipe or 

component. The variations used in this round-robin test are as follows:

• alternating current potential-drop (ACPD) method

• direct current potential-drop (DCPD) method

• closely coupled probe potential-drop (CCPPD) method using direct current

• induced current potential-drop (ICPD) method using induction alternating current.
3.6

Figure 3.5 Four-Probe Potential-Drop Measurement
4.1

4.0 Analysis of Performance

After the teams had completed the round-robin testing, the data were collected, examined, and 

scored to determine the effectiveness of the various techniques. This section describes the 

scoring criteria used to analyze the data and the results. Section 4.1 describes the scoring 

procedures used in the round-robin tests. Section 4.2 contains the probability of detection 

results for the DMW and BMI examinations. Finally, Section 4.3 details the length- and depthsizing results for the DMW and BMI round-robin tests. 

4.1 Scoring Procedure Used for PINC Round Robins

This section describes how inspection results were compared to the true state of the DMW and 

BMI test blocks. Specifically, this section describes (1) the method used to determine whether 

or not an individual flaw was detected; (2) if the flaw was detected, what depth and length size 

should be assigned to it; (3) unintended defects (flaws that occurred during the test block 

fabrication process that were not intended to be part of the test block); and (4) the methodology 

used to determine false calls (i.e., indications not associated with any known flaw).

Scoring merges the inspection results with the true-state results by associating inspection 

indications with true-state flaws. The scoring procedure is summarized by the flowchart in 

Figure 4.1.

Figure 4.1 Scoring Procedure for PINC Round Robins
4.2

The first step of the scoring process consisted of uniquely identifying the flaws in the inspected 

volume of the weld. For this analysis, a table of flaws was developed for each test specimen. 

The inspection volume field indicated in the portable document format (PDF) file record for 

inspections was then compared with the flaw table for each specimen to determine which flaws 

fell within the inspected volume. These flaws are then placed in the inspected flaw table.

The next step of the scoring process compared the entries in the inspected flaw table to the 

entries in the indication table (the indications that were recorded on inspection data sheets) to 

determine which flaw cuboids intersected with which indication cuboids.

A tolerance box was defined around each flaw to account for possible location error. Figure 4.2

shows the probability of detection versus size of tolerance for the DMW round robin, and 

Figure 4.3 shows the same information for the BMI round-robin results. As can be seen in 

Figure 4.2 and Figure 4.3, there is not much improvement in detection for tolerances larger than 

10 mm. The exception is for the tube examinations of the BMI samples, which have closely 

spaced flaws. Therefore, for the analysis used in this report, a tolerance box of 10 mm was 

used to score the DMW and BMI results. Without use of a tolerance box, location errors might 

be misclassified as non-detections. Once the tolerance is defined, ∆X, ∆Y, and ∆Z, then the 

flaw cuboid, X1, X2; Y1, Y2; Z1, Z2, becomes

(X1 - δX, X2 + δX, Y1- δY, Y2 + δY, Z1 - δZ, Z2 + δZ) (4.1)

A list of all indications not intersecting with any flaws was compiled and was termed the false 

call table. The false call table was compiled after the intersecting flaw–indication cuboids had 

been identified for each indication.

The scoring process therefore resulted in two outputs—the detection of flaws, including the 

length and through-wall depth determined for each flaw, and a list of false calls. 

Finally, detection and sizing information were appended to all flaws in the inspected flaw table, 

using the intersection information, to produce the detection and sizing results table. 
4.3

Figure 4.2 Probability of Detection versus Scoring Tolerance for Teams and Flaws for 

DMW Round Robin
4.4 

Figure 4.3 Probability of Detection versus Scoring Tolerance for All Teams and Flaws in 

BMI Round Robin 

4.1.1 Definitions of False Call Probability and Probability of Detection 

False call probability (FCP) and probability of detection quantify inspection performance on 

blank (un-flawed) versus flawed material. The FCP is the probability that an inspector will call a 

flaw in a blank unit of material, while POD is the probability that an inspector will call a flaw in a 

flawed unit of material. With these definitions, (FCP, POD) measure the capability for inspection 

to correctly classify units of material as unflawed or flawed. Another equivalent term for FCP is 

false positive probability while POD is equivalent to 1 minus false negative probability. 

POD is frequently expressed as a function of various flaw, material, or inspection variables that 

might affect detection performance. For example, in PINC, POD is considered to be a function 

of flaw size, so the expression POD(S) is used to represent the probability of calling a detection 

in a unit of material than contains a flaw of size S. 
4.5

One would expect POD(S) to be a monotonically increasing function of flaw size S. Also, one 

should note that using the false call probability as the POD for a flaw of size zero (POD(0) = 

FCP) follows from the definition of FCP and POD. When the S = 0 point is included on the POD 

curve, this curve provides the most basic description of inspection efficacy. An inspection that is 

no more effective than guessing will have a flat POD curve. More specifically, if the POD for 

flaws of size S is equal to FCP, (POD(S) = FCP) then flaws of this size aren’t really being 

detected by the inspection procedure.

To be able to calculate FCP and POD, one has to define the applicable unit of material. We call 

this unit of material the grading unit; In other words, each grading unit in the round robin study 

will generate a detection statistic when inspected. For inspection of dissimilar metal weldments, 

the ideal grading unit would be an entire weld, but a round robin test that used whole weldments 

as the experimental unit would be too costly. Due to cost constraints, the grading unit used is 

the length of a flaw plus an allowance for sizing error. 

To produce unbiased estimates of FCP and POD, the blank and flawed grading units must be 

identical in all important respects (except that the flawed grading units contain a flaw). Also, if 

multiple grading units are to be placed in a single weldment, they must be separated from each 

other by a sufficient distance. These constraints caused problems in defining blank grading 

units in the PINC specimens. Since reasonable blank grading units could not be defined, we 

constructed a probability model (described in the next section), to estimate FCP from available 

PINC false call statistics.

4.1.2 Calculation of FCP

In the PINC inspections, a false call is defined as a call that does not intersect with a flawed 

grading unit. These false calls were used to estimate a false call rate, λfc (false calls per meter)

λ = #False Calls

Length of Material Inspected fc (4.2)

Using this rate and the assumption that false calls are randomly (i.e., Poisson) distributed one 

can then calculate the probability that a call would intersect a blank grading unit of length Lgu. 

Assuming that the average length of a false call is Lfc, the probability of a false call intersecting 

the grading unit is

FCP = Pr(Grading Unit Intersection) = 1 − exp(−λfc(Lgu + Lfc)) (4.3)

4.1.3 Logistic Regression model for POD

In PINC, a logistic regression model was used to relate POD to flaw size, S. Flaw size 

represents either depth or length. The logistic regression model is given by

POD(S) = logistic(β1 + β2S) (4.4)
4.6

where β = (β1, β2) are unknown parameters to be determined by the regression algorithm and 

the function, logistic(x) is defined as

= +

1 logistic(x) 1 exp(-x) (4.5)

Estimates produced by the algorithm are maximum-likelihood estimates. The regression fits 

included data for flaw size zero (i.e., the FCP estimates described in the last section). In the 

regression fit plots, you will sometimes see a data point at S = 0 and that represents false call

data.

4.1.4 Scoring Example for Single Flaws

For all inspections of the DMW test blocks and the inspections of the weld surface of the BMI 

test blocks, the scoring was performed using a 10-mm scoring box. This section presents the 

scoring results for a single inspection, so the reader can more easily understand the scoring 

process. The example used is an inspection of test block 2.9.

This test block was selected because it contains each type of scoring situation, including missed 

flaws, false calls, and hits on poorly documented flaws. The team has inspected the entire 

block (and this is the case for almost all inspections in the round robin), so all flaws in the block 

should be included in the scoring procedure. The indications called by the inspection team 

(using their labeling system) are summarized in Table 4.1.

Table 4.1 Test Block PINC 2.9 Inspection Results

Indication 

ID

X1,

mm

X2,

mm

Y1,

mm

Y2,

mm

Z1,

mm

Z2,

mm

X max,

mm

Y max,

mm

Z max,

mm

1 51 86 −7 −7 16 43 75 1 51

1a 66 108 19 19 35 43 81 2 66

2 163 190 −19 −19 37 43 176 3 163

3 271 304 −18 −18 31 43 298 4 271

4 375 439 14 14 28 43 412 5 375

5 496 527 −1 −1 28 43 513 6 496

6 686 732 −9 −9 27 43 708 7 686

7 787 807 −18 −18 37 43 798 8 787

8 860 880 −5 −5 37 43 870 9 860

9 972 999 −4 −4 36 43 979 10 972

10 1047 1067 −18 −18 38 43 1058 11 1047

11 1105 1125 −4 −4 35 43 1111 12 1105

12 1173 1201 −6 −6 20 43 1180 13 1173

The scoring result is summarized visually by Figure 4.4. Figure 4.4 shows the results in the 

X, Y plane, the plane most relevant to our scoring definition. The locations of the indications 

called by the inspection team are shown as black rectangles in Figure 4.4. The test block 
4.7 

contains 12 flaws used for scoring (shown in red) and 2 poorly documented flaws that were not 

intentionally placed in the test block for the PINC studies but still are detectable (shown in blue). 

When the intersections between the called indications and the actual flaw locations are 

compared, one can determine how well the team performed. 

Missed Flaws

False Call Poorly-Documented Flaws

Figure 4.4 Scoring Inspection Results of Test Block 2.9 with 10-mm Tolerance 

The scored results are presented in Table 4.2 (detection results). In Table 4.2, each row 

describes a flaw in the block. From Table 4.2, we see that Flaws 9.8 and 9.9 were not detected, 

while flaws 9.1–9.7 and 9.10–9.14 were detected and are scored as hits, and the supplied 

lengths and depths were used to evaluate the length and depth sizing capabilities of the 

technique. Both of the poorly documented flaws were detected but are not used for depth or 

length sizing. Missing the poorly documented flaws would not have been counted against the 

inspection because the exact locations of the poorly documented flaws are not known. 

The team conducting the examination successfully detected ten of the flaws used for scoring 

and both poorly documented flaws. Additionally, the team missed two flaws and made one false 

call. Appendix C of this report provides the scoring results of all teams that participated in the 

PINC DMW round-robin tests using this style of plots of indications versus flaw location. 
4.8

Table 4.2 Detection Results for Sample Inspection of PINC Test Block 2.9

Flaw No.

Detection

0 = no

1 = yes X1, mm ° X2, mm °

Indication ID from 

Data Sheet of 

Team 67

F9.1 1 57.3 95.6 1

F9.2 1 518.7 544.3 5

F9.3 1 707.4 745.7 6

F9.4 1 875.8 898.8 8

F9.5 1 990.3 1010 9

F9.6 1 1128 1154 11

F9.7 1 168.4 194 2

F9.8 0 360.4 386 NA

F9.9 0 613.1 638.6 NA

F9.10 1 1054 1080 10

F9.11 1 791.6 814.6 7

F9.12 1 1199 1225 12

F9.13* 1 293 317 4

F9.14* 1 417 435 3

NA = Not applicable.

*Not used for POD or sizing (see page 2.39).

4.1.5 Scoring Process for Multiple Closely Spaced Cracks

As the Data Analysis Task Group (DAG) reviewed the data from the PINC round-robin exercise, 

members of the DAG recognized that the test blocks used in the BMI did not contain a single 

crack; rather, the test blocks contained multiple cracks. In fact, many cracks in the test blocks 

used for the PINC BMI were close together. The DAG decided to analyze the PINC BMI data 

using a set of proximity rules that would account for the multiple flaws in the test blocks.

The DAG used the American Society of Mechanical Engineers (ASME) Section XI IWA-3400 

rules for linear surface flaws to account for the multiple flaws that were close together. The 

scoring process was the same as that described in Section 4.1.1.

Section XI, IWA-3400 of the ASME Code states the following:

(a) Linear flaws detected by surface (PT/MT) or volumetric (RT) examination 

methods shall be considered single linear surface flaws provided the separation 

distance between flaws is equal to or less than the dimension S, where S is 

determined as shown in Figure IWA-3400-1.

(b) The overall length of a single and discontinuous linear flaw shall be 

determined as shown in Figure IWA-3400-1.

Figure 4.5 is a reproduction of IWA-3400-1 to show the methodology used to determine whether 

multiple flaws in a PINC BMI test block should be combined as one flaw with length or whether 

the flaws should be considered as single individual flaws.
4.9

Figure 4.5 Methodology for Determining Singularity or Multiplicity of Linear Surface 

Flaws. Reprinted from ASME 2007 BPVC Section XI, Figure IWA-3400-1, by 

permission of The American Society of Mechanical Engineers. All rights 

reserved.

Once the rules of IWA-3400 were applied to the test blocks, the scoring process described 

under Section 4.1.1 was used on the test blocks.
4.10

One can see from Figure 4.6 that test block 5.1 has six individual flaws that are very close in 

proximity. Figure 4.7 shows that using the rules of IWA-3400, the six individual flaws in test 

block 5.1 could be considered as two.

This procedure was not carried out for Sample 5.2, based on the destructive evaluation results.

Figure 4.6 Test Block 5.1 –Individual Flaws

Figure 4.7 Test Block 5.1 – Individual Flaws Combined Under Rules of IWA-3400

4.2 Evaluation of Detection Capability for the PINC Round Robin

4.2.1 Probability of Detection Results for the PINC DMW Round Robin

The goal of the PINC is to determine which techniques are the most effective and to try to 

understand the physical basis for the high performance of the most effective inspection 

techniques. To allow for a statistical analysis of the techniques, the data were organized and 

grouped by team, technique, and flaw orientation. 
4.11

As stated in Section 4.1, a tolerance of 10 mm was used to analyze the data in the round-robin 

tests. The 10-mm tolerance was chosen based upon the observation that, when reviewing 

Figure 4.2, many of the team tolerance curves seemed to approach an asymptote at roughly 

10 mm. The 10-mm value should also be roughly equal in magnitude to the position 

measurement error of the inspection procedures. For simple cylindrical blocks such as PINC 

2.1-2.6, this tolerance is probably greater than the measurement error. But for PINC test blocks

2.9 and 2.10, which are nozzles with a non-constant outer radius, a 10-mm tolerance may 

correctly describe procedure measurement error.

Tables 4.3 and 4.4 summarize the POD when using a 10-mm tolerance. In Table 4.3, note that 

two teams (70 and 96) detected all flaws, while one team (43) missed all of the flaws. Table 4.3 

also indicates if the inspection procedure and teams performing the inspections have formal 

nondestructive testing qualifications. The definition of “formal qualifications” for the teams and 

procedures was left up to the individual invigilators, and is meant to discriminate between NDE 

professionals and NDE researchers with little or no practical NDE experience. The exact 

qualifications and/or certifications for each team cannot be given without violating the 

confidentiality of the inspections. Possible qualifications or certifications for each inspection 

procedure and personnel include but are not limited to:

Procedures:

• Qualifications given by the Czech Republic

• Japan Electric Association JEAC 4207-2008 : Ultrasonic Examination for Inservice 

Inspection of Light Water Cooled Nuclear Power Plant Components

• ASME Code Section XI Appendix VIII 

Personnel:

• Japanese Industrial Standard (JIS) Z 2305:2001, which is consistent with ISO 9712:1999

• ASNT TC-1A and CP189

• ASME Code Section XI Appendix VIII

Also listed is the data collection method used by the inspectors. The three possibilities are 

“Manual,” “Automated,” and “Manual+Encoded.” A manual exam is one where the inspector 

uses their own hands to move the probe and records the position of the probes using rulers or 

other scales. An automated inspection is one where an electronic scanner is used to move the 

probes and record their positions using encoders. A “Manual+Encoded” scan is one where the 

probe is moved by hand, possibly in a track or with the aid of a manual scanner, and the 

positional data is recorded using encoders. 

The “No. of Observations” column in Table 4.3 describes the number of flaws inspected by each 

team. Notice all flaws were inspected by each team except teams 43 and 16. Also listed is the 

data collection method. Figure 4.8 shows the POD and false call rates for the techniques. The 

procedures and teams with formal qualifications are identified. Table 4.4 describes the POD for 

each flaw. The flaws in test blocks 2.2 and 2.3 had the highest POD of 87%. The lowest POD 

seems to be associated with axial flaws; flaw F10.3 was most difficult to detect with a POD 

of 37%.
4.12

Finally, Table 4.5 summarizes the false calls experienced in each of the blocks. The false call 

rate is determined by dividing the number of false calls by the total length of blank material. For 

example, for PINC test block 2.1 has a total of 2.985 meters of blank material (in 16 inspections); thus, the number of false calls divided by 2.985 meters of blank material equals 3.015 

false calls per meter. The false call rate varies from 0.6 false call per meter to 4 false calls per 

meter. A rate of about 2 false calls per meter is an approximation for this round robin. 

Appendix D of this report contains plots that show the location of indications (hits) and the 

location of actual flaws. In Appendix D, false calls and detections from the scoring are 

summarized by “hitograms”. The hitogram plots show indication intensity in each block, with the 

top plot describing false calls and the bottom, detections. The false call hitogram can be used 

to identify hot spots in the blocks—spots that may contain an unidentified or unintended flaw or 

reflector. An examination of the false call plots in Appendix D should convince the reader that 

no hot spots existed in the blocks, except possibly for one in PINC 2.9 at X = 400, Y = 10.

Table 4.3 DMW POD by Teams with 10-mm Tolerance in DMW Test Blocks

Team

No. of 

Observations POD

False Calls per 

Meter of Weld 

Inspected

Qualified 

Team

Qualified 

Procedure Data Collection

13 27 0.815 0.577 X X Automated

16 2 1.000 0.000 Manual

22 27 0.556 4.838 X Automated

28 27 0.704 2.561 X X Automated

30 27 0.667 0.573 X X Manual

38 27 0.889 3.699 Manual+Encoded

39 27 0.630 2.277 X Automated

43 10 0.000 3.08 Manual+Encoded

48 27 0.556 1.446 X X Manual

63 27 0.815 0.598 X Automated

65 27 0.333 5.182 Manual

66 27 0.889 1.423 X Manual+Encoded

67 27 0.741 0.569 Manual

70 27 1.000 0.437 X Manual+Encoded

72 27 0.519 3.965 X X Automated

82 27 0.741 2.277 X Automated

96 27 1.000 0.569 X X Automated
4.13 

12345

 No Qualifications

Potential Drop

0.0

0.2

0.4

0.6

0.8

1.0

012345

 Qualified Team

 Qualified Team and Procedure

 No Qualifications

Eddy Current Testing

 Qualified Team

 Qualified Procedure

 Qualified Team and Procedure

Phased Array +

Conventional UT

12345

Phased Array Testing

0.0

0.2

0.4

0.6

0.8

1.0

 Qualified Team

 Qualified Team and Procedure

Conventional Ultrasonic Testing

012345

False Calls per Meter

Probability of Detection

ID Inspection

PA and

Conventional UT

OD Inspections

Figure 4.8 DMW Probability of Detection and False Call Rates in DMW Test Blocks for 

the Inspection Techniques Showing Qualifications 
4.14

Table 4.4 Probability of Detection by Flaws in DMW Test Blocks

Flaw

No. of 

Observations POD Type

Depth, 

mm

Length, 

mm

PINC 2.1.SHCCl 16 0.625 C 5.8 21.0

PINC 2.2.SHCC2 16 0.875 C 13.5 42.0

PINC 2.3.SHCC3 16 0.875 C 17.8 86.5

PINC 2.4.STCC1 15 0.400 A 4.9 17.0

PINC 2.5.STCC2 15 0.467 A 13.3 38.0

PINC 2.6.STCC3 15 0.733 A 23.5 42.0

PINC 2.9.F9.1 15 0.800 C 35.0 30.0

PINC 2.9.F9.2 15 0.800 C 18.0 20.0

PINC 2.9.F9.3 15 0.800 C 23.0 30.0

PINC 2.9.F9.4 15 0.800 C 9.0 18.0

PINC 2.9.F9.5 15 0.800 C 6.0 15.0

PINC 2.9.F9.6 15 0.733 C 9.4 20.0

PINC 2.9.F9.7 15 0.800 C 6.2 20.0

PINC 2.9.F9.8 15 0.533 C 6.2 20.0

PINC 2.9.F9.9 15 0.467 C 6.0 20.0

PINC 2.9.F9.10 15 0.600 C 6.0 20.0

PINC 2.9.F9.11 15 0.733 C 12.0 18.0

PINC 2.9.F9.12 15 0.800 C 25.4 20.0

PINC 2.10.F10.1 16 0.750 A 20.0 20.0

PINC 2.10.F10.2 16 0.750 A 10.0 20.0

PINC 2.10.F10.3 16 0.375 A 6.0 12.0

PINC 2.10.F10.4 16 0.812 A 30.0 20.0

PINC 2.10.F10.5 16 0.812 A 12.0 12.0

PINC 2.10.F10.6 16 0.688 A 18.0 20.0

PINC 2.10.F10.7 16 0.625 A 25.0 20.0

C = circumferential; A = axial

Table 4.5 Summary of False Calls in DMW Test Blocks

No. of 

Flaws

No. of 

Inspections

Block 

Length, 

meters

Blank 

Length, 

meters

No. of 

Flaw 

Calls

False 

Calls per 

Meter FCP*

PINC 2.1 1 16 0.240 2.985 9 3.105 0.26

PINC 2.2 1 16 0.240 2.555 5 1.957 0.18

PINC 2.3 1 15 0.240 1.614 1 0.620 0.06

PINC 2.4 1 15 0.408 5.180 11 2.123 0.19

PINC 2.5 1 15 0.408 5.311 11 2.071 0.19

PINC 2.6 1 15 0.408 5.215 9 1.726 0.16

PINC 2.9 12 (14) 16 1.213 11.574 46 3.974 0.33

PINC 2.10 7 16 1.213 18.069 40 2.214 0.20

*FCP = false call probability
4.15

A very important variable for crack detection is the depth of the crack. Deep cracks present 

more surface area for ultrasonic reflection, disrupt electrical flow more than shallow cracks, and 

are easier to detect in the presence of geometrical features. Because crack depth is very 

important in all aspects of crack detection, all POD results for the DMW examinations are given 

in terms of crack depth.

Another important variable in any round-robin test is the skill level of the team performing the 

test. Often, even when test blocks, techniques, and other variables are identical, some teams 

will do significantly better than others based on skill level. Section 4.2.1.1 scores each 

individual team, with their accuracy counted against crack depth.

The results are scored by technique in Section 4.2.1.2. The techniques are broken into four 

groups—eddy current testing, phased array ultrasonic testing, conventional ultrasonic testing, 

and potential-drop testing. The PODs for each technique are scored against the depth of the 

cracks. 

The crack orientation is an important consideration in crack detection. The ability of some 

techniques to detect cracks is sensitive to crack orientation, and the pipe geometry affects the 

application of some techniques. Section 4.2.1.3 examines the effects of crack orientation on the 

flaw PODs based on technique.

Finally, Section 4.2.1.4 describes the probability of detecting small flaws and the relationship 

between POD for small flaws and service experience in the United States.

4.2.1.1 Probability of Detection Curves for Teams

Although the inspection technique and flaw characteristics are very important in flaw detection, 

the skill of the operator often is at least as important as the equipment used in the examination. 

The POD results sorted by team are shown in Table 4.6. Additionally, the teams are grouped 

by detection technique to allow for an easy comparison of team performance within the different 

techniques in Table 4.7 and Table 4.8. The probability of detection is given for 5-mm-deep 

flaws, 10-mm-deep flaws, and 15-mm-deep flaws, along with the false call probability (FCP) and 

data collection method. The POD data are plotted versus depth in Figure 4.9, with the FCP 

given as the zero value. When more than one detection technique is identified for detection (as 

with team 66), these techniques were used in tandem. It is worth noting that most teams used 

the same techniques for detection and sizing. The exceptions are teams 82 and 96, which used 

TOFD for depth sizing on flaws found using conventional UT (82) or eddy current (96). 

Team variability was notable in the phased array examinations, with teams 13 and 66 outperforming teams 39 and 72. Team 63 did much better than the other teams using conventional 

UT. All eddy current teams had a high POD, but team 38 had a high false call probability. 

Notice that teams 70 and 96 performed nearly identically, with a POD close to 1.0 for small 

flaws.

When examining manual vs. automatic data collection for conventional UT, it appears that 

automated data collection has an advantage over manual data collection. More data is needed 

before team variability can be ruled out. 
4.16

Table 4.6 Individual Team PODs Listed versus DMW Flaw Depth Sorted by Team Number

Team

POD for Flaw Depth: False Call 

5 mm 10 mm 15 mm Probability Detection Technique Data Collection

13 0.37 0.83 0.98 0.07 Phased Array UT Automated

22 0.52 0.52 0.53 0.51 Conventional UT Automated

28 0.42 0.6 0.76 0.26 Conventional UT Automated

30 0.24 0.43 0.65 0.11 Conventional UT Manual

38 0.78 0.96 0.99 0.36 Eddy Current Manual+Encoded

39 0.36 0.47 0.59 0.26 Phased Array UT Automated

43 0 0 0 0.31 Potential Drop Manual+Encoded

48 0.24 0.42 0.61 0.13 Conventional UT Manual

63 0.37 0.79 0.96 0.08 Conventional UT Automated

65 0.3 0.32 0.33 0.28 Potential Drop Manual

66 0.62 0.94 0.99 0.14 Phased Array+Conventional UT Manual+Encoded

67 0.32 0.45 0.6 0.2 Potential Drop Manual

70 1 1 1 0.04 Eddy Current Manual+Encoded

72 0.41 0.47 0.54 0.35 Phased Array UT Automated

82 0.44 0.53 0.61 0.35 Conventional UT Automated

96 1 1 1 0.06 Eddy Current Automated

Table 4.7 Individual Team PODs Listed versus DMW Flaw Depth Sorted by ID Technique

Team

POD for Flaw Depth: False Call 

5 mm 10 mm 15 mm Probability Detection Technique Data Collection

38 0.78 0.96 0.99 0.36 Eddy Current Manual+Encoded

70 1 1 1 0.04 Eddy Current Manual+Encoded

96 1 1 1 0.06 Eddy Current Automated

67 0.32 0.45 0.6 0.2 Potential Drop Manual

Table 4.8 Individual Team PODs Listed versus DMW Flaw Depth Sorted by OD Technique

Team

POD for Flaw Depth: False Call 

5 mm 10 mm 15 mm Probability Detection Technique Data Collection

22 0.52 0.52 0.53 0.51 Conventional UT Automated

28 0.42 0.6 0.76 0.26 Conventional UT Automated

30 0.24 0.43 0.65 0.11 Conventional UT Manual

48 0.24 0.42 0.61 0.13 Conventional UT Manual

63 0.37 0.79 0.96 0.08 Conventional UT Automated

82 0.44 0.53 0.61 0.35 Conventional UT Automated

66 0.62 0.94 0.99 0.14 Phased Array + Conventional UT Manual+Encoded

13 0.37 0.83 0.98 0.07 Phased Array UT Automated

39 0.36 0.47 0.59 0.26 Phased Array UT Automated

72 0.41 0.47 0.54 0.35 Phased Array UT Automated

43 0 0 0 0.31 Potential Drop Manual

65 0.3 0.32 0.33 0.28 Potential Drop Manual
4.17

4.2.1.2 Probability of Detection Results for Procedures

While there was variation between teams for each technique, the examination technique had a 

large impact on the probability of detection. Eddy current was the highest performing technique, 

detecting almost all of the flaws and making few false calls. Conventional ultrasound and 

phased array UT appeared to be an effective combination, but only one team used this 

technique, so team variability may be a factor. Using either conventional ultrasound or phased 

array UT alone gave similar results. Potential-drop techniques had the lowest performance, 

with the possible exception of team 67. It should be noted that eddy current tests were 

performed from the ID of the test blocks while the UT techniques were applied from the outside 

surface of the test blocks. The results for inspection procedures are presented in Table 4.9.

Table 4.9 Probability of Detection Summary for Procedures in DMW Test Blocks

Procedure

POD for Flaw Depths of False Call 

5 mm 10 mm 15 mm Probability ID/OD

Eddy Current 0.88 1.00 1.00 0.17 ID

Conventional UT and Phased Array UT 0.62 0.94 0.99 0.14 OD

Conventional UT 0.36 0.51 0.67 0.23 OD

Phased Array UT 0.36 0.51 0.66 0.24 OD

Conventional UT and TOFD 0.44 0.53 0.61 0.35 OD

Potential Drop 0.29 0.33 0.38 0.25 Both

Figure 4.10 shows these POD values and regressions based on the inspection results. The 

values are plotted against sample sizes. Each POD curve is surrounded by a 95% confidence 

bound.
4.18

Figure 4.9 Probability of Detection Plotted versus the Crack Depth in DMW Test Blocks
4.19 

Conventional UT Conventional UT and Phased Array

0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0

0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0

0 5 10 15 20 25 30 35 0 5 10 15 20 25 30 35

Depth (mm) Depth (mm)

POD

POD

Conventional UT and TOFD Eddy Current

0.0 0.2 0.4 0.6 0.8 1.0

0.0 0.2 0.4 0.6 0.8 1.0

0 5 10 15 20 25 30 35 0 5 10 15 20 25 30 35

Depth (mm) Depth (mm)

POD

POD

0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0

0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0

0 5 10 15 20 25 30 35 0 5 10 15 20 25 30 35

Depth (mm) Depth (mm)

POD

POD

Figure 4.10 Probability of Detection Curves for Detection Procedures in DMW Test 

Blocks 
4.20 

Phased Array Potential Drop

0.0 0.2 0.4 0.6 0.8 1.0

0.0 0.2 0.4 0.6 0.8 1.0

0 5 10 15 20 25 30 35 0 5 10 15 20 25 30 35

Depth (mm) Depth (mm)

POD

POD

Figure 4.10 (continued)

4.2.1.3 Effects of Flaw Orientation on Dissimilar Metal Weld Detection Probability 

As some techniques are more easily applied along the length of a pipe as opposed to around a 

pipe, it is important to examine the POD of flaws based on their orientation. The POD results 

are shown in Table 4.10 and Table 4.11. As flaw orientation might be expected to affect each 

procedure differently, POD curves for ultrasonic and electromagnetic procedures were 

computed separately. The results are plotted in Figure 4.11. 

Table 4.10 Probability of Detection for Circumferential Flaws as a Function of Depth in 

DMW Test Blocks 

Procedure 

POD for Flaw Depths of False Call 

5 mm 10 mm 15 mm Probability 

Eddy Current 0.92 1.00 1.00 0.17 

Ultrasound 0.41 0.61 0.61 0.23 

Potential Drop 0.28 0.35 0.43 0.23 
4.21

Table 4.11 Probability of Detection for Axial Flaws as a Function of Depth in DMW Test 

Blocks

Procedure

POD for Flaw Depths of False Call 

5 mm 10 mm 15 mm Probability

Eddy Current 0.80 0.99 1.00 0.17

Ultrasound 0.32 0.45 0.59 0.21

Potential Drop 0.24 0.27 0.32 0.20

Figure 4.11 Probability of Detection Curves for Flaw Orientation in DMW Test Blocks

The results show that circumferential flaws in these blocks were somewhat easier to detect than 

axial flaws using ultrasound, especially for cracks close to 10 mm deep. Eddy current was 

largely unaffected but does show an 11% greater chance of seeing a 5-mm-deep circumferential flaw than a 5-mm-deep axial flaw. Circumferential flaws were somewhat more detectable 

with the potential-drop technique as well.
4.22

4.2.1.4 Probability of Detection for Small Flaws and Service Experience

As shown in Table 4.9, the probability of detection results for small flaws, flaws that are 4 to 

5 mm (approximately 10% through-wall) are as follows:

• Eddy current examinations have a detection rate of 88%.

• The Team that used both conventional UT and phased array UT had a 62% chance of 

finding a 5-mm-deep crack.

• Teams that used conventional UT and TOFD had a 44% chance of detecting a 5-mm-deep 

crack.

• Teams that used conventional UT or phased array UT techniques demonstrated a 37% 

detection rate for 5-mm-deep cracks.

• Potential-drop techniques exhibited a 29% chance of finding 5-mm-deep cracks. 

With the exception of eddy current inspection techniques that are typically used for examination of 

vessel nozzles using the vessel inspection tool, the detection performance for small flaws was low. 

Because PWSCC is a very aggressive degradation mechanism that has demonstrated very fast 

crack growth rates, it is not surprising that service experience has shown that PWSCC either has 

usually grown through-wall or has been detected after cracks are greater than 20% through-wall.

4.2.2 Probability of Detection Results for the BMI Round Robin

The flaws in the BMI test blocks were evaluated by eight teams using several techniques. The 

goal of the PINC BMI round robin was to determine which techniques are the most effective and 

to understand the physical basis for the techniques’ performance. No two teams used identical 

techniques, although some groupings can be made.

There are several approaches to evaluating the abilities of the different teams to detect the 

fabricated cracks in the test blocks. The data analysis is complicated by two factors—not all 

teams examined the same test block set, and some of the test blocks had flaws that proved to 

be more challenging to find than was expected. The average POD, as shown in Table 4.12 for 

each test block, shows that test blocks 5.9 and 5.10 were the most challenging. The other test 

blocks have roughly the same POD of close to 0.8. Test blocks 5.1–5.3 are difficult to interpret 

because there were too few observations and the error was too large to allow one to draw 

conclusions on their difficulty. The results for each team and each sample are given in 

Appendix E. A hitogram showing the numbers of hits and misses and the false call densities for 

each sample is given in Appendix F.

Test blocks 5.6, 5.7, and 5.13–5.16 can be considered “baseline” difficulty, while test blocks 5.9 

and 5.10 can be considered “challenging.” It should be noted that test blocks 5.9 and 5.10 were 

designed to mimic difficult-to-detect indications found in the North Anna 2 Nozzle 31 J-groove 

weld. During subsequent destructive evaluation these indications could were not confirmed as 

being caused by PWSCC. The flaw manufacturer for test blocks 5.9 and 5.10 used a process to 

make the flaws more challenging to detect. All teams inspected the challenging test blocks, 5.9 

and 5.10, and the different teams also examined different numbers of the baseline test blocks. 
4.23

To determine which teams are the most affected by the varying proportion of challenging to 

baseline test blocks, the number of baseline and challenging flaw observations was tallied and 

is shown in Table 4.13.

Table 4.12 Probability of Detection for Each Test Block in BMI Test Blocks

Test Block POD Observations

5.1 0.50 2

5.2 0.50 2

5.3 0.25 4

5.6 0.75 24

5.7 0.81 21

5.9 0.18 28

5.10 0.18 28

5.13 0.70 10

5.14 0.90 10

5.15 0.70 10

5.16 0.90 10

Table 4.13 Number of Baseline and Challenging Flaw Observations for Each Team in 

BMI Test Blocks

Flaw Difficulty

Team

Baseline

Flaw Observations

Challenging

Flaw Observations

% Baseline 

Observations

16 11 8 0.58

373 21 8 0.72

38 17 8 0.68

66 11 8 0.58

67 3 8 0.27

70 17 8 0.68

99 13 8 0.62

Most teams appear to have a ratio of 50–60% of baseline flaws. Team 67 faced a more 

challenging test than the others and this was noted in the data analysis.

4.2.2.1 Probability of Detection Curves for Teams Using a Strict Tolerance Box

The round-robin data were analyzed using a statistical regression to determine the POD for 

each technique. An upper and lower 95% confidence boundary was calculated using the POD 

and the number of flaw observations at each flaw size. It is worth noting that the effect of the 

challenging test blocks is somewhat mitigated in these regressions because all but two of the 

flaws in the challenging test blocks are less than 5 mm in length. All regressions include the 

results for both baseline and challenging flaws. The regressions allow one to draw conclusions 

about the usefulness of the different techniques for finding flaws of various lengths.
4.24

4.2.2.2 Probability of Detection for BMI Tube Examinations

The interiors of the penetration tubes were examined by two teams, 13 and 70. Many of the 

flaws in test blocks 5.1–5.3 were very close to one another, resulting in some flaws being 

considered one flaw by ASME Code proximity rules. The results for Team 70 (provided in 

Appendix E) show some calls made on calibration notches in the penetration tubes. These calls 

on the calibration notches were not considered hits, as the notches are not representative of 

flaws that would be encountered in the field. The calls on the calibration notches were not 

counted as false calls because the notches were present in the penetration tubes. Team 70 

used a surface technique and is only scored using surface breaking flaws, and thus has fewer 

observations than Team 13. The results of the tube examinations are presented in Table 4.14.

Table 4.14 Probability of Detection Scores for Tube Examinations in BMI Test Blocks

Team

Detection 

Technique Observations POD

False Calls per 

Test Block

Qualified 

Team

Data 

Collection

13 ECT and TOFD 17 0.53 1.7 Automatic

70 ECT 4 0.5 0.67 X Automatic

Given the low number of observations, it is challenging to draw meaningful results from the 

examinations. Team 13 achieved a higher POD than Team 70, but with more false calls. An 

examination of the data shows that the teams made calls that grouped multiple flaws together, 

which is understandable given the tight flaw spacing. When the tube examinations are scored 

using ASME Code proximity rules, the POD results improve. The POD results for the combined 

flaws are given in Table 4.15.

Table 4.15 Probability of Detection Scores for Tube Examinations for Flaws Combined 

Using ASME Rules in BMI Test Blocks

Team

Detection 

Technique Observations POD

False Calls 

per Test Block

Qualified 

Team

Data 

Collection

13 ECT and TOFD 12 0.83 1.7 Automatic

70 ECT 4 0.5 0.67 X Automatic

For the tube examinations, the results show low PODs with an insufficient number of 

observations to draw strong conclusions. Some of the flaws are detectable, but a more 

extensive test would need to be performed to quantify the effectiveness of the ECT and TOFD 

techniques. The regressions for the tube interiors are given in Figure 4.12.
4.25

ECT 400 kHz ECT 400 kHz and TOFD

Flaw Length (mm)

POD

0

0.0 0.2 0.4 0.6 0.8 1.00.0 0.2 0.4 0.6 0.8 1.0

10 20 30 40 0 10 20 30 40

Figure 4.12 Probability of Detection Regression for Examinations of the Penetration 

Tube Interiors in BMI Test Blocks

4.2.2.3 Probability of Detection for BMI Weld Surface Examinations

The data were analyzed by comparing the true-state information with fixed scoring boxes 

determined as described in Section 5. This scoring method yields the following results for each 

team and is given in Table 4.16.

Table 4.16 Probability of Detection and False Call Rates for Each Team Using a 10-mm 

Tolerance Box in BMI Test Blocks

Team Detection Technique Observations POD

False Calls 

per Sample

Qualified 

Team Data Collection

16 CCPPD 19 0.26 0.00 Manual

373 ECT 300 kHz 29 0.72 0.15 Automatic

38 Array ECT 100 kHz 25 0.4 4.80 Manual

66 Adaptive Phased Array UT 19 0.58 0.00 X Automatic

67 ICPD 11 0.27 0.67 Automatic

70 ECT 400 kHz 25 0.84 0.00 X Automatic

99 Array ECT 200 kHz 21 0.43 2.50 Automatic

The straight POD scores correlate very closely with the percentage of baseline flaws examined 

by each team. When the POD results are analyzed with the baseline and challenging flaws 

separated out, a trend becomes clear. Teams 66, 70, and 373 were very effective at finding the 

baseline flaws, with PODs at or near 100%. Teams 16 and 38 showed improved performance 

on the baseline flaws, but were still below 50%. Teams 67 and 99 showed greatly improved 

performance on the baseline samples. For the challenging samples, no team performed 
4.26

strongly. The highest scoring team was Team 70, which achieved a POD of 0.40. Teams 16, 

38, 66, and 99 were unable to detect the challenging flaws. The baseline and challenging flaw 

PODs are given in Table 4.17. 

Table 4.17 Probability of Detection Results in BMI Test Blocks for Baseline and 

Challenging Flaws with Upper and Lower 95% Confidence Levels (CL)

Baseline Challenging

Team POD POD

16 0.45 0.00

373 0.85 0.38

38 0.59 0.00

66 1.00 0.00

67 0.67 0.13

70 1.00 0.50

99 0.69 0.00

The examinations showed some clear high-performing techniques and techniques that need to 

be developed further before they are useful for reliably finding flaws in BMIs. The POD 

regression results for each technique for selected flaw lengths (including borderline and 

challenging flaws) are given in Table 4.18. 

Cross-coil probe eddy current at 300–400 kHz proved to be very effective at finding the flaws in 

the test blocks. The high-frequency eddy current was also able to find a small fraction of the 

challenging flaws as well. The 400-kHz eddy current outperformed the 300-kHz eddy current in 

both the baseline and in the challenging flaws, and the 400-kHz examinations had a lower false 

call rate. The POD regressions for the two cross-coil eddy-current inspections are shown in

Figure 4.13.

Table 4.18 Probability of Detection Regression Results for 5-, 10-, and 15-mm Flaws in 

BMI Test Blocks

Detection POD for Flaw Lengths of:

Team Technique 5 10 15 FCP

16 CCPPD 0.04 0.21 0.59 0.01

373 ECT 300 kHz 0.31 0.83 0.98 0.03

38 Array ECT 100 kHz 0.44 0.55 0.65 0.34

66 Adaptive Phased Array UT 0.21 0.96 1.00 0.00

67 ICPD 0.25 0.79 0.98 0.03

70 ECT 400 kHz 0.80 1.00 1.00 0.01

99 Array ECT 200 kHz 0.37 0.58 0.76 0.21
4.27

POD

0.0 0.2 0.4 0.6 0.8 1.0

0.0 0.2 0.4 0.6 0.8 1.0

0 5 10 15 20 25 0 5 10 15 20 25

Flaw Length (mm)

Cross Coil ECT 400 kHz Cross Coil ECT 300 kHz

Figure 4.13 Probability of Detection Regressions for Cross-Coil Eddy-Current 

Techniques with 95% Confidence Intervals in BMI Test Blocks

The results for the array eddy-current techniques were relatively poor compared to the crosscoil probe eddy current, and both array eddy current examinations had a very high false call 

rate. The array eddy current used lower frequencies than the cross-coil probes, which may 

have contributed to the poor performance. The POD regressions are shown in Figure 4.14.

The POD regressions for the potential-drop techniques show that they are able to detect longer 

flaws in test blocks, although the 95% confidence interval is very large based on the small 

number of test blocks in the tests. It is interesting that the potential-drop techniques were able 

to outperform the array ECT techniques. The POD regressions for the potential-drop 

techniques are shown in Figure 4.15.

The adaptive phased array ultrasound provided perfect detection of all flaws in the baseline 

difficulty test blocks and missed all flaws in the challenging test blocks. The POD regression 

curve shows the adaptive phased array technique has a very high probability of detecting flaws 

greater than 10 mm in length. The POD results for the adaptive phased array technique for all 

flaws are shown in Figure 4.16.
4.28

POD

0.0 0.2 0.4 0.6 0.8 1.0

0.0 0.2 0.4 0.6 0.8 1.0

0 5 10 15 20 25 0 5 10 15 20 25

Array ECT 100 kHz Array ECT 200 kHz

Flaw Length (mm)

Figure 4.14 Probability of Detection Regressions in BMI Test Blocks for Array EddyCurrent Techniques POD 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0

0 5 10 15 20 25 0 5 10 15 20 25

Flaw Length (mm)

CCPPD ICPD

Figure 4.15 Probability of Detection Regressions in BMI Test Blocks for Potential-Drop 

Techniques
4.29

0 5 10 15 20 25

Flaw Length (mm)

POD

0.0 0.2 0.4 0.6 0.8 1.0

Adaptive Phased Array UT

Figure 4.16 Probability of Detection Regression in BMI Test Blocks for Adaptive 

Phased Array Technique

4.2.2.4 Probability of Detection versus BMI Test Block Flaw Characteristics

It is important to understand the crack morphologies and characteristics that make flaws reliably 

detectable or challenging to find during inservice inspections. The destructive analysis results 

of BMI test blocks are shown in Appendices A and B. The usual crack characteristics that are 

commonly considered important for NDE reliability include crack length, depth, and COD. The 

true-state information contained the crack lengths and depths, and the destructive examinations 

for test blocks 5.13–5.16 contain information on the CODs for these test blocks.

To better understand the crack characteristics, PNNL performed a series of fingerprinting 

examinations of the surfaces of test blocks 5.6–5.16. These fingerprinting measurements were 

performed in a laboratory with the true-state information available to the inspectors. A 5-MHz 

eddy current examination was performed using a pancake-style coil. The eddy current system 

was calibrated before each examination to ensure consistent results. The flaws were analyzed 

and the maximum voltage for each flaw was recorded. The PNNL fingerprinting results for the 

flaws in the surfaces of test blocks 5.6-5.16, along with the crack lengths, depths, crack POD, 

and flaw fabrication technique, are tabulated in Table 4.18. The complete fingerprinting results 

are shown in Appendix G.

When the data for the surface examinations were analyzed, the overall POD for each flaw was 

largely independent of flaw length, depth, or flaw orientation. The single largest influence in the 

flaw POD was the test block identification. All flaws that were not in test blocks 5.9 and 5.10 

have a POD of approximately 0.8, and the flaws in test blocks 5.9 and 5.10 had much lower 

overall PODs. In test blocks 5.9 and 5.10, the largest influence in the flaw POD was the flaw 

length. The flaw depth was not an important variable for flaw detection in these test blocks. 

The crack PODs for the various crack fabrication techniques are plotted against their length in 

Figure 4.17 and against their depth in Figure 4.18.
4.30

Table 4.19 BMI Flaw Probability of Detection and Important Parameters

Test 

Block Flaw

Radial 

Location, °

PNNL ECT 

Magnitude, V POD

Flaw 

Length, mm

Flaw 

Depth, mm

Flaw 

Orientation

Fabrication 

Technique

5.6 1 45 0.72 0.75 4 2 Axial Weld Solidification

5.6 2 135 1.74 0.75 5 2 Circ. Weld Solidification

5.6 3 180 1.07 0.75 5 2 Axial Weld Solidification

5.6 4 225 1.25 0.75 10 5 Circ. Weld Solidification

5.6 5 255 NR 0.75 11 5 Circ Weld Solidification

5.6 6 315 1.44 0.75 6 1.5 Axial Weld Solidification

5.7 1 15 2.35 0.71 4 2 Circ. Thermal Fatigue

5.7 2 165 1.67 0.86 8 3 Axial Thermal Fatigue

5.7 3 300 2.32 0.86 NA NA Axial Thermal Fatigue

5.9 1 15 0.51 0.29 4 1 Axial Weld Solidification

5.9 2 75 NR 0.14 3 6 Axial Weld Solidification

5.9 3 195 NR 0.14 3 3 Circ. Weld Solidification

5.9 4 345 1.33 0.14 4 7 Axial Weld Solidification

5.10 1 45 2.69 0.14 7.5 9 Circ. Weld Solidification

5.10 2 75 1.79 0.00 5 7 Circ. Weld Solidification

5.10* 3 225 NR 0.00 3.5 0.4 Axial Weld Solidification

5.10 4 255 1.9 0.43 7 2 Circ. Weld Solidification

5.10 5 285 NR 0.14 4.5 2 Axial Weld Solidification

5.10* 6 315 1.96 0.00 1.5 4.5 Axial Weld Solidification

5.13 1 0 2.45 0.80 8 2 Circ. Induced SCC

5.13 2 180 1.62 0.60 12 2 Circ. Induced SCC

5.14 1 0 3.92 1.00 14 11 Circ. Induced SCC

5.14 2 180 1.39 0.80 14 2 Circ. Induced SCC

5.15 1 90 2.94 0.80 12 4 Axial Induced SCC

5.15 2 270 4.01 0.60 13 3 Axial Induced SCC

5.16 1 90 4.42 1.00 16 11 Axial Induced SCC

5.16 2 270 7.08 0.80 19 6 Axial Induced SCC

* During DE, Flaws 5.10 3 and 5.10 6 were determined to be too small for use in scoring.
4.31 

0 2 4 6 8 10 12 14 16 18

0.0

0.2

0.4

0.6

0.8

1.0

Probability of Detection

Length (mm)

 Weld Solidification 5.6

 Thermal Fatigue

 Weld Solidification 5.9 -5.10

 Induced SCC

Figure 4.17 BMI Flaw Probability of Detection versus Flaw Length for Each Flaw 

Fabrication Technique 

0 2 4 6 8 10 12

0.0

0.2

0.4

0.6

0.8

1.0

 Weld Solidification 5.6

 Thermal Fatigue

 Weld Solidification 5.9 -5.10

 Induced SCC

Probability of Detection

Depth (mm)

 Weld Solidification 5.6

 Thermal Fatigue

 Weld Solidification 5.9 -5.10

 Induced SCC

Figure 4.18 BMI Flaw Probability of Detection versus Flaw Depth for Each Flaw 

Fabrication Technique 

Because one of the main goals of the PINC is to discover what makes a crack easy or difficult to 

detect, the flaws in test blocks 5.9 and 5.10 provided an opportunity to explore what it is about 

these flaws that make them different from the thermal fatigue, other SCC, and the weldsolidification flaws fabricated into other test blocks. Sample 5.10 was destructively analyzed, 

and the results are given in Appendix B. 
4.32

4.3 Sizing Results as Measured by the PINC Round Robin Exercises

4.3.1 Sizing Results from the PINC DMW Round Robin

This section of the report discusses the sizing capability that was measured from the DMW 

round robin data. One of the goals of the PINC is to determine which techniques are the most 

effective at characterizing the through-wall depth and length of PWSCC. Some statistical 

analysis of crack length and depth characterization is provided in this section so that 

conclusions may be drawn concerning crack characterization capability. The data have been 

grouped by team, technique, and flaw orientation for a statistical analysis.

Linear regression was used to analyze sizing data that was developed under the PINC DMW 

round robin. PNNL defined an error relation between the measured and true sizes of the flaws 

by the following regression formula:

Mi = B1 + B2 × Ti + Ei (4.6)

where Mi represents the measured size associated with flaw i

Ti represents the true size of flaw i

Ei represents the measurement error in sizing flaw i

B1 and B2 are the regression parameters usually associated with the Y intercept and slope of 

the linear regression. Ideal performance for sizing would occur when B1 = 0, B2 = 1 and Ei = 0. 

To compare two different regression fits, and to order a set of regression fits (from most 

accurate to least accurate as an example), PNNL used the metric of root mean square error 

(RMSE). RMSE is a statistic that summarizes the three deviations of regression analyses from 

their respective ideals. RMSE is defined by 

∑( − ) =

2

i i 2 i

M T

RMSE

n

(4.7)

where all the variables are the same as in the preceding descriptions and n is the total number 

of flaws.

4.3.1.1 Summary of Flaw Depth Characterization for All Flaws and All Teams

According to ASME Code requirements, any indication that is determined to be SCC is not 

allowable in dissimilar metal welds. The practice in most U.S. nuclear power plants where 

PWSCC has been detected or is expected is to perform a mitigation technique such as weld 

overlay or mechanical stress improvement. Before applying the mitigation technique, depth 

sizing of flaws is important because one does not want to perform a mitigation technique that 

would place the flaw in a region of tensile stress that would possibly make the welded joint 

integrity worse after applying the mitigation technique.
4.33

Table 4.20 presents the combined results of all teams for characterizing the depth of flaws. 

Figure 4.19 provides regression plots of measured flaw size versus the true-flaw depths for the 

teams that participated in the round robin, with the team number printed on the top of the 

appropriate inspection plot. The design true-flaw depths have been supplied by the host 

country that provided the test blocks.

Table 4.20 Summary of Depth Sizing Results on All Flaws in DMW Test Blocks

Team

Intercept Slope

Standard 

Error RMSE

No. of 

Observations

Inspection 

Intercept Technique

Std Dev of 

Intercept Slope

Std Dev 

of Slope

13 6.91 2.13 0.57 0.12 4.46 5.72 20 Phased Array UT

22 9.17 3.64 0.14 0.23 6.94 10.09 14 Conventional UT

28 4.99 3.44 0.52 0.18 5.75 7.82 15 Conventional UT

30 9.09 3.33 0.40 0.19 6.39 8.16 16 Conventional UT

38 NA NA NA NA NA NA 0 Eddy Current

39 1.66 1.33 0.76 0.07 2.62 4.01 15 Phased Array UT 

16 NA NA NA NA NA NA 2 Potential Drop

43 NA NA NA NA NA NA 0 Potential Drop

48 12.94 2.20 0.17 0.11 3.10 7.87 13 Conventional UT

63 6.33 1.90 0.62 0.11 4.06 5.19 20 Conventional UT

65 NA NA NA NA NA NA 0 Potential Drop

66 1.61 1.40 0.93 0.08 3.15 3.18 22 Phased Array UT 

+ Conventional UT

67 0.98 1.93 0.21 0.13 4.20 11.47 19 Potential Drop

70 NA NA NA NA NA NA 0 Eddy Current

72 10.41 4.78 0.44 0.24 7.70 9.13 12 Phased Array UT

82 7.07 3.06 0.53 0.23 5.85 6.59 17 Conventional UT

96 6.21 1.59 0.55 0.10 4.07 5.58 25 TOFD + 

Conventional UT + 

Eddy Current

All 5.34 0.84 0.56 0.56 0.56 7.07 208

Table 4.20 shows that some teams had accurate sizing results. Team 66 used phased array 

UT and tip-diffraction techniques and performed well in both detection and sizing. All teams that 

used the phased array UT technology performed better than teams that used conventional 

ultrasonic methods. Teams that used electromagnetic methods did not perform well at all in 

depth sizing. Figure 4.19 presents the depth sizing regression analysis, including 95% 

confidence bounds, from all teams. 

Two teams attempted depth sizing but were not included in the regressions. Team 16 

examined two cracks and did not have enough information to allow for a statistical regression. 

Team 38 was only able to measure the first three millimeters of the surfaces, and only had 

information on a small region of the samples. Team 38 was able to attempt to depth size flaws 

that were less than 3 mm in depth and could refer to deeper flaws as “deeper than 3 mm.” The 

depth sizing results for Team 38 are summarized in Figure 4.20 and the depth sizing results for 

Team 16 are summarized in Table 4.21.
4.34

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

0 5 10 15 20 25 30 35 0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

0 5 10 15 20 25 30 35 0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

All Teams Team 13

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

0 5 10 15 20 25 30 35 0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

0 5 10 15 20 25 30 35 0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

Team 22 Team 28

Figure 4.19 Depth Sizing Regression in DMW Test Blocks
4.35

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

0 5 10 15 20 25 30 35 0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

0 5 10 15 20 25 30 35 0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

Team 30 Team 39

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

0 5 10 15 20 25 30 35 0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

0 5 10 15 20 25 30 35 0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

Team 48 Team 63

Figure 4.19 (continued)
4.36

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

0 5 10 15 20 25 30 35 0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

0 5 10 15 20 25 30 35 0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

Team 66 Team 67

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

0 5 10 15 20 25 30 35 0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

0 5 10 15 20 25 30 35 0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

Team 72 Team 82

Figure 4.19 (continued)
4.37

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

0 5 10 15 20 25 30 35 0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

0 5 10 15 20 25 30 35 0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

Team 96 Conventional UT

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

0 5 10 15 20 25 30 35 0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

0 5 10 15 20 25 30 35 0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

Conventional UT + Phased Array Conventional UT +TOFD

Figure 4.19 (continued)
4.38

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

0 5 10 15 20 25 30 35 0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

0 5 10 15 20 25 30 35 0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

Phased Array Potential Drop

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

Measured Depth (mm)

0 5 10 15 20 25 30 35 0 5 10 15 20 25 30 35

Measured Depth (mm)

True Depth (mm)

TOFD + Tandem UT

Figure 4.19 (continued)
4.39

0 5 10 15 20 25 30 35

0

5

10

15

20

25

30

35

Measured Depth (mm)

Greater Than 3 mm

Measured Depth (mm)

True Depth (mm)

Figure 4.20 Dissimilar Metal Weld Depth Sizing Results for Team 38

Table 4.21 Dissimilar Metal Weld Depth Sizing Results for Team 16

Flaw ID

Measured

Depth (mm)

True

Depth (mm)

PINC 2.1 3.6 5.8

PINC 2.4 2.6 4.9

4.3.2 Flaw Length Sizing in Dissimilar Metal Welds

Table 4.22 and Table 4.23 provide a summary of the length sizing results for the PINC DMW 

round robin. Table 4.22 summarizes the length sizing results for circumferential flaws and Table 

4.23 summarizes the length sizing results for axial flaws. Figure 4.21 and Figure 4.22 provide 

regression plots of the length sizing results for the teams that participated in the round robin. 

Figure 4.21 summarizes the length sizing results for circumferential flaws and Figure 4.22

summarizes the length sizing results for axial flaws. A review of the information in Table 4.22

and Table 4.23 shows that eddy current techniques were the most accurate for length sizing 

flaws followed by phased array ultrasonic techniques. Conventional ultrasonic and potentialdrop techniques were poor at length sizing. Appendix VIII of Section XI of the ASME Code 

states that examination procedures, equipment, and personnel be qualified for length sizing 

when the RMSE of the flaw-length measurements compared to the true flaw lengths do not 

exceed 0.75 in. (19 mm). A review of the data in Table 4.22 and Table 4.23 shows that half 

(8 out of the 16 teams) would have passed a performance demonstration test. Table 4.24 

shows the length sizing results for Team 16.
4.40

Table 4.22 Summary of Length Sizing Results for Circumferential Flaws in DMW Test 

Blocks

Team

Intercept Slope

Standard

Error RMSE

No. of 

ObservationsInspection 

Intercept Technique

Std Dev of 

Intercept Slope

Std Dev of 

Slope

13 30.54 7.54 0.51 0.23 14.98 24.09 13 Phased Array UT

22 16.72 9.86 0.35 0.28 18.46 22.44 10 Conventional UT

28 12.10 5.43 0.71 0.15 10.01 11.78 11 Conventional UT

30 6.66 6.55 0.65 0.17 11.02 13.54 9 Conventional UT

38 17.43 3.72 -0.08 0.11 7.65 24.28 14 Eddy Current

39 3.14 2.46 0.84 0.07 4.89 5.78 13 Phased Array UT

16 NA NA NA NA NA NA CCPPD

43 NA NA NA NA NA NA 0 Potential Drop

48 169.10 23.84 -2.26 0.88 18.95 91.60 7 Conventional UT

63 2.24 2.75 0.83 0.08 5.30 6.62 12 Conventional UT

65 61.30 19.56 -0.60 0.45 26.02 47.67 6 Potential Drop

66 12.46 3.35 0.74 0.10 6.65 9.63 13 Phased Array UT + 

Conventional UT 

67 0.13 2.02 0.90 0.06 3.92 4.94 11 Potential Drop

70 7.08 2.06 0.93 0.06 4.33 6.74 15 Eddy Current

72 24.79 13.53 0.46 0.32 18.94 22.91 6 Phased Array UT

82 28.76 4.77 -0.17 0.15 9.74 24.47 13 Conventional UT

96 4.51 1.23 0.87 0.04 2.58 3.56 15 Conventional UT + 

Eddy Current

All 19.13 3.13 0.48 0.09 22.61 25.01 168

Note: All measurements are in millimeters.
4.41

Table 4.23 Summary of Length Sizing Results for Axial Flaws in DMW Test Blocks

Team

Intercept Slope

Standard

Error RMSE

No. of 

ObservationsInspection 

Intercept Technique

Std Dev of 

Intercept Slope

Std Dev of 

Slope

13 20.70 13.08 0.23 0.55 12.62 14.08 7 Phased Array UT

22 -0.81 14.86 0.71 0.85 5.53 7.39 4 Conventional UT

28 5.40 17.13 1.05 0.91 6.62 8.67 6 Conventional UT

30 20.16 5.13 0.00 0.19 5.19 12.78 7 Conventional UT

38 -2.93 5.48 0.78 0.22 6.14 10.18 9 Eddy Current

39 NA NA NA NA NA 7.14 2 Phased Array UT 

16 NA NA NA NA NA NA

43 NA NA NA NA NA NA 0 Potential Drop

48 11.34 0.76 0.23 0.03 0.71 9.77 6 Conventional UT

63 6.07 3.47 0.20 0.15 3.80 13.34 8 Conventional UT

65 NA NA NA NA NA 30.30 3 Potential Drop

66 17.24 2.23 -0.13 0.09 2.66 14.64 9 Phased Array UT + 

Conventional UT

67 -0.13 1.39 0.86 0.06 1.66 3.92 8 Potential Drop

70 15.13 1.63 0.62 0.07 2.03 7.95 10 Eddy Current

72 17.50 10.35 0.38 0.55 4.00 7.14 6 Phased Array UT

82 6.68 10.12 0.56 0.33 8.20 10.67 4 Conventional UT

96 4.49 2.11 0.72 0.09 2.63 4.11 10 Conventional UT + 

Eddy Current

All 11.85 2.27 0.38 0.09 8.68 10.55 99

Note: All measurements are in millimeters.

Table 4.24 Dissimilar Metal Weld Length Sizing Results for Team 16

Flaw ID

Measured

Length (mm)

True

Length (mm)

PINC 2.1 25 21

PINC 2.4 16 17
4.42

0

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

0

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

0

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

0

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

All Teams Team 13

0

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

0

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

0

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

0

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

Team 22 Team 28

Figure 4.21 Results of Length Sizing on Circumferential Flaws in DMW Test Blocks
4.43

Figure 4.21 (continued)
4.44

0

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

0

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

0

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

0

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

Team 63 Team 65

0

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

0

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

0

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

0

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

Team 66 Team 67

Figure 4.21 (continued)
4.45

0

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

0

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

0

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

0

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

Team 70 Team 72

0

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

0

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

0

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

0

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

Team 82 Team 96

Figure 4.21 (continued)
4.46

0

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

0

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

0

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

0

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

Conventional UT Conventional UT + Phased Array

0

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

0

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

0

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

0

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

Eddy Current Phased Array UT

Figure 4.21 (continued)
4.47

0

0 20 40 60 80 100 120

20 40 60 80 100 120

Measured Length (mm)

True Length (mm)

Potential Drop

Figure 4.21 (continued)
4.48

0 10 20 30 40 50

0 10 20 30 40 50

True Length (mm)

Measured Length (mm)

0 10 20 30 40 50

0 10 20 30 40 50

True Length (mm)

Measured Length (mm)

0 10 20 30 40 50

0 10 20 30 40 50

True Length (mm)

Measured Length (mm)

0 10 20 30 40 50

0 10 20 30 40 50

True Length (mm)

Measured Length (mm)

All Teams Team 13

0 10 20 30 40 50

0 10 20 30 40 50

True Length (mm)

Measured Length (mm)

0 10 20 30 40 50

0 10 20 30 40 50

True Length (mm)

Measured Length (mm)

0 10 20 30 40 50

0 10 20 30 40 50

True Length (mm)

Measured Length (mm)

0 10 20 30 40 50

0 10 20 30 40 50

True Length (mm)

Measured Length (mm)

Team 22 Team 28

Figure 4.22 Results of Length Sizing on Axial Flaws in DMW Test Blocks
4.49

Figure 4.22 (continued)
4.50

Figure 4.22 (continued)
4.51

Figure 4.22 (continued)
4.52

Figure 4.22 (continued)
4.53

Figure 4.22 (continued)

4.3.3 Sizing Results from the PINC BMI Round Robin

For each detected flaw, the ability of the NDE techniques to accurately characterize the flaw 

was evaluated. This section describes the depth-sizing and length-sizing accuracy for the 

inspections in the round-robin tests. The depth-sizing results were sparse and a detailed 

regression was not performed. The length-sizing results for each inspection were scored using 

a length-sizing regression and 95% confidence intervals were determined.

4.3.3.1 Tube Examinations

The small number of flaws detected by the tube examinations makes drawing conclusions from 

the data difficult. An additional challenge in the flaw length sizing was caused by the proximity 

of the flaws to one another; the teams had occasionally combined multiple flaws into one. 

Length-sizing results for team 13 are shown in Table 4.25. Team 70 found two flaws, and a 

detailed regression was not possible. The length-sizing regression showed that the techniques 

had a very large RMSE and a large standard deviation. Flaws tended to be undersized by both 

teams. 
4.54

Table 4.25 Length-Sizing Results for BMI Penetration Tube Examinations

Team Observations Technique RMSE, mm

Standard 

Deviation, mm Bias, mm

13 10 ECT and TOFD 16.53 11.84 −11.54

The length-sizing regressions show little relationship between the flaw size and the called 

indication lengths. The 95% confidence bounds for the tube sizing regressions are so large that 

they cannot be meaningfully interpreted. Examinations of more flaws by additional teams would 

be needed for a better length-sizing assessment for examination of flaws in the interior of the 

penetration tubes.

4.3.3.2 Surface Examinations

Depth sizing was performed by four teams on some flaws. As not all flaws were depth sized by 

any team and there were so few depth sizing attempts, the statistical regressions were not 

performed for the depth-sizing results. The teams, techniques, and errors are summarized in 

Table 4.26 and plotted in Figure 4.23.

Table 4.26 Summary of Depth Sizing Results for BMI Surfaces

Team Observations Technique

RMSE, 

mm

Bias, 

mm

All 29 3.47 1.67

16 3 CCPPD 5.17 4.5

38 7 Array ECT 100 kHz 5.25 3.86

66 7 Adaptive Phased Array 1.52 1.52

373 12 TOFD 2.24 0.88
4.55 

0

2

4

6

8

10

12

 Team 373

0 2 4 6 8 10 12

0

2

4

6

8

10

12

 Team 373

0 2 4 6 8 10 12

0 2 4 6 8 10 12

0

2

4

6

8

10

12

 Team 16

0 2 4 6 8 10 12

 Team 38

0

2

4

6

8

10

12

 Team 66

0

2

4

6

8

10

12

0 2 4 6 8 10 12

TOFD Adaptive Phased Array

CCPPD Eddy Current

True Depth (mm)

Measured Depth (mm)

Figure 4.23 Depth Sizing Results for BMI Surfaces 

The length-sizing results for the surface examinations contained enough observations to allow 

for a complex length-sizing regression. The results for each technique were analyzed, and the 

RMSE, standard deviation, bias, and 95% confidence intervals were determined. 

The length-sizing results for the surface examinations showed that some techniques were able 

to accurately measure the lengths of the flaws. Team 16 had the most accurate length sizing, 

although it had only five observations in the data set. Several other teams achieved an RMSE 

of less than 5 mm. The results for each team are given in Table 4.27. 

The cross-coil eddy current tests were able to accurately length-size the flaws that were 

detected, both with RMSEs on the order of 4 mm. The 400-kHz probe examination 

outperformed the 300-kHz but not by a statistically significant margin. The length-sizing 

regression for the cross-coil ECT is shown in Figure 4.24. 
4.56

Table 4.27 Length-Sizing Results for Surface Examinations in BMI Test Blocks

Team Observations Technique RMSE, mm

Standard 

Deviation, mm Bias, mm

All 79 11.7 11.53 2.01

16 5 CCPPD 2.45 2.45 -0.1

373 20 Cross Coil ECT 300 kHz 3.94 3.94 -0.18

38 10 Array ECT 100 kHz 32.28 28.33 15.48

66 11 Adaptive Phased Array 4.7 4.55 -1.19

67 3 ICPD 5.46 1.86 -5.13

70 21 Cross Coil ECT 400 kHz 3.76 2.92 2.37

99 9 Array ECT 200 kHz 4.33 4.07 -1.49

0 10 20 30 40

0 10 20 30 40 0 10 20 30 40

0 10 20 30 40

Estimated Flaw Length (mm)

Flaw Length (mm)

Figure 4.24 Length-Sizing Results for Cross-Coil Eddy-Current Probes in BMI Test 

Blocks

The array eddy current techniques were less effective than the cross-coil probes in this BMI 

round robin at length-sizing the flaws. The 200-kHz array outperformed the 100-kHz array 

probes. The length-sizing regression for the array probes is given in Figure 4.25.
4.57

 

Array ECT 100 kHz Array ECT 200 kHz

0 10 20 30 40

Estimated Flaw Length (mm)

0 10 20 30 40 0 10 20 30 40

Flaw Length (mm)

0 10 20 30 40

Figure 4.25 Length Sizing Results for Array Eddy-Current Probes in BMI Test Blocks

The length-sizing results for the closely coupled probe potential-drop (CCPPD) technique were 

very accurate, having the lowest RMSE error and standard deviation of any of the techniques, 

including the cross-coil eddy-current examinations. There were not enough observations for the 

induced current potential-drop (ICPD) to perform a meaningful analysis. The length-sizing 

results for the potential-drop techniques are presented in Figure 4.26.

0 10 20 30 40

Estimated Flaw Length (mm)

0 10 20 30 40

0 10 20 30 40 0 10 20 30 40

Flaw Length (mm)

Figure 4.26 Length Sizing Results for Potential-Drop Techniques in BMI Test Blocks

The phased array examinations also were able to accurately size the flaws in the BMI test 

blocks. The RMSE was on the order of 5 mm, which is very similar to the results for the crosscoil eddy current examinations. The length-sizing results for the phased array examinations are 

presented in Figure 4.27.
4.58

Adaptive Phased Array UT

Estimated Length (mm)

Flaw Length (mm)

Figure 4.27 Length-Sizing Results for Adaptive Phased Array Ultrasound Techniques in 

BMI Test Blocks
5.1

5.0 Impact of PWSCC Detection and Sizing Performance 

with Respect to Component Integrity

Inservice inspections should detect degradation (e.g., cracking, wall thinning) before the 

degradation affects the component’s integrity and functional requirements. The key elements of 

an inspection program include

1. an inspection method that ensures reliable detection and accurate sizing of flaws

2. an inspection program that addresses those locations that are most likely to experience 

degradation and/or whose failure could have the greatest impacts on the safety and 

operability of the plant

3. an inspection frequency such that degradation can be detected before it grows to 

unacceptable levels between successive inspections.

The PINC round-robin exercises described in this report have established probabilities of 

detection and sizing accuracies of a variety of inspection methods. The PINC round-robin 

exercises demonstrate that some of these methods can detect PWSCC cracks with relatively high 

detection probabilities (see Section 4.0). The timely detection of cracks in the field is, however, 

more difficult because PWSCC is characterized by long periods during which cracks initiate, which 

are then followed by relatively high crack growth rates. Therefore, even a very reliable inspection 

method can prove to be ineffective in preventing the failure of a component if the inspections are

not conducted often enough to detect the degradation prior to loss of component integrity or 

function. As an example, an inspection may be performed just before a crack initiates and then 

the crack grows to a through-wall depth before the next cycle of the periodic inspections. An 

effective inspection program, therefore, requires an inspection interval consistent both with the 

smallest detectable crack and with the growth rates for this PWSCC crack.

Probabilistic fracture mechanics computer codes can predict reductions in component failure 

probabilities that result from a given inspection program as characterized by a given probability 

of detection and inspection frequency. Future calculations could be performed for components 

subject to degradation by PWSCC using available computer codes such as PRAISE (Harris 

et al. 1992) and PROLOCA (Rudland et al. 2006). Such calculations were beyond the scope of 

work for the present report, so results of similar calculations (Khaleel et al. 1995; Khaleel and 

Simonen 2009) for intergranular stress corrosion cracking of welds in stainless steel piping were 

applied as an alternative. These calculations are based on PWR piping welds at 288°C (550°F).

Although the cracking mechanism did not exactly match the current PWSCC concerns, the key 

features of an incubation period for crack initiation and a potentially rapid growth rate of the 

initiated cracks were addressed. Results of the calculations were used only to establish relative 

failure probabilities (i.e., with and without inspection); therefore, conclusions drawn from the 

calculations should be insensitive to inputs for the cracking mechanism. It should also be noted 

here that the calculations (Khaleel and Simonen 2009) did not address flaw sizing errors but 

rather assumed that any detected crack would be repaired without consideration of the 

measured flaw depth. 
5.2

Probability of detection curves were a key input, and Figure 5.1 (the curve is taken from Khaleel 

and Simonen 2009 and the PINC data curve has been added) provides the curves used in the 

calculations. These curves are labeled marginal, good, very good, and advanced and cover a 

wide range of flaw detection capabilities, as exhibited in the round robin described in this report. 

These curves also cover the capabilities exhibited by inspection teams for qualification by 

ASME Section XI Appendix VIII performance demonstrations. The marginal and good POD 

curves describe teams that would have little chance of meeting the performance demonstration 

requirements. The very good and advanced POD curves would cover a range of teams that 

would likely and readily meet the requirements. The advanced POD curve would also represent 

the potential limit of current technology. The POD curve labeled PINC DMW data corresponds 

to the average performance of the Conventional UT, Phased Array UT, and Conventional UT 

and Phased Array from Table 4.6 as calculated by Khaleel and Simonen (2009). These 

performance curves were chosen because they approximate current field practice. Probability of Detection

Crack Depth as a Fraction of Wall Thickness

Figure 5.1 Probability of Detection Curves from Round Robin and Curves Used for 

Probabilistic Fracture Mechanics Evaluations

Evaluations were performed only for the POD data for dissimilar metal welds. Table 5.1 lists the 

same inspection teams and POD performance levels as given by Table 4.6 of the present 

report. In each case, the POD performance level for each team was represented by one of the 

four POD curves (e.g., very good) that most closely approximated the POD curve for the team 

of interest. This allowed results of the available probabilistic fracture mechanics calculations to 

be applied for the teams listed in Table 5.1.
5.3

Table 5.1 Probabilistic Fracture Mechanics Results for Individual Team PODs from PINC for DMW (based on calculations 

for “Intermediate Pipe” with wall thickness of 0.84 inch)

Team POD for Flaw Depths of: False Detection Selected Improvement Factor in Structural Reliability 

5 mm 10 mm 15 mm Call Probability Technique POD Curve 1 Yr 2 Yr 4 Yr 10 Yr

Interval Interval Interval Interval

13 0.37 0.83 0.98 0.07 Phased Array UT Very Good 4 3.1 1.8 1.4

22 0.52 0.52 0.53 0.51 Conventional UT Good 2.5 2 1.4 1.2

28 0.42 0.6 0.76 0.26 Conventional UT Good 2.5 2 1.4 1.2

30 0.24 0.43 0.65 0.11 Conventional UT Good 2.5 2 1.4 1.2

38 0.78 0.96 0.99 0.36 Eddy Current Very Good 4 3.1 1.8 1.4

39 0.36 0.47 0.59 0.26 Phased Array UT Good 2.5 2 1.4 1.2

43 0 0 0 0.31 Potential Drop Marginal 1.5 1.4 1.3 1.1

48 0.24 0.42 0.61 0.13 Conventional UT Good 2.5 2 1.4 1.2

63 0.37 0.79 0.96 0.08 Conventional UT Very Good 4 3.1 1.8 1.4

65 0.3 0.32 0.33 0.28 Potential Drop Marginal 1.5 1.4 1.3 1.1

66 0.62 0.94 0.99 0.14

Phased Array

+ Conventional 

UT

Very Good 4.0 3.1 1.8 1.4

67 0.32 0.45 0.6 0.2 Potential Drop Good 2.5 2.0 1.4 1.2

70 1 1 1 0.04 Eddy Current Advanced 6.0 4.4 2.1 1.5

72 0.41 0.47 0.54 0.35 Phased Array UT Good 2.5 2.0 1.4 1.2

82 0.44 0.53 0.61 0.35 Conventional UT Good 2.5 2.0 1.4 1.2

96 1 1 1 0.06

Eddy Current

+ Conventional 

UT

Advanced 6.0 4.4 2.1 1.5
5.4

Four inspection intervals were addressed (1, 2, 4, and 10 years) covering a range of intervals,

from inspections at every outage to the standard 10-year interval prescribed by the ASME Code

Section XI. The final four columns give Improvement Factor in Structural Reliability, which is 

defined as the ratio of the calculated failure probability for no ISI to the failure probability given 

ISI for the indicated combination of POD curve and inspection interval. The failure criterion 

used in this evaluation was that a pipe may fail by either breakage or leakage. For example, an 

advanced POD curve in combination with a 1-year inspection interval gives an improvement 

factor of 6.0. Based on the definition of factor of improvement, this example shows that given 

six failures with no ISI inspection, an ISI program that required inspections on a 1-year interval 

would reduce the six failures to one failure.

Clearly the advanced POD curve with a 1-year ISI interval gives the largest improvement factor 

of 6.0. On the other hand, the marginal POD curve in combination with a 10-year ISI interval 

gives the smallest improvement factor of 1.1. This factor of 1.1 provides essentially no benefit 

(only a 10% reduction in the number of failures). Any benefit comes only in the unlikely case 

that an inspection is performed at the most favorable time when a growing crack is at a 

relatively large and detectable size.

The trends of Table 5.1 are consistent with the larger set of results of Khaleel and Simonen 

(2009) that address fatigue failures in addition to stress corrosion cracking. These results show 

only a few cases that give improvement factors of 10 or larger, and then only for the highest 

performing of the POD curves and short ISI intervals. In this regard, a reduction in failure 

probability by a factor of ten should be considered an effective mitigation measure for active 

degradation mechanisms, particularly if augmented ISI is used in combination with other forms 

of mitigation (e.g., stress improvement, water chemistry improvements). In other cases, an 

inspection program with an improvement factor significantly less than a limiting level of 10 still 

could provide a valuable contribution to structural integrity. In such cases, the benefits of ISI 

would provide a means to verify the effectiveness of other mitigating measures.

The current evaluation for PWSCC indicates that the better round-robin POD performance 

levels in combination with relatively small inspection intervals could make an effective 

contribution to component integrity. However, additional probabilistic fracture mechanics 

calculations are recommended to support the preliminary conclusions. These evaluations would 

not require an extrapolation from calculations originally performed to address IGSCC and would 

include inputs to address residual stresses and crack growth rates for welds and materials of 

concern for nickel-alloy components, such as alloy 600 and 82/182 weld metals and alloy 690 

and the associated 52/152 weld metals. 

This evaluation does show that it may be beneficial to tie the inspection interval length to the 

crack growth rates in the materials of interest. Materials with very high crack growth rates may 

require inspections at every outage to provide a sufficient improvement factor.
6.1

6.0 Field Experience with PWSCC

Cracking observed in the early 1990s in reactor components in France and other countries was 

attributed to PWSCC, leading to replacement of reactor vessel heads, piping, and other 

components. Leakage was discovered at the Oconee plant in the United States from a control 

rod drive mechanism penetration fabricated using Alloy 600, resulting in deposits of boric-acid 

crystals on the vessel head. Further investigation led to the identification of PWSCC cracks in 

the reactor penetration tubes and attachment J-groove welds. Circumferential cracking of 

CRDM nozzles has been identified at Oconee Units 2 and 3 and Crystal River Unit 3. An 

extreme consequence of such cracking was illustrated by the discovery of wastage on the 

Davis-Besse reactor vessel head. More recently, boric-acid deposits and NDE indications found 

on the South Texas Project BMI nozzles have been attributed to PWSCC. Cracks also have 

been found in reactor nozzle hot-leg DMWs at the V.C. Summer plant in the United States and 

at the Ringhals plant in Sweden, providing further evidence that PWSCC is a generic concern. 

Circumferential cracking associated with safe-end piping welds is important because of the 

potential for a large loss of coolant inventory, and the cracking of CRDM nozzle welds and 

circumferential cracking of CRDM nozzle base metal is important because of the potential for 

control rod ejection and loss-of-coolant accident (LOCA). Recent events at nuclear stations 

related to damage in Alloy 600 base material and Alloy 182/82 welds have prompted industry 

initiatives directed at reexamining the damage mechanisms, damage morphology, and 

examination practices of the affected components. These events have given high visibility to 

the PWSCC phenomenon and high priority to work on understanding this cracking mechanism.

NRC Generic Letter 97-01 (1997) provides a summary of the domestic and international 

cracking experience on reactor pressure vessel heads from PWSCC. Various aspects of the 

problem of PWSCC cracking have also been addressed by a number of research programs 

within the United States and in other countries. The data collected to date, however, are 

sparse, and the significant factors leading to crack initiation and governing crack growth rate are 

not well understood. Complicating factors include chemistry variations in the nickel-base alloy 

components, evolution of the primary water chemistry within an operating cycle, and residual 

stresses and possible embedded flaws resulting from weld repairs. In addition, detection and 

characterization of PWSCC-related flaws through NDE have proven to be particularly difficult in 

components with complicated geometries. The occurrences of cracking in the United States 

have been identified initially through indirect means, specifically the discovery of boric-acid 

deposits resulting from through-wall cracking in the primary system pressure boundary. Such 

leakage degrades a layer of plant defense-in-depth and should be prevented whenever 

possible. 

Although many different aspects of this issue need to be addressed, NRC proposed research 

concentrated in two interrelated areas. Task 1 focused on characterizing the morphology of 

PWSCC cracks, which has been identified as a contributing factor to the difficulties experienced 

in detecting and sizing cracks in the field. As part of the characterization, work addressed

refining the ability to distinguish PWSCC cracks from other flaws with similar features, such as 

hot cracks in welds. Task 2 focused on the nondestructive testing aspects, including such 
6.2

topics as the manufacture and simulation of PWSCC cracks in test assemblies for use in 

assessing the effectiveness and reliability of NDE techniques.

The research addresses the nickel-base alloys used as pressurized water reactor (PWR) 

pressure boundary components including dissimilar metal welds and reactor pressure vessel 

(RPV) head penetrations. Primarily, the research focused on the Alloy 600/182/82 group of 

materials, but replacement materials (Alloys 690/152/52) were not excluded.

6.1 Swedish Experience

Sweden has applied a qualitative risk-based approach to inservice inspection for many years. 

It is based upon a matrix combining potential risk of damage in a given system with the 

consequences of failure, and the anticipated severity of subsequent radioactive release. The 

matrix is illustrated in Table 6.1.

Table 6.1 Risk-Damage Matrix

Damage Index

Consequence Index

High (I) Medium (II) Low (III)

High (1) A A B

Medium (2) A B C

Low (3) B C C

The consequence index expresses in a qualitative manner the likelihood that a crack or other 

degradation process will result in fuel damage, discharge of large amounts of radioactive 

substances, or other forms of damage that could lead to health problems or an accident. In

nuclear power plants, the consequence index is determined mainly by the margin to such 

consequences as the result of a break or malfunction of the specific component or part of a 

system. Two aspects are important when determining the assignment of the consequence 

index: 

• system margins – how many system circuits are essential in relation to the number available

• thermal margins – how much the fuel can be heated up in relation to acceptable margins.

The damage index expresses in a qualitative manner the likelihood for crack formation or other 

degradation process occurring in the specific component or system part. The damage index is 

determined by the loading, environment, and material in relation to the dimensions of the component. Components or parts that may be exposed to loads or other conditions known to result in 

damage or degradation should be assigned the highest damage index. Components not 

expected to be subjected to loads or other conditions that will result in damage are assigned 

damage index II, and components exposed to minimal loads or other benign operational 

conditions are assigned damage index III.

In systems in which stress corrosion cracking cannot be excluded, the following conditions are 

considered reason for assigning damage index I to a component:
6.3

• high temperatures (>150°C) and high carbon content (>0.04%) in stainless steel, including 

stabilized austenitic stainless steels

• high temperatures (>150°C) and cold-worked stainless steel that has not had a subsequent 

heat treatment

• high temperatures (>150°C) and nickel-base alloys such as Alloys 600, and X-750 with 

compositions and heat treatments that experience has shown are sensitive to stress 

corrosion cracking

• high neutron fluence (5.1020 n/cm2

, E > 1 MeV).

The criteria were first adopted by the Swedish Nuclear Power Inspectorate (SKI) regulations 

SKIFS 1994:1 concerning mechanical components in nuclear facilities and have been applied 

since that date. In the more recent versions of the regulations, the specific conditions listed 

above are no longer included as part of the regulations but are included in the utilities 

documentation approved by SKI.

In the current version of the regulations concerning mechanical components (SKI 2005, SKIFS 

2005:2), the use of quantitative risk-based inspection programs is permitted. One of the utilities 

has been granted permission to apply a modified version of the Westinghouse Owners Group 

methodology but did not have any SCC-sensitive materials to be considered.

The inspection interval is determined on the assumption that a crack exists in the component or 

system of a size for which the applicable inspection method has been qualified. The inspection 

interval is then calculated as the time required for the crack to grow to a critical size using crack 

propagation data for the specific material/environment combination. The same crack 

propagation data are used when a crack is found in a component to permit the component being 

kept in service until a planned repair or replacement can be performed. Qualification of 

inspection techniques has to be performed using realistic (not geometric) cracks in test blocks 

made from typical material. Inspection qualification is required for NDE systems that inspect 

Class 1 and 2 mechanical components.

6.1.1 Development of Inspection Qualification for PWSCC in Sweden

When the PWSCC cracking was found in safe ends in Ringhals 3 and 4 in 2000, destructive 

examination showed that the NDE system had underestimated the crack depths. The NDE 

systems used at Ringhals 3 and 4 had been qualified. SQC and Swedish utility Ringhals began 

to evaluate the inspection results in accordance to qualification to determine why eddy current 

and through-wall sizing did not work as expected. The results of the investigation showed that 

all defects were found with UT; however, the investigation showed that the prerequisites of 

defect type and knowledge of defect simulation failed.

The results of the investigation described above led to a research project, sponsored by 

Swedish utilities, to investigate the degradation mechanism (e.g., PWSCC) and to develop a 

simulation technique to be used for test-piece simulations. The independent organization, SQC 

Qualification Centre, led the project that compared the destructive evaluation (DE) results from 

the field cracks to known simulation methods. The real cracks were tight and had branches in 
6.4

directions, making it very hard for NDE systems to follow the crack propagation. Important 

conclusions (Wåle 2002) were that the cracks were oriented both axially and circumferentially to 

the welds. The cracks were found in weld material of the type Alloy 182 and Alloy 82. The 

cracks were located in the weld material and the buttering. The area of the cracks is repaired 

regions. One characteristic of the PWSCC cracks is that the crack width decreases close to the 

surface. This type of crack has been found in both PWR- and boiling water reactor (BWR) types 

of reactors.

In 2005, SKI initiated another project to investigate statistics of all cracks in Swedish plants, 

including the PWSCC. This was an update of the report published in 1995 (Ekstrom and Wåle 

1995) but now with 10 more years of data and experience (Wåle 2006). The report describes 

and evaluates the morphology of different mechanisms and is also an important tool when 

developing NDE systems for different damage mechanisms. This report also included an 

evaluation of the PWSCC morphology.

6.1.2 Simulated PWSCC Cracks

Cooperation between the qualification body, inspection companies, crack simulation companies, 

and licensees made it possible to develop a new technique to produce cracks with better 

agreement to real PWSCC cracks.

One task within the project was to identify relevant crack characteristics to handle when 

simulating cracks. These were identified as the crack width at the surface, unbroken ligament 

(both in depth and length), crack morphology as the most important, and specific characteristics 

for the PWSCC mechanism. Different simulation techniques were tried and compared to the DE 

result of the real field cracks. The technique that most closely resembled service-induced 

cracks was a new type of solidification crack technique. The solidification technique to produce 

these cracks involved a mechanical tightening process. This process achieved a realistic

simulation of the unbroken ligaments characteristic of the PWSCC mechanism.

One of the significant outcomes that developed from the new crack specification was that all 

qualified procedures for detecting and sizing PWSC cracking needed to be requalified. In the 

subsequent process to requalify the NDE systems, the result was that all inspection companies 

had to reconstruct their procedure to be able to characterize and size the defects in light of 

improved understanding of the crack morphology.

6.1.3 Comparison of the Signal Response from the UT and EC Inspection in the 

Plants and the Response from the Inspections of the Simulated Cracks

After establishing a technique to simulate PWSCC cracks, a task was initiated that 

characterized and mapped the defect characteristics of the PWSCC found in Alloy 182 that 

affect the NDE signal response (SQC 2003). The results for this task are shown in Table 6.2

and Table 6.3. Table 6.2 provides the results to UT signal responses, and Table 6.3 provides 

the results for eddy current signals. These variables should be taken into account when 

manufacturing simulated cracks to be used for detecting with pulse echo, sizing with pulse 

echo–TOFD, and also when using eddy current.
6.5

Table 6.2 Defect Characteristics Found Significant for Ultrasonic Testing

Defect Characteristics Parameter Study

Defect width in depth Min/max > 5 μm–0.3 mm

Unbroken ligaments in depth Number of ligaments: 4–17 

Size: 0.14 mm–0.8 mm

Unbroken ligaments in length 0.6 mm–2 mm

Crack tip radius 7 μm–40 μm

Width at surface 10 μm–35 μm

Surface roughness Rz = 187 μm–471 μm

λ0 = 456 μm–650 μm

Branching 0.25–0.60/mm

Crack shape in depth Winding

Table 6.3 Defect Characteristics Found Significant for Eddy Current Testing

Defect Characteristics Parameter Study

Defect width at the surface (electrical contact 

between the surface of the crack)

10 μm–35 μm

Unbroken ligaments at the surface Length = 1 mm–4 mm

Depth = 0.6 mm–2 mm

Unbroken ligaments in the depth Number: 2–9

Size: 0.14 mm–0.80 mm

Crack shape in depth Winding

Crack shape in length Winding

6.2 United States Experience

The experience in the Unites States with primary water stress corrosion cracking (PWSCC) is 

extensive and includes PWSCC in components ranging from pressurizer components to bottom 

mounted instrumentation nozzles. A detailed list of experiences with cracking in Alloy 600 

material is contained in Appendix H. This appendix uses information from NUREG-1823, U.S. 

Plant Experience With Alloy 600 Cracking and Boric Acid Corrosion of Light-Water Reactor 

Pressure Vessel Materials, published in April 2005. 

One of the first incidents of PWSCC in the U.S. was the discovery of leaks in pressurizer 

instrument nozzles (in 1986 at San Onofre Nuclear Generating Station, Unit 3) and heater 

sleeves (in 1987 at Arkansas Nuclear One). In 1989, 20 leaking heater sleeves were found at 

Calvert Cliffs, Unit 2 (8 additional sleeves had non-leaking, axial crack indications). These

incidents of field cracking were correlated with temperature. The vulnerability of these 

components may have been enhanced by the higher temperatures at the pressurizer 

penetrations than other components, such as vessel head penetrations.

Stress corrosion cracking of a dissimilar piping weld occurred at V.C. Summer in 2000. The 

cracking was discovered during visual testing, in which a large quantity of boric acid deposits
6.6

(≈ 160 kg) were discovered. The cracking was investigated using ultrasonic inspections, eddy 

current, and visual testing. 

Control rod drive mechanism nozzles and other vessel head penetration nozzles welded to the 

upper reactor vessel head are may be subject to primary water stress corrosion cracking. The 

issue is a potential safety concern because a nozzle with sufficient cracking could break off 

during operation. This would compromise the integrity of the reactor coolant system pressure 

boundary—one of three primary barriers that protect the public from exposure to radiation. The 

break may also result in the ejection of a control rod, which could damage nearby components.

On August 3, 2001, the NRC issued Bulletin 2001-01, “Circumferential Cracking of Reactor 

Pressure Vessel Head Penetration Nozzles” (NRC 2001), to licensed holders of U.S. PWRs 

following the discovery of cracked and leaking nozzles in 2000 and 2001. In the bulletin, the 

staff requested information from PWR licensees about the structural integrity of these nozzles at 

their facilities. In response to the bulletin, licensees provided their plans for inspecting their 

nozzles and the outside surfaces of their upper reactor vessel heads to determine whether any 

nozzles were leaking. Inspections by licensees during fall 2001 revealed vessel head 

penetration nozzle cracks at Three Mile Island Unit 1, Crystal River Unit 3, North Anna Unit 1, 

and Oconee Unit 3.

On August 9, 2002, the NRC issued Bulletin 2002-02, “Reactor Pressure Vessel Head and 

Vessel Head Penetration Nozzle Inspection Programs” (NRC 2002). The bulletin suggested 

that visual inspections of upper reactor vessel heads and their nozzles may need to be 

supplemented with non-visual nondestructive examinations to ensure that the structural integrity 

and leakage integrity of the nozzles is maintained. Bulletin 2002-02 requested that PWR 

licensees provide information about their inspection programs and plans to supplement existing 

visual inspections with volumetric and surface examinations. Licensees responded with 

descriptions of inspection plans for at least the first refueling outage following the issuance of 

the bulletin. Many did not offer any long-term inspection plans but instead opted to follow 

guidance being developed by the Materials Reliability Program, an industry-sponsored research 

organization.

Inspections performed at several PWRs in 2002, including those performed at the Davis-Besse 

Nuclear Plant, found leakage and cracks in vessel head penetration nozzles or J-groove welds 

that have required repairs or prompted the replacement of the vessel head. As a result of 

continuing concerns regarding licensee inspection programs in this area, the NRC issued an 

order on February 11, 2003, to all PWR licensees in the United States (NRC 2003). The order 

requires specific inspections of the vessel head and associated penetration nozzles based on 

their susceptibility to PWSCC. The order may be accessed at the following address on NRC’s 

website: http://www.nrc.gov/reactors/operating/ops-experience/vessel-headdegradation/vessel-head-degradation-files/order-rpv-inspections.pdf.

Twenty-six units were identified by the Electric Power Research Institute (EPRI) Materials 

Reliability Program as having a high susceptibility to nozzle cracking. Inspections by licensees 

performed after issuance of the latest bulletin and order revealed nozzle or J-groove weld 

cracks and/or leaks at Oconee Unit 2, North Anna 2, Arkansas Nuclear One Unit 1, St. Lucie 

Unit 2, Milestone Unit 2, and Beaver Valley Unit 1. The utilities owning the Oconee, Surry, 
6.7

Davis-Besse, and North Anna nuclear stations have replaced or are in the process of replacing 

their upper reactor vessel heads. Approximately 20 other units have announced plans to have 

their upper reactor vessel heads replaced within the next few years. A detailed list of 

experiences with cracking in Alloy 600 material is contained in Appendix H. This appendix uses 

information from NUREG-1823, U.S. Plant Experience With Alloy 600 Cracking and Boric Acid 

Corrosion of Light-Water Reactor Pressure Vessel Materials, published in April 2005. 

One instance of a bottom mounted instrumentation nozzle developing stress corrosion cracking 

in the US occurred at the South Texas Project Unit 1 in 2003. The cracking was discovered by 

visual inspection of the lower RPV head, which showed boric acid deposits. While there has 

only been one instance of cracking of a BMI in U.S. reactors, the bottom head cannot be easily 

repaired and it would be challenging to replace. 

6.3 Japanese Experience

In the history of operation of PWR plants in Japan, which started in 1970, PWSCC had not been 

experienced with the exception of steam generator (SG) tubing until the early 2000s.

In 2003, a trace of leakage was found by visual inspection at the top of the PRZ where the safeend was welded with nickel alloy material to a relief valve nozzle in Tsuruga 2 plant. PWSCCs 

including through-wall crack were identified in the DMW by the subsequent investigations. It 

could be the first PWSCC failure that occurred in the nickel components other than SG tubing in 

Japan.

The following year (2004), another leak was found at vessel head penetration (CRDM nozzle) of 

Ohi 3 plant. This failure was also attributed to PWSCC at the weld with nickel-alloy material.

In 2007, DMW failure was found in larger sizes of DMW of SG nozzles of Mihama 2 plant by 

ECT, which was performed prior to the mitigation process. Similar PWSCC indications have 

been found in several other plants as a result of ECT for SG nozzles. Furthermore, an ECT 

indication due to PWSCC was found in a DMW of a reactor vessel (RV) outlet nozzle of Ohi 3 in 

2008.

In all, Japan experienced two different types of failures within the pressure boundary among 

three categories of nickel-alloy components; that is, DMW, CRDM, and BMI. Another indication 

was found in a BMI nozzle bore of the Takahama 1 plant in 2003, although it was thought to be 

spurious and was not confirmed as a true defect or PWSCC.

In the following paragraphs, a more detailed description is presented for each category.

6.3.1 DMW

Failures of DMWs of alloy 600 materials in overseas plants (i.e., V. C. Summer and Ringhals 3 

and 4) were reported in 2000. Since then, Japanese PWR utilities were concerned about the 

possible occurrence of PWSCCs in such components. Unfortunately, similar phenomenon was 

first identified in one of the Japanese PWR plants three years later.
6.8

Tsuruga 2 stopped operation for its 13th annual inspection on September 5, 2003. Four days 

later, there was a trace of leakage observed at the relief valve nozzle located at the top of the 

PRZ after removal of insulation materials. Subsequent investigation identified multiple axial 

cracks at two locations (90° and 315°) in DMW connecting safe-end to the nozzle, which 

included a through-wall crack. The following UT inspections performed for other nozzles of the 

PRZ revealed another axial crack indication in one of three safety valve nozzles.

Detailed investigation including destructive examination was made on the defected relief valve 

nozzle weld to show the following results.

• Cracks were interdendritic and branched in nickel-base weld metal.

• Repair welding made during fabrication of PRZ might cause higher residual stress to initiate 

PWSCC with plant operating stress.

• Cracks were axial and extended only in the weld metal. Therefore, the detected cracks did

not cause safety issues.

It could be the first PWSCC failure that occurred in the nickel components other than SG in 

Japan.

Affected nozzles were finally repaired by welding with replacement safe-end spool pieces and 

alloy 690 weld metal.
6.9

Figure 6.1 DMW Failures of Pressurizer Nozzles in Tsuruga 2

In the continued efforts of preventive maintenance of nickel-alloy components by Japanese 

PWR utilities, ultrasonic shot peening (USP) was determined to apply to alloy 600 DMWs of SG 

nozzles for mitigation. When conducting USP, the inside surface of the SG nozzle was to be 

inspected by ECT and VT before USP operation to ensure the effectiveness of mitigation.

In September 2007, when inside surface of inlet nozzle of A-SG in Mihama 2 plant was scanned 

by ECT prior to USP, 13 indications were detected. One of them was also identified by VT. In 

addition, PT was applied to verify all 13 Indications as relevant Indications. The largest was 

17 mm in length by PT, and approximately 13 mm in depth by UT. These defects were further 

investigated by micro printing and by destructive methods. The results were as follows. 

• The largest crack was formed with multiple small axial cracks of length from 3 mm to 5 mm.

• Maximum depth of the crack was about 11.5 mm.
6.10

• Cracks were considered to be intergranular in nature.

• One of cracks was different from the others in location; that is, all the cracks were within 

nickel-base material except one that was found in a stainless steel safe-end.

Similar ECT indications have been found in several other plants during their USP efforts that 

followed operation at Mihama 2. Alloy 600 DMWs of SG nozzles have been inspected as listed 

in Table 6.4.

Figure 6.2 DMW Failure of Steam Generator Nozzle in Mihama 2
6.11

Table 6.4 SG Nozzle DMW Inspection Results

Plant Material

Operating 

Hours

(as of Dec. 31, 

2008)(a)

SG

Replacement

Inspection

Result(b) Remarks

Takahama 3 Alloy 600/132 179 x 103 --- X

Takahama 4 Alloy 600/132 178 x 103 --- X

Sendai 2 Alloy 600/132 174 x 103 --- X

Tsuruga 2 Alloy600/132 152 x 103 --- X

Tomari 1 Alloy 600/132 148 x 103 --- X

Tomari 2 Alloy 600/132 133 x 103 --- X

Ohi 3 Alloy 600/82 124 x 103 --- ---

Ohi 4 Alloy 600/82 122 x 103 --- ---

Genkai 3 Alloy 600/82 115 x 103 --- ---

Ikata 3 Alloy 600/82 109 x 103 --- ---

Takahama 2 Alloy 600/82 104 x 103 Yes X

Genkai 1 Alloy 600/82 102 x 103 Yes X Defect was shallow 

enough to be 

removed by grinding

Ohi 1 Alloy 600/82 97 x 103 Yes ---

Mihama 2 Alloy 600/82 96 x 103 Yes X

Genkai 4 Alloy 600/82 90 x 103 --- ---

(a) Hours after SG replacement for the plants with SG replaced.

(b) X: Indication detected, ---: No indication

To DMWs of RV nozzles, a water jet peening (WJP) process has been applied in Japan since 

2005. A small crack indication was detected in a DMW of one of the RV outlet nozzles by ECT 

performed prior to WJP at Ohi 3 in March 2008. This was verified by VT to be branched and 

considered to be similar to PWSCCs that had been found in DMWs of SG nozzles. No 

indications were detected in the other three outlet nozzles and four inlet nozzles of the Ohi 3 

RV.

The depth of this crack could not be sized well by UT. It was decided that the crack would be 

removed by grinding, with the assumption that the crack was relatively shallow. Then, the 

grinding and ECT/VT process was iterated. This sequence, though, continued much more than 

anticipated. It ended up with the concavity of about 21 mm in depth, to ensure the crack had 

been completely removed.

The plant resumed operation in November 2008.
6.12

Figure 6.3 DMW Failure of Reactor Vessel Outlet Nozzle in Ohi 3

6.3.2 CRDM

Base materials (Alloy 600) of reactor vessel head penetrations (RVHPs) have been inspected in 

Japan since the early 1990s, and understanding of the inherent susceptibility to PWSCC of 

Alloy 600 materials led to preventive vessel head replacements for older Japanese PWR plants. 

However, it had not been well recognized that possible failure at J-groove welds could pose any 

short-term risk, until the Ohi 3 event.

On May 4, 2004, bare metal visual testing performed during the tenth annual inspection outage 

of the Ohi 3 plant revealed a sign of leakage at the CRDM nozzle. There were boric deposits at 

two nozzle locations, No.47 and No.67. However, subsequent investigation including PT, ECT, 

UT, and He leak testing revealed that there was no indication of a defect at No. 67 CRDM, and 

that a defect existed at the J-groove weld of No. 47 CRDM nozzle that caused leaking. 

Metallographic analysis revealed that cracks branched along the dendrite within the J-weld, and 

the root cause was considered as follows.
6.13

• High tensile residual stress due to no buffing after grinding in a particular area on the J-weld. 

• Crack initiated by PWSCC. (The possibility for the initial crack to be other defects such as

weld defects cannot be denied.)

• The crack went through the J-weld from the J-weld surface in the radial direction (upper 

side) due to PWSCC in the plant operating condition.

• Crack passed through the connected root between the J-weld and the nozzle.

In order to maintain the integrity for the RCS pressure boundary and protect PWSCC 

propagation, weld repair had been performed to the affected weld by using alloy 690 weld 

material before restart of the plant. This vessel head was replaced during the 12th annual 

inspection outage of Ohi 3.

Figure 6.4 Failure of CRDM J-Groove Weld in Ohi 3

6.3.3 BMI

Among the many components to which alloy 600 material is applied, BMI is considered as one 

of the most important parts because of its difficulty of repair and replacement. In most of the 

PWR plants in Japan, BMI nozzle material of alloy 600 was used, and inspection and mitigation 

efforts have been made on such components. In addition, attention has also been paid to 

J-groove welds of BMIs recently as well as those of CRDM. To date, no defect indications have 

been found in either nozzle base materials or J-groove welds of BMIs with one exceptional 

phenomenon as described below.

WJP was performed to BMIs of Takahama 1 plant during its 21st annual inspection outage in 

2003. Prior to WJP operation, inner surfaces of all 50 nozzles had been inspected by the ECT 

method. With this prior inspection, one small indication was found at No. 48 nozzle. It was an 

axial indication of approximately 32 mm in length. Estimated depth, assuming that indication 

was a crack, was less than 1 mm. 
6.14

Eventually, the area concerned was ground in case in the next outage. Retesting with ECT 

after grinding verified that the indication had been completely eliminated.

Figure 6.5 Spurious ECT Indication Found in BMI of Takahama
7.1

7.0 Parametric Studies – NDE Responses and Flaw 

Morphology (NA2 and Simulated Flaws)

One of the objectives of the PINC is to assess methods for manufacturing test blocks and 

mockups with flaws that adequately simulate the NDE response from PWSCC. Existing test 

blocks offered by the PINC participants were analyzed to determine if the objective of the 

program could be supported by the available cracks in offered test blocks. PINC documents 

included the design of the test blocks with available photographs and drawings. Sufficient 

preexisting test blocks were available for a round-robin test of dissimilar metal welds.

The most important needed product form to add to the open test blocks was Alloy 182/82 seal 

weld metal and buttering of CRDM and BMI assemblies. A blind test was proposed using 

50-mm × 50-mm cracked and blank weld metal coupons with a holder for presenting the 

cracked and blank coupons to the inspectors. The EPRI NDE Center reported good results with 

a very similar coupon and mockup system.

7.1 Manufactured Flaw Nondestructive Testing Responses

PNNL proposed to procure the coupons with three different surface finishes—as-welded, handground, and machined smooth. Two different crack orientations were proposed—along and 

across the weld lay. Three different crack types were proposed—thermal fatigue cracks (TFC), 

stress corrosion cracks (SCC), and weld solidification cracks (WSC). The cracks in the coupons 

were proposed to have CODs that fell into four size categories. Cracks with COD less than 

20 microns would be very difficult to detect for eddy current and visual testing, and cracks with 

COD between 20 and 50 microns would be difficult to detect for most systems. Larger cracks 

should not be missed when using a state-of-the-art eddy current or visual testing system. Clearly, 

50 or more coupons would be needed to fill out the test matrix. Furthermore, some or all of the 

crack types should have duplicates to measure repeat performance of the inspection technology. 

For cracks on as-welded surfaces, some of the circumferential cracks would need to be located 

along the fusion line of the weld passes and some located away from the fusion line.

Before PNNL ordered the Alloy 182 weld metal mockup, a simple parametric study was 

performed. The study was used to refine specifications and quality requirements for the cracks 

and coupons, especially the selection of appropriate lengths for the cracks to be used in the 

blind test. Figure 7.1 shows the three cracked Alloy 182 weld metal coupons received at PNNL. 

The coupon on the right has a thermal fatigue crack that is 5.3-mm long and 2.3 mm deep. The 

thermal fatigue crack was introduced into the coupon with controlled thermal fatigue loading 

(Kemppainen et al. 2003). The crack was grown with natural thermal fatigue introduced by 

cyclic application of high-frequency inductive heating coils and water cooling jets. In this 

process, the typical heating time is 2–5 seconds and typical cooling time 5–10 seconds. 

Because the crack is introduced directly into the test material, the crack shape and form are 

affected by local properties, especially inhomogeneities or stress risers. The cracks tend to 

grow in the weakest locations in discontinuous segments or with some branching. Figure 7.2

shows the image of the artificially grown stress corrosion crack on the surface of the coupon. 
7.2

Figure 7.1 Three Cracked Weld Metal Coupons with Thermal Fatigue Crack on the Left, 

Weld Solidification Crack on the Right, and Laboratory Stress Corrosion 

Crack at Center

Figure 7.2 Artificially Grown Stress-Corrosion Crack in Coupon of Alloy 182 Weld Metal
7.3

Although not visible at this magnification, the coupon on the left in Figure 7.1 has a weld 

solidification crack that is 10 mm long and 2 mm deep. Such a crack is introduced by 

performing a weld and adjusting the weld chemistry to produce a centerline crack that is 

bounded by the fused metal (Watson and Edwards 1996). The technique uses a machined 

notch to form a cavity with the length and depth of the desired crack. This cavity is filled with 

poisoned weld metal that cracks starting at the bottom of the notch. The crack breaks the 

surface, is interdendritic, and has some branching. 

A laboratory-grown stress corrosion crack is in the coupon at the center of Figure 7.2. The main 

crack is 28 mm long with a mean crack opening dimension of 50 microns. Growing SCC 

(Daniels et al. 2003) involves the manufacture of a test piece that is suitable for the application 

of tensile stress. The stressed test piece is subjected to a corrosive agent to produce the 

required crack. Figure 7.4 shows a portion of the laboratory-grown stress corrosion crack 

purchased by PNNL.

The eddy current responses and noise levels were recorded from the three manufactured 

cracks at 350 kHz. Figure 7.3 shows eddy current response from the laboratory-grown SCC in 

Alloy 182 weld metal. The indication is 45% of the calibration electro-discharge machining

(EDM) notch. The length of the indication is 25 mm with a secondary crack on the lower edge 

of the image. The main crack is 28 mm (1.1 in.) long. The depth of the crack is unknown 

(because the SCC is laboratory-grown with limited control of the cracking process). Figure 7.4

provides a signal-to-noise analysis of eddy current response from the laboratory-grown SCC. 

The noise level is set to 2.5% of the calibration EDM notch, giving the indication a signal-tonoise ratio of 18.1.

Figure 7.5 shows the eddy current response from a thermal fatigue crack in Alloy 182 weld 

metal. The indication is 58% of the calibration EDM notch. The length of the indication is 4 mm 

using loss of signal. The crack is 5.2 mm (0.2-in.) long and 2.3 mm (0.1-in.) deep. Figure 7.6

provides a signal-to-noise analysis of eddy current response from the TFC. The noise level is 

set to 2.5% of the calibration EDM notch, giving the indication a signal-to-noise ratio of 23.1.

Figure 7.7 shows the eddy current response from a WSC in Alloy 182 weld metal. The 

indication is 39% of the calibration EDM notch. The length of the indication is 12 mm using loss 

of signal. Figure 7.8 provides a signal-to-noise analysis of eddy current response from the weld 

solidification crack. The noise level is set to 3.5% of the calibration EDM notch, giving the 

indication a signal-to-noise ratio of 11.2.
7.4

Figure 7.3 Eddy Current Response from Laboratory-Grown Stress Corrosion Crack in 

Alloy 182 Weld Metal

Figure 7.4 Signal-to-Noise Analysis of Eddy Current Response from Laboratory-Grown 

Stress Corrosion Crack in Alloy 182 Weld Metal
7.5

Figure 7.5 Eddy Current Response from Thermal Fatigue Crack in Alloy 182 Weld Metal

Figure 7.6 Signal-to-Noise Analysis of Eddy Current Response from Thermal Fatigue 

Crack in Alloy 182 Weld Metal
7.6

Figure 7.7 Eddy Current Response from Weld Solidification Crack in Alloy 182 Weld 

Metal

Figure 7.8 Signal-to-Noise Analysis of Eddy Current Response from Weld Solidification 

Crack in Alloy 182 Weld Metal
7.7

7.2 North Anna 2 Flaw Responses

PNNL examined the J-groove weld of a removed-from-service control rod drive nozzle, North 

Anna 2 (NA2) Nozzle 31, which contained PWSCC. The nozzle was inspected under a joint 

NRC and EPRI effort to characterize the NDE effectiveness for control rod drive examinations. 

Nozzle 31 was inspected using a wide variety of NDE techniques, but this section focuses on 

the eddy current responses of the PWSCC and the destructive validation of the PWSCC. The 

J-groove weld was examined using a 350-kHz cross-coil eddy-current probe. The nozzle was 

scanned twice, once with the probe at a 0-degree rotation and again with the probe rotated 

45 degrees. Sixteen eddy current indications clustered in four regions of interest were found.

Dye penetrant examinations of the NA2 nozzle showed that three flaws, at 200, 215, and 

225 degrees, were surface-breaking cracks. Then the four regions were destructively examined 

to validate the four regions of interest. First, the regions were cut out and examined using 

optical microscopy to determine if the flaws were surface-breaking. The regions were cut at 

depths of 6–8 mm below the wetted surface to determine if any of the flaws penetrated into the 

weld. When cracks deeper than 6–8 mm were found, the welds were further sectioned to 

determine how deeply they had propagated. Six indications were found that had penetrated into 

the weld, and two were found to have propagated entirely through the weld and into the 

buttering region. One crack was confirmed as the cause of the leak in the nozzle. The eddy 

current results and the destructive evaluation of these eddy current examinations are 

summarized in Table 7.1.

Table 7.1 North Anna 2 Eddy Current Responses and Destructive Validation

Indication Angle Length

Max 

Voltage

% EDM 

Notch

Confirmed

PWSCC? Depth

1 45° 2 mm 2.1 20% No < 6 mm

2 50° 5 mm 1.9 18% No < 6 mm

3 55° 4 mm 3.3 32% No < 6 mm

4 65° 2 mm 1.8 18% No < 6 mm

5 70° 4 mm 2.2 21% No < 6 mm

6 75° 3 mm 2.5 24% No < 6 mm

7 80° 3 mm 2.3 22% No < 6 mm

8 130° 4 mm 2.3 22% No < 6 mm

9 145° 10 mm 3.2 31% Yes < 25 mm

10 155° 8 mm 3.3 32% Yes Through-Weld Leaking

11 160° 14 mm 4.1 40% Yes < 25 mm

12 170° 5 mm 2.6 25% No < 6mm

13 200° 8 mm 4.6 45% Yes < 25 mm

14 215° 10 mm 1.8 18% No < 6 mm

15 225° 9 mm 4.6 45% Yes < 25mm

16 255° 7 mm 4.2 41% Yes Through-Weld Not Leaking
7.8

The response range for 16 crack indications in CRDM nozzle number 31, from the removedfrom-service top head of the North Anna 2 reactor pressure vessel, is 18% to 45% of the 

calibration response. The response range for the three manufactured cracks is 39% to 58%. 

The manufactured cracks were representative of only the upper portion of the response range 

for the crack indications in nozzle 31. The eddy current response from the PWSCC initiation 

site for a proven leakage path in North Anna 2 nozzle 31 is 32% of the calibration. 

It is worth noting that each of the confirmed PWSCC cracks greater than 6–8 mm in depth was 

found by the inservice examination that was performed prior to the pressure vessel head being 

removed from service.

7.3 Comparison of Eddy Current Response of Manufactured Flaws 

and for PWSCC in North Anna 2

The eddy current responses for the manufactured flaws were compared to the six confirmed 

instances of PWSCC in the nozzle 31 J-groove weld. As there were only six flaws 

characterized in nozzle 31, this comparison is not definitive, but it is still useful to discuss.

The noise levels in the eddy current data from scans of Alloy 182 weld metal are determined by 

surface roughness and, to a lesser extent, by fabrication flaws. The noise level in the eddy 

current scans of North Anna 2 nozzle 31 was 6% of the calibration EDM notch, and the level 

was 2.5% to 3.5% for the Alloy 182 coupons. Factors of two are important in simulating 

inspection conditions.

The lowest responses from crack indications in North Anna 2 nozzle 31 that were confirmed 

with dye penetrant testing were 18% of calibration. The error in manufactured crack responses 

for the simulation of such PWSCC indications is a factor of 4 to 8 in signal-to-noise ratio. 

Figure 7.9 provides a summary of the eddy current response distributions for 13 crack 

indications in the North Anna 2 nozzle 31, 3 manufactured cracks, and 9 EDM notches. The 

0.5-mm EDM notch and 1.0-mm EDM notch approximately bracket the crack indication 

distribution. The responses from manufactured cracks are representative of PWSCC crack 

indications producing the largest NDE responses.
7.9

0

1

2

3

4

5

6

7

8

9

10

5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100

Eddy Current Response (% of Cal.)

Number of Discontinuities

0.5 mm 

notch

1.0 mm 

notch

2.0 mm 

notch

Notches >

4mm

WSC SCC

lab cracks

NA2

notches

TFC

0

1

2

3

4

5

6

7

8

9

10

5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100

Eddy Current Response (% of Cal.)

Number of Discontinuities

0.5 mm 

notch

1.0 mm 

notch

2.0 mm 

notch

Notches >

4mm

WSC SCC

lab cracks

NA2

notches

TFC

Confirmed NA2 PWSCC

Eddy Current Responses

Unconfirmed NA2 PWSCC

Eddy Current Responses

Figure 7.9 Eddy Current Response Distributions for 13 Crack Indications in 

North Anna 2 Nozzle 31, 3 Manufactured Cracks, and 9 Electro-Discharge 

Machined Notches 

After destructive evaluation of the NA2 nozzle 31, it was determined that the confirmed PWSCC 

had eddy current responses of 31% or greater relative to the calibration notch. A destructive 

evaluation of the sample showed no evidence that the low-amplitude indications were caused 

by PWSCC. All low-amplitude indications (25% and below) were shown to be less than 6 mm 

deep. Only one low-response indication, the same that was confirmed using dye penetrant, 

could be found using optical microscopy. The remaining indication may or may not be cracks 

but could be surface irregularities. Based on the destructive validation, the weld solidification 

cracks and the induced stress corrosion cracks are a reasonable, but not conservative, 

approximation of the response of PWSCC in the nickel-based alloys. The through-weld leaking 

flaw had an eddy current response of 31%, which is less than the 40–45% found for the 

implanted flaws. The thermal fatigue flaws produce a large response compared to the eddy 

current response found in nozzle 31. 
7.10
8.1

8.0 Conclusions and Recommendations from 

PINC Round Robins

Inservice inspections, which are scheduled during maintenance outages at nuclear power 

plants, serve as an important layer of the defense-in-depth philosophy. For ISI to be effective, 

the nondestructive examination techniques used during ISI must demonstrate high probabilities 

for crack detection. Demonstrating a high quality of flaw detection and sizing using 

nondestructive technology will become increasingly important as nuclear power plants age and 

as nuclear power plants are operated for longer periods of time. Effective ISI procedures should 

be able to detect and correctly size flaws with a high degree of accuracy so decision makers at 

nuclear power plants may make informed “run, repair, or replace” decisions.

The dissimilar metal weld round-robin exercises that were conducted as part of the PINC are an 

important part of the process in assessing nondestructive testing methods because the data that 

are developed in the round-robin testing offer insight into capabilities of current nondestructive 

methods used to detect PWSCC and insight into the capabilities of more experimental 

nondestructive methods. These insights may then be used in developing regulatory positions 

and help direct additional research plans. 

This section of the report describes the conclusions that may be inferred from the PINC round 

robin results and then offers recommendations agreed on by the international PINC Steering 

Committee that address PWSCC-specific issues. 

8.1 Probability of Detection Performance

8.1.1 Dissimilar Metal Weld Pipe Specimen Round Robin Probability of 

Detection Performance

The conclusions that may be inferred from the experimental results for the dissimilar metal 

welds pipe specimens are as follows:

1. Conclusion: Eddy current inspection from the cracked surface demonstrated the highest 

probability of detection (POD) for all flaws in the DMW round robin.

• PINC Recommendation: The results of this study show that eddy current inspection 

are the preferred detection technique for dissimilar metal welds, where conditions 

allow access to the same surface from which the crack originates and where the 

surface conditions allow for ECT testing.

2. Conclusion: The POD results for the DMW round robin show significant variability in POD 

performance based upon technique, procedure, and team.

• PINC Recommendation: The results illustrate the usefulness of performance 

demonstration as a means to help ensure the reliability of DMW inspections.
8.2

3. Conclusion: The potential-drop techniques that were used in the DMW round robin 

demonstrated the lowest POD performance.

• PINC Recommendation: The potential-drop techniques used in the DMW round robin 

need further development before use as detection techniques in inservice inspection 

programs.

8.1.2 Bottom-Mounted Instrumentation Round Robin Probability of Detection 

Performance

The conclusions that may be inferred from the experimental results for the bottom mounted 

instrumentation tube specimens are as follows

1. Conclusion: Inspections using a single cross-coil eddy-current probe achieved a high POD 

and a low false call rate. These examinations were performed with multiple frequencies, 

with the highest frequency used being 300–400 kHz.

• PINC Recommendation: The results of this study suggest that single cross-coil 

probe eddy current using frequencies of 300–400 kHz are the preferred method for 

finding surface-breaking flaws in BMI J-groove welds.

2. Conclusion: Inspections using adaptive phased array ultrasound were able to detect all 

baseline difficulty flaws and none of the challenging flaws (baseline and challenging flaws 

are defined in Section 4.2.2).

• PINC Recommendation: While adaptive phased array ultrasound was slightly less 

effective than eddy current testing, the results of this study suggest that adaptive 

phased array ultrasound can be effectively used to find flaws in BMI welds.

3. Conclusion: The inspections using array eddy-current techniques used in this BMI round 

robin study had a reduced POD and a much higher false call rate compared to the higher 

frequency cross-coil ECT examinations.

• PINC Recommendation: The results of the BMI round-robin study show that the 

procedures using array ECT probes operating at 100–200 kHz used in this round 

robin test require further development for detection in inservice inspection programs.

4. Conclusion: The closely coupled potential-drop technique was able to detect thermal 

fatigue flaws and SCC flaws with a POD of 50%. For weld solidification flaws, the POD was 

0%. No false calls were made by the inspectors using this technique. 

• PINC Recommendation: The results of the BMI round-robin study show that the 

closely coupled potential-drop technique requires further development before it can 

be used for detection of flaws in inservice inspection programs.

5. Conclusion: Induced-current potential drop was used on only one baseline difficulty test 

block and two challenging test blocks, possibly skewing the results. There are not enough 

inspections on baseline difficulty test blocks to draw meaningful conclusions on the POD 

performance on these test blocks.
8.3

• PINC Recommendation: Further testing needs to be performed to determine if ICPD 

can be used for inservice inspection.

8.2 Sizing Performance

8.2.1 Dissimilar Metal Weld Pipe Specimen Sizing Performance

The conclusions that may be inferred from the experimental results indicate the following:

1. Conclusion: None of the NDE techniques in this round robin study demonstrated the 

capability to accurately depth size flaws in dissimilar metal welds to ASME Section XI code 

standards. The average depth sizing for all techniques tended to slightly undersize the 

flaws and had standard deviations and RMSE errors of approximately 7 mm. Two 

techniques came close to meeting ASME Section XI standards.

• PINC Recommendation: The depth sizing of flaws should be improved. The use of 

phased array UT and conventional ultrasound together showed the most promise.

2. Conclusion: Eight teams length-sized flaws with an RMSE within the ASME Section XI 

standard of 0.75 inch (19 mm). Teams that used phased array UT and eddy current 

achieved higher accuracy than teams that used conventional UT and potential-drop 

techniques.

• PINC Recommendation: Phased array UT or a combination of eddy-current 

techniques and conventional UT are the preferred method for length sizing.

8.2.2 Bottom-Mounted Instrumentation Weld Sizing Performance

The conclusions that may be inferred from the experimental results indicate the following:

1. Conclusion: Cross-coil eddy current, adaptive phased array ultrasound, and closely 

coupled probe potential-drop techniques were able to accurately length-size the flaws in the

J-groove welds (RMSE of 2.45-4.70 mm). 

• PINC Recommendation: These techniques can be used to length-size flaws in BMI 

J-groove welds.

2. Conclusion: The test block geometry made depth-sizing using ultrasound difficult, and not 

enough data was collected in this round-robin test to accurately determine the effectiveness 

of the depth-sizing techniques.

• PINC Recommendation: More work should be performed to determine the depthsizing capabilities of the various techniques.

Based on the round-robin tests, including detection and length-sizing capabilities, several 

techniques need to be used in tandem for flaw detection and sizing in dissimilar metal welds 

comparable to ASME Section XI. Eddy current testing had the highest POD performance, and a 

combination of conventional and phased array ultrasound was the only technique that provided 
8.4

RMSE depth-sizing capabilities close to Section XI requirements. It is worth noting that eddy 

current is not universally applicable for dissimilar metal welds, as many welds are in locations or 

have surface conditions that do not allow for ID inspections. If ID access is not possible, a 

combination of phased array ultrasound and conventional ultrasound appears to be the most 

accurate alternative. 

8.3 General Conclusions

1. Conclusion: The surface conditions, access to both sides of the weld, and inspection 

conditions for the PINC specimens provided the inspectors with less challenging conditions 

than would be expected in field inspections of nuclear power plant components.

• PINC Recommendations: The probability of detection and sizing results should be 

considered an upper bound for the inspection techniques. 

2. Conclusion: Inspection procedures and teams with formal NDE qualifications tended to 

have a higher POD and lower false call rate than teams and procedures with no formal 

qualifications.

• PINC Recommendation: As NDE inspections are carried out by qualified inspectors, 

the probability of detection and length sizing results for the qualified teams and 

procedures should be considered the most representative of field inspections. 

3. Conclusion: An analysis of the POD curves generated by the PINC round robin testing 

showed that the procedures improved safety by factors of 1.1 to 1.5 for a 10 year interval 

and by factors of 1.3 to 2.1 for a four year interval. (These safety factors use the crack 

growth rates for stress corrosion cracks in stainless steel welds.)

• PINC Recommendation: Effective NDE techniques may need to be combined with 

inspection intervals selected based on the crack growth rates. The analysis should 

be refined using PWSCC crack growth rates in nickel-based alloys.
9.1

9.0 References

NRC Order EA-03-009. 2003. "Order Modifying Licenses (Effective Immediately)." U.S. 

Nuclear Regulatory Commission, Washington, D.C.

Bamford WH, et al. 2000. Integrity Evaluation for Future Operation: Virgil C. Summer Nuclear 

Plant Reactor Vessel Nozzle to Pipe Weld Regions. WCAP-15615, Rev. 0, Westinghouse 

Engineering. 

Bamford WH, J Foster, KR Hsu, L Tunon-Sanjur and A McIlree. 2002. "Alloy 182 Crack Growth 

and Its Impact on Service-Induced Cracking in PWR Plant Piping." In 10th International 

Conference on Environmental Degradation of Materials in Nuclear Power Systems - Water 

Reactors, NACE, Houston, Texas.

Daniels W, P Roscoe, DR Tice, C Waites and C Udell. 2003. Qualification of Inspection for 

SCC. Nuclear Engineering International.

Ekstrom P and J Wåle. 1995. Crack Characterization for In-service Inspection Planning. SKI 

Report 95:70, Swedish Nuclear Power Inspectorate, Stockholm, Sweden. 

Frye CR, ML Arey, RR Robinson and DE Whitaker. 2002. "Evaluation and Repair of Primary 

Water Stress Corrosion Cracking In Alloy 600/182 Control Rod Drive Mechanism Nozzles." In 

Proceedings of ICONE10, 10th International Conference on Nuclear Engineering, April 14–18, 

2002, Arlington, Virginia. American Society of Mechanical Engineers, New York.

Halpin ED. 2003. Bottom Mounted Instrumentation Penetration Indications. STP Unit 1 

Licensee Event Report (LER) 03-003, ADAMS, ML031681316, June 11, 2003. 

Harris DO, DD Dedhia and SC Lu. 1992. Theoretical and User’s Manual for pc-PRAISE, A 

Probabilistic Fracture Mechanics Computer Code for Piping Reliability Analysis. NUREG/CR5864, UCRL-ID-109798, U.S. Nuclear Regulatory Commission, Washington, D.C. 

Jenssen A, K Norrgard, G Embring, J Lagerstrom and DR Tice. 2002a. "Assessment of 

Cracking in Dissimilar Metal Welds." In 10th International Conference on Environmental 

Degradation of Materials in Nuclear Power Systems - Water Reactors. NACE, Houston, Texas.

Jenssen A, K Norrgard, C Jansson, J Lagerstrom, G Embring and P Efsing. 2002b. "Structural 

Assessment of Defected Nozzle to Safe-End Welds in Ringhals-3 and -4." In Fontevraud V 

International Symposium. SFEN.

Kemppainen M, I Virkkunen, J Pitkänen, R Paussu and H Hänninen. 2003. "Advanced Flaw 

Production Method for In-service Inspection Qualification Mock-ups." Journal of Nuclear 

Engineering and Design 224:105–117.

Khaleel MA and FA Simonen. 2009. Evaluations of Structural Failure Probabilities and 

Candidate Inservice Inspection Programs. PNNL-13810, Pacific Northwest National Laboratory, 

Richland, Washington. 
9.2

Khaleel MA, FA Simonen, DO Harris and DD Dedhia. 1995. "The Impact of Inspection on 

Intergranular Stress Corrosion Cracking for Stainless Steel Piping." In Risk and Safety 

Assessments: Where Is the Balance?, PVP-Vol. 296, pp. 411–422. American Society of 

Mechanical Engineers, New York.

Lang TA. 2003. "Significant Corrosion of the Davis-Besse Nuclear Reactor Pressure Vessel 

Head." In ASME Pressure Vessels and Piping Conference. July 20–24, 2003, Cleveland, Ohio.

NRC. 2001. Circumferential Cracking of Reactor Pressure Vessel Head Penetration Nozzles. 

NRC Bulletin 2001-01, U.S. Nuclear Regulatory Commission, Washington, D.C. 

NRC. 2002. Reactor Pressure Vessel Head and Vessel Head Penetration Nozzle Inspection 

Programs. NRC Bulletin 2002-02, U.S. Nuclear Regulatory Commission, Washington, D.C. 

NRC Generic Letter 97-01. 1997. Degradation of Control Rod Drive Mechanism Nozzle and 

Other Vessel Closure Head Penetrations. U.S. Nuclear Regulatory Commission, Washington, 

D.C. 

Rudland DL, H Xu, G Wilkowski, P Scott, N Ghadiali and F Brust. 2006. "Development of a 

New Generation Computer Code (PRO-LOCA) for the Prediction of Break Probabilities for 

Commercial Nuclear Power Plants Loss-of-Coolant Accidents." In 2006 Proceedings of the 

ASME Pressure Vessels and Piping Conference, July 23–27, 2006, Vancouver, British 

Columbia, Canada. American Society of Mechanical Engineers, New York.

SKI. 2005. Statens kärnkraftinspektions föreskrifter om mekaniska anordningar i vissa 

kärntekniska anläggningar, (Regulations Concerning Mechanical Equipment). SKIFS 2005:2, 

Swedish Nuclear Power Inspectorate, Stockholm, Sweden. 

SQC. 2003. Project PostDAS - Final Report, Test Specimen Report. Report Nr RAPP0115/03, 

Swedish Qualification Center (SQC), Stockholm, Sweden. 

Wåle J. 2002. Karakterisering av IDSCC i Alloy 182, Delmåi 1 i Projekt DAS182. Rapport Nr 

10521100-1, Det Norske Veritas AB, Stockholm, Sweden. 

Wåle J. 2006. Crack Characterisation for In-service Inspection Planning - An Update. SKI 

Report 2006:24, Swedish Nuclear Power Inspectorate, Stockholm, Sweden. 

Watson PD and RL Edwards. 1996. "Fabrication of Test Specimens Simulating IGSCC for 

Demonstration and Inspection Technology Evaluation." In 14th International Conference on 

NDE in the Nuclear Pressure Vessel Industries. September 24–26, 1996, Stockholm, Sweden.
Appendix A

Destructive Data Analysis for Dissimilar Metal Weld Pipe 

Specimens

A.1

Appendix A

Destructive Data Analysis for Dissimilar Metal Weld Pipe 

Specimens

Destructive analysis was performed on the PINC dissimilar metal weld samples PINC 2.1 to 2.6 

donated to verify the depth of the cracks. This appendix documents the results of the 

destructive tests that were performed. The destructive analysis was conducted by JNES. The 

samples were sectioned and examined to precisely determine the length and depth of the grown 

crack. Other important parameters such as crack opening displacement were recorded. The 

crack morphology was examined via polishing and the use of optical microscopy. 
A.2
A.3
A.4
A.5
A.6
A.7
A.8
A.9
A.10
A.11
A.12
A.13
A.14
A.15
A.16
A.17
A.18
A.19
A.20
A.21
A.22
A.23
A.24
A.25
A.26
A.27
A.28
A.29
A.30
A.31
A.32
A.33
A.34
Appendix B

Destructive Analysis of BMI Samples

B.1

Appendix B

Destructive Analysis of BMI Samples

B.1 Destructive Analysis of Sample 5.2

Figure 1 Analysis of BMI Sample Position
B.2

List of Symbols

O : Origin coordinate of BMI sample

C : Center coordinate

ridp : I.D. radius of pipe

ridpsp : I.D. radius of pipe support plate

rodpsp : O.D. radius of pipe support plate

rm1 : Minimum radial extent measured from pipe inner surface

r1 : Minimum radial extent of flaw, r1 = ridp + rm1

rm2 : Maximum radial extent measured from pipe inner surface

r2 : Maximum radial extent of flaw, r2 = ridp + rm2

Zm1 : Minimum measured vertical position

Zm2 : Maximum measured vertical position

Z1 : Minimum vertical position of flaw measured from origin O

Z2 : Maximum vertical position of flaw measured from origin O

θ1 : Minimum measured circumferential extent

θ2 : Maximum measured circumferential extent

rmin : Minimum radial extent

rmax : Maximum radial extent

Zmin : Minimum vertical position from origin O

Zmax : Maximum vertical position from origin O

θmin : Minimum circumferential extent

θmax : Maximum circumferential extent
B.3

1. Circumferential Crack, Surface Crack of Pipe O.D.

Position of Flaw

Flaw No.

Circ. Extent 

(deg) Radial Extent (mm) Vertical Position (mm)

θ r1 r2 Z1 Z2

#1-10 305 - - - -

#1-09 310 15.8 17.1 296.0 297.4

#1-08 315 15.8 18.7 295.8 297.6

#1-07 320 14.4 18.2 294.0 297.1

#1-06 325 15.0 18.9 292.7 296.4

#1-05 330 14.7 19.5 292.0 295.8

#1-04 335 14.9 19.6 291.4 295.6

#1-03 340 15.8 19.7 290.9 294.0

#1-02 345 16.0 19.7 290.4 293.3

#1-01 350 - - - -

Final Results of Destructive Test on BMI Test Sample

BMI Test 

Block 

Number

Circ. Extent 

(deg) Radial Extent (mm) Vertical Position (mm)

θmin θmax r min rmax Z min Zmax

Flaw No. #1 305 350 14.4 19.7 290.4 297.6

Figure 2 Flaw #1 Surface Crack of Pipe O.D.
B.4
B.5

Figure 3 Depth Profile of Flaw #1 Using r1 and r2

Figure 4 Depth Profile of Flaw # 1 Using dr (= r2 – r1)
B.6

2. Circumferential Crack, Through Wall Crack

Position of Flaw

Flaw No.

Circ. Extent 

(deg)

Radial Extent 

(mm) Vertical Position (mm)

θ r Z1 Z2

#2-13* 225 9.2* 314.5 313.9

#2-12* 230 18.9* 317.0 313.5

#2-11 235 19.1 314.7 312.4

#2-10 240 19.1 313.0 312.1

#2-09 245 19.1 311.9 311.5

#2-08 250 19.1 310.6 310.9

#2-07 255 19.1 308.9 310.0

#2-06 260 19.1 307.8 310.1

#2-05 265 19.1 306.4 309.8

#2-04 270 19.1 305.4 309.6

#2-03 275 19.1 304.5 309.2

#2-02* 280 15.8* 305.4 309.8

#2-01* 285 11.3* 307.0 309.6

* : Not perfectly through wall crack

Final Results of Destructive Test on BMI Test Sample

BMI Test 

Block 

Number

Circ. Extent 

(deg) Radial Extent (mm) Vertical Position (mm)

θmin θmax r min rmax Z min Zmax

Flaw No. #2 220 290 9.2 19.1 304.5 317.0
B.7

Figure 5 Flaw #2 Through Wall Crack
B.8

3. Axial Crack, 0.05” from Interface J-weld and Nozzle O.D.

Position of Flaw

Flaw No.

Circ. Extent 

(deg)

Radial Extent 

(mm)

Vertical Position 

(mm)

θ1 θ2 r1 r2 Z1 Z2

#3-01 - - - - - -

#3-02 150 154 19.9 27.3 327.1 334.0 

#3-03 149 153 19.8 25.9 329.6 335.3 

#3-04 148 155 19.3 24.9 331.7 337.6 

#3-05 149 155 19.5 21.9 334.9 337.8 

#3-06 151 155 21.2 22.6 339.3 341.2 

#3-07 - - - - - -

Final Results of Destructive Test on BMI Test Sample

BMI Test 

Block 

Number

Circ. Extent 

(deg)

Radial Extent 

(mm) Vertical Position (mm)

θmin θmax r min rmax Z min Zmax

Flaw No. #3 148 155 19.3 27.3 327.1 341.2 

Figure 6 Flaw #3 Interface J-weld and Nozzle O.D.
B.9
B.10

3A. Axial Crack, I.D. Notch on Carbon Steel Plate

Position of Flaw

Flaw No.

Circ. Extent 

(deg) Radial Extent (mm) Vertical Position (mm)

θ1 θ2 r1 r2 Z1 Z2

#3A-initial 89.6 91.7 19.0 19.7 305.2 305.9 

#3A-01 89.6 91.7 19.0 19.7 308.0 308.6

#3A-02 89.7 91.8 19.0 20.5 310.8 311.5 

#3A-03 90.0 91.9 19.1 20.8 313.6 314.2 

#3A-04 90.2 91.9 19.0 20.7 316.4 317.0 

#3A-05 90.5 92.1 18.8 20.4 319.2 319.8 

#3A-06 90.5 92.1 19.0 20.7 322.0 322.6 

#3A-07 90.5 92.0 19.1 20.8 324.7 325.3 

#3A-08 90.5 92.0 19.0 20.8 327.5 328.0 

#3A-09 90.6 91.9 19.1 20.9 330.3 330.7 

#3A-10 90.7 92.1 19.1 21.1 333.1 333.6 

#3A-11 89.7 92.5 18.6 20.4 335.5 336.4 

#3A-12 89.9 91.9 18.8 20.0 338.3 339.0 

#3A-13 89.9 91.8 18.9 20.2 341.0 341.7 

#3A-14 89.9 91.8 18.9 20.2 343.8 344.4 

#3A-15 89.9 91.8 18.9 20.3 346.5 347.2 

#3A-16 89.9 91.8 18.9 20.4 349.3 349.9 

#3A-17 89.9 91.8 18.9 20.3 352.0 352.7 

Final Results of Destructive Test on BMI Test Sample

BMI Test 

Block 

Number

Circ. Extent 

(deg) Radial Extent (mm) Vertical Position (mm)

θmin θmax r min rmax Z min Zmax

Flaw No. #3A 89.6 92.5 18.6 21.1 305.2 352.7
B.11

Figure 7 Flaw #3A I.D. Notch on Carbon Steel Plate
B.12

4. Slag Crack, 0.02” from Interface J-weld and Nozzle O.D.

Position of Flaw

Flaw No.

Circ. Extent 

(deg) Radial Extent (mm) Vertical Position (mm)

θ r1 r2 Z1 Z2

#4-10 20 21.1 22.8 297.4 299.8

#4-09 25 19.9 23.7 294.1 301.9

#4-08 30 19.8 23.7 296.7 304.1

#4-07 35 19.6 23.7 297.2 305.2

#4-06 40 19.7 23.6 297.0 305.7

#4-05 45 19.7 23.5 299.2 306.8

#4-04 50 17.4 21.0 300.9 307.9

#4-03 55 19.8 22.6 300.8 307.9

#4-02 60 21.2 21.5 304.6 305.6

#4-01 65 21.2 21.9 306.1 306.8

Final Results of Destructive Test on BMI Test Sample

BMI Test 

Block 

Number

Circ. Extent 

(deg) Radial Extent (mm) Vertical Position (mm)

θmin θmax r min rmax Z min Zmax

Flaw No. #4 15 70 17.4 23.7 294.1 307.9
B.13

Figure 8 Flaw #4 508 from Interface J-weld and Nozzle O.D.

5. Axial Crack, Surface Crack of Pipe I.D.

Position of Flaw

Flaw No.

Circ. Extent 

(deg)

Radial Extent 

(mm)

Vertical Position 

(mm)

θ1 θ2 r1 r2 Z1 Z2

#5-01 102 106 8.4 9.5 296.0 296.8 

#5-02 100 107 7.5 10.7 298.3 300.1 

#5-03 100 107 7.5 10.2 301.1 302.6 

#5-04 100 107 7.5 10.2 303.8 305.4 

#5-05 100 107 7.5 10.2 306.6 308.1 

#5-06 100 107 7.5 10.3 309.3 310.9 

#5-07 100 107 7.5 9.8 312.1 313.5 

#5-08 100 107 7.5 10.3 314.8 316.4 

#5-09 100 107 7.5 10.5 317.6 319.2 

#5-10 100 107 7.5 9.3 320.3 321.6 

Final Results of Destructive Test on BMI Test Sample

BMI Test 

Block 

Number

Circ. Extent 

(deg)

Radial Extent

(mm)

Vertical Position

(mm)

θmin θmax r min rmax Z min Zmax

Flaw No. #5 100 107 7.5 10.7 296.0 321.6 

Figure 9 Flaw #5 Surface Crack of Pipe I.D.
B.14

Figure 10 Flaw #5 Angle of crack
B.15

B.2 Destructive Analysis of Sample 5.10

The six flaws had a consistent profile. Four of the six flaws, 1, 2, 4, and 6, had a shallow 

surface-breaking component and disconnected segments deeper into the material. Flaw 3 was 

very shallow and flaw 5 was continuous. 

The surface and profile of Flaw 1 showed that the flaw was reasonably discontinuous on the 

surface and is not continuous until the first 2 mm of weld. The surface-breaking segment 

measured at the cut surface only penetrated 0.6 mm into the weld. One team was able to 

detect Flaw 1.

Flaw 2 is very discontinuous at the surface, and the surface-breaking component of the crack is 

a mere 0.2 mm into the weld. At a depth of 1.5 mm, the flaw becomes continuous and much 

wider. Flaw 2 can almost be considered an embedded flaw, as the surface-breaking component 

is so tight and shallow. No teams were able to detect Flaw 2. 

Flaw 3 is the smallest measured using DE, with three small surface-breaking components and a 

measured depth of 0.35 mm. No teams were able to detect Flaw 3.

Flaw 4 had a discontinuous surface profile along the surface and along the cross section, but 

the surface-breaking segment of the crack was almost 1-mm deep. Also, the flaw has a 

“T”-shaped profile that would make it more easily detectable by eddy current systems that are 

sensitive to the orientation of the crack. Three teams detected Flaw 4.

Flaw 5 was continuous along the surface and the cross section into the weld. One team was 

able to detect Flaw 5.

Flaw 6 was challenging to characterize at the surface with a scanning electron microscope, and 

is not continuous through the cross section. This flaw may be considered an embedded flaw, as 

the surface-breaking component penetrates only 0.2 mm into the material.

The measured properties are listed in Table B.1 along with the PINC round-robin PODs for the 

flaws are summarized in Table B.1. It should be noted that the crack CODs were measured 

after the surface was polished.

Table B.1. Measured Properties for Flaws in 5.10

Flaw

Length 

(mm) Depth COD SB Depth POD

5.10-1 7.5 9 28 0.6 0.14

5.10-2 5 7 12 0.2 0.00

5.10-3 0.8, 3.5 0.35 15 0.35 0.00

5.10-4 7 2 32 0.95 0.43

5.10-5 4.5 2 12 2 0.14

5.10-6 1.6 4.5 10 0.2 0.00
B.16

Flaw 1

Measured Length 7.5 mm

COD at Surface 28 μm

Depth of Surface Breaking Segment 0.6 mm

Total Depth 9 mm
B.17

Flaw 2

Measured Length 5 mm

COD at Surface 12 μm

Depth of Surface Breaking Segment 0.2 mm

Total Depth 7 mm
B.18

Flaw 3

Measured Length 3.5 mm

COD at Surface 15 μm

Depth of Surface Breaking Segment 0.35 mm

Total Depth 0.35 mm
B.19

Flaw 4

Measured Length 7 mm

COD at Surface 32 μm

Depth of Surface Breaking Segment 0.9 mm

Total Depth 2 mm
B.20

Flaw 5

Measured Length 4.5 mm

COD at Surface 12 μm

Depth of Surface Breaking Segment 1.5 mm
B.21

Total Depth 2 mm

For flaw 6, there was a surface blemish and an apparent crack.

Flaw 6
B.22

Measured Length 1.6 mm

COD at Surface 10 μm

Depth of Surface Breaking Segment 0.2 mm

Total Depth 4.5 mm

B.3 Destructive Analysis of Sample 5.11–5.16
B.23
B.24
B.25
B.26
B.27
B.28
B.29
B.30
B.31
B.32
B.33
B.34
B.35
B.36
B.37
B.38
B.39
B.40
B.41
B.42
B.43
B.44
B.45
B.46
B.47
B.48
B.49
B.50
B.51
B.52
B.53
B.54
B.55
B.56
B.57
B.58
B.59
B.60
Appendix C

Inspection Plots for Dissimilar Metal Weld Samples

C.1

Appendix C

Inspection Plots for Dissimilar Metal Weld Samples

Table of Contents

Team

67 ....................................................................................................................................C.2

70 ..................................................................................................................................C.10

66 ..................................................................................................................................C.18

43 ..................................................................................................................................C.26

38 ..................................................................................................................................C.30

30 ..................................................................................................................................C.38

48 ..................................................................................................................................C.46

65 ..................................................................................................................................C.54

13 ..................................................................................................................................C.62

72 ..................................................................................................................................C.70

28 ..................................................................................................................................C.78

22 ..................................................................................................................................C.86

39 ..................................................................................................................................C.94

63 ................................................................................................................................C.102

82 ................................................................................................................................C.110

92 ................................................................................................................................C.118
C.2
C.3
C.4
C.5
C.6
C.7
C.8

Detection of poorly-documented flaw

Not used for scoring, and not counted as a false call
C.9
C.10
C.11
C.12
C.13
C.14
C.15
C.16

Detection of poorly-documented flaws

Not used for scoring, and not counted as false calls
C.17
C.18
C.19
C.20
C.21
C.22
C.23
C.24

Detection of poorly-documented flaws

Not used for scoring, and not counted as false calls
C.25
C.26
C.27
C.28
C.29
C.30
C.31
C.32
C.33
C.34
C.35
C.36

Detection of a poorly-documented flaw

Not used for scoring, and not counted as a false call
C.37
C.38
C.39
C.40
C.41
C.42
C.43
C.44

Detection of poorly-documented flaws

Not used for scoring, and not counted as false calls
C.45
C.46
C.47
C.48
C.49
C.50
C.51
C.52

Detection of a poorly-documented flaw

Not used for scoring, and not counted as a false call
C.53
C.54
C.55
C.56
C.57
C.58
C.59
C.60
C.61
C.62
C.63
C.64
C.65
C.66
C.67
C.68

Detection of a poorly-documented flaw

Not used for scoring, and not counted as a false call
C.69
C.70
C.71
C.72
C.73
C.74
C.75
C.76
C.77
C.78
C.79
C.80
C.81
C.82
C.83
C.84

Detection of poorly-documented flaws

Not used for scoring, and not counted as false calls
C.85
C.86
C.87
C.88
C.89
C.90
C.91
C.92
C.93
C.94
C.95
C.96
C.97
C.98
C.99
C.100

Detection of poorly-documented flaws

Not used for scoring, and not counted as false calls
C.101
C.102
C.103
C.104
C.105
C.106
C.107
C.108

Detection of poorly-documented flaws

Not used for scoring, and not counted as false calls
C.109
C.110
C.111
C.112
C.113
C.114
C.115
C.116

Detection of poorly-documented flaws

Not used for scoring, and not counted as false calls
C.117
C.118
C.119
C.120
C.121
C.122
C.123
C.124

Detection of poorly-documented flaws

Not used for scoring, and not counted as false calls
C.125
C.126
Appendix D

Block Hitograms for

Dissimilar Metal Weld Samples

D.1

Appendix D

Block Hitograms for

Dissimilar Metal Weld Samples
D.2
D.3
D.4
D.5
D.6
D.7
D.8
Appendix E

Inspection Plots for Bottom-Mounted Instrumentation 

Samples

E.1

Appendix E

Inspection Plots for Bottom-Mounted Instrumentation 

Samples

Table of Contents

Penetration Tube Examinations

13 .................................................................................................................................... E.2

Team

70 .................................................................................................................................. E.15

Weld Surface Examinations

16 .................................................................................................................................. E.18

Team

373 ................................................................................................................................ E.27

38 .................................................................................................................................. E.41

66 .................................................................................................................................. E.52

67 .................................................................................................................................. E.59

70 .................................................................................................................................. E.62

99 .................................................................................................................................. E.73
E.2
E.3
E.4
E.5
E.6
E.7
E.8
E.9
E.10
E.11
E.12
E.13
E.14
E.15

Not Surface Breaking

Not Surface Breaking
E.16

Not Surface Breaking Not Surface Breaking

Not Surface Breaking Not Surface Breaking
E.17

Not Surface Breaking Not Surface Breaking

Not Surface Breaking Not Surface Breaking
E.18
E.19
E.20
E.21
E.22
E.23
E.24
E.25
E.26
E.27
E.28
E.29
E.30
E.31

.
E.32
E.33
E.34
E.35
E.36
E.37
E.38
E.39
E.40
E.41
E.42
E.43
E.44
E.45
E.46
E.47
E.48
E.49
E.50
E.51
E.52
E.53
E.54
E.55
E.56
E.57
E.58
E.59
E.60
E.61
E.62
E.63
E.64
E.65
E.66
E.67
E.68
E.69

.
E.70
E.71
E.72
E.73
E.74
E.75
E.76
E.77
E.78
E.79
E.80
E.81
E.82
Appendix F

Block Hitograms for

Bottom-Mounted Instrumentation Tube Samples

F.1

Appendix F

Block Hitograms for

Bottom-Mounted Instrumentation Tube Samples
F.2
F.3
F.4
F.5
F.6
F.7
F.8
F.9
F.10
F.11
F.12
F.13
F.14
F.15
F.16
F.17
F.18
Appendix G

PINC Data Compilation

G.1

Appendix G

PINC Data Compilation

AF Pardini

R Mathews

Sample Flaw Angle

PNNL ECT 

Magnitude

5.6 Flaw 1 45 0.72

5.6 Flaw 2 135 1.74

5.6 Flaw 3 180 1.07

5.6 Flaw 4 225 1.25

5.6 Flaw 5 255 NR

5.6 Flaw 6 315 1.44

5.7 Flaw 1 15 2.35

5.7 Flaw 2 165 1.67

5.7 Flaw 3 300 2.32

5.9 Flaw 1 15 0.51

5.9 Flaw 2 75 NR

5.9 Flaw 3 195 NR

5.9 Flaw 4 345 1.33

5.10 Flaw 1 45 2.69

5.10 Flaw 2 75 1.79

5.10 Flaw 3 225 NR

5.10 Flaw 4 255 1.9

5.10 Flaw 5 285 NR

5.10 Flaw 6 315 1.96

5.13 No. 1-1 0 2.45

5.13 No. 1-2 180 1.62

5.14 No. 2-1 0 3.92

5.14 No. 2-2 180 1.39

5.15 No. 3-1 90 2.94

5.15 No. 3-2 270 4.01

5.16 No. 4-1 90 4.42

5.16 No. 4-2 270 7.08

Japan EDM 1 Largest NA 1.69

Japan EDM 2 Largest NA 2.43

Japan Ref. 1 Largest NA 1.76

Japan Ref. 2 Largest NA 3.52

Cal Std. 5 mm NA 2.58

Cal Std. 5 mm NA 2.44

Cal Std. 1 mm NA 1.96

Cal Std. 1 mm NA 1.36
G.2

Flaw Observations POD ECT

Surf 5.9.2 6 0.167 0

Surf 5.9.3 6 0.167 0

Surf 5.10.3 6 0 0

Surf 5.10.5 6 0.167 0

Surf 5.9.1 6 0.333 0.51

Surf 5.6.1 4 0.75 0.72

Surf 5.6.3 4 0.75 1.07

Surf 5.6.4 4 0.75 1.25

Surf 5.9.4 6 0.167 1.33

Surf 5.14.2 4 0.75 1.39

Surf 5.6.6 4 0.75 1.44

Surf 5.13.2 4 0.5 1.62

Surf 5.7.2 6 0.833 1.67

Surf 5.6.2 4 0.75 1.74

Surf 5.10.2 6 0 1.79

Surf 5.10.4 6 0.5 1.9

Surf 5.10.6 6 0 1.96

Surf 5.7.1 6 0.667 2.35

Surf 5.13.1 4 0.75 2.45

Surf 5.10.1 6 0.167 2.69

Surf 5.15.1 4 0.75 2.94

Surf 5.14.1 4 1 3.92

Surf 5.15.2 4 0.5 4.01

Surf 5.16.1 4 0.75 4.42

Surf 5.16.2 4 0.75 7.08
G.3

G.1 Calibration/Verification Standard
G.4
G.5

G.2 PINC 5.7
G.6
G.7

G.2.1 Flaw 3

G.2.2 Flaw 1
G.8

G.2.3 Flaw 2
G.9

G.3 PINC 5.8

No flaws were identified in PINC 5.8. A fabricated area was, however, identified and shown in 

the following image.
G.10

G.4 PINC 5.9

Two flaws were visible on PINC 5.9. The image below shows the magnitude of the edge of the 

fabrication.
G.11
G.12

G.5 PINC 5.10

General magnitude of the fabrication area.
G.13
G.14
G.15

Here is another image that we used in a different report which shows six flaws. It is a stretch to 

say you can see them all unless you know what you are looking for. In the example shown 

above, we point to a different area for the flaw location. We would need to zero in on the flaw 

and scan at high resolution to identify.
G.16

G.6 PINC 5.11

General area magnitude.
G.17

G.7 PINC 5.12

General area magnitude.
G.18

G.8 PINC 5.6

Six indications were identified.
G.19
G.20
G.21
G.22

G.9 Japanese Samples

G.9.1 EDM Sample Block 1
G.23

G.9.2 EDM Sample Block 2
G.24

G.9.3 Reference Block 1
G.25

G.9.4 Reference Block 2
G.26

G.10 PINC 5.13
G.27
G.28

G.11 PINC 5.14
G.29
G.30

G.12 PINC 5.15
G.31
G.32
G.33

G.13 PINC 5.16
G.34
G.35
G.36
Appendix H

U.S. Plant Field Experience with Alloy 600 Cracking

H.1

Appendix H

U.S. Plant Field Experience with Alloy 600 Crackinga

Operating Unit

Date of 

PWSCC 

Discovery Method of Discovery

Affected 

Component or 

System

Vermont Yankee 1986/04 Ultrasonic examination of the N5A and N5B core spray safe-end-to-nozzle welds 

indicated intergranular stress-corrosion cracking (IGSCC).

Core spray nozzle 

weld

San Onofre 3 1986/02 Visual – A pressure boundary leak was observed in a 3⁄4-inch diameter 

pressurizer level instrument nozzle. Dye penetrant testing was utilized and 

revealed a crack extending from the end of the nozzle inside the pressurizer 

outward through the RCS pressure boundary.

Pressurizer 

instrument nozzle

St. Lucie 2 1987 Assumed visual - During the replacement of four pressurizer steam-space 

instrument nozzles, it was determined that two nozzles had cracks but there was 

no evidence of leakage.

Pressurizer 

instrument nozzles

ANO-2 1987/04 Leakage Testing - the licensee declared an unusual event and initiated a reactor 

shutdown as a result of a suspected reactor coolant system pressure boundary 

leak of approximately 60 drops per minute from the area of the pressurizer 

vessel lower head. It was determined that the leakage source was the heater 

sleeve for the X1 pressurizer heater. Because of this leakage, there was some 

corrosion damage to the carbon steel pressurizer shell.

Pressurizer heater 

sleeve

Calvert Cliffs 2 1989/05 Assumed visual - an inservice inspection of the Unit 2 pressurizer revealed 

evidence of reactor coolant leakage from 28 of the 120 pressurizer vessel heater 

penetrations and one upper level nozzle. No evidence of leakage was found on 

the Unit 1 pressurizer heater penetrations or pressure/level penetrations. 

Additional inspections using dye penetrant and eddy current tests of 28 Unit 2 

and 12 Unit 1 heater sleeves were conducted. Three sleeves from Unit 2 were

destructively examined. All cracks were axial and determined to have minimal 

safety significance.

Pressurizer heater 

sleeves and level 

nozzle

 

(a) This table uses information from NUREG-1823 titled U.S. Plant Experience With Alloy 600 Cracking and Boric Acid Corrosion of Light-Water Reactor 

Pressure Vessel Materials published in April 2005. Appendix A of this NUREG provides an excellent summary of U.S. and foreign Alloy 600 cracking 

experience.
H.2

Operating Unit

Date of 

PWSCC 

Discovery Method of Discovery

Affected 

Component or 

System

ANO-1 1990/12 Leakage - A potential reactor coolant system leak in the area of a pressurizer

upper-level instrumentation nozzle was identified. During a follow-up inspection, 

it was verified that a very small leak existed at the nozzle. Nondestructive testing 

was conducted which confirmed the existence of a small axial crack in the nozzle 

inner surface which breached the outside diameter of the nozzle at the toe of the 

nozzle-to-vessel weld.

Pressurizer 

instrumentation 

nozzle

San Onofre 3 1992/02 Liquid Penetrant - During refueling outage cycle 6, a dye penetrant examination 

of the pressurizer vapor space level instrument nozzles revealed the presence of 

a through-wall crack. The examination was attributable to boric acid crystals 

being found near the nozzle previously. The leaking nozzle was replaced with a 

new nozzle made of Alloy 690. Liquid penetration testing was conducted on the 

three remaining vapor space nozzles. Much smaller indications on two of the 

three nozzles were revealed in these tests. These three nozzles were also

replaced with nozzles fabricated with Alloy 690.

Pressurizer vapor 

space level 

instrument nozzles

Palo Verde 1 1992/01 Leakage - A pressure boundary leak was discovered in the pressurizer steamspace nozzle. A pad weld was put in place in order to stop the reactor coolant 

leakage. PWSCC is believed to be the cause of the leakage.

Pressurizer steamspace nozzle

San Onofre 2 1992/03 Assumed visual - An inspection on Unit 2 pressurizer vapor space level 

instrument nozzles was conducted. Boric acid crystals were found at two of the 

nozzles. An interim repair of the Unit 2 nozzles with Alloy 690 was implemented 

prior to startup. Inspection of the remaining water and vapor space nozzles 

showed no signs of leakage.

Pressurizer vapor 

space level 

instrument nozzles

St. Lucie 2 1993/03 Visual - Water was discovered dripping onto the floor in containment near the

pressurizer. Visual inspection revealed that four upper instrument nozzles were 

leaking at the entry fitting to the pressurizer. Liquid penetrant and eddy current 

test revealed axial cracking in the four steam-space nozzles extending into the 

surrounding weld area.

Pressurizer 

instrument nozzles

Palisades 1 1993/10 Assumed visual - inspection of the pressurizer upper temperature nozzle 

penetration TE-0101 was found to be leaking. Subsequent inspection of the 

lower temperature nozzle penetration TE-0102 was also found to be leaking. The 

leaks were attributable to cracking in the Alloy 600 nozzle material.

Pressurizer 

temperature nozzle

Palisades 1 1993/09 Visual - Plant personnel identified a leak in the power operated relief valve line

near the nozzle connection to the pressurizer. The crack initiated in the heataffected zone of the power-operated relief valve Alloy 600 safe end. NDE and 

visual inspection revealed a circumferential crack approximately 3 inches in 

length (about 30 percent of the circumference).

Relief valve
H.3

Operating Unit

Date of 

PWSCC 

Discovery Method of Discovery

Affected 

Component or 

System

D.C. Cook 2 1994 Eddy Current - During the cycle 10 refueling outage in 1994, eddy current testing 

examination was performed on 71 of the 78 vessel head penetrations. The 

testing showed crack indications in penetration number 75. Three indications 

were found with lengths of 9 mm, 16 mm, and 45 mm. These indications were 

axial in orientation and were closely spaced. The 3 indications were located near 

the 160-degree location on the high side. The 45-mm crack was located near the 

J-groove weld, but was mostly below the weld.

VHP

Calvert Cliffs 1 1994/03 Assumed visual - Boron deposits were located on the pressurizer heater sleeve 

B-3 after removing insulation. On February 23, 1994, after removing more 

insulation, boron deposits were also discovered on pressurizer heater sleeve FF1. Boroscopic and eddy current tests revealed a circumferential bulge 

approximately 0.5 inch long and 0.019 inch high (diametrical) in the area of the 

boric acid leaks. The leakage area showed evidence of surface metal smearing

and cold work.

Pressurizer heater 

sleeve

St. Lucie 2 1994/02 Visual - Boric acid was observed on the exterior of the pressurizer steam-space 

C instrument nozzle during an inspection. Dye penetrant was utilized and 

identified indications at the A, B, and C steam-space instrument nozzle welds. 

The D instrument nozzle weld was acceptable. The unacceptable cracks were in 

the “J” weld between the Alloy 690 nozzle (replaced in 1993) and the clad on the 

inside of the pressurizer.

Pressurizer 

instrument nozzles

San Onofre 3 1995/07 Assumed visual - During inspection of the Alloy 600 and 690 (see the March 

1992 event for Alloy 690 installation) instrument nozzles, one pressurizer level 

instrumentation nozzle was found with a small amount of boric acid crystals and 

oxidation present. Dye penetrant testing indicated crack initiation in the heataffected zone of the weld butter. The Alloy 690 pressurizer nozzle piece interior 

did not have indications of PWSCC.

Pressurizer level 

instrumentation 

nozzle

San Onofre 3 1995/07 Radio Chemistry - Radio-chemistry evaluation confirmed that RCS weepage had 

occurred on two hot leg instrument nozzles. The accessible exterior of the two 

RCS hot leg nozzles were replaced with new Alloy 690 nozzles. The access to 

the interior of the RCS hot leg piping prevents welding from the inside of the 

RCS. Therefore the old nozzles were cut off half way through the RCS hot leg 

materials and the new nozzles were welded to the exterior of the RCS pipe.

RCS hot leg 

instrument nozzles

St. Lucie 2 1995/10 Visual - During a routine RCS visual leak check, an apparent boric acid buildup

was discovered on the “B” side RCS hot leg instrument nozzle. Further 

investigation confirmed that pressure boundary leakage had previously occurred.

RCS hot leg 

instrument nozzle
H.4

Operating Unit

Date of 

PWSCC 

Discovery Method of Discovery

Affected 

Component or 

System

San Onofre 3 1997/04 Not Specified, presumably visual as above - During a routine inspection, four hot 

leg RCS nozzles were found to have leaks and a fifth was suspected of leaking. 

It was suspected that the leakage was attributable to cracks through the nozzle 

in the heat-affected zone of the partial penetration weld on each of the 

instrument nozzles.

RCS instrument 

nozzle

San Onofre 3 1997/07 Not Specified, presumably visual as above - RCS nozzles were inspected and 

one hot leg spare RTD thermowell nozzle had an increased amount of white 

residue. An isotopic analysis determined the residue was boric acid from the 

RCS. PWSCC was believed to be the root cause of the leaks reported. It was 

believed that the leakage came from a crack in the heat-affected zone of the 

partial penetration weld on each of the instrument nozzles.

RCS instrument 

nozzle

San Onofre 2 1997/03 Visual - Steam was observed emanating from the pressurizer. It was concluded 

that the leak was caused by PWSCC of Alloy 600 type materials of the 

pressurizer liquid temperature thermowell nozzle. The crack was oriented 

parallel to the long axis of the nozzle.

Pressurizer 

temperature nozzle

Hope Creek 1 199/09 Presumably visual - A leak was discovered on core spray nozzle safe-end weld 

#N5BSE associated with the “A” core spray subsystem. The N5BSE weld was 

nondestructively tested in the previous refueling outage. This NDE test had been 

improperly evaluated and the crack had been unrecorded. The cause of the 

through-wall leakage has been attributed to IGSCC in the Alloy 182 weld metal.

Core spray nozzle 

weld

Calvert Cliffs 1 1998 Ultrasonic Testing - Unit 1 heater sleeves were nickel plated in 1994. One nickel 

plated heater sleeve (B-1) was found leaking during the 1998 refueling outage. 

Ultrasonic testing revealed a short axial indication.

Pressurizer heater 

sleeve

San Onofre 2 1998/01 Visual - A steam leak was discovered at an upper-level instrument nozzle on the

pressurizer. A dye penetrant test of the nozzle proved that the Alloy 690 nozzle 

did not contain a leak pathway. Ultrasonic examination of the vessel shell was 

performed to look for defects in the shell material. No defects were found. 

Because no leak path was found in the nozzle or shell material, it was postulated 

that the crack was in the Alloy 600-type weld filler material of the nozzle.

RCS nozzles

Calvert Cliffs 2 1998/07 Visual - A steam leak was discovered at an upper-level instrument nozzle on the

pressurizer. A dye penetrant test of the nozzle proved that the Alloy 690 nozzle 

did not contain a leak pathway. Ultrasonic examination of the vessel shell was 

performed to look for defects in the shell material. No defects were found. 

Because no leak path was found in the nozzle or shell material, it was postulated 

that the crack was in the Alloy 600-type weld filler material of the nozzle.

Pressure level tap
H.5

Operating Unit

Date of 

PWSCC 

Discovery Method of Discovery

Affected 

Component or 

System

San Onofre 3 1999 Eddy Current Testing - A cracked heater sleeve was identified by eddy current 

testing. The heater had failed, swelled, and stuck within the sleeve. The flaw was 

approximately 40 percent through-wall on the inner diameter of the sleeve near 

the attachment weld.

Pressurizer heater 

sleeve

Waterford 3 1999/02 Visual - During a routine visual inspection, evidence of reactor coolant system

leakage was found on two Alloy 600 instrument nozzles located on the top head 

of the pressurizer. The leakage was in the annulus area where the nozzle 

penetrates the pressurizer head. The nozzles are welded on the Inner diameter 

of the pressurizer and joined to instrument valves RC-310 and RC-311.

Pressurizer 

instrument nozzles

Waterford 3 1999/02 Visual - Evidence of boric acid leakage was found on three nozzles. One was on

the RCS hot leg number 1 resistance temperature detector (RTD) nozzle, a 

second was on the RCS hot leg number 1 sampling line, and a third was on the 

RCS hot leg number 2 differential pressure instrument nozzle.

RCS hot leg 

instrument nozzle

Duane Arnold 1 1999/11 Ultrasonic - Two indications of IGSCC were identified in weld RRB-F002. One

indication was approximately 44 percent through-wall and the other was 

approximately 65 percent through-wall. The inspection was expanded and a 65-

percent through-wall crack was found in weld RRD-F002. These two F002 welds 

were repaired by completing weld overlays using Alloy 52. The cause of the 

cracking was IGSCC in the Alloy 182 weld metal.

Recirculation riser 

welds

Palo Verde 1 1999/10 Leakage - Evidence of an RCS pressure boundary leakage was discovered. The

leakage was discovered at two Alloy 600 nozzles, one in each of the RCS hot 

legs. One was at the nozzle upstream of Valve RCV0285 in the line to a steam 

generator number 2 differential pressure instrument. The other was at the nozzle 

upstream of Valve RCV-277 in the line to a steam generator number 1 

differential pressure instrument. The leakage was discovered in the form of small 

deposits of boron accumulated around the circumference of the nozzles. Isotopic

analysis of the boron accumulation detected only long-lived radionuclides, 

indicating that it has taken more than 3 years for the reactor coolant to migrate 

through the nozzle weld and wall thickness.

RCS hot leg valves

ANO-1 2000/02 Visual - A flawed weld was identified on an instrument connection to the reactor

coolant system Loop “A” hot leg piping. Once the insulation had been removed, 

leakage was discovered on five other nozzles. Further investigation using NDE 

revealed that leakage was occurring through flaws in the partial penetration 

weld. Both axial and circumferential flaws were found. There was also a 

subsurface flaw found in a seventh nozzle.

RCS hot leg 

instrumentation

ANO-2 2000/07 RCS hot leg 

instrument nozzle
H.6

Operating Unit

Date of 

PWSCC 

Discovery Method of Discovery

Affected 

Component or 

System

ANO-2 2000/07 Visual - Boron residue was discovered on the reactor coolant system pressurizer 

heater power cables. The boron came from leaks in heaters B2 and D2. B2 is on 

backup heater bank 4, and D2 is on backup heater bank 6. After removing 

insulation from the pressurizer, the licensee discovered 10 additional pressurizer 

heater sleeves that had previous leakage. Eddy current testing on two of the 

heater sleeves indicated that there was a single, through-wall, axial crack in both 

sleeves below the J-groove weld. These cracks initiated from the inside surface 

of the sleeves. Ultrasonic testing showed no cracks in the shell base metal.

Pressurizer heater 

sleeve

ONS-1 2000/11 Visual - During a visual inspection of the top surface of the reactor pressure

vessel head, small amounts of boric acid deposited on the vessel head surface 

was discovered. These deposits appeared to be located at the base of five 

unused thermocouples and the Nozzle #21 weld at points where they all 

penetrate the RPV head surface. On December 4, an eddy current test was 

performed on the inside surface of the eight thermocouple nozzles and revealed 

axial crack-like indications on the ID of the nozzles in the vicinity of the partial

penetration weld. Dye penetrant testing on Nozzle #21 identified two very small 

pin-hole indications running at a slightly skewed angle across the fillet weld.

VHP Weld and 

thermocouple 

nozzles

Waterford 3 2000/10 Visual - During a bare metal inspection, boric acid was found on two of the three

MNSA clamps that had been installed on hot leg nozzles during refueling outage 

9. These clamps had been installed as temporary repairs until a permanent 

repair could be made during refueling outage 10. The MNSA clamp leakage 

could have been caused by the flange not being flat against the pipe. The leak 

could have also arisen from a brief leakage while the clamps seated.

RCS hot leg 

mechanical nozzle 

seal assembly 

clamps

Ft. Calhoun 2000/10 Visual - During a walkdown inspection, leakage was detected from the lower

pressurizer liquid space temperature Nozzle #TE-108 was detected.

Pressurizer 

temperature nozzle

Waterford 3 2000/10 Visual - During a bare metal inspection of the pressurizer heater sleeve number

F-4, a small amount of boric acid residue was discovered.

Pressurizer heater 

sleeve

Palo Verde 2 2000/10 Visual - During an inservice inspection, reactor coolant system pressure 

boundary leakage was discovered. The leakage was discovered at pressurizer 

heater nozzle sleeve A06. The leakage was detected in the form of small deposit 

of boron accumulation on the sleeve. Eddy current testing indicated linear axial 

cracking.

Pressurizer heater 

sleeve
H.7

Operating Unit

Date of 

PWSCC 

Discovery Method of Discovery

Affected 

Component or 

System

V.C. Summer 2000/10/7 Visual - 100 to 200 pounds of boric acid was identified in the “A” hot leg area of 

the reactor vessel. The potential leak area was identified on the first weld off the 

reactor vessel at the nozzle-to-pipe connection of the Loop “A” hot leg.

Ultrasonic and eddy current inspection together with visual inspection identified 

the flaw as axially oriented and about 3 inches in length. The flawed weld was 

removed and a new weld made of Alloy 52/152 material was utilized. 

Subsequent cleaning and destructive examination of the salvaged pipe section

revealed also a short (about one inch) circumferential crack located in the weld 

that may have branched from the axial flaw, or may have nucleated as a 

separate defect.

Primary system hot 

leg

St. Lucie 1 2001/04 Visual - Leakage was discovered on a pipe-to-nozzle connection on line I-3/4-

RC-126. This line was determined to be the “B” RCS hot leg instrument nozzle 

connection for differential pressure (D/P) transmitter PDT-1121D.

RCS hot leg 

instrument nozzle

ONS-2 2001/04 Visual - A preliminary reactor head visual inspection on April 28, 2001, revealed 

small amounts of boron residue surrounding nozzles 4, 16, 18, and 30. 

Subsequent surface dye penetrant test inspections of the weld area and nozzle 

outside diameter identified several axial cracks on four VHP nozzles that initiated 

near the toe of the fillet and propagated radially into the nozzle materials as well 

as axially along the outer diameter surface. Eddy current tests revealed two

shallow axial flaws on Nozzle #16 and craze cracking on all four VHP nozzles’ 

inner diameter surface. The ultrasonic testing confirmed the existence of some 

axial cracks with one short outer diameter initiated circumferential crack on VHP 

18. The circumferential flaw was OD initiated, extended 11 percent through-wall, 

and was 1.26 inch in length.

VHP and VHP Weld

ONS-3 2001/12 Visual - During a visual inspection of the reactor vessel VHP nozzles, leakage

indications were discovered as evidenced by minor boric acid buildup around 4 

VHP nozzles. Nondestructive examination of the suspected nozzles revealed 

that 7 of the 69 total nozzles required repair. Five of these seven nozzles had a 

leak pathway to the top of the reactor vessel head. Some of the indications were 

in the nozzles themselves, while other indications extended slightly into the weld. 

Most of the cracking was axial in nature, however, there was one circumferential 

flaw found in Nozzle #2 above the J-groove weld.

VHP and VHP Weld
H.8

Operating Unit

Date of 

PWSCC 

Discovery Method of Discovery

Affected 

Component or 

System

ONS-3 2001/02 Visual - during a visual inspection of the reactor vessel VHP nozzles, small

amounts of boron residue surrounding the base of several control rod drive 

mechanism head penetrations was discovered. The boric acid deposits were 

identified around nozzles 3, 7, 11, 23, 28, 34, 50, 56, and 63. Subsequent 

surface dye penetrant test inspections of the weld areas and outside diameter 

identified several deep axial cracks that initiated near the toe of the fillet weld 

and propagated radially into the nozzle materials as well as axially along the 

outer diameter surface. Ultrasonic testing confirmed the existence of deep 

cracks in all nine leaking VHP nozzles. Of these 47 original crack indications, 19 

were OD-initiated flaws that were not through-wall. There were 16 flaws that 

were OD-initiated through-wall cracks. There were nine circumferential flaws, 

with one being ID-initiated and the rest being OD-initiated. Two of the outer 

diameter circumferential flaws were above the J-groove weld. Finally, there 

were also three ID-initiated non-through-wall cracks.

VHP and VHP Weld

Palo Verde 1 2001/03 Visual - During visual inspection of the RCS piping, boric acid residue was

discovered on the Alloy 600 RCS hot leg thermowell 1JRCETW0121HB. The 

visual indications were characterized as white streaks fanning out from the hot 

leg and continuing up the taper of the thermowell with some buildup on the top of 

the tapered portion.

RCS hot leg 

thermowell

ANO-1 2001/03 Visual - During a routine visual inspection of the reactor vessel head area, boric

acid crystals were discovered. On March 24, 2001, eddy current testing and 

ultrasonic testing revealed a reactor coolant solution pressure boundary leak. 

The leak was identified in the wall of Nozzle #56. The UT data indicated that the 

crack was on the downhill side of the nozzle and extended approximately 0.8 

inch below the weld and upward to approximately 1.0 inch above the weld. The 

depth of the crack was approximately 0.2 inch.

VHP
H.9

Operating Unit

Date of 

PWSCC 

Discovery Method of Discovery

Affected 

Component or 

System

North Anna 2 2001/11 Visual - A through-wall leak on Nozzle #63 was observed. This event was

treated as a through-wall leak based on the qualified visual inspection results 

and liquid penetrant examination. A portion of the weld around Nozzle #63 was 

excavated to a depth of approximately 1" of weld metal. The liquid penetrant 

exam of this excavation showed 12 indications located at the outside edge of the 

weld almost the full length of the excavation, which turned into the weld at the 

uphill and downhill ends of the excavation. Six of the recorded cracks were 

transverse to the weld, while the other six were parallel. Eddy current testing

revealed a crack 31mm in length in the area of the attachment weld. Ultrasonic 

testing of the same crack revealed that it was less than 1 mm in depth and 14 

mm in length. Nozzle #51 also had nearby boric acid residue on the reactor 

vessel head. A liquid penetrant test revealed 12 indications at the toe of the 

weld. Five of these indications were parallel while the rest were transverse. Eddy 

current testing of the nozzle’s weld revealed six axial indications. These axial

cracks were less than 2 mm in depth and ranged from 6 to 24 mm in length. 

Similarly, Nozzle #62 was also investigated. This nozzle had eight indications at 

the toe of the weld. Two of the cracks were parallel and six were transverse. 

Eddy current testing revealed two axial indications. The dimensions were 74 mm 

and 42 mm in length, while being less than 2 mm and less than 1 mm in depth, 

respectively.

VHP Weld

Crystal River 3 2001/10 Visual - During a visual inspection of the reactor vessel VHP, boric acid buildup

was discovered around Nozzle #32. Ultrasonic testing performed on Nozzle #32 

revealed two through-wall axial cracks. These cracks extended from the bottom 

of the nozzle to above the J-groove weld. These two axial cracks then joined a 

circumferential crack above the J-groove weld. The circumferential flaw was 

about 90° and 50 percent through-wall. There was another circumferential flaw 

below the J-groove weld which extended 30° and was approximately 75 percent 

through-wall.

VHP
H.10

Operating Unit

Date of 

PWSCC 

Discovery Method of Discovery

Affected 

Component or 

System

TMI-1 2001/10 Visual - During a visual inspection of the reactor vessel VHP nozzles, boric acid 

buildup was discovered around 8 different thermocouple nozzles. Liquid 

penetrant testing and ultrasonic testing identified through-wall indications on 

three VHP nozzles. These engineering evaluations concluded that the 

indications at Nozzles #44, 35, and 37 indicate a reactor coolant system 

pressure boundary leaks. During later examinations of the reactor vessel head, 

Nozzles #29 and 64 were shown to contain RCS pressure boundary leaks. The

VHP nozzles were repaired by initially rolling the nozzle above the J-groove 

weld, and then machining the lower portion of the VHP nozzle including portions 

of the J-groove weld. A new pressure boundary weld was formed between the 

VHP nozzle and the RPV head low-alloy steel at the location above the previous 

J-groove weld and below the rolled nozzle area. A surface remediation inducing 

compressive stresses was performed after the repair. The thermocouples were 

repaired by cutting them approximately 1 inch from the outside surface of the 

RPV head. The remaining nozzle portion inside the RPV head was machined out 

of the head.

VHP

Palo Verde 3 2001/09 Visual - Evidence of RCS leakage was discovered. The leakage was discovered 

in an RCS hot leg temperature nozzle. The RCS hot leg nozzle was located in 

the RTD nozzle for an inservice temperature detector (Loop #1, equipment ID: 

3JRCETW112HD). The leakage was identified by the discovery of boron 

deposits accumulated around the circumference of the hot leg nozzle.

RCS hot leg 

temperature nozzle

Palo Verde 3 2001/09 Visual - Evidence of reactor coolant leakage was discovered. The leak was from 

a pressurizer heater sleeve nozzle. The pressurizer heater sleeve leakage is 

located at pressurizer heater B17. The leakage was identified by the discovery of 

boron deposits accumulated around the circumference of the pressurizer. There 

was no evidence of leakage during the last refueling outage.

Pressurizer heater 

sleeve

Catawba 2 2001/09 Visual - A walk down of the SG 2B lower head bowl drain indicated boron

residue buildup on the 1⁄2-inch piping immediately below the SG. The root cause 

of the SG 2B bowl drain leak was PWSCC of Alloy 600 material.

SG bowl drain
H.11

Operating Unit

Date of 

PWSCC 

Discovery Method of Discovery

Affected 

Component or 

System

ONS-1 2002/04 Visual - A qualified visual inspection of the Unit 1 reactor vessel head was 

conducted. Two penetrations had very slight amounts of boron accumulations. 

Ultrasonic testing was then performed on the penetrations and revealed partial 

through-wall outside diameter cracks for nozzles 1, 7, and 8. There were five 

flaws and a potential leak path identified in Nozzle #7. There was one axial flaw 

but no leak path identified in Nozzle #8. Nozzle #1 showed three minor 

indications in a region of rough weld contour. Liquid dye-penetrant was then 

used to examine these three nozzles. PT revealed two axial flaws in the original 

weld on Nozzle #7. PT was also used on Nozzle #1 and there were no 

recordable or rejectable PT indications.

VHP and VHP Weld

ANO-2 2002/04 Visual - Six heater sleeves were found to be leaking in the pressurizer. Five of 

the leaking heater sleeves were discovered on April 15, 2002, while the other 

was found on April 30, 2002. On April 15, boron deposits were discovered on 

five pressurizer heater sleeve penetrations. On April 30, boron residue was 

observed around the sixth pressurizer heater sleeve. Since similar events had 

occurred in the July 2000 outage, no NDE was conducted.

Pressurizer heater 

sleeve

Millstone 2 2002/02 Visual - Pressurizer heater penetrations and pressurizer instrument nozzle

penetration were examined with visual inspection. Two heater sleeves showed 

indications of minor leakage because of the boron precipitates discovered on the 

outside of the penetrations. The cause of this event is through-wall cracks in the 

two pressurizer heater sleeves.

Pressurizer heater 

sleeves

Davis-Besse 2002/02/16 Visual - During machining to facilitate repair of nozzle #3, the licensee found that 

the nozzle had tipped, with the CRDM flange (located above the head) 

contacting the flange of an adjacent CRDM. The licensee cleaned the surface of 

the RPV head and found a large cavity adjacent to nozzle #3, where the RPV 

head base material had been corroded down to the stainless steel cladding. 

Subsequent investigation revealed an additional much smaller degraded area 

near nozzle #2, located within the wall thickness (no cladding was exposed).

Reactor pressure 

vessel top head
H.12

Operating Unit

Date of 

PWSCC 

Discovery Method of Discovery

Affected 

Component or 

System

ANO-1 2002/10 Visual - A routine visual inspection was performed on the reactor vessel head 

area. Small boric acid crystal nodules were found around the area of control rod 

drive mechanism Nozzle #56. On the downhill side of the nozzle, boric acid 

residue was located, extending 180° around the nozzle annulus area, with a 

small boric acid nodule at the most downhill point. Nondestructive examination 

(NDE) revealed indications of cracking in the nozzle, which was the cause of the 

boric acid residue. NDE of all the nozzles revealed indications of non-through

wall cracks in six other nozzles, and a likely porosity weld defect in another. The 

leaking Nozzle #56 had been repaired during the previous outage. The new 

crack indications were located just outside the previous weld repair zone. The 

previous repair technique was the embedded flaw repair. It is believed that the 

same nozzle failed because the previous repair did not isolate the 182 weld, 

which is a susceptible material to PWSCC in the pressurized-water reactor 

(PWR) environment.

VHP and VHP Weld

ONS-2 2002/10 Visual - Evidence of through-wall leakage was discovered on seven VHP 

penetrations. These penetrations were Nozzles #8, 9, 19, 24, 31, 42, and 67. 

None of these nozzles had been previously repaired. Additional nozzle head

penetrations were masked by boric acid deposits suspected of being from 

separate sources of leakage. NDE was used to characterize the cracking. No 

circumferential cracks were reported and 10 VHPs (#11, 15, 19, 21, 24, 31, 33, 

36, 38, and 42) with axial cracks were found.

VHP

Surry 1 2001/10-11 Not specified assumed Visual - Through-wall indications of the J-groove weld 

were identified on VHP Nozzles #27 and 40. On November 2, 2001, indications 

of flaws in the penetration welds were also uncovered on Penetrations #65, 47, 

69, and 18.

VHP Weld
H.13

Operating Unit

Date of 

PWSCC 

Discovery Method of Discovery

Affected 

Component or 

System

North Anna 2 2002/09 Visual - Boric acid residue was discovered during a bare metal visual inspection 

of the reactor vessel head on September 14, 2002. It appears that Nozzles #21 

and 31 had exhibited some leakage, as evidenced by boric acid residue on the 

reactor vessel head. Four additional penetrations were suspected of leaking, and 

several penetrations were masked with boric acid residue. Of the 59 J-groove 

weld penetrations that were inspected using eddy current testing (ET), 57 were 

identified with crack-like indications. The ET identified at least one indication of a 

6-mm crack in about 83 percent of the J-groove welds. During the previous 

year’s outage, no boric acid residue was discovered. The six nozzles (N2-51, 53, 

55, 57, 62, and 63) that could not be inspected with ET had their welds inspected 

using liquid penetrant tests (PTs). Three of these penetrations (N2-51, 62, and 

63) had been previously repaired with weld overlay of the J-groove. Each of the 

six penetrations that were inspected with PT had evidence of rejectable 

indications.

Eddy current examinations of the J-groove welds showed indications of axial and 

circumferential cracking with respect to the welding direction. The range in length 

was from 0.12 inch to 7.0 inches. Some longer flaws were recorded, but they 

actually comprise a series of small flaws with very short distances between. 

Eddy current testing of the inside diameter surface showed twenty of thirty-five 

penetration tubes had axial indications. These indications were believed to be 

less than 0.12 inch deep. Four nozzles (#21, 31, 51, and 63) showed evidence of 

a leak path in the shrink fit area between the vessel head and the tube. Nozzles 

#51 and 63 had been identified as leaking in the Fall of 2001. Repairs of these 

penetrations had been improperly applied because the weld overlay repair did 

not extend out far enough to cover the previous NDE indications. The six 

penetration welds inspected with PT had greater than 1/16-inch linear flaw 

indications. The licensee replaced the reactor vessel head instead of making 

multiple repairs.

VHP and VHP Weld
H.14

Operating Unit

Date of 

PWSCC 

Discovery Method of Discovery

Affected 

Component or 

System

ONS-3 2003/04 Visual - During a visual inspection of the reactor vessel head on May 2, 2003, 

evidence of possible through-wall leakage was observed on two VHP 

penetrations. The locations of these penetrations are Nozzles #4 and 7. Nozzle 

#4 contained a very thin white coating while nozzle 7 appeared to have a small 

accumulation of boron on the head adjacent to the annulus region. 

Approximately 6 to 8 additional nozzles-to-head penetrations were masked by 

deposits from a component cooling system leak above the RV head and were 

unable to be inspected. Prior refueling outage RVH inspection videotapes 

showed that the Nozzle #7 deposits were not associated with a new leak but 

rather were remnants from a prior outage leak and repair where the boron

residue had not been removed. The Nozzle #4 boron deposits were similar to 

previous RVH leaks. The apparent root cause of the nozzle leak is PWSCC.

VHP

St. Lucie 2 2003/04 Visual - During a refueling outage, a defect in Nozzle #72 was found. St. Lucie 

Unit 2 had approximately 14.0 effective degradation years at the start of the 

2003 refueling outage, therefore, this plant has a high susceptibility in 

accordance with Order EA-03-009. Visual inspection of the reactor pressure 

vessel was clean, with no evidence of leakage from the 102 RPVH penetrations 

or wastage on the RPVH surface. The UT inspection identified an axial crack in 

CEDM Nozzle #72. The defect outer diameter connected and extended into the 

nozzle and into the J-groove weld between the nozzle and reactor vessel head. 

The defect was an axial flaw, 0.28 inch deep and 0.96 inch long on the downhill 

side of the penetration. On May 2, 2003, a second defect was identified in CEDM 

Nozzle #18. The defect is also outer diameter connected and described as axial. 

It extended into the nozzle and through the J-groove weld between the nozzle 

and reactor vessel head. This second defect measured 0.26 inch deep and 2.98 

inches long. It was also located on the downhill side of the penetration. Neither 

flaw extended through the wall of the nozzle. Neither nozzle had any evidence of 

leakage from the annulus between the nozzle and the reactor pressure vessel 

head associated with the indications.

CEDM and CEDM 

weld

North Anna 1 2003/03 Visual - Unit 1 entered a scheduled refueling outage. During this outage, visual 

inspection was performed on the reactor vessel head. On March 4, 2003, an 

apparent reactor vessel head through-wall leak was noted on Nozzle #50. The 

inspection was a follow-up to a previous inspection in 2001. Boric acid residue 

was found approximately 1⁄2 inch in diameter on the lower side of the penetrationto-head transition. There were no signs of wastage on the reactor vessel head.

VHP
H.15

Operating Unit

Date of 

PWSCC 

Discovery Method of Discovery

Affected 

Component or 

System

Palo Verde 3 2003/03 Visual - Engineering personnel performing preplanned visual examinations of 

reactor coolant system piping discovered boric acid on the RCS hot leg 

instrument nozzle and a pressurizer heater sleeve. There was boric acid residue 

discovered on the backup pressurizer heater sleeve A01. Eddy current testing on 

the heater sleeve suggested that the cracking was axial in nature.

RCS hot leg 

instrument nozzle

D.C. Cook 2 2003/05 Not Specified - Craze cracking indications were found on a reactor pressure 

vessel head penetration May 17, 2003. Shallow indications were found on the 

inside diameter of Nozzle #74 during the reactor head inspection. These 

indications are closely spaced d inch below the J-groove weld. Initial calculations 

showed a crack depth of 0.117 inch. There was no through-wall leakage 

detected. These same cracking indications were found during the 2002 refueling 

cycle and have not shown any significant growth. This report was retracted 

because it was determined that the craze cracking indications in Nozzle 74 of the 

Unit 2 RPV head do not represent a seriously degraded principal safety barrier of 

the nuclear power plant.

Vessel head 

penetration

TMI-1 2003/11 Not specified visual assumed - An inspection of the pressurizer heater bundle 

identified a primary leak at the lower pressurizer heater bundle diaphragm plate. 

Boric acid residue was found between the diaphragm plate and the cover plate. 

Initially the leak was thought to be coming from a seal weld. Nondestructive 

examination (NDE) determined that the leak path was through the edge of the 

pressurizer heater bundle diaphragm plate, and that there were six indications. 

Four of these indications were surface flaws not associated with a through-wall 

crack. The heater bundle was initially repaired by depositing a seal weld over the 

areas of the pressurizer heater bundle diaphragm plate. A leak was revealed in 

later testing at normal operating pressure and temperature. Because of this leak, 

the lower pressurizer heater bundle assembly including the pressurizer heater 

bundle cover plate was replaced with a new heater bundle assembly.

Pressurizer heater 

sleeve

Waterford 3 2003/10 Not specified Visual assumed - Evidence of leakage was detected on nozzle 

RCIPT- 0106B, which is a pressure transmitter that taps off of the reactor coolant 

system hot leg #2. The leakage was located in the annulus area where the 

nozzle penetrates the head. Nozzle RC-IPT-0106B was corrected with a 

permanent partial nozzle welded repair.

RCS hot leg 

instrument nozzle
H.16

Operating Unit

Date of 

PWSCC 

Discovery Method of Discovery

Affected 

Component or 

System

Pilgrim 1 2003/10 Visual - reactor coolant leakage was detected in a reactor vessel nozzle-to-cap

weld. The crack was contained within the Alloy 182 weld metal. After the nozzle 

was initially welded to the cap, defects were detected and the weld was repaired. 

The leakage was believed to be attributable to a crack left in the weld materials 

during the previous repair procedure. The repair procedure utilized a weld 

overlay technique with Alloy 52.

Reactor vessel 

nozzle to cap weld

Crystal River 3 2003/10 Visual - During a routine visual inspection of the upper-level instrument tap 

nozzles, very small reactor coolant leaks were found on Nozzles RC-1-LT1, RC1-LT2, and RC-1-LT3. The leakage evidence for RC-1-LT1 and RC-1-LT3 

consisted of stains and boric acid residue. The evidence on RC-1-LT2 consisted 

only of stains on the pressurizer carbon steel shell. There was no evidence of 

leakage on any of the similar pressurizer nozzles. The last unidentified leak rate 

completed prior to plant shutdown was 0.15 gpm.

Pressurizer level 

nozzle

Millstone 2 2003/10 Visual - Two leaking pressurizer heater penetrations were identified. These two 

pressurizer heaters, along with the two degraded pressurizer heaters found in 

the previous outage, were planned to be removed during the current outage. 

Ultrasonic testing determined that the flaws were axial in nature.

Pressurizer heater 

sleeves

Waterford 3 2003/10 Visual - Evidence of leakage was detected on pressurizer heater sleeves C-1 

and C-3. The leakage was later determined to be boric acid.

Pressurizer heater 

sleeve

ONS-1 2003/09 Visual - During a scheduled bare metal visual inspection on September 23, 

2003, possible evidence of a through-wall leak on two VHPs (Nozzles #6 and 16) 

and one thermocouple penetration (Nozzle #7) was observed. The thermocouple 

had been repaired (plugged) in December 2000. Reactor coolant leakage prior to 

the unit shutdown varied between 0.15 and 0.24 gallon per minute.

VHP and 

thermocouple 

penetration

South Texas 

Project Unit 1

2003, Spring Visual – The licensee identified apparent boron deposits on the lower RPV head 

near two BMIs.

Lower reactor 

pressure vessel 

head

Palo Verde 3 2004/02 Visual - Engineering personnel were performing a visual examination of the RCS

piping and discovered boric acid residue on the A03 pressurizer heater sleeve. 

The visual observation was characterized as a small white buildup of boron 

residue around the heater sleeve as the sleeve enters the pressurizer bottom 

head. There was no residue running down the outside of the sleeve, and there 

were no signs of dripping, spraying, puddles of liquid or liquid running down the 

nozzle or pressurizer. The residue appeared to be dry.

Pressurize heater 

sleeve
H.17

Operating Unit

Date of 

PWSCC 

Discovery Method of Discovery

Affected 

Component or 

System

Susquehanna 1 2004/03 Not Specified - During a routine inspection an indication was discovered on the 

N1B penetration. This reactor vessel penetration is associated with the reactor 

recirculation B loop. The crack had been detected during previous outages, 

however, it was not designated as a crack. The crack was circumferential and 

was approximately 50 percent through-wall. The length of the crack was roughly 

2.2 inches (approximately 7 percent of the diameter).

Recirculation weld

Catawba 2 2004/09 Visual - The steam generator bowl drain for the 2A, 2C, and 2D steam

generators were visually inspected. Leakage was found on the 2C and 2D SG 

bowls. The leakage occurred sometime after the previous refueling outage, 

because the bowls were clean at that time. Dye penetrant exams were 

conducted on 2D which identified indications. The root cause of the leakage was 

determined to be PWSCC. The cracks initiated in the gap between the pipe 

coupling and the Alloy 600 weld metal buildup. This area is in contact with 

primary water at a temperature of approximately 617 °F.

SG bowl drain

Oconee 1 and 3 Visual - identified small amounts of boron accumulation at the base of CRDM 

nozzle 21 and several T/C nozzles.

CRDM Nozzle
H.18