E-Journal of Advanced Maintenance Vol.1 (2009) 63-67
Japan Society of Maintenology

Progress of Performance Demonstration in Japan
Toshihiko SASAHARA*, Tamotsu JIKIMOTO and Koichiro HIDE
Central Research Institute of Electric Power Industry, 2-6-1 Nagasaka, Yokosuka-shi, Kanagawa-ken,
240-0196, Japan(Received; November 14th, 2008)

Abstract. On November 1, 2005, Central Research Institute of Electric Power Industry (CRIEPI) established
PD Center to promote the Performance Demonstration (PD) qualification examination. The 1st Japanese PD
qualification examination started in March, 2006, and was operated by PD Center of CRIEPI. As of August 31,
2008, 21 examination courses have finished and 24 out of 37 candidates passed the examination. The total
number of test including retest was 60. Increase in the examination pass rate of retest personnel indicates
improvements in the sizing technique by training. A common reason of failure is so called “overcall” that cannot
identify weld to base-metal interface echoes from crack tip echoes. This result suggests an importance of morepractical training using realistic samples.

KEYWORDS: Performance Demonstration, ultrasonic examination, flaw depth sizing, IGSCC

1.

Introduction

At the present time, 38 years have passed since the first commercial light water reactor started
operation in Japan. As more than 20 Japanese nuclear power plants have achieved 20 years ofoperation, the importance of flaw evaluation has been recognized from the view point of plant life
management. In 2000, Japan Society of Mechanical Engineers (JSME) published the first edition of afitness-for-service (FFS) code. The Nuclear and Industrial Safety Agency (NISA) has endorsed theFFS code and it has been in effect since October 2003 [1].
The Japanese FFS code renewed the importance of flaw depth sizing. In 2002, contemporary
with the effort of FFS code application, stress corrosion cracking (SCC) was found in BWR primaryloop recirculation (PLR) piping made of type 316L stainless steel. Through wall depths of these SCC
were measured by the conventional ultrasonic examination technique. And following destructive
examination revealed that some SCC penetrating into weld metal was undervalued in the size. Most
probable reason of this undervaluation was estimated to be the influence of shear wave attenuating in
the dendritic structure of the austenitic weld metal.
To cope with this undervaluation issue, improved ultrasonic depth sizing methods weredeveloped and the effectiveness was successfully verified through a confirmation test. However,NISA directed that a 4.4mm safety redundancy should be added to the measured depth in the flaw
analysis until the UT personnel are qualified by the depth sizing Performance Demonstration (PD).
To establish Japanese PD system, engineers from regulator, academics, utilities, inspectionsocieties, and vendors formed the PD system preparatory committee and in June 2005, the firstJapanese PD standard NDIS 0603 “Qualification and certification of personnel for performance
demonstration of ultrasonic testing systems” was issued [2].
NDIS 0603 is basically similar to Appendix VIII to Section XI of the ASME Code, in its
structure with some modifications reflecting Japanese findings on IGSCC in 316L stainless steel weld.

*

Corresponding author, E-mail: mailto:sasahara@criepi.denken.or.jp

ISSN – 1883 – 9894/09 © 2009 – JSM and the authors. All rights reserved.

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T. Sasahara et al./Progress of Performance Demonstration in Japan

2.

PD organization in JapanFollowing the issue of NDIS 0603, Japanese nuclear industry had to start the effort to build up
qualification organizations and develop a qualification scheme. Figure 1 shows the organizations thatparticipated in the PD qualification examination system of crack depth sizing for austenitic stainlesssteel pipe welds in the nuclear power plant.
The PD advisory committee is posted to the top of the PD qualification system. The PD advisorycommittee members consist of academic experts and staffs of the government or public inspection
organizations. The PD advisory committee reviews activities of PD related organizations and makes
recommendations to them. Another important role of the PD advisory committee is international
coordination of the PD system.
The PD certification body certifies PD related organizations. JSNDI takes the role and operates
the PD certification steering committee to execute this process.
The PD qualification body organizes the qualification examination, i.e. prepares test specimens,
test facility and quality control document. The qualification body also manages the PD qualification
examination, maintains the test results and controls the documents. And the PD examination center
operates the PD qualification examination under the direction of the PD qualification body. PD Centerof CRIEPI takes the role of these PD qualification body and PD examination center.
The PD training center has two functions in the PD system. One is to train the personnel whofailed at the first examination and hope to take re-examination within 30 days. The other is annual
training for license renewal. The PD certification body certifies the PD training center after reviewing
the compliance with the training program which is provided by the PD qualification body. JapanPower Engineering and Inspection Corporation (JAPEIC) and Electron Science Institute (ESI) havebeen qualified as the PD training Center.

PD Advisory Committee（Evaluation of Adequacy, Submission of Advice)

CRIEPIPD Certification Body

(Approval of QB/EC)（JSNDI）
PD Certification Steering Committee

PD Center(Certification）

Applicants

Materials Science
Research Laboratory(Examination)

Qualification Body

(Training)

PD Training Center(Requirement of Training)

Examination Center(Approval of Training Program)

Fig. 1. Organization of PD qualification examination

3.

PD qualification examination

Though the Japanese PD standard NDIS 0603 is basically similar to ASME Code Section XI,Appendix VIII, some adaptations are brought in to reflect our findings on IGSCC in 316L stainlesssteel weld. The followings are outline of the Japanese PD qualification examination.
The qualification test specimens are butt welded austenitic pipes with artificially introduced
IGSCC. Weld crown conditions are ground flush. 10 IGSCC in the following three different sizes ofpipes must be tested.

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Nominal diameter 600 mm with 35mm wall thickness
Nominal diameter 350 mm with 25mm wall thickness
Nominal diameter 150 mm with 10mm wall thickness
Cracks in the depth sizing sample set shall be distributed according to the specification in
Table 1. The remaining cracks shall be in any of the following categories. And at least one IGSCC
should be deeper than 15mm and one IGSCC should penetrate into the weld material.
Table 1 Crack depth distribution

Crack depth h (% wall thickness)

Minimum percentage

0 < h ≤ 30 %

20 %

30 < h ≤ 60 %

20 %

60 < h < 100 %20 %Allowable examination time is 5days per 10 samples and 8 hours per one specimen. The test
specimens are given one at a time and no one carry over of the specimen is allowed to the next day.
The answer sheet and, if automated data recording system is used, a digital record are saved at
the PD Center and all the other examination data will be destroyed to secure the qualification system.
The acceptance criteria are;
Root mean square error (RMSE): less than 3.2mm
Critical miscall: less than -4.4mm.
When a candidate fails in the PD examination, he must wait for 30days before taking retest
unless he could get through the training at the PD training center.
The term of validity of the PD qualification is one year and can be extend to 5 years in maximum
if the qualified personnel took the PD training at the PD training center.
4.

Test result

The 1st PD qualification examination started in March, 2006, and was operated by the PD Centerof CRIEPI. As of August 31, 2008, 21 examination courses have finished and 24 out of 37 candidates
passed the examination. The total number of test including retest is 60.
Figure 2 shows the relationship between RMSE and the average measurement errors of all
candidates. The average measurement errors of candidates who passed the examination are around
1mm. This means that the personnel who were qualified at the PD examination measured the SCC
depth accurately.
Several candidates whose average measurement errors are small, failed because of criticalmiscall. Answer sheets showed that they missed to determine the deepest location of cracks. Figure 3
shows the relationship between RMSE and average scan time per sample of all candidates. These data
indicates that some candidates made critical miscall because they measured the crack size in a hurry.
Figure 3 also shows almost all candidates spent 1.5 to 3.5 hours per crack suggesting that thecrack depth sizing requests the candidate personnel concentration, endurance and skill.

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Fig. 2. RMSE vs. averaged error of candidates

Fig. 3. RMSE vs. averaged examination time per sample of candidates

Figure 4 shows the pass/fail trend of candidates. The pass ratios of first time takers were rapidly
reduced after the first examination period. On the other hand, the pass ratios of repeat takers wereimproved after the first examination period. It seems, almost all the field experienced examination
personnel took the examination at the first examination period and passed. The other personnel, whoseexperiences were insufficient, required practical training program to improve their skill.

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Fig. 4. Number of candidates and pass/fail trend

Many of the candidates used the longitudinal wave tip diffraction technique with theconventional A-scope display equipment or the phased array system. For the IGSCC depth sizing, theplane and sectional view created by the phased array system seems to have an advantage over theconventional A-scope display. The examination pass rate of the candidates who used the conventional
A-scope display was 38%, while the pass rate of the candidates with the phased array system was83%.
The common reason of the failure was overcall that cannot identify weld to base-metal interface
echoes from crack tip echoes. This result suggests an importance of more practical training using
realistic samples.
5.

Conclusion

The Japanese Performance Demonstration for crack depth sizing of austenitic stainless steel pipe
welds in the nuclear power plant started successfully.
As of August 31, 2008, 24 personnel were qualified for the crack depth sizing of austenitic
stainless steel pipe welds.
In 2006, SCC was detected in PLR piping of Kashiwazaki-Kariwa Unit 3 of Tokyo ElectricPower Company. The SCC was sized by PD qualified personnel and the crack growth behavior wasassessed based on the FFS code. In July 2006, the Japanese regulatory agency reviewed the crack
growth assessment report and accepted it as the first application of FFS code for plant operation
renewal.

References[1] Kashima K, Nomura T, Koyama K, “Current Status of Japanese Code on Fitness-for-Service for
Nuclear Power Plants” PVP-Vol. 480, Pressure Vessel and Piping Codes and Standards, San
Diego, USA, 2004.
[2] Sasahara T, Yamashita K and Nomura T “UT Performance Demonstration in Japan” Fifth Int.
Conf on NDE in Relation to Structural Integrity for Nuclear and Pressurized Components, San
Diego, USA, 2006, pp. 163-167.

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