United States Nuclear Regulatory Commission - Protecting People and the Environment

Results of the Program for the Inspection of Nickel Alloy Components (NUREG/CR-7019, Revision 1)

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Publication Information

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
U.S. Nuclear Regulatory Commission
Washington DC 20555-0001

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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.

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