1979 Volume 16 Issue 2 Pages 137-146
Circumferential cracks detected in the JPDR (BWR) near welded joints connecting the nozzle safe-end to pipe (austenitic stainless steel) were studied in reference to the stresses applied in service, the conditions of welding, environment (O2 and Cl- concentra-tion, water flow, temperature etc.), metallurgical structure and operating records, to determine the cause of cracking. Fatigue tests were also undertaken with simulated welded pipe of size to examine possible contribution of fatigue to the cracking.
The analysis indicated stress corrosion to be the principal cause of cracking, and that it had initiated in the heat-affected zone which had been sensitized by the excess heat input of welding. The factors contributing to the stress corrosion were the presence of oxygen in the fluid, which had at times attained a level exceeding 0.2 ppm, and which combined with stress, at times exceeding the yield strength. This had caused the cracks once initiated, to propagate along the grain boundary.
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