Fatigue behaviour of 316 NG stainless steel in EPR primary circuit conditions

Strain controlled constant amplitude and variable amplitude fatigue tests were performed for 316 NG stainless steel in PWR water 320 C. The environment reduced fatigue life as predicted. Variable amplitude test results indicate a further reduction in life by a factor of 5, which is greater than expected. Variable amplitude straining in EPR environment resulted to specimen failure before the fatigue usage factor according to the ASME III design curve reached unity. In other words, the ASME III design curve was conservative for constant amplitude, but non-conservative for variable amplitude straining in environment. Critical tests to confirm or replace this tentative observation are recommended