Fatigue life prediction of 316 stainless steel in simulated PWR primary water by time domain analysis based on short fatigue crack growth behavior AbstractThe fatigue life of austenitic stainless steel is significantly reduced in the environment of a pressurized water reactor (PWR). One of the methods for evaluating the environmental effect involves the use of the environmental correction factor (Fen) determined from the fatigue lives of the material in air and the PWR environment. It has been reported that the environmental correction factor increases with decreasing strain rate, eventually saturating at a low strain rate. However, the exact behavior of the parameter remains unclear considering evidences of a relationship between environmentally assisted fatigue and stress corrosion cracking. It is therefore of importance to examine the possibility of continuity between environmentally assisted fatigue and stress corrosion cracking at very low strain rates. In the present study, time domain analyses of short fatigue cracks initiated in 316 stainless steel in air and simulated PWR water were used to ascertain the existence of such continuity by investigating the relationship between the environmentally assisted fatigue and stress corrosion cracking. The acquired environmentally assisted fatigue life data were uniquely interpreted, and superposition of the plots of the stress corrosion cracking data obtained by slow-strain-rate tensile tests over the time domain analyses and environmentally assisted fatigue data suggested continuity among the parameters. This was clearly substantiated by further time domain analyses.Key words : Short fatigue crack growth behavior, Time domain analysis, Crack initiation, Simulated PWR primary water, Environmentally assisted fatigue, Stress corrosion cracking IntroductionEnvironmentally assisted fatigue (EAF) of structural materials exposed to high temperature, including in the primary water of a pressurized water reactor (PWR), has been studied over the past 30 years. The subject has attracted increased attention in more recent years owing to ongoing efforts toward the long-term operation (LTO) of nuclear power plants for up to 60 years. It is therefore necessary to investigate the safety and structural integrity issues of the long-term operation of a nuclear power plant field, especially regarding the primary coolant system components.Austenitic stainless steel, which is one of the most important structural materials, is utilized in primary pressure boundary components, where it is subjected to low-cycle fatigue (LCF) by repeated start-ups and shut-downs. Since the 1990s, there have been reports about the significance of a PWR environment to reduce the fatigue life of austenitic stainless steel.Both crack initiation and the propagation of a short crack have been investigated through crack initiation tests, with particular interest in the growth behavior of short fatigue cracks. Some fatigue life data are available in the Japan Nuclear Energy Safety Organization (JNES) report and ...
Environmental correction factor (Fen) is one of the parameters to evaluate the effect of a pressurized high temperature water environment. It has been reported that Fen for stainless steel saturates at a very low strain rate. However, the relationship between environmentally assisted fatigue (EAF) and stress corrosion cracking (SCC) is still unclear. The aim of this study is to investigate the short crack growth behavior and possible continuity of EAF and SCC at very low strain rates. Short crack initiation and propagation have similar behaviors, which retard the crack growth between 100–200 μm in depth. We find that the striation spacing correlates well with the maximum crack growth rate (CGR) data. Based on the correlation, it is clarified that the local CGR on an intergranular facet was faster than that on a transgranular facet. Furthermore, the overall maximum and average CGR from the EAF data is well interpreted and compared with the SCC data.
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