Abstract

The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code, Section XI utilizes reference fatigue crack growth rate (FCGR) curves for flaw evaluations. Code Case N-809 describes a reference curve currently used in flaw evaluations of austenitic stainless steels exposed to a pressurized water reactor (PWR) environment in accordance with ASME, Section XI. Recently, an extensive database of Type 304, Type 304L, and Type 304/304L dual-certified stainless steels and the corresponding weld metal in PWR environments was assessed and an updated FCGR model generated. This database includes previously unreported FCGR data in 100°C PWR environments at an R-ratio of 0.7 and a rise time of either 51 sec or 510 sec. The results of this lower temperature testing are reported here and do not support the non-Arrhenius temperature relation in Code Case N-809, which predicts an increase in FCGRs with decreasing temperature below a temperature of 150°C. The updated model more accurately describes the FCGR behavior in the near-threshold, low ΔK regime. Additionally, the updated model eliminates the non-Arrhenius temperature dependence of the Code Case N-809 reference curves for temperatures below 150°C and replaces it with a single Arrhenius temperature dependence between 100°C and 338°C. Similar to the Code Case N-809 reference curve, this model does not describe the severely retarded FCGR behavior that has been observed to occur for austenitic stainless steel under certain conditions, nor does it attempt to predict the conditions under which severe retardation is likely to occur.

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