Grade and Temperature Dependent Reference Curves for Realistic F_en Quantification of Austenitic Stainless Steels

Environmental effects of LWR coolant need to be factored in when defining cumulative fatigue usage of primary circuit components. The basis is a set of codified design rules and fatigue design curves, based on experimental data. To accurately quantify environmental effects, the reference curve in air to which fatigue life in water is compared shall be as reliable as possible. Literature studies and accumulated data at VTT reveal that the use of common reference curves for a wide range of austenitic stainless steel alloys and temperatures is unreliable. Some design codes already include measures to consider this but ASME III is not yet among them. The ASME III design curve is adopted from NUREG/CR-6909 and contains no consideration for dependence of temperature or stainless steel grade. Two different stainless steel grades, AISI 304L and 347, have previously been used in environmentally-assisted fatigue experiments at VTT. In this paper, reference curves for the AISI 304L heat are presented at room temperature and 325 °C to complement the curves already available for AISI 347. Demonstration of realistic environmental effect quantification is done using these reference curves as an alternative to the NUREG methodology.