Discussion on Fatigue Design Curves for Stainless Steels

The new stainless steel air curve endorsed in NRC RG 1.207 for new US designs only was recently adopted into ASME III without restrictions on applicability. We assume that the new (2009b) ASME curve may be applicable to some grades of stainless steel, but not to all. This paper reports contradictory data for stabilized austenitic stainless steels extending up to 10 million cycles in room temperature at air environment. Niobium and titanium stabilized stainless steel specimens were sampled from 100% relevant material batches fabricated for NPP primary piping. Additional research and more recent data for titanium stabilized steel suggest that our PVP 2009-78138 conclusions are not limited to one material grade. Therefore, the revised ASME design curve cannot be considered universally applicable.