Influence of Surface Finish in Fatigue Design of Nuclear Power Plant Components

The fatigue design of nuclear components is based on an S-N curve established in air at 20 °C. To this curve, different penalty factors, representative of various effects (scale effect, material variability, surface finish, environmental effect, etc), are then applied. This method considers that these effects are independent from each other.This paper is focused on the interactions between surface finish effects and environmental effects in the Low Cycle Fatigue (LCF) domain of an austenitic stainless steel type 304L. The aim of this work is to determine whether the effects of these two parameters are really independent or coupled. To better understand the environmental influence, high vacuum is used as reference. Tests were realized with a triangular waveform signal at a total strain amplitude of ± 0.6% in different environments: vacuum, air and simulated Pressurized Water Reactor (PWR) water, at 300 °C. Two surface finishes were considered: ground and polished.Experimental results obtained on ground samples are here compared with results obtained on polished samples in a previous study. It appears that, while the cyclic stress response of the material is not affected by the surface finish, a ground surface finish decreases the fatigue life. Moreover, this surface finish effect seems to be less pronounced when the environmental effect is important, which indicates the presence of a coupling between surface finish influence and environmental effects.