Effect of Static Load Hold Periods on the Corrosion Fatigue Behavior of Austenitic Stainless Steels in Simulated BWR Environments

摘要

The effect of static load hold times of 6 to 744 h on corrosion fatigue life of low- and high-carbon and stabilized austenitic stainless steels was investigated with both sharply notched and pre-cracked fracture mechanics specimens in simulated boiling water reactor (BWR) hydrogen (HWC) and normal water chemistry (NWC) at 288 °C. With regard to continuous cyclic saw tooth loading with a load ratio R close to zero in HWC environment, an increase of the genuine corrosion fatigue initiation life was observed with increasing static load hold periods at maximum or mean load of the applied load range, which seemed to saturate for long hold periods above 12 to 24 h. On the other hand, static hold periods at minimum load, where potential micro-cracks are closed, had no effect on genuine fatigue initiation life. Furthermore, the static load hold times had very little effect on the subsequent stationary short corrosion fatigue crack growth rates. Static hold times of up to 744 h had no effect on the corrosion fatigue crack growth rates in pre-cracked solution annealed stainless steel specimens in NWC and HWC environment. No significant effect of static load hold times on the technical corrosion fatigue initiation life are thus expected based on these preliminary results and the current US NRC regulatory guide 1.207 seems to be adequate from this point of view. A credit for a mitigating effect of long static load hold periods in the field cannot be derived from this work.