Effect of Chloride and Sulfate Transients on Crack Growth Rates of Stainless Steels and Alloy 182 Welds

Abstract

This paper summarizes the results of a multi-year project to evaluate the effect of chloride and sulfate on the stress corrosion cracking (SCC) behavior of cold-worked (CW) austenitic stainless steel and nickel-base Alloy 182 weld in boiling water reactor (BWR) environments. Chloride and sulfate can be introduced into the reactor coolant system during periods of significant condenser in- leakage or other incidents. This paper provides technical guidance and context to the effects of impurities as a function of the material (especially the grain boundary Cr content) and corrosion potential. Effects of up to 100 ppb chloride and sulfate were studied in normal water chemistry (NWC), and up to 500 ppb in hydrogen water chemistry (HWC). The time-transient response was generally a short delay period before the crack growth rate starts to change after chloride or sulfate or ECP is changed, associated with mass transport kinetics in the crack. However, longer times can be observed, especially if the growth rate was low before the change. The time-transient response as the corrosion potential drops is consistently more rapid.