Effects of hydrogen peroxide on intergranular stress corrosion cracking ofstainless steel in nigh temperature water, (III) - Crack growth rates in corrosive environment determined by hydrogen peroxide

The stress corrosion cracking (SCC) of structural materials used in boiling water reactors has been studied at relatively low hydrogen peroxide (H2O2) concentrations, around 10 ppb, which was assumed to be representative of t he corrosion environment formed in hydrogen water chemistry (HWC). The 1/4T compact tension specimen was used for measurement of crack growth rates (C GRs) of sensitized type 304 stainless steel in high temperature and high pu rity water. Crack length was monitored by a reversing direct current potent ial drop method. Since H2O2 is easily decomposed thermally, a polytetrafluo roethylene-lined autoclave was used to minimize its decomposition on the au toclave surface. The CGR in the H2O2 environment differed from that in the O-2 environment even though the electrochemical corrosion potential (ECP) f or both conditions was the same. The data implied that the ECP could not be used as a common environmental deterministic parameter for SCC behavior at higher potentials for different oxidant conditions. The corrosion current density was found to play an important role as an environmental index for S CC, which was given as just the current density at the ECP at a specific ox idant concentration. The CGRs were found to be written as CGR = (3.8+/-0.6) x10(-3)i(cor)+(1.5+/-1.6)x10(-8)mm/s using the calculated corrosion current density i(cor) below 10(-4) A.cm(-2).