Effects of Hydrogen Peroxide on Intergranular Stress Corrosion Cracking of Stainless Steel in High Temperature Water, (III)

Abstract

The stress corrosion cracking (SCC) of structural materials used in boiling water reactors has been studied at relatively low hydrogen peroxide (H₂O₂) concentrations, around lOppb, which was assumed to be representative of the corrosion environment formed in hydrogen water chemistry (HWC). The 1/4T compact tension specimen was used for measurement of crack growth rates (CGRs) of sensitized type 304 stainless steel in high temperature and high purity water. Crack length was monitored by a reversing direct current potential drop method. Since H2O2 is easily decomposed thermally, a polytetrafluoroethylene-lined autoclave was used to minimize its decomposition on the autoclave surface. The CGR in the H₂O₂ environment differed from that in the O₂ environment even though the electrochemical corrosion potential (ECP) for 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 SCC, which was given as just the current density at the ECP at a specific oxidant concentration. The CGRs were found to be written as CGR = (3.8±0.6)xl0^-3 _icor +(l-5±1.6) x 10^-8mm/s using the calculated corrosion current density i_corbelow 10^-4 A-cm^-2.

KEYWORDS:

• intergranular stress corrosion cracking
• hydrogen water chemistry
• hydrogen peroxide
• crack growth rate
• crack propagation
• stainless steels
• electrochemical corrosion potential
• corrosion current