In-situ electrochemical impedance measurement of oxide film formed on type 304 stainless steel in high-temperature water

Environmentally assisted cracking (EAC), such as stress corrosion cracking (SCC), corrosion fatigue, hydrogen embrittlement (HE), etc., continues to be a significant issue to the power generation industry. In particular, intergranular stress corrosion cracking (IGSCC) of sensitized stainless steel (SS) components in boiling after reactors (BWR) under normal water chemistry (NWC) conditions containing high levels of O2 and hydrogen peroxide (H2O2) is known to be a major concern. Electrical resistivity of the oxide film formed on Type 304 (UNS S30400) stainless steel (SS) in 299 C water containing various oxygen (O2) and hydrogen peroxide (H2O2) concentrations was evaluated by in-situ electrochemical impedance and anodic polarization measurements. Higher electrochemical corrosion potentials (ECP) were measured in the presence of H2O2, as compared to the ECP value measured at the same level of O2. It also was clear that the polarization resistance decreased with increases in ECP and H2O2 was present in the water at a given ECP. This impedance data showed the important role of the water chemistry on the degree of oxide resistance. In addition, the polarization resistance result indicated that the oxide film formed on Type 304 SS in 299 C water containing H2O2 could be less resistance and consequently more susceptible to environmentally assisted cracking