Corrosion of ZrO2 treated type 304 stainless steels in high temperature pure water with various amounts of hydrogen peroxide

By Yeh, Tsung-Kuang; Wu, Po-I. & Tsai, Chuen-Horng
Published in Progress in Nuclear Energy NULL 2012

Abstract

As boiling water reactors (BWRs) age, intergranular stress corrosion cracking (IGSCC) of the structural materials in the reactor piping systems and vessel internals has become a major degradation problem. Several approaches to mitigating IGSCC in the structural components have been developed and investigated. Among them, the technique of inhibitive protective coatings is deemed the most promising one since it is expected to work even in the absence of the well-known hydrogen water chemistry technology. Following our earlier work on exploring the electrochemical characteristics of important oxidizing species on zirconium oxide (ZrO2) treated Type 304 stainless steels (SSs), we targeted on the characteristics of hydrogen peroxide, which is another strongly oxidizing species in the reactor coolant other than oxygen, in this study. Tests were conducted to determine electrochemical parameters such as electrochemical corrosion potential (ECP), corrosion current density, exchange current density and Tafel constant of the reduction reaction of hydrogen peroxide on 304 SS specimens before and after the ZrO2 treatment. The surface morphologies of the treated and untreated specimens were examined by scanning electron microscopy, energy dispersive X-ray spectroscopy, and laser Raman spectra. Furthermore, the corrosion mitigation efficiency of ZrO2 treatment was evaluated by electrochemical polarization tests in simulated BWR environments. Test results showed that there were no significant differences in ECP between the untreated and ZrO2 treated specimens in the test environments of various hydrogen peroxide concentrations. However, it was found via polarization analysis that the exchange current density of the reduction reaction on and the corrosion current density of the treated specimens were markedly lower than those on and of the untreated ones in the same environments. The ZrO2 treatment was able to deter the reduction rate of hydrogen peroxide on the Type 304 SS surface.

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