The Influence of Various Treating Parameters on the Corrosion of ZrO2-Treated Type 304 Stainless Steels in High-Temperature Water

Abstract

Corrosion mitigation techniques specifically developed for the vessel internals of boiling water reactors (BWRs) such as hydrogen water chemistry (HWC), catalytic coatings, and inhibitive coatings have been studied and/or adopted worldwide in the past decade. The common goal of these techniques is to mitigate intergranular stress corrosion cracking in the vessel internal components of BWRs. For enhancing the effectiveness of HWC through a more effective reduction in electrochemical corrosion potential accompanied by a lower hydrogen consumption rate or even without any added hydrogen, the technique of inhibitive treatment on structural component surfaces was brought into consideration. In the current study, surfaces of preoxidized square-disk specimens made of Type 304 stainless steel (SS) were treated with zirconium oxide (ZrO2) (particle sizes of 0.7 μm and 0.1 μm) via hydrothermal deposition at either 90 or 150°C for 7 or 14 d, while some preoxidized specimens remained untreated. The concentration of the treating solution was maintained at either 10 parts per million (ppm) or 122 ppm (1mM) during the ZrO2 deposition processes. Electrochemical polarization analyses at 288°C were conducted to characterize the electrochemical properties of the treated and untreated SS specimens in pure water with either dissolved oxygen or dissolved hydrogen. It was found that a smaller particle size, a longer treating time, a lower treating temperature, as well as a higher treating solution concentration seemed to improve the corrosion resistance of the treated specimens in oxygenated environments and to moderately deter the hydrogen oxidation rate on the specimens.