Understanding and Mitigatin of Stress Corrosion Cracking of Reactor Vassel Materials in Oxidizing Supercritical Water Environments

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Corrosion morphology and rates of various corrosion resistant alloys have been examined in simulated environments of supercritical water oxidation processes. Importance of physical property of water, in particular dielectric constant, to corrosion of metals in supercritical water have been demonstrated. It has been demonstrated that corrosion rate of metals in supercritical water is strongly dependent on applied pressure and can he uniquely arranged by dielectric constant of water including both supercritical state and sub-critical liquid phase.Scale oxides formed in supercritical water environments were in good agreement with thermodynamically predicted oxide. Corrosion rate was able to be correlated with types of the scale oxides.Slow strain rate tests have been performed in neutral to acidic supercritical water up to 550℃/6OMPa to evaluate stress corrosion cracking (SCC) behavior of alloys in supercritical water environments. Effects of applied pressure (water density or dielectric … More constant effect) and sulfuric acid have been demonstrated. For sensitized stainless steel -pure water system, effects of phase state of water and applied pressure, more essentially, physical property of water, were clearly observed. SCC did not occur in the oxygenated "gas-like" supercritical water at 400℃/25MPa. Cracking occurred at 400℃/30MPa and the cracking severity was more pronounced as applied pressure was increased up to 60MPa at the same temperature. The results gave a strong evidence of the "dissolution mechanism". In contrast, for non-sensitized stainless steel -sulfuric acid water system, severe cracking with IG occurred even in a "gas-like" supercritical water and dielectric constant did not affect cracking severity. The results would indicate "dissolution mechanism" is not very likely and might suggest "oxidation cracking".Importance of aging degradation in both mechanical properties and corrosion resistance in supercritical water environments has been pointed out.A new corrosion-inhibition method for supercritical water environments has been developed, where dependence of solubility of Cr oxides on temperature and dielectric constant of water is utilized. Less