2003 Fiscal Year Final Research Report Summary
Understanding and Mitigatin of Stress Corrosion Cracking of Reactor Vassel Materials in Oxidizing Supercritical Water Environments
| Project/Area Number |
13450290
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Material processing/treatments
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| Research Institution | Tohoku University |
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Principal Investigator |
WATANABE Yutaka TOHOKU UNIVERSITY, Graduate School of Engineering, Associate Professor, 大学院・工学研究科, 助教授 (10260415)
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| Co-Investigator(Kenkyū-buntansha) |
IKUSHIMA Yutaka National Institute of Advanced Industrial Science and Technology, Supercritical Fluid Research Center, Team Leader, 超臨界流体研究センター, 有機化学チーム長(研究職)
YUGAMI Hiroo TOHOKU UNIVERSITY, Graduate School of Engineering, Professor, 大学院・工学研究科, 教授 (60192803)
AJIRI Tadafumi TOHOKU UNIVERSITY, Institute of Multidisciplinary Research for Advanced Materials, Professor, 多元物質科学研究所, 教授 (60182995)
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| Project Period (FY) |
2001 – 2003
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| Keywords | supercritical water / corrosion / stress corrosion cracking / dielectric constant / stainless steel / Ni base alloy / oxide scale / oxidation |
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| Research Abstract |
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
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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
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