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概要

It becomes to be recognized that material hardening can enhances the SCC growth rate considerably. In SCC growth evaluation in PLR weld joints of BWR, it is confirmed that the material hardening due to thermal shrinkage during welding affects SCC growth rate. In order to ev aluate the degree of hardening of PLR weld joints, Vickers hardness distributions have been measured on some actual pipe joints. In latest researches, however, another parameters such as yield strength and plastic strain are considered to be suitable to evaluate the material hardening effect on SCC growth rate. In this study, detailed measurements of three hardening parameters are conducted on actual PLR pipe joints with various sizes and weld types. From the obtained database, it is clearly shown that (1) yield strength shows good correlation wi th Vickers hardness but plastic strain measured by EBSD doesn't (2) the degree of hardening depends greatly upon the pipe diameter, which suggests the unreasonableness of present fitness-for-service evaluation that assumes same degree of hardening irrespective to pipe sizes.

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