小口径突合せ溶接配管に対する残留応力改善方法の開発（フリージング工法の適用による残留応力の改善）

概要

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To prevent stress corrosion cracking (SCC) initiation at the inner surface of the butt-welding region of a small-diameter pipe, a residual stress improvement method has been developed. In this method, the local expansion process is applied to the butt-welding region with ice plugs. During the local expansion process, tensile yielding is generated in the butt-welding region. The tensile yielding generated at the inner surface is larger than that of the outer one. After this process is applied, compressive residual stress can be introduced at the inner surface due to larger tensile yielding. In this study, residual stresses at the inner surface of the butt-welding region were measured, and SCC initiation tests in the accelerated environment (in boiling 42% Magnesium Chloride) were performed. The measured residual stresses and the results of SCC initiation tests proved this method effectively reduces residual stresses and prevents SCC initiation.