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Effect of cyclic loading on the relaxation of residual stress in the butt-weld joints of nuclear reactor piping

原子力配管の突合せ溶接部における残留応力緩和に及ぼす繰り返し荷重の影響

勝山 仁哉; 山口 義仁; Li, Y.*; 鬼沢 邦雄

Katsuyama, Jinya; Yamaguchi, Yoshihito; Li, Y.*; Onizawa, Kunio

原子炉配管における応力腐食割れ(SCC)の駆動力として、溶接残留応力は最も重要な因子として挙げられる。配管の健全性を評価するためには、地震に伴う過大な繰り返し荷重が残留応力に及ぼす影響を評価する必要がある。本研究では、過大な繰り返し荷重の影響を明らかにするため、SUS316L低炭素ステンレス鋼製250A配管突合せ溶接部を対象に、有限要素解析を行った。溶接シミュレーションの精度を実測値と比較を通じて確かめた後、地震荷重を模擬するため、最大荷重を変化させたさまざまな荷重パターンをモデルに付与し、残留応力分布の変化について評価を行った。その結果、荷重が大きいほど溶接部近傍の溶接残留応力の緩和が大きくなることを見いだした。内表面の引張応力も低減することから、過大な繰り返し荷重はSCCの成長の抑制にも効果があると考えられる。

Weld residual stress is one of the most important factors in stress corrosion cracking (SCC) of nuclear reactor piping. To assess the integrity of piping, it is necessary to understand the effects of excessive cyclic loading, caused by earthquake, on residual stress. In this study, finite element analyses were performed using a model of a 250A pipe butt weld of Type 316L stainless steel. The accuracy of the welding simulation was verified by comparing the calculated results with the experimental measurements. After conducting the welding simulation and residual stress analysis, several loading patterns for the axial cyclic loadings were applied to the model by varying the amount of maximum load, in order to study the effect of excessive cyclic loading. The analysis indicated that higher loading caused a greater relaxation of the weld residual stress near the piping welds. It was thus concluded that excessive cyclic loading on piping butt welds affects the suppression of SCC growth.

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パーセンタイル:47.5

分野:Nuclear Science & Technology

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