Effect of partial welding on residual stress and structural integrity in piping welds

部分溶接が配管溶接部の残留応力と構造健全性に及ぼす影響

勝山 仁哉  ; 眞崎 浩一; 鬼沢 邦雄 

Katsuyama, Jinya; Masaki, Koichi; Onizawa, Kunio

溶接後に検査等で溶接欠陥が見つかった場合、その欠陥を削除した後、部分的に補修溶接が必要となる。この部分補修溶接は残留応力に局所的に高い引張応力を発生させる可能性がある。本研究では、まず熱弾塑性解析により、突合せ溶接後に補修溶接を施した際の残留応力を求め、実験との比較により解析手法の妥当性を確かめた。補修溶接条件を変えた解析の結果、欠陥除去深さが深いほど補修溶接部の引張残留応力は増加すること等がわかった。その結果に基づき、確率論的破壊力学コードPASCAL-SPを用いて、応力腐食割れに伴う配管溶接部の構造健全性について評価を行った。部分補修溶接は配管溶接部の破断確率を提言する可能性のあることを明らかにした。

When weld defects are found by inspection after welding, partial repair welding need to be performed after removing the defects. The partial repair welding has a possibility to produce locally high tensile stress. In this study, we have performed thermal-elastic-plastic analyses to evaluate the weld residual stress produced by repair welding after piping butt-welding. The analysis results were validated through the comparison with experimental measurements. From the analysis results with varying the repair welding conditions, it was found that deeper cutting depth causes higher tensile residual stress at the partial welded region. We also performed structural integrity assessments related to SCC using the weld residual stress distribution calculated and probabilistic fracture mechanics analysis code PASCAL-SP. It was clarified that partial repair welding might have an effect to decrease the break probability of piping welds.