原子炉配管の確率論的構造健全性評価,2; 残留応力解析による溶接条件のばらつきの影響評価

Probabilistic structural integrity assessment of reactor coolant pressure boundary piping, 2; Residual stress analyses of the effect of scatter of welding conditions

勝山 仁哉  ; 飛田 徹; 伊藤 裕人; 鬼沢 邦雄 

Katsuyama, Jinya; Tobita, Toru; Ito, Hiroto; Onizawa, Kunio

圧力バウンダリ配管における突合せ溶接継手を対象に、溶接条件のばらつきが溶接残留応力及びき裂進展挙動に及ぼす影響に関して、有限要素法による溶接残留応力シミュレーションを行い、得られた残留応力分布を用いて決定論的き裂進展解析を行った。その結果、入熱量が大きいほど、内表面の引張応力及び外表面の圧縮応力は増加するとともに、溶接残留応力が生じる範囲も増加することがわかった。また、内表面の溶接残留応力に対して、内表面側の初層付近の溶接は影響せず、外表面の最終パスの溶接が大きく影響することが明らかとなった。さらに、溶接残留応力分布から応力拡大係数を求め、入熱量が大きいほどき裂進展速度は速くなることを示した。

Stress corrosion cracking grows near the welding zone mainly due to high tensile residual stress by welding. The residual stress analysis due to welding of austenitic stainless piping is important and has been already conducted by many researchers. In present work, the effect of scatters of welding conditions such as heat input and welding speed on residual stress have been evaluated by parametric FEM analyses considering the variation of some parameters based on the welding experiments. The effects of welding conditions on crack growth behavior have been also evaluated by SCC growth simulations using calculated residual stress distributions and a procedure in the fitness-for-service code. Welding parameters such as heat input and welding speed have a strong influence on crack growth rate since residual stress is also affected by scatter of these welding parameters.