Evaluation of residual stress near the weld overlay cladding by welding and post-weld heat treatment

Udagawa, Makoto; Katsuyama, Jinya  ; Nishikawa, Hiroyuki; Onizawa, Kunio 

Stainless steel is welded as a cladding on the inner surface of a reactor pressure vessel (RPV) made of low alloy steel. In order to assess the structural integrity of an RPV more precisely, the residual stress distribution caused by weld-overlay cladding and post-weld heat treatment (PWHT) is to be evaluated. Although cladding layer is very thin compared to vessel wall, it is not easy to evaluate steep residual stress distribution which occurs in dissimilar metal weld. In this study, cladded specimens were fabricated using different welding methods. Residual stress measurements using both sectioning and DHD methods were then performed to evaluate the residual stress distributions. It was shown that thermal-elastic-plastic-creep analysis results based on finite element method were agreed with experimental results. It was also clarified that the main cause of residual stress due to welding and PWHT was the difference of thermal expansion between weld and base metals.