Residual stress numerical simulation of two dissimilar metal weld junctions

In nuclear reactors such as Pressurized Water Reactors (PWR), heavy section components made in low alloy steel are connected with stainless steel piping systems. The dissimilar metal weld (DMW) junctions are performed following a special manufacturing procedure to ensure a good resistance of the joint. However, several experiences from the field confirm sensitivity to fatigue, corrosion or the existence of low toughness areas in this type of junction. Fatigue, corrosion and brittle fracture risks are enhanced by tensile residual stress fields, therefore reliable determination of residual stress fields in DMWs are of importance. The high level of residual stresses due to manufacturing process is greatly reduced by a post weld heat treatment (PWHT); however a full relief is impossible at the interface between weld material and the ferritic steel because of the difference in dilatation coefficients of these materials In the present work a full numerical simulation of residual stress fields was conducted on two different Dissimilar Metal Weld mock-ups manufactured respectively for the two EC projects BIMET and ADIMEW. The paper recalls the experimental residual strain measurements performed on the 6" (BIMET) and 16" (ADIMEW) DMW junctions, details the features of the numerical simulations and compares numerical predictions to the measurements. Furthermore in both cases, the effect of the PWHT on the residual stress fields has been investigated numerically.