Finite element simulation of the effect of welding residual stress on hydrogen diffusion

A sequential coupling calculation method on hydrogen diffusion has been developed based on the finite element program-ABAQUS. Using this method, the effect of welding residual stress on the hydrogen diffusion was numerically simulated for the as-weld condition and postweld heat treatment (PWHT) condition. The diffusion without the effect of stress was also taken into account and compared with those with stress. The results show that hydrogen will diffuse and accumulate in the higher stress region under the existence of welding residual stress gradient. A low hydrogen concentration valley exists near the heat affected zone (HAZ), which is caused by the long-range diffusion of hydrogen to the high stress zone. After the PWHT, stress relaxation is obvious and the residual stress is greatly decreased, which influences the hydrogen diffusion and makes the hydrogen concentration decrease about 40%. Therefore, PWHT can effectively improve the susceptibility of material to environment hydrogen cracking.