Numerical Analysis of Hydrogen Distribution in Welds of Structural Materials for Pressure Vessels

In order to predict and prevent cold cracking in welds in structural materials used in pressure vessels, the hydrogen distribution in the welds used to join stainless steel clad Cr-Mo steels, stainless steel overlay Cr-Mo steels and A533B steel was calculated in this study. In the calculation methods employed in this study, the diffusion and concentration of hydrogen in the welds was calculated using the diffusion equation based on activity considering the hardness and stress distributions, as well as the dependence on temperature for hydrogen diffusion coefficient. The diffusion and concentration behavior of hydrogen during welding, post weld heat treatment (PWHT) processing can be simulated using the calculation methods applied in this study. From the comparison between calculated and the experimental results of cold cracking tests such as the y-shape cold cracking test, cracking was prominently observed in the heat affected zone (HAZ), when the hydrogen content and residual stresses were over certain critical values. Based on the results of this analysis, it was suggested that it is possible to use this simulation method to predict the optimal hydrogen removal heat treatment conditions for these materials.