Thermo-Mechanical Simulations of Residual Stresses and Hydrogen Diffusion in a Part-Size Sleeve-on-Pipe Mock-Up for Remote Pipeline Repair Welding

Detrimental hydrogen in the weld reduces its ductility and increases the possibility of cold cracking. The objective of this study has been to use computer simulations to predict residual stresses and decay of hydrogen in and adjacent to a 10 cm test weld which closes the gap between the sleeve and the pipe in a part-size sleeve-on-pipe mock-up for subsea pipeline repair applications. Pre- and post-weld heat treatment was applied to the test geometry which was designed to replicate the highest restraint level of a remote pipeline repair scenario. Two cases from the experiments were chosen for modeling, one successful that produced a weld free for cracks and another which was given a lower PWHT temperature that generated a level of hydrogen assisted cracking. With respect to the incidence of cracking and the position where the crack was initiated, the microstructure composition, the tensile stresses and the level of hydrogen predicted by the computer model is considered to support the experimental findings.