Effect of post weld heat treatment on P9 and P11 steel weld joints produced by GTAW and SMAW methods

Post-weld stress-relieving heat treatments are commonly used to improve the mechanical performance of welded steel joints, especially when there is a risk of cracking in the weld zone. This study investigated four different welding configurations using A335 Gr. P11 and P9 pipes of different thicknesses. Firstly, an 8.18 mm-thick A335 Gr. P11 pipe was welded using the GTAW process with ER80S-B2 filler metal. Secondly, a 30 mm thick A335 Gr. P11 pipe was welded using a combination of the GTAW (ER80S-B2) and SMAW (E8018-B2) processes. Thirdly, a 20.62 mm thick A335 Gr. P9 pipe was welded using the GTAW (ER80S-B8) and SMAW (E8015-B8) processes and finally, dissimilar welding of P9 and P11 pipes (8.18 mm thick) using the GTAW (ER80S-B8) and SMAW (E8015-B8) processes. The effects of the different base materials and welding methods on the mechanical properties of the joints, as well as other changes that occurred following post weld heat treatment, were systematically evaluated. Mechanical characterization included tensile, bending and hardness tests and positive material identification (PMI) in addition to macrostructural analyses. PWHT process produced steady hardness values in both heat-treated P9 steel welds at 230 HV, whereas, this value was stable at 200HV in P11 steel welds. Similarly, yield strengths of P9 and P11 steels were 323, 287 and 311, 307, respectively increased to 460, 469 and 570, 503MPa respectively.