Investigation of weld repair without post-weld heat treatment for P91

Abstract

Post-weld heat treatment (PWHT) is generally required for any grade 91 steel fabrication before entering service, as well as after any repair welding. However, this may sometimes be impractical or not cost-effective. A review of current welding practice for grade 91 showed that, whilst welding is relatively well established, there is a lack of published literature and proven procedures for nonstandard operations, such as weld repair without PWHT. By applying a microstructural refinement criterion (temper bead), SMAW and GTAW weld repairs of grade 91 steel without PWHT have been investigated. Metallographic examination and hardness testing were carried out to evaluate the degree of HAZ refinement and tempering, respectively. For both welding processes, a good level of refinement was produced, but only limited tempering was achieved. Recommendations are provided for the development of weld repair procedures based on an alternative criterion to that explored in this present project.