OBSERVATIONS ON FLAW TOLERANCE AND BRITTLE FRACTURE: THE EFFECT OF POST WELD HEAT TREATMENT

摘要

Post weld heat treatment (PWHT) can have a significant influence on the risk for brittle fracture in welded components. Furthermore, this topic is particularly relevant given the recent changes in PWHT requirements for P-No. 1 carbon steel materials in the 2014 Edition of ASME B31.3, Process Piping [1]. Specifically, PWHT is no longer a mandatory requirement for any wall thickness provided that multi-pass welding is employed for thicknesses greater than 3/16 of an inch and a minimum preheat of 200°F is applied for thicknesses greater than 1 inch. Fracture mechanics calculations have shown that the lack of a mandatory PWHT requirement for thicker carbon steel components may result in a significantly increased risk for brittle fracture failures due to near-yield level weld residual stresses. Given the concern throughout industry regarding the potential for brittle fracture failures, PWHT guidance to address potential issues arising from the change in the 2014 edition as cited previously, is examined in this article, and commentary on the potential reduction in fracture toughness due to PWHT is provided based on a review of published literature.