Hardness prediction models based on HAZ simulation for in-service welded pipeline steels

Abstract

Welding onto pressurised pipelines that contain flammable fluid to facilitate repairs or branch connections, is a critical procedure with considerable risk to personnel and infrastructure. Limiting the heat input is obviously an important consideration to prevent ‘burn-through’, but the potential for rapid cooling of the weldment increases its susceptibility to hydrogen assisted cold cracking (HACC). Therefore, one of the most important factors for in-service welding procedure development relates to the increased risk of formation of hard, brittle microstructures in the grain coarsened heat affected zone (GCHAZ) of the weld, microstructures that increase the risk of HACC. The present work has been successful in utilising heat treatment simulations to derive two new hardness prediction models that more accurately predict hardness in the GCHAZ for typical in-service welding applications than a commercially adopted and widely used hardness prediction algorithm. Although it is acknowledged that further work is required to validate the models for a wider range of in-service welding conditions, the performance of the models demonstrates their potential for developing improved in-service welding procedures.