Effect of welding residual stress on hydrogen-induced fracture and fatigue life of X80 pipeline girth welded joints

Abstract

In this work, elastic–plastic fracture toughness tests were conducted on X80 base metal (BM), weld metal (WM), and heat affected zone (HAZ) under 12 MPa total pressure with 10 vol% and 30 vol% hydrogen-blended environments. Experimental results revealed that as the hydrogen blending ratio increased from 10 vol% to 30 vol%, the hydrogen-induced fracture toughness K_IH values of the BM, WM, and HAZ decreased by 14.6 %, 17.3 %, and 21.4 %, respectively. Within the investigated parameter range, both WM and HAZ exhibited higher hydrogen-induced crack propagation resistance than the BM under identical environments. Based on experimental results, a finite element framework was established to analyze cross-region fatigue crack growth in welded joints under residual stress. Numerical simulations revealed that in 30 vol% hydrogen environments coupled with welding residual stress, the equivalent stress intensity factor K_eq at the crack tip in the weld zone exceeds the K_IH at 45 % of the wall thickness, posing a fracture risk to the welded joint. Moreover, post-weld heat treatment (PWHT) significantly improves the stress state of welded joints. When the PWHT temperature exceeds 500℃, fatigue cracks maintain stable propagation until reaching 80 % of the wall thickness, with K_eq consistently remaining below K_IH throughout the crack growth process.