Study on the hydrogen diffusion behavior in pipeline girth welds based on segmented moving double ellipsoid heat source model

Abstract

This study addresses the increased risk of hydrogen-induced failure caused by localized hydrogen enrichment in the hydrogen-blended pipeline girth welds. A hydrogen diffusion model for the hydrogen-infused pipeline girth weld is established based on the segmented moving double ellipsoid heat source boundary condition. Based on full-scale pipeline welding experiments, a three-dimensional six-layer six-pass model for X80 pipeline girth welds is established using ABAQUS and subroutine technology, considering the segmented moving double ellipsoid heat source boundary condition. Based on model and experimental verification, the temperature and residual stress fields during the welding process are analyzed. Hydrogen diffusion simulations are conducted using diffusion parameters from different regions and weld passes of the pipeline girth weld to investigate the influence of residual stress on the hydrogen diffusion behavior in the weld. The results indicate that the temperature field and residual stress field calculated using the segmented double ellipsoid heat source model show good agreement with experimental data, with computational times being 1/3 of those for the double ellipsoid heat source model, respectively. Regarding the hydrogen diffusion coefficient, the diffusion coefficients in the heat-affected zone and weld metal increased to varying degrees compared to the base metal due to the influence of grain structure and dislocation density. Moreover, welding residual stress promotes the diffusion and accumulation of hydrogen, with the maximum hydrogen concentration in the weld centre region increasing by 3.3 times compared to when residual stress is not considered, while the steady-state time is reduced to 5.2E5 seconds.