Beneficial effect of heat input to improve microbial corrosion resistance of welded joint in X80 steel pipeline

Abstract

In this paper, Desulfovibrio vulgaris corrosion of X80 steel welded joint with different heat inputs was carefully investigated. The results confirmed that in the sterile medium, general corrosion rate and localized corrosion susceptibility of heat affected zone (HAZ) were higher than those of weld zone (WZ) and base metal (BM). In the inoculated medium, the general corrosion rate of HAZ was still higher than that of WZ and BM. However, the number and depth of corrosion pits on WZ and BM surfaces, as well as the localized corrosion susceptibility, were much higher than those in HAZ, which was opposite to that in sterile environment, suggesting that the Desulfovibrio vulgaris corrosion of the welded joint was selective. With heat input increasing from 0.57 kJ/mm to 1.29 kJ/mm, general corrosion rate and localized corrosion susceptibility of HAZ and WZ simultaneously decreased in sterile or inoculated medium. In inoculated medium, localized corrosion of HAZ decreased more sharply than weld zone. Within the range of heat inputs tested, the study discerned a positive correlation: higher heat inputs correlated with an enhanced corrosion resistance of welded joint, irrespective of environmental conditions being sterile or inoculated. The findings provide a solid basis for the welding parameter determination to steel pipelines in oil and gas transportation.