Impact of accelerated corrosion on weld geometry, hardness and residual stresses of offshore steel joints over time
Sulaiman Shojai, Finn Schönamsgruber, Markus Köhler, Elyas Ghafoori
Abstract
• Analysis of weld geometry change based on 3D-scans of up to 12-month corroded specimens in accelerated salt spray chamber test. • 3D-Scan reveals: With higher exposure durations, the sharpness of butt welds increases, while it decreases for fillet welds. Corrosion causes mild notches become sharp and sharp notches become mild. • Hardness measurements show no change over exposure duration, but reveals that the sharpest notch location changes between weld metal, heat affected zone, and base material. • Residual stress measurements showing no significant difference over the exposure duration. The initial residual stresses remain unchanged. Corrosion of offshore support structures can reduce the estimated fatigue life. Pitting corrosion, in particular, is known to lead to local stress concentrations and thus reduce their service life. However, offshore support structures consist of a large number of weld seams, which already have their own stress concentrations and interact with pitting corrosion. So far, there have been no studies on how corrosion can influence the stress concentrations on a long-term basis. In this study, butt- and fillet-welded specimens were exposed to corrosion in a salt spray chamber for up to 12 months and their geometrical development was examined using 3D scans. In addition, hardness and residual stress measurements were carried out. The results were compared to specimens, which were corroded for 12 months in artificial seawater. It could be shown that corrosion causes the notches of the butt welds to become sharper over time, while the fillet welds become narrower. It could be also shown that despite existing scatter, the residual stresses do not change significantly over time. The hardness measurements revealed that although there are no significant changes in the hardness values, the location of the sharpest notch shifted repeatedly within the weld metal, heat affected zone, and base material, which had different hardness values.