Influence of Weld Preparation Procedure and Heat Tinting on Sulfide Stress Corrosion Cracking of Duplex Stainless Steel

Abstract

Corrosion resistant alloys, such as duplex stainless steel (DSS), are increasingly the material of choice for oilfield applications as a result of the trend toward more extreme temperature, higher pressure, and elevated levels of hydrogen sulfide. However, the susceptibility of such materials to localized corrosion and sulfide stress cracking (SSC) is a major consideration, particularly in the vicinity of welds. Here we investigate the effect of surface preparation and oxygen content in the backing gas during welding on the pitting and SSC susceptibility of 22Cr DSS. Four-point bend testing of welded specimens under conditions close to the pass/fail boundary revealed a greater tendency for pitting as a function of oxygen content in the backing gas. Pitting was concentrated in the heat-tinted region, whereas cracking was mainly observed in the adjacent coarse ground parent material, with surface defects from the grinding process acting as primary crack initiation sites. The results demonstrate that control of oxygen levels in the backing gas and careful pipe alignment during welding are critical to avoid undesirable effects of heat tint and stress concentration. In addition, grinding procedures pre- and post-welding should be reviewed, as these may simply replace one type of crack initiation site with another.