Influence of various purging gases on pitting corrosion resistance of super duplex welded pipes

Abstract

Super duplex stainless steel (SDSS) is widely utilized in demanding industries like offshore energy, chemical, and petrochemical sectors due to its exceptional pitting corrosion resistance and mechanical properties. However, welding SDSS presents significant challenge, particularly in meeting stringent pitting corrosion test standards, influenced by various parameters such as consumables, gas combinations, and heat input controls. This study investigated the utilization of different purging gas combinations (100% Ar, 98% Ar + 2% N2, 100% N2) during gas tungsten arc welding (GTAW) using the Bohler Thermanit 25/09 welding consumable while keeping a constant shielding gas composition (98% Ar + 2% N2). Welding was conducted on 6-inch, Sch 80s, ASTM A790, UNS S32750 under identical parameters for all purging gas combinations. The weld root underwent pitting corrosion testing as per ASTM G48, method A, for 24 h at temperatures of 35 and 40°C, with a maximum acceptable weight loss criterion of 4 g/m2. Results indicated that only 100% Nz purging gas achieved corrosion test success at 40°C with minimal weight loss. Furthermore, at 35°C, weight loss decreased significantly across all purging combinations. Microstructural analysis of the weld root revealed no significant metallurgical anomalies. gas The study concludes that 100% N2 purging gas enhances the pitting resistance of super duplex welded pipes, noting its cost-effectiveness and availability compared to other inert gas mixtures.