Corrosion Behavior of the Root Face of No-Backing-Gas (NBG) Austenitic Stainless Steel Welds

Abstract In corrosive environments, austenitic stainless steel welds commonly employ gas tungsten arc welding (GTAW) with inert backing gas to mitigate root pass contamination and oxidation. However, back purging can add substantial complexity and cost in stainless steel pipe welding due to access limitations and safety concerns. This study builds on previous work by the authors that indicated no-backing gas (NBG) modified waveform short-circuit gas metal arc welding (SC-GMAW) as a viable technique to achieve corrosion resistant austenitic stainless steel welds competitive with GTAW with argon backing gas. Electrochemical testing showed no significant differences in pitting corrosion resistance of the backside heat-affected zone (HAZ). The type of shielding gas mixture (98% Ar, 2% CO2 vs. 90% He, 7.5% Ar, 2.5% CO2) used for NBG welding influenced root shape and degree of oxidation. The present paper takes a closer look at the differences in terms of root appearance and surface discoloration as a function of shielding gas. Oxide compounds present in the different heat-tinted regions were characterized using Raman spectroscopy. ASTM G48 Method A immersion test showed no significant difference in corrosion weight loss and pit density between the NBG GMAW welds and the GTAW weld with argon backing.