Corrosion resistance of austenitic stainless steel welds with no-backing gas

Stainless steel pipe welds for service applications in corrosive environments typically use gas tungsten arc welding (GTAW) and require the use of an inert backing gas in order to minimize or prevent root bead contamination and oxidation. This adds significant cost and complexity to the welding of stainless steel pipe due to access restrictions, personnel safety, and/or economic factors. In this work, waveform-controlled gas metal arc welding (GMAW) was used for no-backing gas (NBG) welding of Type 304L austenitic stainless steel. Pitting corrosion behavior locally in the backside heat-affected zone and root bead weld metal was characterized using a syringe cell setup for cyclic potentiodynamic polarization (CPP) measurements. The CPP results indicate that the NBG welds have a similar pitting corrosion resistance as compared to reference GTAW and GMAW welds made with pure argon purging and an argon-oxygen mixture backing gas. The repassivation potential of the NBG welds was comparable to the reference welds, while the pitting potential was slightly lower. Weld bead appearance, weld metal ferrite, and heat tint oxidation were also characterized, and discussed with regard to the observed pitting corrosion resistance.