PITTING CORROSION RESISTANCE IN THE HEAT-AFFECTED ZONE OF NO-BACKING GAS (NBG) AUSTENITIC STAINLESS STEEL WELDS

Stainless steel welds for service applications in corrosive environments are typically performed using gas tungsten arc welding (GTAW) with an inert backing gas in order to minimize or prevent root pass contamination and oxidation. Back purging adds significant cost and complexity to stainless steel pipe welding due to access restrictions, personnel safety, and/or economic factors. In this study, two no-backing gas welds (NBG) were made on Type 304L austenitic stainless steel pipe with Type 316 filler metal. Two different shielding gas mixtures were used (98% Ar-2% CO2 and 90% He-7.5% Ar-2.5% CO2) for the NBG welds. Open gap root pass welds were performed using modified short circuit gas metal arc welding (SC-GMAW) process. A hot pass was welded with pulsed GMAW process. Fill and cap passes were made with flux-cored arc welding (FCAW) process. Cyclic potentiodynamic polarization (CPP) measurements based on ASTM G61 were performed locally on the backside surface heat-affected zone as a function of distance from the fusion line. Electrochemical corrosion testing was done using a simple syringe cell setup. Pitting corrosion resistance of the NBG welds was compared to a reference weld made with 100% argon backing gas and conventional GTAW for the root and hot pass.