Role of managanese in the corrosion of welded 316L

A recent trend in high-purity gas distribution systems has been to specify reduced manganese content for AISI 316L. This reduction is reported to improve the corrosion resistance of the welded material. The present study examines the effect of base chemistry, in particular manganese, on the corrosion of electropolished 316L stainless steel tubing that has been orbitally/autogenously welded. Twenty-one heats of commercially available 316L electropolished tubing with manganese content varying from 0.15 to 1.82 % were tested. Exposure was restricted to the electropolished inside surface of the tubing. Six samples were evaluated per heat. Based on the results of electrochemical pitting corrosion and general corrosion tests, a correlation between location of corrosion, weld gas purge direction, and Mn content was not observed. Furthermore, no appreciable correlation between corrosion resistance of 316L and Mn content was observed. However, a strong correlation between corrosion resistance after welding and base chemistry was observed.