Electrochemical corrosion behaviour of stainless steel grades 1.4404 and 1.4435 butt welds by autogenous GTAW

Abstract

Prefabricated stainless steel welds are usually pickled. However, under certain conditions, the welds are left as-welded, due to the difficulty of implementing pickling. In such cases, the corrosion resistance in chloride environment is related to the heat tint on the root side. Coloration depends on the quality of the backing gas. For example, some specifications require maximum oxygen contamination of the backing gas, to guarantee a minimal oxidation layer on the root weld bead and adjacent heat affected zone. In this work, grade 1.4404 and 1.4435 stainless steels pipes were welded with different backing gases, where oxygen contamination was set to 10, 50, 75 and 100 ppm. Corrosion behaviour was studied by determining the pitting potential in artificial seawater. The major findings of this study are the following: Beyond the backing gas quality, the polishing method of the pipe (mechanical or electrochemical) leads to a different level of coloration. The weld area of an electro-polished pipe is generally less tinted than that of a mechanically polished pipe. The root side surface roughness of the base material appears to be a key factor for service performance under severe corrosive conditions in as-welded state.