Role of Sulfate-Reducing Bacteria in Corrosion of Type 316 Stainless Steel

Abstract

Perforation of 5.5mm thick type 316L austenitic stainless steel (SS) weldments in industrial water containing sulfate-reducing bacteria (SRB) has occurred from internal pitting corrosion in as little as four months after operation. This piping system was operated every one month with low flow rate of 0.44m/s. Results of failure analyses have demonstrated that the preferential attack of austenite leaving δ-ferrite was observed in the pitting at the leak location. The pitting was full of deposits insoluble in water containing significant levels of sulfur as sulfide and chloride. It was thought that SRB in industrial water reduced SO₄^2- to HS^-, this was subsequently oxidized to S₂O₃^2- during the period of shutdown allowing oxygen to enter the system. The severe corrosion was believed to be the result of S₂O₃^2- production which can enhance cathodic reaction, with a resultant increase in anodic dissolution of SS.