Corrosion of mild steel underneath aerobic biofilms containing sulfate-reducing bacteria. part i: at low dissolved oxygen concentration

Abstract

The sulfate‐reducing bacteria (SRB)‐enhanced corrosion of mild steel in the presence of 1.5 mg·l−1 dissolved oxygen (DO) in bulk liquid was investigated. The biofilm process analysis was combined with microelectrode measurements, electrochemical measurements, and surface analysis. In the early stages of biofilm accumulation, the cathodic polarization and the decreasing corrosion rate were attributed to DO consumption by aerobic bacteria. During that time, limited SRB activity was observed. The DO concentration near the steel surface was between 0.6 and 1 mg·l−1. After total depletion of dissolved oxygen near the steel surface, the cathodic depolarization and the increased corrosion rate were associated with the proliferation of SRB near the steel surface. Auger electron spectroscopy analysis indicated localized sulfide attack. High pit density appeared where the coincidence of oxygen and sulfur occurred. The bottom of the pit was enriched with sulfur.