Mechanism of Ennoblement by Bioflims on Active/Passive Alloys Immersed in Seawater, Tri-Service Committee on Corrosion Proceedings

The purpose of this paper is to present a brief review of how microbial fouling films affect the corrosion behavior of passive metals in natural waters. It has often been reported that microbial films shift the open circuit corrosion potential OCP of passive metals in the positive or noble direction and enhance the kinetics of the cathodic oxygen reduction reaction. The significance of this effect lies in its influence on localized corrosion initiation and propagation. In chloride bearing waters, initiation of pitting and crevice corrosion is statistical, with the probability of initiation increasing directly with chloride ion activity and OCP. Thus at a given chloride level, the probability of localized corrosion initiation is increased by anything such as a biofilm and its metabolic products that causes the OCP to become ennobled.