Effect of the surface treatment on microbially influenced corrosion resistance of stainless steels

It has been widely recognized that stainless steels may be subjected to localized corrosion by influences of microorganisms in seawater or river water as Microbially Influenced Corrosion (MIG). In this study, the effect of the surface treatment of stainless steels on the MIC behavior in the aerobic aqueous environment was investigated. The corrosion potentials and the polarization curves were measured on the polished, passivated, electropolished and electrolyzed specimens in the simulated MIC test solution. The corrosion potential ennoblement of the specimen electrolyzed in Fe(III)Cr(VI) containing solution was slight compared with other tested specimens and had high corrosion resistance in the natural seawater. The specimen suppressed the cathodic reaction in the polarization measurement. The surface film had a double layer structure which was composed of an Fe hydride outer layer and a Cr oxide inner layer. It was also made clear that the Fe (OH)(3) membrane was anion selective and Cr2O3 membrane adsorbed MoO42- ions was cation selective from the results of membrane potential measurements, The cathodic polarization reaction of the bipolar membrane which consisted of the anion selective membrane in the outer layer and the cation selective membrane in the inner layer was suppressed, and it was corresponded to the cathodic polarization curve of the specimen electrolyzed in an Fe(III)Cr(VI)-containing solution. From these results, it can be considered that the surface film formed by electrolyzing is the bipolar membrane which suppresses the cathodic reaction. This surface film has high MIC resistance even if the cathodic reaction is accelerated by the aerobic bacterial metabolisms.