Biofilm effect on the cathodic and anodic processes on stainless steel in seawater near the corrosion potential: Part 1 - corrosion potential

The electrochemical behavior of stainless steels in seawater near the corrosion potential is addressed. The effect of biofouling on the corrosion potential during exposure to seawater is investigated in the absence and presence of localized corrosion. A statistical approach is used to characterize the ennoblement of the corrosion potential. The distinction between theoretical and experimental polarization curves is emphasized and used to justify the ennoblement in passive conditions as a consequence of the high slopes of the theoretical polarization curves at the intersection point. Small differences in the corrosion current densities could be enough to scatter the corrosion potential or the open-circuit potential measured on nominally identical coupons in wide-range distributions, hence the need for statistical analysis. Also, the tendency of the corrosion potential of completely different passive materials in completely different biological exposure conditions to approach the thermodynamic value of the oxygen equilibrium potential can be easily justified by the low passive current density of such materials. Significant experimental evidence, often considered as caused by microbial activity at the metal surface, can be easily justified without modified oxygen reduction mechanisms and without enhancement of the cathodic processes.