Evidence for microbiological influenced longer-term corrosion in tidal and coastal atmospheric corrosion of steel elements

This paper demonstrates recent evidence that bacteria are involved in the longerterm corrosion of mild steel in the tidal zone and in marine atmospheres. Bacteria are often associated with marine immersion corrosion but there appears to have been little attempt previously to associate bacterial activity with atmospheric corrosion in the coastal zone. The present paper describes observations of rust conditions on steel strips and coupons exposed in field tests conducted at several locations on the Eastern Australian seaboard. Careful examination revealed rust patterns and corrosion surface characteristics that could not have been caused by conventional oxidation with oxygen as the ultimate electron receptor. The patterns are consistent, however, with the activity of the sulphate-reducing bacteria in which sulphur acts as the electron receptor. Importantly, the most severe corrosion losses occurred away from coupon edges and revealed shiny, heavily pitted metal surfaces. There is evidence also that ferrous oxidizing bacteria are involved. These observations are consistent with the corrosion loss models previously proposed for longer-term immersion corrosion. An important aspect is that the evidence reported herein was obtained only as a result of the investigators expecting to find it, and then exercising unusual care in examining rusts and corroded surfaces.