The Corrosion of Mild Steel by Biogenic Sulfide Films Exposed to Air

Abstract

The influence of sulfate-reducing bacteria on the corrosion of mild steel and the effects of subsequent aeration were investigated using test vessels in which the base of the vessel was formed by steel foil test pieces. Corrosion rates were determined by weight loss measurements from foils and by electrical resistance probe measurements. Corrosion rates of the anaerobic cultures after several days’ incubation were low (1.45 mg/dm2/day). However, exposure to air caused very high corrosion rates (129 mg/dm2/d), and metal loss was not uniform; pitting was the characteristic mode of attack and was equivalent to a local thinning rate of greater than 2 in. (5 cm) per year. Pitting appeared to be entirely a function of the type of film that developed on the foil during the incubation period. The attack was confined to areas beneath tubercles that consisted of loosely adherent material as opposed to the hard, tightly adherent films or tarnishes on uncorroded metal.