Surface conditions for microcosm development and proliferation of SRB on steel with cathodic corrosion protection

Abstract Steel components used in civil infrastructure are susceptible to microbiologically influenced corrosion (MIC) in marine environments due to the interactions between the metal and its environment with varying water quality parameters (chemical and biological). Sulfate-reducing bacteria (SRB) has been associated with MIC by a cathodic depolarization mechanism due to the reaction of surface hydrogen. Recent findings at a Florida bridge showed severe localized corrosion associated with microbial activity and heavy marine fouling of the submerged steel piles. Cathodic protection can be applied to control the corrosion of steel; however, the mitigation may be impaired by the microbial activity and marine fouling. The objective of this work was to explore reduction reactions on cathodically polarized steel surfaces and evaluate the influence of cathodic polarization on sulfate reduction reaction. It was of interest to characterize the reduction reaction in crevices representative of different physical properties of the marine foulers where SRB can be supported. Field testing was conducted to differentiate the cathodic protection currents that develop in the presence of microorganisms under the layer of marine fouling in natural environments. Laboratory tests were conducted to elucidate the cathodic reactions by potentiostatic cathodic polarization of steel specimens in solutions inoculated with SRB. Field testing showed that proliferation of the bacteria was not inhibited in the presence of cathodic polarization at about −1000 mVCSE and corrosion continued in the localized regions under fouling encrustation. The larger cumulative charge relating to the apparent sulfate reduction by SRB corresponded to higher levels of cathodic polarization. Sulfate reduction by SRB can be a significant contributor to the electrochemical process for steel corrosion with cathodic polarization. For the porous crevice environments, large cathodic currents and high sulfate reduction coincided with the development of sustained SRB growth.