Microbially Influenced Steel Corrosion with Crevice Conditions in Natural Water

Abstract Recent findings at a Florida bridge showed that submerged steel piles had severe corrosion that appeared to be associated with microbial activity. Localized corrosion cells/pits were of up to 3" in diameter and penetrated through the steel thickness. Bacteria that have commonly been associated with microbially influenced corrosion (MIC) (e.g., sulfate reducing bacteria) were identified in the water samples collected from the bridge site. The water samples also showed high sulfate and chloride levels. The affected site contained microorganisms that can cause corrosion and as well as heavy marine growth. Although the role of the macrofoulers on the corrosion of the steel piles was not clear, the macrofoulers may have been associated with the corrosion development. It was thought that the effect of localized crevice environments created by the presence of the macrofoulers may support MIC. The objective of this research was to evaluate characteristics of macrofouling crevice environments that can enhance corrosion due to MIC. Laboratory experiments were conducted in simulated water environments. Tests were conducted with nutrient-rich environments inoculated with sulfate reducing bacteria (SRB). The effect of the physical characteristics of crevice environments, caused by macrofoulers on corrosion and in comparison with biotic condition, was studied. Electrochemical tests included the measurement of open circuit potential (OCP), linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS). Effects of parameters (i.e., aerated/ de-aerated conditions) were assessed through the electrochemical testing. In de-aerated environments, MIC due to SRB can be significant regardless of the presence of crevice conditions. In naturally aerated bulk solutions that may not be ideal for SRB, crevice environments may promote SRB proliferation and enhance MIC.