Combined Effects of Methane Producing Archaea (MPA) and Sulfate Reducing Bacteria (SRB) on Corrosion of Iron Coated with Tar Epoxy Resin

Iron corrosion by methane producing archaea (MPA) isolated from sludge in a crude oil reserve tank was examined in artificial seawater medium under N₂:CO₂ = 4:1 using metallic iron as sole electron donor and CO₂ as sole carbon source. MPA corroded iron more significantly when they were associated with sulfate reducing bacteria (SRB). Main component of the corrosion products was FeCO₃. One of possible mechanisms of iron corrosion by MPA associated with SRB is cathodic hydrogen consumption by MPA. Lower oxidation reduction potential (ORP) by HS^- produced from SRB might enhance corrosive activity of MPA because MPA generally prefer lower ORP. Accumulation of Cl^- was observed on the bottom of corrosion pit under the corrosion products layer. Tar epoxy resin coating is often used to prevent iron corrosion in severe corrosive environment. We examined whether MPA associated with SRB would damage carbon steel SS400 plate coated with tar epoxy resin with a defect in the coating. MPA associated with SRB deteriorated the tar epoxy resin coating severely. They also significantly corroded SS400 plate at the defect in the tar epoxy resin coating. Therefore, microbiologically influenced corrosion (MIC) of iron by cooperative effect of MPA and SRB should be paid attention even with tar epoxy resin coating when there are CO₂ in anaerobic seawater like environments.