Combined effects of Methane Producing Archaea (MPA) and Sulfate Reducing Bacteria (SRB) on Corrosion of Iron

摘要

Iron corrosion by methane producing archaea (MPA), isolated from sludge in a crude oil reserve tank, was examined in artificial seawater medium under N_2:CO_2 = 4:1 gas using metallic iron as sole electron donor and CO_2 as sole carbon source. Iron corrosive MPA corroded iron more severely when they were associated with sulfate reducing bacteria (SRB). Main component of the corrosion products was FeCO_3. One of possible mechanisms of iron corrosion is cathodic hydrogen consumption by MPA before formation of the corrosion products layer. But location of cathode sites is unknown after formation of it. Galvanic cell between corrosion products layer and substratum iron was considered as another possible corrosion mechanism. HS～ produced by SRB might stimulate corrosive effects of MPA by lowering oxidation-reduction potential (ORP) in the medium. Accumulation of Cl~- was observed in the bottom of corrosion pit under the corrosion products layer. Tar epoxy resin coating is practically used to prevent iron corrosion in severe corrosive environments. We examined whether MPA and/or SRB would damage iron coupon coated with tar epoxy resin when there was a defect in the coating. MPA associated with SRB deteriorated tar epoxy resin coating severely and corroded iron coupon at the defect in the coating and in the region where the coating detached. Microbiologically influenced corrosion (MIC) of iron by combined effects of MPA and SRB should receive more attention in CO_2 and CF-rich anaerobic environments like anaerobic seawater and brine in oil fields.