Iron Corrosion under the Enrichment Culture of Anaerobic Microorganisms Utilizing Metallic Iron as an Electron Donor

Abstract

Iron corrosion under enrichment culture of anaerobic microorganisms utilizing metallic iron as an electron donor was investigated. Enrichment culture from residual water on bottom of a crude oil storage tank in Kyushu region caused severe iron corrosion. But the other two enrichment cultures from drain water of an oil field in Tohoku region and sediment at mouth of the Edogawa river did not corrode iron severely. Black ferrous sulfide film was detected in the corrosion products under the enrichment cultures from the drain water of the oil field in Tohoku region and the sediment at mouth of the Edogawa river. Therefore, sulfate reducing bacteria (SRB) were considered to be causative microorganisms to iron corrosion. But the ferrous sulfide film was not detected in the corrosion products under the enrichment culture from the crude oil storage tank in Kyushu region. Ferrous carbonate (FeCO₃) was a main component of the corrosion products by the enrichment culture from the crude oil storage tank in Kyushu region. Therefore, iron corrosion under the enrichment culture from the crude oil storage tank in Kyushu region was considered to be not simply caused by the SRB. Open circuit potential of a carbon steel (SS400) coupon with corrosion products under the enrichment culture from the crude oil storage tank in Kyushu region was about 120 to 140 mV higher than that by the other two enrichment cultures or abiotic control in anaerobic artificial seawater deaerated by Ar gas. Therefore, Galvanic coupling between corrosion products layer and base metal was considered to be possible mechanism of iron corrosion under the enrichment culture of the crude oil storage tank in Kyushu region.