Microbiologically Influenced Corrosion by Iodide-Oxidizing Bacteria

Pipeline of iodine-recovering facilities in Chiba, Japan, have been undergone severe corrosion damage.  To elucidate the cause of the corrosion, an analysis of the corrosion products from the corroded pipe, a small-scale corrosion-reproductive test, and DGGE analysis of microbial community were carried out.  The corrosion products were stratified inside the pipe, and consisted mainly of FeOOH and FeCO₃.  As a result of the corrosion-reproductive test using SS400 carbon steel, iodide-oxidizing bacteria (IOB) were dominance in the community, and the amounts of iron dissolved from the carbon steels were about 5-fold higher than that of chemical corrosion.  From the corrosive brine, six strains were isolated as IOB-related species, and four strains of these were actually oxidized potassium iodide to molecular iodine.  To evaluate corrosive abilities of the isolates, monitoring of open circuit potential were carried out using sterilized brine.  As a result, four strains of IOB which produces molecular iodine showed potential ennoblement, and two strains which cannot oxidize potassium iodide did not change the potential.  Furthermore, one iodide-oxidizing strain, dMB-MAT3, showed the significant decrease of the potential and corroded a SUS316-L stainless steel coupon.  These IOB probably involve in the corrosion by producing molecular iodine.