As part of a project to develop a database of seawater corrosion resistance including resistance to microbiologically-influenced corrosion (MIC) seawater MIC exposure tests of five stainless steel alloys were undertaken for three and six month durations. Coupons of each metal which included crevices were exposed to marine conditions at a temperature of 30C in the presence of SRB biofilm under controlled laboratory conditions. Identical sets of coupons were exposed to nominally sterile seawater under the same conditions for the same time.Very severe crevice corrosion in the range 1 to 2 mm in 6 months was observed on specimens of stainless steel alloys UNS S30400 S31603 and lean Duplex S32101 exposed to the biofilm condition. A lesser but still severe amount of crevice corrosion to a maximum depth of ~0.5 mm was observed on Duplex alloy S31803 exposed biofilm conditions over the same period. Some significant crevice corrosion to maximum depth of 0.26 mm was also observed on the S32750 Superduplex material.The results for the nominally sterile control tests were very different to those of the biofilmed specimens. In nominally sterile seawater at the same temperature as the biofilmed coupons only the S30400 coupon specimens showed any crevice corrosion to a maximum depth of only 0.065 mm. This was ~20 times less than the depth of crevice corrosion on the biofilmed S30400 coupon. The S31603 and S32101 coupons showed only minor attack with a few small pits to a maximum depth of 0.059 mm and 0.021 mm respectively. The Duplex S31803 and Superduplex S32750 materials were free of any visible corrosion.A series of photographs and photo-micrographs are presented illustrating the morphology of the damage and the remarkable differences between specimens exposed to the biofilmed and sterile seawater environments.
Key words: downloadable, marine, seawater, microbial, MIC, bacteria, biofilm, stainless steel, duplex, Superduplex, UNS S31603, UNS S30403, UNS S32101, UNS S31803, UNS S32750, crevice, SRB, sulfate-reducing bacteria