Microbiologically influenced corrosion of 1018 plain carbon steel in biodiesels

M.S. University of Hawaii at Manoa 2012.Includes bibliographical references.This research focuses on the microbiological effects of corrosion on 1018 plain carbon steel immersed in biodiesels. Corrosion of steel immersed in sterilized ultra-pure water (18.2 MΩ·cm) contaminated biodiesels of 100% (B100) and 20% (B20) concentration along with ultra-low sulfur diesel (ULSD) was initiated under three environmental conditions: anaerobic, aerobic, and selective (sterile) aerobic. Three time exposures of 1 month, 6 months and 1 year were conducted. Corrosion products were identified via Raman spectroscopy, x-ray diffraction, and scanning electron microscopy equipped with an energy dispersive x-ray system. Corrosion rates were calculated based on mass loss data obtained at the end of the 6 month and 1 year exposure periods. Microorganism contamination was identified based on molecular biology techniques such as colony polymerase chain reaction and DNA sequencing. pH, total acid number, and dissolved oxygen were also measured in the fuel and water layers of the ultra-pure water-fuel mixtures. Raman and x-ray diffraction revealed lepidocrocite, goethite, magnetite, and iron formate hydrate as the dominant corrosion products found on the 1018 steel coupon samples. Corrosion rates were highest among steel coupon samples exposed in ultra-low sulfur diesel in comparison to samples exposed in B100 and B20 fuels. As far as microbiological contamination within samples, two different microorganisms, a fungus, Paecilomyces variotti, and the bacteria Ralstonia solanacearum were successfully cultured and isolated from the fuel-water interface and water layer of the B20 and ULSD fuelwater mixtures in the experiment. Microbiological effects in the form of sludge was observed only on 1018 steel coupons exposed in the B20 fuel-water mixtures set in an aerobic environment