Investigating the mechanism of microbiologically influenced corrosion of carbon steel using X-ray micro-computed tomography
Journal of Materials Science
School of Engineering / Centre for Sustainable Energy and Resources
Australian Government Ministry of Higher Education and Scientific Research, Iraq
The mechanism of pitting corrosion of carbon steel by an oilfield microbial consortium was investigated using a combination of X-ray micro-computed tomography (µCT), surface analytical techniques and DNA/RNA-based 16S sequencing. The most active microorganisms in biofilms were Thermoanaerobacter sp., a type of fermentative, thiosulphate-reducing bacteria. µCT allowed the identification of corrosion products phases as well as their volume percent and surface area at each corrosion layer. µCT revealed that corrosion products of carbon steel exposed to biotic and abiotic conditions were formed by 5 phases with a few differences in the number of the components present. These components were iron sulphides, iron hydroxides, iron sulphates, iron oxide carbonates, iron oxides and iron phosphates. Pyrrhotite Fe S and iron phosphate (Fe7(PO4)6) were only identified in biotic corrosion products. In addition, marked differences in the abundance of corrosion products phases and porosity were observed in the presence of microorganisms, which was important in understanding corrosion mechanisms and kinetics. A new compound was identified that has not been previously reported such as vivianite (Fe3(PO4)2·8H2O) abiotically and chukanovite (Fe2(OH)2CO3) in both conditions. The combination of µCT with molecular identification of active biofilm species on the corroded surface provided insights into the mechanisms of pitting corrosion induced by microorganisms.