Electrochemical Detection of Carbon Steel Corrosion Induced by Fermentative Bacteria From Natural Gas Transmission Lines

Abstract

The metabolic potential and corrosive activities of a fermentative bacterial enrichment culture from a natural gas transmission line were characterised. Three metagenome-assembled genomes (MAGs) attributable to Cytobacillus, Lacrimispora and Staphylococcus spp. were obtained. These MAGs hosted genes involved in the fermentation of carbohydrates to organic acids, which was reflected in the acidification of the growth medium by the culture. To evaluate the corrosive activities of the culture, it was incubated in a split chamber-zero resistance ammetry (SC-ZRA) format. This involved deploying carbon steel coupons immersed in liquid medium in opposing chambers of an electrochemical cell. Measurement of current between the coupons indicated the extent and mechanism of corrosion. When the enrichment culture was added to one side of an SC-ZRA incubation with bicarbonate-buffered medium, pH change and corrosion were minimal. In bicarbonate-free medium, the culture acidified the medium, induced electron transfer from the uninoculated chamber to the inoculated chamber, and caused mass loss. These results indicate that fermenter-induced microbially influenced corrosion (MIC) is due to localised fluid acidification, inducing anodic reactions on the metal surface exposed to the microorganisms and mass loss of the non-exposed metal.

Keywords: acid production; fermenter; microbially influenced corrosion; natural gas.

FIGURE 1

Growth (as indicated by A ₆₀₀; circles in panel A), glucose concentrations and pH (diamonds and squares, respectively in panel B) of FE1 after 10 transfers. Filled and open shapes represent values in uninoculated and inoculated media, respectively. Error bars represent standard deviations of duplicate measurements.

FIGURE 2

Current and potential (A, D, G and J), glucose and acetate concentrations (B, E, H and K) and pH (C, F, I and L) in SC‐ZRA incubations with bicarbonate buffering that were uninoculated (A–C) or inoculated with FE1 (D–F) and without bicarbonate buffering that were uninoculated (G–I) or inoculated with FE1 (J–L). Current and potential are in red and blue, respectively in panels A, D, G and J. pH and glucose concentrations are depicted by open (WE1 chamber) and closed (WE2 chamber) circles in their respective panels. Acetate concentrations are depicted in panel K using open (WE1 chamber) and closed (WE2 chamber) squares.