The influence of sulphate-reducing bacteria on hydrogen absorption by steel during microbial corrosion

During the anaerobic corrosion of steel, hydrogen sulphide (H2S) evolution by the Sulphate-Reducing Bacteria (SRB) promotes hydrogen absorption by enhancing cathodic hydrogen evolution and inhibiting the combination of hydrogen atoms. While the effects of hydrogen damage are well known, it is unclear whether surface SRB films influence hydrogen absorption any differently to the separate effects of H2S. Also, for particularly hydrogen sensitive metals in soured environments, there is some doubt regarding what constitutes a safe but effective level of cathodic protection. Using the electrochemical technique of Devanathan and Stachurski, special apparatus were used to monitor hydrogen permeation through steel foils exposed simultaneously to cells and cell-free dialysates in batch cultures of either Desulfovibrio vulgaris (Woolwich) or Desulfovibrio desulfuricans (Norway 4). Further experiments were performed using applied potentials of -850mV (SCE) and -lOOOmV (SCE), and polarisation scans were performed on replicate steel specimens under the same conditions. Changes in pH, Eh, cell numbers and H2S levels were monitored during SRB growth.