Effect of coexistence of sulfate reducing bacteria and nitrate reducing bacteria on the under-deposit corrosion of carbon steel

The effect of sulfate reducing bacteria (SRB) and nitrate reducing bacteria (NRB) on under-deposit corrosion (UDC) of carbon steel is studied by weight loss tests, electrochemical measurements and surface analysis. The results show that SRB-induced UDC is significantly inhibited by NRB. This inhibition is attributed to the accumulation of NRB in deposits suppressing the growth of SRB, as revealed by the analysis of total accumulation number of bacteria and the characterization of bacteria-formed micro-holes indicating localized accumulation of bacteria in deposits. The suppressed SRB growth in deposits is discussed based on the NRB-induced biologically competitive exclusion and metabolite inhibition mechanisms.