Microbial influenced corrosion due to Desulfovibrio desulfuricans

Purpose - The purpose of this paper is to investigate microbially induced corrosion on stainless steels due to sulfate reducing bacteria sp. Desulfovibrio desulfuricans and correlate it with the composition of extracellular polymeric substances (EPS) of the biofilm formed by these bacteria. Design/methodology/approach - Stainless steels 304L, 316L and 2205 were selected for the test. Modified Baar's media, both control and inoculated, were used as test solutions in anaerobic conditions. The bacteria were identified by scanning electron microscopy and their growth was estimated by bacterial counting. Electrochemical polarization and immersion test were performed to estimate the corrosion rate and the extent of pitting attack. The degree of corrosion and the presence of chemicals present inside/outside pits were determined by SEM/EDS. Biofilm formed on corroded coupons was analyzed spectroscopically to identify its components. An attempt was made to correlate the extent of corrosion with the bacterial concentration and the EPS of the biofilm. The differing corrosion performances of the stainless steels also were compared. Findings - The corrosivity of the solution increased with the addition of SRBs and with increased incubation time. The amount of carbohydrate and protein in EPS was observed to be a minimum when conditions were most corrosive. However, as the corrosivity decreased, these amounts increased. Stainless steel 2205 showed the highest corrosion resistance, followed by 316L and 304L. Originality/value - This work shows that SRB degrades its own EPS. Further, the extent of microbial corrosion on stainless steel coupons due to the presence of SRB correlates with the carbohydrate and protein contents of the EPS of the biofilm.