Carbon steel corrosion by iron oxidising and sulphate reducing bacteria ina freshwater cooling system

Microbiologically influenced corrosion of carbon steel has been investigate d. Carbon steel coupons were exposed online in the cooling water system of a nuclear test reactor to assess the microbial growth on the coupons and th e corrosion phenomena. Iron bacteria, sulphate reducing bacteria (SRB) and culturable aerobic heterotrophic bacteria (CAHB) were monitored both on the coupons and in the cooling water. Corrosion rate was assayed by weight los s method and corrosion products analysed by XRD and Mossbauer spectroscopy. Extensive tuberculation of carbon steel coupons was noticed. SEM pictures revealed the presence of ensheathed filamentous iron bacteria encrusted wit h corrosion products. Beneath the tubercles significant pitting and SRB ind uced corrosion in the form of concentric rings was observed. From the phase analysis, the following compounds were found to be present: gamma-Fe2O3, F e2PO5, FePS3, Fe(PO3)(3) and BaFeO3-x. From the present study it is inferre d that iron bacteria (Leptothrix sp.) and SRB (Desulfovibrio sp.) are respo nsible for the corrosion of carbon steel. The role of these bacteria in inf luencing the corrosion of carbon steel is highlighted. (C) 2000 Elsevier Sc ience Ltd. All rights reserved.