New strain of anaerobic bacteria and its association with corrosion pitting of X52 pipeline steel

Abstract

Studies of microbiologically induced corrosion have been carried out in connection with sea water pipelines used in the oil fields of the Southern Region of Mexico. The bacteria used in the studies were obtained from a sea water pipeline belonging to a secondary oil recovery system and were grown in an API RP 38 liquid medium. The morphological and chemical characteristics of the bacteria isolated from the growth medium were investigated and phylogenetic analysis showed that the most closely related bacterial strain is clostridium sphenoides. However, the existence of significant differences in the phylogenetic codes indicates that the bacteria from the sea water pipeline belongs to a new species of sulphate reducing bacteria. Coupons of API 5L X52 pipeline steel exposed to these bacteria developed corrosion pits which did not form during the exposure of similar coupons to the sterile growth medium. What is more, bacteria from the biofilm formed on the pitted coupons contained iron, which was absent from bacteria cultured in growth medium in which there were no steel coupons. These results demonstrate the existence of an association between the new species of sulphate reducing bacteria and the development of pitting corrosion in X52 pipeline steel.