Study of SRB adherence on carbon steel surfaces by electrochemical and microscopic techniques

Abstract

It is well known that microbiologically influenced corrosion (MIC) is a serious issue in the oil and gas industry. This process is caused by a mixture of microorganisms, including aerobic and anaerobic bacteria. Among the later, the Sulphate Reducing Bacteria (SRB) are often designated as the main responsible of the MIC in anaerobic environments such as those found in the oil extraction industry. Extracellular polymeric substances (EPS) produced by SRB have the ability to accelerate corrosion by binding with metal ions. The aim of this study was to evaluate the formation of biofilms of SRB on carbon steel surfaces by electrochemical and microscopic techniques. Anaerobic bacterial cultures used in the experiments were isolated from different systems that presented problems of MIC. Carbon steel coupons of SAE 1010 were placed in the cultures of different species of SRB to allow biofilm development. At various times, coupons were extracted and bacterial adherence was measured by viable SRB counts, epifluorescence microscopy and by crystal violet assay. The surface attack and biofilm morphology were analyzed by scanning electron microscopy (SEM). The corrosion of the carbon steel surface was monitored using electrochemical techniques: electrochemical impedance spectroscopy and corrosion potential measurements. Studies carried out allowed correlating the adherence and the EPS of the tested SRB strains with the different degree of attack suffered by the SAE 1010 carbon steel coupons.