Microbially influenced corrosion (MIC) of carbon steel may occur in media with microbiological activity of especially sulphate-reducing bacteria (SRB). The applicability and reliability of a number of corrosion monitoring techniques for monitoring MIC has been evaluated in experiments conducted in near neutral sterile hydrogen sulphide saline solutions (pH 6 to 8.5, 0-107 mg/l sulphide), SRB active artificial sea water and SRB active simulated marine sediment.
Electrochemical techniques as LPR, EIS and potentiodynamic polarisations give distorted data dominated by capacitative and diffusional effects and unreliable corrosion rates, when biofilm and ferrous sulphide corrosion products cover the steel surface. Corrosion rates can be overestimated by a factor of 10 to 100 by electrochemical techniques.
Weight loss coupons and ER are recommended as necessary basic monitoring techniques. EIS might be used for detection of MIC as the appearance of very large capacitances can be attributed to the combined ferrous sulphide and biofilm formation. Capacitance correlates directly with sulphide concentration in sterile sulphide media.
Keywords: Corrosion monitoring, carbon steel, MIC, SRB, hydrogen sulphide, EIS