Characterization of sulphate-reducing bacteria as a function of time on buried pipeline steel under cathodic protection

Low-carbon steel electrodes were buried in sterilized and bacterial media. The potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) were sequentially carried out on buried electrodes. The corrosion potential, on the steel electrode buried in a sterilized medium (without sulphate reducing bacteria), was found to be more negative than that of the electrode buried in the sulphate reducing bacteria (SRB) medium. Cathodic and anodic curves electrodes buried in a SRB medium showed the highest current density. Clearly, three phases were observed during the SRB growth within an incubated medium. EIS measurements showed that the effects of biofilms on steel electrodes varied with time. From the bacterial medium, EIS results showed an optimum cathodic protection (CP) potential of -1450 mV Cu/CuSO4. Surface morphologies of electrodes buried in bacterial media revealed dimples on the entire electrode surface, when the slow strain rate tensile test (SSRT) was carried out in air, while quasi-cleavage was discovered on the steel electrode, when the applied CP potential was -950 mV Cu/CuSO4. At -1450 mV Cu/CuSO4, corrosion products were seen all over the electrodes, and a complete cleavage occurred on them at -1890 mV Cu/CuSO4.