Monitoring Oil Pipeline MIC and Its Mitigation Offline Using a True Biofilm Test Kit and a Mechanistic MIC Model

Microbiologically influenced corrosion (MIC) is caused by microbial biofilms. In this work, the water phase of an oilfield oil-water sample was assessed using a new disposable electrochemical biofilm/MIC test kit consisting of two solid-state electrodes in a 10 mL serum vial for biofilm growth, biocorrosivity and biocide efficacy. The water sample was found to be low in microbes and nutrients. To simulate “worst-case scenario,” the water sample was subcultured at 37oC using enriched artificial seawater (EASW) for three rounds before being used as the seed culture for further MIC and biocide tests. Its main corrosive microbes were identified as sulfate reducers from a metagenomics analysis. The 7-d X60 carbon steel weight loss was 1.1 ± 0.2 mg/cm2 (2.9 mpy uniform corrosion rate). With 20 ppm tetrakis hydroxymethyl phosphonium sulfate (THPS) in EASW, it dropped to 0.5 ± 0.2 mg/cm2 (1.3 mpy), and with 50 ppm THPS, it became negligible (0.08 mpy). The corresponding MIC pit depths were 10.5 μm, 8.9 μm, and no well-defined pits, respectively. With the weight loss data, the corrosion resistance (Rp) from linear polarization resistance and corrosion current density (icorr) from Tafel scans were correlated with biofilm aggressiveness in our existing mechanistic model for MIC prediction with and without biocide treatment.