The formation of hydrate and scale deposition is a major challenge in the petroleum industry. To avoid corrosion and hydrate formation, monoethylene glycol (MEG) is been utilized in the pipeline as an antifreeze and anticorrosion agent. It has been observed that the MEG has to be separated from acetic acid (HAc) and acid gases which enhance corrosion of mild steel in the oilfield environments. HAc and MEG also has an adverse effect of lowering the solubility of mineral salts and causing a higher risk of scale formation.
In this study, the mitigation of corrosion of mild steel in the presence of HAc and MEG in CO2 saturated environment were investigated at 25°C and 80°C using 3.5% wt. NaCl solution in a semi-circulated loop setup. Weight loss and electrochemical measurements using linear polarization resistance (LPR) were used to evaluate the efficiencies of two corrosion inhibitor based chemicals (the phosphate ester and the Olei imidazoline salt) at different concentrations. Test results obtained show that the corrosion inhibitors are found to be very effective in reducing the corrosion of mild steel in the presence of HAc and MEG at different conditions tested. At 25°C and 10ppm of inhibitors, the average corrosion rate decreases from 0.22mm/yr to 0.11mm/yr and from 0.21mm/yr to 0.05mm/yr with 50ppm of both inhibitors. At 80°C, the corrosion rate decreased from 0.20mm/yr to 0.07mm/yr with 10ppm of inhibitors, and from 0.19mm/yr to 0.03mm/yr with 50ppm of inhibitors A and B. The decreased in corrosion rate with the inhibitors shows that the active sites of the steel surface are prevented by the inhibitors absorption which in turn inhibits the absorption of the HAc and CO2 on the mild steel surface.