An electrochemical analysis of the influence of acetic acid on corrosion of carbon steel

Acetic acid (HAc) significantly increases the corrosion rate of carbon steel, particularly in CO2-saturated environments, by acting as a source of H ions (buffering effect) that accelerates cathodic reactions, according to electrochemical analyses. The presence of acetic acid disrupts the protective iron carbonate (FeCO) layer that typically forms on carbon steel, leading to higher general corrosion rates and promoting localized pitting corrosion. Several studies have shown that corrosion products (ferrous and anhydrous ions) combine to form porous, non-protective precipitates on iron surfaces. To prevent these issues, Mono-Ethylene Glycol (MEG) is used in pipelines as an antifreeze and anti-corrosion agent. It is important to note that MEG must be separated from acetic acid (HAc) and acid gases, which can accelerate corrosion of mild steel in oil-field environments. The study aims to investigate the effects of acetic acid and mono-ethylene glycol on the corrosion rate of mild steel in saturated brine solutions at different temperatures. Electrochemical measurements using open-circuit potential and linear polarization resistance were employed to determine the corrosion rate as a function of time at different HAc and MEG concentrations. The results show that the corrosion rate in the presence of HAc increases with increasing HAc concentration and decreases with increasing exposure time due to the protective film formed on the electrode surface. This reduction in corrosion rate is attributed to the formation of an iron carbonate film on the surface of the steel sample. At 25 °C, the average corrosion rate upon adding 500 ppm HAc was 0.72 mm/yr. An increase in temperature to 80 °C results in a corresponding increase in the corrosion rate to approximately 1.05 mm/yr. The results showed comparable corrosion rates at both temperatures across a range of HAc concentrations.