An Electrochemical Impedance Spectroscope (EIS) investigation on the influence of acetic acid on corrosion of mild steel

Corrosion affects pipelines and their operation. If corrosion remains undetected or unmanaged, it will cause metal loss, leading to costly repair downtime. Severe corrosion, if left untreated, could lead to catastrophic pipeline failure, resulting in major equipment damage, environmental damage, safety incidents, and even loss of life. 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. Additionally, mono-ethylene glycol and acetic acid can decrease the solubility of mineral salts, thereby increasing the risk of corrosion. 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 an Electrochemical Impedance Spectroscopy (EIS) instrument were employed to measure the corrosion rate as a function of time at different HAc and MEG concentrations. Furthermore, the efficiencies of three corrosion-inhibiting chemicals, the phosphate ester and the oleic imidazoline salt at various concentrations, were evaluated. The EIS 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. The Nyquist and Bode plots of the EIS results indicate that the diameter of the depressed semicircle decreases as various concentrations of HAc and MEG are added to the solution, and the and the sizes of the capacitive semicircle also decrease upon addition of 20% and 80% MEG.This reduction in corrosion rate is attributed to the formation of an iron carbonate film on the surface of the steel sample.