A Potentiodynamic Polarization Investigation on the Influence of Acetic Acid on Corrosion of Mild Steel
Ikeh Lesor *
Department of Petroleum and Gas Engineering, Faculty of Engineering, University of Port Harcourt, East – West Road, Choba, Uniport, Nigeria.
Ebeze, Peter Anene
Department of Petroleum and Gas Engineering, Faculty of Engineering, University of Port Harcourt, East – West Road, Choba, Uniport, Nigeria.
*Author to whom correspondence should be addressed.
Abstract
The presence of corrosion in pipelines remains a significant challenge in the petroleum industry. Internal corrosion reduces and slows down oil and gas production, especially when associated with free water and organic acids. 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 potentiodynamic polarization resistance (PDP) were employed to assess the corrosion potential (Ecorr) and corrosion current density (icorr). Furthermore, the efficiencies of three corrosion-inhibiting chemicals: the phosphate ester, the oleic imidazoline salt, and the silicates at various concentrations were evaluated. The results show that corrosion current density decreases as the electrode potential is scanned from the open circuit potential (OCP) in the anodic direction upon adding different concentrations of inhibitors to the solution. The corrosion reaction was inhibited by adding the three inhibitors to the solutions. It is observed that the corrosion rate for the inhibited samples reduces drastically to less than 0.2 mm/yr, compared to the uninhibited samples with HAc and MEG. Satisfactory inhibition performance was achieved for the inhibitors tested with concentrations ranging from 10 ppm to 50 ppm. Consequently, the XX(the phosphate ester) inhibitor exhibits the highest inhibition efficiency both at 10 ppm and 50 ppm, and reduces the corrosion rate below 0.02 mm/yr compared to the inhibitors YY and ZZ, respectively
Keywords: Corrosion, acetic acid, mild steel, potentiodynamic, mono-ethylene glycol, polarization