This paper presents the results of an investigation into the effect of ppm concentrations of acetic acid on the electrochemical corrosion behavior of API 5L X65 carbon steel in a sour environment.
Electrochemical techniques, Linear Polarization Resistance (LPR), Potentiodynamic Polarization and Electrochemical Impedance Spectroscopy (EIS), were used to characterize the electrochemical behavior of API 5L X65 carbon steel in a 3.5 wt% NaCl solution with 10 ppm of hydrogen sulfide (H2S) and acetic acid at 0, 100, 500 and 1000 ppm concentrations. All tests were conducted at 40°C temperature and 1.0 bar CO2 pressure. The corrosion product film formed on the electrode surface is less protective in the presence of acetic acid than when acetic acid was not present. This is confirmed by a decrease in the polarization resistance and increase in the corrosion rates with increase in acetic acid concentration. EIS shows high impedance of the film with no acetic acid present, indicating a highly protective corrosion product on the electrode surface. However, the impedance significantly decreases as the acetic acid concentration increases.
Examination of the tested electrodes in solutions containing acetic acid shows pitting corrosion on the surface. This appears to be due to the dissolution of iron acetate from the corrosion product scale.
Divi, S., Efird, K.D., Spiller, D., “Electrochemical Study of Acetic Acid Influence on Carbon Steel Corrosion in Sour Environment,” Proceedings of the NACE Corrosion 2017 (NACE-2017-9646), New Orleans, LA, March 26 – 30, 2017.