Electrochemical characterization of the corrosion process of 1018 carbon steel in sour solutions in the presence of different neutralizing amines

To control the corrosion process in primary distillation towers by the influence of acid sour media (HCl+H ₂S), different chemical treatments are widely used in the Mexican oilfield including corrosion inhibitors and neutralizing compounds, among others. Amines are added for neutralizing the acid sour media, typically monoethanolamine (MEA), ethylenediamine (E), ethylenediamine at 60% (E60) and 2-ethylhexillamine (2-EH), with MEA being the most widely used. In this work the Electrochemical Impedance Spectroscopy (EIS) technique is used to characterize the 1018 carbon steel (CS) - sour solution (0.05 M HCl + 500 ppm of H ₂S at 40°C, pH 2) interface in the absence and presence of amines in order to study their effect on the corrosion process. The EIS diagrams were analyzed using a Randles equivalent circuit. An active behavior of the steel in the medium without amine was evidenced. Furthermore, the active condition of the carbon steel increases in the presence of MEA and E probably due to the partial removal of corrosion products and the formation of nonprotective iron oxides. However, at 5 and 15 ppm dosages of both E60 and 2-EH amines, a positive effect was observed on the corrosion of the steel.