Corrosion of SAE 1018 steel in sour water collected from the petroleum industry: effect of temperature.

In this work, the results obtained from the electrochemical evaluation of a SAE 1018 carbon steel system, immersed in a sample of sour water collected in the oil industry, varying the temperature between 25 and 50C, without agitation, are presented. The evaluation was performed using electrochemical noise techniques, impedance, linear polarization, Tafel polarization curves and obtaining SEM images at each temperature evaluated. The electrochemical noise results with respect to the localization index show that the localized corrosion sites increase as the temperature increases up to 40C, then decrease considerably and are even lower than at 25C. Linear polarization results indicate a decrease in Rp although not linear, which may be closely related to the morphology of the corrosion products. Also, it was observed that the cathodic branch boundary current in the Tafel polarization curves has a non-predictable behavior since, up to 40C, the reduction rate increases as the temperature increases and thereafter decreases even more than at 35C. Microscopy images show a compact layer of corrosion products that at 45 and 50C changes its properties completely, showing different corrosion products. These results indicate that the variation in temperature can cause modification of the structure of the corrosion products and thus the severity of the damage caused to the metal.