EIS characterization of corrosion processes of titanium and alloy UNSN10276 in sour environments

Titanium grade 2 (UNS R50400) and nickel-based alloy (UNS N10276) were electrochemically investigated to explore their corrosion susceptibility in sour (H2S) environments typically found on atmospheric distillation units in crude oil refineries. Electrochemical impedance spectroscopy (EIS) was used to attain the experimental results. Two individual solutions (0.05 mol/l HCl and 0.05 mol/l HCl+500 ppm H2S) were utilized in the laboratory work to replicate major corrosive agents present in actual atmospheric distillation systems for a characteristic heavy crude oil produced in Mexico. Metals were examined at pH 1.5, 4, 6, 8, and 10 values for the two solutions to identify the effects of pH modification on corrosion processes. The results disclosed that each metal has dissimilar corrosion susceptibility depending on the pH of the environment. Therefore, pH intervals for which every metal holds minimum susceptibility were identified. In addition, the convenience of controlling the pH of streams within a definite interval (5.5-6.5) is discussed and a few hints on decision-making to improve the operation of atmospheric distillation units are also explained.