Investigation of the Corrosion Behavior of Mild Steel in the NH4Cl/CO2 Corrosive Medium

NH4Cl corrosion failure often occurs in petroleum refinery processing units such as the hydrotreatment unit overhead systems where failure is accompanied by CO2−-induced corrosion. In this paper, EIS and potentiodynamic polarization techniques along with SEM, XRD, and EDS studies are performed to evaluate the effects of temperature, pH, and partial pressure of CO2 on the corrosion behavior of carbon steel in 0.5 mol% NH4Cl solution with CO2. The results reveal the formation of the protective FeCO3 film on the carbon steel surface in this environment. The maximum resistance of FeCO3 film (588.3 Ω cm2) and the minimum corrosion rate of carbon steel (0.734 mm/y) are found at 60 °C. Furthermore, the anodic current curves of the steel move toward the lower values as the pH decreases from 6 to 2. The proposed FeCO3 film formation model successfully predicts the protection of FeCO3 film in the NH4Cl/CO2 medium.