Evaluation of the Pitting Corrosion of Modified Martensitic Stainless Steel in CO2 Environment Using Point Defect Model

Abstract

Pitting corrosion is a significant concern for the broader application of stainless steel in modern industries in which metal and metal alloy are detached preferentially from susceptible parts on the surface, resulting in the creation of holes in passivated alloys that are exposed to an aqueous, neutral electrolyte containing corrosive species. Exposure of SS to brines leads to the localized loss of surface passivity and the onset of isolated pitting, which render the equipment or piping unfit for service. In the present study, the passive layer behavior and the pitting corrosion of the modified martensitic stainless steel (MMSS) were evaluated in a saturated CO2 environment (pH~5) with different NaCl concentrations and temperatures, using various electrochemical techniques. It was found that by increasing the temperature up to 60◦ C, the corrosion resistance of the MMSS increased; however, the corrosion rate dramatically increased at 80◦ C, indicating the destruction of the oxide layer. According to the point defect model (PDM) results, the calculated values of polarizability (α), metal cation diffusivity (D), and the rate of annihilation of cation vacancies (jm), reveal a strong dependence on the solution temperature.