Kinetics and mechanistic reaction pathway of carbon steel dissolution in simulated CO2–H2S medium in the presence of formic acid

Abstract Anodic dissolution of carbon steel in solution mixtures of simulated CO2–H2S in the presence of formic acid (0–500 ppm) was investigated using electrochemical methods such as potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The results show that the corrosion rate increases with an increase in the concentration of formic acid. Potentiodynamic polarization data revealed that the increase in cathodic current density plays a significant role in the increase of carbon steel corrosion rate. A combination of equivalent circuits was employed to model the impedance spectra of the carbon steel electrode acquired at open circuit potential and different overpotentials. The EIS data obtained at various overpotentials were further analyzed by reaction mechanism analysis (RMA) approach to interpret the dissolution mechanism. A multi-step reaction model including two dissolution paths and ferrous intermediate adsorbed species determined the dissolution behaviour of carbon steel. The best fit RMA kinetic parameters were retrieved using an optimization technique and the surface coverage of adsorbed species was estimated. Surface morphology of corroded steel surfaces was also examined with field emission scanning electron microscope demonstrating aggressive uniform corrosion of carbon steel in the presence of formic acid.