Effect of temperature on the corrosion behavior of Carbon steel in Hydrogen sulphide environments

The corrosion behavior of carbon steel exposed to hydrogen sulphide environment at different temperatures was investigated using the methods of weight-loss tests, electrochemical measurements, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results show that corrosion rate increased first and then decreased significantly with increasing temperature. As temperature increased, more fine and compact corrosion film was formed and the corrosion film converted from mackinawite to mackinawite/cubic FeS, indicating better protection to the steel. In addition, the solution equilibrium chemistry of dissolved H₂S at different temperatures was also calculated and analyzed. Compared to the decrease of H⁺ concentration, corrosion films could play a more dominant role in the decrease in corrosion rate. Finally, a probable mechanism is proposed to interpret the reason for corrosion rate result of carbon steel at different temperatures based on the protectiveness of corrosion film and the variation of H⁺ concentration.