Effect of H₂S concentration and temperature on the corrosion behavior of carbon steel in NACE solution

The electrochemical corrosion behavior of 20^# carbon steel in NACE solutions containing different mass concentrations of H₂S (0, 95. 61, 103. 22, and 224. 16 mg·L^-1) at different temperatures (25, 35, and 45℃) was investigated by potentiodynamic polarization tests, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The formation mechanism of corrosion products was also discussed. It is found that the corrosion rate of the carbon steel increases significantly with the addition of a small amount of H₂S in the NACE solution by promoting both the anodic iron dissolution and the cathodic hydrogen evolution. The corrosion current density of the carbon steel enhances with the increment of H₂S concentration. As the temperature of the electrolyte solution increasing, the corrosion rate also increases. The outer loose corrosion products are mainly iron carbonate; but corrosion products formed on the steel surface are mainly composed of iron sulfides.