Electrochemical Behavior of Corrosion of X70 Steel under Thin Layer of Electrolytes Containing Hydrogen Sulfide

Corrosion behavior of X70 steel under thin layer of electrolytes containing hydrogen sulfide was studied by means of polarization curves and electrochemical impedance spectroscopy. The influence of hydrogen sulfide concentration, pH value and layer thickness were examined. The results showed that under thin electrolyte layers the cathodic and anodic processes both were promoted by hydrogen sulfide. With the increase of the hydrogen sulfide concentration, the corrosion potential (Ecorr), corrosion current (Jcorr) and corrosion rate of the steel increased. With the decrease of pH, Ecorr decreased, Jcorr increased to some extent. When the pH value was less than 3.02, a low-frequency inductance loop emerged and the Warburg impedance disappeared. The charge transfer resistance decreased and the corrosion rate increased with layer thickness decreasing.