Evaluation of corrosion and erosion–corrosion resistances of mild steel in sulfide-containing NaCl aerated solutions

This paper reports results of potentiodynamic polarization, electrochemical impedance measurements and erosion–corrosion of mild steel in aerated sulfide containing 3.5% NaCl solutions at room temperature. The pitting corrosion behavior was studied in NaCl solution containing 0.001, 0.005 and 0.010 M Na2S, using potentiodynamic polarization and electrochemical impedance spectroscopy. The erosion–corrosion resistance was evaluated after rotating the samples in sulfide polluted NaCl solution for 24 h at a velocity of 300, 600 and 900 ppm using a rotating disc electrode. Results showed that the presence of sulfide ions in NaCl solution resulted in a significant increase in the corrosion attack due to the local acidification caused by iron sulfide formation. The localized replacement of the protective Fe-oxide film by a non-protective iron sulfide film is responsible for the pitting and erosion–corrosion attack. The study concluded that the higher the concentration of sulfide in NaCl solution, the lower the resistance to pitting and erosion–corrosion. Moreover, increasing the solution rotating velocity affects negatively the erosion–corrosion resistance.