Inhibitory effect of tungstate, molybdate and nitrite ions on the carbon steel pitting corrosion in alkaline formation water containing Cl− ion

The pitting corrosion of carbon steel in carbonate-formation water solution in the presence of chloride ions and the effect of addition WO42−, MoO42− and NO2− anions on the pitting corrosion were studied using cyclic voltammetry and potentiostatic current–time measurements and complemented by scan electron microscope (SEM), energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) investigations. Cyclic voltammograms of carbon steel in the presence of chloride ions in carbonate-formation water solution show one anodic peak, corresponding to the formation green rust carbonate and the two cathodic peaks. As the addition of Cl− ions concentration increases, the anodic peak current density increases and pitting potential Epit shifts to more negative potential. It is shown that the rate of pit initiation (ti−1) decreases and the pitting potential Epit moves to more positive direction upon the addition of inorganic anions. It was found that pitting inhibition of carbon steel increases in the sequence: (WO4)2− > (MoO4)2− > (NO2)−.