Effect of calcium ions on pitting corrosion and inhibition performance in CO2 corrosion of N80 steel

The electrochemical impedance spectroscopy (EIS) and polarization resistance technique were used to investigate the susceptibility of N80 steel to pitting corrosion under stagnant condition and the corrosion behavior under flowing condition with/without precorrosion in 3% NaCl solution, in 3% NaCl + 1.5% CaCl2 solution and in 4.6% NaCl solution (equivalent Cl− concentration to 3% NaCl + 1.5% CaCl2 solution) saturated by CO2 at 57 °C. The results showed that under stagnant condition the initiation period of pitting corrosion decreased with increasing Cl− concentration, but at the same Cl− concentration, Ca2+ could prolong the initiation period. Under flowing condition the corrosion rate without stagnant precorrosion was bigger than that with precorrosion, and the corrosion rate with precorrosion in 3% NaCl solution was bigger than that in 3% NaCl + 1.5% CaCl2 solution. Inhibition of quaternary alkynoxymethyl amine (IMC-80-Q) under stagnant condition showed that the optimum inhibitor concentration significantly increased with the increase of Cl− concentration from 3% NaCl solution to 4.6% NaCl solution, and for the solutions with the same Cl− concentration, adding Ca2+ did not change the optimum inhibitor concentration.