Role of HCO3- and Cl- in the Pitting of 20CrMo Steel in simulated oil field environment

Abstract

In this study, the effects of HCO 3 -and Cl -concentrations on the pitting behavior of 20CrMo steel were investigated by potential polarization curve, electrochemical impedance spectroscopy and MottSchottky measurements. In addition, the concentrations of HCO 3 -and Cl -in a simulated oil field environment were varied to investigate the interactions between HCO 3 -and Cl -. The results indicated that with increasing HCO 3 -concentration, the passivation of HCO 3 -is enhanced, leading to the increase in the corrosion and pitting potentials and decrease in the number of defects in the passivation film as well as the corrosion current. With increasing Cl -concentration, the erosion became severe, resulting in the loosening and breaking of the passivation film as well as the easy formation of holes. The [Cl -]/[HCO 3 -] ratio exhibited a concentration threshold. The passivation of HCO 3 -played a dominant role below the critical value; the erosion effect of Cl -is main role above the critical value and 20CrMo steel occurs dissolution.