An Empirical Model to Determine the Modes of Corrosion of Carbon Steel Under Near Field Environments of Geological Disposal

Carbon steel is an alloy that can be passivated and be attacked by localized corrosion under certain water chemistries. For example, it is known that carbon steel is passivated in solutions above pH_d; the pH at general corrosion/passivation transition. In this study, an empirical model was developed to determine whether near field environments fall in the passivation or non-passivation domain for carbon steel. Using the experimental data obtained by previous studies, the pH_d was defined as a function of four factors, where the activity of proton ion ([H⁺]) for pH_d is assumed to be a linear combination of the logarithms of the total carbonate concentration ([C]), the chloride ion concentration ([Cl⁻]), the limiting current density of dissolved oxygen diffusion (i_O2), and the inverse of absolute temperature of contacting solution (T). The derived equation fitted well with experimental data from previous studies.