Effect of pressure on the rate of corrosion of metals in high subcritical and supercritical aqueous systems

A theory is developed for the effect of pressure on the rates of chemical and corrosion reactions in high subcritical and supercritical aqueous systems, with emphasis on the contributions from activation, system compressibility (volumetric concentration), and chemical dissociation. The theory shows that for high subcritical temperatures (300 °C<T<374 °C), all three contributions are important, but that at supercritical temperatures (T<374.15 °C), the compressibility of the system and the dissociation of solutes (e.g. HCl) to produce reactants (H+) become dominant, with the latter becoming increasingly so as the temperature in increased. The theory is compared with experimental data for the corrosion of 1013 carbon steel in water at 481 °C and at pressures ranging from 170 bar (2500 psi) to 238 bar (3500 psi). Relatively good agreement is obtained between theory and experiment considering the semi-quantitative nature of the experimental reaction rate data.