To accurately predict and mitigate corrosion risk with simulation models, it is necessary to know the properties of corrosive environments, the metallurgical properties of the alloys that undergo corrosion, and the interactions between the metals and the environment, which are in turn is determined by the interfacial reactions and mass transfer effects. Thermodynamics allows us to understand the properties of corrosive environments and determine the equilibrium state for the reactions at the metal-solution interface.
Understanding how potentially corrosive species partition between the aqueous, gaseous, solid and other liquid phases, the activities of aggressive or inhibitive species in the aqueous phase and the behaviour of corrosion products and the stability of solid phases allows us to accurately predict corrosive behaviour. While Pourbaix diagrams are useful to visualize corrosion and passivation of metals, they cannot predict the solution pH or the oxidation-reduction potential. A rigorous thermodynamic model with a deep understanding of solution chemistry and realistic treatment of speciation are required to predict the pH and the behaviour of corrosion products. The OLI software to predict thermodynamics of corrosion is based on the MSE and MSE-SRK thermodynamic models to predict phase and chemical equilibria. It can generate Pourbaix diagrams and real-solution stability diagrams that enable the study of the effects of concentrations of various species, temperature, and their interplay. Practical applications of this technology include refinery overhead corrosion prediction due to amine hydrochlorides and corrosion in HF alkylation units due to water content in HF-containing phases. Availability of experimental data is a key limitation for more widespread of these models; one example is the lack of data to simulate hydrogen sulfide-based corrosion in high pressure, high temperature environments
November 24, 2020 EST