Corrosion thermodynamics
OLI Corrosion Simulation
Understanding the chemistry of the corrosion environment
OLI has combined the ease-of-use and approach of the classical Pourbaix diagrams with a rigorous approach to model the thermodynamic properties of aqueous solutions. This results in the ability to construct stability diagrams for systems involving concentrated solutions, taking into account all of the interdependent ion interaction of a complex chemistry.
Classic Pourbaix diagrams identify species that are passivating, corrosive, or inert across a range of pH and potential. OLI has extended this diagrams to also examine concentrations of components and not only pH as independent variables (E-species diagrams).
In addition, chemical diagrams (either species-species concentration or and yield diagrams) can be used to design the synthesis of compounds (e.g., ceramics) with a desired yield for virtually any chemical mixture.
Modeling general corrosion
General corrosion rates and corrosion potential can be mechanistically predicted for a large selection of alloys, including carbon steel, stainless steels, Ni-based alloys, Cu, Cu-Ni alloys, and aluminum. The predictions are based on an electrochemical model that incorporates surface reactions on the corroding metal in the active and passive state, adsorption of active species, active-passive transition and transport processes to and from the corroding interface.
The mechanism of corrosion can be studied by viewing predicted polarization curves. The polarization curves show the rates at which various anodic and cathodic reactions at the metal surface are proceeding. The sum of all the reactions results in the net current, or polarization curve
Modeling local corrosion
The corrosion and repassivation potentials are calculated for the investigated alloy. In regions where the corrosion potential is larger than the repassivation potential, localized corrosion (pitting or crevice corrosion) can be expected. The maximum propagation rate of individual pits is also estimated.
Special circumstances
Depletion of Cr and Mo near grain boundaries as a result of heat treatment can be predicted for stainless steels and Ni-base alloys. This makes it possible to predict the possibility of intergranular corrosion (through the depletion parameter) and the effect of heat treatment on localized corrosion (via the effect on the repassivation potential).
Solution thermodynamics
OLI's electrolyte thermodynamic framework is the first component of OLI corrosion prediction technology. Understanding the solution thermodynamics and how ions partition between phases is the first step to identifying potentially corrosive situations. This capability is at the heart of every OLI equilibrium calculation.
Including redox chemistry
Elemental and alloy metal oxidation and reduction reactions for 80 inorganic elements and thousands of species are available in the OLI Databank. OLI corrosion technology automatically generates the redox reactions and the resulting species and solves for the equilibrium conditions using its predictive thermodynamic model.
Calculating ORP (oxidation reduction potential)
Also offered is rigorous prediction of ORP for multicomponent systems is computed for aqueous solutions.
Temperature: -50 to 300 C
Pressure: 0 to 1500 bar
Ionic strength: 0 to 30 molal
To help understand OLI's approach to corrosion simulation, we have created this diagram of the layered approach used in OLI corrosion prediction technology.
Technical papers describing each of these aspects of OLI's corrosion technology can be found in the OLI Resource Library.
A summary of each of these layers follows below, starting from the bottom and working up.
Transport properties
Part of the study of corrosion simulation includes the OLI-developed framework to calculate diffusivity, conductivity and viscosity at high salinities and conditions. These properties are described more completely in the thermodynamic model section of this website.
Full list of transport properties
