Free Abstract

Transition from partial pressure to fugacity in corrosion modeling

Figure 1: Simulating HTHP autoclave being charged with a mixed gas

The following abstract describes the presentation that AJ Gerbino, Vice President Customer Success, OLI Systems, Inc made at  NACE Milano Italia 2018 during the Upstream Oil and Gas session, "Workshop on fugacity vs partial  pressure approach in material  susceptibility "on Monday afternoon, 28 May 2018. AJ is available for follow-up meetings on this topic either during the NACE meeting or via web.

In this presentation, we discuss the transition from calculating H2S and CO2 partial pressures to calculating their fugacities.  This transition is essential when predicting high temperature / pressure corrosion.  


The key elements include: an equation of state for predicting equilibrium constants; an activity model for predicting non-ideal effects in each phase; and a chemical reaction / speciation models for quantifying system properties.  

When an increasing number of these elements are applied to corrosion modeling, the result is progressive improvement in prediction: phase behavior and solubility of CO2 and H2S, fugacity and activity of the acid gases, and solution pH.


We will show using hypothetical autoclave loadings the difference in the fluid properties when this transition is made.


Based on this thermodynamic foundation, conductivity and diffusivity can be then calculated from speciation-dependent transport property models. Finally, film stability and corrosion rates can be obtained from electrochemical models on the basis of the predicted solution chemistry. 

AJ Gerbino

Vice President of Client Success


think simulation | getting the chemistry right

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