Introduction to OLI Studio: Corrosion Analyzer for First-Time Users

Table of Contents

Objective

Overview of OLI’s Corrosion Models

Overview of OLI Studio: Corrosion Analyzer Calculations

Example Corrosion Rate Calculations

Interpreting Polarization Curves

Examples of Stability (Pourbaix) Diagrams

Conclusion

References

Disclaimer: The user interface, calculations, and results displayed in this article are from OLI Studio: Corrosion Analyzer Version 12.0.0. Other software versions may appear different or present slightly distinct results due to continual developments in the software and thermodynamic databanks.

Objective

This article introduces new users to OLI Studio: Corrosion Analyzer, including its interface, model, and predictions. We will outline the essential features of the software and demonstrate how it simplifies the complex process of analyzing corrosion in various industrial settings.

Overview of OLI’s Corrosion Models

OLI’s corrosion model is constructed from a thermodynamic module and an electrochemical module.^1-5

• Thermodynamic Module:The OLI corrosion calculations rely on the chemical speciation in bulk solution (activities of species) and the properties related to the transport of electrochemically active species from the bulk solution to the metallic surface (e.g., solution density, diffusivity, and viscosity). These are determined by a thermodynamic model.^1-5 

  • In most cases, this is the AQ thermodynamic model, except for alloys already available in MSE.
  • For more information on OLI’s thermodynamic models, please visit the Thermodynamic Frameworks page of our Support Center.

• Electrochemical Module: The model incorporates an electrochemical module that accounts for the kinetics of electrochemical surface reactions to calculate the corrosion potential and corrosion rate.^1-5 Further details are available in References 1-5, as well as the references listed in this article.^1-5 There are two primary modes of corrosion calculated by OLI’s electrochemical module. More information on the development of both models can be found in our Support Center article.
  • Prediction of General Corrosion
    • General corrosion causes an entire surface to corrode uniformly
    • Corrosion Analyzer leverages the Mixed-Potential Model^1-5 to calculate general corrosion rate and corrosion potential
    • The model is calibrated using experimental corrosion rates and corrosion potentials^1-5 
  • Prediction of Localized Corrosion (Pitting)
    • Localized corrosion represents a localized attack on the metal surface
    • It is a stochastic process
    • Corrosion Analyzer leverages the Repassivation Potential Model^1-5  to determine the conditions for localized corrosion risk
      • Localized corrosion might occur when:

                        Corrosion Potential (E_Corr) > Repassivation Potential (E_rp)

Below is a visual representation that summarizes OLI’s corrosion prediction modules^1-5

Overview of OLI Studio: Corrosion Analyzer Calculations

The OLI Studio: Corrosion Analyzer consists of three main types of calculations:

• Corrosion Rate Calculation: This calculation generates the following outputs:
  • General Corrosion Rate: Calculates loss in thickness in mm/year (mil/year) to determine how quickly materials might corrode at the given conditions.
  • Localized Corrosion: Predicts whether localized corrosion will occur, such as pitting or crevice corrosion.
  • Polarization Curve: Plots a solution’s measured potential vs the current density.
  • For more information, please see Reference 2.²
• Stability (Pourbaix) Diagrams: Also known as Pourbaix Diagrams, stability diagrams help predict how metals will behave in different environments based on temperature, pressure, and chemical stream composition.⁵ They delineate the conditions under which the alloy is predicted to remain stable, corrode, or passivate.⁵ (See OLI's take on Marcel Pourbaix's work: Reference 5.⁵)
• Extreme value statistics (EVS): Not covered in this article.

Example Corrosion Rate Calculations

Most corrosion rate calculations in Corrosion Analyzer require OLI's traditional thermodynamic framework, AQ. This framework has been used to calibrate corrosion rates for various alloys, including stainless steels, carbon steel, and specialty alloys. For a list of the metallurgies available in AQ, please see our Support Center article.  

In V12, two alloys were introduced to the MSE framework, namely 2205 and 2507 (as of June 2025). Future releases will feature additional alloys in MSE.

Note: Since V11, MSE serves as the default framework in OLI Studio. If your metallurgy isn't yet supported in MSE, you must switch to AQ to run corrosion rate calculations.

Units Manager for Corrosion Rate Calculations

After adding a Corrosion Rate calculation, the “Corrosion” tab in the Units Manager will be enabled. This allows users to change the reported units for corrosion rate calculations.

Flow Types for Corrosion Rates

In the Calculation Parameters grid, there are 7 options for Flow Type:

1. Static: The solution is not flowing in this calculation.
2. Pipe Flow: The fluid is flowing through a pipe. The pipe diameter and flow velocity must be defined. The default pipe diameter is 0.1 m, and the default flow velocity is 2 m/s.
3. Rotating Disk: This reproduces a type of experiment that is used quite frequently in the laboratory. A disk is rotated to bring fluid to the surface of the electrode in a predictable manner. The diameter of the disk is specified as well as the revolutions per minute (RPM). The default diameter is 0.01 m and the default RPM is 5000 RPM.
4. Rotating Cylinder: This reproduces a type of experiment that is used quite frequently in the laboratory. A cylindrical rotor is rotated to bring fluid to the surface of the electrode in a predictable manner. The diameter of the rotor is specified as well as the revolutions per minute (RPM). The default diameter is 0.01 m and the default RPM is 5000 RPM.
5. Complete Agitation: This reproduces a type of experiment that is used quite frequently in the laboratory. A cylindrical rotor is rotated to bring fluid to the surface of the electrode in a predictable manner. The diameter of the rotor is specified as well as the revolutions per minute (RPM). The default diameter is 0.01 m and the default RPM is 5000 RPM.
6. Defined (Wall) Shear Stress: Shear stress is used to calculate mass transfer limitations. A user can directly input the value of the shear stress if they can obtain it from a separate fluid dynamics program.

7. Approximate Multiphase Flow (to calculate Wall Shear Stress): In the approximate multiphase flow option, OLI uses a correlation for shear stress that has been published in the NORSOK standard. The shear stress is then used to calculate mass transfer limitations. The mean wall shear stress on the wall at medium to high superficial velocities of one or both phases—liquid and gas—is calculated as follows:

   𝑆 = 0.5 𝜌𝑚 𝑓 𝑢𝑚 2 in [Pa] *

   * More information about this equation can be found in the OLI Corrosion Manual or in the NORSOK standard.

   Key references detailing these methodologies include References 2 and 4.^2,4

Example with Carbon Steel: General Corrosion Rate

The following video demonstrates how to set up a basic corrosion rate calculation using Carbon Steel G10100 as the metallurgy.

Example Gas Condensate Corrosion Calculations

In this example, we’ll look at a gas-sweetening plant case study where corrosion is a concern. The plant uses diethanolamine to neutralize acid gases like CO2 and H2S. As these gases cool and condense, they can become highly corrosive. The video will guide you through calculating the dew point temperature, removing the condensed water, and determining the corrosion rate, including how factors like fluid velocity affect the results.

Interpreting Polarization Curves

A corrosion rate calculation also generates a Polarization Curve output tab. This graph plots a solution’s measured potential vs the current density. Typically, the anodic curve corresponds to the dissolution of the metallurgy species. The sum of the cathodic curves adds up to the anodic curve at the corrosion potential (denoted by an inverted red triangle in the plot). The corrosion potential (E_corr) is the y-value of the point at which the anodic and cathodic currents are equal and therefore intersect; the x-value is the i_corr, or the corrosion current density. The corrosion potential from the plot matches the value listed in the Localized Corrosion tab of the calculation.

As an example, we can run the following corrosion rate calculation for a 0.6M NaCl solution:

1. Add a new stream
2. Select the AQ thermodynamic framework
3. In the Inflows section, add the following species:
   • H2O = 1 mol
   • NaCl = 0.6 mol
4. Add a Corrosion Rate calculation > Single Point Rate.
5. Select carbon steel as the Contact Surface.
6. Run the calculation.
7. In the Polarization Curve tab, enter the Variables window to select the system half-reactions.
8. Select all half-reactions except Fe(3+) and O2. These reactions do not contribute to the construction of this plot.

By inspecting the plot, we see that the corrosion potential is -0.48V and the corrosion current density is 2.95e-3 A/m³. Based on its closer proximity to the net current density line, the H(+) cathodic reaction contributes more to corrosion than the water reduction.

Examples of Stability (Pourbaix) Diagrams

A Stability Diagram (pH vs Potential diagram) provides a visual map of how pH influences the corrosion potential, based on the stream’s specified temperature and pressure.⁵ The diagram of H₂O on iron at 25°C, 1atm includes three regions:

1. Gray Area: The “immune to corrosion” region.
2. Green Area: Region where passivation occurs, which is a thin layer atop the metal surface that can protect the metal from corrosion.
3. Yellow Area: Region where corrosion is possible.

Watch the following short videos to learn how to create and interpret stability diagrams in OLI Studio: Corrosion Analyzer.⁵

Note: The Re button for Redox is turned ON by default when selecting the Stability Diagram calculation.

Interpreting the Diagram: A guide on how to read and understand the stability diagram

Elemental Iron in Water 

A simple stability diagram for iron in pure water

Interpreting the Stability Diagram

Elemental Iron in Sour Water

Introducing hydrogen sulfide into the water stream and analyzing its impact

Stainless Steel 316 Stability Diagram 

A more complex stability diagram for a common industrial alloy

Conclusion

OLI Studio: Corrosion Analyzer is a powerful and user-friendly solution for professionals facing complex corrosion challenges across various industries. This introductory guide empowers first-time users to quickly grasp the tool's functionalities, enabling them to harness its full potential.

References

(1)  Anderko, A.; Young, R. D. Model for Corrosion of Carbon Steel in Lithium Bromide Absorption Refrigeration Systems. CORROSION 2000, 56 (5), 543–555. DOI: 10.5006/1.3280559

(2) Anderko, A.; McKenzie, P.; Young, R. D. Computation of Rates of General Corrosion Using Electrochemical and Thermodynamic Models. CORROSION 2001, 57 (3), 202–213. DOI: 10.5006/1.3290345

(3) Sridhar, N.; Brossia, C. S.; Dunn, D. S.; Anderko, A. Predicting Localized Corrosion in Seawater. CORROSION 2004, 60 (10), 915–936. DOI: 10.5006/1.3287826

(4) Anderko, A.; Young, R. D. Simulation of CO2/H2S Corrosion Using Thermodynamic and Electrochemical Models; NACE International Annual Conference; San Antonio, TX, 1999; Vol. CORROSION 1999, pp 1–19. DOI: 10.5006/C1999-99031

(5) Anderko, A.; Sanders, S. J.; Young, R. D. Real-Solution Stability Diagrams: A Thermodynamic Tool for Modeling Corrosion in Wide Temperature and Concentration Ranges. CORROSION 1997, 53 (1), 43–53. DOI: 10.5006/1.3280432