MICORP - A Practical Mechanistic MIC Pitting Prediction Software

MICORP is the world's first practical theoretical model for the prediction of MIC pitting due to SRB based on electrochemical kinetics and mass transfer. It is based on the BCSR (Biocatalytic Cathodic Sulfate Reduction) theory developed by Prof. Gu. The theory and model equations were first presented at Corrosion/2009. The model has been used to predict pit growth in hydrotest using seawater based on limited lab data. MICORP is based on biofilm catalysis, electrochemistry and mass transfer theories. This revolutionary software will likely guide the future lab testing and field data collection methods. For the first time, we introduced biofilm aggressiveness that is an electrochemical parameter related to how effective the biofilm can catalyze sulfate reactions. It is an intrinsic kinetic parameter. The software allows for automatic calibration of biofilm aggressiveness if there is a lab or field pit depth data point. In the future, a database for the biofilm aggressiveness values for some common SRB and APB species will be established. MICORP is a useful tool for the understanding of MIC behavior.

Due to biodiversity and complications in biological systems, MIC pitting rates can vary greatly. Calibration of biofilm aggressiveness is needed for actually MIC predictions. For example, in SRB MIC in anaerobic vials, increasing the headspace has been shown to increase carbon steel weight loss by 200%. More shockingly, increasing the Fe2+ concentration from 20 ppm to 200 ppm can increase carbon steel weight loss by 500%. Please see my 2018 and 2019 Corrosion Science papers about SRB MIC. In these two cases, dissolved H2S concentration as well as iron sulfide precipitation trends are completely opposite, suggesting that these two parameters are not the underlining casual factors for the increased corrosion with near neutral pH. In both cases, increased sessile cell counts occur in both cases, one due to more H2S escaping to the larger headspace (less H2S toxicity) and another Fe2+ detoxification of H2S. Unfortunately, most literature SRB MIC data do not come with the critical sessile cell data.

 

Some preliminary observations obtained from MICORP software are:

(1) Small pits (< 1 mm) grow linearly with time in the charge transfer control region.

(2) Pit growth slows down over time due to increased mass transfer resistance .

(3) Charge transfer resistance is important initially when pit depth is small (say less than 1 mm).

(4) Mass transfer becomes increasingly important when pits grow deeper. For deep pits, mass transfer resistance is limiting unless pitting rate is very small.

(5) Sulfate concentration effect may not be pronounced in lab tests (usually in charge transfer control region), but it is very important for long-term deep pit growth.

(6) A small biofilm thickness (say 0.1 mm) is not important at all when the pit becomes 1 mm or more.

Download MICORP installation file (installation requires a password and a registered user name)
Here are some results obtained from MICORP
Frequently Asked Questions (FAQ)

Installation: Just unzip the files into a folder and launch Run.exe. MICORP has been tested on Windows 2000, XP, Vista and Windows 7 beta. You can launch MICORP from a USB flash drive instead of your C: drive.

Version 1.5 added time-dependent biofilm aggressiveness, sulfate concentration, temperature, pH (proton concentration), and HAc concentration.

MICORP with NRB is also available based on the BCNR (Biocatalytic Cathodic Nitrate Reduction) theory that is completely analogous to the BCSR. Many people mistakenly believe that NRB can be used to mitigate MIC. However, mitigation of reservoir souring and mitigation of MIC are two different beasts. Some NRB are non-corrosive, but some are very aggressive.

Please contact Professor T. Gu (gu@ohio.edu) for any bugs or trends predicted by the software that you have questions with. 740-593-1499, https://people.ohio.edu/gu/

If your company is interested in licensing the software, please contract gu@ohio.edu. It can be done easily by using simple PO/invoice.

 

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