Microbiologically Influenced Corrosion
Corrosion of metal and other materials by microorganisms is a major problem worldwide and is estimated to cost as much as $30-50 billion per year in damage in the United States. Production, transport, and storage of oil costs several hundred million dollars in the U.S. every year due to sulfate-reducing bacteria (SRB) alone, not including the costs for lost oil and environmental clean-up.
MIC also occurs in many other industries such as chemical processing, water treatment, and nuclear power generation. As water-wetting is becoming more and more common in oil and gas transportation due to increased use of water-flooding for enhanced oil recovery, fast MIC failures will become more and more common. It’s possible that once in the water-wetting flow regime, pipelines can fail in as little as one year or less due to MIC alone.
Professor of Chemical and Biomolecular Engineering Tingyue Gu is the first MIC investigator to apply bioenergetics systematically to investigate the biofilms attack metals. His work has achieved a brand-new understanding of basic MIC mechanisms and synergy in biofilm consortia. This has resulted in several discoveries that have immediate practical applications in biofilm and MIC detections. It has also led to our first mechanistic MIC model based on electrochemical kinetics and mass transfer for the prediction of MIC pit growth. As part of a large corrosion institute with extensive expertise on CO2, H2S and sulfur corrosion, the Institute’s work has benefited greatly from conventional corrosion engineers by performing corrosion tests correctly, thus avoiding costly mistakes easily found in published MIC literature.
MIC mitigation relies on biocide and scrubbing (pigging). Environmental concerns desire more effective biocide applications. It’s unlikely that there will be another blockbuster biocide like THPS or glutaraldehyde on the market any time soon. It’s a rational approach to enhance existing biocides for more effective biofilm treatment. The best way to do it is to "convince" sessile (biofilm) cells to become planktonic cells that are much easier to kill. We have found some chemicals in pet food and soy that are not biocidal. They are analogs to bacterial wall components. They can modify the wall slightly causing sessile cells to detach and move on as planktonic cells under a suitable biocide stress (e.g., 50 ppm THPS). One of the chemicals is effective at 1 ppm or below at a cost of 0.02 cent per liter of biocide cocktail. The biocide cocktail is extremely effective in the prevention of biofilm establishment and removal of established biofilms in lat tests. Please contact us if you are interested in a sample or collaborations.
MIC and biofilm detections are critical in decision-making for treatment that can be costly. Currently, "MIC test kits" are all microbe test kits that can only detect the presence of microbes. The presence of microbes does not automatically mean MIC. Identifying more and more microbes does not advance MIC research to the next stage as we haven't learned enough about how known microbes attack. Our new understanding of MIC mechanisms has made it possible for us to start investigating new ways to detect biofilms online and to sense the MIC process directly.
We are soliciting sponsors for various MIC projects. Our MIC-JIP (joint industry project) started on Jan. 1, 2012. If you’re interested in any of the following projects, please feel free to contact Professor T. Gu at email@example.com or call 740-593-1499. You may also contact Russ Professor Srdjan Nesic at firstname.lastname@example.org or call 740-593-0283. The full proposals are available upon request.
(A) MIC mechanisms and modeling, (B) MIC detection, and (C) MIC mitigation.
A-1. Investigation of APB attacks (Type II) with local pH measurement under a biofilm
A-2. MIC in underdeposit attacks involving sand
A-3. MIC in hydrotesting including high-pressure tests
A-4. Biofilm formation and MIC pitting attack under different flow conditions
A-5. Mechanistic MIC modeling involving Types I and II MIC attacks and establishment of a database for biofilm aggressiveness for pure strain microbes and some field biofilm consortia
A-6 Investigation and mechanistic modeling of synergistic SRB and CO2 corrosion.
B-1. Reliable and inexpensive new online biofilm sensors using novel electrochemical technologies
B-2. Disposable MIC test kits with portable base station
C-1. Evaluations of efficacies of new enhanced biocide cocktails and their compatibilities with corrosion inhibitor and other chemicals
1. New MIC Promoter Technology
In hydrogenase-positive SRB, iron oxidation is coupled with sulfate reduction with the help of hydrogenase enzyme system in the periplasm and other enzymes in the cytoplasm. The hydrogenase enzyme converts the adsorbed hydrogen atoms (on the cathode, i.e., iron surface) to hydrogen gas that is subsequently utilized by SRB. This is the foundation for the so-called cathodic depolarization theory (CDT). Many people questioned CDT primarily because hydrogenase-negative SRB also cause MIC. From an exhaustive investigation in the fundamentals of SRB metabolism and MIC data presented in the literature, Prof. Gu in early 2009 hypothesized the existence of catalysts in biofilm consortia that can assist and even replace hydrogenase enzymes causing severe MIC pitting. Such catalysts are secreted by some SRB and by synergistic microbes such as some Pseudomonas, Shewanella and methanogen species that may appear to be non-corrosive individually. Oxidation of iron is bioenergetically as favorable as oxidation of organic carbon (e.g., lactate) based on our thermodynamic calculations. Pseudomonas can catalyzes the SRB attack on iron and shares the ATP molecules produced and this means the entire biofilm benefits from increased energy supply that is useful as maintenance energy. This MIC promoter theory was proven in lab tests. Our experimental data showed 300% increased in MIC pit depth when a naturally secreted catalyst was added. Our MIC promoter discovery helps explain some mysterious severe MIC pitting cases. There are several potential applications:
- A new assay based on this technology helps convince pipeline operators that if a secreted catalyst is detected in a pipeline, severe MIC pitting is possible and biocide/pigging treatment should be used. This kind of assay indicates the pipeline fluid aggressiveness. This assay can be done in addition to the traditional assay of the microbial conditions in the pipeline, thus an assessment of true MIC threat is possible. We intend to develop a new online sensor to detect MIC promoters online.
- Acceleration of lab tests of MIC pitting.
- New treatment targeted at "non-corrosive" microbes that secrete MIC promoters.
With the intellectual property protection recently put in place, we are making this exciting technology available for licensing in the second half of March 2010.
2. Mechanistic MIC modeling
Existing risk factor MIC models predict the likelihood of MIC. To predict MIC pitting progression with any certainty, mechanistic modeling is needed. However, MIC is complicated phenomenon. A mechanistic model has been an elusive dream until now. A new era in MIC model has arrived since October 2008 when the MIC group led by Professor Tingyue Gu created the world's first practical and 100% MIC model based on a BCSR theory that completely demystified SRB MIC. It can be used to predict pit progression with time. The trend-setting model is based on sound electrochemistry, mass transfer, and biocatalysis mechanisms. The model considers charger transfer and mass transfer resistances with a dual biofilm layer. Almost all parameters are taken or estimated from literature. It can be calibrated using just a single pitting data point. Version 1 of BCSR model is available for evaluation by contacting Prof. Gu at email@example.com. For the first time, corrosion engineers are able to use a mechanistic MIC model to predict pitting progression. This model marks a quantum leap forward in MIC research. It will likely revolutionize strategies for field data collection and lab experiment planning. (Please do not confuse the mechanistic model with risk-factor models. The analogy is that no one can accurately predict when a particular person will get a flu, but we can reliably predict how the flu will progress IF the person gets a flu.)
We are seeking companies to support the development of Version 2 of the software and experiments to calibrate and validate MIC software.
3. MIC in underdeposit attack
Experiments will be conducted in 100 ml anaerobic vials and in a 1” flow loop. The flow loop has dead legs with sand particles. It will be an open “flow through once” flow system without any liquid recycling. The following tasks will be investigated:
- Biofilm formation in sand deposits of varied thicknesses at different bulk flow rates
- MIC pitting attack under sand deposits
- Synergistic effects between underdeposit attack and MIC
- Biocide penetration of sand deposits
4. New biomarker for biofilm and MIC monitoring
Currently, almost all MIC models are simple fault-tree like probability models weighing various factors such as pH, nutrient conditions, temperature, planktonic cell count, etc. Only a likelihood of MIC will be predicted. MIC pitting attack will not occur without the presence of a biofilm. Existing electronic biofilm probes are expensive and are unlikely to be able to detect elusive biofilms in pipelines. The current NACE biofilm assay standards all require actual biofilm samples. Existing DNA and enzyme assays cannot distinguish between the planktonic cells and the elusive sessile (biofilm) cells. A new class of biomarkers is needed to provide a tangible indicator of biofilm formation in pipelines and this can eventually lead to a more reliable quantitative prediction of MIC. This project will investigate biomarkers that are released by sessile cells. These biomarkers are released into the bulk fluid that is easily sampled. For a flow system, it is foreseeable that a self-propelled capsule with multiple chambers can be deployed. The chambers are opened at pre-programmed times to take in the bulk fluid at different locations. By analyzing the biomarker concentration profile, biofilm locations can be found. In this project, we will investigate EPS (extracellular polymeric substances) as a potential biomarker. EPS are secreted by cells to "glue" themselves together for biofilm formation. They account for up to 90% of the organic matters in a biofilm and some EPS molecules are released to the bulk-fluid due to cell metabolism and natural death. This allows the detection of biofilms locally or downstream by sampling the bulk fluid. Below are the tasks:
- Distinguish biofilm EPS from EPS components originated from other sources
- Study the relationship between EPS and MIC
- Develop test kits for specific EPS components for biofilm and MIC monitoring
Other Corrosion Center Projects
1. Hydrotest using seawater
BP America was our first sponsor for this project. Saudi Aramco was the second sponsor. Another major oil company is working with us to start tests in the second half of 2010. Additional sponsors are sought. The project studies MIC time course in hydrotest using both natural seawater and artificial seawater. Glutaraldehyde and THPS are tested. THPS degradation in seawater as functions of time, temperature, and pH are being investigated. The black powder problem resulting from the hydrotest is also being investigated. We have already developed a mechanistic model for THPS degradation that has seen field applications. The new mechanistic MIC pitting model is also a derivative of this project.
2. Modeling of reservoir souring
We are seeking companies to fund the development of a mechanistic model treating a reservoir as a bioreactor and considering cell growth kinetics, nitrate/nitrite injections, and mass transfer.
Please contact T. Gu for more information on the MIC Project.