Microbial Corrosion Mechanisms
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... Iron Reducing Bacteria
Iron reducing bacteria reduce ferric ions (Fe3+) to ferrous ions (Fe2+…
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Iron Reducing Bacteria
Iron reducing bacteria reduce ferric ions (Fe3+) to ferrous ions (Fe2+). Ferric salts are highly insoluble and are chemically inactive, which protects the metal surface from corrosion; in contrast, ferrous salts are soluble and do not offer protection from corrosion [1]. The continual removal of the protective layer of ferric compounds exposes the metal surface, allowing for further corrosion to occur [6]. BiofilmsBiofilmsbiofilms
When adherent bacteria proliferate on a surface and secrete an extracellular matrix, a biofilm is formed [3]. On sites affected by microbially influenced corrosion, it is found that the sites contain a combination of bacteria species rather than a single species [7]. These biofilms contribute to corrosion by altering the local environment [8]. The secreted extracellular matrix is commonly composed of polysaccharides, proteins, nucleic acids, and lipids [7].
Biofilm formation often follows a few critical steps: initial rapid and reversible bacterial attachment to the surface (reversible attachment), a more stable and longer term attachment (irreversible attachment), bacterial growth and matrix secretion (microcolony formation), biofilm maturation (macrocolony formation), and bacterial migration (bacterial dispersal) [7,9].
Sulfate Reducing Bacteria
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... Alternative Theoriesalternativetheories
Later theories of SRB mechanisms place more importanc…
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Alternative Theoriesalternativetheories
Later theories of SRB mechanisms place more importance on corrosion caused by the byproducts of SRB, rather than reaction caused by SRB itself. [2]
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a galvanic cellcell, caused by localized corrosion, that also
{Untitled35.png} Figure 3: Schematic Representation of Miller and King's Mechanism [5]
The theory proposed by Miller and King was later slightly revised by Costello in 1975. While Costello considered that the cathodic depolarization of hydrogen through the Fe/FeS galvanic cell was correct, he proposed an alternative cathodic reaction. Instead of the dissociation of water producing hydrogen ions, Costello suggested that the cathodic reaction is: [2]
The overall mechanism is shown in the image below:
{http://media.noria.com/sites/magazine_images/201210/Jeremy_Water_Iron_Image.jpg} Figure 1. Overall galvanic corrosion mechanism [3]
Localized Corrosionlocalized corrosion
Localized corrosion can be described as a special type of galvanic corrosion where only only material is present. Due to impurities, the composition of a metal may differ at different locations, causing both cathodic and anodic sites to form on the same metal. The localized corrosion phenomenon is explained in the video below: [4]
Acid Corrosionacid corrosion
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with acid: [2]
{http://cronodon.com/images/metals_acid_eqs.jpg}
Dry Corrosion
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most metals. [2]
In petroleum
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high temperature. [5]
Standard Reduction Potential (Half Cell Potential) ListHCP list
Following is the list of standard reduction potential for metals at 25 degree Celsius. When two of them are present in a galvanic cell, the one with higher standard potential would tend to be the cathode and be reduced. The difference between is called the standard electromotive forceEMF. [2]
{http://www.statemaster.com/wikimir/images/upload.wikimedia.org/wikipedia/en/thumb/a/a5/Srptable.JPG/400px-Srptable.JPG} Figure 2. Standard reduction potentials [2]
Possible contributing factors for pipeline corrosion:
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pipeline corrosion: [4][5]
Hydrogen sulfide: cause galvanic cell corrosion, increase acidity, localized breakdown of FeS results in increased pitting;
Carbon dioxide: increase acidity;
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Chlorides: increase the conductivity of water; also serve as oxidant.
Microbially Influenced Corrosion:
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three stages: [5][6]
Stage I: Beginning of film and bio-film formation with hydrogen permeation by redox reaction. This stage is dominant by general galvanic corrosion.
Stage II: Stabilization of film and bio-film and the metal is ennobled;
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[2] S. Zumdahl et al, Chemistry. Houghton Mifflin Company. 5th ed, vol. 18.2000.
[3] askIITians. Electrochemical Series [Online]. Available: http://www.askiitians.com/iit-jee-chemistry/physical-chemistry/electrochemical-series.aspx
[4] CorrConnect. Corrosion Microcell [Online]. Available: https://www.youtube.com/watch?v=hfmD1RyUWgY
[5] Mitigation of
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Available: http://www.capp.ca/getdoc.aspx?DocId=155641&DT=PDF
[5]
[6] S. Kakooei
oxygen or sulfur [1].sulfur. [1] There are
Galvanic (Wet) CorrosionGalvanic
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as the cathode[1].cathode. [1] The anode
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by electromotive force[3].force. [2]
In the
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oxidation occurs: [3]
(Anodic dissolution of Fe)
{Untitled1.png}
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{Untitled4.png}
The overall mechanism is shown in the image below:
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corrosion mechanism [2][3]
Acid Corrosionacid corrosion
Acid Corrosion is a special case of Galvanic Corrosion, where only one metal is present and the standard reduction potential is negative (i.e. lower than the hydrogen). The common mechanism is shown by the reaction of iron with acid:
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In petroleum industries, hydrogen sulfide attacks steel and forms porous FeS scale under high temperature.
Standard Reduction Potential (Half Cell Potential) ListHCP list
reduction potentials [3][2]
Possible contributing factors for pipeline corrosion:
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affecting pipeline corrosion[6]:corrosion: [4]
Hydrogen sulfide: cause galvanic cell corrosion, increase acidity, localized breakdown of FeS results in increased pitting;
Carbon dioxide: increase acidity;
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Chlorides: increase the conductivity of water; also serve as oxidant.
Microbially Influenced Corrosion:
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into three stages [4]:stages: [5]
Stage I: Beginning of film and bio-film formation with hydrogen permeation by redox reaction. This stage is dominant by general galvanic corrosion.
Stage II: Stabilization of film and bio-film and the metal is ennobled;
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Details are discussed in the MIC page.
[1] C. Raymond. Chemistry. New York: McGraw-Hill, 2007, pp. 796-825.
[2] askIITians. Electrochemical Series [Online]. Available: http://www.askiitians.com/iit-jee-chemistry/physical-chemistry/electrochemical-series.aspx
[3] S. Zumdahl
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vol. 18.2000.
[3] askIITians. Electrochemical Series [Online]. Available: http://www.askiitians.com/iit-jee-chemistry/physical-chemistry/electrochemical-series.aspx
[4] Mitigation of Internal Corrosion in Oil Effluent Pipeline Systems [Online]. Available: http://www.capp.ca/getdoc.aspx?DocId=155641&DT=PDF
[5] S. Kakooei
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- 531
[5] Mitigation of Internal Corrosion in Oil Effluent Pipeline Systems [Online]. Available: http://www.capp.ca/getdoc.aspx?DocId=155641&DT=PDF
Prevention and Treatment
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... Monitor the bacteria population after every injection of the biocide
Periodically monitor the…
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Monitor the bacteria population after every injection of the biocide
Periodically monitor the rate of MIC using electrochemical probes.
Monitoring programs are being enhanced through new methods of identifying microbes in biofilms. Identification of microorganisms through the use of molecular techniques examining bacterial RNA and DNA have been recent incorporated into the oil and gas industry. These molecular methods involve extracting DNA from the biofilm microbes, copying and sequencing the DNA, then comparing these DNA samples to database DNA sample obtained from known microbes grown in a controlled environment. DNA probes that bind to specific part of a target microbe's DNA can also be used to identify microbes that are not in the database. These new techniques allow for more accurate identification and quantification of bacterial species in the pipeline, allowing for the application of treatment methods more specific to the instance of corrosion. [5]
[1] Rob. (2010, June), Microbiologically induced corrosion prevention and analysis [Online]. Available:http://failure-analysis.info/2010/06/microbiologically-induced-corrosion-prevention-and-analysis/
[2] J. A. Mountford. (2002) Titanium - properties, advantages and applications solving the corrosion problems in marine service [Online]. Available: http://www.ticotitanium.com/wp-content/uploads/2009/11/paper02170.pdf
CorrosionInternal Pipeline Corrosion Mechanisms
Corrosion is a deterioration process to form metallic compounds by redox reaction of pure metal, which consumes metal and causes pitting, rusting, cracking and even breakdown of industrial units. The redox reaction can be broken down into two steps. The first step is the electrochemical oxidation of metals which entails the formation of metallic cation. Then corrosion continues as the metallic cation react with oxidant such as oxygen or sulfur [1]. There are three major mechanisms:
Galvanic (Wet) CorrosionGalvanic
Microbial Corrosion Mechanisms
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... The co-culture of symbiotic microorganisms can contribute to microbially influenced corrosion.…
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The co-culture of symbiotic microorganisms can contribute to microbially influenced corrosion. Manganese oxidizing bacteria and sulfate reducing bacteria are an example of how the co-culture of symbiotic bacteria allows for the corrosion mechanism to initiate and advance. Manganese oxidizing bacteria deposit MnO2; this creates an anaerobic region which promotes the growth of sulfate reducing bacteria. The manganese oxidizing bacteria initiate the corrosion mechanism and promotes the growth of sulfate reducing bacteria which enhances the rate of corrosion [1].
[1] N. Muthukumar. et al. (2013, Sept). Microbiologically Influenced corrosion in petroleum product pipelines - A review. Indian Journal of Experimental Biology [Online]. 41. 1012-1022. Available: http://nopr.niscair.res.in/bitstream/123456789/17162/1/IJEB%2041%289%29%201012-1022.pdf
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of Metals. [online].[Online]. Available: http://failure-analysis.info/2010/06/biological-corrosion-of-metals/
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Is Biofilm?. [online].[Online]. Available: http://www.colgateprofessional.com/patient-education/articles/what-is-biofilm
[4] J. Wright. Inhibiting Rust and Corrosion to Prevent Machine Failures. [Online]. Available: http://www.machinerylubrication.com/Read/29116/inhibiting-rust-corrosion
[5] Corrosionpedia. Cathodic Polarization. [Online]. Available: http://www.corrosionpedia.com/definition/231/cathodic-polarization
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[10] CLI Houston. Mechanism of microbiologically influenced corrosion, caused by bacteria. [Online]. Available: http://www.clihouston.com/news/mechanism-of-mic-caused-by-bacteria.html
[11] W.H. Dickinson and Z. Lewandowski. (1996, Feb). Manganese biofouling and the corrosion behavior of stainless steel. The Journal or Bioadhesion and Biofilm Research. 10. 79-93. [Online]. Available: http://www.tandfonline.com/doi/pdf/10.1080/08927019609386272
Prevention and Treatment
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... Filters
The use of liquid particulate and gas particulate filters within pipe systems is also…
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Filters
The use of liquid particulate and gas particulate filters within pipe systems is also common. As mentioned earlier, contaminants within pipe fluids provide nutrients for bacteria to populate. The introduction of bacteria will increase the rate of corrosion. Therefore, using filters to remove traces of dirt and other contaminants from the processed fluid will stunt the growth of bacteria and thus inhibit corrosion. Figures 1 and 2 below provide examples of liquid and gas pipeline filters used in industry. [1] Although filters reduce the rate at which contaminants enter the system, they are an added expense to the pipeline and cannot operate indefinitely. Eventually, filters will require replacement to properly function.
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Filters, LL-142 [8][9]
{2.png} Figure
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filter GP-146 [8][9]
Pipe Material
Using a special pipe material that is resistant to MIC is another prevention method. [1] For example, titanium [2] is such a metal that is highly resistant to MIC due to its relative chemical inertness compared to other potential pipe metals such as iron. However, the high cost, roughly 4.5 times the cost of a schedule 40 carbon-steel pipe, and the requirement of special fabrication methods are disadvantages of using titanium pipes. [3] An alternative non-metal that can be used is Polyvinyl Chloride (PVC). PVC also significantly limits the rate of MIC and has a lower cost compared to titanium, costing roughly 0.7 times as much as a schedule 40 carbon-steel pipe. [3] However, PVC pipes are structurally weaker than metal pipes and cannot be used in operations requiring extremely high pressure.
The figures below show examples of titanium and PVC piping.
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titanium pipes [9][10]
{4.png} Figure
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PVC pipes [10][11]
Other Physical Methods
In addition to the techniques discussed above, some general corrosion prevention methods include applying protective pipe coatings and reducing pipe crevices, welds and joints. [1] Protective coatings apply the same principles as using a resistant pipe material. The coating is less expensive, but also less durable. Bacterial growth is more likely to occur at welds and joints, as these structures may contain areas of low fluid velocity. Thus, reducing the number of welds and joints therefore reduces the likelihood of bacterial growth.
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Biocide
The use of biocide, chemicals targeted to kill biological organisms, to combat bio-corrosion is very common. In general, biocides are used to control the activity of bacteria in a system. The biocide treatment approach is recommended whenever bacteria are found to be present within a production system, since a single identified bacterium is a strong indication of large colonies of bacteria that already exist.
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of toxicants. [newref][6] Non-oxidizing biocides
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biocide dosage. [nr][6]
Listed in the table below are some specific examples of biocide compounds used in industry, their properties and usual concentrations [4]
{6.jpg}
New developments in biocides are due to a push to find greener, more environmentally friendly biocides that are still highly effective. These changes are due to new changes in legislation which aim to reduce environmental impact. Some traditional biocides such as chlorine have a significant negative environmental impact, and have now been restricted in their use. [5]
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to detect. [6][7] Therefore, mistake
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MIC rate. [7][8]
Biocompetitive Exclusion
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monitoring program. [7][8]
Monitoring Programs [6][7]
One important
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following aspects [6]:[7]:
Conduct periodic chemical analysis on the water/oil/gas that is transported through the pipeline
Sample and identify the microbial population in the pipe fluid
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[2] J. A. Mountford. (2002) Titanium - properties, advantages and applications solving the corrosion problems in marine service [Online]. Available: http://www.ticotitanium.com/wp-content/uploads/2009/11/paper02170.pdf
[3] The Engineering Toolbox. Piping Materials Cost Ratios [Online]. Available: http://www.engineeringtoolbox.com/piping-materials-cost-ratios-d_864.html
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Materials [Online]. Available:http://www.medwelljournals.com/fulltext/?doi=erj.2011.59.65Available: http://www.medwelljournals.com/fulltext/?doi=erj.2011.59.65
[5] H.A. Videla and L.K. Herrera. (2005). Microbiologically influenced corrosion: looking into the future [Online]. Available: http://scielo.isciii.es/pdf/im/v8n3/04%20Videla.pdf
[6] ChemTreat. Biological Control [Online]. Available: http://www.chemtreat.com/solutions/chemical-treatment-programs/cooling-tower-water-chemicals/biological-control/ [6][7] N.Muhukumar. (2013,
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Available: http://nopr.niscair.res.in/bitstream/123456789/17162/1/IJEB%2041%289%29%201012-1022.pdf
[7]
[8] T. Lundgaar.
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Available: http://www.dti.dk/services/microbiology-management/products/23602,4
[8]
[9] Clean Energy
Sulfate Reducing Bacteria
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... [1] W. A. Hamilton. "Sulphate-reducing Bacteria and Anaerobic Corrosion," Annual Rev…
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[1] W. A. Hamilton. "Sulphate-reducing Bacteria and Anaerobic Corrosion," Annual Review of Microbiology, vol. 39, pp. 195-217, 1985
[2] R Javaherdashti, Microbiologically Influenced Corrosion: An Engineering Insight. London, United Kingdom: Springer London, 2008, pp. 49-57.
[3] P. Marcus.Marcus, Corrosion Mechanisms
[4] S. Kakooei, M. C. Ismail and B. Ariwahjoedi. "Mechanisms of Microbiologically Influenced Corrosion: A Review," World Applied Sciences Journal, vol. 17, pp. 524-531, 2012
[5] R A. King and J. D. A. Miller. "Corrosion by the Sulphate-reducing Bacteria," Nature, vol. 233, pp. 491-492, Oct. 1971
