Microbial Induced Corrosion
Corrosion is the degradation of a material (usually a metal) caused by a reaction with its environment. It has a great economic and environmental impact on the world’s infrastructure. The most recent cost of corrosion study [1] documented that, just in the United States alone; $276 billion were lost annually due to corrosion. This sum includes only the direct cost for replacements. The indirect costs, such as loss of production, environmental impacts, transportation disruptions, injuries, and fatalities, were estimated to be equal to the direct costs. Thus, a more likely cost of corrosion in the US is in the order of a staggering $552 billion representing 6% of the GDP.
The corrosion of metals related to the activities of microorganisms is known as microbiologically influenced corrosion (MIC) or biocorrosion. MIC is a problem in a wide range of industries including drinking water distribution system [2], cooling water systems [3], sewage treatment facilities [4], underground pipes and ships [5], bilges, piping and tanks of maritime vessels [6], nuclear power facilities [4], and especially in the oil and gas industry in its producing, refining and transportation operations. Detailed studies carried out in the United States in 1978 indicated that MIC costs various industries between $16 and $18 billion [7].
In the oil and gas industry, the activity of microorganisms has been blamed for the corrosion of equipment and installations, plugging of petroleum formation, and souring of the reservoir and fluids. Chevron Oil Production Company detected pinhole leaks in several segments of a new oil gathering system only 18 months after the new system began operation [8]. Internal examination of the leaking piping indicated that serious damages due to microorganisms had occurred beneath the deposits of sand and corrosion films. Petrobras, the Brazilian oil company, found severe corrosion of the materials used for sea water injection due to MIC at their offshore plant [9]. Tests performed by BP Corporation on MIC showed that the corrosion rate of steel specimens was accelerated in the presence of microorganisms [10]. The corrosion rate of mild steel increased with exposure time in a system inoculated with bacteria, while a relatively low and constant corrosion rate was obtained in a sterile system. In August 2006, BP suffered a corrosion-induced pipeline failure in its Prudhoe Bay oilfield which was the result of MIC [11]. The necessary shut down for repairs resulted in the loss of up to 400,000 barrels of crude oil production per day and required an environmental clean-up operation. The shutdown lasted nearly six weeks. Even new alloys such as duplex stainless steels (e.g. 2205) which were developed especially for harsh corrosive environments such as sea water in offshore installations. were found to be susceptible to MIC [12]. The annual cost of all forms of corrosion to the oil and gas industry is estimated at $13.4 billion, of which MIC accounts for about $2 billion [1].
As shown above, there is an urgent need for research and development to increase our understanding of the microbial species involved in microbial corrosion, their interactions with metal surfaces and with each other, the root causes of MIC and of means for detecting and preventing MIC. Previous investigations of microbial species present in the oil and gas industry relied upon the use of samples to grow bacterial cultures in the laboratory. However, these techniques are selective of certain organisms, semi-quantitative only, and time consuming. In addition to classical culture such as viable count, biomass assessment, activity measurement, several new bimolecular methods could be used. Microscopy-based methods DAPI (4-,6-diamidino-2-phenylindole stain) and qFISH (quantitative fluorescence in-situ hybridization) yield numbers of cells per sample volume/weight. All living, inactive and dead cells are included in DAPI counts, buts only living cells are counted with qFISH. Polymerase chain reaction (PCR) based methods do not distinguish between live and dead microorganisms. Denaturing gradient gel electrophoresis (DGGE) is not a quantitative method, but it is highly efficient for qualitative comparisons of microorganisms in different samples as well as for identifying individual microorganisms. The quantitative polymerase chain reaction (qPCR) method yields relative or absolute numbers of total microorganisms in a sample. Microbiologists have recognized early on that the vast majority of microbial species do not currently grow in laboratory cultures because these culture tests do not reflect the true conditions within wells, pipelines, tanks. Thus, laboratory culture tests underestimate the bio-complexity of microbial communities. The purpose of this research is to apply modern molecular biology techniques to investigate the microbial species found in oil and gas pipelines and then to determine by electrochemical techniques which bacteria and at which environmental condition (temperature, pressure, gas and brine composition, presence of oil) corrosion of pipelines increases. The research results will contribute to new and improved ways to detect, monitor, and control microbial corrosion of pipelines.
Current Research To be Started Soon at SET Lab
Several microorganisms are known to be present in oilfield operations: (1) metal-reducing bacteria (MRB), (2) metal-depositing bacteria (MDB), (3) slime-producing bacteria, (4) acid-producing bacteria (APB) and (5) sulfate-reducing bacteria (SRB). The current thinking in the oil and gas industry is that only one microorganism – SRB – is the important contributor to corrosion in the field because it produces hydrogen sulfide which accelerates localized corrosion and sour oil reservoirs. New studies have shown that the presence of microorganisms affects the corrosion reactions by forming a biofilm on the metal surface. MIC is most likely not the result of one single organism acting by one mechanism; rather, it is a result of a consortium of different microorganisms acting via different mechanisms. Several other microorganisms other than SRB produce sulfide [13] and must also be taken into account.
The goal of this research is to produce general guidelines to predict the environmental conditions that are more susceptible to MIC. This will be achieved by first testing the growth pattern of microorganisms found in oilfield system in several environmental conditions typical of oilfield pipelines instead of standard culture broth. This first step will be followed by testing the corrosivity toward metals of single bacteria or group of bacteria under conditions that are most conductive to their growth and possible impact on metals. The factors to be studied will be temperature, brine composition, gas composition and presence of oil.
Phase I – Microbiology
The first phase will rely on microbiology to determine the growth pattern for single bacteria in several environmental conditions typical to field conditions. The results will indicate whether specific bacteria may be a factor in the corrosion of steels. Monitoring of the growth will be made using both classical vial culture and modern biomolecular method qPCR. Combinations of bacteria which are compatible with each other in a sense that the waste of one is used as a nutrient for the other will also be tested and the formation of any biofilm will be monitored. Field environmental conditions which are found conductive to growth of bacteria will be tested by electrochemistry in Phase II.
Phase II – Electrochemistry
The second phase will rely on several electrochemical techniques such as open circuit potential (OCP), linear polarization resistance (LPR), electrochemical noise and anodic polarization scans because the effect of bacteria changes corrosion from a general thinning of the steel, which is easy to predict, to localized corrosion pits, which are still unpredictable, and the electrochemical techniques are very fast at detecting these changes. Any metal exposed to an environment stabilize at a constant potential called open circuit potential (OCP). The rise of OCP may result from the low redox potential, which is produced by the bacteria in their initial development. The linear polarization resistance (LPR) technique consist of polarizing the electrode in a small range of potential (-20 mv to +20 mv from the open circuit potential). The slope of the current versus voltage curve is directly proportional to corrosion rate. LPR measurement is very rapid in the range of 2 minutes. Typically, the corrosion rate versus time without bacteria is compared to that with the bacteria to determine any significant changes. Electrochemical noise is a technique where current and potential are monitored continuously at the microsecond level. Increases in noise typically indicate an increase in initiation of pitting. The first three electrochemical techniques do not introduce any change in the electrode and do not disturb the system under study. The anodic polarization scan includes polarizing the working electrode anodically with a linear voltage ramp (up to 2.0 Volts) relative to a reference electrode and monitoring the current response. Shapes of the anodic scans corresponding to different forms of corrosion behavior of the materials and help determine a pitting potential which is the potential at which the current begin to increase dramatically. A lowering of the pitting potential may indicate actions by bacteria.
Phase III – Long-Term Corrosion Testing
Electrochemical techniques are powerful techniques to determine susceptibility to corrosion. However to validate the electrochemical results, longer exposures are needed because localized corrosion, especially pitting resulting from bacteria activity, requires at least two week to initiate and growth to a size large enough to be detected on metal surfaces. Thus, long-term experiments will be performed at conditions found to be severe from Phase II to check if pitting actually form or just initiate but never grow to a depth enough to perforate the whole thickness of a pipe.
Phase IV – Other Areas of Research
The results of this initial area of research can provide opportunities for developing:
- Next generation of sensors and detectors for bacteria responsible for MIC
- Rapid, reliable, automated chemical and biodetection
- Field-ready devices: compatibility/reliability/scalability
- New chemicals for MIC treatment in the field
References
[1] – Koch, G. H., et al “Corrosion costs and preventive strategies in the United States”. FHWARD-01-156. Federal Highway Administration, Washington, D.C. 2001 http://www.corrosioncost.com/.
[2] – Teng, F., Y.T. Guan, W.P. Zhu, “Effect of biofilm on Cast Iron Pipe Corrosion in Drinking Water Distribution System: Corrosion Scales Characterization and Microbial Community Structure Investigation”, Corrosion Science 50 (2008) 2816–2823.
[3] – S.W. Borenstein, “Microbiologically Influenced Corrosion Handbook”, Woodhead, Cambridge, 1994.
[4] – J.M. Odom, Industrial and environmental concerns with sulfate-reducing bacteria, ASM News 56 (1990) 437–476.
[5] – Miller, J.D.A., “Microbial Biodeterioration”, Academic Press, New York, 1981, pp. 149–202.
[6] – Wade, S.A. et al, “Investigation of the Potential for MIC in the Bilge Waters of Australian Naval Vessels”, CORROSION/09 Conference, Paper #09399, NACE International , Houston, Texas, 2009.
[7] – National Bureau of Standards. “Economic Effects on Metallic Corrosion in the United States”. NBS special publication 5 11 -1. Nat. Bur. Stands., Washington. 1978.
[8] – Strickland, L. N.; Fortnum, R. T.; Du Bose, B. W., “A Case History of Microbiologically Influenced Corrosion in the Lost Hills Oilfield, Ken County, California.” Microbiologically Induced Corrosion of Oil and Gas Production Systems. pp. 41- 60, NACE International, Houston, TX 1996.
[9] – Videla, H. A.; Freitas, M. M. S.; Araujo, M. R. (1989). “Corrosion and Biofouling Studies in Brazilian Offshore Seawater Injection Systems.” CORROSION/89 Conference, Paper No. 191, NACE International, Houston, TX 1989.
[10] – Luo, J. S.; Angell, P.; White, D. C; Vance. “MIC of mild steel in oilfield produced water.” CORROSION /94 Conference. Paper No. 265, NACE International, Houston, TX 1994.
[11] – “BP to Shutdown Prudhoe Bay Oil Field”, Press Release August 7, 2006, http://www.bp.com/genericarticle.do?categoryId=2012968&contentId=7020563.
[12] – Vargas-Avila, M.M.et al, “Corrosion Behavior of Duplex Stainless Steels in Marine Media Containing Sulfate Reducing Bacteria. – A Laboratory Study.”, CORROSION /09 Conference, Paper #09388, NACE International , Houston, Texas, 2009.
[13] – Larsen, Jan and Ketil Sørensen, “Significance of Troublesome Sulfate-Reducing Prokaryotes (SRP) in Oil Field Systems”, CORROSION /09 Conference, Paper #09389, NACE International , Houston, Texas, 2009.