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Electric Power Generating - Fossil & Nuclear
Microbiologically-related problems—including biofouling, deposition, and microbiologically influenced corrosion (MIC)—occur in many aspects of the electric power generating (EPG) industry. These problems often compromise the function and integrity of system components by interfering with fluid flow, reducing heat exchange rates, plugging filters, and, in some instances, causing component failures due to blockage or leaks. From heat exchange devices to nuclear waste storage facilities to ultrapure water-utilizing devices, microbiologically-related problems affect a wide range of EPG systems and system components.
Why EPG Facilities Experience Microbiologically-Related Problems
Cooling systems in most EPG facilities often experience such problems due to the use of large quantities of surface waters which contain MIC-related microbes—including aerobes, slime formers, iron-related bacteria, anaerobes, organic acid-producing bacteria, and sulfate-reducing bacteria (which produce corrosive sulfides and consume hydrogen)—and chemical factors capable of promoting corrosion, including MIC. In addition, most EPG facilities are limited in the amount of disinfectant which can be used to treat cooling and process waters. However, those microbes which cause biofouling (slimes), deposition, and MIC are poorly controlled by the levels of disinfectants that are allowed.
Microbiologically-Related Problems Experienced in EPG Systems
EPG systems may experience a variety of microbially-related problems. Many times, these problems occur simultaneously in an affected system and may not affect all systems uniformly, due to differences in environmental, operational, chemical, and biological factors. These microbial problems include:
1. Biofouling of system waters due to biofilms.
Biofilms (also called slimes), which are formed by microbial communities—in most cases composed of many different types of microbes (e.g., aerobic, slime-forming, anaerobic, acid-producing, iron- and manganese-depositing bacteria, molds, and sulfate-reducing bacteria)—attach to surfaces in contact with non-treated or inadequately treated waters. Biofilms are an early indicator of microbial activity.
2. Interference with fluid flow, reduced heat exchange rates, and plugging of filters due to deposition.
Over time, biofilms grow in thickness and areal extent due to microbes depositing iron and manganese and producing anions (such as chlorides). Biofilms mature by collecting more types of microbes (and, therefore, more biochemical reactions) and non-biological materials (e.g., sand, debris, organic and inorganic materials) and form deposits. Discrete deposits indicate microbial activity.
3. Compromise of integrity of system components due to under-deposit pitting-type corrosion.
Once deposits are established, and given the right environmental conditions, microbial metabolic by-products—such as organic and inorganic acids, hydrogen, carbon dioxide, sulfides, and ammonia—accumulate within the deposits due to the activities of microbes and other chemical reactions. These metabolic by-products corrode the underlying metal and often lead to rapid under-deposit pitting-type corrosion beneath the deposits. This type of corrosion is a telltale sign of MIC. Microbes can both initiate corrosion and accelerate any existing corrosion.
4. Component failures due to under-deposit leaks.
Once corrosion and MIC advance to the stage of under-deposit pitting corrosion, the metabolic by-products in deposits corrode the underlying metal until leaks develop under the deposits. Pinhole leaks are another telltale sign of MIC.
5. Damage to coatings and destruction of underlying metal due to microbial activities.
Microbes enter holidays in protective coatings in pipes and storage facilities. Once established, microbial production and accumulation of corrosive materials under the coating (and next to the metal surface) causes further disbonding of the coating, allowing damage to the coating and underlying metal to spread and proceed at very rapid rates. The disbondment acts to trap and concentrate microbes and corrosive materials next to the metal surface, causing even faster corrosion to occur. Since this occurs under the coating, the site is not protected by cathodic protection and cannot be treated using corrosion inhibitors and biocides. These problems can occur on the inside or outside of equipment.
Most metals and alloys, except titanium, are rapidly attacked by MIC under some conditions in facilities using potable water. Thousands of cases of MIC in facilities across North America using potable water have been reported and investigated—many by BTI Products. These cases have involved steel, stainless steels, aluminum, copper, and galvanized steel (see documents prepared by Dr. Dan Pope of BTI Products for Electric Power Research Institute under “Further Reading,” below).
Many cases of MIC in potable water and fire protection systems in homes, office buildings, and commercial facilities have resulted in pinhole leaks within months of construction. Many cases involved stainless steel components used to process potable water, especially filtration equipment. Most of the severe pitting in stainless steels is seen in welds and heat-affected zones (HAZ), although we have seen a few cases where whole pieces of stainless steel were affected.
Austenitic stainless steels, which are very common in nuclear facilities, suffer from very rapid MIC under certain conditions. In fact, stainless steel water box and pipe—both up to 3/4 inch thick— have been completely penetrated by MIC in three months!1 However, most MIC of stainless steels occurs in field (circumferential) welds and associated HAZ.
Although still susceptible to MIC, fewer cases of MIC have been seen in cast iron and ductile iron.
The following EPG facility systems are all potentially susceptible to biofouling, deposition, and MIC:
Heat exchange devices
Storage tanks (including water and fuel tanks)
Nuclear waste storage facilities
Ultrapure water-utilizing devices
Fire protection systems
Whether this “MIC potential” progresses to rapid and severe MIC-type corrosion depends on local conditions—even in the same “system”—over time.
Diagnostic Products for EPG Industry Systems
BTI Products offers test kits designed specifically for diagnosis of microbial problems in EPG industry systems. Our test kits provide microbiological, chemical, and site-specific information important in diagnosis of microbial and other problems and in the design of treatment and prevention strategies. BTI Products and its EPG clients use BTI Products test kits to investigate MIC and design effective treatment programs.
BTI Products kits can be used for all types of samples—including those containing water, particulates, corrosion products, hydrocarbons, and/or other materials. BTI Products test kits are designed to test for MIC-related microbes in samples from freezing to boiling temperatures and from a wide variety of salinities (from fresh water to sea water or production brines). They can be used to test for MIC-related microbes in almost all real-world samples and, most importantly, can be used by untrained industry personnel, on-site, to obtain accurate and pertinent data quickly and inexpensively.2
Recommended Diagnostic Test Kits
MICkit® 4 to test locations using cathodic protection or coatings for chemistries important in corrosion diagnosis and treatment
MICkit® 5 to test EPG facilities for microbes involved in biofouling, deposition, and MIC
MICkit® Comprehensive to test EPG facilities for microbes and chemical parameters involved in biofouling, deposition, MIC, and other forms of corrosion
MICkit® Pipe Inspection Kit to physically inspect pipes in systems that have tested positive for MIC-related bacteria and/or systems with a history of leaks/failures
MICkit® FPS to specifically test fire protection systems for microbes and chemical parameters involved in MIC
MIPkit™ FPS to specifically test fire protection systems for the most common microbes and chemical parameters involved in MIC
Diagnostic & Mitigation Services for EPG Industry Systems
BTI Products can also assist in evaluation of samples, test data, field-site investigations, and design and implementation of mitigation measures. BTI Products performs and supports research and testing programs related to causes, prevention, and treatment of microbial problems for individual clients.
Hayner, G.O., D.H. Pope, and M.D. Clary. 1987. “Microbiologically Influenced Corrosion in the Condenser Water Boxes at Crystal River-3.” In Proceedings of the Third International Symposium on Environmental Degradation of Materials in Nuclear Power Systems-Water Reactors.
Scott, P.J.B. and M. Davies. 1992. Survey of field kits for sulfate reducing bacteria. Materials Performance, May, 64-67.
For more detailed information on MIC in EPG facilities, please refer to the following publications:
Pope, D.H., D.M. Dziewulski, and J.F. Kramer. 1989. “Microbiological Aspects of Microbiologically Influenced Corrosion.” In Microbial Corrosion: 1988 Workshop Proceedings, ER-6345, Research Project 8000-26, edited by George Licina. Palo Alto: Electric Power Research Institute.
Soracco, R.J., D.H. Pope, J. Eggers, and T. Effinger. 1988. Microbiologically influenced corrosion investigations in electric power generating stations. Corrosion/88, paper no. 83.
Pope, Daniel H. 1987. Microbiologically Influenced Corrosion in Fossil Fueled Electric Generating Plants and a Practical Guide for the Investigation, Treatment and Prevention of MIC in Such Facilities. Palo Alto: Electric Power Research Institute.
Pope, Daniel H. 1987. “Microbiologically Influenced Corrosion in Nuclear Generating Facilities.” In Proceedings of Symposium on Nuclear Power Plant Chemistry. Traverse City, Mich., July 1987. Palo Alto: Electric Power Research Institute.
Pope, Daniel H. 1986. Microbiologically Influenced Corrosion in the Nuclear Power Industry. Palo Alto: Electric Power Research Institute.
Pope, Daniel H. 1986. “Microbiologically Influenced Corrosion: Detection, Treatment and Prevention.” In Proceedings of Electric Power Research Institute Condenser Biofouling Control Symposium, May 1985. Palo Alto: Electric Power Research Institute.
Pope, Daniel H. 1986. “Microbiologically Influenced Corrosion: in U.S. Industries: Detection and Prevention.” In Proceedings of Conicet-N.S.F., U.S.-Argentine Workshop on Biodeterioration.
For routine analysis once problematic bacteria have been identified using the MICkit® 3, MICkit® 5, or MICkit® Comprehensive.
Use to enumerate viable bacteria belonging to any two groups. You choose the organisms you wish to test for.
Ideal for all industrial systems that have identified problematic bacteria.
May be used with BTI Products’ MICkit® 4 when chemical information is also needed.
For initial analysis of samples to aid in diagnosing MIC and other corrosion problems.
Use in situations where aerobic conditions predominate and/or low nutrient conditions are present.
Ideal for most industrial applications including: industrial and potable water supplies, cooling waters, nuclear power, hydro-power, cutting and hydraulic fluids, fuels, and samples from external portions of oil and gas facilities.
For initial analysis of samples from FPS and water-related industries for the most common bacteria and chemical factors involved in MIC of FPS.
An economical way to test for the most common bacteria and chemical factors involved in MIC of FPS. Information obtained using this kit is also important in choosing an effective and safe cleaning/treatment package.
Use to test samples from FPS, cooling systems, and other systems using potable or industrial waters.