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Microbiologically Influenced Corrosion (MIC) in Automatic Sprinkler Systems

December 17, 2012

Sprinkler pipingOver the past several decades, microbiologically influenced corrosion (MIC) has been an increasingly frequent problem for owners of both wet and dry automatic sprinkler systems. MIC occurs when bacterial microbes accelerate the natural corrosion (rusting) of metal piping, causing pin holes, accumulation of sediment, and obstructions within the systems.  The presence of oxygen, metal, nutrient-rich water, and minerals within sprinkler systems creates a perfect environment for bacterial microbes to thrive. This can result in decreased water flow and even complete system failure due to blockage in the event of a fire.

Utility companies had been dealing with the effects of MIC for decades before fire protection professionals began taking notice of the problem. This newfound attention is due to a dramatic increase in corrosion leaks in systems under ten years old since the 1990s. Leaks have even been reported in systems less than two years old.

Factors such as, the introduction of thin-walled (Schedule 5 and Schedule 10) piping in the 1980s, changes in the chemicals used by water treatment facilities in the 80s and 90s, the proliferation of electroplating, an increased awareness of MIC, and the rising number of buildings with sprinkler systems all contribute to the sharp increase in reported cases of MIC.

If caught early, sprinkler systems can be treated or repaired before serious damage occurs, but when left untreated, the resulting damage can be very costly, in some cases requiring that the entire system be replaced. Here are some preventative measures that can be taken to help mitigate damages caused by MIC:

  • New sprinkler systems can be flushed with a detergent to remove any oils or debris left on the interior of the pipe. This is easier done with some types of systems than others, so if possible, address the issue with the sprinkler designer before the system is designed.
  • The initial fill in a new system can be treated with biocides and corrosion inhibitors. These additives can also be included when an existing system is refilled after annual maintenance.
  • Try to schedule any modifications, repairs, and maintenance of the system to be done at the same time to reduce the number of times the system has to be drained and refilled. When fresh water and oxygen is introduced into the system it provides a new food source for bacteria, causing an acceleration of growth.
  • Know what to look for. Leeks, weeping joints, and water that is smelly or black when the system is flushed are all indications that you may have MIC.
  • If you live in an area that is prone to MIC and are having a new system installed, consider using thick-walled piping. Whether your system is new or existing, schedule regular MIC inspections.

The presence of MIC is generally determined through water testing, testing of metallurgical properties, and x-ray diffraction tests. However, bacterial microbes are found in all sprinkler systems, so don’t rely solely on the results of water testing.

If it is determined that MIC is present, there are several procedures and chemicals that can be used to treat it, depending on the severity and type of MIC found. Contact a fire protection professional who is familiar with MIC to find out what the appropriate treatment options are for your system.


Learn more about Inspections issues.


Article by: April LaRita Green


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