MIC is a mode of corrosion initiated by microbes that react with metallic materials and cause their deterioration.
What causes MIC?
MIC is caused by bacterial microbes in combination with four other conditions: metals, nutrients, water, and oxygen. Some types of bacteria need only very small amounts of oxygen. These bacteria are present in the environment and piping materials. When all of these environmental conditions are present, microbial growth will occur. As the nutrients in the system are consumed, the microbes become dormant. When nutrients and oxygen, are replenished, the microbial growth resumes. Sources of this replenishment include: flow testing, draining and refilling of systems, addition of water to replenish losses from leaks or maintenance, or the periodic filling of dry fire sprinkler systems for testing.
What happens if MIC is present in pipes?
As MIC bacteria grow, consumption of the metal
in the pipe occurs. Pitting is a likely effect and
the walls of the pipe may be penetrated. The
flow characteristics of the pipes are degraded and loose scale or rust plug sprinklers and
Why should testing for MIC be done?
NFPA 25 requires an obstruction inspection every 5 years or when there is evidence of rust, foreign debris, untreated water or pinhole leaks. Further, it requires that if any tubercles or slimes are observed, they shall be tested for indications of MIC. (NFPA 25-2002 Section 188.8.131.52)
If the building has a dry sprinkler system, can there be a problem with MIC?
In many cases, MIC has been found to have progressed more rapidly in "dry" systems than in wet systems. After a system is flushed or used, stagnant water remains in the fitting edges, drops, and in slight dips in horizontal lengths of pipes. MIC bacteria tend to find more favorable growth conditions in oxygenated stagnant water.