Click here for a printable version of this article.

April 2000: Microbiologically Influenced Corrosion (MIC)

In 1996 the NFPA began receiving inquiries about MIC. What is MIC? MIC is a corrosion problem characterized by pinhole leaks in metallic piping systems often after only a few years of service. MIC is a distinct type of corrosion which microscopic organisms called tubercles, nodules and microbes influence the corrosion on the inside of sprinkler piping. Since 1996 the sprinkler industry has begun to recognize that these living organisms along with tuberculation and corrosion, threaten most sprinkler piping including carbon steel, galvanized and copper tube. MIC affects both wet and dry sprinkler systems.

In April 1997 NFPA 13, Installation of Sprinkler Systems, (9-1.5) added a provision for testing and treatment of water supplies known to have contributed to MIC. Also NFPA 25, Standard for the Inspection, Testing and Maintenance of Water-Based Fire Protection Systems, (Appendix A) now provides detailed information on MIC.

The recommended method for detecting MIC is to consult with a biological and metallurgical laboratory. Some biological and metallurgical laboratories provide test kits for detection, and provide over-the-phone consultation. Some laboratories also allow contractors to bottle water from the infected environment and mail it for testing. These laboratories then notify the contractor with the test results regarding the type of MIC and how to treat it properly.

Where applicable, critical areas such as those occupied by energized equipment have been addressed by removing overhead sprinkler piping and limiting leak exposures by using sidewall sprinkler coverage. While these efforts provide some immediate help they do not address the root cause of the problem.

Several additives and treatments directed at cleaning or flushing the MIC from the sprinkler piping have been introduced recently. The treatments are more directed at eliminating the MIC bacteria from the water supply by using chemicals. Other treatments seek to combine sterilization techniques along with chemical treatment.

Aside from the pinhole leaks that MIC creates, the tubercles, nodules and microbes located on the interior of sprinkler piping are a major concern. MIC is a corrosion problem that the fire sprinkler industry cannot ignore. MIC has the capability to significantly lower the reliability factor of sprinkler systems and must be properly addressed to maintain the excellent performance history of automatic sprinkler systems.