Understanding the science behind Microbiologically Influenced Corrosion is essential for maintaining system integrity and ensuring long-term reliability of fire protection systems.
MIC bacteria colonize silently inside piping — damage is often only discovered during inspection or after a leak.
MIC is the most intrusive and difficult to resolve of all corrosion types found in fire sprinkler systems.
With the right diagnostic tools and a consultant-driven approach, MIC can be accurately scoped and effectively controlled.
Microbiologically Influenced Corrosion (MIC) occurs when microbes form bacterial colonies inside fire sprinkler system piping. Over time, MIC can degrade or cause failure in systems such as boilers, cooling towers, heat exchangers, process piping, and fire protection systems.
It leads to premature metal failure in both wet and dry sprinkler and standpipe systems. MIC can actively or passively attack steel piping, and active infections will continue spreading unless treated. Contributing factors include pH, material defects, nutrients, temperature, low flow, and oxygen levels.
Unlike oxygen cell or cathodic corrosion, MIC is driven by living organisms. Bacteria metabolize nutrients in the water and produce corrosive byproducts that actively attack the pipe wall — and they adapt to changing conditions inside the system.
pH imbalance, material defects, available nutrients, temperature fluctuations, low flow conditions, and trapped oxygen all create environments where MIC bacteria thrive.
MIC is typically localized, meaning specific sections may experience severe degradation, but system-wide failure is rarely found. Unfortunately, the contracting community promotes high-cost system replacements without accurately assessing the actual extent of damage.
Detection tools such as video scoping (utilizing serpentine borescopes) help to visualize internal pipe conditions and substantiate the scope of infections and potential impairments.
Iron Related Bacteria (IrB) oxidize ferrous iron to ferric iron, depositing iron compounds on pipe walls. These deposits create tubercles — mound-like structures that trap corrosive conditions underneath and accelerate localized pitting. IrB are commonly found in municipal water supplies and thrive in low-flow environments inside fire sprinkler piping.
Sulfate Reducing Bacteria (SRB) are anaerobic organisms that produce hydrogen sulfide as a metabolic byproduct. This highly corrosive compound attacks steel piping directly and accelerates pitting corrosion. SRB typically colonize under IrB tubercles where oxygen is depleted — making them particularly aggressive once a biofilm has established.
Acid Producing Bacteria (APB) generate organic acids as metabolic waste products, lowering local pH at the pipe wall surface. This acidic environment dissolves the protective oxide layer on steel and accelerates metal loss. APB are often found in conjunction with IrB and SRB, compounding the overall corrosion rate.
MIC occurs when bacteria in the pipe produce corrosive byproducts that attack the pipe wall. The bacteria that cause MIC are most active in the presence of oxygen (aerobic metabolism). When oxygen is depleted in trapped air pockets, bacterial activity slows but does not stop, as they evolve into an anaerobic state and begin to break down the dissolved oxygen in the water.
If a fresh supply of oxygen is introduced, such as system refilling, water chemistry changes and bacterial activity can increase again. Corrosion damage is driven primarily by changes in water chemistry, not just the presence of bacteria alone.
Bacteria enter fire sprinkler systems through the municipal water supply during installation or refills for testing and maintenance. Once inside, they can quickly colonize and form biofilms and are resistant to removal.
I thought for many years that flushing fire sprinkler systems with fresh water removes bacteria and prevents MIC but this practice only exacerbates the problem. Fresh water introduces new oxygen and nutrients, which can revitalize anaerobic bacteria and re-energize their growth, leading to more aggressive corrosion.
Detecting MIC early and implementing the right program are the two most important steps a building owner or property manager can take to protect their fire sprinkler system.
Detecting MIC early is crucial to preventing extensive damage. Testing methods include water sampling to identify bacterial presence, internal video inspections (borescoping) to visualize corrosion and biofilm formation, and ultrasonic testing to measure pipe wall thickness and detect thinning.
Corrosolve employs a comprehensive 3 step program to diagnosing and addressing MIC. Our process includes initial water sampling, detailed internal video inspections, targeted remediation strategies, and ongoing corrosion control programs to ensure long-term system integrity.
Comprehensive assessment of water quality, system conditions, degree of impairment and scope of necessary repairs.
Removal and replacement of system piping determined to be irreparable. Chemically clean, then treat system water with corrosion inhibitor solution.
On an annual basis, inspect system conditions and conduct corrosion inhibitor solution sampling, to assure piping integrity for the life of the system.
Don't wait for a leak or a failed inspection. Contact Corrosolve to schedule a comprehensive MIC assessment and get a clear picture of your system's condition.
