What is MIC
MIC is caused by bacteria that form biofilms on the interior surfaces of pipes, creating localized environments that accelerate corrosion. The byproducts of their metabolic processes, such as acids and sulfides, directly attack the metal, leading to pitting, tuberculation, and eventual pipe failure.
Why it Matters
Localized Damage
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 systems replacements without accurately assessing the actual extent of damage.
Early Detection
Detection tools such as video scoping (utilizing serpentine borescopes) help to visualize internal pipe conditions and substantiate the scope of infections and potential impairments.
Targeted Repairs
Targeted repairs or partial piping replacement are most often sufficient when identified in a timely manner.
How MIC Develops
Aerobic vs. Anaerobic MIC
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 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.
How Bacteria Enters the System
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.
Don’t Flush!
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.
Warning Signs
Corrosion is cumulative: It worsens over time and becomes increasingly aggressive, especially in piping with poor drainage or by frequent oxygen introduction, such as draining and refilling the system with fresh water.
The most corrosive byproducts: f bacterial activity are Hydrochloric Acid (HCl) and Hydrogen Sulfide (H₂S). Once bacterial colonies begin to form on the sides of the pipe walls they will grow in density and number of layers as biofilms create scale and pockets of trapped HCl and H₂S, which often manifest as tubercules, which are barnicle-like bumps on the piping. These are the “hot-spots” where pinhole leaks usually start, which is the first visual cue that there’s something wrong in the piping.
Both wet and dry fire sprinkler systems are susceptible to corrosion, but MIC targets wet systems, as the water-filled piping provides a controlled and hospitable environment for bacteria. What makes bacterial infections more persistent than other sources of corrosion is that the bacteria known to cause MIC can metabolize with (aerobic) and without (anaerobic) oxygen, whereas the other types of corrosion only occur in the presence of oxygen.
Tubercules are warning signs: These barnacle-like bumps on the piping are “hot-spots” where pinhole leaks usually start, which is the first visual cue that there’s something wrong in the piping.
Common Risk Factors
Thin Wall Piping
Use of Schedule 7 piping, which can be 30% thinner walled than Schedule 10 and 45% less than Schedule 40, significantly increases vulnerability to corrosion.
Frequent Draining
Draining a sprinkler system for testing and maintenance will introduce fresh nutrients in the water supply when the system is re-filled and put back into service
Elevation Differences
Sprinkler systems that contain branch lines ar varying elevations will often lead to air pockets at the highest points in the system. These air pockets will act as a breeding ground for MIC.
Poor Air Release
For decades, the codes and standards governing the installation of fire sprinkler systems did not address MIC prevention, and no means of air release was required. Refilling a system that does not have a means of alleviating trapped air will foster pockets of oxygen-rich atmospheric air, which accelerates bacterial activity.
What You Can Do
Testing for MIC
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.
3-Step Program
Corrosolve employs a comprehensive, stepped approach 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.