Microbiologic Corrosion (MIC)

There are several types of corrosion that can form in sprinkler pipe. When a pipe is leaking you cannot automatically assume the cause is Microbiologic corrosion (commonly referred to as “MIC”). The following is a list of common corrosions:

  • Galvanic Corrosion
  • MIC Corrosion
  • Localized Corrosion
  • Erosion Corrosion
  • Environmental Corrosion
  • Crevice Corrosion

I will be focusing on the form of corrosion commonly referred to as MIC. While there are visual similarities between the aforementioned corrosions there are some key signs of MIC in fire sprinkler systems. I remember when I was an apprentice in the early 90’s working on a job in San Antonio. One morning there were several “scientific- looking” guys waiting for us to drain down a sprinkler system. My foreman asked one of them what they were doing. The “scientist” said they were taking samples of the water to see what was in it that may be causing the pinholes to appear in the sprinkler piping. My foreman instructed me to go inside and open the two inch drain slowly so they could get their sample. When I returned I could hear my foreman telling the scientist, “there’s nothing in there.” As he poured out the last bit of his coffee he filled his cup with the water coming out of the drain. Then turning it up, he chugged it. I know what you’re thinking…. and yes, he’s still alive today. But I would not suggest doing this. We have other ways of testing in the 21st century. There are test kits available where you take a sample of the water and send it to a lab for testing. This is the simplest to verify a system has MIC. Here are the key signs of MIC:

  • Pinhole Leaks
  • Obstructions (decrease in flow rate)
  • Black or red water
  • Rotten egg smell
  • Tubercles or deposits
  • Exterior rusting and condensation

MIC is used to designate the corrosion due to the presence and activities of microorganisms, including microalgae, bacteria and fungi. Simply put, there are organisms living in the pipe that are causing the corrosion. MIC has been found in 45 states throughout theU.S.Consequently, the chances of it being found in your area are great. Totally eliminating corrosion is impossible. However, the following provide ways to slow the process:

  • Eliminate the bacteria
  • Eliminate the oxygen
  • Eliminate the water

Now comes the “how to” section.

Let’s start with eliminating the bacteria. There are two main types of chemicals used in fire sprinkler systems. These include:

  • Biocides – Used to kill MIC. Normally toxic. Will kill all of the bacteria in the system. Drawbacks include: it is toxic, bacteria can become immune to it and it
    is only for wet systems.
  • Dynamic Biostatic Inhibitors – Protects the pipe walls, offers generalized corrosion protection, often non-hazardous and usually have biocidal properties.

For obvious reasons the inhibitors are the best way to go. They may not kill the bacteria but the product is not toxic. Be sure to check for back flow requirements in your area. The inhibitor is simply injected into the water supply as you fill the system. There are several different companies and units used to accomplish this. The unit I prefer is made by Potter. It comes with a pump and two 15 gallon tanks. (Potter is also a great source of information with brochures to aid in selling the system). The pump and tanks come in a self-contained cabinet with a stainless steel braided hose to connect to the sprinkler system. A qualified electrician will be required to connect the pump power supply.

Next, we need to eliminate the oxygen. This is not easy. If possible you will need to eliminate any areas of the system that trap air. These areas may be due to an offset in the piping. Where it is impossible to do this, an automatic air vent will need to be installed. As with the chemical delivery system there are several from which to choose. Their basic function is to release the air as the system is being filled and shutting off as soon as the water hits it. It is similar to the air vent on a fire pump casing.

Finally, eliminate the water. Unless you can change the wet system to a dry system this is close to impossible. Even if you could, you would have the same problems because no dry system is totally dry. If you tried this method you would then be faced with using a nitrogen generating system.

Once you install the inhibitor injection system, introduce the inhibitor into the wet system and vent the trapped air as much as possible; the only thing left to do is install a corrosion monitoring station. This is a unit in which we can make the conditions perfect for MIC and monitor it through site glasses and corrosion coupons. This is how you can tell you are making a difference in the sprinkler system. This monitoring station should be installed at the riser.

In closing, I would recommend that salesmen do a little research on this before talking to your customers. Put your presentation together, go in with confidence and make your pitch. More and more customers are becoming familiar with this and they are looking for an expert o help them. American Fire Protection Group is that expert!  Contact us today!

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