American Fire Protection Group, Inc. (AFPG) is the expert when it comes to detecting and identifying Microbiologic Corrosion in fire sprinkler systems. There are several types of corrosion that can form in sprinkler pipe.
Microbiologic Corrosion (MIC)
When a pipe is leaking, it cannot be automatically assumed that 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
Signs of MIC in sprinkler systems
There are some key signs of Microbiologic Corrosion (MIC) in fire sprinkler systems
While there are visual similarities between the aforementioned corrosions, there are some key signs of Microbiologic Corrosion (MIC) in fire sprinkler systems. There are test kits available where one can take a sample of the water and send it to a lab for testing. This is the simplest way to verify a system has MIC. Mentioned below are the key signs of Microbiologic Corrosion:
- Pinhole Leaks
- Obstructions (decrease in flow rate)
- Black or red water
- Rotten egg smell
- Tubercles or deposits
- Exterior rusting and condensation
Corrosion caused by microorganisms
Microbiologic Corrosion 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 the United States of America. Consequently, the chances of it being found in any particular area are great. Totally eliminating corrosion is impossible. However, listed below are few ways to slow the process of Microbiologic Corrosion.
- Eliminate the bacteria
- Eliminate the oxygen
- Eliminate the water
Now comes the ‘how to’ section.
Eliminating the bacteria
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 sprinkler 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 the area. The inhibitor is simply injected into the water supply at the time of filling the system. There are several different companies and units used to accomplish this.
An example is a Potter unit that 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.
Eliminate the oxygen
The next way of deterring Microbiologic Corrosion is by eliminating the oxygen
The next way of deterring Microbiologic Corrosion is by eliminating the oxygen. This is not easy. If possible, it might by important 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.
Eliminate the water
Finally, eliminate the water. Unless it is possible to change the wet system to a dry system, this is close to impossible. Even if it was possible, they would have the same problems because no dry system is totally dry. On top of that, this method can only be carried out using a nitrogen generating system.
Once the inhibitor injection system is installed, the inhibitor has to be introduced into the wet system and vent the trapped air as much as possible. Then, the only thing left to do is installing a corrosion monitoring station.
Installing corrosion monitoring station
A corrosion monitoring station is a unit in which the conditions can be altered to make it perfect for MIC and monitor it through site glasses and corrosion coupons. This is vital in making a difference in the sprinkler system. This monitoring station should be installed at the riser to get the optimal results.