Corrosion is a costly problem for sprinkler systems. It can cause leakage which can lead to impaired sprinkler systems, water damage, and eventually replacement of the entire system. This blog looks at what corrosion is, where we can find it, how it affects a sprinkler system, and how to spot and prevent it.
What is corrosion?
Generally, when we refer to corrosion we are talking about when a metal reacts with its environment which leads to deterioration of the metal. In sprinkler systems this is often when oxygen reacts with iron to form iron oxides, which we commonly refer to as "rust." This is further accelerated when it occurs in the presence of water, which helps the reaction. While this is the most common, there are other types of corrosion that can affect a sprinkler system such as microbiologically influenced corrosion (MIC) and galvanic corrosion.
For any metallic component of a sprinkler system there is both external and internal corrosion. While both of these issues can lead to system failure, internal corrosion is more difficult to detect and causes more issues. Internal corrosion usually begins to form at the air/water interface while external corrosion is more dependent on the environment.
Where does corrosion occur?
There are many locations where piping and sprinklers are more susceptible to external corrosion. Most of these locations have different elements in the atmosphere that can speed up corrosion. A few common examples include:
- Areas with fertilizer or manure (animal pens)
- Pools or areas containing pool chemicals
- Areas near the ocean that are exposed to outside salt air
- Salt storage
- Pipe is in contact with soil
- Areas with excessive moisture (steam room)
Listed corrosion resistant sprinklers and corrosion resistant piping, fittings and hangars are required to be installed in places where corrosive conditions are known. Meanwhile all pipes and fittings installed on the exterior of the building are required to be corrosion resistant.
Internal corrosion on the other hand occurs most commonly where metal, water and air are in contact with one another. This occurs in both wet and dry pipe systems. For wet pipe systems, corrosion occurs most often near the pockets of air that could be trapped in high points. For dry and preaction systems the corrosion occurs most often at the low points because that is where any residual water builds up.
How does corrosion affect a sprinkler system?
Corrosion has a detrimental effect on sprinkler systems, causing the components to fail. For piping this can take the form of pinhole leaks or having rust buildup limit the flow of water (see image below). For sprinklers, corrosion can clog the water discharge orifice, affect the deflector and discharge pattern, or completely seal the plug, preventing water from reaching the fire. Other components such as piping hangers and fittings can also be susceptible to corrosion, which can lead to further complications.
What can I do to minimize corrosion?
Completely eliminating the possibility of corrosion is nearly impossible, however there are some steps that can be taken to help reduce the amount of corrosion in a system:
- Better pipe material: When trying to delay corrosion a great place to start is looking at the material used. Certain types of piping are more resistant to corrosion, such as plastic CPVC, copper or galvanized steel. There are also benefits to using thicker piping since rust will not eat through the wall of the pipe as quickly. Using higher quality material may cost more up front but it will extend the life of the system and increase reliability.
- Corrosion resistant sprinkler: When sprinklers are installed in areas susceptible to external corrosion, they need to be corrosion resistant. This means that they need to be either made out of corrosion resistant material, covered with a special coating such as wax, or plated with a corrosion resistant metal (see image below).
- Water supply: NFPA 13, Sandard for the Installation of Sprinkler Systems, requires the water supply to be evaluated to determine if it contains any unusual corrosive properties or is likely to contain MIC. If it does, then you need to either install piping that is corrosion/MIC resistant, treat the water with water additives, implement a monitoring plan, or fill your system with nitrogen for dry or preaction systems.
- Wet Pipe: Air Venting: NFPA 13 requires a vent to be located at a high point in the system to allow air to be removed by either a manual or automatic valve. This can be a reasonable approach on wet pipe sprinkler systems to reduce corrosion activity. The purpose of the air venting valve is to exhaust as much trapped air as possible from a single location every time the system is filled, thus having less oxygen for the metal to react with.
- Dry Pipe: Drain Water Out of System: Just like how in wet pipe systems you want to remove the air out of the piping, for dry pipe or preaction systems you want to remove the water. Dry pipe and preaction systems are required to be pitched to a low point drain so that water can be removed from the system. Since most corrosion occurs at the air/water interface this will help prevent corrosion.
- Dry Pipe: Nitrogen: For dry pipe or preaction systems nitrogen can be used to fill the sprinkler piping network instead of air. When a system is filled with nitrogen it contains very little oxygen, which is a vital ingredient in the corrosion process. Nitrogen can be provided through cylinders or a nitrogen generator.
How can I spot corrosion?
Some corrosion can be easily identified while others can be hidden. During your annual floor level inspection of piping, fittings and sprinklers be sure to keep an eye out for exterior corrosion which can be identified by its orange-brown color and rough texture.
Internal corrosion is more difficult to identify during your annual inspection so an assessment of the internal condition of piping is required to be conducted every five years. Outside of that assessment, the effects of both internal and external corrosion can be seen by looking for water stains or leaking pipe where corrosion could have created pinhole leaks in your system by eating through the wall of your piping (see image below).
What do I do if I see corrosion?
When there is significant corrosion buildup that is detrimental to sprinkler system performance, that section of piping, or sprinkler needs to be replaced. If corrosion is bad enough sometimes an entire system needs to be replaced.
Addressing these issues will help ensure the reliability of your sprinkler system, increase the life expectancy of your system and in the long run save you time, energy, and money. Share your experience working on a system that was installed in a corrosive atmosphere in the comments below. What was the biggest challenge or lesson learned?
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