When you think of a fire sprinkler failing the periodical testing as required by NFPA 25 and performed by Dyne Fire Protection Labs, you may assume it is because the glass bulb or soldered release mechanism didn’t activate in time or at all.  However, that can be quite rare especially in the case of a glass bulb.  The actual number one cause of a failure for a sprinkler tested here at Dyne is due to the water seal not releasing as intended.  After being exposed to a specified flow and temperature, the release mechanism has activated just fine but the water seal still remains attached to the sprinkler.  What causes this to happen?  By far the top reason is because of corrosion.  Corrosion, both external and internal, can fuse a water seal to the frame.  This is why NFPA 25 also states that during your floor level inspection, you are to replace any sprinkler that shows signs of corrosion that is detrimental to performance.  Other articles and videos by Dyne in the past have given examples of when corrosion is detrimental to assist in making this very difficult judgment call.  However, we haven’t discussed what causes that corrosion and if there are ways to prevent it – until now.  Let’s break it down into external and internal corrosion.

External Corrosion

Corrosive environments can wreak havoc on your sprinklers.  Examples of corrosive and harsh environments can be found in the annex of NFPA 25. To help prevent corrosion in these environments, different sprinkler finishes are available from sprinkler manufacturers that may increase corrosion resistance.   Generally, your ordinary brass sprinkler is the worst for this type of environment with chrome being only slightly better.  For corrosive environments, various wax coated sprinklers or even stainless steel designs are recommended.  Manufacturers will be able to provide you with data on various sprinkler finishes and their amount of corrosion resistance.  Note that corrosion resistance does not mean corrosion proof.

Another source of external corrosion actually arises from human error.  During installation, it is very important to follow the installation instructions and pay careful attention to the amount of torque applied to the sprinkler.  Overtightening of the sprinkler can actually put stress on the frame, possibly distorting it so that the water seal no longer adequately covers the opening. This may cause leaking.  Think of a round copper gasket trying to now cover an oblong hole.  If you come across a sprinkler where the corrosion is isolated to or originating from the water seal (Figure 1), you have a good candidate for an overtightened sprinkler.

Figure 1: Sprinkler with corrosion originating around the water seal.  Overtightening of the sprinkler may be to blame.

Internal Corrosion

There have also been many times where a sprinkler looks great from a floor level inspection but when we get it in the lab, the water seal won’t release.  In this situation, internal corrosion may be to blame.  Flushing a system for maintenance will replenish oxygen and air pockets within the system which could create great conditions for corrosion to occur.  It is therefore important to understand your water supply.  Each fire suppression system can be different and the avenues for corrosion may not be the same from system to system in a building or even within a single system.  Luckily, there are several companies that specialize in corrosion and even focus on water based fire suppression systems.  You may consider seeking guidance from such companies if corrosion has been an issue in the past or if you are trying to prevent the issue ahead of time.

It is also important to note in this section that not all sprinkler water seal designs are made equal.  O-ring water seals on sprinklers, which haven’t been used in a UL listed sprinkler in over 15 years and were the cause of many voluntary recalls/replacement programs, are notorious for not releasing.  As you can see in Figure 2, the O-ring design allowed a lot of contact with the frame compared to the copper gasket and Belleville spring designs.  The metals can fuse together as the sprinkler corrodes making releasing more difficult.  Sprinklers with a copper gasket or the newer Belleville spring design have better track records to date.

Figure 2: (Left to right) Example of a Belleville spring, O-ring, and copper gasket water seal
that could be found on a fire sprinkler.  

Understanding corrosion’s impact on the performance of a sprinkler and how that corrosion came to be will give you an advantage on maintaining your sprinklers.  Should you need any more information regarding this topic, please contact Dyne Fire Protection Labs at (800)632-2304 or lab@dyneusa.com.

©Dyne Fire Protection Labs 2018