NFPA 25 Commentary and Supplementary Information

(Insert NFPA Copyright legalese here) Any sprinkler that shows signs of any of the following shall be replaced:
(1) Leakage
(2)* Corrosion
(3) Physical damage
(4) Loss of fluid in the glass bulb heat-responsive element
(5)* Loading
(6) Painting unless painted by the sprinkler manufacturer
A. Corrosion found on the seat, or built up on the deflector that could affect the spray pattern, or a buildup on the operating elements that could affect the operation can have a detrimental effect on the performance of the sprinkler. Light surface corrosion on the boss, frame arms, and/or the deflector, and/or surface discoloration, not impacting the operation of the sprinkler should not warrant replacement. A degree of judgment should be exercised in the determination of the extent, location, and character of corrosion that would necessitate replacement.
A. In lieu of replacing sprinklers that are loaded with a coating of dust, it is permitted to clean sprinklers with compressed air or by a vacuum provided that the equipment does not touch the sprinkler.

“Are there situations in which sprinklers can be cleaned of foreign material instead of being replaced?”

Sprinklers that have a light coating of dust or dirt can be cleaned with a vacuum or a blast of compressed air, and they can remain in place, provided the sprinklers are not touched or agitated in the process.  A sprinkler covered with some dust and cobwebs could be cleaned with a vacuum or compressed air. However, if the vacuum or compressed air does not clear the debris, the sprinkler would need to be replaced. Under no circumstances should sprinklers be cleaned with bleach, ammonia, or any other household cleaner. Furthermore, attempting to remove paint with a razor blade or utility knife can further compromise the device and is not permitted. Sprinklers that are heavily loaded with any contaminant such as dirt, dust, grease, or paint must be replaced. Painted sprinklers are never permitted to be cleaned and/or reinstalled, because the potential of damaging the assembly is too great. A “light” overspray or loading can be tolerated when a representative sample is tested to verify that the sprinklers will operate as intended (see A.  Sprinklers that are leaking or that have been damaged must be replaced without testing. Dissolved minerals and other residues in the water can solidify as the sprinkler leaks, hampering  the operation of the sprinkler by changing internal clearances or acting like an adhesive, preventing parts from moving as intended. If corrosion is a significant problem, special corrosion resistant sprinklers can be used.