Photo Gallery F4:  Wet Fire Sprinkler

Wet fire sprinkler systems have long been trouble free, until more recently that is.  Filling steel pipe with water and leaving it stagnant, which is how wet fire sprinkler systems existed many decades ago, results in limited corrosion occurring before the oxygen is expended and corrosion dramatically slows.  This is why UT investigations at much older buildings often produce the best results.  Refresh it with new water on a regular basis and the corrosion mechanism returns to its higher rate.

Today, however, mandated regular flow testing combined with the more common installation of thinwall schedule 10 pipe and even ultra thinwall schedule 7 have greatly accelerated their deterioration.  Long gone is the standard for schedule 40 pipe.  Highest wall loss always exists where fresh water flow is higher – such as prior to a leaking booster pump seal.  Sweating pipe, as well as a frequently running jockey pump, always indicates a downstream leak requiring immediate attention.  Frequent building renovations requiring draining and re-filling are extremely damaging to the entire system, whereas a leaking booster pump seal may only impact 25 ft. of inlet line.  Where short distances exist between the inlet fire line to the city water main, turbulence alone can allow the migration of fresh water which in turn accelerates corrosion’s impact.

In general, corrosion losses decline as the system branches out and the turnover of fresh water decreases.  A common area of failure is where the wet fire system is airbound, such as at the top of the system and more commonly at final branch lines following along a domed warehouse roof.  In such cases, a wet system essentially transitions into a “dry” fire system in that area, with much higher pitting the common result.