Wet fire sprinkler systems have long been trouble free, until more recently that is.  Increases in the amount of flow testing, combined with today’s more common insulation of thinwall schedule 10 pipe, have combined to greatly accelerate their deterioration.  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 indicate a downstream leak requiring immediate attention.  Frequent building renovations requiring draining and re-filling are extremely damaging to the entire system, whereas a leaking pump seal may only impact 25 ft. of inlet line.  Where short distances exist between the inlet fire line to the city water source, turbulence alone can allow the migration of fresh water which in turn accelerate 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 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.

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