Dry Pipe Sprinkler Fitting Failure

[ChristyB]

I am looking into a the cause of failure for a cast iron fitting that is part of a 12 year old dry pipe sprinkler system. The tee-fitting was located at a high point and appears to have broken during freezing weather due to trapped water.

The company who does the annual testing and makes repairs says that the dry lines are very corroded and that debris could have trapped water in the pipe, which then froze and broke the fitting.

Has anyone had experience with water getting trapped in a dry pipe sprinkler system after the dry-valve testing?

Can corrosion trap water in the system?

What other mechanisms could trap water in the dry pipe system?

Is there anyway to prevent this from happening in the future?

Any insight or experience you could give me in this matter would be most appreciated. Thank you.

 

[rconner]

I noticed you had not yet gotten any responses to your inquiry -- a little more information might allow some of the folks on the list to reply, perhaps more helpfully to your inquiry. e.g. What size fitting/line(s) were involved? To what type of piping is the fitting joined? Was there any lining provided in the fitting? Was there any lining provided in the piping? If there are linings, what are they in both components? Is there a record of a hydrostatic test on the line? Does the line drain "automatically" (e.g. is this system in effect sealed or is there opportunity for somehow introduction of water/vapor or condensation), or must drain valves be opened etc.? If hydro-tested, was the water subsequently drained out of the fitting/line, etc.? While the answers to some of these questions might be obvious to someone skilled in such systems, your question perhaps begs for more information that might allow others to try to help from just a basic piping point of view.

 

[ChristyB]

Thanks for the tip. Here is some more information on the system.

The fitting that broke is a 1 1/4 x 1 x 1 1/4 tee. The piping connected to it is unlined black steel threaded pipe called Dyna Thread 40.

The dry system is a closed sprinkler system kept under pressure (33 psig) by way of an air compressor and a regulator. When pressure drops in the system (such as when there is a fire and a sprikler head activates) the dry valve opens and fills the pipe system with water.

The dry valve is wet tested every third year so water is introduced into the piping system every third year. All pipes are sloped to drain out to a main drain and after the test the lines are drained (the dry valve can't be reset unless the system is drained).

Therefore, if there was still water in the system that froze and broke the fitting, it must have not been able to drain when the system was drained after the test.

Has anyone experienced or heard of corrosion causing blockages in a dry pipe system?

Thanks for your help.

 

[TBP]

If the system can't drain out properly, and is corroded to the point of trapping water, how will you ever get enough flow through it to put out a fire? Even if you can initially move enough water, if there's that much debris in the piping, you'll likely get some blocked heads.