water line bridge crossing 4

[bronco77302]

I have installed two 1"1/2 poly water lines complete with inserts to maintain the waterlines in the center of the carrier pipe.The 8" steel carrier pipe crosses a 60'bridge.The carrrier pipe was filled with foam.

I live in Vancouver British Columbia where the tempature does not fall to -10c that often, well guess what The tempature fell to-10c and the waterlines frose

After opening inspection holes on the carrier pipe I found that when the pipes were filled with the foam it raised the water lines more to the top of the pipe,therefor I ended up with 31/2" of foam on the bottom and 11/2" on the top.(it was a little shy of foam at one end)I had the contractor out to fill the missed areas.

I guess my Question is even if the lines were in the middle of the carrier pipe and the foam was filled to the top it may have still frose

I am afraid that it will freeze again.does anyone know what tempature this design would be good for, Or what I should do for future protection on the outside of the pipe.

there was no flow when it froze

 

[AegisFPE]

Sounds like a heat transfer/thermodynamics problem, here's my approach:

If I take a thermos of hot coffee (insulated container, no liquid movement) and place it in my freezer (sub 0deg C)...Eventually, it will freeze. I can't stop it. Eventually the insulation will pass all the heat from the coffee out until there is not heat left, and the system is at equilibrium (everything at sub 0deg C, coffee and insulated container).

Your water pipe is the coffee, the foam is the thermos. It'll probably freeze again given the same conditions, even in the very center of the foam (though this may allow it to withstand a slightly longer cold spell).

 

[LHA]

Aegis is correct.

I hate to say it, because it is probably too late now. But the 1.5" lines need to be heat traced.

The 8" carrier has plenty of room inside, though. Maybe there is a way to get heat tracing into the carrier pipe. But it doesn't seem likely, without disrupting the foam.

Engineering is the practice of the art of science - Steve

 

[JedClampett]

Is there a way to heat trace the exterior pipe without having the heat damage the foam? It seems like just a little help would keep the inner pipes from freezing.

 

[civilperson]

Whatever the temperature that freezes the liquid happens to be will freeze the liquid if enough time passes. Insulation retards the conduction of Heat/Cold, but does not stop it. A heat source must be supplied. Cheap and easy is to recirculate the water in the pipe into the ground below frost depth. The earth maintains a constant 50-55 degree temperature at some depth and this heat is available to keep the liquid from freezing.

 

[Carter05]

If the carrier (the pipe that actually has the water in it) is reasonably straight, AND you can reasonably get secure power to one end, you can insert a heat trace INSIDE the pipe, that should keep the pipe from freezing. The steel? pipe with the foam inside is typically called the "sleeve" or "conduit". Here are some links to manufacturers of internal heat traces. Typically, I believe that these are heat controled such that placing them inside a PVC water line will not cause a hot-spot or melt the PVC.

http://www.morelectric.com/ilh.htm;

http://www.deanbennett.com/heated-in-pipe-freeze-protection.htm