Pipe Freezing Time: 150NB Steel Pipe in -15C

[Padnail]

I am trying to ascertain if a 150NB Stainless Steel pipe lagged with 50mm thick insulation would also require to be trace heated. The insulation used is rockwool. The parameters are that the pipe must not freeze solid given 5 straight days of -15 C with static flow. Wind chill is negligible. The pipe contains potable water. Any information would be greatly appreciated.

 

[Travis_King]

What's the maintenance temp of the potable? The length of the line?

At first glance, though, I'd say you'll have to heat trace that line. If your design parameter is multiple consecutive days at or around -15 C, then I'd say your insulation is not going to be sufficient.

References for you to look at:
Chromalox 1 (by Proheat Inc.)
Chromalox 2

 

[Padnail]

Cheers Travis. Appologies for the lack of detail. The working temperature is 5 C and the pipe runs 1.5m horizontal with a 2.5 m vertical climb feeding a storage tank. I similarly suspect it may require trace heating but do think it is borderline.

 

[Travis_King]

oh, that's a short run of pipe. Are you not worried about the storage tank? Or is that heated?

Either way, with 50 mm rockwool insulation, you're looking at a timeline of hours at that temp, not days. The calcs in the reference assume a few things, but they are fairly good estimates. There's no way you'll get 5 days of -15C temps out of that. More like half a day, if that.

A back-of-the-envelope calc indicates that you'll likely have freeze conditions in ~9-10 hours, probably a bit longer considering these numbers are factored. That's with stagnant water. If it's constantly running, the insulation is fine.