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

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Discussion Overview

The discussion revolves around the feasibility of preventing a 150NB Stainless Steel pipe, insulated with 50mm thick rockwool, from freezing under conditions of -15°C for five consecutive days. Participants explore whether trace heating is necessary given the parameters of static flow and the presence of potable water.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant questions whether trace heating is required for the insulated pipe under the specified conditions, noting the importance of maintaining a temperature above freezing.
  • Another participant suggests that the insulation may not be sufficient for the expected temperatures, indicating that heating might be necessary for multiple days at -15°C.
  • A later reply provides additional details about the pipe's working temperature and dimensions, expressing a belief that trace heating might be borderline necessary.
  • Another participant comments on the short length of the pipe and raises concerns about the storage tank, suggesting that the insulation may lead to freezing conditions within hours rather than days.
  • One participant estimates that freeze conditions could occur in approximately 9-10 hours with stagnant water, while suggesting that constant flow might mitigate freezing risks.

Areas of Agreement / Disagreement

Participants express differing views on the adequacy of the insulation and the necessity of trace heating, with no consensus reached on whether the pipe can remain unfrozen for the entire duration under the specified conditions.

Contextual Notes

Participants note that calculations depend on various assumptions, including the nature of the water flow and the effectiveness of the insulation, which remain unresolved.

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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.
 
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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
 
Last edited:
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.
 
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.
 

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