Cold-Service Process Pipe: Insulate Dummy Legs?

Question

Cold-Service Process Pipe: Insulate Dummy Legs?

Mech_Ben (Mechanical)

(OP)

1 Oct 24 16:09

I'm looking at our company standard drawings for dummy leg pipe supports for insulated lines, and there is no differentiation for use between hot lines and cold lines. No insulation is called out for the dummy leg itself, and the dummy leg is shown supported by a welded-on shoe.

For hot insulation I don't see a problem with this. (Yes, you'd loose some heat to the environment, but out hot pipe isn't THAT hot and heat retention efficiency is not of utmost importance.)

What I'm really wondering about is for cold-service lines (we're anywhere from 20F down to about -120F). I'm not too worried about heat being drawn into the process (though that is a consideration), what I'm most concerned about is condensation on the dummy leg leading to unsightly dripping and (even worse) corrosion over time.

I'm thinking the best answer is to insulate the dummy legs with the pipe and support on a cold shoe. Is this overkill? Has anyone else dealt with these, and is condensation/corrosion a concern here?

Thanks in advance.

Ben

SJones (Petroleum) · Answer 1 · 2024-10-01 17:49:00

Try a Google search on the term “corrosion of pipe support trunnions”

Steve Jones
Corrosion Management Consultant

www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

Mech_Ben (Mechanical) · Answer 2 · 2024-10-02 13:25:02

Thanks, Steve.

I did not find any information directly related to cold service pipes, but did find some examples of corrosion on the inside of trunnions attributed to moisture ingress and condensation on the process pipe. So I'll take that as an example of the importance of keeping the surfaces from holding water and plan to insulate dummy legs unless someone has a good reason not to.

Ben

EngrPaper (Mechanical) · Answer 3 · 2024-10-02 14:13:50

Yes, for just condensation prevention, you can insulate down the trunnion some length. For ice prevention or more severe cold services, you often use a thermal break in the trunnion such as a phenolic block and then you insulate through that block. It also allows a material of construction change for cryo services for the parts of the trunnion after the phenolic block.

Mech_Ben (Mechanical) · Answer 4 · 2024-10-03 12:29:09

Thanks, EngrPaper. Yes, we do that for base ells, with a heat break and change in material.

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Cold-Service Process Pipe: Insulate Dummy Legs?