Insulating Steam Header Drain Deadleg

[Fac_Eng]

Has anyone heard of oversizing insulation on a deadleg to provide an air gap between the piping and the insulation? I'm evaluating a project to cut off a nuisance 2" drain off a 20" high pressure steam header. My plan is to cut it off as close as possible to the header and cap with a closure weld. Our construction team suggested over sizing the insulation on the remaining <1ft of drain pipe. Apparently they had done it before.

I guess the rationale would be the air gap and drain would be kept hot via convection from the steam header (line operates at ~300C). This checks out in my head, just curious whether this is common practice or not.

 

[mk3223]

Interesting... but, not heard it before... and, watch out the CUI issue on the dead leg.

 

[Dhurjati Sen]

The 2" drain must have been provided to drain out water after hydro-test. Obviously, the previous engineers thought it best to keep it as it is and provided excess insulation to minimize heat loss, hence the concept of air gap, etc.

Now the second part. What you suggest is tricky as the 'common' practice is to weld forged plugs (previously called gamma plugs) on the header itself and carry out 100% RT.

Google gamma plugs for better understanding.

Better leave the drain as such. It is more 'common' than what I have mentioned above

DHURJATI SEN
Kolkata, India

 

[gerhardl]

Hi Fac Eng,

I have not heard about your 'oversized air-gap isolation.

A 'nuiscance' drain? Why? Is removing the best solution? Can removing create problems?

Any modification of an excisting steam system must be checked out to not create condensate pockets at start-up. If extra insolation is to hinder condensate in a pocket, steam-trap, not removing, is the solution. Condensate will always gather in pockets in a cold pipeline.

The other solution will be to plug the short small pipeline left thight inside as flush with the larger mainline ID as possible, and THEN an oversied insulation might be sensible to hinder wall/plug temperature difference.