high temperature pipe-in-a-pipe systems 1

[ncstate86a]

I am looking people (someone, anyone) who have experience with high temperature pipe-in-a-pipe systems. I was told of a facility that uses a such a system for hot air at 1350+ F and 650 psig. The inside pipe (12") is vented to the outside pipe (~20") such that it is not pressure retaining; it acts as a conduit for the flow only. The outer pipe is insulated from the inner pipe and is pressurized to 650 psig; However, since no flow exists between the inside and outside pipe, there is very little heat transfer such that normal piping materials can be used The inner vented pipe has expansion joints to allow thermal growth independent of the outside pipe. Is anyone aware of a manufacturer of such a system?

 

[moltenmetal]

Puzzled why in that case you wouldn't just refractory line the larger pipe. That way, the refractory deals with the temperature isolation, and the outer shell deals with the pressure retention but at a lower temperature where the materials are stronger.

 

[ncstate86a]

I am not experienced in using refractory line pipe. I would assume it is very difficult to make modifications after installation. we have always shied away from it due to concerns with particulate in the stream and the potential for plugging small orifices in equipment downstream. Do you recommend any particular manufacturers of refractory lined systems?

 

[LittleInch]

Not aware of such a system and a simple search doesn't bring anything up.

I can see some issues with that design including what insulation is used that is good at that temperature, how do you deal with any bends or tees in the inner pipe and whilst the gas flow will be very low between the inner and outer pipe, there will be some and how do you deal with those hot spots? A lot will be on how many holes there are and how do you stop travel of gas due to pressure difference.

That looks quite a difficult combination ( 730C and 45 barg) so imagine it would have come up with a pretty unique solution.

I've seen cryogenic pipe in pipe systems using low expansion inner pipe and that is quite hard.

What sort of temperatures and pressures are you looking at or is the 1350F/650 psi, your requirement?

Foamglas insulation goes to 650C and it's usually much easier to deal with expansion in one pipe rather than differential. There other external insulations as well.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[ncstate86a]

Thanks LittleInch -

I appreciate your comments.

A system like this exists in Germany but I am having a hard time time finding any information concerning the manufacturer or details concerning the design. 1350 deg F at 650 psig is an the actual operating condition.

 

[LittleInch]

There's likely to be a good reason you can't find any more examples.... Likely to have been a one off special at that temp, pressure and mode of operation.

The differential expansion issues in a pipe in pipe system are a bitch to deal with and expansion joints / bellows etc have a poor track record, especially in terms of fatigue and corrosion

I meant what is your application - identical to the previous one??

what service is this? I've seen hot flue gases before, but not at 650 psi.

No, you need something like space shuttle linings I think and a fairly constant operation. Anything which starts and stops is a difficult scenario to deal with reliably.

If you go for a single pipe with internal thermal protection, you'll probably end up with an outer protective pipe to catch the situation if it fails. Escape of that sort of gas at that sort of pressure will lead to catastrophic failure and possible deaths very quickly if you don't.


Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[ncstate86a]

Thank you again, LittleInch! My application is identical to the other one...air at 1350F @650 psig and velocities between 150 to 250 ft/s. the system thermal cycles 3-5 days a week (on 12 hours/off 12 hours). Conceptually I would think the pitfalls associated with expansion joints installed in the inner piping would be lessened due to the extreme low DP across the bellows wall. What concerned me when i was told of the system was the detection of outer pipe hot spots and, as you so rightly noted, catastrophic failure. I fear you are correct that this is a one off design and will not be available commercially. Thank you again for your comments.