Stainless Steel Bellows or Fabric Expansion Joint Outdoor - Best Option?

[ldeem]

I am redesigning a kiln duct leg that runs to an ID fan. The kiln is used to fire limestone to make quick lime. The duct section is after the cooler and just before the ID fan. Temp is 815 F carrying dust laden air (bag house is after the ID fan). I am good the the thermal movements I have calculated so the question is the type of joint. The current joint is pagoda style made from thin sheets. No drawings possibly field fabricated. OD is 48".

I am looking at fabric style and stainless steel bellows style. General comments I am getting back are fabric is lower cost upfront and stainless is longer life.

Does anyone have comment/opinion on which way would be better - if there is even a clear answer? I really have a hard time with the bellows 0.048" thickness (from one vendor) holding up but it seems to be a pretty standard practice.

I need axial and lateral movement in the joint.

 

[btrueblood]

What fabric are you proposing that will survive 815 deg. F, much less the abrasion from hot dust blowing across it?

 

[LittleInch]

As btueblood says I think internal abrasion and wear is your key issue at 430 C.

what happens now?

~steel bellows to allow axial and lateral or rotational movement need to be pretty thin to work, but are commonplace.

Metal looks the best to me for this sort of duty - any hole or leak would probably start small compared to a "fabric" bellows.

This is a pretty large bellows so will need to request some past examples of use from vendors. It's the operating experience you will find difficult to find.



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

 

[gerhardl]

Other aspects than mentioned will also add to your considerations:

Outdoor in what climate and conditions (gases,acids?) and protection(roof?)?
Expected/probable/wished lifetime?
Cost and consequences for planned and unplanned stop?
Cost of spares and availability?
Custom fabricated or faster supplied/produced more standard unit?
What does suppliers recommend?

I would guess that a combination of metal bellow, fabric coated product could be an interesting product to ealuate as cheapest product over lifetime, all considered.

 

[btrueblood]

I am pretty sure, even in this age of rapid technical developments, that there is NO coating for fabrics that will withstand those temperatures. By coating, I mean an elastomeric type of substance that adheres to the fibers and spans the gaps to seal against minor pressure differentials, and is flexible enough to not excessively restrict, or be damaged by, the bending and stretching of the fabric.

Metal bellows are a thing. Our sister company has spent many tens of thousands of dollars developing an in-house formed bellows in a special alloy, after the original producer stopped. Field fabricated bellows? Hmm.

A simpler method might be to evaluate the impact of a leak at a slip joint. How tightly can you keep that joint, and what is the impact of the resultant leakage flow? If you want a fair bit less leakage, think along the lines of piston rings, perhaps several of them. Piston rings require some pretty precision machining, but that is cheap and simple compared to formed bellows of any size, and cheap compared to welded bellows of any size.

 

[EdStainless]

BT beat me to it, a slip joint may be your best bet for this. I have seen them on slightly smaller lines (30"-36") and they were actually a series of slip joints, I believe 3 nested. The inner one is clear at the far end to try and minimize dust ingress. You do have to check these regularly to assure free movement.
I would expect that your bellows has a slip liner in it also? You don't want debris packing the convolutions.

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P.E. Metallurgy

 

[gerhardl]

Tried now to search in German for high-temperature elastic pipes, and are finding producers of pipes for up to 900 mm and 500 deg C, but with strong limitations for pressure.

https://www.masterflex.de/en/hoses-connection-systems/article-details/pimarticle/6_7_752_5632.html

A possible, but perhaps not the best solution. Might be similar producers locally?