Use of bellows for pipe misalignment

[Boiler1]

I heave a situation where a bellow is installed to compensate for pipe misalignment. Would this be a common practice?
Even without any load in the system the stretch of the bellow it’s clearly visible as the flanges on both sides of a bellow are quite misaligned.
My fear is that when the thermal expansion and vibrations occur – the bellow may give in which, in this case, would cause a catastrophic leak.
Would there be any standards referring to the installation of bellows in relation to pipe alignment? I only came across the bellows manufacturer stipulation that the below must not be under any stress when the system is ‘at rest’.
On the other hand, I am aware of the requirements for axial and angular alignment in case of flange-to-flange joints.

Regards

 

[1503-44]

Follow the manufacturer's instructions. Those will override the requirements of any "standard", which I don't think exists, but there are so many standards today, you might find one somewhere. If the present configuration deviates from the instructions, put it right.

A "catastrophic leak" would suggest that you need to immediately do whatever is necessary to guarantee that it such an event is impossible.

 

[StressGuy]

I would say it is not common at all. When you say the joint was installed to compensate for pipe misalignment - what that joint put in as part of the piping design, or was it something that was added during construction to fix an alignment problem that was identified?

While an expansion joint can give some extra play for piping alignment, that's not what it's purpose is.

Edward L. Klein
Pipe Stress Engineer
Houston, Texas

"All the world is a Spring"

All opinions expressed here are my own and not my company's.

 

[TugboatEng]

Offset misalignment can cause the flow liner to contact the outer bellows. This will cause it to wear through and leak.

 

[LittleInch]

So taking the points in order.

No it is not common practice and is in fact a poor practice normally not permitted by the piping construction specification or design. Whoever permitted this if it was indeed not part of the original design should have justified it via a change procedure.

I assume from your handle that you are looking at steam?

The pipe design would have been based on the use of rigid pipe unless this bellows is part of it but simply poorly put together? You don't say and it makes a big difference.

Bellows are a weak point in any system and often fail in fatigue of the bellows themselves.

Unless in operation that mis alignment reduces and it is under less stress/ elastic flex then your room for any expansion has maybe already use dup - you tell me as I can't see your system. (A photo is always good).

Also is this system in operation yet?
What is your role / responsibility for this system?

Lots of unknown here so lots of unknown in the response.


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

 

[1503-44]

Just fix it.

Nobody here is going to say leave it as it is when you also say the consequence is catastrophic.

 

[Boiler1]

Hi All,
Many thanks for all the info! Just to clarify a few of your queries.
The system is a machinery coolant, essentially a chilled water & antifreeze solution. As the machinery is quite pressure sensitive, a rupture of this kind means a downtime. So, it’s perhaps rather critical than the catastrophic failure considering that there are no health & safety implications in the failure.
The system is at the installation stage with me as the future owner, so not operational yet and about to be tested. The joint in question wasn’t shown on construction P&ID’s
This bellow has been fitted on one of the Heat Exchanger (HX) flanges to connect to the pipework. Other three HX flanges are connected directly flange to flange with no visible misalignment.
A 12” flanged pipe that was to be connected to a 12” flange on a HX is approximately ¼” off. This was compensated with the bellow in question.
The installer claims the bellow was required due to the stress analysis although the skid was modelled and issued for construction without it. To rectify it, I assume, a length of pipework should be taken down and realigned with the HX flange.
I’m really looking for relevant ASME or other standards to back the rejection of the installation up. I am aware of permitted axial and angular tolerances when jointing two flanged pipes up, but I’m not sure how to look at it when one side of the flanged connection is flexible.
Regards

 

[1503-44]

Then my guess is that are probably better off to pull the pipe together with flanges, or cold spring it rather than install a bellows. A bellows should not be used to connect misaligned pipe. If needed because the piping is not designed to be flexible and there is no way to make it so, that may be another story. I doubt the installer's claim that it was necessary, given the spool was issued without it. Get the stress engineer on the phone. If this is the fault of the contractor, especially if not even in service yet, make him fix it. It is so obviously out of tolerance, you don't need a bellows API as justification, reference a pipe fabrication standard is all that should be needed, if that. Sounds like a simple sloppy work mess up.

If you keep the bellows, show the installer the picture in the installation instructions.

 

[EdStainless]

Is this alignment withing the alwance of the bellows mfg?
Even if it is this will have a finite life that is shorter than the rest of the system.
Not a good practice.
Ask for the stress analysis paperwork and ECN.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[LittleInch]

6mm out of alignment and they installed a bellows?

How? You need a lot of space to install a bellows. So what else have they not installed??

but this has red flags all over the place.
1) The design, as certified and analysed (hopefully) by the designer did not include this bellows right?
2) Therefore what the contractor built was not in accordance with the issued for construction drawings
3) The installer is simply trying to not do re-work due to poor line up control. Tough sh1t.
4) You don't need any international standards here, you simply need the construction SOW, the construction spec and the issued for construction drawings. ASME etc won't help you.
5) No mention of a MOC or approved change from the designer??

Basically just hold firm, tell the installer what you want is what was designed and analysed and issued for construction, not some hack up to stop the installer doing some work again. He will shout and scream and claim delay etc etc, but hold firm. You do not want to accept this long term

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