Seal forced in pipe

[Matt17]

Gents,

I hope that today problem will be simple for a mechanical engineer, but trust me I'm a poor chemical engineer so don't take anything for granted

Well ... we're speaking about an annulus-type seal cup which is forced inside a pipeline having an internal diameter smaller than the diameter of the seal cup (see attachment drawing). Seal cup is composed by an elastic material (say a plastic material) and annulus is fixed in the inner part. Of course, we know all the data about materials, dimensions, etc.

My questions are: what is the generated force of the seal against the wall? Is it possible to have an analytical solution (and what assumptions in this case)?

To make the problem more interesting, two are the different configuration I'm looking for, i.e.:
[ul]
[li]when p=0[/li]
[/ul]
[ul]
[li]when p>0[/li]
[/ul]

Any information and/or indication (also similar solved problem from scholastic books, etc.) is welcome.

Thank you in advance for your attention and help.

Matt17
Process Engineer

 

[LittleInch]

My question, apart from why do you want / need to know, is after forcing what looks very much like a standard cupped pig to me into the pipe, does it then move once you apply pressure or is your tube like thing that the disc is attached to stay in a fixed location whilst you are applying a differential pressure accross the cup?

At a basic level, the force will be the pressure plus any mechnical force from bending of the material.

All pretty negligible stuff for a steel pipeline.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Matt17]

Hi LittleInch,

thank you foryour interest. Yes, of course it's very close to a pig, you're right ... my interest to this problem is that I want to know exactly the mechanical force from bending of the material that you have mentioned, however my mechanical knowledge is not enough to analyze this kind of geometry (i.e. annulus fixed in the inner part), but I hope that the axial symmetry can help.
Of course this is not a problem for the pipeline, but my interest is to study the behavior of the seal inside the pipeline.

I hope that this problem could be such simple to have an indication of an analytical solution.

Thank you and Regards,

Matt17
Process Engineer

 

[ConstantEffort]

No answers here, but empirically you could find the force required to move the seal through the pipe by putting it in a short run of pipe and pulling it through with a force gauge. That force is the friction force, which is equal to the coefficient of friction times the normal force. The normal force is the "F" you were after in your sketch. The coefficient of friction between two materials is usually found in a table or could be empirically determined.

A scale model won't be a linear relation to the real size since the stiffness of the ring is geometric.

 

[Matt17]

Hi Constant Effort,
thank you for your time. I understand you suggest a trial with something closer to the real problem. However, what about if I want find the solution on the paper? Can you indicate me a reference (also a scholar reference like a book) with a similar problem?

Matt17
Process Engineer

 

[LittleInch]

Try looking and talking to these guys -

http://ppsa-online.com/

or try someone like TD williamson or GD engineering or any of the links on the PPSA website. The extra selaing force is a function of material, degree of over size and hence bending. There is a large amount of data on making it work, but maybe not for your requirment.

If you can expand on why you want to know this, you might get a bit more interest.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Matt17]

Thank you again for your answer, I'll try for sure.
Again, my interest is to study the behavior of the seal inside the pipeline and, in detail, the force to push the item.

Matt17
Process Engineer

 

[LittleInch]

If we're talking typically, you tend to find that a pig moving smoothly (0.7 to 1.0 m/sec min) in a steel pipe without any dirt etc takes beteen 0.3 to 0.7 bar accross it when it is new and correctly sized - ususally about 105 to 110% of ID - to get sufficient sealing without too much friction.

As it wears or is incorrectly sized this diff pressure can fall or rise accordingly.

I still don't know what ypu're trying to do, but hope this helps.

LI

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way