i m doing analysis for Cold blast line...for that i m doing the combined analysis with the existing piping. In the existing piping they have used flexible type RGF ( i dunno..what it is...& where this type of bellow to be used)..plz help me...how to model this in CII & what its function. Herewith i attached the image.

can be modelled as a slip joint.

thnx muthu.

1. Is it correct to modell like Simple expansion joint, with less stiffness values & no pressure thrust.

No matter what you do, you'll need stiffness data from the vendor. Ask them how they suggest you model this thing in a flexibility program.

Moorthi,

By the way the Tie-Rod seats are detailed, I believe this joint is intended to absorb some lateral offset.

Also, you mention "no pressure thrust". If your two ends move towards each other, your tie-rods will become slack and you WILL have pressure thrust.

If you do have axial movement, it's going to take a huge force to over come the friction caused by the packing to allow the movement. When/if this happens, your anchors will see this friction load and the pressure thrust.

Awhile back the was another thread on this board with a lot of discussion about slip joints. I think it was about pipe rack design. You might do a search, it had a lot of replies if I remember correctly.

As Richard Ay said, you need to get the values for stiffnesses and friction from the vendor. Before contacting them, you might review the other vendor data sheets for this item.

Good luck,

I cannot read all the details from the image. And I do not have the line drawing. For me this looks like "Universal compensator" without convolutions. You could get similar effect with 2 flange adapters from Viking and Johnson. My bet is that it is not designed to absorp any axial movement. It had 2 purposes. Its axial length has some adjustment possibility during installation and it can take reasonable lateral movement because its length. It looks like old design. 1984?? If I am correct you need only lateral stiffness for your calculation, which is quite low I would think. I should be able to give you magnitude if i have a bit better drawing, see below.

Lateral movement is limited by maximum angle the centre pipe can rotate. Look for "cold pull" in the system. You can double the available movement by that.

This is actually a clever design. Must remember.

If you e mail direct readable copy plus line drawing I may be able to confirm.