How can I modeing 'Dresser Coupling' in expansion joint modeler.

Koo Keun Hoe,

I cannot be specific in modeling these couplings as I have no direct knowledge of them. I believe they serve as connectors between sections of pipe or pipe and other components such as pump nozzles. These connectors have some play and perhaps some "nonrigid" stiffness.

Of course, the important considerations in CAESAR II center on stiffness, displacement and load. You can model these terms for your coupling through a restraint with stiffness and gaps. For example, to model a coupling between two pipes run a pipe from 10 to 20 and a second pipe from 21 to 30. Model the coupling as a set of six restraints at node 20 with a CNODE of 21. Specify a stiffness if a gasket with a given stiffness is present and add a gap if there is some play in the joint.

There is more information on this approach in a newsletter article on Victaulic couplings in the June 1998 issue. You can find this on our website under the Support heading.

Dave

I am going to model Victaulic flexible coupling (DN350)on the pump suction line. The pipe runs on the X axis. The typical way for modelling seems to restrain all six degree of X,Y,Z,Rx,Ry and Rz with gaps specified from the vendor catalogue using CNode. However, I read the article on the Coade News letter prepared by David Diehl, and it mentioned only X, Ry and RZ have to be restrained with gaps(not mentioned for other directions).

Please advise which way is correct.

Regards
Sok

The focus was on those three DOFs (X, RY, RZ).
I believe the other two translation DOFs had rigid restraints with CNodes as there are no gaps and the RX was ignored - allowing the joint to spin. Or maybe also rigid restraint to assume math stability but then check the torque magnitude.

Certainly do not let them free.

STC,

The Dresser coupling and the Victaulic flexible coupling are not alike. The Dresser coupling would clamp on to plain pipe, while the Victaulic flexible coupling works within the grooved pipe limits. The Victaulic style 77 flexible coupling might be close to the Dresser coupling within small displacement limits. The Victaulic style W155 expansion joint with its multiple sections would be an order of magnitude more flexible, more like a hose.

If you have a anchor support on piping side close to the Victaulic coupling, then the loads on the pump suction will be negligible. The anchor support would take the pressure thrust plus piping loads, and the Victaulic coupling would allow small vertical + lateral + rotational movements between the anchor and the pump suction connection displacements.

Thanks for your reply Dave and Richard.

I can't add an anchor or line stop as you suggested, as the pipe runs straight into a tank. The system pressure is very low (10kpa for operating), so the pressure thrust will not cause a big problem for the pump and tank nozzles.

Do we need to consider pressure thrust for the Victaulic style 77 flexible coupling as we do for simple bellows? I remember Dave has mentioned in the Coade News letter that this can be evaluated manually. What is the best way to include this in Caesar if we have to consider?

Can we assume the vertical and lateral movements the same as an axial movement? The vendor table only shows the axial movement.

Pump will cause vibration. Which is better application between the flexible coupling and simple bellows for pump line from the vibration point of view?

Regards
Sok

You can include the pressure thrust by adding F1 at the upstream and downstream surfaces that you would see if you stood inside your coupling. Be sure to include this F1 in your load sets.

I would not assume that the transverse gap is the same as the axial gap.