Caesar II with Tie-rod Ex-joint 4

[T5580]

Hello all,
I'm using using Caesar II to model the piping system with the use of tied-rod expansion joint to reduce forces and moments excert on equipment nozzle. The joint was modeled per Caesar II application page 5-6 with restraints RX, RZ, and rigid Y.
The system designed to allow the ex-joint to compress due to thermal and of course the tied-rod will resist the pressure force in tension. I have found the axial force acting on nozzle = Kx + (Press x Area)
The question is how do I get rid of the pressure force acting on the equipment nozzle? Note that I have tried the rigid Y, +Y, -Y but none is help. Your help is appreciated.

Best Regards,

 

[chogben]

T5580,

You may need to relocate your expansion joint, or modify the piping layout.

If you use a rigid Y then there will be no pressure thrust from the expansion joint since the rods take the loads, but the expansion joint will not compress. If you allow the joint to compress then the pressure thrust will be transfered to the next anchor.

You can also try using a joint with a lower stiffness to reduce the nozzle loads.

 

[VBHMBG]

Dear T5580,

By using an expansion joint as shown on page 5-6 of the Caesar II Application Guide you must have a lateral displacement between the two e.j. ends. This means that the e.j. only works in the intended way if there is a bend / change in pipe routing between the nozzle to protect and the axis of the e.j. .

Take care of the friction in the tie-rod ends, as this is often overlooked. The higher the pressure and therefore tie-rod forces, the stiffer the e.j. assemly will become.

Regards,
VBHMBG

http://www.pipestressanalysis.com

 

[JohnBreen]

Did you notice that in the example in the application guide, the effective ID window is left blank (i.e., zeo) for the tied joints?

 

[T5580]

JohnBreen,
So, you suggested the effective ID should be left blank as shown an eample?
Regards,

 

[StressGuy]

You said:

The system designed to allow the ex-joint to compress due to thermal and of course the tied-rod will resist the pressure force in tension.

These are contradictory statements. Your joint won't compress an iota until the force of the pressure thrust is overcome. If you are truly designing the joint to compress, then your tie rods serve no purpose. The pressure thrust load gets carried by the restraints outside the joint. If one of those restrtaints is your pump nozzle, it's probably going to be feeling some pain.

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.

 

[stanier]

In Algor's Pipepak the Pressure Area field is left blank for tied rods.

 

[DSB123]

StressGuy is correct. If the Expansion joint is needed for axial thermal expansion of the pipework an hence compresses then the full Pressure thrust must be seen by the pipe restraints on either side of the unit. Suggest you consider re-routing pipe to incorporate a leg perpendicular to the main run of the piping and possibly using a lateral tied bellows unit if possible which will accommodate the thermal movement and also negate the pressure thrust on the equipment.

 

[JohnBreen]

JohnBreen,
So, you suggested the effective ID should be left blank as shown an eample?

Yes. C2 just uses effective ID to calculate the area and uses that to calculate the bore thrust due to pressure (pressure times area equals force). So since the tie rods eliminate the bore thrust just leave the field blank and C2 will calculate a zero bore thrust (equal and opposite forces "cancel").