Dear Sir/Madam,
I am a beginner in Piping Stress. I tried to understand how CII incorporates Expansion Joint in its analysis.I thought the Pressure thrust is "Pressure * Eff.ID" which is irrespective of piping configuration and Restraint arrangements.

First Picture shows piping configuration

Second Picture shows restraint summary without Axial stop at node 1180
(No pressure thrust, No forces acting on the anchor)

Third Picture shows restraint summary With axial stop @node 1180
(Pressure thrust 2914N is acting on the restrains.)

P.S: Bourdon Effect excluded in the analysis.

Force = Pressure X Area.

0.105 MPa x π x (188mm)²/4 = 2914.7 N

A note of caution: This is only the static pressure. You may need to at times consider dynamic pressure, as well.

Dear Michael thanks for helping. can you please help me to understand "Pressure Thrust" in expansion joints and CII incorporates pressure thrust in a piping system?

Thanks in Advance

An expansion joint is primarily designed to take up some lateral movement, not axial. However, the nature of an expansion joint makes it more susceptible to the bourdon effect compared to standard piping, hence "pressure thrust."

The unit wants to unravel like an accordion. This is why the piping system has to be designed to protect the unit as much as it protects the piping system, or the unit has to have self-limiters installed on it.

Being that your system cannot transfer any thermal growth from axial to bending, you'll always see that entire force on your nozzle/support.

Thank you sir. That means If i put a expansion joint with stiffness equal to stiffness of pipe, I wont get any pressure thrust (Bourdon effect switched off).
Am i right?

Not quite... Enabling the bourdon effect tells CAESAR all piping elements have the bourdon effect. Enabling the expansion joint tells CAESAR enables the bourdon effect for the element. Using the stiffness of pipe will still enable the bourdon effect for the element, but just change it to a specific value.

To turn it off, I recommend you click (once) on the "Expansion Joint" check box and hit the F1 button. Here is the help file for expansion joints.
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Expansion Joints
Indicates that you are supplying expansion joint data. Select or clear this option by double-clicking Expansion Joint on the Classic Piping Input dialog box.

This auxiliary dialog box tab controls options for expansion joint stiffness parameters and effective diameter. For a non-zero length expansion joint, you must omit either the transverse or the bending stiffness.

NOTE Setting the effective diameter to zero deactivates the pressure thrust load. Use this method in conjunction with setting a large axial stiffness to simulate the effect of axial tie-rods.

Clearly Understood. Thank you sir!!!!

Older post but I have not been around here for a long time either.

I have not used later versions of CAESAR II but I do not think that there are many changes in expansion joint modelling.

Pressure thrust is always present in expansion joints. Question is if there are unit restraints to hold it or not. Unrestrained expansion joint pressure thrust have to be "carried" by main anchors on both side of the bellows element. Such element can accommodate axial, lateral and rotation movement. Element should not see torsion moment. If such exists you have to specify it in your technical specification to order the unit.

Correct guiding of a line having expansion joint is absolute must. READ EJMA to get it right.

I recommend the simple modelling is not used. Use the complex modelling and model rods and other restrains. Rods can expand due to increased temperature and they can get longer due to loading. There are other elements also and not one of them is rigid. In critical applications work together with EXPERIENCED expansion joint designer to get usable values.

Unrestrained expansion joint connected to a vessel or pump or similar has a pressure thrust. But not full pressure thrust is on the nozzle. Nozzle load is bellows pressure thrust less pressure thrust calculated using pipe ID. Vessel/equipment anchor sees the full thrust plus bending moment. EJMA has very good sample and explanation on this issue.

Expansion joint has also spring rates. Large number of pipe designers specify very low maximum spring rates. Result is unstable system. Designer should also realize that expansion joint stresses go often past yield point and the element deforms. Spring force direction changes! Use always as stiff element as possible! It is safer and system is more stable.

Expansion joint modeler in CAESAR II used to be very good. I expect the same be the case with the new versions. There used to be one issue with 2 rod joint modelling. See my old postings from 2006 to 2008 for details.

As a general issue. I work constantly on expansion joints, piping and training. I see constant problems and mistakes. And they are increasing. Some of them have resulted in fatalities and system failures. Never use expansion joint if you do not know fully what is required!

Hi

Can some one help me how to model a dismantling joint using caesar II.This joint is placed after a valve and I have trouble in modelling the same.Please advise

Do we have Mild Steel material available in Caesar database or do we need to create a new material for this.

Pls advise
Jojo

Jojo,

What is happening that prevents you from modelling the joint?