No examples are provided on as to how to model a Pathway "X-Press" single expansion joint. Do you have any examples?

Dear Terry;

Coade has asked me to respond to your inquiry. I am Pathway's pipe stress engineer and have worked extensively with Coade in the past.

The X-Press expansion joint is intended to absorb large amounts of axial movement only. They are intended for long runs of straight pipe, ie loading docks and distribution systems. They are a self guiding unrestrained expansion joint. There are two ways of modeling this type of joint.

Method I (Spring rate modification method)

Define a zero length expansion joint and input the catalog values for axial spring rate and effective diameter. Enter infinite for the lateral and angular spring rates.

Method II (Actual Model)

There is insufficient information in the catalog to allow you to prepare an depth model of the bellows element. The best thing to do is to contact Pathway with the catalog part number you are interested in and request the input information. Once you have done this you can input a defined length bellows and input all values except the angular spring rate. Then you would have to add a rigid element over the length of the bellows with a dumpy number at one end. You can then restrain the dumpy node to the corresponding bellows node. If you line is running in the X axis, the restrains would be Y,Z, Ry & Rz.


Additional weight should be added on each end of the zero length bellows to account for the extra weight of the unit. X-Press joints have a hardened outer shell surrounding the bellows, they also have two heavy rings at each end. Therefore, the weight that should be added is equal to the jacket pipe plus two end rings. Unfortunately I can not give you guidance on sizes and thickness without knowing the size you are working with.

Also, be advised that CAESAR II applies the system pressure thrust at the expansion joint. This is not the correct location as the pressure thrust develops at the elbows up and down stream of the expansion joints. Therefore, if you were to look at the axial load in the pipe line, you will see a large axial compressive load which is not accurate. The pipe will be in compression and hence must be guided in accordance with guiding recommendations in our catalog (also in EJMA), however it is significantly smaller load then CAESAR indicates.

If you would like to know more about this, feel free to contact:

Dan Edgar @ pipesol@connectnet.com
Russell Cochrun @ cochrun@pathwayb.com

The trust forces on bellow induced by internal pressure really exist if expansion joint is not rod-tied and piping system is not properly anchored. So Caesar II give you the option to include the trust force when you meet the case as mentioned above.

Regards

Alvin Zhu