Translational Stiffness Estimates for Expansion Joints 2

[UtilityLouie]

I am modeling some steam piping in a stress program and need to input translational stiffness information on some expansion joints.

This is a typical problem I have run into before. I found some old catalog information, but I don't have good confidence in it.

Does anyone have any suggestions?

I am not comfortable with modeling the joint as "free" in all directions.

Thanks!

 

[CRG]

Have you tried to get the information from the manufacturer?

 

[UtilityLouie]

We don't have the manufacturer selected yet - that would make too much sense!

Also, some of the manufacturers standard literature that I have found don't publish this information. I have found that you have to buy the joint and then you get the EJMA form with all the data.

The problem is -- I am trying to figure out where and when I need flex joints -- my stress model doesn't converge if I give the joints too much freedom and I'm thinking that if I give them a stiffness, it will help with convergence.

 

[77mccoy]

Normally input some resistance say 1000 lbs per inch for XYZ forces then put some rotational forces. Play with numbers and it will give you a feel for your model.
Be sure to anchor your system to make piping move in direstion to take advantage of expansion joint

 

[StressGuy]

Since you're working with steam, I'll assume you're working with metal bellows joints. You can get some working numbers from the vendor catalogs. You definitely do not want to model the joint as free, as there are still some substantial stiffnesses involved with metal joints.

You should be able to download the senior flexonics catalog here and get some reference values for lateral, axial and angular spring rates:

http://www.myej.net/Catalogs/MetalCatalog.pdf

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.