14. Appears that the Flexible joint in my AutoPIPE model is not relieving pipe stresses, why?

Applies To
Version(s):2004, XM, V8i, CONNECT;
Area: Modeling
Original Author:Bentley Technical Support Group
Date Logged
& Current Version
Nov 2014


I have a model that shows the code stresses > 1 for a specific thermal loading. How do I get the stresses to become less than 1 or lower than manufacture allowable? I would have thought the expansion joints would help. But looks like they have no effect. Pipe stress do not change when a flexible joint is modeled. Why?


If the expansion joint does not seem to be flexing enough, review the Flexible Joint Stiffness values by opening the Dialog or Flexible Joint Input grid tab:

In some cases, the flexible joint stiffness settings were found to be all Rigid (as seen above). If a flexible joint has all stiffnesses set to Rigid, this would be the same as a piece of rigid pipe and will offer no flexibility. Suggest modifying the stiffness values as outlined by the Flexible Joint Manufacture.

If the flexible joint is entered as specified by the manufacture and still exceeds a nozzle allowable, suggest the following:

1. Perform a through review of the loads on the flexible joint to better understand why the forces / loads being transmitted are so high.

2. Remember when using a flexible joint there is a pressure thrust component related to the Pressure Area specified on the Flexible joint. You may need to add tie bars to the flexible joint or other suitable supports to restrain the pipe from pressure thrust.

3. Suggest contacting the Flexible Joint manufacture for assistance in designing a suitable  flexible joint for your application.  

See Also

Flexible Joint - Modeling Approaches, Tips, Techniques

Bentley AutoPIPE