| Applies To | |||
| Product(s): | AutoPIPE | ||
| Version(s): | 2004, XM, V8i | ||
| Area: | Analysis | ||
| Original Author: | Bentley Technical Support Group | ||
| Date Logged & Current Version | June 2015 09.06.02.06 |
Problem:
Why are membrane stresses from pipe supports not included in AutoPIPE?
How to calculate the local stresses in pipe wall due to support welded to it.?
How to calculate local stresses in pipe wall when a clamp is placed around the pipe (restricting the radial growth of pipe)?
Background
In addition to the general large scale pipe stresses calculated in AutoPIPE. there are local pipe membrane stresses produced by pipe supports acting on the pipe wall. The transfer of load from the pipe support surface to the pipe wall over a given contact area may produce substantial membrane stresses. Another example is restraint of the thermal and internal pressure radial expansion. A pipe expanding within a full encirclement clamp support may again lead to substantial membrane stresses. Membrane stresses are a largely influenced by support type, support stiffness, and contact area. There is general lack of knowledge about membrane stresses that occur at supports within the pipe stress industry.
Solution:
In plane and out of plane membrane stresses may occur at a pipe support due to normal bearing action or due to friction between the pipe and support. A centerline model created using beam bending elements is not able to capture these effects. Hence, membrane stresses are not included in AutoPIPE centerline models.
The effects of these membrane stresses may not be significant in small bore pipelines (D/t < 100) which is the normal range of application of majority of piping codes. For large bore pipelines (D/t >100), these stresses can be significant and may lead to an un-conservative estimation of total stresses if they are not considered using FEA or Roark's formula. Hence, it is important to account for these stresses using special methods like FEA or Roark's formula.
We plan to address this in future release of AutoPIPE by including ability to model local membrane effects using shell elements. User defined stress concentration factors may be used to model these effects in AutoPIPE which could give a close approximation to refined FEA analysis. We appreciate your suggestion and will consider adding a note or warning in our product documentation.
By user defined stress concentration factors we meant Insert/Extra Data/ Joint Type and user SIF.
This issue has been logged as a new enhancement, TFS-72841: Include an ability to model local membrane effects using shell elements for pipe supports, to be added to a future version of the application.
Workaround:
Using AutoPIPE Nozzle seems to be one option that could be used at least for the pipe support welded to the pipe. In AutoPIPE Nozzle, use Attachment or Solid-Round, Solid-Rect type nozzle. Export the forces and moments from AutoPIPE and then be able to calculate the stress values.
Other options could be to use generalized finite element analysis like ANSYS and model the problem in those applications. Specifically for the radial stresses due to clamp, a general finite element analysis with shell, solid elements would give good results for the local stresses.
Alternatively, could use rules or equations provided by ASME Section III Div. 1, App Y, ignoring the limitation and calculate the local stress values.
Conclusion:
Pipe stress analysis applications like AutoPIPE are in general not concerned with and do not calculate local stress values.