| 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:
I have a model where the support values do not change regardless if the weight of contents is checked on or off. How can that be? Seems as if weight of contents is not considered in my analysis, how to check and prove that Weight of pipe contents is being considered in my model?
Solution:
Multiple responses:
Response #1:
FAQ answer:
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. A future release of AutoPIPE will include an ability to model local membrane effects using shell elements. For now, user-defined stress concentration factors (Insert/Extra Data/ Joint Type and user SIF) may be used to model these effects in AutoPIPE which could give a close approximation to refined FEA analysis.
Response #2:
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 the restraint of 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 largely influenced by support type, support stiffness, and contact area. There is a general lack of knowledge about membrane stresses that occur at supports withing the pipe stress industry.
Response #3:
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 formulae. Hence, it is important to account for these stresses using special methods like FEA or Roark's formulae.
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.
A new enhancement has been logged, TFS-E72841:include an ability to model local membrane effects using shell elements for pipe supports