Allowable Bending Stress Near Support/Shell Interface
Allowable Bending Stress Near Support/Shell Interface
(OP)
I am working on a small vessel which is basically supported (cantilevered) using (1) 4" Sc 40 pipe support . I want to calculate the stresses near the support/shell interface.
Do you know of any method which could be used to calculate the stresses near the interface and on the shell ? Is WRC-107 too conservative for this case ?
Also, what would be the allowable limit on bending stress close to interface(i.e., should it be considered as secondary bending stress or primary bending stress ? The loading is dead weight + seismic load.
Thanks
Viks
OH
Do you know of any method which could be used to calculate the stresses near the interface and on the shell ? Is WRC-107 too conservative for this case ?
Also, what would be the allowable limit on bending stress close to interface(i.e., should it be considered as secondary bending stress or primary bending stress ? The loading is dead weight + seismic load.
Thanks
Viks
OH





RE: Allowable Bending Stress Near Support/Shell Interface
It is not the same as Nozzle/Shell interface since there is no opening at support/shell joint.
RE: Allowable Bending Stress Near Support/Shell Interface
So... this is one of those rare cases where the physical situation matches up with WRC-107 / -297...
As for primary or secondary... A dead weight load is secondary after the vessel has fallen down to the ground and the load on the support has therefore self limited. If you plan to evaluate the support load with the vessel substantially undamaged, then the load is not self limiting and thus would be considered primary. Likewise with seismic.
jt
RE: Allowable Bending Stress Near Support/Shell Interface
NandViks
RE: Allowable Bending Stress Near Support/Shell Interface
This statement is not necesserely true. You as the engineer performing the evaluation need to determine whether the loading which is causing the stress is self limiting. Some studies have shown that piping loads caused by thermal expansion of piping are self limiting - but only after substantial damage has been done to the vessel. It is a common misconception that all thermally induced loads are secondary. When you read this in the Code, pay very close attention to the wording. They do not include external loads such as those due to attached piping in the "thermal loading is secondary" part.
jt
RE: Allowable Bending Stress Near Support/Shell Interface
Now, per ASME Sec VIII Div. 2, Table 5.6, under,
Vessel Component - Any shell including cylinders, cones, spheres and formed heads
Location - Near nozzle or other opening
Origin of Stress - Net-section axial force and/or bending
moment applied to the nozzle, and/or internal pressure
The bending stress can be considered as Q, no matter what kind of loads (self limiting or not) are applied on nozzles.
Would you agree with interpretation ??
NandViks
RE: Allowable Bending Stress Near Support/Shell Interface
In your jugement, do your loads physically behave in a self limiting manner? Then secondary. If not, then can you feel that you have acted in good faith if you do not consider them to be of a primary nature?
Once again, we have a situation where... "Just go with the nonlinear analysis and avoid this primary vs secondary discussion" is definitely applicable.
jt
RE: Allowable Bending Stress Near Support/Shell Interface
Agreed.
RE: Allowable Bending Stress Near Support/Shell Interface
Given this constraint...could you plz explain why the local bending stress can be treated as secondary at nozzle/shell intersection(per ASME), while at support/shell interface they have to be treated as primary (per jte's response)while performing a linear analysis ?
RE: Allowable Bending Stress Near Support/Shell Interface
RE: Allowable Bending Stress Near Support/Shell Interface
jt