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Non-circular PV under External pressure

Non-circular PV under External pressure

Non-circular PV under External pressure

(OP)
I need to do a buckling check on a rather non-standard PV.

Titanium Grade 5
Box shaped vessel (One dimension much longer than the other two)
External Pressure of 450 bars
Checking for collapse from buckling

I have seen that only ASME VIII Division 2 can give some design rules to this kind of vessel. I have a FE analysis results from this so I thought I could go by the design by Analysis req. But given the combination spec above is resulting in a lot of dead ends. Anyone experience from this? Thnks for any help.

RE: Non-circular PV under External pressure

I have lots of experience in DBA for buckling. Specifically, what are your concerns?

RE: Non-circular PV under External pressure

(OP)
TGS4, thank you for your reply.

My concerns are mostly related to finding the buckling pressure for the PV. I have completed a linear buckling eigenvlue analysis and my first eigenvalue is at 10,8 using the defined external pressure. That was great and I was rather optimistic about the design. When doing a check against ASME VIII Div2, I saw that it wasn't that easey. I have used ASME VIII some years back for a more standard PV for internal pressure, but not for external pressure. The DBA does not seem to help me very much here. At least not a linear analysis.
I might consider doing a non-linear progressive collapse analysis. A linear buckling analysis supposes that everything is perfect or according to the model. Wall thickness exactly as modelled, Straightness exactly as modelled. Perfect material properties. Of course, that is not the case.
Do you have any experience with ASME VIII,external pressure, non circular PV?

RE: Non-circular PV under External pressure

I sure do have experience with that. I have even taught a tutorial and a DBA (Design By Analysis) class on it.

Here's my take on DBA for buckling failure:
- Eigenvalue buckling is somewhat useful for trying to understand the potential failure modes/shapes. It is not useful for anything else.
- The "design margins" in VIII-2, 5.4.1.3 are guesses, at best. Most real vessels will not fall into one of the categories provided, and so the designer is left to their own devices to determine an appropriate margin for eigenvalue buckling. Either way, that's dumb.
- Non-linear (elastic-plastic) buckling is the only method that I trust to find real failure modes.

RE: Non-circular PV under External pressure

(OP)
TGS4, thanks for useful input. I am tending to think the same as you.I have been going through all the calculations in ASME VIII, and I end up with a very heavy PV. (If I have understood the Code correctly) I will go for a non-linear elastic-plastic buckling analysis.

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