Inventor Natran MAWP of storage tank shell 1

[Vijay93]

Hello,

We have a shell component with a shell thickness of 5mm. We are trying to do a buckling analysis. We have constraints placed on the bottom. 50mbar is the input pressure and the self-weight of the roof is 1000kg. the result we got, out of the 8 nodes, we got the highest eigenvalue of -1.3. on further research, for eigenvalues less than -1, it is understood that buckling is not expected. so in conclusion, can we say 50 mbar is the MAWP? Any input would be highly appreciated.

 

[JStephen]

What kind of tank is this? What code is it built and/or being evaluated to?
For common tank types (API-650 flat-bottom, ASME coded vessels), the design codes specify how pressure/vacuum ratings are established or evaluated.

 

[Vijay93]

Hello,

Thank you for your response. We are trying to analyse an existing tank based on API 650 - Appendix F. But we are trying to check with NASTRAN the MAWP to show the client a simulation result.

 

[JStephen]

If this is an external pressure, the external design pressure could be limited by the shell, the roof, uplift on the bottom, or buckling/yielding in the corner weld, top angle, or intermediate stiffener areas. See Annex V.
If this is an internal pressure, the internal design pressure could be limited by the shell, roof, top angle area, anchorage and lack thereof, or by other construction details required for certain pressures, or by load combinations with pressure and wind or pressure and seismic. See Annex F and E.
In either case, the operating pressure would generally be different from the design pressure.
MAWP is an ASME term that is not defined in API-650.
Using FEM to show shell buckling is precluded doesn't really say anything about allowable pressures as defined by API-650.

 

[Vijay93]

Thank you for the response. So to check for compliance of internal pressure with API 650, it is best to follow the steps mentioned in API 650 appendix F and E? The maximum pressures as defined by the formulae in the appendix would give us better results than FEM?

design external pressure shall not be less than 0.25 kpa
internal design pressure shall not exceed 18kpa based on 5.2 Design conditions
Are these the limiting factor based on API 650?

we are figuring out the maximum working conditions for the tank so that it can be equipped with the safety valves like PVRV and blanketing valves and their set points.

 

[MJCronin]

Vijay

Can you post a sketch or FEA model mesh or something ?

It is hard to visualize your problem with out a picture .... Can you post a cross section view of your tank ?


"We are figuring out the maximum working conditions for the tank so that it can be equipped with the safety valves like PVRV and blanketing valves and their set points"

Ah.... You have an old existing tank and are doing a reevaluation of a relief device installation ... Is that correct

MJCronin
Sr. Process Engineer

 

[Vijay93]

Hello,

Please find here an image of the tank under study.

 

[Vijay93]

"Ah.... You have an old existing tank and are doing a reevaluation of a relief device installation ... Is that correct" yes that is correct.