Div 2 - Internal Support Attachment Methodology

[rbel038]

Hi All,

We are designing our first Div 2 vessel after many Div 1 vessels over the past few years. My question is when it comes to internal support structures for say a demister pad or tower tray how do you approach this? As i understand Div.1 allows you to use generally acceptable rules to prove the design of such items however Div.2 from reading seems to point you directly to design by analysis (Part 5, FEA).

Do you have any room to move when it comes to this items to use the standard calcs from say PVElite to design internal supports? It would be an expensive exercise to design these most probably lightly loaded components using FEA when we can design the rest of the pressure components for far less work in PVElite / NozzlePRO.

 

[gr2vessels]

I have never used FEA or other 'special' method of calculation for simple support rings, brackets, etc in ASME VIII-2. I might be wrong, but where did you get the impression of being directed to FEA in ASME VIII-2 ?

 

[rbel038]

gr2vessels,

Probably through my lack of experience with div.2 .

para 4.15.5.2 in Div.2 gives the options for lugs which i took as being applicable to a support bracket to hold a demister element. This then points to either Part 5 or WRC or another 'analytical method'.

If you dont mind me asking , what calculation methodology would you use for say a support ring in a Div.2 vessel? I thought the whole point of Div.2 was that you either design with the rules provided, which check against stress intensity allowables or you opt for numerical analysis and check against the same criteria. The formula im use to working with in Div.1 of course only summarise in an allowable stresses , or do i simply re-use them and look at things from a membrane and bending stress perspective.

Thanks again. Im sure it will eventually be clear.

 

[TGS4]

The directions in Part 4 to Part 5 do NOT automatically mean that you are required to do an FEA. You could continue to use whatever method you were using before (for your Div. 1 vessels). These methods would likewise be calculating a stress in the shell. Therefore, when you evaluate the additional stress in the shell due to the internals, you would need to follow the approach in Part 5. There might be a small modification necessary (probably based on the stress invariant), but otherwise you should be fine.