Nozzle on Flat Head - FEA (Stress concentrations)
Nozzle on Flat Head - FEA (Stress concentrations)
(OP)
The pressure vessel i'm designing is basically a box, i.e. flat plates. And i've understood that WRC107/297 are not applicable for nozzles attached to flat plates (correct me if i'm wrong), soo FEA it is.
The nozzle is welded to the plate. The weld is simply modelled as a straight line. This causes a stress concentration in the top-weld / nozzle junction. In an earlier report they assesed the stress values a distance away from this stress concentration (they simply put the path a distance of ~10mm above the stress concentration) - but this was however according to another code. Is this allowable according to ASME code?
The nozzle is welded to the plate. The weld is simply modelled as a straight line. This causes a stress concentration in the top-weld / nozzle junction. In an earlier report they assesed the stress values a distance away from this stress concentration (they simply put the path a distance of ~10mm above the stress concentration) - but this was however according to another code. Is this allowable according to ASME code?





RE: Nozzle on Flat Head - FEA (Stress concentrations)
You say that the weld is modelled as a "straight line". Are you using shell elements of 3D-solid elements? That will make a huge difference in how you post-process the results for compliance to ASME Section VIII, Division 2, Part 5 (I assume that when you say "ASME", this is the Code that you mean...).
RE: Nozzle on Flat Head - FEA (Stress concentrations)
The FE model is made of solid 3D elements. What i mean by a 'straight line' is that there is no fillets where weld meets nozzle / vessel.
Regarding which ASME code i'm following, i should have stated that. However i think the reason that i didnt, is that i'm not really quite sure. I've only been told to follow ASME VIII div 1, and also "Stress analysis by FEM". I guess i should clarify with the customer which code to follow when looking at FE results.
RE: Nozzle on Flat Head - FEA (Stress concentrations)
If you are not including the fillet weld cap, then I would not place the SCL any distance from the junction. I would suggest that the stress linearization be done appropriately. If there are actual issues, you can either add the fillet weld and place the SCL at the toe of the fillet, or modify the loads.
RE: Nozzle on Flat Head - FEA (Stress concentrations)
About the WRC bulletins being applicable for flat plates.. When i search around different forums, i find that the bulletins hold some limitations regarding thickness ratios etc.
If i have a flat plate of thickness 80mm, with an attached nozzle of wall thickness 8,2 mm (NPS8 - placed on top of the plate) - would WRC107/297 still be applicable?
PS. i'm sorry i keep asking about WRC, but it'll take a while before i can acces the bulletins. And it would be extremely helpful if i could get confident whether i need them or not. And i tried emailing WRC already (no answer so far though)
RE: Nozzle on Flat Head - FEA (Stress concentrations)
Regards,
Mike
RE: Nozzle on Flat Head - FEA (Stress concentrations)
If i take D as infinite (due to flat plate) i have the following ratios:
d/t = 26, OK
D/T = inf OK
d/T = 2.7 NOT OK (should be larger than 5)
and (d/D)*sqrt(D/T) = 0 (i guess d/D goes faster to 0 than sqrt(D/T) goes towards inf, but not quite sure.
the bulletins doesnt mention flat plates. What you you guys in here think about using WRC with these ratios - would it be useless or useful?
d=219, D=inf, T=80, t=8,2 (in mm)
RE: Nozzle on Flat Head - FEA (Stress concentrations)
Some other failure mechanism will be at play. Since WRC537 doesn't address the nozzle itself, I'm going I lean towards useless.