I have a frp vessel with four legs build as EN-13121-3.
the nozzle is vertical and is on the top of vessel.
I try to model in this way

flange (of pipe)
anchor + cnode
flange (equipment)
pipe ( for the distance nozzle-top vessel)
rigid element- no weight d=dia vessel th=thinkness vessel
lenght= height from tangent line to tangent line
anchor (on the bottom)


can you check this model?
(I'm sorry, I have an image but I'm not able to upload it)
and also is it possibile to use wrc 297 in this case?

Regard

Your model should be fine for normal level of detail. You can replace the rigid without weight with a normal pipe with dia= dia vessel and thickness of vessel and if the legs are flexible you can try to model also the legs.

But since you can not transfer big load on vessel I think it is not required.

Regarding the use of WRC - no, it is not applicable.

Ask manufacturer.

Regards,