As we know, in CII we can model the nozzle with WRC291 OR API650 and pd5500,in the technical document, there has some description about how to
model it. but the example is always to model the nozzle along the side.
now I need a top nozzle to calculate the connected pipe. what can I do?

thanks everyone.

Are you talking about a top nozzle on a horizontal vessel, or a top nozzle on a vertical vessel ?

Do you want to include nozzle flexibility in your pipe model, or calculate local stresses in the nozzle / shell ? Or maybe both ?

If the vessel is horizontal, just follow the CAESAR II manual examples. If you have vertical vessel with a nozzle in a curved head such as elliptical, spherical, torispherical, talk to a vessels engineer for stresses. For modelling, probably assume it's rigid with thermal displacements.

WRC297 and API650 only address nozzles on cylinders. So you technically can't apply either of these Codes to a nozzle on a head. PD5500 does address nozzles on heads, but before you attempt this you should review the appropriate sections of this code.

thanks everyone