The effect of analysis model on the stress intensity calculation for the nozzle attached to pressure vessel under internal pressure loading

The stress behavior of a nozzle attached to the pressure vessel is usually analyzed using a simplified 2-D axi-symmetric model, where part of the vessel is also included in the numerical model. For conservatism, the modeled vessel radius sometimes is larger than the actual value. This paper creates three different 2-D axi-symmetric finite element models, where different vessel radii are modeled, i.e. 1, 1.5 and 2 times the actual vessel radius. Using these simplified numerical models to calculate the membrane and membrane plus bending stress intensities along some selected sections when undergoing internal pressure loading, and comparing these results with those evaluated from the realistic 3-D model, it shows that the 2-D model with vessel radius equaling to the actual value could well represent the behavior of a nozzle attached to the vessel.