The stresses and deflections developed due to all piping loads produce some significant deformation in the nozzles of the pressure vessels. In this paper a spherical pressure vessel with two cylindrical nozzles are analyzed. The stresses in the nozzles are evaluated using two comparative methods: one of them represents the classical way of using the superposition of the axial, bending and torsional loads; the other one is based on the requirements of the ASME Boiler and Pressure Vessel Cod, Section VIII, Division 2 and is developed by a FE analysis. In order to obtain the loads (forces and moments) at the end of the nozzle a specialized finite element program has been used. This program (Coade Caesar 5.30) allows studying the strength and flexibility behavior of the pipes that connect the analyzed nozzle with the rest of the plant. The results obtained are compared in order to find when the using of the classical methods of strength of materials can be used as conservative approaches. The finite element method is applied in order to check the most important load cases that appear during the interaction between pipes and shell. In this respect the sustained (proper gravity loads), expansion (thermal loads) and occasional (wind and seismic loads) are combined in order to check all the requirements of ASME. This study contains also the effect of the pressure trust and the influence of the real geometry of the junction (nozzle-shell) in the peaks of the stresses.