Classification of shell stresses resulting from piping nozzle loads

In a previous paper, the authors discussed the classification of membrane stresses caused by piping loads resulting from restrained free thermal expansion. In that paper the authors proposed that although these stresses exhibit both primary and secondary characteristics, it is more appropriate to classify the resulting stresses as primary. In this paper, the authors present further FEA-based justification of this hypothesis. First, the vessel-nozzle intersection is modeled with 3D solid elements. Next, an elastic-plastic analysis of the previously examined piping/vessel layout is presented, with an examination of the final strain levels. Finally, a shakedown evaluation is performed. The results of these evaluations show that, unless additional analysis indicates otherwise, the membrane stresses resulting from restrained free thermal expansion piping loads should be classified as primary.