Stability Design Criterion for Vessels Subjected to Concurrent External Pressure and Longitudinal Compressive Loads

This paper presents a design procedure for determining the maximum allowable compressive stress and the maximum allowable external pressure for cylindrical vessels subjected to loadings which produce both longitudinal and circumferential stresses simultaneously. Although the ASME Pressure Vessel Code Section VIII [1] mentions the combinations of loadings as a factor in determining the thickness of vessels, the Code procedures (UG-23) for longitudinal compressive stress and (UG-28) for external pressure do not consider the interaction of these two buckling loads when acting concurrently. Calculations of typical vessels subjected to these conditions reveal that adherence to the Code rules without inclusion of these effects may yield results which fall below the safe design limits established by the Code. The design procedure developed herein extends the existing Code formulations as applicable; and incorporates established elastic stability data as necessary.