The plastic load of a hemispherical head with a cylindrical nozzle subject to an internal pressure and/or moment is established using two new plastic criteria; the plastic work curvature (PWC) criterion and the ratio of plastic to total work curvature (RPWC) criterion. The calculated plastic loads are compared to ASME Design by Analysis stress categorization and limit analysis allowable loads. The stress categorization approach is seen to be dependant on the appropriate choice of stress classification lines and the classification of primary, secondary and peak stresses. The limit load approach is simpler to apply but does not consider material strain hardening and/or large deformation behaviour and may often lead to conservative design loads. In the plastic analyses, strain hardening material models and large deformation analyses are considered. The calculated allowable pressure-moment interaction surfaces are assessed and compared for the different methods.
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