scope:

This Case provides alternative rules to those given in Section III, Division 1, NB-3133, NC-3133, ND-3133, and Appendix XXII, for determining allowable compressive stresses for unstiffened and ring stiffened circular cylinders and cones, and for unstiffened spherical, ellipsoidal, and torispherical heads. The allowable stress equations are based upon theoretical buckling equations that have been reduced by knockdown factors and by plasticity reduction factors that were determined from tests on fabricated shells. (Nomenclature is provided in 1.4.)

This Case expands the coverage of load conditions and shell geometries, and includes equations for combinations of loads not considered in the Code paragraphs referenced above. These alternative rules are applicable to D_o/t ratios not exceeding 2,000, compared to the D_o/t = 1,000 limit in Fig. G in Subpart 3 of Section II, Part D. The slenderness limit for these rules is KL_u/r ≤ 200. Use of these alternative rules assumes the shell section to be axisymmetric with uniform thickness for unstiffened cylinders and formed heads. Stiffened cylinders and cones are also assumed to be of uniform thickness between stiffeners. Where nozzles with reinforcing plates or locally thickened shell sections exist, use the thinnest uniform thickness in the applicable unstiffened or stiffened shell section for calculation of allowable compressive stress.

The maximum temperature permitted for use of this Case cannot exceed the maximum temperature permitted in Section III, Subsection NB, NC, and ND, or Table 1. In Class 1 applications, all references to Subsections NC and ND should be ignored. In Class 2 applications, all references to Subsections NB and ND should be ignored. In Class 3 applications, all references to Subsections NB and NC should be ignored.