scope:

This Case provides alternative rules to those given in Section VIII, Division 1, UG-23(b), UG-28, UG-29, UG-33 and Appendix 1-8, or Section VIII, Division 2, Article D-3 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 para. 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 Do/t ratios not exceeding 2,000, compared to the Do/t = 1,000 limit is Fig. G in Subpart 3 of Section II, Part D. The slenderness limit for these rules in KLu/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 is shown in Table 1.

When applying this Case for Section VIII, Division 1, all references to Section VIII, Division 2 shall be ignored. Likewise, when using this Case for Section VIII, Division 2 applications, all references to Section VIII, Division 1 shall be ignored.

Alternative equations for determination of allowable compressive stress due to loads specified in UG-22 or AD-110 are provided. A listing of the allowable stress cases, combinations of cases, requirements for tolerances, and reinforcement of openings by Case paragraph number is given in Table 2, with indication of present coverage in Divisions 1 and 2.