Allowable Compressive Stress – Appendix 46
COMPRESS features the option to use the provisions of Appendix 46 for external pressure design. This allows designers to take advantage of the more accurate equations from ASME VIII-2, Part 4.4 (Division 2). Appendix 46 requires that Division 1 vessels still be designed using Division 1 allowable tensile stresses. As buckling is the failure mode for external pressure, the allowable compressive stresses calculated by Part 4.4 are allowed in Division 1 designs.
One advantage of using the Appendix 46\Part 4.4 equations is that they include consideration of external pressure plus axial compression. This means that a U-2(g) analysis is not required. Another advantage is that cylinders designed to Part 4.4 are often thinner than those designed with UG-28. Although Appendix 46 is just as safe as UG-28, some jurisdictions do not yet permit the use of Appendix 46 so it’s best to check before relying on this method.