The Effects of Geometric Irregularities on the Design Analysis of Thin-Walled Piping Elbows

Abstract

Geometric irregularities, such as ovality, in thin-walled elbows are known to give additional stresses under internal pressure loading. This paper presents results of detailed analyses, using the STAGS program, of a range of elbow geometries which have specified nonuniformities. Nonuniformities considered were thickness variation, initial ovality, intrados wrinkling and shrinkage of longitudinal welds. Loadings were in-plane bending and internal pressure. Results show that stresses due to in-plane bending are not significantly affected by the nonuniformities. However, stresses due to internal pressure are amplified by through-the-wall bending due to noncircularity of the cross section. Ovality, wrinkling and longitudinal weld shrinkage produce stress perturbations of comparable magnitude under internal pressure. Numerical data from the analyses are reduced to polynomial functions which give the maximum stress in the elbow as a function of pressure, radius-thickness ratio and degree of nonuniformity for long and short radius elbows.