Elastic Stresses in Elbows Submitted to In-Plane Bending Moment

Abstract

New analytical equations are developed to calculate stresses in an elbow submitted to an in-plane bending moment. If a detailed stress analysis is asked (for example, for the elastic stress intensity factor calculation KI), available code equations are not accurate enough because their determination is based on an axi-symmetric analysis, where the elbow is compared to a torus, and therefore the end effects are not taken into account. This work relies on elastic finite element calculations using shell elements. Longitudinal and circumferential stresses are calculated in the median section and in the junction section between the elbow and the straight pipe. Elbows considered here have a bend angle αc=45, 90, and 180 deg and show a ratio rm/t between 5 and 20 and a parameter λ up to 1. Analytical expressions are proposed to fit the membrane and bending components of each stress. Coefficients of these equations are tabulated and expressed only as a function of the ratio rm/t and the parameter λ for the median section and the junction section. An interpolation methodology is also given for intermediate elbow angles: these analytical relations give a simple solution to have an accurate estimate of the elastic stress distribution in the median section and the junction section in a elbow submitted to an in-plane bending moment, for a wide range of elbow angles, ratios rm/t and parameters λ.