SCF and Fatigue Analysis of Sphere-Nozzle Intersections With LTA

Abstract

A linear elastic finite element analysis (FEA) is carried out to determine the stress concentration factor (SCF) of a pressurized sphere-nozzle intersection. Nine-noded axi-symmetric 2D (ring) elements are used, and vessels without and with inner-wall local thinned areas (LTA) are considered. The SCF values obtained for vessels with uniform wall thickness are compared with previously published experimental and analytical results, and also with results from standard formulas given in the literature. An evaluation is made of the effect on the SCF of three types of inner-wall LTA; thinning in the nozzle, in the sphere, and in both components. As well, an evaluation is made of the effect on the SCF of growth of the LTA away from the intersection. A detailed parametric study is then carried out to determine the SCF for vessels with different depths of LTA. An elastic-plastic fatigue analysis for simulated seismic action is next carried out for some sample intersections, without and with LTA. The results provided are intended to contribute to the information available on the stress and fatigue characteristics of sphere-nozzle intersections with LTA.