Ramifications of Structural Deformations on Collapse Loads of Critically Cracked Pipe Bends Under In-Plane Bending and Internal Pressure

Finite-element analysis based on elasticeperfectly plastic material was conducted to examine the influence of structural deformations on collapse loads of circumferential through-wall critically cracked 90 degrees pipe bends undergoing in-plane closing bending and internal pressure. The critical crack is defined for a through-wall circumferential crack at the extrados with a subtended angle below which there is no weakening effect on collapse moment of elbows subjected to in-plane closing bending. Elliptical and semioval cross sections were postulated at the bend regions and compared. Twice-elastic-slope method was utilized to obtain the collapse loads. Structural deformations, namely, ovality and thinning, were each varied from 0% to 20% in steps of 5% and the normalized internal pressure was varied from 0.2 to 0.6. Results indicate that elliptic cross sections were suitable for pipe ratios 5 and 10, whereas for pipe ratio 20, semioval cross sections gave satisfactory solutions. The effect of ovality on collapse loads is significant, although it cancelled out at a certain value of applied internal pressure. Thinning had a negligible effect on collapse loads of bends with crack geometries considered. Copyright (C) 2016, Published by Elsevier Korea LLC on behalf of Korean Nuclear Society. This is an open access article under the CC BY-NC-ND license (http://creativecommons. org/licenses/by-nc-nd/4.0/).