Effect of shape imperfections on elastic stresses of U-bends subjected to in-plane moment

Abstract

PurposePrecise assessment of elastic stress is required in the field of fracture mechanics. While bending a straight pipe, the deformation of the circular cross section out of roundness called ovality and thinning are foreseeable. The ovality has a significant effect on the structural integrity of the pipe. The sole objective of this paper is to provide new analytical solutions to predict accurate elastic stress distribution at the median section of the U-bend, with deformities such as ovality and thinning when subjected to in-plane closing moment by using elastic finite element analysis.Design/methodology/approachThe quarter model of the U bend has been analysed by using ABAQUS. The elastic stress components included in this analysis are longitudinal bending stress, longitudinal membrane stress, circumferential bending stress and circumferential membrane stress. Based on finite element results, analytical elastic stress solutions are also provided for both longitudinal and circumferential stresses by using these stress components.FindingsAs the ovality has a significant effect, it is further included in the analytical solution. The thinning is not included since it has very little effect. Analytical stress solutions are provided for a wide range of bend characteristics to include ovality, mean radius and thickness.Originality/valueSignificance of ovality and thinning on elastic stress of U-bend has not been reported in the existing literature.

Effect of structural deformations and bend angle on the collapse load of pipe bends subjected to in-plane closing bending moment

“…In industries, the outline of the pipe bend’s cross-section is normally taken in the first off trial test to calculate the shape imperfection. The magnitude of the shape imperfection is calculated as given in equations (1)–(3) (Balakrishnan et al , 2019a, 2019b; Christo Michael et al , 2018; Krishna et al , 2020; Sasidharan et al , 2017). …”

“…Despite the fact that the allowable thinning limit was not clearly stated, the maximum allowable limit of ovality shall not exceed 8%, as prescribed by ASME. The literature (Balakrishnan et al , 2019a, 2019b; Christo Michael et al , 2012a, 2013, 2018; Krishna et al , 2020; Sasidharan et al , 2017) contains reports on ovality and thinning up to 20% for pipe bend analysis. Straight pipes are attached at both ends of the pipe bend to eliminate the end effect due to boundary conditions.…”

Determination of bend angle and shape imperfection effect on collapse load of pipe bends under in-plane opening moment

“…Moreover, in the distribution of stress components, ovality plays a vital role whereas thinning has a negligible impact. 20 However, the pipe bend's cross-section is stiffened and the collapse load is increased to a load of IP with IPCM. The stiffening effect due to IP with IPCM varies with ovality.…”