Limit Loads for Pipe Elbows Subjected to In-Plane Opening Moments and Internal Pressure

Abstract

The purpose of this study is to determine limit loads for pipe elbows subjected to inplane bending moments that tend to open the elbow (i.e., increase its radius of curvature), and the influence of internal pressure on the value of the limit load. Load-deflection curves were obtained, and from these curves plastic collapse and instability loads at various values of internal pressure were determined. This was done for different pipe bend factors (h = Rt/r2) using the nonlinear finite element analysis code (ABAQUS) with its special elbow element. A set of limit curves was generated from the results. These curves show the variation of collapse and instability loads with internal pressure for different elbows. Collapse loads were found to increase and then decrease with increasing pressure for all the elbow geometries studied. Instability loads were difficult to reach because of the large stiffening effect of the elbow cross-sectional deformation, and they were generally found to decrease with increasing pressure.

Plastic loads for 90° thick-walled elbows under combined pressure and bending

“…It is known that plastic behaviours of thin-walled elbows under combined pressure and bending are quite complex, particularly because of ovalization of the cross-section resulting from the large geometry change effect [10][11][12][13][14][15][16][17]. For instance, the addition of internal pressure could affect the cross-sectional ovalization, which in turn could affect plastic behaviours.…”

“…It shows that equation (9b) gives lower plastic loads than equation (10) for r/t 5 5 up to l 5 0.5. Thus it is recommended to use equation (11) with equation (10) for r/t ( 5 and l > 0.5. Otherwise equation (9a) with equation (9b) should be used.…”

A method to estimate plastic loads for elbows with non‐uniform thicknesses

“…Determination of plastic loads for elbows is important in structural integrity analysis of piping components. Numerous papers can be found in literature, including analytical works, 1–3 experimental works 4–7 and numerical works 7–20 . Closed‐form solutions for plastic loads of elbows have been proposed, for instance, under internal pressure, 3 in‐plane bending, 1–3,13,17–20 and combined pressure and bending 12,13,18 .…”

“…E-mail: kimy0308@korea.ac.kr merous papers can be found in literature, including analytical works, 1-3 experimental works [4][5][6][7] and numerical works. [7][8][9][10][11][12][13][14][15][16][17][18][19][20] Closed-form solutions for plastic loads of elbows have been proposed, for instance, under internal pressure, 3 in-plane bending, [1][2][3]13,[17][18][19][20] and combined pressure and bending. 12,13,18 One interesting point to note is that all existing works assume that elbows have a constant thickness.…”

Uncertainty Analysis of Data-Based Models for Estimating Collapse Moments of Wall-Thinned Pipe Bends and Elbows

“…In addition, the pipe bends and elbows can absorb substantial thermal expansion and seismic movement through the energy dissipation incurred as a result of local plastic deformation. Therefore, they can maintain the integrity of the piping system under transiently loading conditions [1][2]. On the other hand, care must be taken to ensure that the collapse load is avoided.…”