Research Papers

Out-of-Plane Pipe Whip for a Bent Cantilever Pipe: Comparison Between Experiment and FEM Models

[+] Author and Article Information
S. R. Reid, M. Aleyaasin, B. Wang

School of Engineering,  University of Aberdeen, Aberdeen AB24 3UE, UK

J. Appl. Mech 79(1), 011005 (Nov 14, 2011) (7 pages) doi:10.1115/1.4004712 History: Received March 14, 2011; Revised July 12, 2011; Posted July 26, 2011; Published November 14, 2011; Online November 14, 2011

The three-dimensional, dynamic, elastic-plastic response of a right-angle bent cantilever pipe, with an initially uniform, circular cross section, subjected to out-of-plane loading is examined using finite element beam and shell models in ABAQUS. The large-deflection behavior involves both bending and torsional elastoplastic deformations of the pipe, phenomena which have not been previously studied in the context of the dynamic problem of pipe whip. Initially, neglecting ovalization and local collapse (kinking), the bent pipe is modeled as a beam, using spatial beam elements in ABAQUS. This enables the basic three-dimensional kinematic behavior of the pipe to be analyzed. A similar, but potentially more accurate, analysis was then performed using shell elements. It is shown that there is no significant difference in the global dynamic plastic response. However the ovalization of the pipe cross section and formation and movement of the plastic zones (hinges) can be captured by using shell elements. This provides data which could form the basis for examining local failures in the pipe run. Previously unpublished experimental results, obtained in an earlier study by some of the present authors, are compared with the simulated results. Good agreement is observed and it is concluded that a nonlinear dynamic model using finite elements provides a rigorous approach for estimating the hazard zone (HZ) and, also, for treating the kinematics of a whipping pipe for this complex three-dimensional situation.

Copyright © 2012 by American Society of Mechanical Engineers
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Figure 1

Original geometry and dimensions (m) of a right-angled bent pipe

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Figure 2

Test 41—a right-angle bent pipe (diameter = 28 mm) subject to an out-of-plane pulse of 90 ms duration (reservoir pressure 1000 psi)—comparison between experiment and models

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Figure 3

(a) Pipe tip speed, determined by FEM dotted curve for shell element analysis; solid for beam element analysis. (b) Pipe tip speed history (using beam model) for a 90 ms duration blow-down pulse. The transient phase is shown in solid and the subsequent motion in dotted curve. After 580 ms the dynamic whip motion stops and the pipe undergoes elastic oscillations from ∼600 ms. (c) Test 41—pressure traces for calculation of the pulse loading.

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Figure 4

Shell element analysis for local deformation: ovalization and kinking in vicinity of the root with the moving plastic zone approaching the end

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Figure 5

Three phases of motion from FE analysis: bending hinge only in AC; double-hinge mode in AC and CB; single hinge at B

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Figure 6

(a) Pipe path for a 90 ms pulse loading. Pipe’s transient profiles are shown in dark solid curves. Paths of the corner (C) and tip (A) are denoted in dotted and lighter curves, respectively. Motion stages: 0 (t = 0), 1 (t = 89 ms), 2 (t = 222 ms), 3 (t = 344 ms), 4 (t = 600 ms). Coordinate limits show the borders of the hazard zone—space swept by the freely whipping pipe. (b) Pipe paths for the first 90 ms during the loading pulse. The path of tip A is shown with solid curve and of corner C dotted curve. Again, coordinate limits shows the hazard zone.

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Figure 7

(a) Development of the plastic deformation in pipe: A (tip) is node 1 and B (root) is node 42, C (the corner) is node 23. After 44 ms the plastic deformation switches over from C to the root (B) and remains there until the pipe comes to a rest. (b) History of equivalent plastic strain: solid (root or B), circles (corner or C), diamonds (midpoint between root B and corner C), squares (midpoint between tip A and corner C).

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Figure 8

Spatial beam cross section



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