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TECHNICAL PAPERS

Initial Imperfection Models for Segments of Line Pipe

[+] Author and Article Information
Alfred B. Dorey

Department of Civil and Environmental Engineering, University of Alberta, Edmonton, Alberta, Canada T6G 2G7adorey@shaw.ca

David W. Murray

Department of Civil and Environmental Engineering, University of Alberta, Edmonton, Alberta, Canada T6G 2G7dwm@civil.ualberta.ca

J. J. Cheng

Department of Civil and Environmental Engineering, University of Alberta, Edmonton, Alberta, Canada T6G 2G7jjrcheng@civil.ualberta.ca

J. Offshore Mech. Arct. Eng 128(4), 322-329 (Oct 02, 2005) (8 pages) doi:10.1115/1.2199565 History: Received July 07, 2004; Revised October 02, 2005

Initial imperfections have long been acknowledged as having an effect on the behavior of shell structures, affecting both the global and local behavior. Yet, despite their significance, initial imperfections are rarely included in analytical models for pipelines. This is usually because of the complicated nature of initial imperfections, the difficulty in measuring them, and the small amount of available literature that describes their geometry. Some recent investigations at the University of Alberta in Edmonton have focused on the effect of initial imperfections on the behavior of segments of line pipe. Imperfections measured across the inside surface of pipe test specimens were incorporated into a finite element model that was developed to predict the experimental behavior of the specimens tested under combined loads of internal pressure, axial load and bending moment. Test-to-predicted ratios for the load carrying capacity of the test specimens had a mean value of 1.035 with a coefficient of variation of 0.047. The improvements in the accuracy of the finite element analysis models that include the initial imperfection pattern indicate their importance in modeling the experimental behavior. Once the importance of initial imperfections was established, idealized patterns were developed to simplify numerical modeling. This paper presents the results of different patterns investigated for both plain and girth-welded segments of line pipe and provides recommended simplified assumed initial imperfection patterns.

Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Load-displacement response of shell structures

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Figure 2

Imperfection device at the top of a test specimen

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Figure 3

Comparison of imperfection meshes

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Figure 4

Global moment versus global curvature comparison for a typical plain pipe

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Figure 5

Global moment versus global curvature comparison for a typical girth-welded pipe

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Figure 6

Schematics of assumed imperfection patterns

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Figure 7

Wall variation for the assumed imperfection pattern

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Figure 8

Comparison of global response for the different initial imperfection patterns for specimen CP20N-2

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Figure 9

Typical offset between top and bottom cans

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Figure 10

Comparison of global response using different imperfection patterns on specimen CP40W

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Figure 11

Imperfection study for D∕t=51 plain specimens

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Figure 12

Comparison of global moment versus global curvature plots for specimen dt51d324x52ip2p72

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Figure 13

Comparison of global moment versus global curvature plots for specimen dt64d508x56ip3p00

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Figure 14

Results of initial imperfection study for D∕t=51 girth-welded specimens

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Figure 15

Comparison of global moment versus global curvature plots for specimen dt51d324x52ip0.20wp36

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Figure 16

Comparison of global moment versus global curvature plots for specimen dt64d508x56ip0.25wp00

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