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Research Papers: Materials and Fabrication

Fracture of Wrinkled Pipes Subjected to Monotonic Deformation: An Experimental Investigation

[+] Author and Article Information
Arman U. Ahmed

Department of Civil and Environmental Engineering,  University of Alberta, Edmonton, AB, Canada T6G 2R3

Mehmet Aydin

 Mela Consulting, Inc., Edmonton, AB T5Y OC6, Canada

J. J. Roger Cheng

Department of Civil and Environmental Engineering,  University of Alberta, Edmonton, AB, Canada

Joe Zhou

 TransCanada Pipelines Ltd., Calgary, AB, Canada T2P 5H1

J. Pressure Vessel Technol 133(1), 011401 (Jan 20, 2011) (9 pages) doi:10.1115/1.4002499 History: Received April 14, 2010; Revised July 20, 2010; Published January 20, 2011; Online January 20, 2011

Buried pipelines, used by petrochemical industries in North America for transporting oil and derivatives, are often subjected to large deformations resulting from geo-environmental factors and operating conditions, such as geotechnical movements, thermal strains, and internal fluid pressure. Exceeding the critical deformation limit of these pipes initiates wrinkles, and further increase may result in fracture, thus jeopardizing the safe operation of a field pipeline. A recent field fracture and failed laboratory specimens under monotonic load history address the necessity of conducting a full-scale test program to better understand the complete post-wrinkling behavior and failure modes of wrinkled pipes under similar loading conditions. Six tests with two sizes of pipe (NPS16 and NPS20), which are typical of those used in the field for transmission of hydrocarbons, were tested under monotonic axial and bending deformation. Test results in general had shown that both NPS16 (pipe material grade X60) and NPS20 (pipe material grade X65) steel pipelines generally exhibited a ductile behavior after wrinkling. Eventually, these pipe specimens failed due to excessive cross-sectional deformation. Several incidents of rupture or fracture in the pipe wall were observed at the sharp fold of the wrinkle on the compression side of the deformed pipe.

Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Typical wrinkle shapes (7,12)

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Figure 2

(a) Accordion type failure under monotonic loading (5) and (b) fractures under cyclic deformation (9)

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Figure 3

Final deformed shapes of the specimens obtained from (a) the WestCoast Energy Inc. (5), (b) the test (5), and (c) the numerical work (11)

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Figure 4

Engineering stress-strain plot of X60- and X65-grade-steel obtained from tension coupon test

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Figure 5

Schematic of test setup

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Figure 6

Typical layouts of strain gauges and Demec points

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Figure 7

MTS load versus displacement response of specimens 2 and 3

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Figure 8

MTS load versus displacement response of specimens 4–6

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Figure 9

Global moment-curvature behavior of specimens 2 and 3

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Figure 10

Global moment-curvature behavior of specimens 4–6

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Figure 11

Local moment-curvature behavior of specimens 3 and 5

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Figure 12

Initial deformed configurations of specimens 2–5

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Figure 13

Local longitudinal strains versus global curvature for specimens 2–4 and 6

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Figure 14

Local circumferential strains versus global curvature for 16 in. pipes

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Figure 15

Local circumferential strains versus global curvature for 20 in. pipes

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Figure 16

Global curvature-global longitudinal compressive strain relationships for specimens 2–5

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Figure 17

Global longitudinal compressive (Demec) strain growth with axial shortening

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Figure 18

Global longitudinal compressive (Caliper) strain growth with axial shortening

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Figure 19

Comparison of final deformed shapes between (a) specimens 2 and 5 and (b) specimens 3 and 6

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Figure 20

Cut segment from the compression side of specimens 2 and 3

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Figure 21

Fracture in the wrinkle fold of (a) the field (5), (b) the test specimen (5), and (c) location of strain reversal in FE model (11)

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