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Offshore and Structural Mechanics

Numerical Investigation of Tearing Fracture of Wrinkled Pipe

[+] Author and Article Information
Arman U. Ahmed

Department of Civil and Environmental Engineering, University of Alberta, Edmonton, AB, T6G 2W2, Canadaauahmed@ualberta.ca

Sreekanta Das

Department of Civil and Environmental Engineering, University of Windsor, Windsor, ON, N9B 3P4, Canadasdas@uwindsor.ca

J. J. Roger Cheng

Department of Civil and Environmental Engineering, University of Alberta, Edmonton, AB, T6G 2W2, Canadaroger.cheng@ualberta.ca

J. Offshore Mech. Arct. Eng 132(1), 011302 (Dec 22, 2009) (10 pages) doi:10.1115/1.4000402 History: Received November 18, 2008; Revised August 13, 2009; Published December 22, 2009; Online December 22, 2009

Steel pipelines, buried in cold regions, often respond to thermal strains and/or geotechnical movement caused by factors such as thaw settlement, frost heave, and slope instability. These complex field conditions can impose large displacements on these pipelines, resulting in localized wrinkles well into the plastic range of the pipe material. Eventually, there is a possibility of a fracture occurring at a wrinkled location under continuous deformation. A recent field fracture and a failed laboratory specimen have been observed within a telescopic wrinkle under tearing action and the loading histories have been found to be monotonic, without significant strain reversals. These incidents underscore the need for a detailed investigation, which seeks to answer fundamental questions regarding this unique mode of failure. In this study, a finite element model has been developed, which is capable of accounting for material nonlinearity effects, large displacements, large rotations, initial imperfections, and possible complex contact surfaces. Based on limited test data, the comparison of the numerical and the experimental results demonstrates the ability of the present model to predict the local buckling behavior of pipes when deformed well into the postwrinkling range. The results of this analytical work include the global and local deformation patterns and a detailed assessment of the stress-strain relations at the region of the telescopic wrinkle. The results obtained from this study have recognized the occurrence of strain reversal at the sharp fold of the wrinkle on the compression side of the pipe, a phenomenon that could be considered to be the key factor for triggering this unique failure mechanism.

Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Accordion type failure under monotonic loading (2)

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Figure 2

Pipe segment showing tearing fracture at wrinkle location obtained from WestCoast Energy (2)

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Figure 3

Schematic view of the test set with sequence of applied axial and transverse load (2)

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Figure 4

Load-displacement response for the test specimen (2)

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Figure 5

Fracture (through-thickness crack) in the wrinkle fold of the pipe specimen (2)

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Figure 6

Schematic view of the developed FE model

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Figure 7

Configuration of section points in a homogeneous shell element (3)

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Figure 8

Typical geometry and initial boundary condition for pipes

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Figure 9

True stress versus true plastic strain behavior until failure

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Figure 10

Schematic views of assumed initial imperfection patterns where the X-axis represents the longitudinal direction of pipe (10)

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Figure 11

Predicted location of self-contact between inner surfaces of pipe wall (η+ is the direction of normal indicating outer surface of the pipe)

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Figure 12

MTS load-displacement relationship obtained from FE analysis and test result (2)

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Figure 13

Comparison of deformed shapes of the specimen obtained from (a) the present analytical work, (b) the experiment, and (c) the WestCoast Energy Inc. (2).

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Figure 14

Predicted progression of deformed configuration for the pipe specimen

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Figure 15

Predicted wrinkle formation process on the compression side of the pipe

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Figure 16

Longitudinal stress-strain relationship at some selected elements

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