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Research Papers: Pipeline Systems

Mechanical Properties of Cold Bend Pipes

[+] Author and Article Information
M. Sen, J. J. Cheng, D. W. Murray

Department of Civil and Environmental Engineering, University of Alberta, Edmonton, AB, T6G 2G7, Canada

J. Zhou

 TransCanada Pipelines Ltd., 450-1st Street Southwest, Calgary, AB, T2P 5H1, Canada

J. Pressure Vessel Technol 130(2), 021708 (May 13, 2008) (6 pages) doi:10.1115/1.2892034 History: Received January 15, 2007; Revised December 12, 2007; Published May 13, 2008

Cold bends are frequently required in energy pipelines in order to change the vertical and horizontal orientations of the pipeline route. They are produced by plastically bending a pipe joint in a cold bending machine by creating a series of uniformly spaced incremental bends. This procedure acts to reduce the moment capacity and buckling strain of the pipe, and studying the changes in pipe properties caused by cold bending is valuable in assessing the level of this strength reduction. Accordingly, the initial imperfections and material transformations of five full-scale cold bend pipes were assessed in this research program. The imperfections were measured at several locations around the circumference of the specimens, along the entire bend length. It was determined that the distribution of imperfections was similar in shape to a sine function, and their amplitude ranged from 0.3mmto1.0mm. Tension coupon tests were conducted on the intrados, extrados, and virgin materials of the specimens. It was revealed that the extrados material exhibited an increase in yield strength due to work hardening and that the intrados material demonstrated a reduction in yield strength due to the Bauschinger effect. It was established that the imperfections, and material transformations in the specimens were predominantly unaffected by the incremental-bend magnitude or spacing that was employed during the cold bending procedure.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of cold bending machine

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Figure 2

Imperfections caused by cold bending

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Figure 4

Specimen 1 intial imperfections

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Figure 5

Determination of imperfection amplitude and period

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Figure 6

Predicting the level of work hardening using residual strains

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Figure 7

Example of the Bauschinger effect in intrados materials

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