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Materials Technology

Effect of the Yield to Tensile Ratio on Structural Integrity of Line Pipes Subjected to Bending Loads

[+] Author and Article Information
Hugo A. Ernst

 TENARIS Center for Industrial Research, Simini 250, Campana (2804), Buenos Aires, Argentinahernst@tenaris.com

Richard E. Bravo

 TENARIS Center for Industrial Research, Simini 250, Campana (2804), Buenos Aires, Argentinarbravo@tenaris.com

J. Offshore Mech. Arct. Eng 133(3), 031402 (Mar 29, 2011) (8 pages) doi:10.1115/1.2948944 History: Received October 07, 2005; Revised May 15, 2008; Published March 29, 2011; Online March 29, 2011

This work studies the effect of the yield (Y) to tensile (T) ratio, YT, on the structural integrity of line pipes with part through the thickness (PTT) circumferential defects subject to bend loading. A model based on elastic-plastic fracture mechanics and plasticity theory was developed for that purpose. The analysis handles situation with load or deformation control conditions. The results are shown in terms of curves of critical defect size versus the controlling variable, i.e., load or deformation. For each one of the different materials studied, cases with different YT values were considered. Even for the lower limits of experimental data, i.e., larger YT, the materials have adequate defect tolerance. A leak before break analysis of a PTT circumferential defect growing into a through the thickness defect growing circumferentially was performed.

Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Tube subjected to bend loading with PTT circumferential surface defect

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Figure 2

Structural integrity assessment methodology

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Figure 3

Y∕T, BC, and best-fit curve versus Y. X60—tube ∅323.9×14.3mm2.

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Figure 4

T versus Y, acceptability limits, BC, best-fit curve, and Cases X60-∅323.9×14.3mm2

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Figure 5

Typical critical load versus crack depth/thickness curve

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Figure 6

Bending moment versus critical crack depth for a∕c=0.2—Cases A and B. X60-tube ∅323.9×14.3mm2

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Figure 7

Bending moment versus longitudinal deformation curves for the four cases. X60-tube ∅323.9×14.3mm2

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Figure 8

Longitudinal deformation versus critical crack depth for a∕c=0.2—Cases A and B. X60-tube ∅323.9×14.3mm2

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Figure 9

Y∕T versus aSMYS∕t and a0.5%∕t. X60-tube ∅323.9×14.3mm2

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Figure 10

Crack evolving from superficial defect to through wall crack

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Figure 11

Bending moment versus crack depth, for a tube with different aspect (a∕c) ratios—Case A. X60-tube ∅323.9×14.3mm2

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Figure 12

Bending moment versus crack length, for a TTT defect—Growing circumferentially—Case A. X60-tube ∅323.9×14.3mm2

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Figure 13

Critical defect geometry, for an initial PIT defect—Case A. X60—Tube ∅323.9×14.3mm2

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Figure 14

Plastic collapse evaluation

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Figure 15

Stress-strain relationship determination

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