Research Papers: Materials and Fabrication

Fracture Assessment Procedures for Steel Pipelines Using a Modified Reference Stress Solution

[+] Author and Article Information
Tomasz Tkaczyk1

Offshore Engineering Division, Technip, Westhill, Aberdeenshire AB32 6TQ, UKttkaczyk@technip.com

Noel P. O’Dowd

Department of Mechanical and Aeronautical Engineering, Materials and Surface Science Institute, University of Limerick, Limerick, Irelandnoel.odowd@ul.ie

Kamran Nikbin

Department of Mechanical Engineering, Imperial College London, London SW7 2AZ, UKk.nikbin@imperial.ac.uk


Corresponding author.

J. Pressure Vessel Technol 131(3), 031409 (Apr 29, 2009) (11 pages) doi:10.1115/1.3122769 History: Received February 24, 2008; Revised November 12, 2008; Published April 29, 2009

An accurate defect assessment procedure is needed to ensure integrity of girth welded steel pipelines while avoiding unnecessary repairs. An integral part of such a procedure is an estimation scheme for the crack driving force. In this work, a modified reference stress solution was developed for the assessment of elastic-plastic pipes with surface breaking defects. For the particular case of interest (reeled offshore pipelines), the loading is phrased in terms of applied strain. The stress-based approach has therefore been extended to the case of strain/displacement control. The results obtained using the modified reference stress solution have been compared with a three-dimensional finite-element analysis. Very good agreement has been obtained. The predictions are also significantly better than those obtained from existing approaches. A comparison between the proposed method and full scale testing will be presented in a separate paper.

Copyright © 2009 by American Society of Mechanical Engineers
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Figure 4

Dependence of γ on geometry and strain hardening: (a) dependence on a/t and β for r/t=15; (b) dependence on r/t and β for n=20

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Figure 5

API 5L X65: J versus bending strain for D=14 in. (355.6 mm), t=15.9 mm and flaw size: (a) 2c=200 mm, a=3.02 mm; (b) 2c=25 mm, a=6.10 mm.

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Figure 6

API 5L X65: maximum acceptable flaw sizes for D=10.75 in. (273.1 mm), t=8.7 mm

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Figure 7

API 5L X65: normalized maximum acceptable flaw sizes for (a) D=10.75 in. (273.1 mm), t=8.7 mm; (b) D=14 in. (355.6 mm), t=15.9 mm; (c) D=18 in. (457.0 mm), t=25.4 mm

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Figure 8

API 5L X70: tensile response of pipe material

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Figure 9

API 5L X70: J versus bending strain for D=16 in. (406.4 mm), t=19.1 mm and flaw size: (a) 2c=100 mm, a=3.6 mm; (b) 2c=25 mm, a=6.4 mm

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Figure 10

API 5L X70: normalized maximum acceptable flaw sizes for D=16 in. (406.4 mm), t=19.1 mm

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Figure 1

Schematic of pipe installation by reeling

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Figure 2

Pipe and crack geometry

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Figure 3

Finite-element model: (a) typical mesh, (b) crack region, and (c) crack tip mesh



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