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Research Papers

An Investigation of the Fatigue Performance of Riser Girth Welds

[+] Author and Article Information
Stephen J. Maddox

 TWI Ltd., Granta Park, Great Abington, Cambridge CB1 6AL, UKstephen.maddox@twi.co.uk

Julian B. Speck, G. Reza Razmjoo

 TWI Ltd., Granta Park, Great Abington, Cambridge CB1 6AL, UK

J. Offshore Mech. Arct. Eng 130(1), 011007 (Feb 08, 2008) (11 pages) doi:10.1115/1.2827956 History: Received June 22, 2006; Revised June 14, 2007; Published February 08, 2008

Increasing deep-water oil and gas recovery has highlighted the need for high integrity, high fatigue performance girth welds in steel catenary riser systems. Such systems include girth welds made from one side. However, the widely used fatigue design classification, UK Class F2, for such welds is not well founded, but probably overconservative for pipeline welds. In an attempt to justify upgrading current fatigue design classifications and providing a better basis for design, fatigue tests were performed on a range of girth-welded pipes produced by pipeline welding contractors. This paper presents the results of those tests and their evaluation in terms of the factors that influence the fatigue performance of girth welds, including welding process, welding position, backing system, joint alignment, weld quality, specimen type, and fatigue loading conditions. Conclusions are drawn regarding the scope for adopting higher design classifications and the conditions that must be met to justify them.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Full-scale girth-welded fatigue test specimens (thickness change only in Series C; two welds only in Series C, extra H, and I; three welds only in Series H): (a) overall dimension; (b) strain gauge locations

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Figure 2

Small-scale strip specimen extracted from full-scale girth-welded pipe

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Figure 3

Examples of girth welds in test specimens: (a) sections of 5G girth welds; (b) section and inner surface of copper backed 2G Series G girth weld with cold lap at weld root; (c) section of extra Series H 2G girth weld with good profile GTAW root pass; (d) sections of 1G girth welds

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Figure 4

(a) Fatigue test results from full-scale and strip specimens incorporating 5G girth welds; (b) comparison of present and published results for 5G girth welds with design curves

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Figure 5

(a) Fatigue test results from full-scale and strip specimens incorporating 2G girth welds; (b) comparison of present and published results for 2G girth welds with design curves

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Figure 6

Fatigue test results from full-scale and strip specimens incorporating 1G girth welds

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Figure 7

Variation in stress magnification factor km due to misalignment in test specimens

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Figure 8

(a) Variation in mean and mean ±1SD hi-lo on insides of girth-welded joints tested; (b) variation in full range of hi-lo values on insides of girth-welded joints tested

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Figure 9

Variation of weld root bead height in girth welds tested

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Figure 10

Effect of hi-lo on fatigue strength of 5G girth welds; (b) effect of hi-lo on fatigue strength of 2G girth welds; (c) effect of hi-lo on fatigue strength of 1G girth welds

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