Analysis and Design of Buried Pipelines for Ice Gouging Hazard: A Probabilistic Approach

[+] Author and Article Information
Arash Nobahar

 Fugro-McClelland Marine Geosciences, Inc., Houston, TX 77081

Shawn Kenny, Tony King, Ryan Phillips

 C-CORE, St. John’s, NL, A1B 3X5, Canada

Richard McKenna

 Consultant, Ice, Environment and Risk, Wakefield, QC, J0X 3G0, Canada

J. Offshore Mech. Arct. Eng 129(3), 219-228 (Aug 03, 2006) (10 pages) doi:10.1115/1.2426989 History: Received August 01, 2005; Revised August 03, 2006

In cold environments, marine pipelines may be at risk from ice keels that gouge the seabed. Large quantities of material are displaced and soil deformations beneath a gouge may be substantial. To meet safety criteria, excessive strains are avoided by burying pipelines to a sufficient depth. In this paper, a probabilistic approach for the analysis and design of buried pipelines is outlined. Environmental actions are applied through distributions of gouge width, gouge depth, subgouge soil deformations, and bearing pressure. Three-dimensional pipe/soil interaction problem is modeled using nonlinear soil springs and special beam elements using the finite element method to estimate pipe response for statistically possible ranges of gouge depths, gouge widths, and burial depths. Relevant failure mechanisms have been considered, including local buckling and a variety of strain and stress based criteria. The methodology presented in the paper was developed and successfully used for several pipeline and electrical cable projects in ice gouge environments. Significantly reduced burial depth requirements have been demonstrated through the application of the probabilistic approach and through the use of strain-based design criteria. Because ice actions are applied through displacements of the soil, more ductile pipes are often necessary to meet reliability targets.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 1

Schematic representation of ice feature gouging seabed

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Figure 2

Soil-pipeline interaction (a) continuum analysis, (b) idealized structural model, and (c) soil load-displacement response (tu,xu, pu,yu, quu, zuu, qud, zud are spring characteristics)

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Figure 3

Schematic representation of (a) compressive strain Load Resistance Factored Design (LRFD) and (b) compressive strain reliability based approaches

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Figure 4

Schematic pipeline burial depth definition

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Figure 5

Clearance depth contours (m) to satisfy factored compressive strain limit for 762mm(30in) diameter pipeline with 15.9mm(0.625in.) wall thickness

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Figure 6

Probability of exceedance curves for 762mm(30in.) diameter pipeline with 15.9, 22.2, and 32mm(a), (b), and (c) wall thickness

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Figure 7

Illustrative example of pipeline route burial depth requirements (after Ref. 8)

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Figure 8

Probability of exceedance curves/target probability level to determine cover depth requirements



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