Pipeline Systems

A Comprehensive Parametric Finite Element Study on the Development of Strain Concentration in Concrete Coated Offshore Pipelines

[+] Author and Article Information
F. Taheri

e-mail: farid.taheri@dal.ca

Department of Civil & Resource Engineering,
Dalhousie University,
1360 Barrington Street,
Halifax, NS, B3J 1Z1, Canada

1Corresponding author.

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received September 22, 2010; final manuscript received March 23, 2012; published online October 18, 2012. Assoc. Editor: Shawn Kenny.

J. Pressure Vessel Technol 134(6), 061701 (Oct 18, 2012) (10 pages) doi:10.1115/1.4006556 History: Received September 22, 2010; Revised March 23, 2012

The strain concentration at the field joint (FJ) of the commonly used concrete coated offshore pipelines is considered and discussed in this paper. The details of a 3D finite element (FE) modeling framework, developed using the commercial software ABAQUS, are presented. The numerical results are verified against the experimental results available in the literature. The FE model considered in this study captures several nonlinear phenomena associated with the problem, including the plastic deformation of the steel and anticorrosion layer (ACL) material, the cracking and crushing of the concrete, and also the large deformation effects. The developed FE framework is subsequently used to perform a parametric study to assess the effect of each influencing parameter on the strain concentration factor (SCF) developed within the FJ region. The influence of the geometric features of the coated pipe and the relevant mechanical properties of the materials as well as various combined loading scenarios are investigated. Results indicate that pipeline diameter, thickness, and coating thickness affect the SCF more than the strength of either concrete coating or ACL. Also, the postyield properties of the steel, especially the strain hardening capacity, may significantly influence the SCF. The combination of the internal pressure loading (causing a biaxial stress state) or tensile loading with the primary bending load is found to also increase the SCF significantly after steel yielding is initiated. Moreover, these combined loading scenarios cause different and more severe plastic deformation patterns in the FJ.

Copyright © 2012 by ASME
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Fig. 1

(a) Typical concrete coated pipes with their FJ regions (from Ref. [17]) and (b) schematic of a coated linepipe with the relevant dimensions and identifiers

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Fig. 2

Schematic illustration of the moment–strain variation within a typical coated pipe and its FJ region, resulting in strain concentration

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Fig. 3

Schematic illustration of the variation of the SCF as a function of the global bending strain ɛg

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Fig. 4

(a) A typical FE mesh along with the BCs (Lt = 6000 mm and Lf = 350 mm) and (b) schematic of the four-point bending test setup of Ness and Verley (taken from Ref. [7]).

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Fig. 5

Schematic uniaxial stress–strain response of concrete

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Fig. 6

Moment–strain response of the benchmark pipeline model (symbols represent the experimental data of Ness and Verley [7])

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Fig. 7

Distribution of the average bending strains along the length of pipeline (circles represent the experimental data of Ness and Verley [7])

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Fig. 8

Uniaxial true stress–strain response of the steel for the considered range of strain hardening indices

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Fig. 9

Effect of D/t on the SCF for (a) Regime I loading and (b) Regime II loading

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Fig. 10

Effect of the coating thickness on the SCF in (a) Regime I loading and (b) Regime II loading

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Fig. 11

Effect of concrete coating’s compressive strength (f′ c) on the SCF for (a) Regime I loading and (b) Regime II loading

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Fig. 18

Contours of the equivalent plastic strain in the steel pipe subject to: (top) pure bending; (middle) bending + pressure (σhy = 0.5); and (bottom) bending + tension (N/Ny = 0.5). Concrete coating and ACL are hidden for clarity.

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Fig. 17

Schematic illustrating the Mises yield surface and the different load paths: (1) initial pressurization, (2) bending of the tensile chord, and (3) bending of the compressive chord

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Fig. 16

Effect of tensile load (N/Ny) combined with bending load (B + T) on the SCF

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Fig. 15

Evolution of the SCF versus ɛave for the family of combined hoop stress and bending loads (B + P)

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Fig. 14

Effect of the strain hardening index, n, on the SCF, along with the perfectly plastic case (n→∞)

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Fig. 13

Effect of steel’s yield strength, σy, on the SCF

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Fig. 12

Variation of the SCF as a function ACL’s shear strength (τy) for (a) Regime I loading and (b) Regime II loading




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