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Research Papers: Pipeline Systems

Analysis of Laminations in X52 Steel Pipes by Nonlinear by Finite Element

[+] Author and Article Information
Jorge Luis González

Departamento de Ingeniería Metalúrgica, IPN-ESIQIE Unidad Profesional Adolfo López Mateos, Mexico, Distrito Federale, 07738 Mexico

Alfredo Morales

 Instituto Tecnológico de Puebla Posgrado, Avenida Tecnológico 420, Col. Maravillas, Mexico, Puebla 72420, Mexico

J. Pressure Vessel Technol 130(2), 021706 (Mar 31, 2008) (7 pages) doi:10.1115/1.2894295 History: Received January 17, 2007; Revised November 09, 2007; Published March 31, 2008

Hydrogen induced cracking is of great interest in the mechanical integrity assessment of sour gas pipelines. Multiple stepwise cracks with internal pressure called laminations are often observed in pipelines and their interaction and coalescence may significantly affect the residual strength of the pipes. In this work, the interacting fields of noncoplanar pressurized laminations in the wall of a pipe under pressure are analyzed by nonlinear finite element, considering an isotropic hardening law and the real tensile properties of the X52 steel. The results are presented as the evolution of the stress fields in the interlaminar region as a function of the pressure inside the laminations. It is found that for two approaching stepwise laminations, the critical pressure follows a hyperbolic type law. It is observed that for two cracks with lengths of less than 6.35 mm, the interlaminar region resists a critical pressure between 110 Mpa and 124 Mpa, respectively, for thicknesses 15.8 mm and 25.4 mm. The critical pressure is defined as the pressure inside the lamination that causes plastification of the interlaminar region.

Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic representation of the formation of a stepwise crack by pressure mechanism

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Figure 2

Typical stress-strain curve of X52 steel

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Figure 3

Geometrical model and FE-mesh division using solid element

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Figure 4

Variables of the model

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Figure 5

von Mises stress (MPa) behavior of the interlaminar region with the pressure on the defect

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Figure 6

Possible trajectory of the interconnecting crack at the interlaminar region, for Case 2

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Figure 7

Side view of the interlaminar region of HIC cracks in X52 steel, as polished, metallographic microscope, bright field

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Figure 8

Maximum von Mises stress in the interlaminar region as a function of the pressure in the defect for ri=38mm

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Figure 9

Maximum von Mises stress in the interlaminar region as a function of the pressure in the defect for a ri=63.5mm in a 609mm o.d. pipe with 25.4mm thickness

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Figure 10

Maximum von Mises stress in the interlaminar region as a function of the pressure in the defect for a ri=88.9mm in a 609mm o.d. pipe with 25.4mm thickness

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Figure 11

Variation of m as a function of the defect size ratio (ri∕rd) in a 609mm o.d. pipe with 25.4mm thickness

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Figure 12

Maximum von Mises stress in the interlaminar region as a function of the pressure in the defect for a ri=38mm in a 609mm o.d. pipe with 15.8mm thickness

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Figure 13

Maximum von Mises stress in the interlaminar region as a function of the pressure in the defect for a ri=63.5mm in a 609mm o.d. pipe with 15.8mm thickness

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Figure 14

Maximum von Mises stress in the interlaminar region as a function of the pressure in the defect for a ri=88.9mm in a 609mm o.d. pipe with 15.8mm thickness

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Figure 15

Maximum pressure variation on the defects versus defect half length of symmetric defects

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