Research Papers: Codes and Standards

Improvements to the ASME B31.8 Dent Strain Equations

[+] Author and Article Information
Chike Okoloekwe, Nikko Aranas, J. J. Roger Cheng, Samer Adeeb

Department of Civil and Environmental Engineering,
University of Alberta,
Edmonton, AB T6G 2R3, Canada

Muntaseer Kainat, Doug Langer, Sherif Hassanien

Enbridge Liquids Pipelines Inc.,
Edmonton, AB T5J 0H3, Canada

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received September 12, 2017; final manuscript received April 2, 2018; published online May 28, 2018. Assoc. Editor: Kiminobu Hojo.

J. Pressure Vessel Technol 140(4), 041101 (May 28, 2018) (9 pages) Paper No: PVT-17-1181; doi: 10.1115/1.4040096 History: Received September 12, 2017; Revised April 02, 2018

Pipelines used to transport oil and gas products are often subjected to external forces during its construction or operation, which can result in the formation of dents in the pipe. Various pipeline codes have stipulations on how a dent's severity can be ascertained in order to prioritize repairs. The most prominent being the depth-based criterion, which determines the severity of a dent by its depth. The depth-based criterion fails to consider the fact that the geometry of the dent can result in high strain concentration and eventually lead to integrity issues at the dented region. Alternatively, the strains associated with the dent can be an indicator of the dent's severity. Nonmandatory codified equations are available for evaluating the strains at the dented region of the pipe. The current implementation of these equations might fail to capture the strains that are not aligned with the most severe deformation profile of the dent and as such a global view of the strain distribution of the dented profile would be more informative as per the localized strain distribution. The study presented herein is the implementation of ASME B31.8 formulations together with the suggested modifications to evaluate the three-dimensional (3D) strain state of the dented pipe. The strain distributions obtained are compared against the strains predicted by finite element analysis (FEA) model. The correlation in the predicted strains indicates the possibility of the rapid and concise strain based characterization of dented pipes with the proposed technique.

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Fig. 1

Strain components of a dented pipe [14]

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Fig. 2

Material model of a typical X60 steel pipe

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Fig. 3

Setup up of the numerical model and the indenter

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Fig. 4

Numerical models: (a) 2%OD, (b) 4%OD, (c) 6%OD, (d) 10% OD, and (e) 12% OD

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Fig. 5

Analytical dent surface of the 2% OD model

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Fig. 6

Curvature plot in the circumferential direction of the 2% OD model

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Fig. 7

Curvature plot in the longitudinal direction of the 2% OD model

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Fig. 8

Circumferential strains developed at (a) external surface-numerical model, (b) external surface-ASME B31.8, (c) internal surface-numerical model, and (d) internal surface-ASME B31.8

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Fig. 9

Longitudinal strains developed at (a) external surface-numerical model, (b) external surface ASME B31.8, (c) internal surface numerical model, and (d) internal surface–ASME B31.8

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Fig. 10

Equivalent plastic strains developed at (a) external surface-numerical model, (b) external surface-ASME B31.8 equation, and (c) external surface-modified ASME B31.8 equation

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Fig. 11

Equivalent plastic strains developed by the investigated dent models

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Fig. 12

Equivalent plastic strains developed at (a) 64-sensors, (b) 32-sensors, (c) 16-sensors, and (d) 8-sensor

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Fig. 13

Equivalent plastic strains developed at (a) 64-sensors, (b) 32-sensors, (c) 16-sensors, (d) 8-sensors, and (e) numerical model




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