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Research Papers: Piper and Riser Technology

Ovalization Defect in Energy Pipes Caused by Concentrated Load

[+] Author and Article Information
Hossein Ghaednia

Centre for Engineering Research in Pipelines (CERP),
University of Windsor,
Windsor, ON N9B 3P4, Canada
e-mail: ghaedni@uwindsor.ca

Sreekanta Das

Professor
Mem. ASME
Centre for Engineering Research in Pipelines (CERP),
University of Windsor,
Windsor, ON N9B 3P4, Canada
e-mail: sdas@uwindsor.ca

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received November 27, 2015; final manuscript received March 16, 2016; published online June 2, 2016. Assoc. Editor: Jonas W. Ringsberg.

J. Offshore Mech. Arct. Eng 138(5), 051701 (Jun 02, 2016) (10 pages) Paper No: OMAE-15-1122; doi: 10.1115/1.4033181 History: Received November 27, 2015; Revised March 16, 2016

Steel pipes are used to build pipelines that carry gas and oil across a country or a continent. The majority of onshore pipelines run underground; hence, they are called buried pipelines. These buried pipelines must endure external interferences and complex loading that result from geotechnical causes, aggressive environments, and operational requirements. Many segments of an underground pipeline may rest on rock tips and other localized hard surfaces, resulting in concentrated reaction load acting on small area of the outer wall of the operating pipeline. As a result, permanent inward deformations in the pipe wall, known as dent defect, can form. In addition, a resulting cross-sectional irregularity, known as an ovalization defect, can also occur. Pipe ovalization defects are a concern of pipeline operating companies, as the defect may challenge a pipeline's operation and/or structural integrity and safety. This research was completed by the Centre of Engineering Research in Pipelines located at the University of Windsor to examine the effects that rock tip shape, operating (internal) pressure, and a pipe's diameter-to-thickness ratio (D/t) have on an NPS30 X70-grade pipe's ovalization defect when it is subjected to such a concentrated load. This article discusses the lab-based full-scale examinations, finite element analysis (FEA) simulations, results, and discussions.

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Figures

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Fig. 6

Strain gauge arrangements

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Fig. 7

Load-deformation behaviors: (a) specimens S1–S3 and S6 and (b) specimens S1, S4, and S5

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Fig. 8

Deformed and undeformed cross sections of a pipe specimen

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Fig. 9

Cross section distortion measured from various test specimens: (a) effect of internal pressure, (b) effect of plastic deformation, and (c) effect of LP size

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Fig. 5

Six LVDT's around the pipe: (a) schematic and (b) photo

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Fig. 10

FE model for half-pipe with meshing scheme

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Fig. 11

Stress–strain relationship for the material of the pipe

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Fig. 4

Photo of test setup

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Fig. 3

Schematic of test setup

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Fig. 2

Two different LPs used to apply concentrate load: (a) short LP and (b) long LP

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Fig. 1

Schematic of a section of buried pipe resting on a rock tip

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Fig. 19

The relationship between dent depth and D/t: (a) square LP and (b) sphere LP

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Fig. 12

Comparison of load-deformation behavior for specimens S2 and S3: (a) specimen S2-SP-D4-P30 and (b) specimen S3-SP-D4-P60

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Fig. 13

Comparison of cross section distortions for specimens S2 and S3: (a) specimen S2-SP-D4-P30 and (b) specimen S3-SP-D4-P60

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Fig. 14

Comparison of strain distribution for specimens S2 and S3: (a) specimen S2-SP-D4-P30 and (b) specimen S3-SP-D4-P60

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Fig. 15

Shapes of LPs utilized in the parametric study: (a) square LP and (b) spherical LP

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Fig. 16

Effect that D/t and operating pressure have on the maximum ovalization for the square LP: (a) displacement control method and (b) load control method

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Fig. 17

The effect that D/t has on the maximum ovalization for a spherical LP: (a) displacement control method and (b) load control method

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Fig. 18

Effect that operating pressure has on the maximum ovalization for a spherical LP: (a) displacement control method and (b) load control method

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