Research Papers: Materials and Fabrication

Fracture Toughness of HSLA Coiled Tubing Used in Oil Wells Operations

[+] Author and Article Information
J. Wainstein, J. Perez Ipiña

GMF-LPM,  Univ. Nac. del Comahue-CONICET, Bs. As. 1400, Neuquén, Argentina

J. Pressure Vessel Technol 134(1), 011403 (Dec 20, 2011) (9 pages) doi:10.1115/1.4004569 History: Received June 05, 2010; Revised April 28, 2011; Published December 20, 2011; Online December 20, 2011

Coiled Tubings are thin walled steel tubes of 25–89 mm diameter and thousands meters long, used in the oil industry for production and maintenance services. They suffer plastic deformation during unwinding of the reel, passing through a goosneck arch guide and an injector unit. Strain levels are of 2–3%, making the tubing fail by low cycle fatigue in around 100 wrap–unwrap cycles. As coiled tubing material generally behaves in a ductile manner at surface and down well temperatures, the R curve has to be known to make instability analyses. J-R curves were determined to characterize the fracture toughness of nonused coiled tubing, using nonstandard specimens due to difficulties with their small thickness and diameters. Different crack lengths and crack locations were tested to analyze the 2C0 /W ratio and the influence of the longitudinal weld. The R curves obtained show crack arc length dependence and are influenced by the position of the longitudinal weld.

Copyright © 2012 by American Society of Mechanical Engineers
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Figure 1

Coiled tubing unit in service

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Figure 2

Geometry of a tube with a circumferential through wall crack

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Figure 3

Crack location with respect to longitudinal welding

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Figure 4

Potential drop versus normalized arc length

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Figure 5

Load versus load line displacement records for coiled tubing (a) tube 1 and (b) tube 2

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Figure 6

Crack extension (2ΔC) versus displacement records. (a) Tube 1 and (b) tube 2.

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Figure 7

Fracture surface macrograph

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Figure 8

J-R curve for coiled tubing, tube 1

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Figure 9

J-R curve for coiled tubing, tube 2

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Figure 10

Fracture surfaces of four of the tested coiled tubing

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Figure 11

J-R curves CTAs and CTBs (a) tube 1 and (b) tube 2

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Figure 12

Stable crack growth through the longitudinal weld

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Figure 13

CTB-4 J-R curve

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Figure 14

CTB-5 J-R curve



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