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Research Papers: Design and Analysis

A Study on Stress Corrosion Crack of Thick-Walled Elbow in Manifold for Acid Fracturing

[+] Author and Article Information
Yong-Jin Xie

College of Mechanical and
Transportation Engineering,
China University of Petroleum,
Beijing, 102249, China; Jianghan Petroleum
Administration Bureau of SinoPec,
Hubei, 433124, China

Hong Zhang

e-mail: hzhang@cup.edu.cn

Xi Luo

College of Mechanical and
Transportation Engineering,
China University of Petroleum,
Beijing, 102249, China

1Corresponding author.

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the Journal of Pressure Vessel Technology. Manuscript received February 11, 2012; final manuscript received December 16, 2012; published online March 18, 2013. Assoc. Editor: Haofeng Chen.

J. Pressure Vessel Technol 135(2), 021207 (Mar 18, 2013) (5 pages) Paper No: PVT-12-1017; doi: 10.1115/1.4023420 History: Received February 11, 2012; Revised December 16, 2012

Acid fracturing, with a pumping pressure up to 140 MPa for fractural liquid injection, is commonly used in enhanced oil recovery. Subjected to severely high hoop stress, stress corrosion cracking (SCC) often occurs at cracks inside manifold elbows which are due to acid corrosion and fracturing propping agent erosion. To avoid the occurrence of SCC, it is necessary to establish a substantial understanding of the fracture strength of thick-walled elbow, including the stress state distribution in elbow and SCC properties of elbow material. Base on the hoop stress calculation for thin wall straight pipe, a formula for hoop stress of thick-walled elbow is derived and also verified with finite element method (FEM). This is accomplished by introduce curvature factor and wall thickness factor into the formula. Furthermore, the critical stress intensity factor, KISCC, is determined subsequently in simulated acid fracturing corrosion condition. However, part of the considerable contribution of this work is to scale the critical crack depth. A simplified hoop stress formula proposed in this paper can be used in design of elbow wall thickness and strength evaluation. The established critical crack depth calculation formula can be applied to safety assessment of elbows with initial erosion cracks. The proposed method has been proved to be a simple and useful method to calculate the stress and fractural strength of thick-walled elbow.

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References

Qian, W., and Zheng, S., 1980, “General Solution of Axi-Symmetrical Ring Shells,” Appl. Math. Mech., 1(3), pp. 287–299. (in Chinese)
Chen, G., 1988, “Problem of Axi-Symmetric Uni-Thickness Shell Ring,” Appl. Math. Mech., 9(6), pp. 555–558. (in Chinese)
Wang, S., 1988, “Study of the Series Solution Convergence of Axi-Symmetric Thin Ring Shell Equations,” Chin. J. Theor. Appl. Mech., 20(6), pp. 563–569.
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Willbur, W. E., 1963, “Analyzing Pipeline Stresses,” Pipeline Ind., (2), pp. 25–31.
Xiaobing, C., 2009, “Cui Xiaobing's Academic Selections—Analyzing of Stress in Pressure Loaded Elbow,” Press of China University of Petroleum, Shandong, pp. 49–54. (in Chinese)
Timoshenko, S. P., and Gooder, J. N., 1970, Theory of Elasticity, 3rd ed., Press of Tsinghua University, Beijing.
NACE Standard TM0177-2005, “Laboratory Testing of Metals for Resistance to Sulfide Stress Cracking and Stress Corrosion Cracking in H2S Environments.”
Cheng, J., 2008, Fractural Mechanics, Press of Science, Beijing. (in Chinese)

Figures

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Fig. 2

Hyperbolic cycle ring

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Fig. 3

Hoop stress contour of elbow

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Fig. 4

Relationships between the hoop stress and pressure, where diameter D = 168.3 mm, wall thickness t = 17.5 mm, radius of curvature R = 420.75 mm

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Fig. 5

Relationships between hoop stress and curvature radius, where diameter D = 168.3 mm, wall thickness t = 17.5 mm, and pressure P = 100 MPa

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Fig. 6

Relationships between hoop stress and outer diameter, where radius of curvature R = 400 mm, wall thickness t = 20 mm, and internal pressure P = 100 MPa

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Fig. 7

Relationships between hoop stress and wall thickness where curvature radius R = 400 mm, diameter D = 219.1 mm, and pressure P = 100 MPa

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Fig. 8

Standard double cantilever beam specimens (a) before corrosion and (b) after corrosion

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