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RESEARCH PAPERS

Application of Constraint Corrected J-R Curves to Fracture Analysis of Pipelines

[+] Author and Article Information
Xian-Kui Zhu

 Battelle Memorial Institute, 505 King Avenue, Columbus, OH 43201zhux@battelle.org

Brian N. Leis

 Battelle Memorial Institute, 505 King Avenue, Columbus, OH 43201

J. Pressure Vessel Technol 128(4), 581-589 (Dec 06, 2005) (9 pages) doi:10.1115/1.2349571 History: Received July 26, 2005; Revised December 06, 2005

Fracture properties of an API X80 pipeline steel have been developed using a set of single edge notched bend (SENB) and single edge notched tension (SENT) specimens with shallow and deep cracks to generate different crack-tip constraint levels. The test data show that the J-R curves for the X80 pipeline steel are strongly constraint dependent. To facilitate transfer of the experimental J-R curves to those for actual cracked components, like flawed pipeline, constraint corrected J-R curves are developed. The two-parameter J-A2 formulation is adopted to quantify constraint effect on the crack-tip fields and the J-R curves. The constraint parameter A2 is extracted by matching the J-A2 solution with finite element results for a specific crack configuration. A constraint corrected J-R curve is then formulated as a function of the constraint parameter A2 and crack extension Δa. A general method and procedure to transfer the experimentalJ-R curves from laboratory to actual cracked components are proposed. Using the test data of J-R curves for the SENB specimens, a mathematical expression representing a family of the J-R curves is constructed for the X80. It is shown that the predicted J-R curves developed in this paper agree well with experimental data for both SENB and SENT specimens. To demonstrate its application in assessing flaw instability, a pipeline with an axial surface crack is considered. For a crack depth of 50% of the wall thickness, the predicted J-R curve is found to be higher than that for the SENB specimen with the same crack length to width ratio. From this predicted J-R curve and crack driving force obtained by finite element analysis, the failure pressures of the pipeline at the crack initiation and instability are determined and discussed.

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Copyright © 2006 by American Society of Mechanical Engineers
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References

Figures

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Figure 8

Comparison of predicted and experimental J-R curves for SENB specimens

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Figure 9

Comparison of predicted and experimental J-R curves for SENT specimens

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Figure 10

Finite element mesh for 762×23mm2 pipe with an axial surface crack of a∕t=0.5

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Figure 11

Distribution of the opening stress determined from the FEA and J-A2 solution along the distance from the crack tip

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Figure 12

Predicted J-R curve for X80 pipe with a surface crack and compared with those for SENB specimens

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Figure 13

Variation of J integral with internal pressure for the cracked pipe

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Figure 7

Variations of J0.2mm and J1.0mm with constraint parameter A2 for SENB specimens

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Figure 6

Variation of A2 with J for SENB specimens by (a) the J-A2 solution and (b) the modified J-A2 solution

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Figure 5

Distribution of opening stress σθθ along the distance from the crack tip. Symbols are FEA results, lines are asymptotic solutions. (a)a∕W=0.24, (b)a∕W=0.42.

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Figure 4

Typical finite element mesh for test specimens

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Figure 3

Experimental J-R curves for SENT specimens

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Figure 2

Experimental J-R curves for SENB specimens

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Figure 1

True stress-strain curve of X80 pipeline steel

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