SEDL / STP / STP1480-EB / STP45524S

Constraint Corrected J-R- Curve and its Application to Fracture Assessment for X80 Pipelines

Zhu, Xian-Kui
Senior Research Scientist and Senior Research Leader, Battelle Memorial Institute, Columbus, OH

Leis, Brian N.
Senior Research Scientist and Senior Research Leader, Battelle Memorial Institute, Columbus, OH

Pages: 17    Published: Jan 2007

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Abstract

Single specimen J-R curve testing for X80 pipeline steel was conducted using single edge notched bend (SENB) and single edge notched tension (SENT) specimens with various crack lengths. Test data indicate that the J-R curves for this steel are strongly constraint dependent. To facilitate transferability of experimental J-R curves to those for actual cracked components, this paper develops a constraint corrected J-R curve for X80 steel. A modified J-Q theory that can consider the global bending stress influence is proposed so as to correctly quantify constraint effect on the crack-tip fields and the J-R curves. Results show that the modified J-Q solution can well match numerical crack-tip fields for bending specimens, with Q being a load-independent constraint parameter under large scale yielding. Based on the experimental data and numerical analysis, a constraint corrected J-R curve is formulated as a function of the parameter Q and crack extension ▵a for X80 steel. A general procedure to predict J-R curves for actual cracked components is then outlined.Comparison indicates that the predicted J-R curves developed in this paper agree well with the experimental data for both SENB and SENT specimens. To demonstrate its application in failure assessment, the constraint corrected J-R curve for X80 steel is used to determine failure loads for a surface cracked pipeline. Reasonable agreement to available analytic solution is achieved.