3D-VCCT based fracture analysis method for gas pipelines with multiple cracks

Abstract

The current national criteria cannot accurately reflect the multi-crack interference effect of defective gas pipelines, and thus result in conservative assessment results. In order to improve the safety assessment accuracy of defective gas pipelines, we compared the singular element method with the three-dimensional virtual crack closure technology (3D-VCCT), then, selected the 3D-VCCT to build a multi-crack interference model of gas pipelines, and finally, studied the interference effect of subsidiary cracks on the front points of the main crack by analyzing the variation of the interference factors between cracks. The following research results were obtained: first, as the subsidiary crack size changes, the strongest interference effect of a parallel collinear crack occurs near the surface of the crack, exhibiting an enhances effect; second, under certain conditions, the interference effect of a parallel coaxial crack is more significant at the deepest point and the surface point of the crack, and exhibits an enhanced effect at the deepest point and a weakened effect at the surface point; third, when the horizontal spacing between cracks is 6 times greater than the major semi-axis of the main crack, the interference effect of parallel collinear cracks and parallel bias cracks is very little, and multi-cracks can be simplified as a single crack for analysis. The research results not only can provide technical references for fracture analysis of multi-crack gas pipelines, but also can provide theoretical basis for the safety assessment of multi-cracks of the gas pipelines. Keywords: Gas pipeline, Pipeline fracture, Multi-cracks, Main crack, Subsidiary crack, Interference effect, Stress intensity factor, Singular element method, 3D-VCCT