Numerical Investigation of High-Speed Dynamic Fractures and Crack Arresting of High-Grade Gas Pipelines

Abstract

The fracture speed of a high-grade gas pipeline subjected to high gas pressure is usually very high, such that the gas pressure near the crack-tip could not decompress rapidly. It is difficult for a high-grade pipeline to arrest crack propagation by itself; hence, an arrestor should be installed to prevent the pipeline from fracturing continuously. Because the optimization of the geometric size of the arrestor has not been well-recognized at present, it is of interest to study the dependence of crack arresting ability on arrestor size and obtain a satisfactory method to design the geometric size of the arrestor. Based on Hill’s yield theory and a plastic strain–dependent damage evolution law, a transversely isotropic elastic-plastic damage model is established. The mechanical responses of X80 pipeline material under static and dynamic loadings were successfully simulated by the proposed constitutive law. Using the cohesive zone model, the high-speed dynamic fracture and crack arresting ability of the X80 gas pipeline were simulated. The dependences of crack arresting ability on the thickness and length of the arrestor were numerically investigated. The simulation results showed that the crack arresting performance increases significantly with the thickness of the arrestor. The satisfactory geometrical size of an arrestor is economically suggested. Gas pipelines might be at risk of fracture and explosion after years of service. In order to prevent high-grade gas pipelines from fracturing continuously and avoid serious hazards, an arrestor should be installed outside the pipelines. The geometric size of the arrestor should be optimized to achieve both satisfactory crack arresting performance and lower cost of material consumption. This work attempts to study the dependences of crack arresting on the thickness and length of the arrestor and obtain a satisfactory method to design the geometric size of arrestor for high-grade gas pipelines. The West–East Gas Transmission Project of China was employed as an example, and the high-speed dynamic fracture and crack arresting ability of an X80 gas pipeline with different sizes of arrestor were investigated through finite-element simulations. The results showed that the crack arresting performance increases significantly with the thickness of arrestor. It is economically suggested to design the arrestor thickness to be same of gas pipeline and design the arrestor length to be equal to the diameter of the gas pipeline.