Study On Dynamic Fracture Simulation And Crack Arrest Of Natural Gas/Oil Pipeline

With the increasing global consumption of the natural gas,the infrastructure of high pressure pipelines are developing rapidly.With the recent upgrading of pipeline steel,the modern pipelines gradually become of larger-diameter,thinner-wall(i.e.higher radius-tothickness ratio)and higher-pressure for purpose of increasing the capacity of gas transportation.However,it is obvious that the fracture driving force would also become higher due to the higher-pressure combined with the higher radius-to-thickness ratio,and consequently it would be more difficult to stop a running fracture once it starts.Therefore,for the safety and integrity of the modern pipeline,analyses and prediction of the dynamic fracture of pipelines should be concerned seriously for the pipeline design and management.Besides getting experience from full-scale pipeline test,a reliable finite element model also has important practical guiding significance for cost saving and the determination of the pipeline design parameters.A finite element model of the dynamic fracture in a full size gas pipeline is established based on the cohesive zone model.The dynamic crack growth of X80 pipeline steel was simulated using this model and the quantitative relationship between the crack growth rate and the internal pressure predicted is in agreement with the existing semi-empirical formula.Based on this model,some key parameters which are difficult to be directly measured in pipe blasting test(such as the crack tip opening angle,the stress and strain field surrounding the crack tip,energy dissipation,etc)could be quantitatively studied especially when the crack speed is very high.Accordingly,the proposed model would be a supplementary mean for the full-scale test.Moreover,the crack arrest design of the full-scale pipeline is also discussed based on this model.The main works are as follows:1.A 3D finite element model of full-scale pipeline is established based on the cohesive zone model.The key parameters of the numerical model is obtained based on the standard material test and drop-weight tear test.2.A test date-based semi-empirical formula of full-scale pipeline is used to validate the 3D finite element model proposed in this paper.The comparisons of the predicted fracture parameters between the numerical model and the semi-empirical formula shows good agreement in a wide range of internal pressure and size of pipe.3.Based on the 3D finite element model of the full-scale pipeline,the crack propagation in the dynamic process is simulated,and the crack tip opening angle and the crack tip stress distribution field for a moving crack tip are obtained under different crack speeds.Moreover,the critical length of initial crack,thickness of the pipeline wall are analyzed systematically.Finally,the crack-arresting is simulated by setting an arrest ring bundled surrounding the pipe external wall.All the simulations in this work is implemented in the platform of ABAQUS software.The dynamic fracture criteria of moving crack is governed by the cohesive zone model.The results of the simulation is in good agreement with tests,which prepared the foundation for the further study of the dynamic fracture in engineering pipeline structures.