Study On Fracture Characteristics And Repair Of Natural Gas Pipeline With Axial Crack

With the increase of natural gas in the proportion of energy consumption,the construction of natural gas transmission pipelines in China has shown rapid development momentum.The first-line and second-line projects of the West-East Gas Pipeline have been completed one after another.The third-line project has also been basically completed,forming an energy artery network that traverses the north and south of China.What followed was the safety of natural gas pipelines.Due to the inevitable defects caused by environmental corrosion and mechanical damage during the manufacture and installation of the pipeline,these defects are easily induced into axial cracks under the action of the internal medium,which seriously reduces the strength and reliability of the pipeline.The traditional strength theory cannot evaluate the state of the pipeline,nor can it give a reasonable solution to the repair and crack prevention of the pipeline.Based on the theory of elastoplastic fracture mechanics and the theory of composite mechanics,the fracture characteristics and pipeline repair of natural gas pipelines with axial penetrating cracks are studied.Based on the theoretical study of Elastoplastic Fracture Mechanics,the finite element model of natural gas pipeline with axial crack is established.The test of small-sized cracked pipeline is designed.The feasibility of the finite element model is verified by measuring the circumferential strain near the crack tip.Based on the model,the distribution law of the J-point along the wall thickness is studied.The results show that the J-integral shows the distribution of the J-integral along the wall thickness.The influence of the pipe parameters on the J-integration is studied.The crack length is positively correlated and negatively correlated with the wall thickness of the pipeline.Based on the crack tip opening angle criterion,the calculation model of the ultimate load of the cracked pipeline is established.The experimental data show that the model has high accuracy.The Cohesive Model theory and its application in crack propagation are studied.The dynamic expansion finite element model of axial cracks in natural gas pipelines is established based on the cohesive force model.The feasibility of the model is verified by the ultimate load of the pipeline.Based on the model,the variation of crack propagation velocity and crack tip opening angle with time under different loads is studied.The results show that the two exhibit negative correlation and reflect the driving force of crack propagation force on crack propagation.The theory of Composite Mechanics was studied,and the finite element model of composite materials for repairing axially cracked pipelines was established.The ratio of the J-integral of the crack tip before and after repair was defined as the crack arrest coefficient of the repair effect,and the laying angle of the composite was studied.The effects of repair length,repair thickness and pipe size parameters on the crack arrest performance,and the calculation formula of the crack arrest coefficient under specific repair parameters are given.