Research On Dynamic Crack Propagation And Crack Arrest Of Buried Long Distance Gas Pipeline

Due to the inevitable original defects in pipeline steel,the natural gas pipeline may fracture or even explode after long-term service.Long distance gas transmission pipeline of high steel grade has a large fracture speed,and it is difficult to stop the crack by itself through the toughness of the material,so the crack arrest device can be installed to strongly stop the crack.West of this second phase of west-east gas pipeline project as an example,studies the stress and deformation characteristics of buried gas pipeline,analyzed the material of X80 pipeline steel under different strain rate deformation behavior,established the strain rate of elastoplastic damage constitutive model and cohesion fracture model,studies the crack propagation characteristics of long distance gas transmission pipeline is X80,The effects of length,thickness and steel grade of crack arrest device on crack arrest of X80 long-distance gas pipeline were studied.The main work of this paper is as follows:(1)Based on Marston's earth pressure theory,the earth pressure distribution characteristics of buried natural gas pipeline were analyzed.By using Drucker-Prager yield criterion and finite element calculation,the stress distribution and deformation characteristics of buried natural gas pipeline under the action of overburden and internal pressure were studied,and the influence law of buried depth on the force and deformation of pipeline was analyzed.(2)The effects of strain rate on the elastic modulus,tensile strength and yield stress of X80 pipeline steel under uniaxial tension were analyzed.The Mises stress and strain rate correlation strengthening function was used to establish the elastoplastic constitutive model of X80 pipeline steel.The uniaxial tensile tests of X80 pipeline steel under different strain rates were numerically calculated.The material damage model of X80 pipeline steel was established by using the damage variable related to the equivalent plastic strain,and the strain softening behavior of X80 pipeline steel under uniaxial tension was numerically calculated.(3)The fracture criterion of pipeline steel is established by using the cohesive force model and the damage evolution rule of cohesive zone is established.Using the elastoplastic damage constitutive model and cohesive force model,the dynamic crack propagation behavior of X80long-distance gas transmission pipeline was simulated by finite element method,and the evolution relationship of crack propagation rate,crack opening Angle and plastic dissipated energy with time was analyzed.(4)The dynamic fracture and crack arrest behavior of X80 long-distance gas pipeline after installing crack arrest device was simulated by finite element method.The influences of thickness,length and material steel grade of crack arrest device on crack arrest behavior of gas pipeline were analyzed.The evolution characteristics of fracture velocity and plastic dissipated energy with time in the process of crack arrest were analyzed.The calculation results show that the thickness of the crack arrest device is more economical when it is one times the thickness of the gas pipeline,and the crack arrest effect of the X100 steel class crack arrest device is slightly better than that of the X80 steel class crack arrest device.When the crack arresting device has a large thickness and a small length,the crack may pass over the crack arresting zone and result in crack arrest failure.