Study On The Sealing Performance Of Fibrous Particles In Gas Pipelines With Tiny Leaks

Most of China’s gas pipelines are buried underground,and most of them were built at the beginning of urban construction,which is close to their design life,and the probability of pipeline leakage has increased greatly.The existing pipeline repair technology needs to determine the location of pipeline leaks,while the current pipeline leak detection technology cannot accurately locate the location of small leaks,increasing the probability of small leaks developing into large leaks,which brings great difficulties to the sealing of pipelines.The development of this project provides a new method for online internal sealing of gas pipelines,which can prevent small leaks from developing into large leaks and ensure the safe transmission of pipelines.Firstly,this paper uses ICEM CFD software to establish the pipe leakage model with the leakage hole located at 6 o’clock direction,and it uses the control variable method to study the flow field characteristics such as pressure field,velocity field and temperature field near the leakage hole by FLUENT software.Then,based on the above flow field characteristics at the leakage hole of the pipe,the in-pipe sealing process of fibrous particles is studied by coupling EDEM-FLUENT.Secondly,the experimental design is carried out by Central Composite and Box-Behnken to investigate the effects of particle density,particle number,particle surface energy,initial particle velocity and material properties on the pipe plugging effect(the ratio of the difference between the mass flow rate at the leak hole after and before sealing to the mass flow rate before sealing).In addition,the effects of particle number and particle density on the minimum plugging length of particles are also investigated.Finally,The effect of leak hole parameters on pipe leak plugging was studied under equal cross-sectional area conditions.The results show that:(1)the degree of influence of pipe plugging effect is ranked as particle density > particle number > particle surface energy > particle initial velocity,Poisson’s ratio > rolling friction coefficient > coefficient of restitution.(2)The number of spherical units should be considered when using the multi-sphere unit method for fibrous particle simulation,and the spacing between the circle centers of each spherical unit constituting a fibrous particle should be equal to the particle radius.(3)The closer the shape of the leak hole is to a circle,the better the effect of the particles on the leak sealing.Compared with before the sealing,the overall pressure at the leak hole will drop after the sealing,but the trend of the pressure change of the circular leak hole is the most gentle.(4)Taking the circular leak hole as the boundary,as the shape of the leak hole keeps moving away from circular,the ratio of the minimum plugging length of the particles to the minimum shaft length of the leak hole increases continuously;the more the shape of the leak hole tends to be circular,the greater the minimum plugging length of the particles,and the particle length required to plug the circular leak hole is the largest.(5)There is a positive correlation between the diameter of the leak hole and the minimum plugging length of the particles and the influence of the number of particles on the minimum particle plugging length of different sizes of leak holes is greater than the particle density,in addition,in the case of a certain density of particles,the ratio between the diameter of the leak hole and the minimum plugging length of particles between different particle numbers is approximately equal.