Research Of Effect Of Particle Properties And Flow Field On Erosion In Gas Pipelines

As a kind of clean energy,natural gas has become more important around the world gradually with the technology and industry developing.As the main transportation method of natural gas,pipeline has a significant role in the natural gas exploring and transporting.Once pipelines or components are broken during the natural gas transporting,they may cause very serious accidents and even influence lives and properties of citizens,because of higher natural gas pressure in the pipelines.Recent years,accidents caused by broken natural gas pipelines always happened,more attentions of people had been caught about the safety of the pipelines.Based on the researches about erosion-corrosion of pipelines,erosion caused by solid particles is the main reason of wall thickness reduction and wall boring on the natural gas pipelines.Moreover,the failure of the pipelines caused by erosion-corrosion with solid particles is much easier than that caused by corrosion only.Therefore,research about effect of particle properties and flow field on particle erosion is meaningful.Further,modifying the method of erosion calculation and proposing an erosion ratio prediction model for pipelines have a great significance on pipeline life prediction,safety operation and protection in oil and gas industry.The main research work in the thesis is shown as follows:(1)Based on the experiments of particle erosion under the different conditions,effect of particle properties(such as size,shape and particle rate)on erosion rate had been studied in a detail.Particle velocities were calculated by PIV(Particle Image Velocimetry)and PTV(Particle Tracking Velocimetry),and the differences between these two methods for particle velocity calculating were also compared.According to the results of experiments,influence of the particle rate on the particle velocity under the same gas-phase condition was investigated,and the significance of the particle rate control in the particle erosion experiment was emphasized.Based on the summary of effect of the particle properties on the erosion rate,the equation about relation between the particle size and the erosion rate and that about relation between the particle rate and erosion rate are proposed separately.(2)Erosion of four typical materials for gas pipelines(X70,X80,X65 and 20G)were tested on the solid particle erosion experiment rig.According to the results,the erosion resistance performances of the different materials were analyzed,and the conclusions were compared with test results obtained from the MSE standard erosion test.Collision between particles and the surfaces of specimens were researched based on analysis of erosion experiment results under various impact angles.To be a foundation of particle erosion modeling for typical components under complicated flow field conditions,the computational fluid dynamics(CFD)model was set up based on particle erosion experiments.(3)The simplified elbow erosion experiment rig was set up and the CFD simulations of the elbows were established.Based on the model of the elbow in experiment,the simulation model of elbows under on-site conditions was set considering the results of erosion tests of typical materials of the pipelines.The coupling effects of particle properties on the erosion rate were discussed through the CFD modeling.The coupling effects of the particle velocity and the particle size,the particle velocity and the particle particle rate,the particle velocity and the particle shape on the erosion rate were analyzed separately,equations about coupling effects of the properties on the erosion can be used to calculate the erosion rates while two different particle properties changing at the same time.(4)Effect of the flow field on the erosion rate was studied.Based on the models of the elbows in the simplified elbow erosion experiment and gathering pipelines,erosion of elbows under low and high pressures were compared while the particle velocity and gas velocity were different.According to the comparison results,the gas velocity was more significant while calculating the erosion rate of elbows under high pressure.By comparing recent simplified erosion equations,a mothed to modify the simplified erosion equation was proposed,which considering effect of the gas velocity on the erosion rate while velocities of the gas-solid two phases are different.(5)Effect of flow field on the maximum erosion position on tees was analyzed in the last part.According to a gas pipeline accident of Xijiang Oilfiled Company,the inside flow field of the tees were analyzed and corresponding CFD model were established to analyze the effect of the gas flow on the particle movement.Based on the accident report and results of CFD calculations,the equation about relation between the maximum erosion position and velocities of the two inlets was proposed.It can be a guide for probable broken position predicting in the industry.