Structural Stress Analysis Of A Natural Gas Pipeline Through The Tunnel Under Different Laying Methods

Natural gas pipelines are usually laid by crossing the tunnel in the complex terrain of the mountainous areas.In addition,China is not only a mountainous country,but also widely seismic zones distributed.It is necessary to carry out finite element mechanics analysis to ensure the safety of natural gas pipeline running.In this paper,taking natural gas pipeline through the tunnel as our research target.The static analysis and seismic response analysis were carried out for the different laying way of pipeline through tunnel.Base on ANSYS finite element analysis software.I model the natural gas pipeline and lay out the static analysis,using soil spring to simulate the restriction of soil to the pipe.Firstly,the maximum equivalent stress of gas pipeline under operating condition is calculated,and the maximum equivalent stress is found in the pipe elbow,the value is 198.8MPa,less than the allowable stress 289.8MPa.Afterwards,The maximum equivalent stress of the pipeline under different influences is analyzed,it proposed that the maximum equivalent stress of the pipe could be reduced by changing the soil type and increasing the thickness of the pipe.The static analysis of the natural gas pipeline through the tunnel is carried out when the pier is used,using axial soil spring to simulate the constraint of pipeline in tunnel.It is concluded that the maximum equivalent stress of the pipe appears at the elbow under the operating conditions,its value is 264.0MPa,which is greater than the maximum equivalent stress of the pipe when using direct burial.The maximum equivalent stress condition is analyzed under different influence factors,and I proposes to reduce the maximum equivalent stress of the pipe by changing the radius of curvature of the elbow,reducing the pitch of the sliding piers in the tunnel or by adding a fixed pier near the elbow in the tunnel.The time-history analysis method is used to analyze the seismic response of the natural gas pipeline through tunnel.The maximum equivalent stress appears at the lower elbow on both sides of the pipeline by analyzing the maximum equivalent stress distribution of different nodes on the pipeline.The maximum equivalent stress of the pipe when the pier is laid is greater than the maximum equivalent stress of the pipe when it is buried,the maximum equivalent stress of the natural gas pipeline is 310 MPa which has exceeded the allowable stress when the magnitude of the earthquake is 8.In view of this situation,This paper propose a method to reduce the stress of the pipe by increasing the wall thickness of the lower elbow and the inclined straight pipe.