Research On Leakage And Explosion Characteristics And Risk Assessment Of Buried Natural Gas Pipeline In Tunnel

There are a large number of natural gas transportation pipelines buried in tunnels in the western and southwestern regions of China.The environment where the pipelines are located is complex,and there are significant safety hazards.At present,research on the diffusion and explosion of leaked natural gas in tunnels is mostly focused on exposed natural gas pipelines.There is a lack of research on the process of natural gas diffusion and explosion accidents from soil into tunnels after underground natural gas pipelines leak,and a risk assessment method for leakage and explosion of buried natural gas pipelines in tunnels has not been established.This article focuses on buried natural gas pipelines in tunnels as the main research object.Through theoretical analysis,similar experiments,and numerical simulation,the leakage and explosion characteristics and risk assessment methods of buried natural gas pipelines in tunnels under different environmental and leakage factors are studied.The research results are of great significance for improving on-site emergency response capabilities and reducing accident consequences.The mathematical statistics method is used to analyze the typical cases of gas pipeline leakage accidents at home and abroad,and it is determined that the inherent hazard,pipeline third-party damage,personnel misoperation,etc.are the main risk factors of natural gas pipeline leakage accidents.Based on the Analytic Hierarchy Process(AHP),four first level indicator factors and fifteen second level indicator factors affecting the severity of leakage accidents in buried natural gas pipelines in tunnels were established.By analyzing the weight of the first level indicator,the order was:pipeline factors>tunnel environmental conditions>tunnel structural factors>other factors;Based on the comprehensive weight analysis results of various influencing factors,factors such as leakage aperture,direction,and pressure that have a significant impact on accident consequences are selected for experimental and simulation analysis.Based on the location of the leakage hole of the buried natural gas pipeline in the tunnel,a three-dimensional coordinate system was established.The seepage diffusion theory and Fick’s law were used to derive and establish a mathematical model describing the leakage diffusion of the buried natural gas pipeline.The Navier Stokes equation was used to theoretically analyze the diffusion and propagation law of the leakage of the buried natural gas pipeline from solid infiltration into air;At the same time,the mechanism of natural gas explosion in the tunnel was studied,and the natural gas during the explosion process met the turbulent flame law.A similarity criterion number was derived for the Guozigou Tunnel,and a similarity experimental model for buried natural gas pipelines in the tunnel with a geometric similarity ratio of 1:4 was established.The effects of factors such as pipeline leakage aperture,pressure,and location on the diffusion and explosion characteristics of natural gas were studied.It was determined that as the leakage aperture increased,the increase in leakage concentration showed a gradually decreasing trend.When the leakage aperture increased by 4 mm,the increase in leakage concentration decreased from 128.57%to 62.25%;The concentration of natural gas in the tunnel is positively correlated with pipeline pressure.The larger the leakage pressure,the more leakage occurs within the same time period,and the shorter the time to reach the lower limit of natural gas explosion;The overlying soil layer only affects the rate of increase in natural gas concentration.The thickness of the overlying soil layer increases by 10 cm,and at the same time,the natural gas concentration in the space decreases by a maximum of 60%.The influence of pipeline leakage characteristics and tunnel environmental factors on natural gas leakage and explosion was studied using numerical simulation.It is determined that the larger the inclination angle is,the faster the gas diffusion speed is,and the smaller the concentration of natural gas accumulated in the tunnel is.The relationship between gas concentration and inclination angle is full of exponential function relationship.Increasing the air flow speed can effectively reduce the amount of natural gas accumulation in the environment,thus effectively reducing pipeline leakage and explosion accidents.When a pipeline leaks and explodes in a tunnel,the concentration of natural gas decreases rapidly,slowly,and steadily in three stages.A secondary explosion occurs at the tunnel entrance,and the distance from the tunnel entrance is directly proportional to the peak explosion pressure and pressure increase rate;When an underground natural gas pipeline leaks and explodes,due to the absorption of natural gas by the ground soil,there will be no secondary explosion at the tunnel entrance.The length from the tunnel entrance is directly proportional to the peak explosion pressure and the rate of pressure rise.Based on theoretical analysis,similar experiments,and numerical simulations,the laws and quantitative relationships of natural gas leakage,diffusion,and explosion are established.Evaluation criteria for accident failure probability and consequences are constructed,and a failure probability and accident consequence calculation model based on cloud model and extension theory is established.Combined with the risk matrix analysis method,a risk assessment method for leakage and explosion of buried natural gas pipelines in tunnels is established,Realized the analysis and prediction of the risk of leakage and explosion accidents of buried natural gas pipelines in tunnels.