Research On Risk Assessment Method Of Underground Adjacent Natural Gas Pipelines Under The Erosion Of Leakage Water Jetting

With the construction of urban underground pipelines and the expansion of urban areas,there were more and more parallel crossings between underground water supply pipelines and underground natural gas pipelines.During the service of underground natural gas pipeline,if the pipeline was eroded by water-sand jetting caused by the leakage of adjacent pipelines,it will easily lead to pipeline failure and leakage,which will lead to catastrophic accident consequences.Therefore,in view of this universal,hidden and harmful scenario,it is of great engineering significance to study the risk assessment method of adjacent underground natural gas pipelines under the impact of jet erosion of leakage pipelines.The main research contents are as follows:(1)Research on erosion wear rate model and reliability analysis of natural gas pipeline under jet erosion.Considering the critical strain of pipe and the effect of plastic ridge formed by sand particles on the surface of pipe wall,an improved erosion wear rate model was derived based on the "cutting-deformation" mechanism.Combining with Fluent simulation of water pipe leakage jet,the erosion area and impact velocity distribution of water jet were obtained.Based on the minimum wall thickness criterion,the limit state equation of natural gas pipeline was established.Monte-Carlo method was used to calculate the failure probability and analyze the parameter sensitivity of natural gas pipeline in this scenario.Finally,based on the failure probability of adjacent underground natural gas pipelines under jet erosion,the safe distance between pipelines and natural gas pipelines was proposed.(2)Erosion and Wear Test of Water-Sand Jet on Typical Pipe Material of Underground Natural Gas Pipeline.Taking 20 steel pipe as the research object,experiments were carried out at different injection angles and particle sizes.By observing the wear surface morphology of the sample,the failure mechanism of sand particles on 20 steel at different injection angles was analyzed.The critical erosion angle of the material was determined by the weight loss rate and roughness of the sample.Finally,the velocity of sand particles from nozzle to sample surface was calculated,and the theoretical value of erosion wear rate was calculated,which was compared with the experimental value to verify the reliability of the improved erosion wear rate model.(3)Establishment of risk assessment method for adjacent underground natural gas pipelines under the action of leakage water jet erosion.According to the structure size and adjacent laying distance of pipeline and natural gas pipeline,the effective factor of jet direction was deduced.The accident probability was calculated by combining the leakage probability of pipeline,failure probability and ignition probability of natural gas pipeline under jet erosion.The three-dimensional explosion model of LS-DYNA simulation software was established by using event tree to analyze the consequences of accidents,and the radius of casualties was divided by the threshold of the degree of damage caused by shock wave overpressure to human body.Considering the burial depth of natural gas pipeline,the calculation model of individual risk and social risk in this scenario was improved,and the acceptance criterion of individual risk and social risk based on the principle of ALARP were selected.(4)Case study on risk assessment of adjacent underground natural gas pipelines under the action of leakage water jet erosion.The risk assessment of natural gas pipeline and pipeline adjacent laying scenarios in Guangdong and Malaysia were carried out respectively.The individual risk level and social risk level of the scene were obtained by calculating the probability of accident occurrence and the loss of accident consequences.Finally,according to the adjacent laying scenario of groundwater pipe and natural pipe,the corresponding risk prevention and control measures were proposed,and the risk level of groundwater pipe and natural gas pipeline near-distance laying after the implementation of prevention and control measures was calculated to analyze the effectiveness of prevention and control measures.