Failure Analysis Of The Third-Party Damage To Urban Gas Pipeline

As critical infrastructures,urban gas pipelines are widely distributed and important for people's life and industrial production.The safe operation of them meets great challenge for the gas' s flammability and susceptibility to explosion.Especially,cities and towns' infrastructures have increasingly developed,the accidents of urban gas pipelines crossing streets and lanes induced by the third-party damage are frequent,and the third-party damage has become a major factor.Hence,the study on the management and control of the third-party damage to the urban gas pipelines is of great importance for ensuring the safe operation of them.The accident data of the gas pipeline system in the latest five years was obtained by extensive statistics,and the database containing 1014 urban gas pipeline accidents was built up.Basing on statics,the typical failure event analysis was carried out,and three factors of the third-party damage were summarized,i.e.,the management of urban gas industry,the thirdparty effects and behavior management.The quantitative evaluation model for the failure probability of urban gas pipeline accidents induced by the third-party damage was studied.A fault tree of third-party damage containing 56 basic events was built,which is the broadest for the present.The fuzzy probability study for all the basic events was carried out,where the expert opinion was quantified by the membership functions,and the scoring results from experts were rationally optimized by analytic hierarchy process(AHP).The model of fuzzy probability was validated by comparison with the site data.Then the failure probability grading was conducted by the model mentioned above,providing a software,applicable for engineering,for the calculation of pipeline failure.Basing on the basic theory of Elastic-Plastic Mechanics,the research on the failure mechanism and behavior of urban gas pipeline under third-party digging was carried out.The main failure mode and criteria was discussed,and the response model of pipe was build,considering the nonlinearity of pipe and soil interaction and the pipe.The failure process of pipeline under digging was deduced,obtaining the quantitative relation of three indexes,i.e.,the maximum stress,maximum strain and ovality between the digging position,pipe diameter,wall thickness and internal pressure,which will provide the references for the strength evaluation of the pipe.The impact analysis on the typical gas leakage accident was conducted.Basing on the FLACS software,the trend of gas leakage and diffusion was studied,along with the effect of the wind direction on the diffusion.The consequence of the explosion induced by the third-party damage was quantitatively investigated,determining the explosive range,and thermal radiation effects were analyzed by theory.On the basis of the accident analyzing results,the emergency procedure of typical accidents induced by the third-party was proposed,which can be referenced for the prevention and treatment of accidents.