Study On Quantitative Risk Assessment Of The Whole Process Of Urban Gas Pipe Network Construction

The study object of this paper was the newly built urban gas pipeline network.The environmental risk factors in the three stages of design,construction and operation of urban gas pipeline network were analyzed by fault tree analysis.Factors of design stage included the design personnel’s technical level,location selection,safety distance setting,pressure design,selection of the pipe materials.Factors of construction stage included crossing engineering,pipeline welding and installation,construction personnel misoperation,ground recovery.Factors of operation stage included corrosion,third party damage,misoperation damage,nature disasters.And then the fault tree was established.Based on the result of fault tree,quantitative analysis of fault tree was obtained by the expert scoring method,fuzzy set theory and combined with the situation of Nanchuan district.Each basic event and the top event in the fault tree,top events and intermediate events in sub failure trees occurrence probability in Nanchuan district were calculated.The probability of the top event was 4.679×10-2.In top events of sub failure trees,the probability of ‘failure of the design scheme’ was 1.275×10-2,the probability of ‘failure of the construction process’ was 1.191×10-2,and the probability of ‘failure of the operation process’ was 2.176×10-2.According to the fault tree structure,the structural importance degree of each basic event was obtained,and the probability importance degree was obtained by the probability of each basic event.Combined with the probability of each basic event in Nanchuan and probability importance degree,the key environmental risk factors for network engineering in Nanchuan district were analyzed,including ensity sensitive points,the landslide prone area,large undulating terrain,complex rock mass structure in the stratum of the excavation,the lack of safety distance with other municipal pipe network,the lack of safety distance with surrounding buildings,improper welding operation,barbaric operation,the pipeline of long service life,the corrosion degree detected difficulty in pipeline location,ground subsidence caused by underground engineering,road load increasing after the transformation,insufficient the pipeline buried depth,overloading of vehicles illegal driving,barbaric construction,inadequate supervision of the construction site,Incomplete or faulty ground marking,construction personnel technical error,inaccurate positioning drawings provided by operating company,no implementation of the safe operation,using overdue and easily damaged parts,pipe disrepair,mproper fault handling.Finally,based on the analysis of the key environmental risk factors for the whole process of urban gas network construction in Nanchuan district,the corresponding measures to mitigate the environmental risk accidents were proposed.And the mitigation measures of common environmental risk factors were put forward.This paper provided theoretical basis to ensure the safety of urban gas pipe network construction and operation,provided reference for construction and operation units to formulate relevant management regulations and emergency plans.At the same time,providing guidance significance for environmental risk assessment quantitative analysis of the whole process from design,construction and operation of the urban gas network construction in different areas.