Dynamic Risk Assessment Of Urban Gas Pipeline Network Based On System Dynamic

The rapid development of the gas industry and continuous aging of existing gas pipelines have led to the frequent occurrence of fires,explosions,poisonings,and other similar accidents due to pipeline failure.This has seriously affected public safety and social harmony and stability.Accident investigation shows that the fundamental reason for frequent accidents in gas pipeline network is that gas companies can not predict the real-time risk state of pipeline operation because of the lack of dynamic risk feedback mechanism and the main reason for the expansion of gas accidents is the lack of scientific emergency decision-making methods after gas leakage because of the inability to accurately predict the corresponding accident consequences.Therefore,it is more scientific and instructive to study the dynamic change trend of urban gas pipeline risk than static risk assessment.System dynamics(SD)offers unique advantages in revealing the dynamic characteristics of system behavior.Considering the two aspects of failure probability and accident consequences,a dynamic risk assessment model of urban gas pipeline network based on system dynamics is constructed in this paper.The proposed model achieves the goal of dynamic tracking and control of urban gas pipeline network risk,lays a theoretical foundation for the integrity management,and improves the safety and reliability of gas pipeline network operation.(1)The failure causes are divided into two categories according to their correlation with time.For corrosion,which is closely related to time,the power function corrosion model is modified by combining actual survey data of soil corrosion characteristics.Then,the structural reliability theory was adopted to establish two calculation models for pipeline corrosion failure: the pressure failure model and von Mises stress failure model.The dynamic corrosion failure probability is calculated by Monte-Carlo simulation and subset simulation respectively,and a sensitivity analysis was carried out on the relevant parameters that affect the failure probability.The results showed that multiple loads caused by the covering soil,residual stress,temperature differential,and bending stress have anon-negligible effect on the pipeline reliability.The corrosion coefficients gradually become the most important factors that affect the failure probability with increased service time.On the other hand,for the time-independent failure causes(third-party damage,incorrect operation,and construction defect/material failure),a failure probability calculation model based on modification factors is proposed by using historical data to reduce the subjectivity of the calculation results.(2)According to the evolution process of gas accidents,the failure form of gas pipelines are analyzed.A method for calculating the gas leakage rate,the physical effects of fireball,jet fire,and vapor cloud explosion,fatality probability unit and death probability,individual risk,and social risk are proposed.(3)The SD model for the risk assessment of buried gas pipelines is constructed by considering the two aspects of failure probability and accident consequences.The failure probability calculation models and the accident consequence analysis models are directly set as SD model equations to describe the dynamic evolution behavior of the system.The overall failure probability,the consequences of gas accidents,and the evolution law of individual risk over time are simulated and analyzed by considering a natural gas pipeline in Zhuhai,China,as an example.The results show that the dynamic development laws of gas pipeline risk are consistent with the actual situation and the proposed model can effectively characterize the temporal and spatial laws of risk evolution and the risk degree of buried gas pipelines.In summary,the proposed model can be used to dynamically track the individual risk of pipelines and realize the functions of “pre-prevention” and “pre-warning” of gas accidents.