Study On External Risk Assessment Of City Gas System

China’s energy industry is in the crucial period of green and low-carbon transformation,and the high-quality development of energy has become the main goal.In recent years,with the improvement of city gas infrastructure and the continuous promotion of coal-to-gas policy,natural gas,as a clean,efficient and environmentally friendly green energy,has relatively improved its consumption level and supply capacity.With the rapid development of the gas industry,the city gas system is also facing many risks.Besides its own system risks,the external risk situation it faces is also increasingly complex,such as the failure of the city gas supply system caused by natural disasters,cyber attacks,terrorist attacks,external force damage by third parties,etc.,which leads to the shortage of gas supply and even accidents,seriously affecting the overall safe operation of the city.In order to reduce the possibility of external risks threatening the city gas system,this paper takes the external risks of the city gas system as the research object,and provides a complete and comprehensive external risk assessment method for the city gas system.The prime research contents are as follows:(1)From the perspectives of accident cases and expert experience,identify and analyze the risks of the gas system induced by natural disasters.Based on the results of literature investigation and accident case analysis,the FTA model is constructed and transformed into a BN model for reverse reasoning.The Delphi method is used to build the disaster chain model and complex network model.The disaster chain probability formula is used for quantitative analysis to find out the key links.Compared with the key nodes of the BN model,the typical natural disaster categories were identified.(2)Based on the statistical analysis and literature research of external intrusion accidents of gas system at home and abroad,the risk of external intrusion of city gas system is focused on three aspects: network information security,terrorist attacks and third-party external force damage.In the aspect of information security,based on the composition of SCADA system of city gas,the improved attack and defense tree model is used to calculate the probability of attack nodes and the concept of "attack and defense reward" is introduced to quantify the loss of attack and defense nodes.In terms of terrorist attacks and third-party destruction,the index system of terrorist attacks and third-party destruction of city gas system is constructed by combining relevant cases and literature research.Summarize the risk factors of network attack,terrorist attack and third-party external force damage to the city gas system,and build an index system of external intrusion risk of the city gas system.(3)On the basis of identifying the risks of natural disasters and external intrusions in city gas system,using disaster chain theory,OWA operator fuzzy evaluation and other methods,the evaluation methods of natural disasters and external intrusions in city gas system are put forward.The external comprehensive risk index system of city gas system is constructed,and the effectiveness of the model is verified by taking Beijing gas system as an evaluation example.