Risk Assessment Of Natural Gas Pipeline In Urban Utility Tunnel

According to the Technical Code for Utility Tunnel Engineering,the natural gas pipeline can be put into the utility tunnel.However,the natural gas is flammable,explosive and poisonous.Once the pipeline occurred failure in utility tunnel,it will not only affect the gas supply and the safety of personnel,but also can cause the collapse of utility tunnel and the damage of other pipelines,and the resulting losses are immeasurable.Therefore,it is necessary to the risk assessment for natural gas pipelines in utility tunnel,so the weak parts can be found and the risk of natural gas pipelines can be reduce by maintenance measures taken in timely.(1)By analyzing and comparing the common risk assessment methods,the Kent method is selected to evaluate the risk which is suitable for the natural gas pipeline in utility tunnel.A subsection method for natural gas pipeline in utility tunnel is proposed.Besides,the failure influence factors of Kent evaluation method is classified into six categories:the third party failure index,the corrosion index,the design index,the misoperation index,the gas corridor accessory equipment index and the external disturbance index.(2)The failure factors of gas pipeline can be obtained through statistics of gas pipeline failure,summary of Pipeline Risk Management Manual and induction of influencing factors of gas pipeline.Then,according to the difference between the natural gas pipeline is built in utility tunnel and the direct buried gas pipeline,the factors are adjusted.Then the composition distribution of'third party failure index','corrosion index','design index' and 'misoperation index' were obtained.Then the composition distribution of 'third party failure index','corrosion index','design index' and 'misoperation index' were obtained.(3)Analysis of pipe failure factors related to various accessories of natural gas pipeline and natural gas corridor.Including valve,compensator,discharge tube,pressure regulator,and ventilation equipment,power supply equipment,lighting equipment,monitoring and alarm system.And list the composition and distribution of the factors at all levels and the detailed criteria for scoring.(4)Considering the failure of other pipelines included in the integrated corridor may threaten the safe operation of natural gas pipelines.Therefore,by analyzing the failure factors of other pipelines,the composition and distribution of the 'external interference index' are determined.(5)The devices located in natural gas corridor that can influence the consequences of failure,such as fire detector,alarm device,fire extinguishing system,network reliability,electrical equipment explosion protection,smoke exhaust valve,fire compartment distance,fire isolation,fire station and escape port.And the effect of natural gas pipeline failure on other pipelines in the utility tunnel has been taken into consideration.Through the analysis and summary of those influence,the composition distribution of the consequences of the failure is put forward.(6)The FLUENT is used to simulate the leakage of the pipeline in natural gas corridor.And the different distribution laws of natural gas are obtained by changing the operating pressure of the pipeline and the velocity of the accident exhaust.It can be concluded that the accident exhausting wind can effectively reduce the effect of failure.Besides,by increasing the speed of accident exhaust,the natural gas diffusion concentration in the corridor can be significantly reduced,and the safety area in the corridor will be increased,so that the explosion accident can be avoided to a large extent.(7)In this paper,a risk assessment system for natural gas pipeline in utility tunnel is proposed.We use this system in engineering examples,then summarize and analyze the results of risk assessment,finally propose risk management suggestions for relatively high risk management.It embodies the objective value and application value of the evaluation system.According to the established risk assessment system for natural gas pipeline in utility tunnel,the measures to reduce the risk of natural gas pipeline in utility tunnel can be put forward.It provides a reference for the construction and management of natural gas pipeline set up in utility tunnel.