Hazard Assessment Of Natural Gas Pipeline Leakage And Diffusion

The transmitting pipeline is regarded as a relatively safe and economic manner for transporting natural gas. Like other engineering structures, gas pipeline during operation will also be disturbed by internal and external fators, such as corrosion, material defects, and third party damage, etc. leading to pipeline hole leaks or fracture. After natural gas diffusing into the atmosphere, it is likely to initiate fire or explosion if meeting finite concentration and ignition sourees, and causing the serious casualties, significant economic loss and bad influence of society and political at the same time. Therefore, quantitative risk assessment for the contingent accident of natural gas pipeline leakage, will transform the gas pipeline maintenance from blind and passive maintenance into provisional and active service, in order to achieve minimum risk and maximum efficiency goals.In order to accurately evaluate the hazardous degree of accident, researching the rule of the gas diffusing and evaluating the hazardous consequence when the gas pipeline is having leaked are primary works in this paper. Firstly the research status of gas leakage, diffusion and the theory for accident analysis in domestic and abroad have been introduce briefly. Then, the jet theory have been studied, and based on hydromechanics elementary theory, the mathematical models for calculating the leakage rate of natural gas pipeline have been deduced systemically, that is the nozzle model, the hole model and the pipe model. The useness scope of each model has been determined: the nozzle model, d / D≤0.2; the hole model, 0.2≤d / D≥0.8; the pipe model, d / D≥0.8. And based on the hydromechanics and thermodynamics elementary theory, this paper establishes a mathematical model of natural gas diffusion after leaking into atmosphere, adopts computational fluid mechanics simulation software Fluent to simulate the natural gas leakage and diffusion, and analyses diffusion impacted by different leakage aperture, wind speed, and impediments. After comparing the diffuseness models systematically, this paper chooses the Gaussian model to simulate the hazardous region caused by leakage and diffusion of the natural gas, and studies the relationship between the hazardous region and leakage aperture, wind speed. Finally, this paper generalizes the fault tree of gas pipeline leakage generalized systematically, establishes the physical models and hazardous models of jet fire, fireball and vapor cloud explosion, demarcates the radiuses with various hazardous degrees. Then we know hazardous degrees caused by the accidents will be lower if the distance from the hazard source is farther, and finally be a constant.Based on theory analysis and computer simulation as main tools, this paper analyzed and researched on the hazardous region and accident consequence of natural gas transmitting pipeline leakage roundly. The methods and conclusions may be useful to the quantitative risk assessment of natural gas transmitting pipeline leakage.