Leakage And Diffusion Of Natural Gas Pipeline In Water And Its Consequences

In recent years, with the increase of the people’s environmental awareness, natural gas has been regarded as the third largest energy next to oil and coal at home and abroad. As an important means to transport natural gas, pipelines have also been developing rapidly. Hence pipeline industry is playing an increasingly important role in economic construction. However, it is inevitable for pipelines to meet the aquatic environment in the construction process. With the advancement of China’s major international projects these years, there have been more and more underwater pipeline projects, and leakage accidents have also occurred frequently.Therefore, the analysis of natural gas pipeline leakage diffusion rules in water is essential. At present, most of the research on natural gas pipeline leakage diffusion is related to buried or overhead pipelines. Thanks to many more people pay attention to pipelines in water, the analysis of pipeline in water also emerge as the times require in recent years. But its subjects are mostly oil pipeline, a few studies for gas pipelines is limited to qualitative analysis, or only consider the single factor, the analysis is not comprehensive enough. Hence, the analysis of natural gas pipeline leakage diffusion rules in water can provide theoretical basis for the safe operation and leak detection of gas pipelines in water. Meanwhile, the study for the consequence of pipeline leakage has important implications for the prevention and control of water pipeline accidents.First, this paper analyzes the features of gas pipeline leakage in water and proposes that the greatest difference between water pipelines and land pipeline is environmental pressure, establishes the basic equations as well as the mathematical models of underwater pipeline leakage diffusion, and studies the calculation formulas of steady-state and dynamic leakage rates of gas pipelines. With the aid of CFD (Computational Fluid Dynamics) simulation software and the VOF(Volume of Fluid)model, a numerical simulation study of underwater pipeline leakage process by PISO (Pressure-Implicit with Splitting of Operators) algorithm of velocity coupling is made so as to obtain the gas leakage diffusion rules under the influence of different breakage diameters, water velocities and pipeline internal pressures. A regulation can be given as follows through the quantitative analysis, when the water velocity remains the same, the leakage rate and amount increase with the increase of the leakage diameter, thus enlarging the water surface area with gas. When the leakage diameter is same, the time that gas float to the water surface increases with the increase of water speed. The increase of the pipe pressure can weaken the influence of water flow on gaseous phase and shorten the time of gas floating to the water surface. Through the analysis of the effecting rules of parameters such as leakage diameter, water velocity and pipeline pressure, the fitting formula of the time needed for gas floating to the water surface and gas horizontal migration distance is obtained.In addition, the rationality and applicability of the fitting formula can be proved by comparing the experimental data of the third party, which can provide theoretical guidance for the emergency measures after the failure of the pipeline.By introducing the triangular fuzzy number in paper, the grade judgment should be applied to leakage consequence events including Jet fire, vapor cloud explosion water and air pollution caused by pipeline failure, obtain the failure probability and the severity of the consequences of each event.Meanwhile, the risk index of the incident can be drawn based on the principle of fuzzy rule base. Finally, a quantitative calculation shows that the vapor cloud explosion is the most serious consequence after water pipeline leakage. Simultaneously, this paper also studies the jet fire caused by underwater pipeline failure and the post-accident model of vaporous cloud explosion. The concentration chart of the leaked gas diffusing to the water surface can be calculated under different wind speeds and different modes of pipeline failure, and visually presents the damage radius of different degrees of jet fire and vapor cloud explosion through drawing the corresponding curve. The damage radius not only provides a reference to determine the safety distance and after the accident, but has important practical significance on quantitative risk analysis of the pipeline leakage accident.