Environmental Heating Effects on the Gas Parameters during the Long-distance Gas Pipelines Leakage Process

Gas pipeline is one of the most economical transportation methods. However, in the long-time operation process, leakage from pipelines may take place due to various effects such as the corrosion, natural or mam-made destruction and inherent defects. The leakage may produce unpredictable damage on the human beings, animals, plants and the environment, especially the leakage from the high-pressure gas pipelines. So it is important to predict the influence area of the leakage for making emergency plan. Leakage rate is one of the basic and important parameters used for simulating and predicting the dispersion influence area of the leakage accidents, whose accuracy can improve reliability of the simulation prediction. Taking the heat exchange effect between the pipeline and the environment into consideration, with a reasonable simplification and assumptions, ignoring the influences of fluid flow inside the pipeline, a physical model is proposed. Then with the application of thermodynamics and gas dynamics theory, combining with the ideal gas state equation and the energy conservation equation, the mathematical model is established and solved. Studies and analyses are carried out for the leakage process of high-pressure gas pipelines. A leakage rate formula of the non-adiabatic leakage for both the critical and subcritical leaking process is proposed. And taking CO2 gas pipeline leakage as an example, the variation of the temperature, the pressure and the leakage rate with the time is presented under different environmental heat transfer conditions. The results show that the environmental heating has a strong influence on the gas temperature in the pipeline, but its effect on the pressure and the leakage rate is very limited compared with the adiabatic leakage process without considering the environmental heating. Therefore, when calculating the leakage of the high pressure gas pipelines, the heating of the environment can be neglected or simplified as a first-order approximation.