Exploration of the leakage and diffusion dynamics in small and medium-sized holes at a 45-degree inclination within extensive open-air high-pressure natural gas pipelines

This study aims to improve the reliability of emergency management for accidental natural gas pipeline leaks by analyzing the effects of different conditions on gas leakage and diffusion in large open spaces through both simulations and experimental investigations. The experiments involved a 25 mm diameter leak test, accompanied by numerical simulations for 5 mm and 25 mm leak apertures. A Computational Fluid Dynamics (CFD) model was employed to assess the distribution of gas cloud dimensions and hazard zones, with large-scale experiments conducted to validate the simulation outcomes. The results reveal that size variations of the near-field flammable area remain within 8 % in response to changes in wind speed and pipeline pressure, while far-field variations exceed 15 %, indicating greater stability in the near-field gas cloud. As wind speed increases, the gas cloud spreads downwind, and the flammable area height and width gradually decrease, with a maximum attenuation rate of 31.6 % observed at a horizontal distance of 40 m. Additionally, with rising pipeline pressure, the size variations of the near-field flammable area are minimal, with changes in height and width both staying under 5 %. Both wind speed and pipeline pressure variations influence the extent of high-concentration areas. While wind speed has a minor effect, it does cause a shift in the high-concentration area, whereas increased pipeline pressure enlarges the high-concentration area without affecting the degree of offset. The average attenuation rate of the offset for high-concentration areas due to increased wind speed is 9.2 %. These findings demonstrate that the established CFD model can effectively simulate and predict the diffusion behavior of natural gas during accidental leaks. The research outcomes provide valuable insights for early warning systems associated with natural gas pipeline leaks, thus contributing to the prevention of accidents.