Research on the mechanism and prediction model of gas leakage and diffusion from shallow-buried natural gas pipelines

Abstract As a crucial component of urban lifeline projects, shallow-buried gas pipelines pose a significant threat to society and people's lives, as well as property in the event of a leakage accident. To investigate the diffusion mechanism of gas leakage out of pipelines, the CFD method is employed to establish a validated numerical model for gas diffusion in backfilled soil. The effects of operating pressure, burial depth, leakage direction of pipelines, and soil resistance coefficient were discussed. The calculated results indicate that the numerical model can accurately predicte the diffusion process and the resistance coefficient of methane in soil-sand, loam, and clay-based. It was found that the burial depth affects the speed of gas diffusion to the soil surface but has little impacts on the concentration distribution range. The diffusion process in the same type of backfilled soil was found very similar under varying pipeline operating pressures, though the pipeline pressure significantly impacts the diffusion range. The shape of the leaked gas cloud in the soil is affected by soil resistance, leak direction, and air buoyancy. A new diffusion model for methane leaking in soil was proposed by introducing two time-related concentration adjustment parameters to the existing natural gas diffusion model. The average error between the calculated results of the proposed diffusion model and the established numerical model was found to be within 10%.