Leakage and diffusion behavior of a buried pipeline of hydrogen-blended natural gas

Buried pipelines are one method of conservation transfer for widely used gases such as natural gas and hydrogen. The safety of these pipelines is of great importance because of the potential leakage risks posed by the flammable gas and the special properties of the hydrogen mixture. Estimating the leakage behavior and quantifying the diffusion range outside the pipeline are important but challenging goals due to the hydrogen mixture and presence of soil. This study provides essential information about the diffusion behavior and concentration distribution of underground hydrogen and natural gas mixture leakages. Therefore, a large-scale experimental system was developed to simulate high-pressure leaks of hydrogen mixture natural gas from small holes in three different directions from a pipeline buried in soil. The diffusion of hydrogen-doped natural gas in soil was experimentally measured under different conditions, such as different hydrogen mixture ratios, release pressures, and leakage directions. The experimental results verified the applicability of the gas leakage mass flow model, with an error of 6.85%. When a larger proportion of a single component was present in the hydrogen-doped natural gas, the leakage pressure showed a greater diffusion range. In addition, the diffusion range of hydrogen-doped natural gas in the leakage direction was larger at 3 o'clock than that at 12 o'clock. The hydrogen blend carried methane and diffused, which shortened the methane saturation time. Moreover, a quantitative relationship between the concentration of hydrogen-doped natural gas and the diffusion distance over which the hydrogen-doped natural gas reached the lower limit of the explosion was obtained by quantitative analysis of the experimental data.