Numerical investigation and estimation method of leakage behaviour for hydrogen-blended natural gas in overhead pipelines

Blending hydrogen into existing high-pressure natural gas pipelines can cause hydrogen embrittlement, which further leads to pipeline leakage and even serious explosions. Therefore, a mathematical-physical model is established for the leakage of hydrogen-blended natural gas (HBNG) in high-pressure overhead pipelines based on species transport and a real-gas model. The model is validated by the experimental values from the literature, with validation errors falling below 15%. The influence of various operating and structural parameters on the leakage rate of HBNG is analyzed. The results show that the leakage rate decreases with the hydrogenblending ratio increasing because of the low density and rapid diffusion characteristics of hydrogen, which reduce the total leakage mass rate.. The leakage rate increases with an increase in leakage hole diameter and operating pressure, but it is poorly affected by the pipeline diameter and wall thickness. The orthogonal design is used in this simulation to analyse the effect of different factors on the leakage rate. The sensitivity for each factor ranks as follows: leakage hole diameter > hydrogen blending ratio > operating pressure > wall thickness > pipeline diameter. Finally, a new prediction model of leakage rate for high-pressure overhead pipelines of HBNG is proposed, and it takes into account the compressibility effects of gas and properties of the gas mixture. The prediction deviation of the new model is less than 5%. The above results can be used as guidance for risk assessment and prevention of leakage accidents for HBNG in high-pressure overhead pipelines.