A review on hazards and risks to pipeline operation under transporting hydrogen energy and hydrogen-mixed natural gas

As an efficient and clean fuel, hydrogen energy plays an important role in relieving the energy crisis and achieving the orientation of zero carbon emissions. Transportation is the key link in the construction of hydrogen energy infrastructure. For large-scale and long-distance transportation of hydrogen, pipeline transportation has the advantages of high efficiency and cost saving. While using the existing natural gas pipeline to transport hydrogen, it would economize the economic cost, time cost and labor cost. However, the transportation of hydrogen may bring more hazards and risks. Based on the investigation of a large number of literatures, the research advance in hydrogen embrittlement, leakage, combustion and explosion risk of hydrogen and hydrogen-mixed natural gas pipelines was reviewed. The mechanism, research means and evaluation methods of hydrogen embrittlement, as well as the experimental and numerical simulation research results of leakage, combustion and explosion were discussed in detail. The definite and important conclusions include: (1) For buried hydrogen-mixed natural gas transportation pipeline, the leakage rate of hydrogen and methane is the same, the formation of the leakage crater is foreign to the nature of leakage gas. (2) When adding less than 25 volume percentage of hydrogen into the natural gas pipelines, the explosion risk would not be increased. Future research should focus on the risk prediction, quantitative risk assessment, intelligent monitoring, and explosion-suppression technical measures of hydrogen and hydrogen-mixed natural gas transportation pipelines, so as to establish comprehensive and multi-level pipeline safety protection barriers.