Research progress on leakage and diffusion of CH<sub>4</sub> and H<sub>2</sub>/CH<sub>4</sub> in buried and submarine pipeline transportation processes

Most countries globally are actively advancing efforts towards achieving carbon peak and carbon neutrality goals. CH₄ and H₂ serve as vital clean energy carriers in support of these objectives. Pipeline transportation is an essential method for the large-scale, efficient, low-cost, and safe delivery of CH₄ and H₂. However, it also presents safety risks that may lead to leaks, fires, and other accidents. This paper reviews research conducted by scholars worldwide on the impact of various factors on the consequences of H₂/CH₄ leakage and diffusion in buried and subsea pipeline scenarios. The core focus of research under these conditions is to study how factors such as the depth of the leak orifice, soil properties, underwater leak depth, and current speed affect the diffusion time and range of the gas, thereby analyzing their impact on the severity of the accidents. Despite progress, challenges remain. On the theoretical front, there is a need to further deepen the quantitative study of diffusion mechanisms and their impact on their consequences. On the technical front, efforts are needed to develop efficient and accurate monitoring and prediction systems for real-time detection and risk early warning. To improve efficiency and accuracy, future work will require larger-scale and more diverse experimental studies to obtain relevant data and fully leverage cutting-edge technologies such as big data and artificial intelligence to optimize leak prediction and monitoring systems.