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The mechanical properties of materials deteriorate when hydrogen embrittlement (HE) occurs, seriously threatening the reliability and durability of the hydrogen system. Therefore, it is important to summarize the status and development trends of research on HE. This study reviewed 6676 publications concerned with HE from 1997 to 2022 based on the Web of Science Core Collection. VOSviewer was used to conduct the bibliometric analysis and produce visualizations of the publications. The results showed that the number of publications on HE increased after 2007, especially between 2017 and 2019. Japan was the country with the highest numbers of productive authors and citations of publications, and the total number of citations of Japanese publications was 24,589. Kyushu University was the most influential university, and the total number of citations of Kyushu University publications was 7999. Akiyama was the most prolific and influential author, publishing 88 publications with a total of 2565 citations. The USA, South Korea and some European countries are also leading in HE research; these countries have published more than 200 publications. It was also found that the HE publications generally covered five topics: “Hydrogen embrittlement in different materials”, “Effect of hydrogen on mechanical properties of materials”, “Effect of alloying elements or microstructure on hydrogen embrittlement”, “Hydrogen transport”, and “Characteristics and mechanisms of hydrogen related failures”. Research hotspots included “Fracture failure behavior and analysis”, “Microstructure”, “Hydrogen diffusion and transport”, “Mechanical properties”, “Hydrogen resistance”, and so on. These covered the basic methods and purposes of HE research. Finally, the distribution of the main subject categories of the publications was determined, and these categories covered various topics and disciplines. This study establishes valuable reference information for the application and development of HE research and provides a convenient resource to help researchers and scholars understand the development trends and research directions in this field.

The rubber ring is an essential component of high-pressure hydrogen storage systems. However, the fretting damage can lead to the seal failure of the rubber ring, which may cause hydrogen leakage. Rubber X-ring has been proven to own excellent static sealing performance, while its fretting characteristics under high-pressure hydrogen remain unclear. In this study, a numerical model is developed to explore the fretting characteristics of the X-ring combined seal, in which the effect of hydrogen swelling is well considered. The stress distribution of the fretting seal and the effects of fretting amplitude, friction coefficient, hydrogen pressure, and pre-compression ratio on the fretting behavior of the X-ring are investigated. Moreover, the similarities and differences in the fretting performance of X-ring and O-ring under high-pressure hydrogen are discussed. It is shown that the evolution of the stress concentration zone inside the X-ring is closely linked to the cover’s drag direction and the wedge-ring’s blocking action. The X-ring enters the fretting cycle earlier with increased fretting amplitude, whereas the fretting period remains unchanged. Furthermore, increasing the hydrogen pressure and pre-compression ratio could enhance the fretting sealing performance. The friction coefficient and hydrogen pressure increase the possibility of failure due to cracks or elasticity. The fretting characteristics of the X-ring are superior to those of the O-ring, denoting that X-ring may be an alternative to the O-ring in the fretting seal structure. This work is of theoretical importance for the quantitative evaluation and reliable prevention of fretting damage to rubber rings and improving the safety of high-pressure hydrogen storage systems.

The liquefied petroleum gas (LPG) cylinder incineration test is an important part of the cylinder periodic inspection to clean up the residual gas and ensure the safety of subsequent inspection items. However, the cylinder needs to be incinerated several times due to the uneven temperature distribution of the cylinder, leading to low incineration efficiency and waste of energy. In this study, a cylinder incineration test is experimentally investigated and a computational fluid dynamics (CFD) model is established to analyze the influence of incinerator structure parameters and cylinder types on the temperature uniformity of the cylinder. The results show that the temperature distribution of the middle surface of the cylinder is most uneven. With the increase of the burner nozzle diameter and the incinerator diameter, the standard deviation of temperature decreases at first and then increases, and the minimum is reached at 150 mm and 530 mm, respectively. The optimized design is found to have a better temperature uniformity of the cylinder with the burner nozzle angle of 0?. The optimal incinerator diameter for different types of LPG cylinders is different and decreases as the cylinder diameter decreases.