Research progress on corrosion and hydrogen embrittlement in hydrogen–natural gas pipeline transportation

Hydrogen, clean, efficient and zero-carbon, is seen as a most promising energy source. The use of existing gas pipelines for hydrogen–natural gas transportation is considered to be an effective way to achieve long-distance, large-scale, efficient, and economical hydrogen transportation. However, the pipelines for hydrogen–natural gas transportation contain lots of impurities (e.g., CH4, high-pressure H2, H2S and CO2) and free water, which will inevitably lead to corrosion and hydrogen embrittlement. This paper presents a systematic review of research and an outlook for corrosion and hydrogen embrittlement in hydrogen–natural gas pipeline transportation. The results show that gas-phase hydrogen charging is suitable for hydrogen–natural gas transportation, but this technique lacks technical standards. By contrast, the liquid-phase hydrogen charging technique is more mature but has large deviation from the engineering reality. In the hydrogen–natural gas transportation pipelines, corrosion and hydrogen embrittlement are synergetic and competitive, but the failure mechanism and change law when corrosion and hydrogen embrittlement coexist remain unclear, which need to be further clarified by experiments. The failure mechanism is believed to be mainly sensitive to three key factors, i.e., the H2S/CO2 partial pressure ratio, the hydrogen blending ratio, and material strength. The increase of the three factors will make the pipeline materials more corrosive and more sensitive to hydrogen embrittlement. The research findings can be used as a reference for research and development of long-distance hydrogen–natural gas transportation technology and will drive the high-quality development of the hydrogen–natural gas blending industry.