Research On The Long-Term Performance And Permeation Characteristics Of Hydrogen Transport Via Polyethylene Pipelines

Hydrogen, as an important energy carrier, is playing an increasingly significant role in promoting the green energy transition. It can be produced using the surplus electricity from renewable energy sources and serves as a core component of the "Power-to-X" energy strategy. It can be transported through existing polymer pipeline networks. However, converting natural gas pipelines to hydrogen transportation applications requires a systematic assessment of their short-term and long-term impacts on polymer pipelines, especially issues related to hydrogen permeation and gas loss.
Previous studies have shown that the short-term impact of hydrogen on polyethylene pipes is relatively limited, but its long-term effects - especially on the service life of the pipes - have not been fully investigated. This study focuses on evaluating the change in the service life of a PE100-RC pipe after being exposed to 8.9 bar hydrogen for two years. Through the cyclic crack rod test, it was found that the CRB failure curve only showed a slight slope change. Similar phenomena also occurred in another PE100-RC pipe test that was exposed to 10 bar water pressure for 1000 hours. The changes observed in the CRB test and the anti-slow crack propagation performance may be due to the material morphology changes caused by pressure, and are not related to the hydrogen exposure itself. Therefore, it can be concluded that hydrogen exposure has not had a substantive impact on the anti-slow crack propagation performance and service life of polyethylene pipes.
As the smallest gas molecule, the permeability of hydrogen gas in PE pipes is approximately four times that of gas loss compared to natural gas. In semi-crystalline polymers, the permeability of gas in the crystalline phase is much lower than that in the amorphous phase. To explore the relationship between the morphology of polyethylene and its permeability, the research team analyzed seven types of PE pipes produced using different injection molding process parameters. The difference in crystallinity measured by infrared spectroscopy was as high as 25%, but the permeability coefficient only changed by 13%, indicating that the influence of crystallinity on hydrogen gas permeation is relatively limited. A deeper understanding of this relationship will help optimize the anti-permeation performance of PE pipes in the future and provide a theoretical basis for the impact of material morphology changes on permeation behavior during long-term use.