The uncertain role of the natural gas infrastructure in the decarbonized energy system and the limitations of hydrogen blending raise the question of whether natural gas pipelines can be economically utilized for the transport of hydrogen. To investigate this question, this study derives cost functions for the selected pipeline reassignment methods. By applying geospatial hydrogen supply chain modeling, the technical and economic potential of natural gas pipeline reassignment during a hydrogen market introduction is assessed.The results of this study show a technically viable potential of more than 80% of the analyzed representative German pipeline network. By comparing the derived pipeline cost functions it could be derived that pipeline reassignment can reduce the hydrogen transmission costs by more than 60%. Finally, a countrywide analysis of pipeline availability constraints for the year 2030 shows a cost reduction of the transmission system by 30% in comparison to a newly built hydrogen pipeline system.The technical viability of pipeline reassignment relies on the capability of minimizing material failure due to hydrogen-induced damage and enabling secure hydrogen delivery. Hydrogeninduced material fracturing is caused by hydrogen permeation into the crystalline steel structure, and serves to diminish the material's mechanical properties, which are required for proper pipeline utilization [10]. The underlying hydrogen-induced material fracturing mechanisms of carbon steels are well understood, and is one of the reasons for equipment failure in the oil and gas industry [10,11]. Drawing on the analyses in the literature, this study will focus on the two main mechanisms of pipeline material degradation that most likely result in the premature failure of conventional steel, namely: the degradation of heat-affected zones (HAZ) and fatigue crack propagation (FCP) in the base pipeline material [12]. Degradation of the HAZ occurs due to hydrogen-induced subcritical crack growth under static load in pipeline welds, while the hydrogen-induced FCP rate increase takes place in the base material of the pipeline.The two aforementioned mechanisms have been analyzed in the literature with the result that the use of pipeline steel X70 is found to be a suitable option to eliminate the former, and to partially address the latter degradation mechanism [12][13][14][15][16][17]. Xu investigated the subcritical crack growth of the HAZ in pipeline segments of steel X70 and X42, with his results showing no sign of subcritical crack growth in either type of steel [15]. Similar tests conducted on X70 steel to assess the resistance of these materials to subcritical cracking in 6.9 and 4.1 MPa hydrogen gas partial pressures reported no subcritical crack growth for either type [12].Lastly, Raymond et al. reported that steels with a yield strength ranging from 200 to 580 MPa will not show signs of subcritical crack growth under static loads when exposed to a gaseous hydrogen environment [16]. In the case of steel type X70, the yield stren...

The technological lock-in of the transportation and industrial sector can be largely attributed to the limited availability of alternative fuel infrastructures. Herein, a countrywide supply chain analysis of Germany, spanning until 2050, is applied to investigate promising infrastructure development pathways and associated hydrogen distribution costs for each analyzed hydrogen market. Analyzed supply chain pathways include seasonal storage to balance fluctuating renewable power generation with necessary purification, as well as trailer- and pipeline-based hydrogen delivery. The analysis encompasses green hydrogen feedstock in the chemical industry and fuel cell-based mobility applications, such as local buses, non-electrified regional trains, material handling vehicles, and trucks, as well as passenger cars. Our results indicate that the utilization of low-cost, long-term storage and improved refueling station utilization have the highest impact during the market introduction phase. We find that public transport and captive fleets offer a cost-efficient countrywide renewable hydrogen supply roll-out option. Furthermore, we show that, at comparable effective carbon tax resulting from the current energy tax rates in Germany, hydrogen is cost-competitive in the transportation sector by the year 2025. Moreover, we show that sector-specific CO2 taxes are required to provide a cost-competitive green hydrogen supply in both the transportation and industrial sectors.

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