PSI - Issue 77

Niels Grigat et al. / Procedia Structural Integrity 77 (2026) 365–375 N. Grigat, B. Vollbrecht et. al. / Structural Integrity Procedia 00 (2026) 000 – 000

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understanding of the interrelation between material composition, manufacturing parameters, and mechanical performance. The objective of this discussion is to ascertain the most efficacious material configurations and design strategies for optimising hydrogen resistance and mechanical strength. Moreover, the findings provide a foundation for validating the proposed numerical models and assessing the scalability of the continuous manufacturing process developed in this study. Collectively, these findings contribute to the ongoing development of a reliable, corrosion free, and lightweight FRP pipeline solution for future hydrogen infrastructure applications. 4.1. Diffusion Barrier The diffusion barrier performance of the developed FRP materials is evaluated through hydrogen permeation testing under controlled laboratory conditions. The experimental procedure involved the execution of tests at a temperature of 20°C and at hydrogen pressures that varied in order to ascertain the steady-state permeation coefficients of various combinations of materials. The results are summarised in Figure 4.1, which illustrates the measured permeability for both thermoset-based and thermoplastic reference systems. For the epoxy-based composites, a clear influence of the fibre type on the diffusion behaviour is observed. Pure epoxy resin (EP) exhibits the highest permeability, confirming that the polymer matrix alone offers only limited hydrogen barrier capability. When reinforced with glass fibres (GF-EP), the overall permeability of the material is significantly reduced due to the decreased polymer fraction and the tortuous diffusion path introduced by the fibre architecture. It has been demonstrated that carbon fibre-reinforced epoxy (CF-EP) exhibits an even lower permeability, a phenomenon that can be attributed to the higher fibre content and the denser microstructure of the carbon composite. The hybrid configuration, combining glass fibre, epoxy, and an additional aluminium liner (GFEP-AL), achieves the lowest permeation coefficient of all the thermoset systems that were tested; this finding indicates the effectiveness of hybrid barrier layers in suppressing hydrogen diffusion. For the purpose of comparison, a number of thermoplastic materials that are frequently utilised in gas transport systems have also been examined, including polyamide (PA), high-density polyethylene (HDPE), and polycarbonate (PC). Among these, PA demonstrates the most effective hydrogen barrier performance, outperforming HDPE and PC by approximately one order of magnitude. However, even the most effective thermoplastics demonstrate higher permeability in comparison to the hybrid GFEP-AL composite, thereby emphasising the superior gas barrier potential of fibre-reinforced epoxy laminates when meticulously designed.

Figure 4.1: Permeation coefficients depending on the material combination The findings of this study underscore the pivotal function of fibre reinforcement and multi-material design in diminishing hydrogen diffusion. The integration of metallic or ceramic barrier layers has been demonstrated to enhance the impermeability of FRP pipelines, thereby providing a pathway to replace conventional steel systems without compromising safety or performance. It is therefore concluded that the optimized FRP configurations