X-Ray Computed Tomography of Polymers exposed to High-pressure Hydrogen Gas

Hydrogen (H2) is a highly versatile energy carrier with growing significance in energy storage and transportation. As a clean alternative to fossil fuels, its use is rapidly expanding, particularly in the mobility sector, where compact storage solutions are essential. However, hydrogen's low volumetric energy density necessitates compression to pressures exceeding 350 bar, creating unique engineering challenges. While polymers, often combined with metals, are widely used in dry-running high-pressure hydrogen compressors to avoid contamination of the process gas with oil lubricants, they are subject to thermo-mechanical stresses that can lead to fatigue and degradation. This study leverages X-ray computed tomography (CT) to characterize such degradation in polymers, providing insights into their performance and long-term viability in hydrogen applications. The first part of the study focuses on elastomeric O-rings, commonly used for sealing in hydrogen infrastructure. These components operate under demanding cyclic pressure conditions, ranging from 0.9 MPa to 87 MPa. Initial defects in the O-rings were identified using CT imaging before subjecting the samples to repeated pressure cycling. The progression of these defects was tracked over hundreds of cycles to assess both their growth and the emergence of new damage sites. By employing model compounds of known compositions, the study evaluates the role of fillers and additives in the formation of voids and other defects. These insights are critical for understanding how operational stresses influence damage evolution and for improving the design of materials resistant to hydrogen-induced wear and fatigue. The second focus of the research is on Polyphenylene sulfide (PPS) composites, which are increasingly used as pistons and packing rings in high-pressure hydrogen compressors. PPS is a high-performance polymer known for its thermal stability, chemical resistance, and high mechanical strength, making it suitable for extreme operating environments like reciprocating piston compressors. However, pure PPS suffers from high friction and wear, limiting its application in non-lubricated use. To address these limitations, the study investigates the addition of carbon fibers and polytetrafluoroethylene (PTFE) to the PPS matrix. The inclusion of carbon fibers enhances the material's mechanical properties, while PTFE serves as a solid lubricant, forming tribo-films that reduce friction and improve wear resistance. The modified PPS formulations from this study will be exposed to select hydrogen environments to evaluate for friction properties which can be further co-related to polymer-filler distribution studied using X-ray CT towards understanding the influence of filler type and loading in the PPS matrix as necessary to applications such as pistons and packing rings.