Sylvie Castagnet

New Materials for Hydrogen Distribution Networks: Materials Development & Technico-Economic Benchmark

In France, the steel transportation network for natural gas is connected to the distribution network which operates at lower pressure. This one (total length of 165 000 km) is mainly made of polymer pipes like polyethylene. With the introduction of hydrogen in mixture with natural gas and finally the transport of pure hydrogen, the key challenge is the high level of permeability that is to say the flow rate of hydrogen through polymer infrastructures (pipes or components like connecting parts). This high flow rate of hydrogen has to be taken into account for safety and economic requirements. Long-term behaviour must be carefully assessed: permeation/diffusion properties, thermo-mechanical behaviour and ageing. It is important to characterize the existing distribution network and to propose more innovative materials than polyethylene that could meet the targets for future hydrogen distribution applications. The aim of this project was to develop and assess material solutions to cope with today problems in term of high flow rate of hydrogen and ageing under a hydrogen environment. Polyethylene is considered as a reference material since it is used today in natural gas distribution pipes. Test benches and protocols for testing materials in term of mechanical and barrier properties were first developed. On the other hand, technical polymers (multi-layers, other thermoplastics, polymer blends) have been proposed and studied to improve gas-barrier performances compared to polyethylene. Step by step, permeation and basic mechanical tests have been performed and then more specific characterisations have been done (for long-term ageing under various conditions) in order to choose one or several materials that could meet the specifications required by hydrogen distribution. The design of a pipe prototype was also carried out at the end the project and an economic study was performed for the different potential solutions.

Influence of pressure cycling on damage evolution in an unfilled EPDM exposed to high-pressure hydrogen

This study aims to reveal the internal damage evolution process in a transparent ethylene propylene diene rubber (EPDM) under high-pressure hydrogen cycles (9 and 15 MPa). Damage accumulation of EPDM was tracked from in-situ pictures during cycling. Several dedicated image processing routines allowed the discrimination of mechanisms (separated cavities, clusters and cracks) and sometimes the qualification of their morphology (size distribution, number, ratio of cavities reappearing at any cycle). Numerous small cavities were observed at any cycle, some of them being clustered under the highest pressure. Only part of them systematically appeared again. Some of these cavities inflated and “absorbed” small cavities around them when clustered. Finally, a few cracks were nucleated from some large cavities and grew, following a “stop and grow” process.

Analysis of the creep behavior of thin polymer films by finite elements simulation of micro‐bubble inflation

Finite elements simulations have been performed to investigate the various effects bound to influence the viscoelastic response of nano‐confined polystyrene films, among which surface tension, residual stresses, properties gradient. The work is based on the micro‐bubble inflation experiment developed by McKenna et al. [1,2]. The preliminary results presented here focus on the analysis of the stress gradients into the film, the influence of the boundary conditions and some aspects of the film preparation.