Deliverable D3.2, Material Assessment for Barriers and Insulation Materials, presents the experimental results obtained for the mechanical and thermal characterization of metallic materials, as well as insulation materials.
The testing campaign is extensive, covering several materials under three different temperature conditions: Room Temperature (RT), Low Temperature (LT, liquid nitrogen at 77 K), and Cryogenic Temperature (CT, liquid helium at 4 K).
For the metallic materials, two austenitic stainless steel grades intended for the primary and secondary metallic barriers of the Cargo Containment System (CCS) were investigated. Besides the as-received condition, testing was also performed on pre-strained and welded material to represent the conditions introduced due to corrugation and welding processes. In addition, cathodically hydrogen pre-charged specimens from all material conditions were tested to assess the influence of hydrogen on material performance.
Progress and Main Results
Metallic Materials
LH₂ Immersion Tests
The metallic materials were evaluated for hydrogen permeability by immersion in liquid hydrogen (LH₂) for a certain period. Hydrogen uptake was assessed using Thermal Desorption Spectroscopy (TDS). The results showed no measurable hydrogen ingress during the exposure period, confirming the suitability of the investigated materials for LH₂ service.
Material Pre-treatment and Mechanical Testing
Pre-straining was applied to selected specimens to induce martensitic phase transformation, simulating the deformation-induced phase transformation that occurs during the corrugation process of the metallic membrane. Cathodic hydrogen charging was performed in accordance with the standard to introduce hydrogen into the material. A beaker-type electrochemical cell was used, with the specimens serving as the cathode and a Pt wire as the anode. The charging current density and charging duration were selected according to the standard. TDS analysis was subsequently conducted to quantify the hydrogen absorbed by the charged specimens.
Conventional tensile tests were performed on the as-received material of both stainless steel grades at RT, LT, and CT. The results showed that the yield strength remained relatively stable across the three temperatures, whereas the tensile strength increased significantly as temperature decreased. As expected, elongation decreased with decreasing temperature, although both materials maintained good ductility even at 4 K, confirming the excellent cryogenic performance of austenitic stainless steels.
Slow strain rate tensile testing (SSRT) was conducted to evaluate the hydrogen embrittlement susceptibility of the materials. Both the as-received and pre-strained specimens exhibited a greater reduction in ductility after hydrogen charging under RT conditions than at LT and CT. In the as-received condition, the reduction in elongation became more pronounced as temperature decreased, whereas the pre-strained material showed a smaller temperature dependence. The two stainless steel grades also exhibited differences in their response to hydrogen embrittlement. Nevertheless, both materials demonstrated good overall compatibility with hydrogen under all testing conditions.
The Relative Reduction of Area (RRA), defined as the ratio of the reduction in area of hydrogen-charged specimens to that of uncharged specimens, was calculated for all testing conditions. This parameter provides an additional measure of hydrogen embrittlement susceptibility and complements the SSRT results.
Next Steps
For the metallic materials, the next phase of work will focus on completing the analysis of the welded specimens. The results from the additional tests currently under evaluation, including notched SSRT tests, will also be analyzed. Furthermore, the experimental campaign will be extended to fatigue testing, providing a more comprehensive assessment of the materials’ suitability and long-term compatibility for liquid hydrogen applications.
Non-metallic Materials
Various tests of the non-metallic materials (mainly reinforced polyurethane) are on-going, with results expected by the end of 2026. The corresponding test standards and procedures have already been reported.
Due to the sensitive nature of the technical information included, the full deliverable is not publicly available.
