Design, usage and safety aspects for tubular specimens for materials qualification with pressurised hydrogen

Typically, autoclaves are used to characterise materials under a hydrogen atmosphere. Those systems are expensive in installation and usage due to high safety requirements. A cost-efficient and reliable alternative without the need for explosive protection might be the tubular specimen technique. In this technique, a small diameter axial hole is machined in the centre of the specimen, which is pressurised with gas. Comparing the results of specimens filled with pressurised hydrogen and, for reference, with ambient air or pressurised nitrogen allows us to conclude for the effect of hydrogen on material properties. The advantage of the tubular specimen technique is the very low volume of the explosive gas, compared to conventional autoclaves. This reduces safety risks and allows the implementation in existing testing machines with low efforts. This paper describes in detail the setup of a tubular specimen test system for tensile tests, addresses safety aspects and shows exemplary results.