In a hydrogen energy system, high-pressure gas is typically delivered through pipelines or tube trailers and stored in pressure vessels at bulk storage facilities. The metal alloys used in these systems, such as pipelines and pipeline welds, storage vessels (earlier modes), valves, valve components (fasteners, spring steel, and bolt steel), and many other structural components, are exposed to a wide range of temperatures and high-pressure hydrogen gas cycles. Hydrogen atoms diffuse into steels and accumulate at defect sites, causing microcracking that manifests as hydrogen embrittlement (HE) at the macroscale, degrading alloys by reducing ductility, tensile strength, fracture toughness, elongation, fatigue life, and resistance to crack propagation [1, 2]. The slow strain rate tensile (SSRT) test is used as a screening method to evaluate the effects of hydrogen, typically performed in an autoclave with a fixed cylindrical specimen, which requires high capital and operating costs and significant safety measures. However, as shown by a few studies [2,3], a hollow specimen, also known as a tubular specimen, can provide reliable and consistent results similar to conventional autoclave measurements.
At SCIOFLEX Hydrogen GmbH a hollow specimen test system is being developed that can measure up to 20 MPa and is integrated with the ZwickRoell Kappa 100 to perform SSRT, creep/relaxation, compression, fracture and fatigue up to 300 mm/min max and 100 kN.
This novel approach can successfully replace conventional testing methods, providing faster, more reproducible results while reducing the volume of hydrogen gas, making it safer, more effective and less costly. In addition, notching the specimen allows for local characterization of HE at specific regions of the specimen and, most importantly, characterization of HE on weld materials and compatibility of different materials in a system.