Fraunhofer IWM has developed and successfully commissioned an autoclave for crack growth tests on CT samples in hydrogen at pressures of up to 170 bar. The compact design enables the cost-effective creation of a database for the design and safe operation of hydrogen infrastructure components.
To ensure the safety of hydrogen infrastructures (pipelines, pressure vessels, valves, and fittings), questions such as the following must be answered: How does hydrogen affect the service life, crack formation, and crack growth in components? How safe is operation under cyclic loads such as pressure changes? How can service life be predicted? To answer these questions, material samples are tested under the influence of hydrogen.
For safety-related issues, mechanical tests are preferably carried out on material samples in a pressurized hydrogen atmosphere, with which the formation and propagation of cracks starting from a notch are measured. Crack growth tests on so-called CT (compact tension) specimens in a hydrogen environment provide information about the durability of the material. They help to assess damage tolerance, determine safety factors, and estimate service life under cyclic loading. They form the bridge between the laboratory and application, especially for safety certification of hydrogen infrastructure components.
Fraunhofer IWM has developed and built a cost-effective testing system for crack growth tests consisting of a testing machine, an autoclave, a hydrogen supply, and explosion protection specifically for these requirements. The testing pressure is limited to a maximum of 170 bar and the test temperature is limited to room temperature, eliminating the need for complex and costly temperature control of the autoclave. Test frequencies of up to 1 Hz are sufficient for investigating hydrogen effects, as hydrogen diffusion in the metallic structure is slow at room temperature. The size of the interior is dimensioned so that CT samples of the maximum size W=25.4 mm can be tested.
The crack growth rates measured with the new testing system are comparable to the reference curves in the DVGW G464 and ASME B31.12 guidelines and show satisfactory consistency with the literature data.
Fraunhofer Institute for Mechanics of Materials IWM