Detection of microstructural material changes due to hydrogen pressure atmosphere under cyclic load using eddy current testing

The absorption of hydrogen into the metal lattice can cause a deterioration in the mechanical properties, leading to brittle fracture and sudden failure of the material. To investigate these effects, this paper presents fatigue tests on a hollow specimen geometry. The specimens are internally exposed to a pressurized hydrogen atmosphere during the fatigue tests. This led to a reduction in service life of up to 22 % compared to the reference group exposed to argon. Material fatigue is noticeable in microstructural changes before crack growth is initiated. These changes shall be detected using non-destructive testing (NDT) methods. For this purpose, an eddy current (EC) testing method is used to characterize the material, as it allows both electrical and magnetic changes to be recorded. A clear separation between the argon and hydrogen specimens was achieved at a test frequency of 400 kHz. However, the assessment of the state of fatigue, namely the probability of crack formation and crack propagation, is a challenging task. Nevertheless, this issue can be addressed through the implementation of an NDT methodology. EC testing is suitable for detecting changes in the microstructure at an early stage and could therefore develop into an option for fatigue monitoring.