In-situ 3D X-ray tomography under high-pressure H2: Direct observation and quantification of hydrogen-induced damage evolution in steel during tensile testing

We introduce a novel experimental device for tensile testing in high-pressure hydrogen environments, coupled with in situ 3D synchrotron X-ray tomography. Demonstrated on E355 steel, this setup enables repeated tomographic imaging during deformation, offering unprecedented time-resolved insight into hydrogen-assisted damage mechanisms. It allows full 3D quantification of crack and void volume, shape, orientation, and spatial distribution, opening new pathways for understanding hydrogen embrittlement at the microscale. Specimens were tested at 20 and 130 bar H 2 at a strain rate of 1 × 10 −4 s −1 , with ductility loss of 20% at 20 bar and 69% at 130 bar. The new methodology enabled precise tracking of surface crack penetration during the test, which increased from 4 μ m at the Ultimate Tensile Strength to an average of 24 μ m near fracture at 130 bar. Finally, the approach enabled the direct observation of internal hydrogen-induced cracks coalescing with surface cracks, demonstrating their contribution to final fracture.