With the global increase of hydrogen applications and industries comes an increase in the demands for the hydrogen infrastructure, where reliability is essential. Compressors are an important part of the hydrogen infrastructure, with rolling element bearings being a key component. However, hydrogen is known to significantly reduce the mechanical properties of rolling element bearings, a phenomenon called hydrogen embrittlement. Studies report that bearings which are subjected to hydrogen can fail up to ten times faster compared to bearings operating in other conditions. This detrimental effect on bearing performance has led to research within the subject of hydrogen embrittlement in bearing steels. While it is well established in research that hydrogen affects bearings negatively, several research challenges remain. This includes both the fundamental level to further understand the interaction of hydrogen with the steel as well on a more applied level when it comes to the quantification of hydrogen damage, as most of the research available in hydrogen embrittlement has a qualitative character. 

In this research, rolling sliding tribotesting using a micropitting rig (MPR) as well as full bearing testing were performed to further understand the interaction between hydrogen and bearing steel. These tribotests were combined with electrochemical hydrogen charging, thermal desorption mass spectrometry (TDMS) as well as extended material analysis to connect the wear to the hydrogen concentration as well as hydrogen trapping state in the bearing steel. The hydrogen trapping state in the material is of importance, as a lower hydrogen trapping energy is often correlated with a higher potential of hydrogen embrittlement. The results have shown that the cyclic straining of bearing steel during tribotesting can lower the hydrogen trapping energy, highlighting the increased embrittling effect of hydrogen in bearing applications. Another finding was a quantitative correlation between diffusible hydrogen concentration of bearing steel and surface-initiated damage. The hydrogen concentration of bearing steel was systematically varied by different hydrogen pre-charging conditions, which was then followed by tribotesting and wear quantification. Results revealed that at a hydrogen concentration between 1.4-2 wppm, the wear quantity doubled, while the wear mechanisms remained the same. A novel in situ hydrogen charging full thrust bearing test rig, the Hydrogen Embrittlement in Rolling Element Bearings (HERo) rig, has been developed. This test rig offers several advantages compared to test setups previously described in the literature. As a result of in situ charging, the diffusible hydrogen concentration during tribotesting is not decreasing as in conventional setups where pre-charging is performed prior to tribotesting. This allows for a more precise measurement of the influence of hydrogen on bearing steel. Furthermore, the charging in the HERo rig is performed via the backside of the bearing washer, meaning that the electrolyte is never in contact with the wear track, preventing corrosion or alteration of the surface roughness. The experiments performed with the HERo test rig show a significant decrease in bearing runtime under the influence of hydrogen by a factor of 3. While tests without hydrogen charging failed due to lubricant degradation and surface-initiated wear, hydrogen charged tests failed due to sub-surface initiated macropitting with the presence of white etching cracks. When varying hydrogen pre-charging and in situ charging procedures, it was found that longer pre-charging led to earlier bearing fatigue, while the damage mechanism stayed identical for the different hydrogen concentrations. This indicates that a critical hydrogen concentration exists not only for surface-initiated wear as mentioned above, but also for the initiation of sub-surface crack networks and macropitting. Lastly, it was found that hydrogen promoted not only the formation of white etching cracks and white etching areas, but also martensitic decay and formation of dark etching areas. 

In summary, results of the project confirm the detrimental effect of hydrogen on bearing steel, and add quantitative data to the state of knowledge, making it possible to industrially use the research data for more reliable bearings in hydrogen environments.