No set of rules can be made for how often your part have to be maintained. Our sealed bearings protected with alloy covers enable a longer lifespan. We designed these parts in a way that you will not have to worry about maintenance or technical issues. No lubricants or grease are required to put on the bearings. During your rides, dirt may get between the cover and the bearings, you can remove it with water or a degreaser. Fully ceramic sealed bearings so indeed there is no risk of oxidation.
Please note, they are dry bearings so do not use lubricant.