iirc you need about 5+ passes to have visible xray fogging start to show up from normal carry on scanners from film. Each pass obviously does damage, otherwise no amount of passes would ever affect it.
More than that, I think. If I recall the research correctly, 5 passes results in the most miniscule, barely measurable effect on fast film. I think the number for visually noticable fogging was closer to 14 passes.