Forum:Repeatable challenges?

Hy!

I recently completed the challenge involving the use of doctor bags (Dr Mojave MD or something), I got the XP for it, then later I used a doctor bag, and I noticed the challenge is in the PiPboy again (they are not greyed out like my water drining challenge). I noticed this in other challenges (disarm mines). Are these challenges repeatable indefinitely or you repeat them 2-3 times and done?