I just found a pipe wrench with a base damage of 209, after modding, it has the same as a fat man. It isn't legendary, just a normal pipe wrench. Is it a glitch?

Have you tried killing anything with it to see if the dmg rating is true?

That pipe wrench is infused with the soul of a Jedi!

Yeah, I went on a massacre around town and everyone, including Strong the super mutant, was one hit kill. I can try to post an image later.

This is a glitch with melee weapons. They randomly gain massive amounts of damage to their base. I've seen it happen to other people a few times.

Should probably do the right thing and exploit it while you can..

I don't think it's random. Roasted bear meat is known to boost melee damage by waaay more than just 10. The OP could have consumed some.

Will it wear off any time soon?

It's obviously the same pipe wrench used by Jack from Bioshock.