[zizazziza]

Alright, lets think about hands he might be limping UTG with 30bbs. Now he is probably not limping TT-KK/AK UTG. So we are looking at KQ-, low-middle PP, crap, and obviously AA and possibly KK (but less likely).
Now, as you stated there is 18k in the pot, and you are raising an extra 20k on top. Now looking from his point of view, this looks like a huge steal attempt and he can be shoving with a very large range here thinking that you will fold a lot or it will at worst be a coinflip.

I think that b/c of your huge raise you need to call the shove here. I think that in the future, that if you thought that UTG could have something that big, that you should try raising to 5xBB at most. Small-ball poker is ok.