I had 2 iv's for a spinal surgery now i have noticed a vein in my arm is very hard the length of my forearm and is sore. is this something dangerous ?

This is common: This is very common and not dangerous. This is probably a small blood clot in the vein and will go away by itself. You can help it go away quicker by applying warm compressed a few times a day.

No: Sounds like you have superficial thrombophlebitis from your IV . The vein becomes hard and tender . Try heat packs, and Ibuprofen acutely and this will resolve w/ time( usually in 2 weeks).If it doesn't see your pcp.