This video shows how to remove a broken bolt using 4 different methods-
1. Knocking the bolt round in an anti-clockwise direction with a chisel or centre punch.
2. Welding on a nut.
3. Drilling a hole and using a easy out/screw extractor.
4. Left handed drill bit.
Removing broken bolts can be challenging but in most cases the job can be done quickly and efficiently. The worst case scenario is that you have to drill the bolt out completely and re-tap the hole or use a thread insert kit.