Bending thin walled metal tubing can be a lot of trouble. When bending quickly, without specialized tools and with small bending radii, the tube may collapse and break. It won't, when a steel spring with an internal diameter only slightly larger than the external diameter of the pipe is put on a pipe bent in a hand or in a vice. A fairly stiff spring with a length should be chosen for bending 20-25 cm, but one that will be easy to bend in your hand.
