When welding your spiral on pipe it is required that the spiral be pulled tight on pipe as the spiral inside diameter is normally over sizes by approximately 2mm to 3mm so that pipe slides in easier there are many different ways of doing this but we have found that the easiest way to pull your spiral tight on pipe is to use a chain block or something similar
1. cut 1 hole on either end of the spiral
2. slide your inner pipe into the spiral
3. fasten one end of spiral securely
4. fast other end with chain block
Once this is all set up then using the chain block start tightening so that the spiral is pulled tight onto pipe this will now able you to weld your spiral on pipe.