First and formost, the weapon must be safe. If a weapon is determined to be unsafe in any way, it will not be allowed in play.
Secondly, there must be at least 2 inches of foam beyond the end of the pipe at the tip, and 1 inch beyond at the hilt, and no pipe at all in the crosspiece.
And lastly, the tape must be applied along the length of the foam, not wrapped around, as wrapping tends to pack the foam and harden it.
Any rules beyond this are simply suggestions to help extend the life of the weapon.