HVAC Spiral pipe is up to 20% stronger than smooth pipe systems of the same gauge, due to the added 4-ply spiral lockseam reinforcement. Our spiral pipe requires no painting; it will last years outdoors. Spiral pipe is formed from a coil of prime metal into rigid steel tubing with a 4-ply spiral lock seam. Smooth interior pipe for low friction loss with the grooved seam entirely on the outside. Crushing resistance is approximately 2 ½ times that of longitudinal lock seam or welded pipe.