SW Spiral 23-1/2"x14"x6' Single Wall HVAC Spiral Pipe. Spiral pipe is formed from a coil of metal into a rigid steel tube with a 4-ply spiral lockseam. The SW Spiral 23-1/2"x14"x6' Single Wall HVAC Spiral Pipe features a smooth interior that delivers air seamlessly and a grooved seam for extreme resistance to crushing.