Profile and pipe extrusion is normally carried out using a single screw extruder which melts and conveys the pellets through an annular die. Under vacuum (pressure sizing is less common), the profile/pipe is then formed by cooling in a water bath with its outside diameter dimension controlled by a calibration sleeve. The profile/pipe is continually taken away from the die head by a haul-off and then cut to size.
Profiles and pipes can vary in diameter with corresponding increases in wall thickness. Processing pellets into pipes and profiles for such a large range of sizes presents different extrusion challenges. However, basic pipe extrusion requirements hold good for most sizes.