Large diameter PE , PP and Rigid PVC pipes are used for sewage and storm-water management. Diameters frequently exceed 1000 mm and may reach 3000 mm. They are usually dual wall pipes, having a smooth inner wall and a corrugated exterior for increased stiffness. Pipe sections are frequently joined by belled couplings at one end, fitting the next. Such pipes are expected to withstand heavy loads as cars, trucks and other vehicles may travel over the soil below which they are buried. They are expected to pass certain compression tests and they are designed to last for at least 100 years without serious reduction of the water carrying capacity and load bearing characteristics. Resistance to environmental stress cracking (ESC) is of great importance and consequently materials must be carefully selected. Single screw extruders are used for PE and PP and counter-rotating twin screw extruders for PVC. The molten polymer must be free of unmelts and of excellent quality as it arrives at the die entry and must have a good melt strength as it exits. Melt strength is necessary because the formation of the corrugations and belled couplings is akin to blow molding. Dies are usually of the “spiderleg” variety, but spiral dies are also used. Behind the spiderlegs, weldlines form which have detrimental effects on the mechanical properties. Careful control of temperatures is required in the die to prevent problems associated with heat transfer imbalance. To reduce the cost, Calcium Carbonate filler is frequently added. As a result, the melt viscosity increases and the temperature rises due to viscous dissipation. The end product has increased stiffness and reduced ductility. In PVC extrusions several external and internal lubricants must be added to facilitate the flow and increase the degree of gelation (fusion). Partially melted PVC exhibits some sort of microcrystalline 3D structure and upon recrystallization may not produce a pipe of the required mechanical properties.