The steel pipes used in the manufacturing of pre-insulated pipes are manufactured longitudinally welded (ERW) or spirally welded (SAW) in accordance with the norms required by the standard TS EN 253 or customer demands. Pipes comprise three basic materials. Carrier pipes are established as steel, copper or plastic based according to the properties of the carried fluids. Casing pipes are manufactured from high density polyethylene (HDPE) raw material, with UV resistance, 100% waterproof and with online corona. PUR ( POLYURETHANE INSULATION MATERIAL) that is injected between the carrier pipe and casing pipe provides heat insulation besides enabling two pipes operating as one pipe by bonding them together.