HDPE Fittings

1.  Injection Moulded Fittings: Injection molded PE fittings are manufactured in sizes through 12-inch nominal diameter. Typical molded fittings are tees, 45° and 90° elbows, reducers, couplings, caps, flange adapters and stub ends, branch and service saddles, and self-tapping saddle tees. Very large parts may exceed common injection molding equipment capacities, so these are usually fabricated. Equipment to mold fittings consists of a mold and an injection molding press. The mold is a split metal block that is machined to form a part shaped cavity in the block. Hollows in the part are created by core pins shaped into the part cavity. The molded part is created by filling the cavity in the mold block through a filling port, called a gate. The material volume needed to fill the mold cavity is called a shot. The injection molding press has two parts; a press to open and close the mold block, and an injection extruder to inject material into the mold block cavity. The injection extruder is similar to a conventional extruder except that, in addition to rotating, the extruder screw also moves lengthwise in the barrel. Injection molding is a cyclical process. The mold block is closed and the extruder barrel is moved into contact with the mold gate. The screw is rotated and then drawn back, filling the barrel ahead of the screw with material. Screw rotation is stopped and the screw is rammed forward, injecting molten material into the mold cavity under high pressure.

2. Fabricated Fittings: Fully pressure-rated, full bore fabricated fittings are available from select fittings fabricators. Fabricated fittings are constructed by joining sections of pipe, machined blocks, or molded fittings together to produce the desired configuration. Components are joined by heat fusion, hot gas welding, or extrusion welding techniques. It is not recommended to use either hot gas or extrusion welding for pressure service fittings since the joint strength regions that are subject to high localized stress. The common commercial practice is to increase wall thickness in high-stress areas by fabricating fittings from heavier wall pipe sections. The increased wall thickness may be added to the OD, which provides for a full-flow ID; or it may be added to the ID, which slightly restricts ID flow. This is similar to molded fittings that are molded with a larger OD, heavier body wall thickness. If heavy-wall pipe sections are not used, the conventional practice is to reduce the pressure rating of the fitting. The lowest-pressure-rated component in a pipeline determines the operating pressure of the piping system.

3. Thermoformed Fittings: Thermoformed fittings are manufactured by heating a section of pipe and then using a forming tool to reshape the heated area. Examples are sweep elbows, swaged reducers, and forged stub ends. The area to be shaped is immersed in a hot liquid bath and heated to make it pliable. It is removed from the heating bath and reshaped in the forming tool. Then the new shape must be held until the part has cooled.

4. Electrofusion Couplings Electrofusion couplings and fittings are manufactured by either molding in a similar manner as that previously described for butt and socket fusion fittings or manufactured from pipe stock. A wide variety of couplings and other associated fittings are available from ½” CTS thru 28” IPS. Fittings are also available for ductile iron sized PE pipe. These couplings are rated as high as FM 200. Electrofusion fittings are manufactured with a coil-like integral heating element. These fittings are installed utilizing a fusion processor, which provides the proper energy to provide a fusion joint stronger than the joined pipe sections. All electrofusion fittings are manufactured to meet the requirements of ASTM F-1055.

5. Injection Molded Couplings Some mechanical couplings are manufactured by injection molding in a similar manner as previously described for butt and socket fusion fittings. The external coupling body is typically injection molded and upon final assembly will include internal components such as steel stiffeners, O-rings, gripping collets, and other components depending upon the design. A wide variety of coupling configurations are available including tees, ells, caps, reducers, and repair couplings. Sizes for joining PE pipe and tubing are typically from ½” CTS through 2” IPS. All injection molded couplings are manufactured to
meet the requirements of ASTM D2513.