Polyethylene(PE) offers many advantages over steel and ductile iron piping. PE is used widely to transport potable water, waste water, slurries, chemicals and effluents.
PE pipes are specified in terms of nominal outside diameter (OD) rather than by nominal bore (NB).
Features of PE piping
Light weight and Impact resistant
PE piping is easier to handle and install resulting in lower construction costs. It has better impact resistance and is suitable for cold weather installations. As temperature goes to subzero, PE pipes expand to accommodate the volumetric expansion of fluids.
Flexible and fatigue resistant
PE pipes can be bent to a radius of 25 times its diameter allowing directional change without the use of fittings. In addition, the flexibility of PE pipes makes it suitable for dynamic soils, sea beds and areas prone to earthquake. PE pipes can accept repetitive pressure surges that exceed the static pressure rating of the pipe. This property also enables long lengths of small diameter pipes to be transported as coils thus saving on joints.
Leak Proof Joints
PE piping can be joined by thermal fusion to form a joint that is as strong as the pipe itself and is leak free. Thermal fusion eliminates potential leak joints found in concrete and ductile iron piping. Since the fused joints are self-restraining, it eliminates the need for thrust blocks.
Corrosion and chemical resistant
PE piping does not corrode, tuberculate or support biological growth. Resistance to electrolytic and galvanic corrosion makes PE piping suitable for buried applications. It has excellent chemical resistance making it suitable for handling corrosive acids and alkalies.
Flange guards are available for use on various types of valves, expansion joints, hoses, pipe vents, sight glasses, instruments etc.
Type of Heat Fusion joints in PE piping
The principle behind heat fusion is to heat two surfaces to the fusion temperature, and then fuse them together by application of a controlled force. This applied force joins the melted surfaces resulting in a permanent, monolithic fusion joint. There are three types of heat fusion joints : butt, saddle and socket fusion.
Butt Fusion
Butt fusion technique consists of heating the ends of two pipes, a pipe and fitting, or two fittings by holding them against a heated plate, removing the plate when the proper melt is obtained, bringing the ends together and allowing the joint to cool while maintaining the appropriate applied force. Butt fusion jointing must be used only to join components with similar techniques. Fusion jointing should be carried out only by trained personnel.
Saddle Fusion
Saddle fusion technique involves melting the concave surface of the base of a saddle fitting, while simultaneously melting a matching pattern on the surface of the pipe, bringing the two melted surfaces together and allowing the joint to cool while maintaining the appropriate applied force.
Socket Fusion
Socket fusion technique involves simultaneously heating the outside surface of a pipe end and the inside surface of a fitting socket, which is sized to be smaller than the smallest outside diameter of the pipe. After the proper melt has been generated at each face to be mated, the two components are joined by inserting the pipe into the fitting. The fusion is formed at the interface resulting from the interference fit. The melts from the two components flow together and fuse as the joint cools.
Relevant Standards for PE piping
- ASTM D3350 - Standard Specification for Polyethylene Plastics Pipe and Fittings Materials
- ASTM F714 - Standard Specification for Polyethylene (PE) Plastic Pipe (DR-PR) Based on Outside Diameter
- ASTM F2619 - Standard Specification for High Density Polyethylene(PE) line pipe
- ASTM D2513 - Specification for Polyethylene (PE) Gas Pressure Pipe, Tubing, and Fittings
- ASTM D2683 - Specification for Socket-Type Polyethylene Fittings for Outside Diameter-Controlled Polyethylene Pipe and Tubing
- ASTM D2837 - Test Method for Obtaining Hydrostatic Design Basis for Thermoplastic Pipe Materials or Pressure Design Basis for Thermoplastic Pipe Products
- ASTM D3261 - Specification for Butt Heat Fusion Polyethylene (PE) Plastic Fittings for Polyethylene (PE) Plastic Pipe and Tubing
- ASTM D2683 - Specification for Socket-Type Polyethylene Fittings for Outside Diameter-Controlled Polyethylene Pipe and Tubing
- ISO 12176-1 - Plastics pipes and fittings - Equipment for fusion jointing polyethylene systems - Part 1: Butt fusion