Polyethylene pipe connections are abundant, ranging from pipe to pipe, pipe to PE pipe, pipe to accessories, and connections between polyethylene pipes and metal pipes. Each connection method has its own advantages and limitations. Users can choose the appropriate connection method based on the pipe diameter, working pressure, usage location, and other environmental factors. Common connection methods for urban water supply polyethylene pipes include hot melt connections, electric melt connections, socket-and-spigot flexible connections, flange connections, and steel-plastic transition joint connections.
Hot Melt Connection
Hot melt connection involves heating the mating surfaces of polyethylene pipes or fittings using a specialized heating tool under pressure. After melting, the heating tool is removed, and pressure is applied to join the two melted surfaces together. The connection is then held under stable pressure for a period until the joint cools. Hot melt connections include hot melt butt joints, hot melt socket joints, and hot melt saddle joints.
2. Electric fusion joining
Electrofusion joining involves tightly contacting the connection area of a special electrofusion fitting with an embedded resistance wire to PE piping or fittings, then applying electricity to heat the connection area through the embedded wire, melting it into a single unit until the joint cools. Electrofusion joints can be used to connect PE piping or fittings of various types and melt flow rates. Electrofusion joints are categorized into electrofusion socket joints and electrofusion saddle joints.
3. Socket and spigot flexible joint
The push-fit flexible connection for polyethylene (PE) pipes is a new type of connection developed based on the principles of push-fit flexible connections used in cast iron pipes and polyvinyl chloride (PVC-U) pipes. It involves welding a reinforced polyethylene socket to one end of the PE pipe. The push-fit flexible connection method consists of directly inserting one end of the PE pipe into a specialized socket of the pipe or fitting, where it is secured by a locking ring within the socket to prevent pulling out and a rubber seal to ensure tightness, thereby connecting the PE pipe to the fitting.
4. Flange Connection
Flange connections are primarily used for the connection of polyethylene pipelines with metal pipelines or accessories such as valves, flowmeters, and pressure gauges. They are mainly composed of polyethylene flange connectors, steel or aluminum back pressure sleeve flanges, steel or aluminum flange plates, gaskets or seals, bolts, nuts, etc. Flange connections are achieved by securing the bolts and nuts, ensuring a tight contact between the flange connectors and the flange plates, thereby accomplishing the connection purpose.
5. Steel-plastic transition joint connection
Steel-plastic transition joints are used to connect polyethylene pipelines with metallic pipelines by employing pre-fabricated transition joints via cold pressing or other methods. The steel-plastic transition joints are equipped with pull-out-resistant locking rings and sealing rings, which are typically required to have superior sealing properties and tensile and pressure resistance greater than that of the polyethylene pipelines in the system.
That concludes the methods of PE pipe connections. It is imperative to note that it is strictly forbidden to directly cut pipe threads on polyethylene pipes and fittings using any form of threading; threaded connections are prohibited. It is also strictly forbidden to use open flames to heat polyethylene pipes and fittings for direct connection.
Polyethylene's connection technology is highly mature. Statistics show that the leakage rate of polyethylene pipes is less than 0.02%, significantly lower than the 2-3% of ductile iron pipes, greatly enhancing both pipeline safety and economic benefits. This is also a crucial reason why polyethylene pipes are widely used in gas pipelines.
