There are five assembly methods for HDPE pipes: Butt Fusion / Welding, Electro Fusion, Compression Fitting, Socket Fusion and Mechanical Bolt Type Couplings.
Butt Fusion / Welding
Butt Fusion or Welding is an economical, permanent and flow efficient jointing method done by parallelly heating both ends of the pipes to the desired temperature using a metal plate at an aligned position. The heated ends of the pipes are then pushed into the correct depth with sufficient force and left to cool. The usage of support structures is recommended during the jointing of long pipes.
Electro Fusion is a jointing method which requires a prefabricated fitting (double socket coupler) equipped with heating elements within the bore. Squared and scraped pipe ends are inserted into the coupler and a current is supplied through the two connection terminals. The heating elements melt the pipe and fitting and fuses the jointing surfaces. The assembly is held stationary for the cooling process to occur.The joints should be allowed to cool before handling.
Compression Fitting is commonly used to join PE to PE or other pipes with bolt type and stab type couplings. The couplings consist of a body, threaded compression nut, an 0-ring acting as an elastomer seal ring and a stiffener along with a grip ring. When compressed, the seal and grip rings provide griping to the outside of the pipe, thus creating a pressure-tight seal.
Fusion jointing is when two pipes are slightly melted and joined together to create a homogenous bond,essentially turning two lengths of pipe into a single system. No cement or glue is needed, greatly lowering the risk of any solvents that could affect the bond and the water quality. Fusion jointed pipes are leak proof, reliable and durable.
Mechanical Bolt Type Couplings
There are many styles and varieties of "Bolt Type" couplings available to join HDPE pipe to HDPE pipe or other types of pipes such as PVC, Mild steel and Ductile iron in sizes from 90mm and larger. Components for this style of fitting are shown in picture. As with the mechanical compression fittings, these couplings work on the general principle of compressing an elastomeric gasket around each pipe end to be joined, to form a seal. The gasket, when compressed against the outside of the pipe by tightening the bolts, produces a pressure seal and it expands a little and shortens slightly due to Poisson's effect.