As of today, the most well-known making a joint of polyethylene pipes have two ways: butt welding of polyethylene pipes and electrofusion welding. 

Description of butt-welding of polyethylene pipes process. 

Butt-welding of polyethylene pipes PND is the heating of ends of welded pipes or parts to viscous-flow condition of polyethylene due to contact with a heater and with following connection the ends under the pressure after the removal of the heater. The welding process can be divided into the following stages: melting of polyethylene pipes and fittings, heating, removal of the heater, welding and cooling. When melting the formation of primary flash takes place. When heating, the heat is distributed inside the material. The pressure at that is close to zero (it only provides the contact between the ends of pipes and heater). When heater removing, the removing of heating element from the welding zone (technological pause) and the connection of welding surfaces takes place. The pause should be as short as possible, to avoid lowering the temperature and falling dirt (dust, sand, etc.) that affect the quality of the welded connection. During welding of low-pressure polyethylene pipes the final flash and molecular bonds, providing congeners is formed. When cooling the setting of joint occurs and joint gets maximum strength. Upon welding of polyethylene pipes this stage allow avoiding stress or shocks that could affect the strength of the welded connection. 

The main stages of welding of polyethylene pipes 

The process of welding of low-pressure polyethylene pipes includes preparatory operations (the same for all types of apparatus), welding and final operation after the cooling of pipes welded: 

1. Preparation of the weld area, placement and preparation of the welding equipment. 
2. Preparation of pipes and fittings for welding. 
3. Compilation and alignment of pipes and fittings. 
4. Mechanical treatment of the welded pipes and fittings ends. 

The welding equipment for polyethylene pipes shall be placed on the pre-cleaned and leveled site after placing of plastic pipes on it. Preparation of welding equipment is to be done on disconnected from the power supply unit before starting welding, and includes: 

1. visual check of the assemblies of welding machine and accessories, 
2. checking of electrical cable insulation and earthing, 
3. fuelling for electric generator and checking the reliability of its work by test switching on, 
4. checking for oil in the hydraulic system, 
5. verify the operation of the mobile clamp 
6. verify proper operation and sharpening of facing machine blades, 
7. verify the operation of instrumentation, 
8. selection of clamps and reduction inserts, corresponding to the diameter of pipes to be welded, 
9. greasing of rubbing surfaces and detachable connections with grease recommended by the manufacturer of the device, 
10. cleaning from dust and residues of polyethylene and degreasing with a clean cotton cloths and solvent (if necessary) of the surface 
11. heater in a cold condition, as well as facing machine and scraper. 
Preparation and setup of welding equipment for polyethylene pipes should be done by specialist strictly according to the manufacturer's recommendations. Data of welding equipment verification can be recorded into the working log. 



Description of welding of polyethylene pipes with embedded heaters process 

Welding using the parts with electric spiral is the melting of polyethylene in the connecting surfaces of parts (couplings, elbows, reducers, etc.) and polyethylene pipes due to heat generated during the flow of electric current in the electric spiral inherent inside the detail of metal wire, and following natural cooling of welded connection. As a result of this welding method the interpenetration of molecular chains between two contacting surfaces takes place, and then in the process of cooling one-piece weld connection is formed.