HDPE Pipelines and their design & construction
HDPE butt welding put simply is the process of joining two pieces of HDPE pipe together to create a fusion weld. It works by first by inserting the two ends of the HDPE pipe into the butt fusion welding machine. A facer or facing machine is used to trim and cut the end of the pipe to create both a flat surface and to remove oxidized polyurethane. Once completed the facer is removed and an electric heating plate is lowered between the two ends of the HDPE in the buttwelding machine. The anti-stick PTFE coated heating plate is used to simultaneously heat up and melt the two pipes forming a small bead at each end. Once the two pipes are suitably hot and melted, the hot plate is removed and the two ends are thrust together using the hydraulic rams and clamps on the buttwelding machine forming a bond. As the pipe cools the two pieces join together in permanent bond.
The time it takes to suitably melt and cool down to create a strong fusion bond will depend on the thickness, diameter and material of pipe. The larger the diameter and thickness of the pipe, the longer it will take to form each joint. Some butt welding machines include automated times that take the properties of the pipe and calculate the time for fusion and cooling. Pipe rollers are used to support the HDPE pipe during butt welding to reduce strain on the hydraulic rams, reduce manual handling and increase speed of works.
When selecting the specification of the HDPE pipe there are a few key points to consider:
- Diameter of pipe
- Standard Dimension Ratio (SDR) is the pressure rating for piping. SDR is the ratio of the outer pipe diameter (D) to wall thickness (s). The lower the SDR value the thicker the pipe. The average internal diameter will stay roughly the same for all SDR ratios, and the outer diameter will increase/decrease accordingly.
- PE80 or PE100 relates to the strength of the pipe in accordance with ISO 12162.
- Length of pipe
The benefits of HDPE over layflat hoses include a reduction in friction loss leading to reduced fuel consumption and pump sizes, higher quality finish, aesthetically pleasing, resistant to sunlight and salt water, and more robust and less prone to damage.
Electrofusion is a little different to fusion butt welding as it uses factory made polyethylene (PE) electrofusion fittings to melt and join pipes together. Inside each electrofusion fitting or coupling there is a resistance wire heating coil mechanism. An electrofusion control unit when temporarily connected to the fitting via two cables passes a controlled electrical voltage to the heating coils, resulting in the coils heating up and melting the fitting and pipe surfaces together. As the pipes heat up they will expand and fill up the gap between the pipe and fitting creating a strong joint. The majority of electrofusion fittings come with a bar code which is scanned into the electrofusion machine by the operator to determine the temperature and time for heating. As with fusion butt welding, it is important to keep the pipes clean, free of any oil, grease and dust, remove oxidized surface with a scraper prior to joining, heating for sufficient time and temperature, and providing sufficient cooling down time to achieve a strong weld.
Key benefits of electrofusion over butt welding is that the equipment is much smaller and can be carried out in confined spaces. WJ have used electrofusion for emergency repairs to damaged or burst pipes, for making intricate joints in tight locations, and for joining vertical HDPE pipes in stairwells.
Why use WJ?
WJ have expanded our expertise through in-house experience of HDPE installation services since its inception. We have worked with many main contractors and are a highly regarded sub-contractor for major construction projects in Middle East.
We offer our HDPE installation services to the regional construction, industrial, water and waste water industries. We carry out HDPE pipeline installation & welding services with Butt Fusion & Electro Fusion techniques. Our operations team consists of skilled, qualified and certified technicians with the know-how of up to date technology and are experienced with precise accuracy and perfection for the works. WJ can supply a wide range of pipes in different class, accessories and fittings.
WJ use Wassertek high performance butt fusion welding machines and we keep a range of sizes readily available in stock.