There are many different jointing/fittings styles for HDPE (high-density polyethylene), or HDCLPE (high-density cross-laminated polyethylene), which for many people is the preferred piping material for water or compressed air. The advantages of heavy-wall HDPE, especially for compressed air applications, include a smooth bore for reduced friction loss, it does not corrode, and it usually won’t stay crushed, like copper or steel, if it’s run into by heavy machinery.

For jointing, there are several good options available, each with their pros and cons. The metric compression fittings system is very user friendly and requires very little training, plus it can be uninstalled for re-use at a later date. With compression fittings though, it is important never to exceed 8 bar working pressure for compressed air or 16 bar for water. Care should also be taken to install compression fittings away from heat or vibration. A stainless steel braided hose assembly between an air compressor and the first compression fitting will ensure the air has time to cool first and take away a large amount of the vibration.

 

Socket-fusion fittings* are made of the same plastic as the pipe, and are an interference fit when cold. When fitting, they are heated with a special iron, at the same time as the pipe, so that the outside of the pipe and the inside of the fitting is turned soft. The iron is then removed and the two softened surfaces are pressed into each other and held or clamped while the two molten surfaces cool and harden together. The result is a very secure joint which is both low-profile and strong. The fittings are single-piece injection-moulded plastic with no moving parts, which makes them an economical fitting (with the possible exception of threaded fittings which have nickel-coated brass or stainless steel inserts). Socket-fusion fittings are roughly 2/3 the price of the same compression fittings.

Connections made with the socket-fusion process are suitable for very high pressures; we have an installation in 25mm that we pressure-tested in excess of 25 bar (compressed air) without any issues; however, the downside is that it is a permanent joint (unlike compression fittings), and requires specialist equipment and a little effort to make the connections. Anything over 63mm is not practical to do with socket-fusion without some mechanical aid, due to the effort required.

 

Finally, electro-fusion fittings are the preferred method for a welded connection on anything over 40mm. Again, a permanent connection involving molten plastic both of the pipe and the fitting which cools and hardens together to provide a strong joint. There is no limit to how big the pipe and fittings get, in fact the bigger the fitting, the more viable electro-fusion gets for high-pressure connections. The process is less labour-intensive than socket-fusion, with possibly a more secure joint.

The electro-fusion welding process has very strict preparation procedures involving scraping the oxide layer off the pipe (or spigot) with a knife or scraping tool, wiping both the pipe and inside of the fitting with an alcohol-based fluid and taking care not to touch the cleaned surfaces before fitting. The electro-fusion welding unit (or ‘control box’) is an expensive piece of equipment that requires regular servicing and maintenance. However the possibilities are endless and for a plumbing company or contractor, the investment would yield benefits to the users.

 

So, depending on the size and pressure requirements, and the condition of the area to be installed in, there is a HDPE jointing solution available for your every need. If you would like a quote or have a general inquiry, let us know and we’ll do our best to get you sorted.

 

*While not available on our website, we do carry large stocks of these fittings in our Adelaide-Hills based store, as well as welding equipment. If you have a requirement for this style fitting, give us a call and we can send you through pricing and information.