HDPE pipe

HDPE Pipe is used in many applications, and is the prime choice for replacing ageing concrete or steel mains pipelines. HDPE (High Density Poly-Ethylene) material is a polyethylene thermoplastic made from petroleum, and has excellent properties for pipelines. HDPE Pipe is widely used across the globe for Water Mains, Gas Mains, Sewer Mains, Slurry Transfer Lines, Rural Irrigation, Fire System Supply Lines, Electrical & Communications Conduit, Stormwater and Drainage Pipes, and other applications.

Coils of HDPE Pipe

Benefits of HDPE Pipe

The toughness and resistance to chemicals of Polyethylene, as well as the corrosion resistance and low weight have contributed to its growing use in situations where cost-effective and durable fluid and gas piping systems are required. “Polyethylene has been successfully used for water pipe in Europe and North America since the late 1950’s due to its leak-free joints, durability, resistance to galvanic corrosion, and long-term cost effectiveness" . HDPE pipe can be joined by Butt Welding, Electrofusion Welding, Socket Welding or Extrusion Welding. These joints heat the pipe during the joining process, creating a completely homogenous joint so the weld becomes as strong, or stronger than the existing pipe on either side of the weld. There is no need to use rubber seals or jointing chemicals, as is used for joining PVC pipe, which cause environmental health issues and increase the chance of failure over time. PE is less likely to have root intrusion problems, and provides integrity for the pipeline, even when installed in unstable soils.

Due to the fusion welded system, anchor or thrust restraint blocks are eliminated, as the joints become fully end load resistant, reducing costs for material and installation time. This also allows for safer excavation close to the pipeline in future, which is particularly important for high pressure gas pipelines. Coils of conduit make trench-less installation much easier. HDPE Pipe Systems are available for many applications, providing for common trenching of water, gas and fire ring main pipelines, as well as horizontal drilling for electrical and telecommunications conduits . HDPE Systems are cost effective to install and have long term maintenance cost savings, and also allow for cheaper installation methods, such as Horizontal Directional Drilling, Slip-lining, Pipe Bursting, Floating or Submerged Pipe.

HDPE pipe is very durable and flexible, and can be bent in the field to a radius 25x the nominal pipe diameter - for SDR11 and SDR17 pipe, at or below 20°C ambient temperature. For example, Acu-Tech's PE100 125mm Pipe can be cold formed to a 3.2 metre radius. This provides major cost savings, when compared to different pipe systems, some of which require glued fittings, restraints or thrust blocks for even minor changes in direction. Because of HDPE's excellent impact resistance and flexibility, it is well suited to installation in dynamic soils including in earthquake prone areas. HDPE pipe has very high flow capacity, because of its smooth bore and end-to-end jointing methods. HDPE pipe doesn't corrode in the environment, and will maintain its flow capability over time, unlike ferrous piping systems, which will rust and build up internal resistance to fluid flowing through it .

Because food grade polyethylene virgin material is used to fabricate HDPE pipes, they are safe for the transfer of potable water, as long as any initial debris has been flushed out. Unlike PVC pipe, no dangerous glues or chemicals are involved during jointing. and HDPE is resistant to many chemicals, facilitating its use in process plants or around acidic and corrosive environments, without needing to pay for protective coatings or galvanising, as is required on steel pipes. As HDPE has an very low thermal conductivity, it can maintain more uniform temperatures compared to metal pipes, when carrying fluids. The low thermal conductivity of the pipe wall will greatly reduce any need for insulation to control condensation around the pipeline .

How HDPE Pipe is made

HDPE Pipe - Yellow Jacket Gas Pipe, White Jacket Communications Conduit, and Orange Jacket Electrical Conduit.

To make Pipe lengths, HDPE material is heated and extruded through a die, which determines the diameter of the pipeline. The wall thickness of the pipe is determined by a combination of the size of the die, speed of the screw and the speed of the haul-off tractor. Polyethylene pipe is usually black, due to the carbon content added to the clear polyethylene material, in order to prevent UV damage. Other colours are available, but are less common. Coloured or striped HDPE Pipe is usually 90-95% black material, with just a coloured skin or stripe on the outside 5%.

The following shows the process for HDPE Pipe Extrusion:

Polyethylene raw material is pulled from a silo, into the hopper dryer, which removes any moisture from the pellets. Then it is pulled by a vacuum pump into the blender, where it is heated by a barrel heater. The PE material becomes molten at around 180 degrees celsius, allowing it to be fed through a mould/die, which shapes the molten material into a circular shape. After coming through the die, the newly formed pipe quickly enters the 3-4 cooling tanks, which submerge or spray water at the pipe exterior, each one reducing the temperature of the pipe by 10-20 degrees. Because Polyethylene has a high specific heat capacity, the pipe must be cooled in stages, to avoid deforming the shape, and by the time it reaches the 'haul-off tractor', it is hard enough to be gently pulled by the 2-3 belts. A digital or powder printer printer, the size, type, date and manufacturers name is printed on the side of the pipe. It is then cut by a saw cutter, either into lengths of 3, 6, 12, or 24 meters, or it is coiled to 50m, 100m, 200m lengths on a coiler.

HDPE Pipe with Blue stripes

A different die is used for striped HDPE Pipe, which has small channels that the coloured material runs through, just before it is pushed through the die. This means the stripes are formed as an integral part of the pipe, and are not likely to separate from the main pipe body. Co-extruded, or Co-ex HDPE pipe, has a second extrusion screw which adds an extra skin of colour around the black HDPE Pipe, this allows the pipe to be coloured on the outside, for identification or thermal cooling requirements. A list of pipe colours and typical uses is available at this website: [1]

HDPE Pipe in use

A great example of the durability of HDPE Pipe is the 600m long HDPE boom used for the ocean cleanup project. The HDPE Pipeline is being released into the ocean to clean up the Great Pacific Garbage Patch. See Ocean Cleanup's website for more information: https://www.theoceancleanup.com/

HDPE Pipe has been used in rural and mining environments in Australia for over 50 years, proving to be a very durable and effective means of fluid and gas transfer .

Although HDPE Pipe is often estimated to last 50 years, it is in fact more likely to have a life expectancy of 100 years. PIPA (Plastics Industry Pipe Association) has a technical white paper called 'Life Expectancy for Plastics Pipes'. which states "Based on the use of 50 year stress regression data, it has been incorrectly assumed that plastics pipe systems have a life expectancy of 50 years. In reality, such systems can reasonably be expected to last 100 years or more. PE and PVC pipes and fittings were introduced into Australia during the 1950’s, mainly for water supply and irrigation, but also for fuel gas and industrial applications. ... The time chosen was 50 years, already adopted in Europe, and is still in use today in AS/NZS, ISO, and CEN Standards. The use of this particular time interval has led to the misunderstanding that it represents the pipe life. ... For correctly manufactured and installed systems, the actual life cannot be predicted, but can logically be expected to be well in excess of 100 years before major rehabilitation is required."