What is High-Density Polyethylene Pipe Used For?

 

HDPE pipe

Type of flexible plastic pipe

HDPE pipe is a type of flexible plastic pipe used for fluid and gas transfer and is often used to replace ageing concrete or steel mains pipelines. Made from the thermoplastic HDPE (high-density polyethylene), its high level of impermeability and strong molecular bond make it suitable for high pressure pipelines. HDPE pipe is used across the globe for applications such as water mains, gas mains,[1][self-published source?] sewer mains, slurry transfer lines, rural irrigation, fire system supply lines, electrical and communications conduit, and stormwater and drainage pipes.

 

Benefits

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. According to a press release from the Plastics Pipe Institute, "PE piping has been used for water and other fluids in Europe and America since the 1950s due to its durability, leak free joints, resistance to corrosion, and long-term cost-effectiveness."[2][self-published source?]

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 homogeneous 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 problems with root intrusion, and provides integrity for the pipeline, even when installed in unstable soils.

HDPE communications conduit pipe being installed by directional drilling in Perth, Western Australia

Due to the fusion welding system, the need for anchors 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 PE Pipe make trench-less installation safer and less intrusive on the surrounding environment.

HDPE pipe systems are available for many applications, providing for standard trenching of water mains, fire ring mains, sewer mains, and gas mains pipelines, as well as horizontal drilling for electrical and telecommunications conduits.[3] According to a company that manufactures HDPE, HDPE systems are cost-effective to install and have long-term maintenance cost savings, and also allow for cheaper installation methods, such as HDD (horizontal directional drilling), sliplining, pipe bursting, floating and submerged pipe.[4]

HDPE pipe is very durable and flexible and can be bent on site to a radius twenty-five times the nominal pipe diameter - for SDR11 and SDR17 pipe, at or below 20°C ambient temperature. 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 the high impact resistance and flexibility of HDPE pipe, 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 does not corrode in the environment, and will maintain its flow capabilities over time, unlike ferrous piping systems, which will rust and build up internal resistance to fluid flowing through it.[5][self-published source?]

Because food-grade polyethylene virgin material is used to fabricate HDPE pipes, they are safe for the transfer of drinking water, provided that any initial debris has been flushed out. HDPE pipe is resistant to many chemicals, facilitating its use in process plants or around corrosive or acidic environments, without needing to use protective coatings or galvanising, as is required on steel pipes. As HDPE has a very low thermal conductivity, it can maintain more uniform temperatures compared to metal pipes when carrying fluids, which will greatly reduce any need for insulation to control condensation around the pipeline.[6][self-published source?]

 

Manufacture

To make pipe lengths, HDPE resin 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 in color due to the addition of 3-5% of carbon black being added to the clear polyethylene material. The addition of carbon black creates a product which is UV light resistant. 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:

Freshly Extruded 800 mm (31.50 in) HDPE Pipe

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 °C (356 °F), 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 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 laser or powder printer prints the size, type, date and manufacturers name on the side of the pipe. It is then cut by a saw cutter, either into lengths of 3 or 6 or 12 or 24 meters (9.8 or 19.7 or 39.4 or 78.7 ft), or it is coiled to 50 or 100 or 200 m (164 or 328 or 656 ft) 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.

 

Uses

An example of the durability of HDPE pipe is the 600 m (1,969 ft) 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.[7]

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.[8][self-published source?]

 

Life expectancy

HDPE yellow jacket gas pipe, white jacket communications conduit, and orange jacket electrical conduit

Although HDPE pipe is often estimated to last 50 years, they are in fact more likely to have life expectancies of 100 years. PIPA (Plastics Industry Pipe Association) and the Plastic Pipe Institute (PPI) have written technical white papers on HDPE design life. The PIPA paper is called "Life Expectancy for Plastics Pipes" which mentions that because of the fifty-year stress regression data, people[who?] falsely assume that plastic pipe systems' life expectancy is only fifty years. In fact, these pipe systems can be reasonably expected to last up to or more than 100 years.[5][self-published source?] In Australia, PE pipes and PE fittings were introduced during the mid-1900s, mainly for irrigation or water supply, but also for gas, fuel, and other industrial applications. The use of this 50-year time interval, leads to a misunderstanding that it represents a 50-year pipe life. For pipe systems that have been correctly manufactured and installed, the actual life cannot be predicted, but can be expected to be over 100 years until major rehabilitation is needed.[5][self-published source?]

 

References

High-Density Polyethylene (HDPE) pipe is a flexible piping solution used for various projects. HDPE is made from thermoplastic, which is made with polymer resin. HDPE piping is mainly used for conveying fluid as well gas at low temperatures. This includes hazardous wastes, slurry, and also stormwater. This is why HDPE has a distinguished and long service history in the oil, mining, gas, and water industries, among others.

What is High-Density Polyethylene Pipe Used For?

Although it has been around for ages, recently many developments and construction companies are choosing the HDPE option over the long-standing, standard PVC piping option. High-density polyethylene pipe has specific features that makes it easily identifiable and also useful. These key features of HDPE pipes are what make them beneficial, from being easier to carry around on-site to the fewer fittings that are required in the assembly and installation processes, which makes them less labor-intensive.

Types of HDPE Pipes

The three types of HDPE pipes to choose from include:

Single-wall polyethylene pipes – Single-wall pipes of different diameters can be used at pressures between two and forty bars.

Double-wall polyethylene pipes – Double-wall polyethylene piping is also known as corrugated polyethylene piping. They have two walls with the outer layer being corrugated and the inner layer which is smoother allowing for the easier flow of fluids through the piping. The corrugation of the outer layer makes the pipe a lot more resistant to pressure and impact while still allowing for the flexibility of the pipe.

Spiral polyethylene pipes – Spiral polyethylene pipes are very similar to double-wall pipes, the main difference coming in the production of the pipes. The spiral piping has a corrugated outer layer but can withstand slightly higher pressures. Spiral corrugated pipes are generally connected with extrusion attachments.

Uses of HDPE Pipes

This innovative piping is used in infrastructure construction. HDPE pipes are used as or in:

High-pressure pipelines

Water mains

Gas mains

Sewer mains

Slurry transfer lines

Rural irrigation

Fire system supply lines

Electrical conduit

Communications conducting

Stormwater pipes

Drainage pipes

Advantages and Disadvantages of HDPE Pipes

The use of HDPE High-Density Polyethylene piping systems is becoming more of a first choice for people in the industrial sector and construction industry. People are including the use of HDPE pipes because it has incredible benefits.

HDPE pipes are of high quality, which makes them an extremely reliable piping option. Fittings for HDPE are readily available and easily attached to the piping making it easier for the setup of the system. HDPE pipes are also flexible, so they allow for easy installation of the piping systems for contractors, making installation simpler and thereby quicker.

Being lightweight, DDPE pipes are also easier to load, transport, offload and move around for various projects as well as installations on site. Polyethylene pipes are also made to have a bending radius which allows for the piping to have good resistance to pressure and impact at low temperatures. One of the most important benefits of HDPE pipes is that they are very resistant to different chemicals especially acidic ones, but of course only at lower temperatures.

Advantages of HDPE Pipes

In addition to being impact and chemical resistant, as well as durable in low-temperatures, other advantages include:

Cheaper than other piping solutions

Preserving the safety and quality of potable (drinking) water

Long-term reliability

Resistant to corrosion, tuberculation, and deposits

Freeze damage resistant in colder climates

Low value, making them pointless to steal from construction sites

Durable and hardy which increases their cost-effectiveness

Flameless joining of sections and fittings

Made from eco-friendly, recyclable material

Heat fusible ensuring a virtually leak-free performance

Erosion resistant so good for transporting liquids containing non-soluble elements

Lightweight, especially compared to concrete as well as steel pipes. Therefore, lowering labor requirements.

Able to withstand compressive stress as well as tension stress.

Resistant to fluids and gases at lower temperatures

Flexibility makes elbows and also bends redundant

Disadvantages of HDPE Pipes

Though there are not many disadvantages of HDPE pipes, they are certainly important to be familiar with. The disadvantages include:

High thermal expansion

Low weather resistance

Vulnerable to stress cracking

Tricky to bond

Flammable

Poor high-temperature conduction

Low strength/stiffness

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Why Use HDPE

Some of the distinctive advantages of specifying HDPE for your next project include:

Handling – HDPE pipe is much easier to handle and install compared to other pipe materials, allowing for significant cost advantages and ROI. Because high-density polyethylene is about one-eighth the density of steel, it does not require the use of heavy lifting equipment during installation. HDPE’s flexibility allows for bending without the need for additional fittings and can be installed over uneven terrain easily in continuous lengths.

Reduced installation costs – HDPE is especially well suited for trenchless applications due to its seamless capabilities and flexible characteristics which allow for a bending radius of 20 to 25 times outside diameter of pipe. HDPE is commonly used in directional boring, plowing, river crossings, pipe bursting and sliplining. High-density polyethylene pipe systems require fewer fittings and can be welded into seamless leak-free pipe runs, allowing for significant savings in labor and equipment.

Heat-fused joints – HDPE pipe can be heat fused together to form a joint that is as strong as or stronger than the pipe itself while being virtually leak free. Butt fusion and electrofusion are the most common and reliable welding techniques used to weld high-density polyethylene and offer significant installation advantages compared to traditional pipe materials.

Corrosion and Chemical Resistance – HDPE pipe will not rust, corrode, tuberculate or support biological scale or growth, and has superb chemical resistance compared to traditional pipe materials. HDPE performs exceptionally well in mining, dredging and similar applications, outwearing many more costly piping materials, and offers excellent corrosion resistance to corrosive acids, bases and salts. HDPE is also unaffected by bacteria and fungi, offering resistance to many organic substances.

Superior Flow Characteristics – Because high-density polyethylene pipe is smoother than steel, cast iron, ductile iron, or concrete, a smaller diameter HDPE pipe can produce an equivalent volumetric flow rate at the same pressure.

It has less drag and a lower tendency for turbulence at high flow rates. HDPE’s superior chemical resistance and non-stick surface characteristics nearly eliminate scaling and pitting, preserving the excellent hydraulic characteristics throughout the pipe system’s service life.

Fast Learning Curve for Installers – Learning how to use HDPE in the design and installation of piping systems is easier than you think. Through the HDPE, Inc. training services, contractors and installers can train their team to use this highly advantageous material in new and existing applications.

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