How is HDPE pipe made?

HDPE pipe is a type of plastic pipe that&#;s used to transfer fluids and gases or to replace ageing concrete or steel mains pipelines. HDPE pipe (which stands for high-density polyethylene pipe) is flexible, highly impermeable, and suitable for high pressure pipelines. Most commonly, HDPE pipe is used for water mains, gas mains, sewer mains, slurry transfer lines, rural irrigation, fire system supply lines, electrical conduits, communication conduits and drainage pipes.

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HDPE pipe is made of food-grade polyethylene virgin material, which makes it safe for the transfer of drinking water. It is also resistant to many chemicals, which makes it a good choice for use in process plants or around corrosive environments without needing to use protective coatings (such as is required with steel pipes). Since HDPE pipe has a low thermal conductivity, it can maintain more uniform temperatures compared to metal pipes, which reduces the need for insulation to control condensation around the pipeline. Unlike metal piping systems that corrode over time, HDPE pipe does not rot, rust or corrode. With the use of HDPE pipe, water does not need to be treated to help slow the rust and pitting that is inevitable with metal pipes.

To manufacture HDPE pipe, HDPE resin is heated and squeezed through a mold in a process called extrusion. First, raw polyethylene material in the form of pellets is moved from a silo into a hopper dryer in order to remove any moisture. The raw material is then pulled out by a vacuum pump and moved into a device called the blender. Inside the blender, a barrel heater heats the raw material until it becomes molten (at about 356 degrees Fahrenheit), which makes the material soft enough to feed through a mold. The mold, called a die, shapes the molten material into its final cylindrical form.
Once exiting the die, the pipe quickly enters the cooling tank, which spray water onto the pipe&#;s exterior in order to reduce the temperature of the pipe. This is done in 10-degree increments; since polyethylene has a high specific heat capacity, the pipe must be cooled in stages to avoid its shape from deforming.

By the time the pipe is set onto the &#;haul-off tractor,&#; it has cooled and is solid enough to be pulled by the belts. At this stage, a laser printer prints the size, type, date, and manufacturer&#;s name on the side of the pipe, and the pipe is cut by a saw cutter into the appropriate length, or coiled on a coiler.

When working with striped pipe, a different type of mold is used. This mold has small channels into which the colored material is fed before it is pushed through the mold. With this process, the stripes are crafted as part of the pipe and will not separate from the main body or wash away.

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Many sectors have historically relied on concrete, metal, and clay for pipe products. However, because of the pressing need to keep production costs down and maintain quality, performance, and efficiency, HDPE pipes have become the preferred material of choice for nearly any project.

Today, HDPE pipes are a necessity as they are built to address modern-day challenges in contemporary development. As demand for water, gas and many more industries continue to soar, the use of HDPE is on the rise and is expected to keep growing.

Technical innovation and development are continually propelling HDPE as a superior material of choice in various applications.

Are Hdpe Pipes Worth It or Are We Biased to Their Use Due to Their Cost Effectiveness?

It wouldn&#;t be much of an article if the answer was yes. The costs are undoubtedly a significant plus, but what good would HDPE products be if they couldn&#;t stand the test of time?

HDPE pipes are a favourite for their &#;green&#; attributes as they can safely convey potable water, wastewater, hazardous waste, chemicals and even compressed gases. We&#;ll look at the how the pipes are manufactured later in the article, but you can read more about HDPE material in its entirety:

To put it all in perspective let&#;s have a look at everything you need to know about HDPE pipes starting with a brief history.    

1. Historic Development of HDPE Pipe

The first ever polyethylene (PE) pipe was produced in . But, the manufacturing costs were extraordinarily high, and chemists had to find new and innovative ways of reducing costs while achieving better yields. After a staggering 20 years, they finally had a breakthrough.

In the &#;s, the first HDPE pipe was created by chemists working at the Phillips Petroleum Co.

HDPE materials were first used to manufacture baby bottles since it was safe and didn&#;t break like glass bottles used at the time.

Here&#;s a short timeline of HDPE&#;s rise to fame:

In the late &#;s, hard-wall HDPE pipe began taking over the functions of metal pipes in gas and oil gathering systems.

In the &#;s PE started replacing iron pipes in nearly all distribution systems. Soon enough, HDPE took over the functions of clay pipes in agricultural drainage frameworks.

In the &#;s, HDPE pipe made headway with advanced diameter width and was corrugated to become a better replacement for metal and concretes in the construction of stormwater culverts.

Today, HDPE is a thermoplastic resin that has continued to evolve throughout the centuries with constant developments in its performance capabilities. They are currently in the fourth generation stage of development. Its uses have diversified to replace glass in bottling and metal making of bails, gas tanks, and drums.

20 years into the future, HDPE pipes are expected to replace cast iron, concrete, and steel in all piping and conduit systems. Which promises a great future in a variety of sectors, including:  

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• Natural gas distribution

• Potable (drinking) water

• Plumbing

• Industrial chemicals conveyance

• Oil and gas production

• Underfloor heating

• Mining (slurry and leachates)

• Road heating and cooling

A fairly quick rise to fame and it&#;s not slowing down anytime soon. 

2. How Are HDPE Pipes Manufactured

HDPE, like many other thermoplastic materials, does not possess cross-linked molecular chains and therefore can be melted after application of the right amount of heat. Manufacturing an HDPE Pipe relies heavily on the melting point of PE &#; the temperature at which the plastic gets to an entirely amorphous state (between 120 to 180 °C (248 to 356 °F). 

What Form is HDPE Before it&#;s Melted?

HDPE starts out as pellets, also known as thermoplastic resins. At this point, the first stage of quality control should take place. The raw material quality to be used to manufacture the pipes is the first essential (and necessary) step towards compliance with the specified requirements of a quality finished product.

Most companies use three different types of HDPE pellets which are well mixed before adding it to the hopper &#; plain, recycled and pellets with colorants for UV protection. The mix ratio depends on the specific application of the pipes. If the pipes are going to be buried or used as culverts the need for UV protection is limited, but not excluded as the pipes will still be exposed to UV during installation.

&#;Depending on the application of the pipe

the quality testing could be very in-depth,

or at least should be if the manufacturer

is worth their salt.&#;

Which means it would use less coloured pellets for productions. Typically, the process starts by feeding the thermoplastic resins into the extrusion machine using a hopper that feeds the pellets onto a rotating screw using gravity. The rotation of the screw moves the plastic along the heated barrel.

As the plastic runs along the channel depth decreases, forcing the plastic through a smaller area. The combination of compression and screw rotation causes friction and rotation, called sheer heating. This heat, with the heat of the barrel, melts the HDPE (at a temperature of about 230 degrees Celcius.) By the time it reaches the end of the line, the material is melted down and hot enough to go through the die.

The hot and melted HDPE is then forced through a die which then causes the solid particles to align in an extruding cavity. After which it can be molded, shaped, and extruded to be formed into a pipe. The hot liquid HDPE is then injected into the pipe mold while applying vacuum pressure for even distribution. An even flow is essential to maintaining the overall integrity of the final product. Any variations in the flow can produce weak areas.

The molten plastic then flows evenly around the mold to form and results in the diameter of the pipe being produced. A built-in cooling system hardens the plastic just enough to set the shape, enabling the pipe to be extracted from the mold. The pipe then passes through a cold shower to completely harden the plastic.

Random pipe samples are then selected for quality inspection. Depending on the application of the pipe the quality testing could be very in-depth, or at least should be if the manufacturer is worth their salt.

3. HDPE Pipe Quality Control