Q&A format guide
On this page, we’ll cover all of the basic questions that get asked about HDPE pipe. Much of what you might find on the topic is either heavy reading, (getting really scientifically in-depth), or shows simple price lists and size charts. Here, we set out a list of questions and answers that you can scroll through, in order to answer some common queries on the topic.
What does HDPE stand for?
High-density polyethylene. Note that polyethylene can be confused with polythene but these are not the same substances. Polythene is much softer and is used for plastic bags, among other things.
Interestingly, the word polyethene CAN be used interchangeably with polyethylene. (If any chemists are reading this, you might care to clarify why in the comments section).
What is HDPE pipe?
Structure, properties and basic information:
HDPE is a thermoplastic made from petroleum. The term ‘thermoplastic’ means that it can melt and be reformed. This is different from thermosetting plastic that can’t be melted again. This is a benefit for HDPE because it can be welded, but a disadvantage because it can melt under high temperature.
The benefits of this material include the following facts:
- It has a high strength to density ratio, as well as a high strength to weight ratio.
- It’s abrasion and corrosion resistant, flexible and has a high tensile strength.
- It’s resistant to biological buildup up such as bacteria, algae and mould.
- It‘s highly resistant to freezing (and the expansion of any fluids inside).
- The smooth inner surface of the pipe will increase fluid flow, and the smooth outer surface makes installation easier, even retrofitting (sliplining) into damaged or corrupted piping.
- It’s a great insulator and does not get brittle at different temperatures or with age.
- With a high-pressure rating, it’s surge resistant too.
The properties make it most suitable for water piping. It’s used for drinking water, wastewater, and in the oilfield, it’s used for gas pipelines and frac water delivery and disposal, among other things.
It’s also used for dozens of other commercial applications because of its low cost, easily transformed and solvent/chemical resistant properties.
Here are a few examples of common uses:
- Storage containers
- Fuel tanks
- Plastic furniture
- Plastic bottles
Incidentally, HDPE gained in popularity when it was discovered that baby bottles were dissolving bisphenol A into the water. A new generation of drinking bottles were designed and discerning consumers moved away from the traditional PVC options. Polyethylene is a virtually inert plastic, which is beneficial in practical use.
How are the pipes joined?
HDPE pipe can be joined by fusion/welding, or by creating a factory made custom joint with a gasket. A decision would depend on the application involved.
A multi-gasket solution makes sense if you want to disassemble and re-use the piping. Also, if you were laying long distances, it makes it simple to use a snap together solution. A factory welded solution for specific applications might be better if you want a high-pressure application.
How is HDPE pipe welding/fusion done?
The joints are heat-fused with specialist equipment. There’s no traditional welder type person with a visor. (Although every good oil worker will wear the specified personal protection equipment!)
The heat fusion process creates a homogenous, monolithic system where the join is stronger than the main pipe wall. The pipe can be butt or socket welded, or electrofusion or sidewall fusion methods are used.
HDPE pipe suppliers/manufacturers
Because of the fact that the raw material is petroleum, and that the manufacturing process is straightforward, there are plenty of manufacturers in the world. There are around 20 in North America alone.
It makes sense to stick to a trusted distributor or wholesaler, rather than being concerned about manufacturers. These intermediaries will know whats going on inside this particular industry, have quality control processes and have back up options if an issue presents itself. They can keep their finger on the pulse better than you could, and they buy such large amounts, you won’t necessarily get your pipe cheaper by going directly to the manufacturer anyway.
In what external environment is it used?
It’s one of the most flexible piping solutions and is equally suited to above ground, underground, underwater, or floating conditions. It can be used on uneven surfaces and can be bent to a certain extent without the need for coupling or corner joints.
Underground installation is trenchless since it can be sliplined or attached to directional boring equipment. It will survive better, and for longer than most traditional piping, with a few exceptions such as copper pipe, (which isn’t really a direct alternative in most situations).
It can handle high pressure, but not high temperature, softening at around 120 degrees centigrade. Polyethylene has been used for a very long time in the oil and gas industry and has the lowest repair frequency per mile than other pipeline alternatives.
How does HDPE pipe behave in a fire?
We mentioned in the last paragraph that this material softens at 120°C and this can cause the pipe to be mishapen or lose structural integrity. There are many factors that would influence whether we end up with a leak or complete meltdown.
The duration of the fire is important, if it’s a grass fire, the flames would die out as the grass does. The thickness of the pipe makes a difference as the outer wall will be hotter than the inner, which will be cooled to some extent by fluid flow.
HDPE pipe fuses at around 200°C and self-ignites at around 400°C.
HDPE pipe sizes/dimensions
Since there are so many manufacturers, and polyethylene is easy to work with, all imaginable sizes could be created.
HDPE pipe is available in a range of lengths, diameters, and wall thicknesses. There are standard dimensions that are most easily available. Due to the ease of joining the sections, it makes sense for the manufacturers to make the lengths best for trucks and warehouses.
Standard lengths are 10, 13 or 20 feet (or 3, 4 or 6 metres). Diameters range from 3/4” to 63’ (1.9 centimetres to 1.6 meters).
HDPE pipe fittings
You can find:
… Or any type of accessory that you’re likely to require in practical use.
HDPE corrugated pipe
Is more flexible and versatile. The corrugations create a weaker structure that is more likely to get damaged or clogged. It’s used in specific short-term situations such as drainage, or anywhere where the structural integrity is less important. For reasons such as these, corrugated pipe tends to get used more in agriculture as drainage pipe, or for domestic applications.
Perforated HDPE pipe
Is used for irrigation and drainage purposes. Wastewater can be distributed over a large area, rather than all in one place. This has the benefit of not causing artificial rivers or flooded areas. It’s not really used in the oil and gas industry.
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