Compare the advantages and disadvantages to using HDPE versus PVC

There are continuous debates as to which pipe is the best to work with for each type of project.

HDPE vs PVC – HDPE advantages and disadvantages

Here, we provide an impartial comparison of the pros and cons of HDPE versus PVC pipe. HDPE pipe has been the material of choice for trenchless installation practices almost since the technology first appeared in the mid-to-late 1960s.

Common Features

Durability

PVC is a fairly durable vinyl polymer, while HDPE is a thermoplastic made from petroleum. They are both considered plastics. When comparing failure ratings, PVC has shown to be higher than HDPE. PVC has a rating of one in 48,650 events compared to HPDE with one in 10 million. These failure events included rain stress, wind, heat or cold. Therefore, one of the advantages of HDPE pipes is that they are known to be more durable in these events. PVC is more useful in one-time projects.

Joining

When joining PVC, a gasket or gluing sealant must be used. It can also be joined underwater while HDPE cannot. HDPE is joined by heat fusion (see our Push/Lock Couplings). However, HDPE is able to withstand and dampen more shock waves than PVC.
 
Another of the advantages of HDPE pipes is that when covering fiber builds, HDPE works best for many reasons:

• HDPE can handle season stress (heat and cold). Low temperature impact.
• HDPE can withstand 20 years or more of the sun’s UV rays, while PVC may not last three years.
• HDPE is more resistant to salt, sand, dust and corrosive materials.

Installation

HDPE can be installed in the following ways: 

• Open trench
• Directional bore
• Horizontal bore
• Drop burial

 
PVC can be installed in the following ways: 

• Open trench
• Drop burial
• HDPE pipe

 

Which one’s better, PVC or HDPE? – HDPE advantages and disadvantages

When looking for a more suitable pipe for lower pressure, HDPE is more efficient. HDPE is softer and more bendable and has a tight bending radius.
However, HDPE is a strong choice for both pressure and non-pressure piping application. HDPE is known for its flexibility, chemical stability and high strength-to-density ratio. HDPE offers a leak-free system via heat fusion joints. While PVC is a stronger and stiffer material, it makes it suitable for direct burial and trenchless installation.
The stiffness of PVC pipe allows its direct connection to mechanical valves, non-plastic fittings and various other water and wastewater connections. One of the biggest issues with mechanically joined traditional pipes (PVC) is the high incidence of background leakage. This is water that leaks out of the pipe through pipe joints. It is estimated that in the United States, about 14% of drinking water is lost each day due to background leakage! This represents more than 12 million gallons of water a year in a city of 100,000. HDPE pipes, and their fittings and connections, offer a distinct advantage in that they can be used to create leak-free joints that can prevent this issue.

Key Difference – PVC vs HDPE

 

PVC and HDPE are two types of polymeric synthetic plastic materials which are used in many industrial applications. The key difference between HDPE and PVC is the difference in density; HDPE is denser than PVC, and this leads to differences in their physical properties and industrial applications. In addition, the difference in chemical structure and manufacturing process also give them some unique material properties.

What is PVC?

PVC is the abbreviation for Polyvinyl Chloride. PVC is the third-most extensively produced synthetic plastic polymer, next to polyethylene and polypropylene. It is a synthetic polymeric material which is available in two forms: rigid and flexible. The pure form of polyvinyl chloride is a white colored brittle solid which is insoluble in alcohol, but fairly soluble in tetrahydrofuran. The composition of PVC is about 57% of chlorine which is derived from industrial grade salt and about 43% of carbon, mostly taken from oil and gas from ethylene. Therefore, PVC is less dependent on crude oil or natural gas than the other polymers. Chlorine gives PVC an excellent fire resistance.

What is HDPE?

HDPE stands for High Density Polyethylene, and it is the high density version of polyethylene plastic. Compared to the other types (LDPE), it is hard, strong and a little heavy, but is less ductile and lighter than water. HDPE can be moulded, machined, and welded together. The weather resistance of HDPE can be improved by using UV-stabilizators (carbon black); however they are black in colour.

HDPE is produced from petroleum, and its physical appearance of HDPE is wax-like, lustreless and opaque. Although HDPE is a denser material, it can be recycled and has the number “2” for its resin identification code.

What is the difference between PVC and HDPE?

Chemical Structure of PVC and HDPE

PVC: PVC is produced by the polymerization of vinyl chloride molecules.

HDPE: The polymerization of ethylene molecules gives polyethylene polymer having the molecular formula of -(C2H4)n–

Properties of PVC and HDPE

PVC comes in two forms (rigid PVC – RPVC and flexible PVC – FPVC), and some of their properties slightly vary.

Density

PVC: RPVC (1.3–1.45 g cm-3) is denser than FPVC (1.1–1.35 g cm-3).

HDPE: HDPE has a large value for strength-to-density ratio, and its density ranges from 0.93 g cm-3 to 0.97 g cm-3.

Thermal Conductivity

PVC: RPVC (0.14–0.28 Wm-1K-1) has a wide range of the thermal conductivity and FPVC (0.14–0.17 Wm-1K-1) has a narrow range.

HDPE: Thermal conductivity of HDPE is around 0.45 – 0.52 Wm-1K-1.

Mechanical Properties

PVC: Hardness and mechanical properties of PVC are relatively high, and mechanical properties increase as the molecular weight increases, and it decreases with the temperature. When comparing RPVC and FPVC, RPVC has good mechanical properties.

HDPE: HDPE is a non-linear viscoelastic material and it has time-dependent properties. It can withstand relatively high temperatures (120 0C) for short time intervals, but it can’t withstand normal autoclaving conditions.

Applications of PVC and HDPE

PVC: As PVC has two forms; rigid PVC and flexible PVC, they are used in distinct applications according to their properties.

RPVC: The rigid PVC is used in manufacturing pipes, bottles, non-food packaging materials, cards (bank cards), doors and windows.

FPVC: The flexible PVC is used in many areas including plumbing, electrical cable insulation, imitation leather production, signage and in inflatable products. Moreover, it is an alternative material for rubber.

HDPE: HDPE is used to produce many plastic products; some examples are chemical drums, jerricans, carboys, toys, picnic ware, plastic bottles, corrosion resistant pipes, geomembranes, plastic lumber, household and kitchenware, cable insulation, carrier bags, a food wrapping material.

Definitions:

Thermoplastic: They are the materials or resins which become plastic upon heating and harden on cooling; these processes can be repeated too.

References: Polyethylene. (n.d.). Retrieved July 04, 2016, from here Polyvinyl chloride. (n.d.). Retrieved July 04, 2016, from here High density polyethylene (n.d.). Retrieved July 04, 2016, from here   Image Courtesy: “Polyethylene repeat unit” By Magmar452 – Own work (CCo) via Commons Wikimedia “Polyvinylchloride-repeat-2D-flat” By Cvf-ps – Self made with ISIS Draw / eigene Arbeit (Public Domain) via Commons Wikimedia “Plastic tubing” By Paul Goyette – (CC BY-SA 2.0) via Commons Wikimedia  “Multi-use water bottle”By Amraepowell – Own work (CC BY-SA 3.0) via Commons Wikimedia 

Choosing the right kind of pipe for any irrigation project is as important as choosing the size and type of pump, the control system and even the source of water. In simple terms, the pipe will need to be not only durable but light weight and flexible.

The longer the pipe you install can stay in place without succumbing to excessive movement, leaks and splits is a vital consideration; with more hard-wearing the pipe, repair bills will be lower and the system more efficient and dependable. In simple terms, anyone designing and installing an irrigation system needs to decide whether they want to use lines made of polyvinyl chloride (PVC) or high-density polyethylene (HDPE). The answer to this question will be dictated, in large part, by the specifics of the irrigation project, such as the source from which the water is being drawn and the size and complexity of the overall requirement. Because of this it’s useful to understand the different characteristics of each material in order to make an informed choice about the piping that's best suited to a particular installation.

Characteristics Shared by HDPE and PVC

Before detailing the features which differentiate HDPE and PVC it’s probably worth pointing out the properties that both materials have in common. In brief, both materials are lightweight and corrosion proof, both are a form of plastic, and both are resistant to the buildup of bacteria and chemicals. In terms of irrigation projects, the main advantage offered by both PVC and HDPE piping is that it has a higher life expectancy than traditional solutions such as iron, copper, and steel.

Durability

Although both types of piping are more durable in the long term than traditional metal pipes, there is some difference between the two. Studies have shown that PVC has a failure rating of one in 48,650 events, compared to the failure rating of HDPE, which is one in 10,000,000. In irrigation settings, failure events of this kind would generally occur because of low or high temperatures, or fluctuations in the water pressure being applied through the piping. The fact that HDPE is much more resistant to the damaging impact of the sun’s UV rays than PVC makes it a much safer choice in a climate such as that found in Florida, where extremely strong sunlight is a feature throughout several months of the year.

The greater ability of HDPE to cope with incidents and issues of this kind make it the better choice for long term irrigation projects, whereas the ease and simplicity with which PVC piping can be installed may make it the better choice for smaller projects which need to be completed at speed.

Installation

There are two ways of looking at the differences between the installation techniques required when using HDPE and PVC piping. Before examining these different viewpoints, it’s probably useful to outline exactly what those techniques are:

• HDPE – to install HDPE piping, a technician needs to have been certified by the HDPE manufacturer and completed a factory certified training course. This is because among other skills, the methods used for installing and assembling lengths of HDPE piping involve the specialist technique of heat fusing.
• PVC – in contrast to HDPE, PVC piping can be installed and assembled quickly and simply using a specific PVC gasket or glue. No special training or certification is required, and the process is much quicker and simpler.

As stated, there are two ways of looking at this contrast. The first is to be glad that PVC piping can be installed much more quickly by any competent technician, and in any weather conditions; factors which will cut the cost of an installation and the time it takes to deliver. The other point of view, however, is that the certification needed to install and attach HDPE piping guarantees, at the very least, a basic level of competence and expertise. In addition to this, any joins in HDPE piping created through heat fusing are always going to be stronger and more durable than the PVC joins created using glue or gaskets.

Flexibility

PVC is the stronger and stiffer of the two materials, but the extra flexibility of HDPE makes it a better choice for projects which require a sharper bending radius in places. The rigidity of PVC makes it easier to join to some other parts of the irrigation system such as valves and pumps, but it is at these connection points where leaks are most likely to occur. The connections and fittings on HDPE piping, thanks to the heat fusing method of attachment, are far more likely to create a leak-free system, since the heat-fused joints are actually even stronger than the piping itself. The relative lack of flexibility inherent in PVC piping means that the body of the pipe is at higher risk of cracking and breaking if it is placed under stress, such as might occur when the level of the water source in which it is located rises and falls. 

Suction Lines

If the piping in question is being used to facilitate a suction line then there are some differences in the operation of that suction line which may impact on the wider efficiency of the irrigation system. An HDPE suction line, for example, is designed to float slightly above the bed of any lake or pond in which it is located. This position is important as it removes much of the risk of foreign materials or debris entering the system and causing damage.

When PVC is used, on the other hand, the intake screen assembly could settle onto the bed of the lake or pond, leading to poor performance across the pump system. The less durable nature of PVC means that small air leaks are also more likely to occur, leading to a system shut down while they are located and repaired.

Taken as a whole, HDPE piping within a system – provided it has been installed and connected by a certified and qualified technician – could have a working life of some 30 to 40 years. With PVC, conversely, the length of time over which the system works efficiently could vary wildly depending upon the diameter of the piping and the competence of the technician responsible for installation. Due to the lack of a formal certification process, sourcing a technician who can offer a guarantee of the skill levels needed to ensure longevity can be difficult, but is a key part of getting the most out of any PVC based system. To be blunt, a PVC system which is poorly installed and connected may never function efficiently in the first place, while HDPE piping, thanks to the methods required to set it up for use, is arguably more likely to have been installed correctly from day one.