PVC (polyvinyl chloride) and HDPE (high-density polyethylene) are both versatile thermoplastics used in a wide variety of applications, most notably in plastic piping systems. Though they share some similar characteristics and applications, there are several key differences between PVC and HDPE when it comes to their properties, manufacturing, performance, and uses.

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Chemical Structure and Properties

The most fundamental difference between PVC and HDPE is their chemical makeup. PVC is made by polymerizing vinyl chloride monomers into long chains. HDPE is made by polymerizing ethylene gas molecules into long chains under pressure.

This variation in chemistry lends different material properties to each plastic:

- PVC has moderate strength, chemical and weathering resistance, and thermoplastic properties. It also has inherently high flame and smoke characteristics.

- HDPE is known for high impact strength, low moisture absorption, chemical resistance, weathering resistance, and relatively low thermal expansion coefficient. It has better stress-cracking resistance than PVC.

Density

As their names indicate, PVC is less dense than HDPE. The density of rigid PVC ranges from 1.3-1.45 g/cm3 while HDPE has a density ranging from 0.93-0.97 g/cm3. The higher density of PVC allows it to be stiff and rigid, which is advantageous for certain piping applications. HDPE's lighter weight has advantages for transportation, installation, and seismic applications.

Thermal Properties

PVC can withstand temperatures up to 140°F continuously, while HDPE can handle temperatures up to 250°F continuously. Above these temperatures, material properties start to deteriorate. HDPE remains flexible and usable in cold temperatures down to -220°F. Its lack of plasticizers prevents it from becoming brittle. PVC becomes glass-like and breakable below -10°F.

Manufacturing

PVC resins and compounds are manufactured by several processes, including suspension, bulk, emulsion, and dispersion. Different manufacturing techniques produce different grades of PVC. HDPE is manufactured by both slurry loop polymerization and gas-phased polymerization of ethylene, using catalysts like Ziegler-Natta or metallocenes.

PVC often requires the use of plasticizers, stabilizers, lubricants, and fillers which allow it to be formulated into different types and grades of material. HDPE does not require the use of plasticizers or stabilizers in either resin or pipe production. This makes the HDPE manufacturing process simpler overall with fewer additives required.

Durability and Lifespan

Both PVC and HDPE pipes can have long lifespans of 50 years or more. High quality pipes of either material can last over 100 years if properly manufactured, installed and maintained.

HDPE is considered to have better long-term durability and chemical resistance properties overall. In particular, its resistance to environmental stress cracking gives it better longevity than PVC. However, PVC can also offer excellent longevity when properly formulated and reinforced for the intended application and environment.

Maintenance needs differ between the materials. PVC may require the use of plasticizers to retain its flexibility over its service life. HDPE is more resistant to aging and chemical attack and has less issues with environmental stress cracking. Good initial installation practices and periodic inspection and maintenance is recommended for either material.

Pipe Applications

Both PVC and HDPE are used extensively in piping systems, though HDPE dominates water and gas distribution piping while PVC dominates sewer collection networks.

PVC piping is widely used in the municipal wastewater industry for sewers, being suitable up to 18” diameter gravity sewers. It is also popular for residential drain, waste and vent (DWV) systems. Specialty grades of PVC can handle chemical transport applications.

HDPE is the preferred piping material for natural gas and drinking water systems, including mains and service lines up to 60” diameter pipes. It is also popular for geothermal piping systems. HDPE is not suitable for waste or vent piping applications.

PVC piping is generally joined using solvent cements while HDPE piping utilizes heat fusion welding to connect pipe sections and fittings. Overall installation and maintenance costs can differ between materials depending on technique.

Sustainability and Recycling

Both PVC and HDPE are recyclable materials, however rates of recycling vastly differ. HDPE has an extensive recycling stream while PVC recycling is limited.

HDPE is one of the most recycled plastic materials. Recycling rates reached 33% in 2020 as infrastructure, technology, and markets continue to develop. Recycled HDPE is in demand for manufacturing new products and piping systems.

While technically recyclable, PVC recycling is economically and logistically challenging. In 2020, less than 1% of PVC was recycled in the United States. The primary strategy has focused on reuse rather than mechanical recycling of PVC. Developing larger scale recycling has been hindered by lack of profitable markets for recycled PVC resin.

Cost Comparison

In general, PVC piping costs are lower than HDPE piping costs. PVC resins are cheaper and easier to manufacture using less complex processes. PVC also uses less energy in the production process relative to production output when compared to HDPE. In large diameter piping suitable for both materials, installed PVC piping historically has cost 10-30% less than HDPE.

However, looking past initial costs, there are cases where HDPE provides longer term value thanks to superior durability and lower maintenance costs over its lifespan. Installed costs also depend heavily on project particulars. In smaller diameter tubing, HDPE can be more affordable while still providing longevity. As sustainable infrastructure goals drive changes in the piping industry, costs profiles may shift between these materials over time.

Conclusion

In summary, while PVC and HDPE share similarities as versatile thermoplastic piping materials, they have distinct differences when it comes to chemical makeup, mechanical properties, manufacturing methods, lifecycle attributes, and product applications. These differences make each material suitable for distinct uses in piping markets as well as sustainability considerations. Understanding their unique strengths and limitations allows infrastructure designers to select the optimal material solution for piping system needs. Ongoing advances in both materials offer choices to improve piping system performance across public works, and industrial and residential projects.

HDPE and PVC pipe have several similarities, but there are important differences that you should understand when choosing a product. At Piedmont Plastics, we want you to have the right plastic for your specific application, and that’s why we want to point out these differences.

Both PVC and HDPE are durable and lightweight options for piping in residential and commercial buildings. They carry a low risk of leaks, can carry gas and liquid, and can be used underground and in the water. Both are corrosion-proof and resistant to bacteria and chemical buildup as well. Yet, despite these similarities, distinct differences can dictate which choice is best for your needs.

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Differences Between PVC & HDPE

PVC and HDPE have some distinct differences. In general, HDPE is a flexible, strong, and impermeable plastic. PVC is also strong but less flexible and more prone to cracking and failure.

Both pipes can handle standard water pressure surges common in pipelines. However, with PVC, the pipe can handle 100 psi above its pressure class. With HDPE, the pipe can withstand twice the pressure class. In addition, PVC can handle 5.5 feet per second of flow rate before changing its water pressure rating, while HDPE can handle 14 feet per second. Overall, HDPE is 2,500 more resistant to cracking and failure due to water hammer and fatigue.

PVC has a higher pressure class for static water, but HDPE has a higher working pressure rating. In addition, when creating pipe systems, HDPE has a greater bend radius, so it works well for applications that require a curved or bent design.

These two materials also vary in how they are joined. For example, HDPE is joined with heat fusion, while PFC must have a spigot or bell joint with cement. This means HDPE has less of a risk of leaks at the joints.

Finally, HDPE is more durable under extreme conditions. Unlike PVC, it is completely UV resistant and can be installed in extreme temperatures ranging from -40 to 140 degrees. It also has a service life of over a century.

Different Applications of PVC & HDPE Pipe

While the most common use of HDPE and PVC pipe is plumbing, these products have additional applications:

Common HDPE Applications

• Water and gas mains

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• Sewage

• Irrigation

• Slurry transfers

• Stormwater and drainage

• Electrical and communications conduits

• Mining applications

• Firewater

• Brine lines

• Process chemicals

• Ocean clean-up

• Outtfall lines

Common PVC Applications

• Water mains

• Chemical transfers

• Stormwater drainage

• Sewage

• Household plumbing

• Irrigation

• Underwater Piping

• Exhust fumes

Chemical Resistance and Compatability

HDPE and PVC differ in their resistance to certain chemicals. They have the same chemical resistance for the following:

Acetic acid, Ammonium Sulfate, Ammonium Hydroxide, Borax, Calcium hypochlorite, Ferrous sulfate, Hydrochloric acid, Hypochlorous acid, Phosphoric acid, Sodium bicarbonate, Sodium carbonate, Sodium chloride, Sulfur, Urine, Water, and Saltwater.

Some chemicals had distinct differences. These include:

• Chlorine at 50+ ppm: PVC is more resistant

• Nitric acid: HDPE is more resistant

• Lubricating oil: HDPE is more resistant

• Sodium HypoChlorite: PVC is more resistant

• Sulfuric Acid: HDPE is more resistant at most concentrations

Which Is More Cost -Effective: HDPE or PVC?

Even though HDPE is more durable and flexible than PVC and lasts longer without degradation, it costs a little more than its competition. However, when considering cost-effectiveness, you must look beyond the purchase price.

With HDPE, you don’t have to use cement to join pieces. Because it is joined with heat, the process requires minimal wait time. As a result, you do not have to wait for the cement to cure, and you can use your new pipes more quickly.

HDPE is also more cost-effective to transport. You do not have to protect it from sunlight as you do with PVC because it is UV resistant. This combination of less cost and time to install and less cost for transportation helps counter the higher purchase cost.

Finally, HDPE will last longer than PVC in most applications. Not having to replace and repair pipes as often adds up to major cost savings. In light of these factors, HDPE is typically the more cost-effective option.

Get Expert Guidance

If you are curious about whether to choose PVC or HDPE, the sales professionals at Piedmont Plastics can help. Our knowledgeable team will help you learn more about the benefits and drawbacks of each material so that you can choose the best one for your application. Reach out today.

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