CPVC vs. PVC

CPVC and PVC pipes both move water and share other characteristics, but only one is used in fire protection

Since its first use in fire protection systems in the 1980s, chlorinated polyvinyl chloride (CPVC) pipes have emerged as a corrosion-resistant, lighter weight, less expensive, longer-lasting alternative to metal pipes in residential and light hazard wet sprinklers. And while steel has traditionally dominated the market, CPVC fire sprinkler pipe’s unique advantages have it rapidly gaining share.

Previously, we’ve weighed the benefits of CPVC against other pipe materials for residential uses, and taken a hard look at the pros and cons of CPVC and another nonmetallic material popular in residential fire sprinklers: cross-linked polyethylene (PEX).

In this blog, we clear up any confusion between CPVC vs PVC (polyvinyl chloride), the thermoplastic material popular in plumbing and drainage solutions but not approved for fire protection systems.

Feel free to check out our selection of CPVC pipe fittings and glue.

PVC 101: the history of nonmetallic pipe

Commonly used to create plumbing pipes and fittings, PVC is a man-made, plastic polymer material comprised of 57 percent chlorine and 43 percent carbon. The chlorine comes from industrial-grade salt and the carbon is derived from oil or gas ethylene.

PVC was accidentally synthesized by a German chemist in the late 19th century, appearing as a white solid inside a flask of vinyl chloride gas that had been left exposed to sunlight. But it wasn’t until 1925 that an industrial scientist at BFGoodrich stumbled upon a way to make PVC useful. While looking for a way to bond metal to rubber, he instead discovered how to make PVC elastic and moldable, paving the way for commercial applications such as electric-wire insulations, fabric coatings, and shock-absorber seals.

After World War II, American sewage, drainage, and water distribution enterprises became intrigued with PVC piping used in Europe, drawn to its ability to resist rust and rot. But it was the scarcity of metal after the Korean War ended that cemented the popularity of thermoplastic pipes in the U.S., causing PVC to stand out as a durable and affordable alternative in the 1950s.

Today, the material’s strength, reliability, relatively low cost, and ease of use have led to the installation of more than two million miles of PVC pipe throughout North America. PVC pipes enjoy an average lifespan of 50 years or longer, with most reasons for failure boiling down to manufacturing defects or improper usages such as poorly glued joints, over-pressurization, or exposure to incompatible chemicals.

Stacks of PVC pipe

The strength, durability, and low cost of PVC piping makes it a top choice for plumbing and drainage needs.

CPVC vs PVC: So, what’s really different?

PVC has a major drawback: its use is limited to colder-water applications because it can only withstand temperatures of 140°F before it risks softening, cracks, or leaks that can cause pipe or joint failures. So, in 1959, BFGoodrich Performance Materials (now Lubrizol Corp.) pioneered the first CPVC pipes, offering a corrosion-resistant alternative to traditional metallic piping systems that could also handle hotter temperatures.

The difference is right there in the name: chlorinated polyvinyl chloride.

In the world of chemical science, a single, small change to a molecular structure can have a huge impact on how a material behaves in real-world situations. PVC and CPVC are made of the same basic elements with one difference: CPVC manufacturers take strong, moldable PVC and alter it with a free radical chlorination reaction, boosting its chlorine content from 57 percent to as high as 74 percent.

The chart below demonstrates a typical CPVC engineering and production process:

Flow chart showing how CPVC is made

Source: Corzan

Essentially, the process involves bombarding PVC material with UV radiation, causing hydrogen molecules to be displaced by chlorine ions. The increased chlorine content protects the polymer’s carbon backbone, enabling CPVC pipes to withstand temperatures as high as 200°F before beginning to soften. Even so, NFPA 13: Standard for the Installation of Sprinkler Systems (A.7.3.2) notes that the upper service temperature of currently listed CPVC sprinkler pipe is 150°F (65.5°C) at 175 psi (12.1 bar).

The bigger chlorine atoms also physically block oxidants and chemicals from attacking the CPVC chain structure, enhancing its inherent resistance to degradation. After the CPVC resin is formed, it can be infused with additives that also boost other protective properties, such as UV resistance.

CPVC vs. PVC molecule

A free radical chlorination reaction significantly increases the amount of chlorine in a CPVC polymer (left), compared to PVC (right). The red spheres represent chlorine, the blue is hydrogen, and the gray shows the carbon backbone. Source: Corzan

CPVC vs PVC: The practical differences

Like PVC, CPVC is a thermoplastic material that can be easily molded into different shapes to create pipes, fittings, valves, and other liquid-handling supplies. CPVC shares PVC’s other compelling characteristics as well: it’s impact-resistant, sturdy, doesn’t corrode like metal, and resists degradation from chemicals classified as acid, alkali, or inorganic material. These pipes also have innate insulation that reduces condensation and helps maintain water temperature.

A slick, impermeable surface keeps bacterial contamination at bay in both pipes, although the extra chlorine in CPVC adds an additional layer of protection. Deposits are also less likely to cling to the smooth surface and clog these pipes, keeping flow characteristics high and increasing energy efficiency.

CPVC mirrors PVC’s longevity as well: the first CPVC piping systems installed in 1959 remain in service 60 years later, although the average lifespan is 50 years. They can be sized differently: PVC pipe uses nominal pipe size, which measures the diameter of the interior hole, and CPVC relies on nominal size or copper tube size, which references the outside diameter of the tube.

CPVC is more expensive, but both materials are cheaper than metal pipes. They are also available in similar lengths and end-shape options. In fact, PVC and CPVC look so similar that manufacturers use different colors to tell them apart. The CPVC pipe and fittings used in fire sprinkler systems is orange.

The unique advantages of CPVC for fire sprinklers

The first CPVC pipes and fittings targeted hot-water residential plumbing applications. But it wasn’t long before manufacturers realized that the greater resistance to heat from added chlorine also made CPVC perfect for the fire protection market.

CPVC material maintains a flash ignition temperature of 900°F (482°C), which is the lowest temperature at which sufficient combustible gas can be ignited by a small external flame. PVC pipe carries a flash ignition temperature of only 750°F (399°C). In comparison, many ordinary combustibles such as wood ignite at 500°F or less.

CPVC material also maintains a Limiting Oxygen Index (LOI) of 60, meaning it needs 60 percent oxygen in its surrounding atmosphere to sustain a flame. Since the Earth’s atmosphere only contains 21 percent oxygen, CPVC must be forced to burn, and stops smoldering as soon as the blaze is removed. Instead, a charring layer forms on the outside of the pipe when it comes in direct contact with fire, creating a thermal barrier that reduces heat conduction into the pipe and enables the inside to remain smooth, so flame-retarding water can continue to flow quickly. CPVC produces low smoke development and no burning drops as well, so it won’t spread a fire.

Watch this video to see how BlazeMaster CPVC pipes performed during UL (formerly Underwriter Laboratories) fire testing:

CPVC’s inherent immunity to corrosion is also a game-changer for the fire protection industry, which struggles with leaks, obstructions, and system failures caused by rust and microbiologically influenced corrosion (MIC) in metal pipes. More than 70 percent of dry sprinkler systems suffer significant corrosion issues within 12.5 years of installation, and 35 percent of wet sprinklers experience major problems after 25 years.

Even so, the first CPVC sprinkler system faced an uphill battle when it hit the market in 1984 under the BlazeMaster brand. Some property owners were wary of using plastic for fire protection, convinced that it would simply melt or burn like many other plastics when confronted with flames.

Extensive testing and approval from the respected safety organization UL slowly extinguished fears that CPVC pipes would fall apart during a large fire. Aggressive marketing campaigns also emphasized the material’s lower cost, easy handling due to its light weight, and faster, safer installation because joints are assembled by hand using a compound that chemically welds them together—without flame or heavy equipment. The faster installation generally leads to labor-cost savings as well.

Charred CPVC pipe

A charring layer forms on the outside of CPVC pipe when it’s directly exposed to flame, creating a thermal barrier that protects the inside of the pipe. Source: BlazeMaster

Not all CPVC is created equal

The National Fire Protection Association (NFPA) allows the use of CPVC pipe in sprinklers for single- and multi-family housing and other light hazard occupancies where fires tend to develop slower with lower heat, including churches, schools, nursing homes, and offices. It can also be used in rooms rated “ordinary hazard” that are smaller than 400 square feet and within an otherwise light-hazard setting, such as kitchens in an institutional facility. CPVC is NFPA-approved for some underground piping and air plenums as well. These latter spaces facilitate air circulation for heating and air conditioning systems in a building.

But read this carefully: manufacturers may use different compounds to produce CPVC pipe and fittings. And many are specially engineered for the fire sprinkler market. Different resins and additives can yield different performance, so it’s important to research the manufacturer’s reputation and testing protocol before deciding which pipe to use. Fire sprinkler contractors now have access to a range of quality, brand-name products designed specifically for sprinkler system installations. These include BlazeMaster®, TFI, FlameGuard™, and FireLock™.

School classrooms are a light hazard occupancy

CPVC pipes are approved for “light hazard” occupancies, such as schools.

CPVC is not listed for use in exposed outdoor settings, as prolonged exposure to sunlight can impact its strength. It is also not recommended for commercial dry systems since it can become brittle at cold temperatures, creating a serious safety hazard if the energy of the pressurized gas is released suddenly due to a pipe rupture. That said, Tyco does carry a UL-listed, CPVC-based dry pipe system for residential occupancies. It serves as a viable option for homeowners who leave their homes without climate control for lengthy stretches of time.

Another caveat: CPVC sprinkler pipes and fittings are listed to UL 1821, the standard for thermoplastic pipe and fittings for fire protection service—but not all CPVC pipes and components are listed for the same exact use in fire sprinkler systems. It’s essential for contractors to confirm via the manufacturer that a product they want to install is not only listed for fire sprinklers but also for the specific application within the system.

While BlazeMaster, TFI, FlameGuard, and FireLock CPVC are all listed for sprinklers, BlazeMaster CPVC has a different manufacturing process that gives it an American Society for Testing and Materials (ASTM) 06 rating vs. the ASTM 05 rating of other brands. This means it has 25% greater estimated long-term strength, or hydrostatic design pressure, and is slightly less likely to burst at higher temperatures. This difference and the fact that it’s been tested and listed in specific ways means Blazemaster has slightly broader applications in unfinished basements in NFPA 13D installations, for example. You can read about that and whether it makes a difference in your installation in our previous blog: “CPVC Pipe and Fittings in Fire Sprinkler Systems: Use and Care.”

CPVC glue

The creation of a strong joint depends upon the cement’s ability to chemically soften the pipe, so it’s imperative to use a product specifically designed for CPVC.

Also note that while PVC and CPVC pipes may look similar, the differences in their chemical makeup prevent their primers, solvent cements, and bonding agents from being used interchangeably. The creation of a strong joint depends on the cement’s ability to chemically soften the plastic. For instance, CPVC solvent cements must meet ASTM F493 specifications, and PVC solvent cements must adhere to ASTM D2564. There are also different requirements based on the pipe’s size and intended application, so it’s imperative to check the product container to ensure you matched it correctly.

CPVC sprinkler slip coupling

CPVC builds on the benefits of PVC for reliable fire protection

Metal's strength, durability, and resistance to extreme heat established it as the material of choice in the fire protection industry, but its susceptibility to corrosion and surging cost pose challenges. Less-costly CPVC pipe shares the many benefits of PVC plus has temperature resistance—offering the fire protection industry a piping option with lower costs, easier installation, significantly less chance of corrosion, and less friction for flowing water than traditional metal pipes.

Ready to start shopping for CPVC pipe components? Browse our selection of CPVC pipe fittings and glue. Questions about QRFS products or need a brand or item not in our online inventory? Just call us at +1 (888) 361-6662 or email support@qrfs.com.

This blog was originally posted at QRFS.com/blog. If this article helped you understand the evolution of CPVC pipes for fire sprinkler systems, check us out at Facebook.com/QuickResponseFireSupply or on Twitter @QuickResponseFS.

Source for the image at the top of this post: International Fire Protection magazine