Polyvinyl chloride (PVC) is a familiar and versatile thermoplastic especially known as a piping and fitting material used for residential and commercial plumbing applications.
In the same thermoplastic family as PVC is chlorinated polyvinyl chloride (CPVC).
Though similar to PVC in name and available product types, CPVC exhibits superior resistance to heat and pressure, which enables it to be used in more demanding industrial applications. A high-quality CPVC like Corzan® CPVC has a proven record of performance in a very broad range of commercial and industrial applications.
The difference between CPVC and PVC resin is at the molecular level, affecting each material’s heat and pressure resistance. CPVC is a PVC homopolymer that has been subjected to a chlorination reaction. Typically, the chlorine and PVC react through a basic free radical mechanism, which can be initiated by thermal and/or UV energy.
In PVC, a chlorine atom occupies 25% of the bonding sites on the carbon backbone, and the remaining sites are filled by hydrogen.
CPVC differs from PVC in that approximately 40% of the bonding sites on the backbone are filled with chlorine atoms. The chlorine atoms surrounding the carbon backbone of CPVC are large enough to protect its carbon chain from conditions that often weaken other thermoplastics.
The chlorine content of base PVC can be increased from 56.7 mass percent to as high as 74 mass percent, though typically, most commercial CPVC resins contain 63 to 69 mass percent chlorine.
Diagram of CPVC (left) at a molecular level compared to PVC (right). The red spheres represent chlorine elements.
Many important characteristics of CPVC and PVC are consistent between the materials. But in other ways, CPVC piping—especially a high-quality product like Corzan CPVC—will outperform PVC, especially as chemicals increase in harshness, temperatures and pressures rise, or the risk of fire grows.
Thermoplastics are growing in popularity, often as an alternative to traditional metal materials. The PVC market, for instance, which was valued at almost $69 billion in 2022, is expected to reach nearly $96 billion by 2030. Unlike metals, which are susceptible to corrosion, scaling and pitting, PVC and CPVC are inherently inert to most acids, bases and salts, as well as aliphatic hydrocarbons. This can extend their service life often for years or decades longer. Chemical resistance is a clear advantage for both CPVC and PVC.
The difference in chlorine content gives each material a niche advantage. One example is with higher concentrations of sulfuric acid. Assuming the material is expertly manufactured, like Corzan CPVC, CPVC is superior to PVC. Alternatively, a chemical like ammonia is highly reactive with chlorine. The increased chlorine content of CPVC means PVC actually performs better against ammonia and most amines.
Before specifying any CPVC, consult a chemical compatibility chart and contact technical support to ensure it is suitable for your application.
This chart shows the chemical resistance of CPVC for use with different chemical groups. For Corzan® CPVC’s chemical compatibility with more 400 chemicals, see the Corzan CPVC Chemical Resistance Data.
The glass transition temperature (Tg) is the point where the polymer transitions from a hard, glassy material to a soft, rubbery substance, losing its structural integrity. The Tg rises as the chlorine content in CPVC is increased. Corzan CPVC’s superior temperature resistance is exhibited in the ASTM standards for each material: The maximum service temperature for PVC is up to 140°F (60°C), but the CPVC pipe temperature rating is up to 200°F (93.3°C). Always check manufacturer data to confirm each product’s individual operating capabilities for specific applications before use.
Not only can Corzan CPVC be used above the maximum service temperature of PVC, but its increased temperature resistance also enables it to perform better at temperatures within PVC’s working range. For example, even below 140°F (60°C), CPVC is superior to PVC in terms of impact strength and tensile strength. And the fluid temperature within the pipe is not the only consideration: in certain outside installations, the fluid being transported may be within the temperature range of PVC, but because the piping is exposed to sunlight, the radiant heat causes the PVC to exceed its capability, which can result in failure.
CPVC and PVC piping test to the same pressure rating at 73°F (22.8°C), but as the temperature increases, testing shows that Corzan CPVC maintains its pressure rating better than PVC.
For example, let’s calculate the pressure rating for 10-inch Schedule 80 piping at 130°F (54.4°C) for both PVC and Corzan CPVC. Note that each material is pressure-rated to 230 psi at 73°F (22.8°C).
While PVC can still be specified for applications at 130°F (54.4°C), the material can withstand significantly less pressure at elevated temperatures (those above 73°F or 22.8°C) than Corzan CPVC. To ensure the highest standard of performance, Corzan CPVC undergoes extensive in-house and third-party testing, including burst tests and long-term pressure tests.
This chart shows that CPVC upholds a higher pressure rating than PVC as temperature increases. Above 140°F (60°C), PVC is beyond its maximum working temperature.
Industrial CPVC, like Corzan CPVC, is engineered to limit flammability and smoke production per ASTM testing standards. In fact, select Corzan® CPVC compounds have been evaluated and tested in accordance with the FM 4910 test protocol for fire propagation and smoke development. This includes both pipe compound and the compound used to manufacture sheet, allowing Corzan CPVC to be used in semiconductor cleanrooms.
Flash Ignition Temperature is the lowest temperature at which sufficient combustible gas can be ignited by a small external flame. Corzan CPVC, for example, must be at 900°F (482°C) for this to occur, while rigid PVC must be only at 750°F (399°C).
Limiting Oxygen Index (LOI) is the percentage of oxygen needed in the surrounding atmosphere to sustain a flame. Corzan CPVC’s LOI is 60, and PVC’s is 45. For reference, Earth’s atmosphere is 21% oxygen.
Products made of PVC and CPVC compounds begin in either a powder or pellet form, with the additives already blended in. The compound is then shaped or molded into the products used for residential, commercial and industrial use.
Two main molding methods are used for PVC and CPVC:
Pipe, Fittings and Valves: The ease of installation and corrosion resistance make it a valuable replacement for alternative materials. Corzan CPVC is commonly specified as pipe, fittings and valves where heat, pressure and chemical resistance are concerns.
Ducting: With increasing air emission regulations, the need for reliable fume-handling systems, especially in corrosive environments, is growing rapidly. Depending on the demands, primarily temperature, both PVC and CPVC are specified where dependability is needed. Corzan CPVC, for example, has been used for chemical exhaust ducting in lithium-ion battery recycling facilities.
Sheet and Lining: The excellent corrosion resistance and fire performance of CPVC can be applied to various industrial applications and be overwrapped with Fiber Reinforced Plastic (FRP). And, when the sheet or liner will face less temperature and pressure demands, PVC can be specified.
Other product types: Often starting with CPVC or PVC sheet as a base, fabricators can cut and form the material for use in a number of varying applications.
The value of plastic options like PVC and CPVC is in their versatility, relative cost, ease of installation and corrosion resistance. Keeping those advantages in mind, common uses for each differ depending on the demands of the application.
PVC is a low-cost, reliable material that can also be installed without the use of skilled, expensive welders. Globally, more than 70% of PVC resin is manufactured for use in construction.
Water: The relative corrosion resistance and low cost make PVC the popular choice in low-temperature and low-pressure plumbing applications such as:
Housing: PVC sheet can be fabricated to replace other materials, such as wood, as a lightweight, sturdy substitute. The material is often painted or finished to give the appearance of other traditional materials.
CPVC can also be utilized in these applications to achieve higher temperature resistance and better flame and smoke properties.
Electric cable insulation: Plasticizers can make PVC softer and more flexible for use as cable insulation. Additionally, PVC is resistant to fire and inexpensive.
Signage: Because PVC can be economical, relatively durable and easily painted, sheets of this material are commonly used for signage.
Since CPVC builds on the strengths of PVC, it can be used in many of the same applications but can be cost-prohibitive with inexpensive PVC as a viable alternative.
However, when an application requires the chemical resistance under demanding temperature and pressure conditions, CPVC is the reliable option. This is especially true for industrial installations.
Industrial Applications: CPVC is a dependable, long-lasting solution for the harshest industrial environments, and Corzan CPVC is often specified in a number of demanding industries such as:
Residential and Commercial Plumbing: For plumbing applications that require more temperature and pressure reliability, Corzan CPVC provides a safe, efficient and flexible system resistant to scaling, pitting, and bacteria buildup—regardless of the water pH or chlorine levels. Some of the applications in which pipe and fittings made with Corzan CPVC have been installed are:
Residential and Commercial Fire Sprinklers: The flame and smoke resistance of CPVC, along with its simple joining method, make it ideal for different housing applications.
For certain applications, PVC and CPVC are commonly specified to replace metal. Check out our resource article, Metal v. CPVC Piping Systems, to learn more about how CPVC stands up to metal alternatives.