Corzan® CPVC versus Other Plastics
For their overall greater sustainability and corrosion resistance, many designers and contractors are turning to plastics as an alternative to traditional metals like copper and steel. But these plastics are as diverse from one another as they are from their metallic alternatives – and not all perform equally. The molecular makeup of Corzan® CPVC makes it extremely resilient amidst harsh chemicals, varied temperatures and high pressures.
Polyvinyl chloride (PVC) and chlorinated polyvinyl chloride (CPVC) share many traits in common but have important chemical composition differences. In PVC, a chlorine atom occupies 25% of the bonding sites on the carbon backbone, with the remaining 75% of sites filled by hydrogen. CPVC, by contrast, has approximately 40% of the bonding sites on the backbone 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. This structural difference means PVC is not code-accepted for potable water, unlike Corzan CPVC.
Both CPVC and PVC are inherently chemically resistant to corrosion, scaling and pitting and are inert to most acids, bases and salts, as well as aliphatic hydrocarbons. Ammonia-heavy applications are better suited to PVC, as ammonia is highly reactive with chlorine, but expertly manufactured CPVC like Corzan CPVC otherwise has superior chemical compatibility than PVC.
Because PVC isn’t protected by those additional chlorine atoms, PVC has a maximum service temperature of 140°F (60°C), while the maximum service temperature for CPVC is up to 200°F (93.3°C). And PVC’s derating factor is 0.31 at 130°F (54.4°C), which means that it cannot hold up to high pressures at higher temperatures as well as CPVC, which has a derating factor of 0.57 at the same temperature. This reliable performance at high temperatures and pressures while transporting aggressive chemicals is why Delta Airlines made the switch from PVC to Corzan CPVC.
Cross-linked polyethylene, known as PEX, is a polyethylene made more flexible and durable through its cross-linked molecules. It has the same smooth finish of other thermoplastics, but it is thicker than Corzan CPVC and much thicker than copper, giving it a smaller inside diameter, which results in greater velocity and pressure loss. It is a very common solution in commercial plumbing situations, but it is almost never acceptable for industrial applications.
Like other polyolefins, PEX has only hydrogen atoms surrounding its chain structures, which do not protect the chain structure. Antioxidant additives act as a ‘sacrificial barrier’ against degradation from aggressive chemicals and naturally occurring free radicals produced by exposure to light and heat. Once these additives are stripped away, PEX begins to break down, which can result in leaks or even total failure. By contrast, Corzan CPVC stands up over time even under high temperatures and pressures, as the added chlorine atoms protect the original PVC chain.
At its smallest diameters, PEX is significantly more flexible than CPVC, which can reduce the number of fittings compared to CPVC, but the pressure drops through them are greater. Furthermore, this flexibility advantage tapers off when diameters reach two inches and greater. And PEX fittings are inserts, rather than surrounding the exterior of the pipe, which creates piping system orifices that restrict flow. PEX also sags and fails quickly when exposed to open flame, which can compound losses from fire.
Polypropylene-Based Products (PP, PP-R and PP-RCT)
Polypropylene-based products are another popular thermoplastic alternative to metal. This polyolefin is available in multiple forms including PP, polypropylene random copolymer (PP-R) and polypropylene resistant to the temperature of the crystalline structure at random (PP-RCT).
PP-R in particular is rated for high-pressure and high-temperature applications, making it an option for commercial plumbing and HVAC. But in material cost, performance over the life of the product, joining methods and installation times, Corzan CPVC is the superior product compared to PP-based products.
PP-based products can be 25 to 200% more expensive than Corzan CPVC, which is an extreme initial expense made worse by PP products’ shorter lifespan. PP-R, for example, is more susceptible to leaks than CPVC: When PP-R is exposed to a byproduct of chlorine water disinfection, hypochlorous acid, the piping material becomes thinner and weaker through oxidation stress cracking that erodes material from the pipe walls. Corzan CPVC’s inherent chlorine resistance makes it immune to this vulnerability. And when exposed to flame, PP-R rapidly drips burning plastic, causing additional safety hazards, while Corzan CPVC is self-extinguishing.
Joining PP-R takes at least twice the time and labor as Corzan CPVC. A piece of an overhead installation of Corzan CPVC, joined with solvent cement welding, can be done by a single worker in just 60 seconds. That same portion of a PP-R installation would take up to seven minutes and requires two workers because it requires a heat fusion joint.
PVC, PEX and PP-R are the most commonly used non-metallic materials besides CPVC, but some other plastics are somewhat common.
- Acrylonitrile butadiene styrene (ABS) ABS should not be used in high-temperature applications – unlike Corzan CPVC, which stands up to high heat.
- Polyethylene raised temperature (PE-RT) is such a new material in the U.S. that its qualities are less known than other plastics.
- High-density polyethylene (HDPE) is a more bendable thermoplastic than CPVC, but has a much lower pressure rating at elevated temperatures.
- Polyvinylidene difluoride (PVDF) has a higher operation temperature than CPVC, but it is more expensive and often overengineered for the required application.