Figure 2. Solvent cement creates a permanent bond stronger than either the pipe or fitting.
CPVC can safely handle certain organic solvents that are soluble in water, such as alcohols, below a specific concentration. (The acceptable concentration level varies with the type of solvent — consult the CPVC manufacturer for specific recommendations.) However, solvents insoluble in water, such as aromatics, likely will be absorbed by the piping system over time, even when they’re present at very low levels in the water. This may lead to a decreased service life expectancy for the system depending on the operating conditions.
Temperature and pressure also pose restrictions. In general CPVC can safely be used at temperatures up to 200°F in pressure applications and as high as 220°F in non-pressurized applications.
Pipe size and temperature determine the specific pressure rating — the smaller the pipe size, the higher the pressure rating allowed; the higher the temperature, the lower the pressure rating. For example, a ½-inch pipe operating at room temperature can handle up to 900 psi., while a 16-inch pipe operating at the same temperature only can withstand 200 psi. All pressure ratings are based on a 50-year service life with a safety factor of two.
Another limitation relates to hanger spacing. Because CPVC piping systems aren’t as rigid as metal, hangers must be installed closer together, resulting in more hangers. In certain situations, space limitations may preclude the additional hangers required for CPVC installations.
It’s impossible to accurately assess the cost to install a piping system without considering the joining system. That’s because the joining method directly impacts labor costs and productivity.
CPVC offers a number of benefits over metal with regard to joining. Because no welding is involved, no hot work permits or specialized, cumbersome equipment are required. In the majority of situations CPVC pipe is joined with solvent cement. This is a fast, easy and highly reliable process that produces a joint that’s actually stronger than either the pipe or fitting alone. This contrasts with other piping systems, in which the joint typically is the weakest part of the system and the most likely to fail.
Although some people liken solvent cement to glue, it’s very different — the solvent cement actually creates a welded permanent bond. The solvents in the cement soften the surfaces of the pipe and fitting socket. Because the socket is tapered, the softened surfaces bond once they are fit together. CPVC in the solvent cement fills in any gaps that might otherwise exist in the joint. As the solvent cement cures, the solvents flash off.
It’s imperative that only CPVC solvent cement be used. For applications in exceptionally harsh chemical environments, check with the manufacturer regarding the performance of the solvent cement.
Although solvent cementing is the preferred joining method for CPVC piping systems, there are alternatives. If it’s necessary to connect to an existing metal pipe or if the system needs to be disassembled for any reason, the CPVC pipe can be joined via flanges or threading. Full lines of transitions, threaded connections and flanges are available — as are CPVC valves. It’s possible to create an all-CPVC system that facilitates maintenance in the future.
An analysis of piping should go beyond initial price to consider lifecycle costs. The challenge is choosing a system that meets the performance and budget criteria at installation and over the long term. On that basis, CPVC has proven to be a highly viable option for many chemical processors.
CPVC offers a material cost that is highly competitive with most other options, especially compared with high-end metallics. Its fast and easy joining system reduces labor costs. And its corrosion resistance and ability to withstand harsh chemicals, high temperatures, pressure and impact lead to reduced maintenance requirements, less downtime and greater productivity over an extended service life.
Donald Townley, P.E., is market manager for Corzan Industrial Systems, Lubrizol Corp., Cleveland, Ohio. E-mail him at email@example.com.