Of course, the various plastics differ in cost and capabilities. PVC, for example, offers significant economic advantages but can’t handle high-temperature applications. CPVC, on the other hand, provides superior chemical resistance as well as a high heat distortion temperature, due to its molecular structure — large chlorine atoms surround the carbon backbone to protect it like armor plating. So, CPVC has grown in popularity in both corrosive and high-temperature applications.
Hybrids. In recent years manufacturers have been able to increase CPVC’s temperature and pressure-bearing capabilities by wrapping it with fiberglass. Other hybrid systems include various plastic-lined metallic pipe, which combines the advantages of metal and plastic while minimizing many of their disadvantages. This type of piping system eliminates scale buildup concerns while offering the same superior pressure-bearing capabilities as metal. Such pipe is immune to internal corrosion but still subject to external corrosion. A major disadvantage of plastic-lined pipe is cost. In addition, it requires a difficult labor-intensive joining process. And, any break that occurs in the lining can become a source for future pipe failures.
Of course, cost always is an overriding factor in pipe selection. An authoritative study documented that when allowing for direct and indirect costs — material cost, labor, maintenance, productivity, etc. — CPVC was the bottom-line best choice. Its nearest rival, strictly from a total-installed-cost standpoint, was carbon steel. At the extreme high end were PVDF and titanium.
Due to its high heat distortion temperature, chemical inertness and outstanding mechanical, dielectric, flame and smoke properties, CPVC likely can serve a role in nearly any chemical plant today. Indeed, wherever corrosion resistance and mechanical strength are crucial, consider CPVC. Applications extend beyond processing operations — the material often is the most effective choice for cleaning systems involving high temperatures and harsh cleaning agents.
CPVC piping can handle chemicals that cause process leaks, flow restrictions and, ultimately, premature failure in metal systems. That’s because CPVC withstands most mineral acids, bases and salts, as well as aliphatic hydrocarbons.
However, not all CPVC compounds on the market perform similarly. You can gauge how well your specific CPVC piping system will perform from its cell class, which is defined by ASTM D1784 and certified by NSF International. There’re now two cell classifications — 23337 and 24448. A large majority of CPVC pipe falls into the standard 23337 level. Pipe systems that meet the 24448 classification — all are made from second-generation CPVC formulations — exhibit three times the impact strength of standard CPVC, resulting in fewer breaks and fractures, a lower scrap rate and easier cutting. They also provide a higher heat distortion temperature, 230°F compared to 212°F for standard CPVC. This translates into a lower probability of sagging or bending.
Second-generation CPVC systems also uniquely feature fittings manufactured from pressure-rated compounds. These fitting compounds carry the same pressure-rating classes as the pipe compound. The fittings provide improved creep resistance and can better withstand long-term high-temperature hydrostatic pressure.
It’s important to check with the manufacturer of the pipe and fittings being specified to confirm how well they will perform in a specific application.
No single material is ideal for every application. CPVC isn’t recommended for use with most polar organic materials, including various solvents. CPVC test samples exposed while under stress to surfactants, certain oils or grease have shown signs of environmental stress cracking, softening and swelling.