Chlorinated polyvinyl chloride, or CPVC, pipes are often used in homes without much thought. But the piping can become problematic and may lead to expensive repair bills.

While CPVC is approved for drain, vent, and fire sprinkler systems, it has issues in hydronic applications, too. The problems involve incompatible chemicals and stress.

1. Corrosion

Corrosion in metal pipes can occur due to harsh chemicals, water pressure or even the natural elements in the environment. CPVC pipe systems are not susceptible to any of these issues.

Unlike copper, which can have a plastic taste, CPVC pipe is nontoxic for drinking (potable) water applications. It’s also code compliant and safe for light-hazard occupancies like restaurants and low-rise office buildings.

CPVC is made from chlorinated polyvinyl chloride, which is a strong thermoplastic that has superior chemical resistance to most acids, bases and salts, as well as aliphatic hydrocarbons. It also has high heat distortion temperatures, superior stress tolerance and outstanding dielectric and flame/smoke properties.

2. Cracking

CPVC is an amorphous polymer that gets its strength from a tangle of molecular chains. These chains can weaken if the molecules untangle or break apart from environmental stress cracking (ESC). This type of failure usually starts at one point in the pipe and moves along the surface.

ESC often results from a combination of factors, like improper installation. For example, if the pipes are torqued too much during installation or a connection is not tight enough, the pipe will be stressed. This stress may also make the pipe more susceptible to the effects of an incompatible chemical.

Another common cause of ESC is using a caulk that is incompatible with CPVC piping systems. For instance, some general-purpose caulks contain plasticizers that can soften CPVC. It’s best to use a caulk that is specifically made for CPVC systems, such as 100% silicone or the polyurethane “foam-in-a-can” products. Fortunately, CPVC manufacturers publish lists of chemicals that can and cannot be used with their products.

3. Leaks

CPVC is an excellent option for fire sprinkler systems because of its corrosion resistance and relatively low failure rate. Unfortunately, leaks are common with these pipe systems and often go undetected until significant damage has occurred. Most CPVC leaks are caused by contamination and improper installation.

Typically, contaminants infiltrate the system when chemicals that are incompatible with CPVC are used. Several of these chemicals are powerful solvents that destroy the plastic by disrupting or disentangling molecular chains. These contaminants are commonly found in drains, cleaning solutions and even the paint used on fire sprinkler systems.

It’s important for tradesmen to use caution when working with CPVC, particularly around these types of corrosive chemicals. It’s also important to leave plenty of room for expansion and contraction in long runs of CPVC. Always remember that CPVC expands and contracts more than copper tubing. Avoid butting CPVC against framing members, especially for runs that are 10 ft. or longer.

4. Oils

In some cases, chemicals used during installation or servicing can cause CPVC problems. These substances may react with the plastic and interfere with its strength by breaking or disentangling molecular chains. CPVC manufacturers are aware of these problems and publish lists of incompatible chemicals, as well as guidelines for handling, storing, and installing the product properly.

Cooking oils, for example, are incompatible with CPVC. This means that sprinkler systems located in kitchen areas are susceptible to a risk of premature failure caused by environmental stress cracking.

This type of chemical interaction can occur in any part of a pipe system, but is most common where a hanger has been incorrectly installed or over tightened. This can place undue mechanical stress on the piping, and in some cases, this stress will trigger an ESC response. The result is a brittle piping system that fails over time, leading to leaks and system failures. Fortunately, this problem can be avoided by making sure all ancillary products are compatible with CPVC, and ensuring that pipes are adequately supported.

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