Built to Last: CPVC Resists Oxidative Degradation

Occasionally, piping professionals and contractors question why CPVC does not carry a CI-R or CI-TD chlorine-resistance rating based on ASTM F2023, while PE-X does. PE-X must be tested and certified according to ASTM standards to determine its chlorine resistance cell classification; however, an ASTM F2023 rating is not necessary to prove CPVC’s resistance to oxidative degradation by chlorine. The chlorine resistance of CPVC is proven by its inherently chlorine resistant molecular structure, its successful 50-year service history of handling hot chlorinated water and its successful use in much more demanding chlorine-delivery systems, including heated pool and spa water applications, industrial bleaching applications and the production of chlorine.

ASTM F2023 testing evaluates the efficiency and longevity of the antioxidant additives used to protect PE-X material. The antioxidants in PE-X react with chlorine to prevent it from damaging the PE-X polymer—the antioxidants are “sacrificial” in nature. Thus, over time, the antioxidant additives are used up, and a strong oxidizer like chlorine can reach the PE-X molecule and break its chain structure until the polymer weakens then fails.

CPVC is structured differently. The large chlorine atoms that surround the CPVC chain block the chlorine radicals in chlorinated water from reaching the chain. There is no antioxidant material that will be used up overtime, so there is no need to attempt to predict when the material’s protection will be depleted.

Following the highly publicized failures of polybutylene pipe and polypropylene dip tubes for hot water heaters, resistance to degradation by hot chlorinated drinking water garnered more attention—and took on new importance. In 2000, ASTM F2023 was developed to test PE-X, a material that had amassed barely 10 years of history in U.S. plumbing applications. Like polybutylene and polypropylene, PE-X relies on antioxidant additives for oxidation resistance.

Using ASTM F2023, a PE-X tubing manufacturer can use short-term accelerated laboratory test data to estimate the potential service life of the tubing in hot chlorinated water. Lab-generated service life estimations are a moot point for CPVC since it has already demonstrated a 50-year service life in real-world installations and has been proven not to fail under accelerated chlorine testing.