Are you Risking Failure of Your C-PVC Piping?

By John Stephenson

Chlorinated polyvinyl chloride, or C-PVC, is commonly used in construction due to its high heat deflection temperature, resistance to corrosive chemicals and relative low cost. C-PVC is available in both nominal pipe sizes, and copper tube sizes. While copper tubing can corrode, is expensive to buy, and is prone to theft due to high scrap value. C-PVC is 100 percent corrosion resistant and inexpensive compared to metallic piping. Due to its chemical makeup, C-PVC outperforms other plastic alternatives in the presence of a fire, which has led to its widespread adoption. (1)

To create C-PVC, a free radical chlorination reaction is created by adding chlorine to PVC in a water slurry or fluidized bed reactor. The chlorination reaction is initiated by ultraviolet light. After the resin is chlorinated, Chlorine (Cl) atoms make up 40% of the bonding sites of the C-PVC molecule. It is these additional large Chlorine (Cl) atoms which provide additional resistance from thermal & chemical attack, protecting the carbon backbone from breaking down.

C-PVC tolerates higher temperatures (200 °F vs. 140 °F) and is significantly more flexible than PVC. C-PVC piping is used for hot water, strong acids, and high pH caustics. In addition to the unique thermal and chemical properties, C-PVC provides greater insulation than metallic pipes, which maintain the temperature of the fluid more efficiently, and results in less condensation.(2)

As many building codes began to address the use of plastic pipe in fire resistive construction, demand for C-PVC’s characteristics became widespread. ASTM E 84 established requirements for Flame-Spread Index (FSI), Smoke Development Index (SDI.) 

The International Building Code (IBC) requires interior walls and ceilings are in compliance with ASTM E-84. The International Mechanical Code (IMC) similarly requires all plenums to comply with the ASTM E-84 25/50 requirement (explained below). There are exceptions to these requirements for single- and two-family dwellings, and combustible materials which are enclosed within approved materials or assemblies, but the majority of new buildings must meet this requirement. C-PVC is the preferred piping used in fire suppression systems in commercial, industrial, and residential buildings.

“CPVC compound when formed into pipe and fittings...exhibited a flame-spread index (FSI) of less than 25 and a smoke developed index (SDI) less than 50, satisfying the requirements for installation in plenums spaces or within ducts in accordance with UMC and IMC Sections 602.2” (3)

For comparison “PVC has low flame spread, but smoke developed ratings may be as high as 900, so PVC will not pass the 25/50 criteria of the ASTM E 84 test and may not be installed in plenum spaces.” (4)

This is an example of how making the assumption that C-PVC and PVC piping can be treated as the same application can be dangerous. When designing your system you must treat C-PVC uniquely to avoid compromising the longevity of the system or causing a catastrophic failure!