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Why is sunlight exposure bad for PVC pipe?
Sunday, July 15, 2018
The ultraviolet radiation in sunlight causes degradation of the plastic composition of PVC pipe over time and, although it produces discoloration, the main problem is reduction in the impact resistance of the pipe. Instead of flexing under an impact, it is more likely to crack. CPVC pipe also has the same issue.
Although a small amount of titanium dioxide is added to the formulation of many plastic pipes to boost their UV-resistance, JM Eagle, a major plastic pipe manufacturer, is typical of most other companies in their recommendation for protecting PVC installed in an exterior location and exposed to sunlight:
“For permanent above-ground PVC pipe installations, it is recommended that the pipe be protected from sunlight exposure. This can be accomplished by wrapping the pipe with an opaque material or, more commonly, by painting it. If the pipe is to be painted, a water-based latex paint formulated for exterior use is recommended. Oil or solvent-based paints may damage the pipe and/or not adhere well. In order to minimize heat build-up, white or light-colored latex paints are best.”
The drain pipe shown in the photo at the top of this page, that runs from a mobile home to the septic tank, has another defect besides the exposure to sunlight of the PVC. The area above ground has no required protection from damage. While the amount of soil coverage or other protection necessary will vary according to the dictates of the local building department, some sort of shielding from damage is also required. Since the degradation of PVC stops when it is no longer exposed to sunlight, if soil coverage over the exposed pipe is provided, painting the PVC is not necessary.
Also see our blog post Are plastic pipes (PVC, CPVC, and PEX) safe for drinking water?
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