Additional documentation for bimr
's and my posts above, plus for UV sterilizers, which could be considered accelerated sunlight UV testers. From Harrington Plastics Engineering Handbook for Industrial Plastic Piping Systems
, page 71. Lots of useful info. Free download from http://www.harringtonplastics.com/
“SUNLIGHT WEATHERING AND PAINTING
Plastic pipe and fittings have varying resistance to weathering. PVC, CPVC, and Polypropylene undergo surface oxidation and embrittlement by exposure to sunlight over a period of several years. The surface oxidation is evident by a change in pipe color from gray to white. Oxidized piping does not lose any of its pressure capability. It does, however, become much more susceptible to impact damage.
PVDF is unaffected by sunlight but is translucent when unpigmented.
PVC and CPVC pipe and fittings can be easily protected from ultraviolet oxidation by painting with a heavily pigmented, exterior water base latex paint. The color of the paint is of no particular importance, as the pigment acts as an ultraviolet screen and prevents sunlight damage. White or some other light color is recommended as it helps reduce pipe temperature. The latex paint must be thickly applied as an opaque coating on the pipe and fittings that have been cleaned well and very lightly sanded.
Polypropylene and PVDF pipe and fittings are very difficult to paint properly and should be protected by insulation.”
“ULTRA-VIOLET LIGHT STERILIZATION
UV sterilizers for killing bacteria in deionized water are becoming common. The intense light generated will stress crack PVC, CPVC, polypropylene, and PVDF piping over time that is directly connected to the sterilizer. PVDF goes through a cross-linking of H-F causing a discoloration of the fitting and pipe material, and joint stress cracking.”