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•  What effect does exposure to ultraviolet radiation have on PVC pipe?

Prolonged exposure of PVC pipes to direct sunlight may cause a thin film of degradation on the exposed surface of the pipe over time. This microscopic layer, with a thickness of about 0.05 mm, will gradually become visible as discolouration (so called bleaching) and it stops once the surface exposure ceases¹.

Experience has shown that this microscopic layer protects the underlying material from ultra-violet light ensuring that the rest of the pipe wall is unaffected by the sunlight 1 . If you make a gentle scratch on the outer pipe surface you will see that the normal colour is visible just under this very thin layer.

Extensive tests carried out on pipes exposed to sunlight over a period of up to 4 years demonstrate that there is a slight increase in tensile strength and modulus of elasticity and a minor decrease in impact strength. In practical terms the overall pipe properties are virtually unchanged, and pipes affected by this phenomenon may be used for normal installation.

1 BPF Plastics Pipes Group 2002 "PVC Pipe Systems for Water Supply" Version 01/02 (Revised)