Metal stabilizers (tin) are added to PVC-U pipes for UV stabilization. This also gives the PVC-U pipes their typical gray color. The stabilizers exhibit a higher reactivity and thus decompose before the carbon compounds in the PVC. UV rays promote this behavior. PVC-U pipes used outdoors should not be exposed to direct sunlight. UV radiation causes the PVC pipe to discolor. Over time (several years), the pipe material becomes brittle, and its pressure resistance may decrease. This phenomenon is rare in our latitudes. For safety reasons, PVC-U pipes used outdoors can be coated with a UV-protective coating.
