PVC Hose pipe can suffer surface discoloration when exposed to ultraviolet (UV) radiation from sunlight. UV radiation affects PVC when energy from the sun causes excitation of the molecular bonds in the plastic. The resulting reaction occurs only on the exposed surface of the pipe and down to extremely shallow depths of 0.001 to 0.003 in. The effect does not continue when exposure to sunlight is terminated.

The study found that exposure to UV radiation results in a change in the pipe’s sur- face color and a slight reduction in impact strength. Other properties such as tensile strength (pressure rating) and modulus of elasticity (pipe stiffness) are not adversely affected.

The presence of an opaque shield between the sun and the pipe prevents UV degradation. While UV radiation will not penetrate even thin shields such as paint coatings or wrappings, the burial of PVC pipe provides complete protection against UV attack.

The most common method used to protect above-ground PVC pipe from the sun is the application of latex (water-based) paint. Preparation of the surface to be painted is very important: The pipe should be cleaned first to remove moisture, dirt, and oil; the sur- face should be roughened with fine sandpaper and then wiped with a clean, dry cloth. Petroleum-based paints should not be used, since the presence of petroleum will prevent proper bonding of paint to pipe. At the same time, anti-ultraviolet materials can be added to the production process to prevent and delay the influence of ultraviolet rays on the tube.

PVC pipe products with enhanced sunlight resistance properties—which do not need protection from UV light exposure—are also available for above-ground applications.

PVC pipe can incur surface damage when subjected to long-term exposure to ultraviolet (UV) radiation from sunlight. This effect is called ultraviolet degradation. Unless specifically formulated to provide substantial protection from UV radiation (for example, PVC house siding), or unless a limited-service life is acceptable, PVC pipe is not recommended for applications where it will be continuously exposed to direct sunlight without some form of physical protection (such as paint or wrapping).
Ultraviolet degradation in PVC occurs when energy from the UV radiation causes excitation of the molecular bonds in the plastic. The resulting reaction occurs only on the exposed surface of the PVC pipe and penetrates the material less than 0.001 in. (0.025 mm). Within the affected zone of reaction, the structure of the PVC molecule is permanently altered with the molecules being converted into a complex structure typified by polyene formations. The polyene molecule causes a light yellow coloration on the PVC pipe and slightly increases its tensile strength.

Regarding the organic chemical reactions that characterize ultraviolet deterioration of PVC, the following should be noted:
• UV degradation results in color change, a slight increase in tensile strength, a slight increase in the modulus of tensile elasticity, and a decrease in impact strength in PVC pipe.
• UV degradation does not continue when exposure to UV radiation is terminated.
• UV degradation occurs only in the plastic material directly exposed to UV radiation and to an extremely shallow penetration depth.
• UV degradation of PVC pipe formulated for buried use will not have a significant adverse effect with up to two full years of outdoor weathering and direct exposure to sunlight.
The above is also true in regard to PVCO pipe.