Why Do PVC Pipes Crack & Become Brittle?

PVC pipe is a popular construction material for its low cost and durability. PVC pipe can be used for most any drain, water, or ventilation application. Many homeowners believe PVC to be a maintenance-free product, however, which may or may not be accurate depending on its application. PVC can become brittle and crack when placed in a few scenarios for prolonged periods of time.

White PVC pipe, the sort used for plumbing, will break down when exposed to ultraviolet light, as from the sun. This makes the material unsuitable for outdoor applications where it will not be covered, such as flag poles and rooftop applications. Over time, ultraviolet exposure can reduce the flexibility of the material through polymer degradation, leading to splintering, cracking and splitting.

PVC becomes increasingly brittle as the temperature drops. When exposed to freezing temperatures for prolonged periods of time, it can become brittle enough to crack quite easily. PVC is not suitable for applications where it will be subjected to consistent freezing temperatures, and water should never be allowed to freeze inside a PVC pipe, as it can cause splitting and bursting.

All polymers, or plastics, undergo some amount of degradation over time. It is an artefact of their chemical composition. Over time, PVC leeches materials known as plasticisers. Plasticisers are added to the PVC at the time of manufacturing to increase their flexibility. As they migrate away from the PVC pipe, the pipe not only becomes less flexible because of their absence, but is left with imperfections caused by the missing molecules of plasticisers, which can give a split or crack a place to start on the pipe.

PVC pipe can become brittle due to chemical exposure. As a polymer, chemicals can have a profound negative effect on the make-up of PVC, causing loosening of bonds between molecules in the plastic and hastening the rate of plasticiser migration out of the pipe. PVC drains can become brittle if exposed to large amounts of chemicals, such as those found in liquid drain clog remover.