By Amanda Hill
PVC is an exceptionally durable material that has a low rate of failure. In fact, the failure rate of this material is so low that, when failures occur, it is almost always the result of poor installation or usage practices. To ensure that your crew is not contributing to failure of the PVC and CPVC pipes you work with, make sure you are aware of these potential problems.
Improper Installation or Engineering
If the system is not properly planned or installed, the pipe could fail. One common problem is the use of too much cement to bond a pipe to a fitting. The porous PVC will absorb the cement, and an excessive amount breaks down the integrity of the pipe. The cement also allows more water to be absorbed, which can hurt the integrity of the pipe. Insufficient cement use will also be problematic, as it makes the bond too weak. Use enough cement to create a complete bond on the inside of the fitting and the outside of the pipe, but not enough that it pools in large amounts.
If the installation requires you to cut the pipe, make sure that you do not create any residue on the end of the pipe. If you see any burrs or other problems, remove them. Also, smooth the sharp outer edge of the pipe. These faults can make it difficult for the cement to bond with the pipe, leading to pipe failure. Short insertion is another type of installation error. When installing a pipe into a fitting, make sure you push it all the way to the stop. If you don’t, the gap will allow contaminants to accumulate and the pipe system will fail.
Engineering of the system can also be at fault. For example, PVC has a high coefficient of linear thermal expansion and needs room to expand when temperatures fluctuate. Expansion loops or roller hangers can help eliminate this problem. Using a qualified system engineer will also ensure that the system is designed to account for expansion. Similarly, the pipe must be installed so that it does not have excessive bending deflection. This will lead to both pipe and fitting failure, as it places too much stress on the plastic. Pipes need to be installed into fittings in the proper alignment to avoid this problem.
Improper Use of System
PVC is incredibly strong when used properly. However, improper operation of the system will lead to failure. For example, exposing the system to freezing temperatures without proper freeze protection is a recipe for failure. Filling the pipes with glycerin solution can help. Over-pressurization of the system is another problem. Be certain the system uses the proper schedule of PVC for the amount of pressure you will be placing on it.
Sometimes the system will be set up so that conduit bends around the PVC pipe. This places stress on the PVC at the point of contact with the conduit. This can also cause the conduit to fail and should be completely avoided.
Contamination of the System
For external contamination, watch for exposure to elements used in other systems that are not compatible with PVC use. For instance, PVC should never be in contact with aromatic ester plasticizers or flame retardants. These components are commonly found in fire caulk, and even a drop of the caulk that falls onto the PVC can damage the plastic and lead to failure. Similarly, black grommets, which are incompatible with PVC use, should never be used to seal any part of a PVC system. The phthalate ester plasticizers in a black grommet will damage PVC. Solder flux, polyurethane spray foam and antimicrobial linings found in steel pipes can also contaminate PVC.
PVC’s durability means it can handle many corrosive chemicals once the system is installed. Interior contamination typically happens during installation when non-approved materials are used in the PVC system. That being said, some products, like fire protection foam, should not be delivered via PVC systems, as they will cause internal contamination.
To avoid internal contamination, discuss the system with the PVC manufacturer, and only use PVC for transporting fluids it is designed to carry. If you are concerned about the product it will be carrying, ask before installing.
Manufacturing defects in PVC are quite rare, but they can happen. If the extrusion and cooling process is not carefully monitored and performed, defects in the pipe can lead to failure. These defects can occur because of a dirty die, which causes extrusion lines or improper cooling, which cause stresses throughout the pipe. When pipes are frozen with stresses from the manufacturing process, they react like coiled springs seeking a way to relieve that stress. While you can’t avoid this problem entirely, working with a trusted manufacturer can help.
Defects in the Resin
The resin used to create PVC and CPVC pipes must be carefully mixed to avoid defects. If the filler content is wrong, the pipe will not be as strong as it should be. Similarly, if the chlorine content is wrong in a CPVC pipe, it will not be able to withstand normal operating pressures. Additives or pigments that are added in the wrong way can also cause problems. Again, using a quality distributor and manufacturer you trust can help limit these issues.
PVC should not be stored in direct sunlight for extended periods of time. While the material should be strong enough to withstand repeated exposure to the elements, lengthy storage in this way could damage its integrity. Also, if the PVC is damaged in transport, it can lead to pipe failure. Buy your PVC from a supplier you trust, and inspect every pipe thoroughly before putting it into the system to avoid this problem.
Careful installation, using the right distributor and manufacturer, and avoiding contamination issues are the keys to preventing pipe failure in your PVC systems. Pay careful attention to these areas, and your systems should remain strong for years.