Plumbing Expert Witness Opines on Faulty Plastic Plumbing Fittings

This case involves a group of homeowners who lived in a community of townhouses and condominiums. The developers of the community hired a subcontractor to install a plumbing system that contained plastic NIBCO CPI PEX plumbing fittings. Some homeowners began to complain about toilet leaks as well as other leaks in the rest of their plumbing system. Over 50 of the homes in the community experienced failure of the fittings. In several cases, there were multiple failures of the fittings in a single unit. The failure of the fittings was believed to be due to fatigue caused by a molding defect in the manufacturing process. The water leaks that occurred in the homes presented a health hazard to the residents.

Question(s) For Expert Witness

1. How could a plastic plumbing fitting in a home cause water leaks and how could this issue have been avoided?

Expert Witness Response

Most plastic pipe fittings are made of polyvinyl chloride, which is a thermoplastic polymer. This type of pipe fitting is popular in the plumbing industry because it is low cost and is easy to install. The problem with this type of fitting system is that does not bear loads in the same way that metal fittings do. Metal fittings either successfully bear a load or they will fail. Plastic fittings can bear a load at the moment of initial application but, over time, they may fail as cracks initiate and slowly grow. When this happens, the fittings can fail and lead to water leaks. Another problem with plastic fittings is that failure can come from accumulated fatigue damage and this can reduce the burst strength of the fitting. When this type of plastic fitting fails, it can be very costly. If a failure occurs, the entire fitting system will probably need to be replaced and the cost is generally thousands of dollars. In general, failures of pipe fittings usually result from design defects. To prevent this type of failure in pipe fittings, it is usually necessary to use a more robust fitting to reduce or eliminate the stress that causes the fitting to fail. Sometimes fatigue failure of a plastic pipe fitting can show up through a crack in the elbow. When this happens, the pipe will leak. This type of fatigue failure of a plastic pipe fitting is caused when cyclic stresses are applied to the elbow from vibrations or stresses created by the thermal expansion of the attached pipes when hot water flows through them and heats them up. In this case, metal fittings should have utilized to avoid this problem.