Rapid Response Question: Metal pipe and plumbing materials have historically had issues with corrosion, sediment build-up, pressure resistance, thermal conductivity, and chemical resistance. Cross-linked polyethylene (PEX) piping is one alternative, but the available sizes are too small for major commercial installations.
Cross-linked polyethylene (PEX) has been used since the 1980’s for radiant heating systems, and has become popular for potable water in recent years. PEX or PEX-lined pipe has wide code acceptance across the country, but PEX requires special fittings and is not recyclable. The chemical crosslinking required to produce PEX adds expense, and increases the potential for contaminant migration from plastic to water. For example, when PEX piping is used underground, the piping can come in contact with ground water.
During the California state code approval process, Reid (in 2005) provided testimony that in areas where groundwater has been contaminated by petroleum products, the gasoline additive methyl tertiary butyl ether (MTBE), or pesticides, may permeate through the PEX pipe.
The final environmental impact report suggests that while chemical migration is an issue, contaminant levels rapidly decline over time to safe levels. Opponents argued for more thorough testing of polymer formulations and chemical leachates.
High-Density Polyethylene (HDPE) pipe has been used for decades in non-potable water applications. In particular, HDPE pipes are often preferred for their welded joints.While special equipment is required to form the weld, welding eliminates the need for separate fittings, a common source of leaks and contaminant infiltration. HDPE is very flexible and can endure harsher site handling than more brittle polymers. Flexibility also allows turns in the piping system without the need for additional joints.
For potable water, HDPE was initially limited to cold water service applications, as early formulations were not strong enough for the high temperatures of hot water systems. Suppliers then developed cross-linked polyethylene (PEX) with superior strength and high temperature performance.EX is common in radiant floor heating applications and, increasingly, in domestic hot/cold water systems. But, as noted above in the initial question, the available pipe sizes are too small for larger commercial installations. Both HDPE and PEX are polyethylene (PE), but because of their different properties care should be taken to not confuse these two very different materials.
HDPE can be used for hot water as a liner in multilayer pipe, where the strength is provided by another pipe layer, such as aluminum, but multilayer pipes don’t offer all of the performance advantages of plastic alone.
HDPE is widely approved by both standards organizations and code agencies for potable cold water applications. High-temperature HDPE formulations have been widely used in Europe for some time, but there are only a few materials ANSI/NSF certified for domestic hot water in the United States.
Independent research studies have identified that chemical contaminants do migrate from HDPE pipe materials to water, and can permeate certain plastic pipes when in contact with contaminated soil. However, these studies are inconclusive as to human health impacts of these contaminants.
Those anticipating the use of HDPE, especially in hot water applications, should ask vendors for data and certifications regarding chemical migration, taste and odor, and high-temperature performance.
Those most concerned about chemical contamination may prefer to forgo the use of plastics entirely, but plastic piping offers some significant installation, use, cost and environmental advantages over copper.
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