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HDPE & PVC (DECISION MAKING BETWEEN HDPE AND PVC)

THUrsday - 03/11/2016 21:57
HDPE & PVC (DECISION MAKING BETWEEN HDPE AND PVC)

HDPE & PVC (DECISION MAKING BETWEEN HDPE AND PVC)

Is High-density Polyethylene (HDPE) a Good Choice For Potable Water?

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. Is high-density polyethylene (HDPE) pipe a good environmental choice for potable water applications?

In potable water applications, plastics have created some controversy. Polybutylene plumbing materials, introduced in the 1970s, led to unacceptable leakage problems culminating in a large class-action lawsuit. Polyvinyl chloride (PVC) and chlorinated-PVC (CPVC) pipe are common. However, some environmental groups have suggested that the risks associated with PVC production and pipe disposal outweigh the advantages of these materials. [1]
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 like PVC. Flexibility also allows turns in the piping system without the need for additional joints. [2]
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. Over the past decade or so, new HDPE formulations, for example Dow’s PE-RT (polyethylene of raised temperature resistance), have been available for high temperature use, including domestic hot water.


Do Chemicals Migrate or Leach from HDPE Pipe in Presence of Potable Water?

All plastics contain some residual of the chemicals required for their manufacture. These may include one or more catalysts that assist the polymerization reaction, as well as traces of unreacted raw material. A number of additives are typically compounded along with polymer resin prior to forming the final product. These may include stabilizers, UV-blockers, plasticizers, antioxidants, colorants, etc., to enhance both processing and performance characteristics. These additives may not be disclosed by the company producing the piping, so the risk of chemical migration must be evaluated for any material that comes into contact with potable water, food, or beverages. [3]
By and large, HDPE is reported to be one of the “good” plastics, safe for use with food and water. A common plastics memory aid can be found in various sources: “One, four, five and two, all of these are good for you.” This rhyme refers to the recycle code numbers found on plastic containers, where one is PET, two is high-density polyethylene (HDPE), four is low-density polyethylene (LDPE) and five is polypropylene (PP). PPRC found no evidence of any widespread health problems related to the use of HDPE in food and beverage or potable water applications. [4]


Key Findings

  • HDPE is widely approved by both standards organizations and code agencies for potable coldwater 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.
 

Reference

[1] Thornton, Joe. Environmental Impacts of Polyvinyl Chloride Building Materials. net. [Online] 2002.http://www.healthybuilding.net/pvc/Thornton_Enviro_Impacts_of_PVC.pdf.

[2] Final Environmental Impact Report: Adoption of Statewide Regulations Allowing the Use of PEX Tubing. [Online] January 2009. www.documents.dgs.ca.gov/bsc/pex/…/PEX%20FEIR_01-08-09.pdf.

[3] Science News. Plastic Water Pipes Affect Odor And Taste Of Drinking Water. Science News. [Online] August 28, 2007. http://www.sciencedaily.com/releases/2007/08/070823141100.htm.

[4] Build It Green. HDPE (High Density Polyethylene Pipe). org. [Online]http://www.builditgreen.org/attachments/wysiwyg/22/HDPE-Pipe.pdf.

[5] Harvey, Jamie and Lent, Tom. PVC-Free Pipe Purchasers’ Report. net. [Online]http://www.healthybuilding.net/pvc/pipes_report.pdf
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