Crosslinked polyethylene (PEX) is a high-temperature, flexible, polymer pipe. Crosslinking technology was first developed in Europe in the late 1960s and has since come into use around the world for a variety of applications. PEX has a 50-year history of successful use around the world with extensive testing for durability and material performance.
In North America, PEX is primarily produced in "nominal tube sizes" (NTS), with outside diameters matching copper tubing of the same nominal diameters (i.e., copper tube size, or CTS). PEX tubing has a standard dimension ratio (SDR) of 9 and is available in nominal diameters ranging from 1/4 to 4. PEX is also available in so-called pipe diameters in both nominal pipe size (NPS, also known as IPS) and metric sizes (DN). SDR 9 PEX tubing has standard hydrostatic pressure ratings of 160 psi at 73°F (1105 kPa at 23°C) and 100 psi at 180°F (690 kPa at 82°C). For PEX pipe, the pressure rating depends on the wall thickness and dimension ratio. Consult the specific PEX manufacturer's literature and listings for appropriate pressure ratings. Most diameters of PEX tubing and pipe are sold in both coils and straight lengths, with larger diameters primarily available in straight lengths.
Thanks to its smooth inner wall and flexibility, which allows installers to avoid the use of most elbow fittings, PEX tubing in hot- and cold-water distribution systems can generally be installed in place of copper tubing on size-for size basis.
Definition
PEX is a polyethylene material which has undergone a change in molecular structure using a chemical or a physical process whereby the polymer chains are chemically linked. Crosslinking of the polymer chains of polyethylene (HDPE) into PEX for pipes results in improved properties such as elevated temperature strength and performance, flexibility, chemical resistance, environmental stress crack resistance (ESCR), resistance to slow crack growth (SCG), toughness, and abrasion. Crosslinking makes PEX a "semi-thermoset" polymer, providing excellent long-term stability.