Material PEX Tubing

Cross-Linked Polyethylene (PEX) is a thermoset material made from medium or high density, cross-linkable polyethylene. Important characteristics of PEX include resistance to high-temperature allowing for use with hot water, and its flexibility, which aids in installation. PEX tubing is manufactured by extrusion in sizes from ¼-inch through 6-inch diameter to copper tube size, outside diameter (CTS-OD) controlled dimensions. The wall thickness is based on Standard Dimension Ratio 9 (SDR 9) values. It is available in coils (up to 1000') and straight lengths (up to 20'). PEX finds applications in hot and cold potable water distribution, radiant heating systems, snow melt, water service, and fire suppression systems.

All PEX is cross-linked polyethylene, but there are three different manufacturing methods are used. The resulting PEX is listed as PEX-A, PEX-B, and PEX-C. Of these PEX-B is the most common. All must conform to the same standards, with only negligible differences between them. The main difference is compatibility with connection systems.

PEX-A is the most flexible, followed by PEX-C. Both of these are compatible with ASTM F1807, F1960, F2080 & F2159 connection types. PEX-B is a bit stiffer than PEX-C, and small cracks can appear when using with fittings that require the tube to be expanded. PEX-B works best with insert fittings (ASTM 1807) held in place using a crimp ring round the outside of the pipe.

PEX is available in non-barrier, oxygen barrier, and PEX-AL-PEX. Non barrier PEX is used for potable water applications and is sometimes referred to as PEX plumbing pipe.  Oxygen from the air will permeate non barrier PEX, even if it is embedded in concrete. This oxygen will rust cast iron components in heating systems such as pumps, valves, and cast iron boilers. Because of this, PEX with an oxygen barrier is used for radiant floor and baseboard/radiator heating, as well as ice/snow melting applications, including the supply and return lines to boilers and fan coils. The oxygen barrier consists of Ethylene vinyl alcohol (EVOH), a polymer coating on the exterior of the pipe.

PEX-AL-PEX has a layer of aluminum sandwiched between inner and outer layers of PEX. Of the three types, PEX-AL-PEX is the only one with a “memory” feature. This means that it will retain the shape to which it was bent, while non barrier and Oxygen barrier PEX has “coil memory,” which means it wants to return to the shape it had before it was uncoiled. The aluminum layer also acts as an oxygen barrier, reduces the expansion rate, and allows higher pressure ratings than regular PEX.

UV rays will degrade PEX. As such, PEX must always be transported and installed in closed areas or covered with insulation. While this is true of all PEX, it is especially important with oxygen barrier PEX, as the barrier will be damaged in direct sunlight.

PEX can be used in temperature ranges up to 180°F in plumbing applications and up to 200°F in heating applications. It is tested for use with temperature and pressure relief valves set at 150 psi and 210°F. As a general rule, fitting systems and installation tools used should be those recommended by the manufacturer of the tubing. The exterior of all PEX tubing is required to be marked with applicable standards, including Canadian Standards Association (CSA) and American Society for Testing and Materials (ASTM).  Each manufacturer offers directional and transitional fittings made to applicable standards and approved to be used on PEX tubing. 



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