The cross-linked polyethylene tubing(PEX) that provides an excellent option for plumbing, radiant and hydronic systems in both residential and commercial plumbing applications is widely used in America, Europe as well as Australia. Each area has its standard in PEX installation which is searchable on www.astm.org. Hope you can help yourself choosing the best PEX type for your upcoming domestic or industrial projects after reading this essay.
Manufacture Process of PEX Tubing
The PEX-A & PEX-B & PEX-C are all processed by Crosslinking, which is a chemical reaction that occurs between polyethylene polymer chains.
Crosslinking causes the HDPE to become stronger and resistant to cold temperature cracking or brittleness on impact while retaining its flexibility.
The three methods of crosslinking HDPE are:
- PEX-A : Peroxide (Engels) method. During the manufacturing process, free radicals are created when HDPE polymer is melted and cross-links between molecules occur at temperatures that exceed the decomposition temperature of the polymer
- PEX-B : Silane (Moisture Cure) Method. After the extrusion process, cross-linking where links between the molecules of the HDPE using a catalyst and exposing PEX tubing to hot water. This type of PEX is the most
- PEX-C : Radiation (Electronic Irradiation) method. Cross-linking of the molecules is done after the process of extrusion by exposing the pipe to an electron radiation beam. The radiation emitted allows to break the existing links between molecules of the polymer and initiate cross-linking process.
Pros&Cons of PEX-A, PEX-B, PEX-C Tubing
- The most flexible and highest quality tubing on the market, which makes it the most expensive of all those 3 types.
- The kinks in the pipe could be repaired by merely heating the pipe with a heat gun for it is more elastic than PEX-B.
- The wall thickness of PEX-A systems is normally greater than PEX B because it has a lower burst strength and hence requires the greater thickness to cope with the same operating pressures.
As a result of the thicker wall of PEX-A pipe, it will generally have a lower SDR and hence a lower flow rate.
- The pipe is expanded around the fitting rather than the fitting being fit inside the pipe. This may make fittings harder to install if you’re working in cold conditions.
Tips: This PEX is slightly more flexible than the other types at temperature above 60oF. However, below this temperature, PEX-B tends to be more flexible and offer an advantage during installation in colder climates.
Several industry participants claim that the PEX-a method yield more flexible tubing than the other methods
- The cheapest one of those 3 types.
- The expansion fitting s couldn’t work with PEX-B.
- The flow rate is superior in comparison to PEX-A, as it is often rated for higher pressure than PEX-A.
- The most commonly use PEX in North America, including compression, pushfit and copper crimp rings. It is more affordable because is is more rigid.
- The higher crystallinity molecular structure results in PEX B product having a higher surface hardness, better scratch resistance, higher thermo stability, higher rigidity, harder body, better resistance to chlorine solutions and a higher burst strength.
- Though all PEX types are vulnerable to high chlorine counts, it performs better in chlorine testing than other types.
- The pipe can degrade if exposed to high levels of the chemical.
- The kinks in the PEX-B must be cut and repaired with a fitting.
- Similar price to PEX-B, similar quality to PEX-A, but not enough to be used with full-flow fittings.
- The pipe is more flexible than PEX-B, although it may feel slightly more “plastic-like” than other PEX types.
- The more environmentally-friendly manufacturing process it may in fact become a more popular choice in the future.
- The cross-linking process for this type creates the least amount of bonds, which makes it closer to a regular PolyEthylene plastic pipe as opposed to true PEX tubing PEX A and B.
Comparison of Main Attributes
|Flexibility||Better flexibility than PEX-B||Stiffer to work and bend than the other 2||Varies|
(Most vulnerable to be kinked than PEX-A or PEX-C)
(More vulnerable to be Kinked)
|Kink Reparability||Excellent||Not Possible||Decreases after heating to transparency|
|Strength||Meets ASTM||Meets ASTM||Meets ASTM|
|Homogeneity||Not very good||Good||Good|
|Barrier property||Meets DIN 4726||Meets DIN 4726||Meets DIN 4726|
|Thermostability||Better than ASTM requirements||Better than ASTM requirements||Better than ASTM requirements|
|Memory effect of being coiled||Fair – Better than PEX-B||Poor||Fair – Better than PEX-B|
|Minimum bending radius||Good – Better than PEX-B||Poor – The worst of all PEX types||Varies|
|Density||0.938 – higher||0.941 – highest||0.941 – highest|