A cross-linked polyethylene (PEX) pipe

Cross-linked polyethylene, commonly abbreviated PEX, XPE or XLPE, is a form of polyethylene with cross-links. It is used predominantly in building services pipework systems, hydronic radiant heating and cooling systems, domestic water piping, insulation for high tension (high voltage) electrical cables, and baby play mats. It is also used for natural gas and offshore oil applications, chemical transportation, and transportation of sewage and slurries. PEX is an alternative to polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC) or copper tubing for use as residential water pipes.


Low-temperature impact strength, abrasion resistance and environmental stress cracking resistance can be increased significantly by crosslinking, whereas hardness and rigidity are somewhat reduced. Compared to thermoplastic polyethylene, PEX does not melt (analogous to elastomers) and is thermally resistant (over longer periods of up to 120 °C, for short periods without electrical or mechanical load up to 250 °C). With increasing crosslinking density also the maximum shear modulus increases (even at higher temperatures).[1][2] PEX has significantly enhanced properties compared with ordinary PE.

Almost all PEX used for pipe and tubing is made from high-density polyethylene (HDPE). PEX contains cross-linked bonds in the polymer structure, changing the thermoplastic to a thermoset. Cross-linking is accomplished during or after the extrusion of the tubing. The required degree of cross-linking, according to ASTM Standard F876, is between 65% and 89%. A higher degree of cross-linking could result in brittleness and stress cracking of the material, while a lower degree of cross-linking could result in product with poorer physical properties.

PEX has significantly enhanced properties compared to ordinary PE.[3] This is due to the introduction of crosslinks in the system, which can significantly improve the chemical, thermal, and mechanical properties of the polymer.[4] While HDPE and PEX both display increases in the initial tangent modulus and yield stress under temperature or strain-rate increases when undergoing compression, HDPE tends to exhibit flow behavior after reaching a higher yield stress and PEX tends to exhibit strain-hardening after reaching its slightly lower yield stress.[5] The latter exhibits some flow behavior but only after reaching higher true strains. The behavior observed in PEX is also mimicked by the thermoplastic ultra-high molecular weight polyethylene (UHMWPE). However, PEX displays a stronger temperature and strain-rate dependence than UHMWPE. Additionally, PEX is notable for its high thermal stability. It displays improved creep behavior (i.e. resists creep deformation) and maintains high strength and hardness at very high temperatures compared to thermoplastic polyethylene.[6]

The type of initial polymer structure and amount of crosslinking can have a large impact on the resulting mechanical properties of PEX.[7] One study looked at the effect of crosslinking low-density polyethylene (LDPE) with different amounts of dicumyl peroxide (DCP).[8] It was found that increasing the weight percent of the peroxide crosslinker resulted in a lower degree of crystallinity, as observed via differential scanning calorimetry (DSC). The degree to which a polymer crystallizes and crosslinks can have a significant impact on its properties, and it was indeed found that the increase in crosslinking degree and corresponding decrease in crystallinity correlated to a lower elongation at break. It was suggested that this was due to the higher presence of chemical crosslinks (the peroxides) compared to the physical crosslinks (formed by the crystallites), as chemical crosslinks tend to inhibit the elongation behavior of polymers. Additionally, it was found that the maximum tensile strength tended to increase since the intermolecular forces between chains increases with additional crosslinks. Similar results have been found with the addition of silane crosslinkers. In another study, the amount of silane crosslinker added to linear low-density polyethylene (LLDPE) was varied.[9] The resulting Young’s modulus and maximum tensile strength increased with crosslinker concentration but the elongation at break decreased due to decreases in crystallinity. The presence of fillers can further strengthen PEX’s mechanical properties. In the same study, the researchers looked at the effect of adding a filler known as montmorillonite (MMT) nanoclay and observed even higher Young’s moduli and tensile strengths, indicating a strong interfacial interaction between the silane crosslinked LLDPE and the MMT.

Almost all cross-linkable polyethylene compounds (XLPE) for wire and cable applications are based on LDPE. XLPE-insulated cables have a rated maximum conductor temperature of 90 °C and an emergency rating up to 140 °C, depending on the standard used. They have a conductor short-circuit rating of 250 °C. XLPE has excellent dielectric properties, making it useful for medium voltage—1 to 69 kV AC, and high-voltage cables—up to 380 kV AC-voltage, and several hundred kV DC.

Numerous modifications in the basic polymer structure can be made to maximize productivity during the manufacturing process. For medium voltage applications, reactivity can be boosted significantly. This results in higher line speeds in cases where limitations in either the curing or cooling processes within the continuous vulcanization (CV) tubes used to cross-link the insulation.[citation needed] This is particularly useful for high-voltage cable and extra-high voltage cable applications, where degassing requirements can significantly lengthen cable manufacturing time.

Preparation methods

Various methods can be used to prepare PEX from thermoplastic polyethylene (PE-LD, PE-LLD or PE-HD). The first PEX material was prepared in the 1930s, by irradiating the extruded tube with an electron beam. The electron beam processing method was made feasible in the 1970s, but was still expensive. In the 1960s, Engel cross-linking was developed. In this method, a peroxide is mixed with the HDPE before extruding.[10] In 1968, the Sioplas process using silicon hydride (silane) was patented, followed by another silane-based process, Monosil, in 1974. A process using vinylsilane followed in 1986.[citation needed]

Raw material: XLPE powder used in rotational molding in a factory

Types of crosslinking

A basic distinction is made between peroxide crosslinking (PE-Xa), silane crosslinking (PE-Xb), electron beam crosslinking (PE-Xc) and azo crosslinking (PE-Xd).[2]

Shown are the peroxide, the silane and irradiation crosslinking

Shown are the peroxide, the silane and irradiation crosslinking. In each method, a hydrogen atom is removed from the polyethylene chain (top center), either by radiation () or by peroxides (R-O-O-R), forming a radical. Then, two radical chains can crosslink, either directly (bottom left) or indirectly via silane compounds (bottom right).

Degree of crosslinking

A low degree of crosslinking leads initially only to a multiplication of the molecular weight. The individual macromolecules are not linked and no covalent network is formed yet. Polyethylene that consists of those large molecules behaves similar to polyethylene of ultra high molecular weight (PE-UHMW), i.e. like a thermoplastic elastomer.[12]

Upon further crosslinking (crosslinking degree about 80%),[13] the individual macromolecules are eventually connected to a network. This crosslinked polyethylene (PE-X) is chemically seen a thermoset, it shows above the melting point rubber-elastic behavior and cannot be processed in the melt anymore.[12]

The degree of crosslinking (and hence the extent of the change) is different in intensity depending on the process. According to DIN 16892 (a quality requirement for pipes made of PE-X) at least the following degree of crosslinking must be achieved:[13]


North America

All PEX pipe is manufactured with its design specifications listed directly on the pipe. These specifications are listed to explain the pipe's many standards as well as giving specific detailing about the manufacturer. The reason that all these specifications are given, are so that the installer is aware if the product is meeting standards for the necessary local codes. The labeling ensures the user that the tubing is up to all the standards listed.[14]

Materials used in PEX pipes in North America are defined by cell classifications that are described in ASTM standards, the most common being ASTM F876. Cell classifications for PEX include 0006, 0008, 1006, 1008, 3006, 3008, 5006 and 5008, the most common being 5006. Classifications 0306, 3306, 5206 and 5306 are also common, these materials containing ultraviolet blockers and/or inhibitors for limited UV resistance. In North America all PEX tubing products are manufactured to ASTM, NSF and CSA product standards, among them the aforementioned ASTM standard F876 as well as F877, NSF International standards NSF 14 and NSF 61 ("NSF-pw"), and Canadian Standards Association standard B137.5, to which the pipes are tested, certified and listed. The listings and certifications met by each product appear on the printline of the pipe or tubing to ensure the product is used in the proper applications for which it was designed.


In European standards. there are three classifications referred to as PEX-A, -B, and -C. The classes are not related to any type of rating system.


PEX-A is produced by the peroxide (Engel) method. This method performs "hot" cross-linking, above the crystal melting point. However, the process takes slightly longer than the other two methods as the polymer has to be kept at high temperature and pressure for long periods during the extrusion process. The cross-linked bonds are between carbon atoms.


The silane method, also called the "moisture cure" method, results in PEX-B. In this method, cross-linking is performed in a secondary post-extrusion process, producing cross-links between a cross-linking agent. The process is accelerated with heat and moisture. The cross-linked bonds are formed through silanol condensation between two grafted vinyltrimethoxysilane (VTMS) units, connecting the polyethylene chains with C-C-Si-O-Si-C-C bridges.


PEX-C is produced through electron beam processing, in a "cold" cross-linking process (below the crystal melting point). It provides less uniform, lower-degree cross-linking than the Engel method, especially at tube diameters over one inch (2.5 cm). When the process is not controlled properly, the outer layer of the tube may become brittle. However, it is the cleanest, most environmentally friendly method of the three, since it does not involve other chemicals and uses only high-energy electrons to split the carbon-hydrogen bonds and facilitate cross-linking.


Radiant heating system manifold using PEX tubing
This copper exterior valve has burst from freezing; several reports suggest that PEX takes longer to burst under freezing conditions.
PEX's flexibility allows for fewer connections, better water flow, and faster, simpler, and less expensive installation than comparable materials.
A PEX push fitting allows an installer to join copper and PEX pipes by simply pushing them together for a watertight fit.
Brass crimp fittings, another popular type of fittings primarily used for connection PEX to PEX, PEX to Threaded pipes. 1.Drop Ear Elbows connect PEX and threaded pipe at a 90-degree 2.PEX to Copper Solder Adapter 3.PEX to Copper Threaded Adapter 4.PEX to Female Threaded Adapter 5.PEX Plug - terminate end of pipe 6.PEX to PEX Coupling 7.PEX to PEX 90-degree Elbow 8.PEX to Copper Adapter 9.PEX to Copper 90-degree Elbow 10. PEX x PEX x PEX 3-way PEX Tee.
Tools and fittings used in a plumbing installation with PEX piping. (1) crimping tool to squeeze a metal band to join a pipe and a fitting (2) compression coupling joining two 1/2 inch pipes (copper or PEX) (3) "T-joint" to connect 3/4", 3/4", and 1/2" pipes (4) Copper-to-PEX 1/2" connection (requires soldering) (5 and 6) tools to undo PEX connections (7) crimp rings to squeeze metal band to connect PEX to a fixture (8) PEX tube cutter.

PEX tubing is widely used to replace copper in plumbing applications. One estimate from 2006 was that residential use of PEX for delivering drinking water to home faucets was increasing by 40% annually.[15] In 2006, The Philadelphia Inquirer recommended that plumbing installers switch from copper pipes to PEX.[16]

In the early to mid 20th century, mass-produced plumbing pipes were made from galvanized steel. As users experienced problems with the internal build-up of rust, which reduced water volume, these were replaced by copper pipes in the late 1960s.[17] Plastic pipes with fittings using glue were used as well in later decades. Initially PEX tubing was the most popular way to transport water in hydronic radiant heating systems, and it was used first in hydronic systems from the 1960s onwards.[15] Hydronic systems circulate water from a boiler or heater to places in the house needing heat, such as baseboard heaters or radiators.[18] PEX is suitable for recirculating hot water.[19]

Gradually, PEX became more accepted for more indoor plumbing uses, such as carrying pressurized water to fixtures throughout the house. Increasingly, since the 2000s, copper pipes as well as plastic PVC pipes are being replaced with PEX.[17] PEX can be used for underground purposes, although one report suggested that appropriate "sleeves" be used for such applications.[19]


Benefits of using PEX in plumbing include:


Government approvals

PEX has been approved for use in all fifty states of the United States as well as Canada,[14] including the state of California, which approved its use in 2009.[19] California allowed the use of PEX for domestic water systems on a case-by-case basis only in 2007.[38] This was due mostly to concerns about corrosion of the manifolds (rather than the tubing itself) and California allowed PEX to be used for hydronic radiant heating systems but not potable water. In 2009, the Building Standards Commission approved PEX plastic pipe and tubing to the California Plumbing Code (CPC), allowing its use in hospitals, clinics, residences, and commercial construction throughout the state.[19] Formal adoption of PEX into the CPC occurred on August 1, 2009, allowing local jurisdictions to approve its general use,[39] although there were additional issues, and new approvals were issued in 2010 with revised wordings to the 2007 act.[40]

Alternative materials

Alternative plumbing choices include


PEX-AL-PEX pipes, or AluPEX, or PEX/Aluminum/PEX, or Multilayer pipes are made of a layer of aluminum sandwiched between two layers of PEX. The metal layer serves as an oxygen barrier, stopping the oxygen diffusion through the polymer matrix, so it cannot dissolve into the water in the tube and corrode the metal components of the system.[41] The aluminium layer is thin, typically 1 or 2 mm, and provides some rigidity to the tube such that when bent it retains the shape formed (normal PEX tube will spring back to straight). The aluminium layer also provides additional structural rigidity such that the tube will be suitable for higher safe operating temperatures and pressures.

The use of AluPex tubing has grown greatly since 2010. It is easy to work and position. Curves may be easily formed by hand. Tube exists for use with both hot and cold water and also for gas.[citation needed]

This product in Canada has been discontinued due to water infiltrating between the Layers resulting in premature failures.

PEX tools

There are two types of fitting that may be used. Crimped or compressive. Crimped connectors are less expensive but require a specialised crimping tool. Compression fittings are tightened with normal spanners and are designed to allow sections of the system to be easily disassembled, they are also popular for small works, esp. DIY, avoiding the need for extra tools.

A PEX tool kit includes a number of basic tools required for making fittings and connections with PEX tubing. In most cases, such kits are either bought at a local hardware store, plumbing supply store or assembled by either a home owner or a contractor. PEX tools kits range from under $100 and can go up to $300+. A typical PEX tool kit includes crimp tools, an expander tool for joining, clamp tools, PEX cutters, rings, boards, and staplers.[further explanation needed]

Multilayer AluPex tube and connector

Other uses

This section does not cite any sources. Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed. (May 2024) (Learn how and when to remove this message)

See also


  1. ^ a b c Elsner, Peter; Eyerer, Peter; Hirth, Thomas (2012). Domininghaus - Kunststoffe (8 ed.). Berlin Heidelberg: Springer-Verlag. p. 224. ISBN 978-3-642-16173-5.
  2. ^ a b c d e f Baur, Erwin; Osswald, Tim A. (October 2013). Saechtling Kunststoff Taschenbuch. Hanser, Carl. p. 443. ISBN 978-3-446-43729-6. Vorschau auf kunststoffe.de
  3. ^ a b Koltzenburg, Sebastian; Maskos, Michael; Nuyken, Oskar (2014). Polymere: Synthese, Eigenschaften und Anwendungen (1 ed.). Springer Spektrum. p. 406. ISBN 978-3-642-34773-3.
  4. ^ Ahmad, H; Rodrigue, D (2022). "Crosslinked polyethylene: A review on the crosslinking techniques, manufacturing methods, applications, and recycling". Polymer Engineering and Science. 62 (8): 2376. doi:10.1002/pen.26049.
  5. ^ Brown, E.N; Willms, R.B; Gray, G.T; et, al (2007). "Influence of Molecular Conformation on the Constitutive Response of Polyethylene: A Comparison of HDPE, UHMWPE, and PEX". Experimental Mechanics. 47 (3): 381–393. doi:10.1007/s11340-007-9045-9.
  6. ^ Selvin, M; Shah, S; Maria, H.J; et, al (2024). "Review on Recycling of Cross-Linked Polyethylene". Industrial Engineering and Chemistry Research. 63 (3): 1200–1214. doi:10.1021/acs.iecr.3c02580.
  7. ^ Ahmad, H; Rodrigue, D (2022). "Crosslinked polyethylene: A review on the crosslinking techniques, manufacturing methods, applications, and recycling". Polymer Engineering and Science. 62 (8): 2376. doi:10.1002/pen.26049.
  8. ^ Liu, S.Q; Gong, W.G; Zheng, B.C (2014). "The Effect of Peroxide Cross-Linking on the Properties of Low-Density Polyethylene". Journal of Macromolecular Science, Part B. 53 (1): 67–77. Bibcode:2014JMSB...53...67L. doi:10.1080/00222348.2013.789360.
  9. ^ Yussuf, A.A; Al-Saleh, M.A; Al-Enezi, S.T; Abraham, G (2021). "Effect of silane concentration on the properties of crosslinked linear low density polyethylene-montmorillonite nanocomposite". Polymer Composites. 42 (5): 2268–2281. doi:10.1002/pc.25975.
  10. ^ "High-Density Crosslinked Polyethylene (XLPE)". Poly Processing. Retrieved February 1, 2017.
  11. ^ a b c Whiteley, Kenneth S. (2011). "Polyethylene". Ullmann's Encyclopedia of Industrial Chemistry. doi:10.1002/14356007.a21_487.pub2. ISBN 978-3527306732.
  12. ^ a b Kaiser, Wolfgang (2011). Kunststoffchemie für Ingenieure von der Synthese bis zur Anwendung (3 ed.). München: Hanser. ISBN 978-3-446-43047-1.
  13. ^ a b Günter Neroth, Dieter Vollenschaar: Wendehorst Baustoffkunde: Grundlagen – Baustoffe – Oberflächenschutz. 27. Auflage. Vieweg+Teubner Verlag/Springer Fachmedien, Wiesbaden 2011, ISBN 9783834899194, p. 931
  14. ^ a b c d e f g "PEX Pipe Markings". July 19, 2015. Retrieved 2015-07-30. All PEX pipe is manufactured with its design specifications listed directly on the pipe. These specifications are listed to explain the pipe's many standards as well as giving specific detailing about the manufacturer. The reason that all these specifications are given, are so that the installer is aware if the product is meeting standards for the necessary local codes. The labeling ensures the user that the tubing is up to all the standards listed.
  15. ^ a b c d e f Romano, Jay (September 3, 2006). "If Copper Pipes Are Too Costly ..." The New York Times. Retrieved 2011-07-09. The price of copper has nearly quadrupled over the last four years, and plumbers and do-it-yourselfers are taking a fresh look at alternatives to copper tubing and fittings. And what some are turning to is a flexible synthetic material called PEX.
  16. ^ Heavens, Alan J. (July 29, 2006). "Shortages Persist In Building Materials: Even as Demand for New Homes Falls, Cost of Cement and Copper Skyrockets'". The Philadelphia Inquirer. p. F25. Retrieved 2011-07-09. Recommended alternatives to copper piping include: (1) Cross-linked polyethylene, which is known as PEX and has been adopted by installers of radiant-floor heating since it neither corrodes nor develops pinhole leaks. PEX also resists chlorine and scaling, and uses fewer fittings than rigid plastic and metallic pipe. The piping is approved for potable hot- and cold-water plumbing systems as well as for hydronic heating systems in all plumbing and mechanical codes in the United States and Canada. (2) Aluminum plastic composite, a multipurpose pressure piping that can distribute hot and cold water indoors and outdoors, and also is well-suited for under-the-floor heating and snowmelt systems. It is made of aluminum tube laminated to interior and exterior layers of plastic. (3) Corrugated stainless-steel tubing, which is used as an alternative to traditional threaded black-iron gas piping for residential, commercial and industrial applications. It consists of a continuous, flexible stainless-steel pipe with an exterior PVC covering. The piping is produced in coils that are air-tested for leaks.
  17. ^ a b Stone, Barry (July 22, 2006). "50-Year-Old House Warrants Special Scrutiny". The Washington Post. Retrieved 2011-07-09. The use of galvanized steel water piping was abandoned in favor of copper in the late 1960s, and now the plumbing industry has moved from copper to PEX (cross-link polyethylene). The problem with old galvanized pipes is that they usually have internal rust build-up, which reduces water volume.... (Barry Stone => home inspector)
  18. ^ Heavens, Al (January 20, 2011). "Trying to keep radiant floor project out of hot water". Chicago Tribune. McClatchy/Tribune News. Retrieved 2011-07-09. Hydronic systems circulate water from a boiler or water heater through loops of polyethylene tubing, often called by the brand name Pex, but there are others. Tubing is typically installed on top of the subfloor in grooved panels or snap-in grids; clipped into aluminum strips on the underside of the floor; or embedded in poured concrete, or a lighter, concrete-like material in bathrooms or kitchens especially.
  19. ^ a b c d e f Mader, Robert P. (Sep 2, 2010). "California Approves PEX for Plumbing – Again". Contractor Mag. Retrieved 2011-07-09. PEX became part of the California Plumbing Code in August 2009, following the CBSC's January 2009 certification of an Environmental Impact Report (EIR) on PEX and the commission's ensuing unanimous adoption of regulations approving PEX water distribution systems.... The Commission's action allows the statewide use of PEX in hospitals, clinics, schools, residences and commercial structures.... The CBSC reinstated PEX with the caveats that underground PEX must be sleeved, the material had to stand up to recirculating hot water, the fittings won't de-zincify, and PEX systems had to be filled and flushed....
  20. ^ a b Heavens, Alan J. (August 11, 2006). "No Cool Solution to Removing Heated Tiles". The Philadelphia Inquirer. Retrieved 2011-07-09. I assume that the radiant floor heating involves piping that is embedded in Gypcrete, a lightweight blend of concrete and gypsum that, in concert with a shift to flexible PEX piping, has made installation easy and operation problem-free.
  21. ^ a b Television program Ed The Plumber, DIY Network, 2006
  22. ^ Spiegel, Jan Ellen (April 20, 2008). "The House That Green Built". The New York Times. Retrieved 2011-07-09. (Page 2 of 4) There is radiant floor heating, and the toilets use rainwater stored in a cistern. The floors, doors and wall paneling are reclaimed from vintage homes that were torn down elsewhere in the state. Instead of copper pipes, water will travel through Pex piping, less expensive flexible polyethylene tubes that are petroleum-based, but still may be greener than copper pipe. "It is a compromise," said Mr. Johnson, who said he worried a little about the health aspects of Pex. "I couldn't get a good read on that, to tell you the truth. I sort of got exhausted in asking a bunch of people."
  23. ^ "Inflation Adjusted Price of Copper". GuruFocus.com. Retrieved 2022-10-27.
  24. ^ a b Kogel, John (2009-07-13). "Pex Issues". Inspection News. Retrieved 2011-07-09. Once you've worked with PEX, you'll never go back to that other stinky glue stuff. We see copper stubs at the water heater (sometimes), the rest is PEX. Also, when they use the red and blue colors, hot is hot and cold is cold
  25. ^ "Fire Risks of Metallic Plumbing Systems Draw National Attention" (PDF). Lubrizol. 2003-01-03. Archived from the original (PDF) on 2016-09-16. Retrieved 2023-03-14.
  26. ^ Romano, Jay (January 28, 2009). "Before, and After, the Last Drop". The New York Times. Retrieved 2011-07-09. Pipes, traditionally made of copper, can burst if the water inside freezes, because water expands when frozen, but copper does not. If the water expands too much, it has nowhere to go but out, forcing the pipe to burst at the frozen spot. Tom Kraeutler, a host of the syndicated radio show "The Money Pit", said most houses have one particular spot where the pipes tend to freeze. If there is fairly consistent freezing in an area, he said, it is wise to reroute the pipes and to replace them with PEX — a flexible plastic tubing that is much less likely to burst than copper. Like copper, though, PEX can freeze, as Mr. Carter, who moved in December, now knows. The house was built with modern materials, including PEX, but because the place was only six years old, he didn't think he had to worry about frozen pipes.
  27. ^ Downs, Stacy (February 24, 2006). "Frozen Pipes Can Lead to Flood of Woe". Chicago Tribune. Knight Ridder/Tribune. Retrieved 2011-07-09. Frozen pipes break differently depending on the material, Water said. Copper rips, PVC (polyvinyl chloride) shatters and PEX (polyethylene) swells and tears.
  28. ^ a b Maxwell, Steve (Jul 14, 2007). "Drywall may not work on waterfront". Toronto Star. Retrieved 2011-07-09. Start by making sure that all runs of water supply pipe are sloped downwards slightly to central drain valves. Also, be sure to specify that all drain traps remain accessible, and be the kind that includes a removable plug on the bottom. As an added precaution, install PEX-al-PEX supply pipes instead of copper. If water accidentally remains in these pipes, they'll endure five or six freeze-thaw cycles without splitting. Copper pipe, on the other hand, splits apart promptly when it contains water that freezes.
  29. ^ a b Maxwell, Steve (Feb 28, 2009). "Put Basement Repair to Wet Weather Test". Toronto Star. Retrieved 2011-07-09. Q: Is it safe to use pipe wrap insulation on PEX water supply pipes? In a magazine put out by a home improvement retailer, it warns that a chemical reaction between insulation and PEX will eventually destroy the pipes. Is this true? A: To answer your question, I contacted one of the world's largest producers of PEX pipe. The only potential issue they know of has to do with certain types of adhesives touching the pipe surface. PEX includes antioxidants for stabilizing against chlorine, and these antioxidants can become destabilized in a reaction with adhesives, possibly aging the pipe prematurely. That said, they don't know of any issues relating to a chemical reaction between PEX and conventional foam pipe wrap insulation. I've installed foam insulation on PEX in my own house about a year ago, and there's no visible signs of trouble.
  30. ^ a b Kibbel, Bill; Katen, Jim; Kienitz, Nolan E. (2006–2007). "PEX and sunlight issues". The Inspector's Journal. Archived from the original on 2011-10-03. Retrieved 2011-07-09. Well, the manufacturers' instruction I've read and the Plastic Pipe Assoc. says it can't be installed where exposed to direct sunlight.... I've heard of some pretty serious problems with PEX that's exposed to sunlight. Your client's concerns are valid.... Another big factor is how the product has been "handled" from manufacture to site installation.... I had a client, with a new home, that was purchased back by the plumbing company due to mis-handling of the PEX that had caused over 10 leaks in less than 7 months.
  31. ^ Bates, S.L. 2005. Damage to common plumbing materials caused by overwintering Leptoglossus occidentalis (Hemiptera: Coreidae). Canadian Entomologist 137: 492-496.[journals.cambridge.org/article_S0008347X00002807]
  32. ^ a b Pope, Jeff (Jan 22, 2009). "Pipe work begins in homes involved in Kitec lawsuit". Las Vegas Sun. Retrieved 2011-07-09. The polyethylene pipes contained a thin layer of aluminum that held its shape as plumbers twisted and bent it. Plastic pipes without the aluminum require more anchoring because they spring back to a straight line. The pipes aren't failing though. It's the brass fittings that connect the pipes to copper fixtures on valves, water heaters and softeners. The problem is a chemical reaction known as dezincification, which accelerates corrosion in brass fittings when they are exposed to oxygen and moisture. Brass is an alloy primarily composed of copper and zinc. When dezincification occurs, zinc leaches out of the fittings, leaving a blockage of zinc oxide that leads to leaks, restricted water flow and breaks.
  33. ^ Pope, Jeff (Feb 23, 2009). "Plumbing Problems May Continue to Grow". Las Vegas Sun. Retrieved 2011-07-09. Yellow brass typically has about 30 percent zinc. When the yellow brass is exposed to Southern Nevada's mineral-rich hard water, the zinc is removed and builds up inside the pipes leading to blockages and breaks, according to court documents in the Kitec lawsuit. The process is called dezincification. Red brass typically has 5 percent to 10 percent zinc and is being used to replace the yellow brass in valley homes built by Richmond American and Pulte.
  34. ^ Menelly, Ted (2009-07-13). "Pex Issues". Inspection News. Retrieved 2011-07-09. Just a couple of leaks at poorly applied connections. Other than that I have not really seen any. Most, not all, but most new homes have PEX. There are some that still use only copper. have seen it used a lot in remodel with many homes I have inspected that have had repiping. It is easier to run through the attics and crawls. I guess it has been, what, 10 years or so since its major use. I guess only time will tell. There were many complaints in the very beginning but not much now.
  35. ^ "California Building Standards Code" (PDF). State of California. 2007. Retrieved 2011-08-15. ... PEX material is susceptible to chemical leaching, both from the outside environment and chemicals leaching out of the PEX material itself....
  36. ^ a b "Pipe Rollercoaster: After a recent exclusion, PEX pipe is back in the California Plumbing Code". Plumbing & Mechanical. October 1, 2010. Retrieved 2011-08-15. ... controversy in California ... resulting in a flurry of back-and-forth legal wrangling over health, safety and performance issues related to the flexible pipe.... That judicial rollercoaster finally came to a halt in mid-August when a coalition of consumer, environmental, public health and labor organizations reached an agreement with the state and the plastic pipe industry ... As a result, the California Building Standards Commission now allows the use of PEX in all occupancies...
  37. ^ Sweet, Jack (October 1, 2010). "What was that flurry of activity this past summer?". Reeves Journal. Retrieved 2011-08-15. It boiled up, came to a head and was then over almost as quickly as it takes to tell the tale. PEX, formally known as crosslinked polyethylene tubing-was given the administrative heave-ho from the California plumbing codes. Then, almost as quickly as the word could get passed out to the industry-at-large, PEX was back the state's good graces, albeit with a few stipulations on its use that weren't there before.
  38. ^ 2007 CPC Table 6-4 Footnote 1; previously: 2001 CPC 604.1 #2
  39. ^ "(Press Release) PEX Plastic Pipe Unanimously Added to California Plumbing Code; State Officials Certify Favorable Environmental Impact Report". Reuters. January 27, 2009. Archived from the original on September 13, 2012. Retrieved June 23, 2009.
  40. ^ "Building Standards Commission". State of California. 2010. Retrieved 2011-07-09. On August 16, 2010, the California Building Standards Commission certified the Final Environmental Impact Report and approved regulations allowing the use of PEX tubing. The Approved Final Express Terms document represents the final language that will be published into the 2007 California Plumbing Code and the 2010 California Plumbing Code (Effective Jan. 1, 2011) with the strikeout and underlining removed for clarity. All remaining agencies' rulemaking documents appearing on this page, were also approved by the Commission, but do not have the strikeout and underlined removed.
  41. ^ "PEX choices". Home Heating Systems Newsletter. Archived from the original on June 11, 2008. Retrieved 2008-06-12.