|What is PEX?||Silane Method PEX||FAQ's|
|WHAT IS PEX?||TOP|
PEX is an acronym, which stands for cross-linked polyethylene. PEX is essentially
polyethylene (PE) material (a thermoplastic that consists of a series of ethylene
hydrocarbon chains) which has undergone a chemical or physical reaction that causes
the molecular structure of the PE chains to link together. This reaction creates a three
dimensional structure which has superior resistance to high temperature and pressure.
Properly manufactured PEX tubing demonstrates superior characteristics at elevated
temperatures and pressures (as compared to uncross-linked polyethylene) in the areas of
tensile strength, resistance to deformation, resistance to corrosion and mineral buildup,
creep resistance, abrasion resistance, impact strength and chemical resistance. This makes
PEX as perfect product for high temperature and pressure fluid distribution piping. There
are three primary commercial methods for producing PEX tubing: Silane method, Peroxide
(or Engel) method, and Radiation (or E-beam) method.
The American Society for Testing and Measurements (ASTM) has developed minimum performance standards to determine PEX tubing's suitability for high temperature/pressure fluid distribution applications (F876) at three different temperature and pressure ranges (160 psi @ 73.4º, 100 psi @ 180ºF and 80 psi @ 200ºF). All PEX tubing that is manufactured in accordance with the ASTM F876 standard is perfectly suited for use in hot water fluid applications at these temperatures and pressure ranges if they are marked on the tubing by the manufacturer.
PEX was developed to replace rigid and non-corrosion resistant fluid distribution materials such as steel pipe, copper tubing, CPVC - among other products. The Zurn PEX system demonstrates these advantages over rigid piping systems:
|SILANE METHOD PEX||TOP|
Zurn utilizes the Silane method of production which was developed by DOW Corning in the
late 1960's. It is initiated by grafting vinyl silane onto the backbone of the polyethylene.
This material is then mixed with the optimal levels of antioxidant stabilizers, initiators,
colorant dyes and a catalyst during extrusion. A standard thermoplastic extruder is used to
form the tubing. Although the mixture would cross-link on its own, the extruded tubing is
then run through a water or steam bath to speed the curing time. The compound formulation
is the determining factor in the degree of cross-linking so precise control is achieved
(71-74%). Higher degrees of cross-linking are achievable (up to 90%) by simply grafting
more silane molecules onto the polyethylene. This is not necessary though because the
starting density of the base polyethylene used Silane production can be and is typically
higher than the other two methods. The starting density of Zurn PEX is 0.952 g/cm3 which
gives Zurn PEX the highest burst pressure ratings and highest tensile strength in the
industry. Unlike the Peroxide/Engel and Radiation/E-beam methods, Zurn PEX/Silane produced
pipes will continue to cross-link to completion, if necessary, even after the extrusion
process is completed. This ensures a perfectly cross-linked product every time. Every foot
of Zurn PEX tubing is placed in high temperature steam chambers to drive the cross-linking
of the tubing to completion before it ever leaves our production plants.
Zurn chose the Silane method of production for very significant reasons. Although all PEX tubing that is manufactured in accordance with the ASTM standard is a quality product, Silane method Zurn PES far surpasses the quality standards of ASTM, more than any other commercial production method.
Tensile Yield Strength Testing Results
Tensile Yield Strength (psi) testing performed at an independent laboratory. Yield strength is the stress point at which the material becomes permanently deformed.
Quick Burst Testing Results
Quick Burst (psi) testing performed at an independent laboratory. Average quick burst pressure at 180ºF in accordance with ASTM requirements.
Additionally, the Silane method affords greater flexibility and efficiency than other methods. Additives like dyes (for producing colored tubing), antioxidant stabilizers and ultraviolet (UV) stabilizers are critical to the benefits and overall quality of our tubing. During Silane production, these additives do not interfere with the material's ability to cross-link (as in other methods) so the optimal levels of each of these products are in every inch of Zurn PEX that is installed, ensuring long term resistance to chemical and oxidative degradation and very good service life for our products. Because the Silane method relies on a chemical mixture and not high temperature and pressure to cause the material to cross-link, the dimensional stability is much more consistent as well. This consistency allows Zurn to utilize the QICKSERT I insert and crimp fitting for permanent, worry-free connections every time - and we back it with a 25-year limited warranty (the best in the industry)! Special tools that stretch the tubing to a consistent diameter are not necessary.
Zurn PEX Hydrostatic Data - reviewed by the Hydrostatic Stress Board of the Plastic Pipe Institute. Peroxide data is derived from a peroxide manufacturer's published literature ("Rehau RauPEX Radiant Floor Heating Systems Technical Information" booklet).
Silane method Zurn PEX demonstrates superior performance in these areas:
|FREQUENTLY ASKED QUESTIONS||TOP|
Yes and No! ASTM has developed stringent standards to measure the quality of PEX tubing (ASTM F876 and F877). All PEX tubing that passes these tests is a high quality product and perfectly suitable for fluid distribution applications. All three methods of commercial production produce quality tubing, but Silane method Zurn PEX is the highest quality when considering the features that are important to fluid distribution (burst ratings, long term life expectancy at elevated temperatures and pressures, chemical resistance, impact resistance, etc.
Does the PEX-a designation mean that it is better than PEX-b or PEX-c? BACK UP
No! The a, b, and c designations are used in Europe to distinguish between manufacturing methods but they are not a rating method. Zurn fought to keep this designation out of the ASTM standards because they thought competitors would try to imply it was a rating. All PEX's that meet the ASTM standard will give good service in plumbing and heating applications.
Is Zurn PEX tubing resistant to chlorine? BACK UP
Yes! Based on tests Zurn has performed and ongoing testing by NSF, Zurn PEX may be used in recirculating plumbing systems at temperatures up to 140ºF and chlorine levels up to 2 ppm. (Most municipalities are between 0.5 and 1.4 ppm.)
Can Zurn PEX be stored and/or installed outdoors? BACK UP
No. All plastic pipes can breakdown when exposed to ultraviolet rays (sunlight) unless they contain certain pigments or stabilizers intended to prevent the damage. Exposure of unstabilized pipe to ultraviolet rays (UV) causes the molecular structure to breakdown and oxidize causing the pipe to become brittle and eventually rupture. Zurn PEX contains UV stabilizers that are intended to protect it for 6 months of exposure, which is intended for protection on the job site in case the project is delayed. Most other PEX tubing has only 30-60 day protection. If it must be installed outside, it must be sheathed in a protective sleeve. Zurn PEX should not be stored outdoors.
Is a Carbon-Carbon bond (Peroxide/Engel) stronger than Carbon-Silane bond (Silane)? BACK UP
No! There is much more to tube strength than the strength of the molecular bond. Some relative bond energies are:
How well does Zurn PEX tubing resist freeze damage? BACK UP
Very well! Zurn PEX will expand before rupture, typically allowing enough room for freeze expansion. Rigid products like copper and CPVC rupture when expanded causing expensive repairs. Zurn PEX that is buried in concrete or otherwise restrained to prevent uniform expansion should be protected from freezing.
Does having a higher degree of cross-linking make a PEX tubing better? BACK UP
No! The density of the base polyethylene (PE) material chosen for production determines the needed percentage or degree of cross-linking. The lower the density of the base PE the higher the percentage of molecules that must be linked together to achieve the necessary strength to meet the requirements of the ASTM standard. Other manufacturing processes requires lower density PE due to their manufacturing method. If they did not cross-link to very high levels they would not pass the ASTM standard. It is possible to formulate Silane method Zurn PEX at the same levels of cross-linking but it is not necessary or desirable.
Does bending PEX back and forth (kinking it) until it breaks show strength? BACK UP
No! Bending back and forth merely demonstrates a material's elastic behavior. Because other methods for producing PEX require a lower PE material density, they are more elastic - not stronger! (It's like comparing clear vinyl tubing or a plastic straw to a copper pipe. Because the clear vinyl and the straw are a lower density material, it can't be easily broken in two but it does not have as high of temperature/pressure strength as copper pipe).
How is Zurn PEX tubing connected? BACK UP
The QICKSERT I insert and crimp fitting system were developed more than 30 years ago. With more than 100 million QICKSERT I fittings in service, it is by far the most widely used system to connect PEX tubing. An appealed copper ring designed specifically for PEX tubing (black in color) is first slid over the Zurn PEX tubing. The QICKSERT I insert and crimp fittings are then inserted into the Zurn PEX tubing and our crimping tool compresses the ring, permanently sealing the joint. Tensile strength tests show that the QICKSERT I connection is stronger that the Zurn PEX tubing so Zurn has backed their tube and fittings with a 25-year warranty when installed together as a system.
Can I use my polybutylene crimping tool with QICKSERT I fittings? BACK UP
Yes. Polybutylene crimping tools are suitable for use with QICKSERT I fittings as long as they are not worn and will crimp within specification, as determined by the "Go/No Go" gauge.
Do QICKSERT I fittings require time for curing or shrinkage before pressure can be applied and are they affected by cold weather? BACK UP
No. Zurn's QICKSERT I fittings are full strength as soon as they are crimped and they are not affected by cold weather. QICKSERT I fittings do not rely on solvents, chemicals or the memory of PEX to seal the connections. The compressive strength of the copper crimp ring guarantees a uniform, high strength connection every time. With QICKSERT I there is no more frozen glue or waiting for the PEX to shrink before system pressure testing.
|QestPEX Specification sheets:|
|*Adobe Acrobat Document. If you do not have this program, click here.|