The A, B, C’s of PEX pipe
Although PEX, or Crosslinked PolyEthylene is not a new material for piping, it is seeing new applications in the commercial building market. For decades in North America, PEX has been used in radiant floor heating and snowmelting systems. Then its use migrated into residential plumbing systems. Today, you will find more and more PEX being used in commercial buildings. Not just in the traditional radiant floors, but now in commercial plumbing systems and commercial hydronic distribution systems.
However, the challenge is to understand that not all PEX pipe is the same. Not only are there several BRANDS of PEX pipe available in the market in North America, there are also several TYPES.
In the world of PEX piping, you may hear three very common terms when talking about PEX pipe. These are PEX-a, PEX-b and PEX-c.
Quite often, people believe that this relates to the pressure ratings of the pipe, the temperature ratings of the pipe or some other measure of the quality of the pipe. These are all incorrect.
In reality, PEX-a, PEX-b and PEX-c just describe the way in which the pipe is manufactured. In reality, this is a bit of a history lesson.
In the late 60’s, Thomas Engel developed a process to take Polyethylene molecules and to crosslink or bond them together using organic peroxide as a “crosslinking agent”. In this process, the mixture of polyethylene and organic peroxide are combined and put into an extruder. The extruded puts the mixture under extreme pressure and temperature. In this environment, the polyethylene melts into a liquid state and the organic peroxide allows the polyethylene to “crosslink”. Once it has been crosslinked in this liquid state, it is then extruded into pipe in a single process.
This product became known as PEX-a or “Engel Method PEX” or “Peroxide Method PEX”. In this method, approximately 80% to 83% of the polyethylene becomes uniformly crosslinked in the pipe.
Later, a second process was developed for crosslinking polyethylene using a chemical called Silane. In this process, polyethylene is combined with Silane, placed in an extruder and extruded into pipe. Then it is taken to a high temperature and high humidity environment to “active” the Silane to create the crosslinking between the polyethylene molecules. This is a two-step process where most of the crosslinking is contained in the outer surface of the pipe as this is where the pipe sees the highest temperature and humidity.
This product is known as PEX-b or “Silane Method PEX”. In this method, approximately 65% to 70% of the polyethylene becomes crosslinked with most of that crosslinking happening near the outer surface of the pipe.
Then a third method was developed that required the use of an electron beam. In this process, polyethylene is extruded into the shape of pipe and then taken to a secondary process. In the secondary process, the pipe is exposed to an electron beam to create the crosslinking between the polyethylene molecules. This is also a two-step process where most of the crosslinking is contained in the outer surface of the pipe where it sees the most exposure to the electron beam.
This product is known as PEX-C or “Electron Beam PEX”. In this method, approximately 70% to 75% of the polyethylene becomes crosslinked with most of that crosslinking happening near the outer surface of the pipe.
Why does it matter?
You may ask, why does all of this matter? At the end of the day, all of these products are considered to be PEX and in Canada fall under the CSA Standard know as CSA B137.5. This standard is the guideline for the minimum temperature and pressure ratings as well as the dimensional standards for all PEX pipe available in Canada.
However, the crosslinking percentage and the uniformity of the crosslinking gives the different types of PEX different characteristics. The more uniform the crosslinking and the higher the percentage of crosslinking leads to an increase in the flexibility of the pipe along with an increase in its elastic characteristics.
An example of this would be that most PEX-a products can use an oversized fitting and take advantage of the elastic properties of the pipe to make connections. This allows for a system that has a lower overall pressure drop and better flow characteristics.
Another advantage to high, uniform crosslinking is the ability to “repair” a pipe with the application of heat. If a PEX-b or PEX-c pipe is kinked during installation, the installer must cut out the damaged section of pipe and replace it. If a PEX-a pipe is kinked during installation, the installer can “repair” this pipe by applying a suitable amount of controlled heat to the pipe, allowing it to reform to its original shape, size and integrity.
Choose your TYPE then Choose your BRAND
In North America and in Canada, you will find a large number of BRANDS of PEX pipe available in the marketplace. However, there are only three TYPES of PEX available. As you gain a better understanding of the TYPES of PEX, this will allow you to make an informed decision about the TYPE of PEX that is best for the application that you have. Once you know the TYPE of PEX that you want to use, then you can choose the BRAND of pipe based on the support, product offering and warranty that the manufacturer offers for their BRAND.
Original Article supplied by Uponor
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The TLJ Team