Difference Between PEX-A and PEX-B

What is the Difference Between PEX-A and PEX-B?

How much do you know about the plumbing pipes that ensure a steady flow of water in your home? A lot of people don’t actually know much about plumbing. For instance, have you heard about PEX plumbing systems?

A lot of houses feature PEX plumbing systems and yours probably isn’t an exception.  PEX is an abbreviation standing for cross-linked polyethylene. There are three types of PEX: A, B, and C. In this article we will look at PEX-A and B and break down the differences between the two.

Types of PEX

There are three main types of PEX: A, B, and C. These letters are only used as an identification of the manufacturing process. Considerations of the quality of their respective performance ratings are not involved in the naming.

All PEX systems must (particularly those made by reputable manufacturers/companies) adhere to the same set of international performance standards, regardless of whether it’s type A, B, or C. There are American standards (ASTM876/877) and international standards (ISO21003).

PEX A, B, and C must adhere to the same standards in terms of:

  • Pipe wall thickness
  • Minimum bending radius
  • Temperature and pressure ratings

Note, however, that these standards are only applicable to brands selling in the US. A lot of obscure or no-brand products probably don’t meet these criteria.

Difference in Production Methods

The method of producing PEX-A tubing is known as Peroxide method. Another name: Engel method, from the name of the inventor Thomas Engel.  In this process, creation of free radicals occurs due to the melting of HDPE polymer. When the temperatures go above the decomposition temperature of the polymer, cross-links between the molecules begin to occur.

The method for creating PEX-B tubing is a “Moisture Cure” or “Silane” method in which cross-linking of molecules happens after an extrusion process which involves using a catalyst and exposure of PEX tubing to hot water. PEX-B tubing is the most commonly used in the industry – it is what many companies manufacture.

Difference in Cross-linking Threshold

In PEX-A, the degree of cross-linking must be over 70%. On the other hand, the threshold for cross-linking in PEX-B is at over 65%.

Reason: PEX-A’s chemical structure is low in crystallinity, because of the manufacturing method. As a result, the piping has lower strength and density, which is why PEX-A requires a higher degree of cross-linking than PEX-B.

The molecular structure of PEX-B is high in crystallinity. As a result, the piping’s surface is harder, with higher thermo stability, better scratch resistance, higher burst strength harder body, higher rigidity, and more resistance to chlorine solutions.

Differences in Wall Thickness

PEX-A systems have a greater wall thickness than PEX-B.

Reason: PEX-A piping has lower burst strength. As a result, PEX-A piping needs to be thicker to be able to cope with operating pressures at an equal footing with PEX-B.

However, the thickness of PEX-A walls means the pipe has a lower SDR (standard dimension ratio) and that results in a lower flow rate.  PEX-B’s flow rate is therefore superior to PEX-A’s.

Similarities

PEX-A has higher flexibility and any kinks are repairable using a heat gun. However, while PEX-A has more flexibility than PEX-B, it’s worth mentioning that the minimum bending radius is the same for both.

Furthermore, since all pipes that get exposure to the sun have to be lagged (fitting special type of insulation around the pipes), it is irrelevant to talk about either of the two having better UV resistance than the other.

At the end of the day, the most important point is that both PEX types comply with the same minimum performance requirements set in Building Codes and American standards.

Conclusion

Of the two, PEX-A has more flexibility and possesses little or no coil memory, which means you can easily repair any existing kinks with a heat gun. The main downside is high rate of chemical leaching – as much as 50% to 200% higher than PEX-B.

PEX-B is a winner in many ways. For one, it is able to handle continuous hot water while PEX-A needs either a timer or limited exposure. Furthermore, PEX-B’s bursting pressure is higher as well as its level of resistance to oxidation. The main downside is stiffness and having coil memory, which means you can’t repair kinks with a heat gun.

Ultimately, however, both PEX-A and PEX-B attain the required performance requirements set for manufacturers.

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