Polybutylene (PolyB) crimp rings seem to be much harder to source alone (not as part of an adapter set) than PEX rings. As such, it would be so much more convenient to just use PEX rings. Yet, the visible differences between PolyB and PEX rings are understandably enough to introduce doubt.
There is an official answer to the question of whether PEX crimp rings will work on PolyB pipes, and there are some really good reasons for this answer. However, the reality is always a little different to the ideal world put forward by manufacturers.
Officially, PEX crimp rings can’t be used on PolyB pipes. They have thicker, short walls, creating greater and more concentrated force on the pipe they are crimping. PolyB pipes have thinner walls, making the excess force damaging to the pipe. Yet, people have successfully used PEX rings for PolyB pipes.
Are PEX & PolyB Crimp Rings Interchangeable?
The official answer to this question is no; they are not interchangeable.
However, people have reported successfully using PEX crimp rings (amazon link) for PolyB.
On the other hand, using PolyB rings for PEX is not recommended.
So, how do we explain the official stance, the success of using PEX rings for PolyB, and why PolyB rings are not similarly appropriate for both uses?
Why They Are Considered Non-Interchangeable
PEX and PolyB pipes have different inner diameters with the same (or very similar) outer diameters. If they are different, the PEX pipes are bigger.
Slightly Different Outer Diameters
If the outer diameters are slightly different, then the PEX crimp ring will be too large for the PolyB pipes.
You want the rings to crimp around the pipe without any excess material having to be folded as this will not be a good seal, and the folds will also compromise the strength of the ring, which can more easily crack or break.
Thick Ring Wall Exerts Too Much Force
Even if the outer diameters are the same, PEX rings have thicker walls to match the thicker pipe walls.
To truly crimp the pipe around the fitting, the ring needs to be able to squeeze the pipe wall closed against the fitting.
Thicker pipe walls make this harder because they are more resistant to deformation. The thicker crimp rings allow them to exert the necessary force without breaking.
It is entirely possible that this greater wall thickness of the PEX ring could damage the PolyB pipe when crimped around it, exerting too much force against the thinner wall.
Supporting this theory is the fact that PolyB crimp rings are taller as well as thinner-walled.
PolyB Rings Are Taller/Wider
Due to the thinner walls of the PolyB pipes, the force of the crimp ring is likely better off being spread over a greater area, which is where the additional ring height comes in.
The PEX rings would focus too much force over a smaller area of the pipe, potentially damaging and weakening it, making for a less secure seal.
If you know anything about PolyB pipes, then you know that they are destined to fail. The chlorine in the water carried by the pipes has an unfortunate reaction with the plastic, making it weak.
If the pipe was already weakened by this reaction, then the excess force of the PEX crimp ring can cause the pipes to fail sooner.
Reason PEX Crimp Rings Can Work on PolyB Pipes
As I said, people have reportedly used PEX crimp rings on PolyB pipes with success. It is possible that the thicker walls and more concentrated force (shorter walls) are not actually enough to make a difference.
However, because there are differences in the rings, for the manufacturer to say that they are interchangeable opens them up to lawsuits if the PEX ring fails with the PolyB pipes.
Furthermore, it means that making and selling both types of rings becomes pointless.
PolyB Rings Are Not Appropriate for PEX Pipes
Those who say PEX and PolyB rings are not interchangeable and those who say that PEX rings can be used for PolyB pipes agree that PolyB rings cannot be used for PEX pipes.
The thick wall of the PEX pipe does require a stronger crimp ring to compress it. The thinner, taller PolyB ring would not be able to exert the force required to achieve this.
In a way, this fact actually supports the theory that they are not interchangeable at all, but how can we deny practical success? This leads me to my final verdict on this query.
Final Verdict
If you are buying PolyB fittings, you will likely get PolyB rings with them. Don’t go out and buy separate PEX rings; just use what was provided.
In the case where you are replacing the crimp ring, and you only have PEX rings on hand, then give it a go. Keep an eye on the connection and make your own conclusion based on practical evidence in your situation.
Another idea to consider is to actually replace your PolyB pipes with PEX. PolyB is going to fail, so why not start slowly replacing it?
Sources
https://www.pexsuperstore.com/wp-content/uploads/2020/03/PEX-piping-vs.-PB-piping.pdf
https://www.plumbingforums.com/threads/crimp-rings-for-pex-to-polybutylene-coupling.10101/