Pipe dope on pex fitting

[hardwite]

I recently reworked a plumbing system on my 3 year old house. The plumbing system was installed by a licensed plumber.
I noticed a white residue and build-up inside the pipes. The residue was formed in bubbles or nodules on the inside of the fittings. The material holds together but will crumble if you squeeze it.
I also removed some fittings from the pex and found white reside on the interface between the pex and the fitting (ridges). It looked like oxidation (just a descriptor, I don't think it was oxidation).

I am thinking the plumber put pipe dope on the pex fittings. I searched around on the internet and did not find recommendations for this practice. If it is a practice, I would be interested in a comment on material compatibility. This is hot and flowing water.

Has anyone ever heard of this, or have an idea of what it might be?

3/4 pex fitting with unknown white material 2

• hardwite
• Jun 14, 2019

3/4 pex fitting with unknown white material 1

• hardwite
• Jun 14, 2019

 

[Diehard]

I have no experience with it but I wonder if it could be residue from Hard Water.

 

[frodo]

calcium build up due to hard water

pex advertises pex pipe does not have calcium build up
this is true
they do not tell you that the fittings will build up.

 

[hardwite]

The material analysis shows zinc is the main ingredient. This would indicate some brass component corroded. Probably the fitting itself. The other materials might be salts in the water.

Matl_analysis1

• hardwite
• Jun 30, 2019

SEM analysis showing zinc is primary material

Matl_analysis2

• hardwite
• Jun 30, 2019

Percentages of materials

A good write-up on corrosion
https://www.pmengineer.com/articles/86921-corrosion-in-open-closed-loop-systems

A write-up specific to corrosion of pex fittings, and cites hot water circ loops!
https://safetyequipmentsupplies.knoji.com/problems-with-pex-fittings-the-class-action-lawsuits/