PVC vs CPVC

[jldv]

I'm designing a sodium hypochlorite system with PVC piping/valving. I've heard that PVC will get brittle after a few years, but not CPVC. Anybody who can back this statement ? Which one would be the best choice for my application ?

Thanks,

JLDV
Mech Eng.

 

[Metalguy]

Probably too late to help, but I would avoid PVC like the plague for that app. CPVC should do fine, but run tests to make sure the glue is also resistant. I could make you cry with my PVC/CPVC experiences-*I* sure did!

 

[jldv]

Thanks, Metalguy. What was the major problem with PVC in your painful experiences ?
Powell's 'Sodium Hypo General Handbook' states that CPVC can get brittle after a few years, any experience with that ? at what pressure do you run your CPVC piping ?

 

[Metalguy]

Seems that PVC doesn't like real high pH solutions. We had two buried long (about 1 mile) buried 4" CPVC lines, one with NaOH and the other w/sodium hypo--~10% ea. They hadn't been glued well and started leaking at the joints. We replaced them with new CPVC, but this time we made sure they were very well glued--even UT'd every joint. Again the joints leaked after a while. Problem traced to the glue itself-the high pH actually dissolved it. We tested and tested various glues and found that most were fine. We then decided to use the much easier to glue reg. PVC. No more leaking joints, but the pipe itself started cracking all over.

Not a good time in my career!

 

[EdStainless]

The CPVC is more highly crosslinked making it more stable. As bonds break the material looses mechanical integrity.
The joints are a real pain. I never found a failsafe way to select glue other than testing.

= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.

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