Stainless Steel to CPVC Connections

[elecman13]

I am running stainless steel tanks with NPTF half couplings on it. I want to connect NPTM CPVC adapters directly to the stainless steel. The problem is somebody higher up persists that the connections will leak. Is there any good place to look for information that would help me get my point across, or a good way to prove it to a non-engineer?

 

[rconner]

I don't have any experience in such connections; however, I think I have heard that at least in some threaded connections it is generally better at least in some applications to have the pvc on the male end of the connection. Also, might want to be a little careful in some applications with pvc to stainless couplings/connections in general, as it appears the chlorine in some pvc apparently might eventually not do some stainless much good (see e.g.

http://www.thermon.com/article/ThermoTips/Stress Corrosion Cracking in Tubing Bundles.pdf).

 

[moltenmetal]

You have things the right way around: the female part is stainless steel and the male is CPVC. If you use the right type of thread sealant, compatible with the fluid you're sealing and with both CPVC and stainless steel, you will be fine- as long as the temperature is below about 80 C such that the CPVC doesn't begin to "creep" on you, and you're within the P/T limits of the CPVC components.

I recommend that you use an anaerobic paste thread sealant rather than just Teflon tape if possible. It will be more forgiving- but only if you choose one which will not embrittle CPVC. Check with the mfg. An example is Loctite (Henkel) "No More Leaks" sealant, but there are many others.

You have bigger problems with SS NPT male parts in CPVC female parts due to the tendency of the fitter to over-tighten the fittings to the point that the female part splits. Better quality CPVC female parts will have an external ring, often SS, to reduce the tendency for the parts to split.