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I am wanting to add a permanent electronic temperature sensor to a brass rough-in shower valve. For this particular rough-in valve, I can thread a thermowell into the outlet that is normally used for the tub spout, since no tub spout is used.

I can easily turn and thread an aluminum thermowell with my lathe, but I want to ensure that the aluminum and brass will be compatible (i.e. no corrosion) in this application. I have not been able to find any data on using these two metals together in a potable water application.

The reason is I'm trying to avoid having to purchase the more expensive brass stock, and utilize my existing aluminum bar stock instead :)

Thanks!

  • I might be concerned using aluminum fittings with potable water. I don't know for sure if there's a problem, but my gut says it's not right. Don't think I've ever seen an aluminum pipe fitting. – Tester101 May 10 '15 at 12:33
  • Thanks everyone for your answers thus far. I did find on the wikipedia Brass article that aluminum is added to brass to create an alloy with improved corrosion resistance. While this doesn't speak to the issue of using the two metals side by side, does it indicate some compatibility between them? – Ryan Griggs May 11 '15 at 2:33
  • I agree tester that I've never seen an aluminum potable water fitting. But there are aluminum natural gas fittings, as well as aluminum fittings used in refrigerant applications... Would those be more corrosive environments? – Ryan Griggs May 11 '15 at 2:36
  • @RyanGriggs The reason the mix of aluminum and brass mixed is less subject to corrosive it because of the strong bond the two have to one another. Basically, they "fight" so hard to connect they they prevent other connections from forming. This is the opposite of what you would want in a mechanical bond. – BrownRedHawk Aug 29 '16 at 20:11
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It will corrode quickly. The Aluminum will break down.I recommend that you put a non-metallic barrier between the two. If you want to do it on the cheap, and If you have some Never-Seez or even some PTFE tape laying around, do it. Check it in a few months, replace the barrier, check again later.

Galvanic Corrosion happens because of the different in electrical potential. The amount of difference (and the environment) that determines how fast one metal will corrode.

  • Aluminum has an anodic index -.9
  • Brass has an anodic index of about -.4

A difference of .25 is acceptable, in harsh environments (heat, salt water) the max is .15.

http://www.fastenal.com/content/feds/pdf/Article%20-%20Corrosion.pdf https://en.wikipedia.org/wiki/Galvanic_corrosion

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Aluminum and brass with an electrolyte between them (water) can still result in galvanic corrosion. Are there any plastic (PVC) fittings you could use for this application? I would choose a plastic fitting if possible.

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I want to post the answer I discovered after trial and error. I installed an aluminum thermowell in the brass faucet fitting. I wrapped the aluminum in PFTE tape but since the threads are sharp they cut through the tape.

After leaving the unit for only a few days, I observed fairly heavy corrosion and pitting of the aluminum fitting.

This occurred during testing of the pipes, so it was not pressurized most of the time and only had residual water from testing operations.

I can very definitely say "aluminum and brass don't mix" when there's potable water involved.

Replaced with a brass thermowell from Amazon and all's "well" haha.

Hopefully this is helpful to someone.

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Go for it. The only thing that doesn't work well with aluminum is steel like black pipe etc. Aluminum and brass are compatible.

  • can you please some proof for your answer? Any kind really...because I'm curious and all the other answers are pointing out that it shouldn't be done. Don’t know the answer but I would like to get to the bottom of this. – python starter Jul 17 '15 at 7:27

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