Brass on stainless-steel, OK or not?

Stephane

Hi folks,

As I am a very very poor CCR diver (), I'd like to re-use a brass Swagelok fitting onto a stainless-steel QC4 stem.
Is this thing going to corrode in fresh-water, in salt-water?
Please help me keep my money so I can buy some more ... beers!

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Stéphane

keith_d

On high pressure pipework I'd never use a brass fitting on stainless. The brass ferrule isn't hard enough to bite into the stainless and just deforms. Replacing the ferrule with a stainless one doesn't work because the fitting just bells out (one guess how I know!!).

On the corrosion front there's bound to be some electrolytic corrosion of the brass in salt water, but I haven't got a handle on how fast it will progress. Perhaps one of the others can comment.

Regards,

Keith.

Stephane

Hi Keith,

That will be for low pressure, around 10 bars.

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Stéphane

JCdesign97

Hi Stephane,

There are a few different charts online that attempt to simplify the compatibility of dissimilar metals, but this one may be the easiest:

Galvanic and Corrosion Capatability Chart - Engineers Edge

In short, for salt water any more than 0.15V difference in two metals' anodic index should be avoided. Not knowing exactly what kind of brass/stainless you're dealing with, but you will likely be Ok. Only the best brass mated to the worst stainless results in a difference of 0.20V - the intermediate combinations are within 0.15V. I would still inspect the fitting frequently for corrosion, though ...

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Cheers,

John Cogan

Stephane

Thank you John, that's a great link I'm going to bookmark.

Swagelok doesn't mention the type of brass they are using, only the stainless steel which is 316.
Il will have a little use of this setup but I will have a look at it every time I will it.

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Stéphane

keith_d

Hi Stephane,

I've not tried this on a low pressure system so I don't know how well brass would seal on stainless. Our low pressure stuff was all in plastic with single ferrule brass fittings and the high pressure systems were all stainless Swagelok fittings.

I'd guess a brass fitting is cheap enough that you could try it out. If it doesn't work just slide the deformed brass ferrule off and install a stainless fitting.

Keith.