Dissimilar Metals [RE-wrenches]

Jeffrey Wolfe, Global Resources global at sover.net
Thu Oct 11 15:03:21 PDT 2001


The problem is called galvanic corrosion, and is basically a result of the 
physics effect that dissimilar metals in contact create an electrical 
current (kind of like a battery...) and one will be corroded. It is VERY 
difficult to predict what will happen in any given case. There are books 
with "galvanic potentials" listed for different metal combinations, but the 
situation in the field, whether its in piping systems or in structural 
connections, is very difficult to absolutely predict. Thus, the best action 
is to keep metals separated, especially "active" metals like copper, 
aluminum, steel, and zinc.

So the basic results are that either nothing will happen (the copper plug 
stays in the threaded end of the galvanized pipe for 40 years) or that 
failure occurs quickly (the copper plug blows out of the fitting due to 
corroded threads in a year or two). I've heard of "identical" situations 
with widely differing results. So, in this case, separation is good.

Jeff

On Thursday, October 11, 2001 3:09 PM, Baran Galocy 
[SMTP:livewire at c-zone.net] wrote:
> Wrenches,
>
> Would someone be so kind as to educate me on why it is not advisable to 
use
> hot-dipped zinc galvanized products in direct contact with aluminum. 
 I've
> been told it is a no-no, but I've not been told the long-term results of
> such an action.
>
> Thanks - Baran Galocy DBA HelioElectric
>
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