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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