The biggest problem with joining copper to galvanized towers is that when it
rains the copper ions from the copper will wash away the galvanized
material.
You want to avoid any bare copper on a tower anywhere that rain water
running off the copper will come in contact with the tower.
73
Gary K4FMX
> -----Original Message-----
> From: towertalk-bounces@contesting.com [mailto:towertalk-
> bounces@contesting.com] On Behalf Of K4SAV
> Sent: Tuesday, January 15, 2008 12:51 AM
> To: towertalk@contesting.com
> Subject: Re: [TowerTalk] tower leg ground
>
>
> >............BUT it's advisable to separate the
> >bronze clamp from the tower leg (presumably galvanized) by a layer of
> >stainless steel to minimize the galvanic (corrosive) action: .........
> >
> >
> ---------------
> I have asked this question on a couple of other reflectors and got no
> answer, so I will try this one also. Can anyone explain how putting a
> stainless steel shim between a copper wire and a zinc plated tower
> reduces galvanic corrosion of the tower?
>
> Obviously the stainless steel shim will have little corrosion, but I
> don't care about the shim. I need to protect the tower.
>
> When I went thru this mental exercise, here is what I found.
>
> The data in the table below came from the galvanic series for metals
> which you can find on the internet.
>
> In the galvanic series, in flowing sea water, in order from least noble
> to more noble:
> Zinc is -.98 to -1.03
> Aluminum alloys are -.76 to -1.0
> Steel is -0.60 to -0.71
> Copper is -.3 to -.57
> Tin is -.3 to -.33
> Stainless steel -.57 to 0.0 (depending upon the alloy)
>
> You have at least three goals in avoiding galvanic corrosion.
> 1) Maximize the contact area of the least noble metal exposed to the
> electrolyte (water),
> 2) Minimize the potential difference between the metals in contact, and
> 3) Keep the water out.
>
> The least noble metal will corrode. The higher the potential
> difference, the faster it will corrode. If you look at the list above,
> you will see there is no commonly available metal less noble than zinc
> (your tower). In order to minimize corrosion of the tower plating you
> should put something as closely matched to the tower as possible. Seems
> to me that should be aluminum. Another zinc plated shim might work but
> probably would need more frequent replacement because of the copper to
> zinc junction. Still, shims are easy to replace, a tower leg is not.
>
> As far as maximizing the area of the least noble metal (the tower), in
> the case of a shim, the contact area is the same for both metals because
> water may collect within the junction but the whole tower is not going
> to immersed in a liquid. This item may be important within a clamp
> (depending on how it is made) but for a shim there is no difference.
>
> As for keeping the water out, sealing the whole thing in duct seal seems
> to work for me.
>
> If you see any error in this please post any corrections.
>
> Jerry, K4SAV
>
>
>
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