Actually, Bill, its a phenomenon called electrolysis that caused the steel
bolts to appear to be "rotten in the middle", as you say. It is caused not
by the steel, the aluminum, or the rain, but a combination of the three.
When two dissimilar metals, such as aluminum and steel come together at a
junction, a small electrical voltage is created and over time one material,
in this case the steel of the bolt, becomes the sacrificial anode, while the
aluminum tower becomes the cathode. When you add moisture to the mix, from
rain and humidity, the electrolysis is accelerated and the sacrificial anode
gets eaten away at the junction area, while leaving the bolt head and
exposed surface of the nut appearing fine. The area of the bolt in contact
with the aluminum tower was rapidly corroding away but was hidden from
sight. You could actually take a millivolt meter and measure the voltage
created by these junctions, measuring from the head of the bolt to the tower
leg. The "electrolyte" created from these junctions of dissimilar metals is
acidic, which further accelerates the corrosion of the sacrificial elements,
in this case, the bolt shanks.
Steel bolts, being plain, cadmium plated, galvanized (zinc coated), or
whatever is a poor choice of fasteners against an aluminum surface but the
degradation could be slowed significantly by the utilization of a anti-seize
type of coating, such as penetrox or noalux on the bolts or better yet,
using this type of coating on stainless steel hardware, which also prevents
the stainless steel hardware from galling upon assembly and disassembly.
Stainless Steel fasteners should never be installed dry as galling will
occur guaranteed! When coated with an anti-seize paste stainless steel
hardware for fastening all antenna and towers applications will last a
lifetime.
The above facts can be verified in any primer books on metallurgy. The
minute voltages created by dissimilar metal junctions is the principle of
which thermocouples operate.
73, -=Rog-K9RB=-
----- Original Message -----
From: Bill Steffey <ny9h@arrl.net>
To: <TOWERTALK@contesting.com>
Sent: Wednesday, February 06, 2002 3:58 PM
Subject: Re: [TowerTalk] Universal Freestanding Tower
>
> Five months ago I took down a 40 foot heights tower. It had been up since
> the 60s. Larry went SK qrt. We lowered the kt34 and the 2 meter beams,
> then we just tilted it over !!! The Big Aluminum ADVANTAGE!
> While taking out the bolts, they twisted apart. We discovered they were
> rotten in the middle, disintegrated ! I mention this again after just
> seeing a similar post.
> So when I got home I checked the bolts in my 50 ft Universal Tower......
> Rotten in the middle also. After 20 years or so, the bolts had rotted just
> like Larry's had. Hidden within the tubular section, the rain and crud did
it.
> I write this to remind YOU. Check your old hardware.
> bill
>
>
> ________________________________________________________________________
> Where do you get ICE bandpass filters & beverage matching boxes? The
> same place that pays for the hosting of this list: The eHam Store.
> Order online at http://store.eham.net.
> -----------------------------------------------------------------------
>
> -----
> FAQ on WWW: http://www.contesting.com/FAQ/towertalk
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>
>
________________________________________________________________________
Where do you get ICE bandpass filters & beverage matching boxes? The
same place that pays for the hosting of this list: The eHam Store.
Order online at http://store.eham.net.
-----------------------------------------------------------------------
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