Regarding corroded bolts in towers. It is advisable to inspect the
hardware every 5 years or so and replace any that is deteriorating.
Stainless steel is superior but may be hard to find or very expensive
for the larger sizes. Shear strength is the more critical parameter in
the tower assembly.
I recently disassembled a tower after about 10 years and found the bolts
near the top quite noticeably more corroded than those near the bottom.
An article about corrosion by Scott Roleson, KC7CJ, appears in the April
1993 QST. It includes a table of the galvanic series showing aluminum
is more anodic than iron or mild steel, which would cause the aluminum
to corrode instead of iron if galvanic corrosion is the problem. I have
no information on the potential of the alloy from which Grade 5 or Grade
8 bolts are made or that of the 6063-T832 alloy from which the Universl
Tower legs are made.
The table of reduction potentials in the McGraw-Hill Encyclopedia of
Science and Technology confirms that aluminum is more anodic than iron,
but says nothing about alloys of steel or the many alloys of aluminum.
Atmospheric corrosion is a more likely cause. An acid producing
material, such as sulfur dioxide, will attack the iron but not the
Keeping the interior of the legs dry will inhibit either cause of
corrosion. As noted in an earlier submittal, the legs of the Universal
Tower sections fit inside the legs of the section below, which may
encourage water entry. The legs are not ventilated, as I recall.
Hence, moisture gets in and does not get out. They need sealant at the
joints, rapid drainage of free water and ventilation to remove water
Most of all, every tower needs periodic inspection to detect
deterioration before it becomes dangerous. An advantage of the aluminum
tower is that it is relatively easy to tilt for service and
experimenting. Of course, be sure to use a correctly designed harness
and pole or A frame for lowering and raising it!
Additional references regarding corrosion are:
Corrosion Basics, L. Van Delinder, ed., from the National Association of
Corrosion Engineers, 1440 South Creek Drive, Houston, Tx 770.
Corrosion Basics - An Introduction, N A C E International, 01-Jan-1984,
ISBN: 0915567024 (May be same as above)
Corrosion Engineers Reference Book by R. S. Treseder (Editor), 1991;
The National Association of Corrosion Engineers.
Basic Corrosion Technology for Scientists & Engineers by Mattson, Einar,
Basic Corrosion Technology for Scientists & Engineers, Second Edition,
by E. Mattsson (I suspect one of these is mis-spelled)
Corrosion : Understanding the Basics 01-Jan-2000, Davis, J. R.
Basic Corrosion & Oxidation 01-Mar-1986; West, John M.
73 de WOØW
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