I mentioned this morning that I had some question about the copper bonding
across the tower joints, and raised the question that it could create
corrosion. Copper has a .35 volt potential and hot-dip-zinc has a 1.20 volt
potential. Even though the tower is bolted together with bolts, there is a
process called "fretting" that can cause corrosion to occur between the
metals that are otherwise solidly joined. My point was that if corrosion
occurs, it will tend to create a barrier between the joined surfaces, no
matter how much force is used to make contact.
The ASM Handbook on Fatigue and Fracture defines fretting as: "A special
wear process that occurs at the contact area between two materials under
load and subject to minute relative motion by vibration or some other
force."
There is debate among engineers as to how much corrosion would occur at such
a joint and I claim no expertise at all. I just wanted to raise the
question. Even the use of dielectric unions in water heaters (joint between
galvanized steel pipe and copper pipe) is subject to debate. It might be
down on the list - but sometimes you get desperate when looking for cross
modulation. At some point, you might suspect your neighbors false teeth.
Colin K7FM
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