By coating a guy anchor rod with an protective material such as tar, one
is attempting to prevent galvanic corrosion by removing one of the
necessary components, the electrolyte (water) in contact with the metal
of the guy rod. In theory, this sounds like a reasonable approach. as
long as the coating is complete and intact, this will work to prevent
galvanic corrosion. However, if there is any small void in the coating,
water can again contact the guy rod. In this case, there is an area
concentration effect at the void, which actually increases the rate of
corrosion at the void. All the current is concentrated in this small
area. In the case of a zinc coated (galvanized) guy rod, the zinc
coating will be corroded more rapidly because of the concentration of
current at this location. Once the zinc is gone, the steel will also be
corroded.
A tar or other waterproof insulated coating may increase the life of guy
rods, but must be complete in it's covering of the guy rod. If not, it
could be worse than nothing at all. The best way to prevent galvanic
corrosion is by preventing the flow of current in the first place, by
providing a sacrificial anode that changes the potential of the guy rod
and diverts the current to the sacrificial anode.
-Tony, K1KP
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