On Thu, 24 Apr 1997 04:20:49 -0500 "Joseph L. Rossmiller"
>I've heard of a similiar failure to this before. I work for the
>Illinois State Police as a radio technician. In the mid 1980s, we had
>the failure of a 400 foot tower at one of the district headquarters in
>the state. Upon investigation, they found the anchor rod for one of
>guy points on this tower had been eaten away until it was no wider
>a pencil lead. It was determined that this rapid corrosion was due to
>the tower anchor being located near a buried gas line. The utility
>company had place a small voltage on the buried pipe to keep it from
>corroding. This voltage protected the gas pipe, but caused any other
>buried metal in the area to corrode at a faster rate. This caused the
>anchor rod to grow thinner and thinner until it finally gave way. We
>now have anodes of magnesium buried at the anchor points of any tower
>located close to a gas line. The magnesium is attached to the anchor
>rod. The idea is that the magnesium will corrode before the anchor
>does, thus saving the anchor rod, and the tower, from failing.
Thanks for taking the time to write. AA0CY at Polyphaser
sent me a report which describes the failure modes of
anchor shafts due to galvanic corrosion. In my case,
there is a layer of "Caliche" about two feet underground that
the anchor rod passes through. Apparently, the difference
in alkalinity between Caliche and the other soil creates a
little corrosion cell battery that eats the rod. I am installing
new anchors this week and will bury a magnesium sacrificial anode
next to each rod, attached to the rod with galvanized wire.
The report also mentions the special problem, such as you experienced,
with petroleum pipelines having impressed protective currents. 73.
Dave Hachadorian, K6LL
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