Galvanized steel transmission tower footings in direct contact with most aerated native soils in southeastern Michigan have practically indefinite lives if not connected to electropositive structures such as switching station ground masses. The galvanizing in these soils forms over its surface a dense, superficial, protective coating. The resulting electropotential of the footing may be as much as 0.3 volt more electropositive than a fresh zinc surface. Mild corrosion occurs at and below the water table on towers having part of their footings in “permanent” moisture. Serious corrosion has been found only on footings that have been metallically connected to electropositive structures or that have been in direct contact with cinders and other coal products.
The condition of tower footings may be predicted with fair accuracy by means of electropotential measurements. The measured potentials vary with seasonal change, being lowest after prolonged dry weather.
Magnesium anodes furnish adequate protection for galvanized tower footings if protection is applied before the corroded area becomes too extensive. Need for an electropotential survey at approximately 10-year intervals is indicated. 7.7
