The problems presented in attempting to provide cathodic protection for existing bare structures are much more difficult than those on coated structures. The major difficulty arises because of the much greater magnitude of current required. On a well-coated underground storage tank, it is not unusual to be able to provide protection with one or two galvanic anodes while it is not uncommon to have several rectifier units in a large complex tank farm.
Because of the much greater current requirement, interference problems can be created on other nearby underground utility systems. On systems using sacrificial anodes, the number of anodes required is similarly much greater on bare structures than on coated.
We have seen one example where one anode was sufficient to provide protection for a coated 10,000 gallon tank. On the other hand, a poorly coated or bare 10,000 gallon tank can require in excess of 1.5 amps to achieve effective corrosion control. For one bare UST piping system in Ohio consisting of 1,200 feet of 3" diameter pipe, 2 amperes of current was required for full corrosion control. If magnesium anodes were selected for use, over 60 anodes would be required.
Source:www.bushman.cc/pdf/corrosion_theory.pdf
Because of the much greater current requirement, interference problems can be created on other nearby underground utility systems. On systems using sacrificial anodes, the number of anodes required is similarly much greater on bare structures than on coated.
We have seen one example where one anode was sufficient to provide protection for a coated 10,000 gallon tank. On the other hand, a poorly coated or bare 10,000 gallon tank can require in excess of 1.5 amps to achieve effective corrosion control. For one bare UST piping system in Ohio consisting of 1,200 feet of 3" diameter pipe, 2 amperes of current was required for full corrosion control. If magnesium anodes were selected for use, over 60 anodes would be required.
Source:www.bushman.cc/pdf/corrosion_theory.pdf
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