Separate current drainage systems or special blocking circuits are required for heterogeneous structures which are closely located to each other. This precaution is essential for the elimination of metallic short-circuit paths between the structures, liable to cause dangerous local corrosion currents when the protective circuit is disturbed.
Galvanic anodes used for the protection of parallel pipe and cable lines must therefore be grouped separately. Applied current generators are equipped with rectifier elements to block circulating currents between the components of the plant protected. AC circuits are fitted with separate rectifier units for each section.
Concentric steel ducting is best completely insulated from the metal body contained in it. Where this is not possible as in the case of bore-hole wells, two separate drainage circuits are required with provision for keeping the potentials of the casing and the inner body on the same level.
A further investigation will be published as soon as experience has been gained with the methods suggested.
