Means for Reducing Stray-Current Corrosion

Intentional Anodes and Cathodic Protection. If a bond from if to C in Fig. 12.1 is not feasible, an intentional anode of scrap iron may be buried in the direction of the rails and attached by a copper conductor to point B. Stray currents then cause corrosion only of the intentional anode, which is easily replaced at low cost. If a source of dc current is inserted between the intentional anode and the pipe such that current flows in the soil in a direction opposite to that of the stray current, the arrangement is equivalent to cathodically protecting the pipe. Cathodic protection is installed whenever the intentional anode is not sufficient to overcome all corrosion caused by stray currents. 

Fitzgerald III, Stray current analysis, in Uhlig s Corrosion Handbook, 2nd edition, R. W. Revie, editor, Wiley, New York, 2000, pp. 1079-1087. 

Michael J. Szeliga, Stray current corrosion, in Peabody s Control of Pipeline Corrosion, 2nd edition, R. L. Bianchetti, editor, NACE International, Houston, Texas, 2001, pp. 211-236. 

Szeliga, editor. Stray Current Corrosion The Past, Present and Future of Rail Transit Systems, NACE International, Houston, TX, 1994. 

a) A direct current of 10 A enters and leaves a steel water pipe of 2-in. outside diameter and 0.25-in. wall thickness, containing water with resistivity of 10 Q-cm. Calculate the current carried by the steel and that carried by the water. Assume that the resistivity of the pipe equals lO Q-cm. 

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