The Action of Stray Currents

The data for J and Af/ in Eq. (3-26) change simultaneously with changes in the protection current or by the action of stray currents. Inserting them in Eq. (3-25) gives ... 

Considerations analogous to those used for cathodic protection are also valid for the action of stray currents (Chapter 9), in zones where the cathodic process occurs. 

The corrosion of underground pipes and cables caused by the electrolytic action of stray currents from d.c. electric railway and tramway systems has long been a serious problem. Regulations limiting the maximum potential between tramway rails and neighbouring buried structures and the maximum potential difference between points on the rail systems have been in operation in the UK since 1894 and in Germany since 1910 . 

Electric Drainage means of electric protection of an underground system against the corrosive action of stray currents arising from a d.c. electric traction system employing one or more connections (drainage bonds) made between the system to be protected and the return circuit of the traction system (rail, return current feeder, negative busbar of the sub-stations). 

Wyer, Samuel, Digest of Publications of Bureau of Standards on Electrolysis of Underground Structures caused by the Disintegrating Action of Stray Electric Current from Electric Railways, National Bureau of Standards, Washington, DC, 1918. 

On disbonded areas under the protective coating, corrosion of the metal may occur as a result of the action of corrosion micro-and macrocells and stray currents. In microcells, oxidation and reduction reactions may proceed locally in the area of the defect and the disbonded surface. In the macrocell, the oxidation reaction takes place in the defect and the reduction reaction in another place in the structure, causing cathodic disbonding. Corrosion caused by stray currents is similar to corrosion in the macrocell. The oxidation reaction occurs in such a case in the area of the defect or on the disbonded... 

At low current densities, local-action corrosion supplements stray-current corrosion. At high current densities in some environments, oxygen may be evolved, reducing the amount of metal corroding per faraday of electricity. 

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