Stray current corrosion welding generators

Stray-current Corrosion. Stray currents in the past have resulted from DC-powered trolled systems, which have become obsolete. An electric welding machine on board a ship with a grounded DC line located on shore will cause accelerated attack of the ship s hull as the stray currents generated at the welding electrodes pass out of the ship s hull through the water back to the shore. Houses in close proximity can dramatically corrode at the waterline. The pipes in one house can be completely corroded, while those in the neighboring house may be intact. 

Electrical leakage currents, cathodic corrosion protection In electrically conductive equipment stray or leakage currents can flow as reverse currents to electric generators (in particular in the area of electric trains and major welding equipment), if, for example, conductors like rails, pipes and cable liners laid on or in the earth reduce the resistance of the reverse path, due to earth contact in faulty electrical equipment, due to induction (e.g. in the vicinity of electrical equipment with high currents or high frequencies), due to lightning. Potential equalization, respectively additional electrical override required... 

Where stray currents from a man-made source of direct current are a potential problem, metallically bonding the structure of concern to the source of the dc is often used to mitigate the corrosion that would otherwise occur. This is a common method of control where pipelines are subject to the adverse effects from stray currents generated by light rail transit systems, d-c welding machines, and impressed current cathodic protection systems installed on other nearby structures. 

Stray currents encountered in practice are usually dc (for example, fiom a welding generator) but can also be ac. For most metals, ac corrosion is negligible, but with aluminum it can be appreciable (Ref 33). Below a critical small ac current density, no corrosion of alumi-... 

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