Electrolysis can occur at steel pipe which is supported by structural steel depending upon the difference between its ground potential and the ground potential of the building itself.  This is a relatively rare event which typically occurs hidden from view at the contact surface of only one metal side.  A different but more common issue occurs when copper pipe is support by a steel pipe hanger.

It is most common for pipe which is wet for any reason, given that the surface moisture then becomes an electrolyte favoring the movement of electrons.  Steel to steel electrolysis has been identified in the immediate vicinity of the pipe hangers of fire sprinkler systems and where condenser water lines are supported by floor mounted pedestals.  Improper grounding is a common source of the problem, and extremely difficult to diagnose.  Computer room power distribution units, PDUs, have been found to shed voltage to ground – thereby producing such an impact.

When failure occurs, its location at the contact point between pipe and support adds further difficulty in effecting emergency repairs.

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