impressed current - direct current supplied by a power source external to the electrode system.
*insulating coating system - all components that comprise the protective coating, the sum of which provides
effective electrical insulation of the coated structure.
*interference bond - metallic connection designed to control electrical interchange between metallic systems.
ion - electrically charged atom or molecule.
*IR drop - voltage across a resistance according to Ohm's Law.
*line current - direct current flowing on a pipeline.
local action - corrosion caused by local cells on a metal surface.
mill scale - heavy oxide layer formed during hot fabrication or heat-treatment of metals. Applied chiefly to
iron and steel.
Molality - concentration of a solution expressed as the number of gram molecules of the dissolved substance
per 1000 grams of solvent.
PH - measure of hydrogen ion activity defined by pH log 10 (1/aH+), where aH+ = hydrogen ion activity =
molal concentration of hydrogen ions multiplied by ion activity coefficient (a = 1 for simplified
polarization - deviation from the open circuit potential of an electrode resulting from the passage of current.
*reference electrode - device for which the open circuit potential is constant under similar conditions of
* reverse-current switch - device that prevents the reversal of direct current through a metallic conductor.
*stray current - current flowing through paths other than the intended circuit.
*stray current corrosion - corrosion resulting from direct current flow through paths other than the intended
*structure-to-electrolyte voltage (also structure-to-soil potential or pipe-to-soil potential) - voltage difference
between a buried metallic structure and the electrolyte, measured with a reference electrode in contact
with the electrolyte.
*structure-to-structure voltage (also structure-to-structure potential) - difference in voltage between metallic
structures in a common electrolyte.
*voltage - electromotive force, or a difference in electrode potentials, expressed in volts.