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TM0101-2001
Electrode: A conductor used to establish contact with an
electrolyte and through which current is transferred to or
from an electrolyte.
Electrode Potential: The potential of an electrode in an
electrolyte as measured against a reference electrode.
(The electrode potential does not include any resistance
losses in potential in either the electrolyte or the external
circuit. It represents the reversible work to move a unit
charge from the electrode surface through the electrolyte to
the reference electrode.)
Electrolyte:
A chemical substance containing ions that
migrate in an electric field. (For the purpose of this test
method, electrolyte refers to the soil or liquid, including
contained moisture and other chemicals, next to and in
contact with a buried or submerged metallic tank system.)
Foreign Structure:
Any metallic structure that is not
intended as part of a system under cathodic protection.
Free Corrosion Potential: See Corrosion Potential.
Galvanic Anode:
A metal that provides sacrificial
protection to another metal that is more noble when
electrically coupled in an electrolyte. This type of anode is
the electron source in one type of cathodic protection.
Groundbed:
One or more anodes installed below the
earth's surface for the purpose of supplying cathodic
protection.
Holiday:
A discontinuity in a protective coating that
exposes unprotected surface to the environment.
Impressed Current:
An electric current supplied by a
device employing a power source that is external to the
electrode system. (An example is direct current for cathodic
protection.)
"Instant-Off" Potential:
electrolyte potential made without perceptible delay
following the interruption of cathodic protection.
Interference:
Any electrical disturbance on a metallic
structure as a result of stray current.
Isolation: See Electrical Isolation .
"Off" or "On": A condition whereby cathodic protection
current is either turned off or on.
Polarization: The change from the open-circuit potential as
a result of current across the electrode/electrolyte interface.
Polarized
Potential:
structure/electrolyte interface that is the sum of the
corrosion potential and the cathodic polarization.
Potential Gradient: A change in the potential with respect
to distance, expressed in mV per unit of distance.
2
A measurement of a tank-to-
The
potential
across
Potentiometer:
electromotive force by comparison with a known potential
difference.
Protection Potential: A measured potential meeting the
requirements of a cathodic protection criterion.
Reference Electrode:
potential
is
measurement, which is used for measuring the relative
potentials of other electrodes.
Remote Earth: A location of the earth far enough from the
affected
structure
associated with currents entering the earth from the affected
structure are insignificant.
Resistance to Electrolyte: The resistance of a structure to
the surrounding electrolyte.
Reverse-Current Switch:
reversal of direct current through a metallic conductor.
Shielding: Preventing or diverting the cathodic protection
current from its intended path to the structure to be
protected.
Sound Engineering Practices: Reasoning exhibited or
based on thorough knowledge and experience, logically
valid, and having technically correct premises that
demonstrate good judgment or sense in the application of
science.
Stray Current:
intended circuit.
Structure: Tanks, piping, and associated equipment that
may/may not be under the influence of a cathodic protection
system.
Tank System: The equipment and facility constructed,
maintained, or used for underground storage of products
including
tanks, piping, pumps, and appurtenances
associated with filling, storage, and dispensing of the stored
products.
Tank-to-Electrolyte Potential:
between the tank metallic surface and the electrolyte that is
measured with reference to an electrode in contact with the
electrolyte. This measurement is commonly called tank-to-
soil (T/S).
Tank-to-Soil
Potential .
the
Telluric Current: A current flowing through the ground due
to natural causes, such as the earth's magnetic field or
auroral activity.
A device for the measurement of an
An electrode whose open-circuit
constant
under
similar
that
the
soil
potential
A device that prevents the
Current through paths other than the
The potential difference
Potential:
See
Tank-to-Electrolyte
NACE International
conditions
of
gradients
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