TM0497-2002
NACE International 1
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Section 1: General
1.1 This standard provides testing procedures to comply
with the requirements of a criterion at a test site on a buried
or submerged steel, cast iron, copper, or aluminum pipeline.
1.2 The provisions of this standard shall be applied by
personnel who have acquired by education and related
practical experience the principles of cathodic protection of
buried and submerged metallic piping systems.
1.3 Special conditions in which a given test technique is
ineffective or only partially effective sometimes exist. Such
conditions may include elevated temperatures, disbonded
dielectric or thermally insulating coatings, shielding,
bacterial attack, and unusual contaminants in the
electrolyte. Deviation from this standard may be warranted
in specific situations. In such situations corrosion control
personnel should be able to demonstrate that adequate
cathodic protection has been achieved.
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Section 2: Definitions
(1)
Anode: The electrode of an electrochemical cell at which
oxidation occurs. Electrons flow away from the anode in the
external circuit. Corrosion usually occurs and metal ions
enter the solution at the anode.
Cable: A bound or sheathed group of insulated conductors.
Cathode: The electrode of an electrochemical cell at which
reduction is the principal reaction. Electrons flow toward the
cathode in the external circuit.
Cathodic Disbondment: The destruction of adhesion
between a coating and the coated surface caused by
products of a cathodic reaction.
Cathodic Polarization: The change of electrode potential
in the active (negative) direction caused by current across
the electrode/electrolyte interface. See also Polarization.
Cathodic Protection: A technique to reduce the corrosion
of a metal surface by making that surface the cathode of an
electrochemical cell.
Cathodic Protection Coupon: A metal sample
representing the pipeline at the test site, used for cathodic
protection testing, and having a chemical composition
approximating that of the pipe. The coupon size should be
small to avoid excessive current drain on the cathodic
protection system.
Coating: A liquid, liquefiable, or mastic composition that,
after application to a surface, is converted into a solid
protective, decorative, or functional adherent film.
Conductor: A bare or insulated material suitable for
carrying electric current.
Corrosion: The deterioration of a material, usually a metal,
that results from a reaction with its environment.
Corrosion Potential (E
corr
): The potential of a corroding
surface in an electrolyte relative to a reference electrode
under open-circuit conditions (also known as rest potential,
open-circuit potential,orfreely corroding potential).
Criterion: A standard for assessment of the effectiveness
of a cathodic protection system.
Current Density: The current to or from a unit area of an
electrode surface.
Electrical Isolation: The condition of being electrically
separated from other metallic structures or the environment.
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
standard, electrolyte refers to the soil or liquid, including
contained moisture and other chemicals, next to and in
contact with a buried or submerged metallic piping system.)
Foreign Structure: Any metallic structure that is not
intended as part of a system under cathodic protection.
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(1)
Definitions in this section reflect common usage among practicing corrosion control personnel and apply specifically to how terms are used
in this standard. As much as possible, these definitions are in accord with those in the “NACE Glossary of Corrosion-Related Terms”
(Houston, TX: NACE).
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