Nace CP 1 Course Manual Download Page 273

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RP0169-2002

NACE International

Cathodic Protection: A technique to reduce the corrosion
of a metal surface by making that surface the cathode of an
electrochemical cell.

Coating: A liquid, liquefiable, or mastic composition that,
after application to a surface, is converted into a solid
protective, decorative, or functional adherent film.

Coating Disbondment: The loss of adhesion between a
coating and the pipe surface.

Conductor:

A material suitable for carrying an electric

current. It may be bare or insulated.

Continuity Bond:

A connection, usually metallic, that

provides electrical continuity between structures that can
conduct electricity.

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, or freely corroding potential).

Corrosion Rate: The rate at which corrosion proceeds.

Criterion: 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.

Diode:

A bipolar semiconducting device having a low

resistance in one direction and a high resistance in the
other.

Distributed-Anode Impressed Current System:

impressed current anode configuration in which the anodes
are “distributed” along the structure at relatively close
intervals such that the structure is within each anode’s
voltage gradient.

This anode configuration causes the

electrolyte around the structure to become positive with
respect to remte earth.

Electrical Isolation:

The condition of being electrically

separated from other metallic structures or the environment.

Electrical Survey: Any technique that involves coordinated
electrical measurements taken to provide a basis for
deduction concerning a particular electrochemical condition
relating to corrosion or corrosion control.

Electrode: A conductor used to establish contact with an
electrolyte and through which current is transferred to or
from an electrolyte.

Electroosmotic Effect:

Passage of a charged particle

through a membrane under the influence of a voltage. Soil
or coatings may act as the membrane.

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 adjacent to and in
contact with a buried or submerged metallic piping system,
including the moisture and other chemicals contained
therein.

Foreign Structure:

Any metallic structure that is not

intended as a part of a system under cathodic protection.

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.

Galvanic Series:

A list of metals and alloys arranged

according

their

corrosion

potentials

given

environment.

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.)

In-Line Inspection:

The inspection of a steel pipeline

using an electronic instrument or tool that travels along the
interior of the pipeline.

Insulating Coating System:

All components of the

protective coating, the sum of which provides effective
electrical isolation of the coated structure.

Interference:

Any electrical disturbance on a metallic

structure as a result of stray current.

Interference Bond:

A metallic connection designed to

control electrical current interchange between metallic
systems.

IR Drop: The voltage across a resistance in accordance
with Ohm’s Law.

Isolation: See

Electrical Isolation.

Line Current: The direct current flowing on a pipeline.

Long-Line Corrosion Activity: Current through the earth
between an anodic and a cathodic area that returns along
an underground metallic structure.

Mixed Potential: A potential resulting from two or more
electrochemical reactions occurring simultaneously on one
metal surface.

Pipe-to-Electrolyte Potential:

The potential difference

between the pipe metallic surface and electrolyte that is
measured with reference to an electrode in contact with the
electrolyte.