Nace CP 1, Course Manual

Page: 272 / 535

RP0169-2002
NACE International 1
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Section 1: General
1.1 This standard presents acknowledged practices for the
control of external corrosion on buried or submerged steel,
cast iron, ductile iron, copper, and aluminum piping
systems.
1.2 This standard is intended to serve as a guide for
establishing minimum requirements for control of external
corrosion on the following systems:
1.2.1 New piping systems: Corrosion control by a
coating supplemented with cathodic protection, or by
some other proven method, should be provided in the
initial design and maintained during the service life of
the piping system, unless investigations indicate that
corrosion control is not required. Consideration should
be given to the construction of pipelines in a manner
that facilitates the use of in-line inspection tools.
1.2.2 Existing coated piping systems: Cathodic
protection should be provided and maintained, unless
investigations indicate that cathodic protection is not
required.
1.2.3 Existing bare piping systems: Studies should be
made to determine the extent and rate of corrosion on
existing bare piping systems.
When these studies
indicate that corrosion will affect the safe or economic
operation of the system, adequate corrosion control
measures shall be taken.
1.3 The provisions of this standard should be applied
under the direction of competent persons who, by reason of
knowledge of the physical sciences and the principles of
engineering and mathematics, acquired by education and
related practical experience, are qualified to engage in the
practice of corrosion control on buried or submerged
metallic piping systems. Such persons may be registered
professional engineers or persons recognized as corrosion
specialists or cathodic protection specialists by NACE if
their professional activities include suitable experience in
external corrosion control of buried or submerged metallic
piping systems.
1.4 Special conditions in which cathodic protection is
ineffective or only partially effective sometimes exist. Such
conditions may include elevated temperatures, disbonded
coatings, thermal insulating coatings, shielding, bacterial
attack, and unusual contaminants in the electrolyte.
Deviation from this standard may be warranted in specific
situations provided that corrosion control personnel in
responsible charge are able to demonstrate that the
objectives expressed in this standard have been achieved.
1.5 This standard does not include corrosion control
methods based on chemical control of the environment, on
the use of electrically conductive coatings, or on control of
internal corrosion.
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Section 2: Definitions
(1)
Amphoteric Metal: A metal that is susceptible to corrosion
in both acid and alkaline environments.
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 solution at the anode.
Anodic Polarization: The change of the electrode
potential in the noble (positive) direction caused by current
across the electrode/electrolyte interface.
Beta Curve: A plot of dynamic (fluctuating) interference
current or related proportional voltage (ordinate) versus
values of corresponding structure-to-soil potentials at a
selected location on the affected structure (abscissa) (see
Appendix A).
Cable: One conductor or multiple conductors insulated
from one another.
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.
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(1)
Definitions in this section reflect common usage among practicing corrosion control personnel and apply specifically to how the terms are
used in this standard. In many cases, in the interests of brevity and practical usefulness, the scientific definitons are abbreviated or
paraphrased.