Nace CP 1, Course Manual

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RP0388-2001
NACE International 1
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Section 1: General
1.1 This standard presents recommended practices for
applying impressed current cathodic protection to the
internal submerged surfaces of steel tanks used for the
storage of natural waters. These tanks may be provided
with an interior barrier coating. It is not intended for use with
metallic coatings or linings, such as zinc or aluminum.
1.2 It is recognized that galvanic anode systems can, at
times, be used for cathodic protection of the internal
surfaces of water storage tanks; however, this standard
addresses only impressed current systems.
NOTE: Information regarding galvanic cathodic protection of
water storage tanks may be found in RP0196,”Galvanic
Anode Cathodic Protection of Internal Submerged Surfaces
of Steel Water Storage Tanks.”
1
1.3 Natural waters, as used in this standard, include both
potable and nonpotable fresh waters associated with water
supply systems and fire protection.
1.4 The ground level and elevated storage tanks
considered in this standard are of welded, bolted, or riveted
steel construction and include many shapes and sizes.
1.5 Cathodic protection, as described in this standard, may
be used alone to control corrosion of submerged steel
surfaces or used as a complement to the protection
afforded by protective coatings. Cathodic protection cannot
protect surfaces that are not submerged. These surfaces
must be protected by coatings alone. Cathodic protection
does not reverse structural damage already caused by
corrosion.
1.6 Cathodic protection may be installed to control
corrosion in both newly constructed and existing tanks.
When cathodic protection is used on existing tanks, it is not
necessary to prepare the surfaces to be protected;
however, it may be necessary to drain the tank during
installation.
1.7 It is recognized that the tanks under consideration are
often associated with potable water and fire protection
systems, which may be subject to public health and safety
regulations. This standard should not infringe upon those
regulations.
Proper disinfection of the tanks may be
required after installation. Any applicable regulations such
as those from the U.S. Environmental Protection Agency
(EPA)
(1)
and ANSI
(2)
/NSF
(3)
-612 should be checked. In the
United States, all materials in contact with potable water or
exposed to the interior of potable water tanks must be
classified in accordance with ANSI/NSF-61.
1.8 The provisions of this standard should be applied
under the direction of a competent corrosion engineer. The
term “corrosion engineer,” as used in this standard, refers to
a person who by reason of knowledge of the physical
sciences
and the principles of engineering and
mathematics, as acquired by professional education and
related
practical experience, is qualified to practice
corrosion control and cathodic protection for water storage
tanks.
Such persons may be registered professional
engineers or persons certified by NACE International as
Cathodic Protection or Corrosion Specialists, if their
professional
activities include suitable experience in
corrosion control and cathodic protection.
1.9 This standard may not be applicable in all situations.
The responsible corrosion engineer may consider alternate
corrosion control methods.
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Section 2: Definitions
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.
Calcareous Coating: A layer consisting of calcium
carbonate and other salts deposited on the surface. When
the surface is cathodically polarized as in cathodic
protection, this layer is the result of the increased pH
adjacent to the protected surface.
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 Protection: A technique to reduce the corrosion
of a metal surface by making that surface the cathode of an
electrochemical cell.
__________________________________________
(1)
U.S. Environmental Protection Agency (EPA), 401 M Street SW, Washington, DC 20460.
(2)
American National Standards Institute (ANSI), 11 W 42
nd
St, New York, NY 10036.
(3)
NSF International, P.O. Box 130140, Ann Arbor, MI 48113-0140.