Nace CP 1, Руководство по эксплуатации

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RP0193-2001
NACE International 1
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Section 1: General
1.1 This standard presents guidelines for the design,
installation, and maintenance of cathodic protection for the
exterior bottoms of on-grade carbon steel storage tanks.
Cathodic protection can be installed to protect new or
existing tanks, but cannot protect carbon steel surfaces that
are not in contact with an electrolyte.
1.2 This standard is applicable to welded, bolted, and
riveted carbon steel tanks that are either field- or shop-
fabricated.
1.3 It is understood in this standard that cathodic protection
may be used alone or in conjunction with protective
coatings.
1.4 All cathodic protection systems should be installed with
the intent of conducting uninterrupted, safe operations.
When cathodic protection is applied, it should be operated
continuously to maintain polarization.
1.5 The criteria for cathodic protection are based on
current industry standards.
1.6 Corrosion control must be a consideration during the
design of on-grade carbon steel storage tanks.
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Section 2: Definitions
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 the solution at the anode.
Backfill: Material placed in a hole to fill the space around
the anodes, vent pipe, and buried components of a cathodic
protection system.
Cathode: The electrode of an electrochemical cell at which
reduction is the principal reaction. Electrons flow toward the
cathode in the external circuit.
Cathodic Protection (CP): A technique to reduce the
corrosion of a metal surface by making that surface the
cathode of an electrochemical cell.
Cell: See Electrochemical Cell.
Current Density: The current to or from a unit area of an
electrode surface.
Deep Groundbed: One or more anodes installed vertically
at a nominal depth of 15 m (50 ft) or more below the earth’s
surface in a drilled hole for the purpose of supplying
cathodic protection.
Differential Aeration Cell: An electrochemical cell, the
electromotive force of which is due to a difference in air
(oxygen) concentration at one electrode as compared with
that at another electrode of the same material.
Electrical Isolation: The condition of being electrically
separated from other metallic structures or the environment.
Electrochemical Cell: A system consisting of an anode
and a cathode immersed in an electrolyte so as to create an
electrical circuit. The anode and cathode may be different
metals or dissimilar areas on the same metal surface.
Electrolyte: A chemical substance containing ions that
migrate in an electric field.
External Circuit: The wires, connectors, measuring
devices, current sources, etc., that are used to bring about
or measure the desired electrical conditions within an
electrochemical cell.
It is this portion of the cell through
which electrons travel.
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.
Groundbed: One or more anodes installed below the
earth’s surface for the purpose of supplying cathodic
protection. For the purposes of this standard, a groundbed
is defined as a single anode or group of anodes installed in
the electrolyte for the purposes of discharging direct current
to the protected structure.
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).
On-Grade Storage Tank: A tank constructed on sand or
earthen pads, concrete ringwalls, or concrete pads.