Nace CP 1, Руководство по эксплуатации

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RP0285-2002
8 NACE International
5.2 Criteria for Steel Structures
5.2.1 Corrosion control can be achieved at various
levels of cathodic polarization depending on the
environmental condition. However, in the absence of
data
that demonstrate adequate CP has been
achieved, one or more of the following shall apply:
5.2.1.1 A negative (cathodic) potential of at least
850 mV with the CP applied.
This potential is
measured with respect to a CSE contacting the
electrolyte. Voltage drops other than those across
the
structure/electrolyte boundary must be
considered for valid interpretation of this voltage
measurement.
5.2.1.2 A negative polarized potential (see
definition in Section 2) of at least 850 mV relative
to a CSE.
5.2.1.3 A minimum of 100 mV of cathodic
polarization.
The formation or decay of
polarization can be used to satisfy this criterion.
5.3 Alternative Reference Electrodes
5.3.1 Other standard reference electrodes may be
substituted for the CSEs.
However, their voltage
measurements must be converted to the CSE
equivalents as in Table 1:
Table 1: Conversion of Voltage Measurements to
CSE Equivalents
Equivalent
to -0.85 V
CSE
Correction
Calomel -0.776 V Add -0.074 V
Silver/Silver Chloride -0.78 V Add -0.07 V
Zinc +0.25 V Add -1.10 V
5.4 Special Considerations
5.4.1 Special cases, such as those involving stray
currents and stray electrical gradients, that require the
use of criteria different from those listed above, may
exist. Measurements for current loss and gain on the
structure and current tracing in the electrolyte have
been useful in such cases.
5.4.2 Abnormal conditions in which protection is
ineffective or only partially effective sometimes exist.
Such conditions may include elevated temperatures,
disbonded coatings, shielding, bacterial attack, and
unusual contaminants in the electrolyte.
5.4.3 When structures that have dissimilar metals are
protected, a negative structure-to-soil potential voltage
equal to that for protection of the most anodic metal
should be maintained.
______________________________________________________________________
Section 6: Cathodic Protection Design
6.1 General
6.1.1 Information regarding the design of impressed
current and galvanic anode systems can be found in
NACE Standard RP0169
15
and in this standard.
Information useful in the design includes:
(a) site plan and system layout;
(b) pipe, fittings, and other appurtenances;
(c) pumps and power supplies;
(d) existing and proposed CP systems;
(e) nearby buried metallic structures;
(f)
site accessibility;
(g) soil conditions (e.g., resistivity, chemical
composition, aeration, and moisture);
(h) electrical isolation;
(i)
coating integrity;
(j) elevated temperatures;
(k) shielding;
(l)
treated tank backfill material;
(m) dissimilar metals and concrete/metal interfaces;
and
(n) complexing agents.
6.2 Galvanic Systems
6.2.1 This subsection describes the factors that should
be considered in the design of external corrosion
protection for existing UST systems using galvanic
anode CP.
6.2.2 Galvanic protection systems can be applied to
tank systems when the metallic surface area exposed
to the soil is minimized through the application of a
dielectric coating or when the surface area is small due
to tank size. When current requirements are high, the
use of impressed current CP should be considered to
minimize the cost of the protection system (see
Paragraph 6.3).
6.2.3 Electrical Isolation
6.2.3.1 Electrical isolation methods can be used
to isolate the primary UST from other electrically
grounded systems.
6.2.3.2 All uncoated associated piping can be
electrically isolated from the tank.
Submersible
pumps can be isolated from the metallic piping