Nace CP 1, Руководство по эксплуатации

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RP0193-2001
NACE International 3
3.3.2 Electrical Isolation
3.3.2.1 Electrical isolation facilities must be
compatible
with electrical grounding
requirements conforming to applicable codes
and safety requirements. If the tank bottom is to
be cathodically protected, the use of alternative
electrical
grounding materials, such as
galvanized steel and galvanic anodes, should be
considered.
3.3.2.2 The designer of a cathodic protection
system should consider the possible need for
electrical isolation of the tank from piping and
other interconnecting structures.
Isolation may
be necessary for effective cathodic protection or
safety considerations.
3.3.2.3 Electrical isolation of interconnecting
piping can be accomplished through the use of
isolating flanges, dielectric bushings or unions, or
other devices
specifically designed for this
purpose. These devices shall be rated for the
proper operating pressure and be compatible
with the products being transported.
3.3.2.4 Polarization cells, lightning arresters,
grounding cells, and other decoupling devices
may be useful in some situations for maintaining
isolation under normal operating conditions and
providing protection for an isolating device during
lightning
strikes, power surges, and other
abnormal situations.
3.3.2.5 Tests to determine tank electrical
characteristics include:
(a) Tank-to-earth resistance tests
(b) Tank-to-grounding system resistance and
potential tests
(c) Tank-to-electrolyte potential tests
(d) Electrical continuity tests for mechanical
joints in interconnecting piping systems
(e) Electrical leakage tests for isolating fittings
installed in interconnecting piping and between
the tanks and safety ground conductors
3.3.3 Cathodic Protection Type, Current Require-
ments, and Anode Configuration
3.3.3.1 Soil resistivity tests should be
performed in sufficient quantity as to aid in
determining the type of cathodic protection
(galvanic or impressed current) required and the
configuration for the anode system.
Figure 1
illustrates the four-pin method of soil resistivity
testing.
3.3.3.2 Resistivities can be determined using
the four-pin method described in ASTM
(1)
G 57,
1
with pin spacings corresponding to depths of at
least that expected for the anode system, or by
using an equivalent testing method (in very dry
environments,
electromagnetic conductivity
testing may be used to measure resistivities).
2
The resistivity measurements should be obtained
in sufficient detail to identify possible variations
with respect to depth and location. As a general
guideline, resistivity data should be obtained at a
minimum of two locations per tank.
Figure 1: Soil Resistivity Testing (Four-Pin Method)
Note: a = Depth of interest for the soil resistivity measurement.
___________________________
(1)
American Society for Testing and Materials (ASTM), 100 Barr Harbor Dr., West Conshohocken, P.A. 19428.
a a a