Nace CP 1, Course Manual

Page: 446 / 535

RP0290-2000
4 NACE International
less permeable, coated, or water-saturated
concrete.
2.3.2 E-log I Test
2.3.2.1 An E-log I test is conducted by application
of cathodic current to the steel, followed by
measurement of the potential response of the
steel. The results are analyzed graphically after
plotting (E) versus the logarithm of the applied
current (log I). The use of the E-log I test
procedure is subject to the practitioner’s
interpretation of the data obtained. Consequently,
this technique is more often used to determine the
initial cathodic protection current requirement.
_______________________________________________________________________
Section 3: Design of Impressed Current Cathodic Protection Systems
3.1 Introduction
3.1.1 This section provides guidelines for designing
impressed current cathodic protection systems that will
satisfy the criteria listed in Section 2 and that will exhibit
maximum reliability over the intended operating life of
the systems.
3.2 Impressed current cathodic protection systems
3.2.1 Impressed current cathodic protection systems
consist of anodes and a source of direct current power.
3.2.2 The following types of impressed current
cathodic protection system anodes are currently
available:
3.2.2.1 Conductive overlays, which consist of
conductive materials dispersed in a binder applied
to the surface of the concrete structure.
3.2.2.2 Carbon-based conductive coatings
applied to the concrete.
3.2.2.3 Thermally sprayed metallic coatings.
3.2.2.4 Conductive materials that are mechan-
ically attached to the concrete structure surface
and overlayed with a cementitious material.
3.2.3 Impressed current anodes can be materials such
as platinum clad or electroplated on niobium or
titanium, conductive polymers, carbon-based or
metallic coatings, mixed-metal-oxide coated titanium,
conductive grouts, and conductive asphaltic concrete.
3.3 Information useful for selecting and designing an
impressed current cathodic protection system includes:
3.3.1 As-built drawings of the concrete structure
3.3.2 Condition survey (in accordance with ACI 201
9
)
3.3.3 Potential survey (in accordance with ASTM C
876)
3.3.4 Chloride analysis of the concrete
3.3.5 Electrical continuity of the embedded metal
3.3.6 Repair and maintenance history
3.3.7 Concrete cover
3.3.8 AC power availability
3.3.9 Concrete resistivity data
NOTE: Some additional information useful for design
is included in Appendix B.
3.4 Parameters for selection of the impressed current
cathodic protection system
3.4.1 The cathodic protection system shall provide
sufficient current to the structure to be protected and
distribute this current so that the selected criterion for
cathodic protection is attained.
3.4.2 The design life of the cathodic protection system
must be commensurate with the required life of the
protected concrete structure.
3.4.3 Electrochemical performance of the anodes
3.4.3.1 Anode materials have different rates of
consumption when discharging a given current
density from the anode surface in a specific
environment. Therefore, for a given current
density, the anode life depends on the
electrochemical properties of the anode material,
volume, surface area, and geometry.
3.4.3.2 The system shall be designed to limit the
maximum sustained current density at the effective
surface contact area between the anode and the
concrete to levels below 108 mA/m
2
(10.0 mA/ft
2
).
Sustained operation at current densities above
these levels may result in deterioration of the
concrete at the anode-concrete interface.