Nace CP 1, Course Manual

Page: 371 / 535

RP0388-2001
NACE International 5
4.4.2 Impressed Current Anode Materials
4.4.2.1 In designs in which only one year of
anode life is required, anode materials such as
aluminum alloy UNS
(4)
A92017 may be used.
4.4.2.2 Impressed current anodes whose service
life must exceed one year should be composed of
more permanent material, such as mixed metal
oxide-coated
titanium, platinized titanium or
niobium, or high-silicon cast iron. The material
should be selected for its suitability in the service
environment. Anode materials used in nonpotable
water service may be different from those used in
potable water.
4.4.2.3 Impressed current anodes, as well as all
cathodic protection equipment to be installed in
the tank, shall be chosen such that there is no
contamination
of potable water. Refer to
ANSI/NSF-61
2
requirements.
4.4.3 Impressed Current Anode Life
The impressed current anode life depends on the
consumption rate of the material selected, the weight of
that material, and the current output of the system. In
the case of mixed-metal oxide coated anodes, the life
is dependent on the current density rating of the
coating. The design should reflect the desired anode
life in the specific electrolyte.
4.5 Hardware
4.5.1 All impressed current anode support hardware
and
wiring should be selected for maximum
economical life for the conditions inside the steel tank.
4.5.2 For vertically suspended impressed current
anode systems, hand holes or mounting devices
should be provided so that the anodes can be serviced
without entering the tank. Any hand holes should have
suitably designed weatherproof covers.
4.5.3 Horizontally oriented impressed current anode
systems located below the normal water level do not
normally require hand holes but may require drainage
of the tank for servicing.
4.5.4 All wiring on the outside of the steel tank shall be
in rigid conduit and installed with applicable codes. The
use of conduit for insulated impressed current anode
wiring inside the tank is not necessary.
4.5.5 Permanent reference electrodes lead wire
should be brought to the rectifier location to facilitate
readings.
Reference cell wiring shall not be routed
through the same conduit used for system DC wiring.
________________________________________________________________________
Section 5: Installation of Impressed Current Cathodic Protection Systems
5.1 Introduction
This section outlines installation techniques for water
storage tank impressed current cathodic protection systems
that protect the structure when design recommendations in
Section 4 have been followed.
5.2 Construction Specifications
All construction work on impressed current cathodic
protection systems shall be done in accordance with
construction drawings and specifications.
The drawings
and specifications should be prepared by a qualified
corrosion engineer, in accordance with the recommended
procedures in Sections 1 and 4, and any other applicable
codes. If changes are necessary, they shall be approved in
writing by the engineer or owner.
5.3 Construction Supervision
5.3.1 All construction work should be performed by or
under the direction of a person who is trained and
qualified in the installation of impressed current
cathodic protection systems in water storage tanks,
and who shall verify that the installation is made in strict
accordance with the drawings and specifications.
Exceptions may be made only with the consent of the
corrosion engineer when it can be demonstrated that
the effectiveness of the system will not be impaired.
5.3.2 All deviations from original design shall be noted
on record drawings.
__________________________________________
(4)
Metals and Alloys in the Unified Numbering System (latest revision), a joint publication of the American Society for Testing and Materials
(ASTM), 100 Barr Harbor Drive, West Conshohocken, PA 19428, and the American Society of Automotive Engineers Inc. (SAE), 400
Commonwealth Drive, Warrendale, PA 15096.