Nace CP 1, Course Manual

Page: 374 / 535

RP0388-2001
8 NACE International
________________________________________________________________________
Section 8: Operation and Maintenance
8.1 This section outlines the procedures necessary for the
effective operation and maintenance of impressed current
cathodic protection systems.
8.2 Operation
8.2.1 For an impressed current cathodic protection
system to control corrosion effectively, it must be kept
in continuous operation and maintain a level of
protection that satisfies the criteria.
8.2.2 When the system is energized, it shall be
adjusted to obtain the desired tank-to-water potential in
accordance with Paragraph 6.2.
8.3 Maintenance
8.3.1 Monthly
8.3.1.1 The power unit should be inspected at
least once each month to verify that it is operating
correctly
and that the proper tank-to-water
potentials are being maintained.
8.3.1.2 In a manually controlled system, the
voltage and current of the power unit and the tank-
to-water potential using permanent reference
electrodes, if any, shall be measured. If the tank-
to-water potential is outside the proper range, the
cause shall be determined and adjustments made
accordingly.
8.3.1.3 In an automatic system, the tank-to-water
potential shall be measured to determine that the
system is maintaining the predetermined potential
within the tolerance indicated in Paragraph 7.3.1.4.
A log shall be maintained to establish an operating
profile and shall be referred to when making
regular inspections. If the potential is outside the
proper range, the cause shall be determined.
Among the possible causes of potential drift are
wiring faults exceeding the current capacity of the
unit or a defective reference electrode. Among the
possible causes of a change in current are
defective
reference electrode, wiring faults,
establishment of calcareous deposits, and coating
deterioration.
The first two require immediate
replacement or repair. The third normally requires
a decrease and the fourth, an increase, in current
requirement.
8.3.1.4 More frequent inspection of the systems
may be desirable in critically corrosive situations,
when the tank has previously suffered extensive
metal loss as a result of corrosion or when there
are highly variable conditions.
8.3.1.5 Remote monitoring equipment can aid in
the collection of the data, reduce monitoring costs,
and allow for more frequent, real-time data
collection during a variety of tank operations, such
as filling and sudden drops in water level.
8.3.2 Annual
8.3.2.1 All impressed current cathodic protection
system
components should be completely
inspected annually. This inspection should include
potential profile testing with portable instruments to
ensure that the system is operating properly. The
power source, controls, anodes, wiring, and
reference electrodes should be examined and
replaced as required.
8.3.2.2 Power Source—The power unit is usually
designed for long life with little maintenance
required.
The monthly inspection indicated in
Paragraph 8.3.1.1 should reveal any failures
requiring repairs and replacements.
Annual
maintenance should include removing debris at
the openings required for cooling, checking that all
connections and wiring are secure and unaffected
by corrosion, inspecting the electrical grounding,
and painting of cabinets and housings, if required.
8.3.2.3 Impressed Current Anodes and Wiring
8.3.2.3.1 In systems using impressed current
anodes
designed for one-year life (see
Paragraph 4.4.2.1), all anodes shall be
replaced annually (or according to design life).
In water storage tanks subject to icing
conditions, anodes should be replaced in the
spring after the opportunity for freezing has
passed.
Alternatively, the tank may be
operated in a manner to raise and lower the
water level during freezing conditions and
thereby extend anode life.
8.3.2.3.2 Lowering the water level provides
an opportunity to inspect the interior surface
of the tank. If the tank is coated, the condition
of the coating should be recorded. Also, the
presence of either corrosion or calcareous
deposits should be recorded.
8.3.2.4 Reference Electrodes
8.3.2.4.1 Reference electrodes and
connecting wire should be inspected to
determine
whether they are physically
capable of operating until the next annual
inspection. Any breaks in the wiring insulation
must
be repaired. If insulation has