Nace CP 1, Course Manual

Page: 293 / 535

RP0169-2002
22 NACE International
8.5.1.4 Anode backfill material should conform to
specifications.
8.5.2 Installation Provisions
8.5.2.1 A rectifier or other power source should be
installed so that the possibility of damage or
vandalism is minimized.
8.5.2.2 Wiring to rectifiers shall comply with local
and national electrical codes and requirements of
the utility supplying power. An external disconnect
switch should be provided in the AC circuit.
A
rectifier case shall be properly grounded.
8.5.2.3 On thermoelectric generators, a reverse-
current device should be installed to prevent
galvanic action between the anode bed and the
pipe if the flame is extinguished.
8.5.2.4 Impressed current anodes can be buried
vertically, horizontally, or in deep holes (see NACE
Standard RP0572
1
) as indicated in construction
specifications. Backfill material should be installed
to ensure that there are no voids around anodes.
Care should be exercised during backfilling to
avoid damage to the anode and cable.
8.5.2.5 The cable from the rectifier negative
terminal to the pipe should be connected to the
pipe as described in Paragraph 8.6.
Cable
connections to the rectifier must be mechanically
secure and electrically conductive.
Before the
power source is energized, it must be verified that
the negative cable is connected to the structure to
be protected and that the positive cable is
connected to the anodes.
After the DC power
source has been energized, suitable
measurements should be made to verify that these
connections are correct.
8.5.2.6 Underground splices on the header
(positive) cable to the groundbed should be kept to
a minimum. Connections between the header and
anode cables should be mechanically secure and
electrically conductive.
If buried or submerged,
these connections must be sealed to prevent
moisture penetration so that electrical isolation
from the environment is ensured.
8.5.2.7 Care must be taken during installation of
direct-burial cable to the anodes (positive cable) to
avoid damage to insulation.
Sufficient slack
should be left to avoid strain on all cables. Backfill
material around the cable should be free of rocks
and foreign matter that might cause damage to the
insulation when the cable is installed in a trench.
Cable can be installed by plowing if proper
precautions are taken.
8.5.2.8 If insulation integrity on the buried or
submerged header cable, including splices, is not
maintained, this cable may fail because of
corrosion.
8.6 Corrosion Control Test Stations, Connections, and
Bonds (see Paragraph 4.5)
8.6.1 Pipe and test lead wires should be clean, dry,
and free of foreign materials at points of connection
when the connections are made. Connections of test
lead wires to the pipe must be installed so they will
remain
mechanically secure and electrically
conductive.
8.6.2 All buried or submerged lead-wire attachments
should be coated with an electrically insulating
material, compatible with the external pipe coating and
wire insulation.
8.6.3 Test lead wires should be color coded or
otherwise permanently identified.
Wires should be
installed with slack. Damage to insulation should be
avoided and repairs made if damage occurs.
Test
leads should not be exposed to excessive heat and
sunlight. Aboveground test stations are preferred. If
test stations are flush with the ground, adequate slack
should be provided within the test station to facilitate
test connections.
8.6.4 Cable connections at bonds to other structures
or across isolating joints should be mechanically
secure, electrically conductive, and suitably coated.
Bond connections should be accessible for testing.
8.7 Electrical Isolation
8.7.1 Inspection and electrical measurements should
ensure that electrical isolation is adequate (see NACE
Standard RP0286
5
).
________________________________________________________________________
Section 9: Control of Interference Currents
9.1 Introduction
9.1.1 This section recommends practices for the
detection and control of interference currents.
The
mechanism and its detrimental effects are described.
9.2 Mechanism of Interference-Current Corrosion (Stray-
Current Corrosion)
9.2.1 Interference-current corrosion on buried or
submerged metallic structures differs from other
causes of corrosion damage in that the direct current,