Nace CP 1, Course Manual

Page: 295 / 535

RP0169-2002
24 NACE International
9.4.2.3 The attachment of electrical bonds can
reduce the level of cathodic protection on the
interfering structure.
Supplementary cathodic
protection may then be required on the interfering
structure to compensate for this effect.
9.4.2.4 A bond may not effectively mitigate the
interference problem in the case of a cathodically
protected bare or poorly externally coated pipeline
that is causing interference on an externally
coated pipeline.
9.4.3 Cathodic protection current can be applied to the
affected structure at those locations at which the
interfering current is being discharged. The source of
cathodic
protection current may be galvanic or
impressed current anodes.
9.4.4 Adjustment of the current output from interfering
cathodic protection rectifiers may resolve interference
problems.
9.4.5 Relocation of the groundbeds of cathodic
protection rectifiers can reduce or eliminate the pickup
of interference currents on nearby structures.
9.4.6 Rerouting of proposed pipelines may avoid
sources of interference current.
9.4.7 Properly located isolating fittings in the affected
structure may reduce or resolve interference problems.
9.4.8 Application of external coating to current pick-up
area(s) may reduce or resolve interference problems.
9.5 Indications of Resolved Interference Problems
9.5.1 Restoration of the structure-electrolyte potentials
on the affected structure to those values that existed
prior to the interference.
9.5.2 Measured line currents on the affected structure
that show that the interference current is not being
discharged to the electrolyte.
9.5.3 Adjustment of the slope of the beta curve to
show that current discharge has been eliminated at the
location of maximum exposure (see Appendix A).
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Section 10: Operation and Maintenance of Cathodic Protection Systems
10.1Introduction
10.1.1 This section recommends procedures and
practices for energizing and maintaining continuous,
effective, and efficient operation of cathodic protection
systems.
10.1.1.1 Electrical measurements and
inspection are necessary to determine that
protection has been established according to
applicable criteria and that each part of the
cathodic protection system is operating properly.
Conditions that affect protection are subject to
change.
Correspondingly, changes may be
required in the cathodic protection system to
maintain protection. Periodic measurements and
inspections are necessary to detect changes in the
cathodic protection system. Conditions in which
operating experience indicates that testing and
inspections need to be made more frequently than
recommended herein may exist.
10.1.1.2 Care should be exercised in selecting
the location, number, and type of electrical
measurements used to determine the adequacy of
cathodic protection.
10.1.1.3 When practicable and determined
necessary by sound engineering practice, a
detailed (close-interval) potential survey should be
conducted to (a) assess the effectiveness of the
cathodic protection system; (b) provide base line
operating data; (c) locate areas of inadequate
protection levels; (d) identify locations likely to be
adversely affected by construction, stray currents,
or other unusual environmental conditions; or (e)
select areas to be monitored periodically.
10.1.1.4 Adjustments to a cathodic protection
system should be accompanied by sufficient
testing to assure the criteria remain satisfied and
to reassess interference to other structures or
isolation points.
10.2 A survey should be conducted after each
cathodic
protection system is energized and/or
adjusted to determine whether the applicable criterion
or criteria from Section 6 have been satisfied.
10.3 The effectiveness of the cathodic protection system
should be monitored annually. Longer or shorter intervals
for monitoring may be appropriate, depending on the
variability
of cathodic protection factors, safety
considerations, and economics of monitoring.
10.4 Inspection and tests of cathodic protection facilities
should be made to ensure their proper operation and
maintenance as follows:
10.4.1 All sources of impressed current should be
checked at intervals of two months. Longer or shorter
intervals for monitoring may be appropriate. Evidence