Nace CP 1, Course Manual

Page: 424 / 535

RP0193-2001
NACE International 17
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Section 10: Energizing and Testing
10.1 This section discusses factors that should be
considered when energizing and testing a cathodic
protection system for on-grade carbon steel storage tank
bottoms. If the tank has a secondary containment system,
suitable access ports through the ringwall must be provided
for testing.
10.2 Design Parameters
10.2.1 Knowledge of the performance criteria
considered during the design of a cathodic protection
system as well as the operational limits of cathodic
protection devices and hardware should be available to
the personnel setting operating levels for the cathodic
protection system.
10.3 Initial Data
10.3.1 Verification of cathodic protection devices
and hardware, such as the following, should be done
prior to energizing:
(a) Location of anodes
(b) Ratings of impressed current sources
(c) Location of reference electrodes
(d) Location of test facilities
(e) Location of cathodic protection system cables
10.3.2 Prior to energizing the cathodic protection
system, the following data and information should be
collected:
(a) Tank bottom-to-electrolyte potentials
(b) Pipe-to-electrolyte
potentials on connected
piping
(c) Verification of dielectric isolation
(d) Foreign structure-to-electrolyte potentials
(e) Test coupon data
(f)
Fluid level in the tank during testing, and
(f) Corrosion-rate probe data.
10.3.3 All initial baseline data should be
documented and the records maintained for the life of
the cathodic protection system or the on-grade
storage tank. Any deviations from the design or as-
built documentation should be noted and included
with the initial baseline data.
10.3.4 When measuring the structure-to-electrolyte
potential, the portable reference electrodes should be
placed at sufficient intervals around the perimeter and
under the tank to ensure the potentials measured are
representative of the entire tank bottom.
The
potential measured at the perimeter of a large-
diameter tank does not represent the potential at the
center of the tank.
10.4 Current Adjustment
10.4.1 The desired operating level of a cathodic
protection system must often be determined by a
series of trial tests at various operating levels. The
specific operating level depends on the criterion for
cathodic protection used for the on-grade storage
tank(s).
Section 4 defines the various criteria for
achieving cathodic protection of on-grade carbon
steel storage tank bottoms. Time required to achieve
polarization on a bare tank bottom can be different
from tank to tank.
10.4.2 When the operating levels of cathodic
protection systems are adjusted, consideration must
be given to the effect of stray current on adjacent
structures.
Owners of these structures should be
notified of the installation of a new cathodic protection
system.
10.4.2.1 Among the structures that should be
considered as being possibly affected by stray
current are:
(a) On-grade and buried storage tanks
(b) Piping separated from the tank(s) by high-
resistance fittings
(c) Buried electric facilities
(d) Buried fire-protection piping
(e) Buried water piping
(f)
Transmission or distribution piping serving
storage tank(s)
(g) Municipal or public utility structures serving
the facility in which a storage tank(s) is located
(h) Fencing
10.4.2.2 Structures that may contain
discontinuous fittings or joints, such as cast iron
systems, ductile iron piping systems, or piping
with mechanically connected fittings, require
special attention to ensure that stray current
effects are detected and mitigated.
10.4.3 The final operating level of a cathodic
protection system should be established to achieve
the cathodic protection criterion established by the
design documents as set forth in Section 4, or by the
operating policies of the facility owner.
10.5 Documentation
10.5.1 Documentation of all operating parameters
should be completed after the system is energized.
Those parameters should include:
(a) Initial baseline data
(b) As-built drawings