Nace CP 1, Course Manual

Page: 495 / 535

TM0497-2002
NACE International 15
10.2.4.4 Reference electrode
10.2.4.4.1 CSE.
10.2.4.4.2 Other standard reference
electrodes may be substituted for the CSE.
These reference electrodes are described in
Appendix A, Paragraph A2.
10.2.5 Procedure
10.2.5.1 Before the test, verify that cathodic
protection equipment has been installed and is
operating properly. Time should be allowed for the
pipeline potentials to reach polarized values.
10.2.5.2 Install and place in operation necessary
interrupter equipment in all significant DC sources
protecting the pipe at the test site, and place in
operation with a synchronized and/or known “off”
and “on” cycle. The “off” cycle should be kept as
short as possible but still long enough to read a
polarized pipe-to-electrolyte potential after any
“spike” as shown in Figure 3a has collapsed.
10.2.5.3 Determine the location of the site to be
tested. Selection of a site may be based on:
(a) Location accessible for future monitoring;
(b) Other protection systems, structures, and
anodes that may influence the pipe-to-electrolyte
potential;
(c)
Electrical midpoints between protection
devices;
(d)
Known location of an ineffective coating if
the pipeline is coated; and
(e)
Location of a known or suspected corrosive
environment.
10.2.5.4 Make electrical contact between the
reference electrode and the electrolyte at the test
site, directly over the centerline of the pipeline or
as close to it as is practicable.
10.2.5.4.1 Identify the location of the
electrode to allow it to be returned to the
same location for subsequent tests.
10.2.5.5 Connect the voltmeter to the pipeline and
reference electrode as described in Paragraph
5.6.
10.2.5.5.1 If spiking may be present, use an
appropriate
instrument, such as an
oscilloscope or high-speed recording device,
to verify that the measured values are not
influenced by a voltage spike.
10.2.5.6 Measure and record the pipe-to-
electrolyte “on” and “instant off” potentials and their
polarities with respect to the reference electrode.
10.2.5.6.1 The “instant off” pipe-to-electrolyte
potential is the “baseline” potential from which
the polarization decay is calculated.
10.2.5.7 Turn off sufficient cathodic protection
current sources that influence the pipe at the test
site until at least 100 mV cathodic polarization
decay has been attained.
10.2.5.7.1 Continue to measure and record
the pipe-to-electrolyte potential until it either:
(a) Has become at least 100 mV less
negative than the “off” potential; or
(b)
Has reached a stable depolarized level.
10.2.5.7.2 Measurements shall be made at
sufficiently frequent intervals to avoid attaining
and remaining at a corrosion potential for an
unnecessarily extended period.
10.2.5.7.3 When extended polarization
decay time periods are anticipated, it may be
desirable to use recording voltmeters to
determine when adequate polarization decay
or a corrosion potential has been attained.
10.2.6 Evaluation of Data
Cathodic protection shall be judged adequate at the
test site if 100 mV or more of polarization decay is
measured with respect to a standard reference
electrode.
10.2.7 Monitoring
When at least 100 mV or more of polarization decay
has been measured, the pipeline “on” potential at the
test site may be used for monitoring unless significant
environmental, structural, coating integrity, or cathodic
protection system parameters have changed.
10.3 Test Method 3b—Use of Pipeline Polarization
Formation (Figure 3b)
10.3.1 Scope
This method provides a procedure using the formation
of polarization to assess the adequacy of cathodic
protection at a test site on steel, cast iron, aluminum, or
copper piping according to the criteria stated in NACE
Standard RP0169,
1
Paragraphs 6.2.2.1.3, 6.2.3.1, or
6.2.4.1 (depending on the pipe metal). The paragraph
below states Paragraph 6.2.2.1.3:
The following criterion shall apply: A minimum of
100 mV of cathodic polarization between the
structure surface and a stable reference electrode
contacting the electrolyte. The formation or decay
of polarization can be measured to satisfy this
criterion.