Nace CP 1, Руководство по эксплуатации

Страница: 508 / 535

TM0497-2002
28 NACE International
C3.5.9 Measure and record the coupon-to-
electrolyte potential periodically. The difference
between it and the “off” potential is the amount of
polarization decay.
Continue to measure and
record the coupon-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.
C3.5.10 Reconnect the coupon test lead to the
pipeline test lead for normal operations.
C3.6 Evaluation of Data
Cathodic protection may be judged adequate at the
test site when 100 mV or more of polarization decay is
measured with respect to a standard reference
electrode. The depolarized potential of the coupon
depends on the coupon surface condition, the soil in
which the coupon is placed, its level of polarization,
and its time polarized.
Therefore, the depolarized
potential of the coupon may not be the same as that of
the pipe and may not accurately reflect the polarization
on the pipe at the coupon location. It must also be
understood that the polarization measured on the
pipeline is a “resultant” of the variations of polarization
on the pipe at the test site.
These variations are
caused by the pipe surface condition, soil strata
variations, oxygen differentials, and time the pipe has
been polarized. Making precise comparisons may not
be possible.
C3.7 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.