Nace CP 1, Course Manual

Page: 445 / 535

RP0290-2000
NACE International 3
2.3.1.4 Changes in environmental conditions such
as temperature and moisture can significantly
change the native corrosion potential, decayed off-
potential, and rate of decay being measured from
one day to the next. Therefore, during the
polarization measurement interval, the corrosion
engineer shall monitor for the impact of these
phenomena throughout the test period to ensure that these conditions have not affected the
readings. The period for potential decay or
polarization development is largely determined by
oxygen availability at the reinforcement surface
and is not a reflection of the efficiency of the
cathodic protection system. Longer periods of
decay or polarization development are required for
FIGURE 1—Typical Polarization Decay Curve
P
O
T
E
NT
IA
L (
M
ILLI
V
O
LT
S
)
CURRENT OFF
CURRENT ON
DEPOLARIZED
CURRENT ON
STATIC
POLARIZED
P
O
T
E
NT
IA
L (
M
ILLI
V
O
LT
S
)
% TIME
% TIME
FIGURE 2—Typical Polarization Development Curve Showing “Instant-Off” Potentials Only