Nace CP 1 - Typical Polarization Decay Curve; Typical Polarization Development Curve Showing “Instant-Off”

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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

POTENTIAL (MILLIVOLTS)

CURRENT OFF

CURRENT ON

DEPOLARIZED

CURRENT ON

STATIC

POLARIZED

POTENTIAL (MILLIVOLTS)

% TIME

FIGURE 2—Typical Polarization Development Curve Showing “Instant-Off” Potentials Only