UFC 3-570-06
JANUARY 31 2003
Low temperatures, which decrease the corrosion rate.
Current density.
Lack of bimetallic connections. If present they would raise the corrosion
rate.
Lack of interference corrosion. Interference raises the potential in the
pickup area (lowers corrosion) and lowers the potential in the discharge
area (increases the corrosion rate).
7-3.3
Test Methods for the -0.85 Instant-OFF Criterion. For this criterion,
measurements of potential must be taken when there is no cathodic protection current
flowing. The measurement of the instant-OFF or the potential when the cathodic
protection is not flowing is required as the means of removing errors from the
measurement. For various methods used to measure the instant-OFF potential, see
paragraph 7-3.5. If the potential measurement meets or exceeds -0.85 volts DC (in
comparison to a copper/copper sulfate reference electrode) using these methods, this
criterion has been met. Other reference electrodes must be corrected to the factor for a
copper/copper sulfate reference to be valid under this criterion.
7-3.4
Test Methods for the 100 mV Polarization Criterion. The test method for
this criterion is exactly like the method for the negative 0.85 instant-OFF criterion, with
the additional requirement of either comparing the measurements to a native survey
(potentials taken before the cathodic protection current was applied), or allowing for the
measurement of the polarization decay. It is recommended that the native potentials be
used to compare the instant-OFF readings for the 100 mV polarization criterion. After
cathodic protection has been applied, the structure is polarized, and even after current
interruption, considerable time may be required before the potential returns to the native
potential value. Measuring polarization decay guarantees the proper shift, but may
require considerably more current to polarize the structure to a level where the 100 mV
depolarization would occur in a relatively short time.
7-3.5
Instant-OFF Test Methods. The test method used for an instant-OFF
potential measurement is determined by the type of equipment used and the type of
current interrupter used. The test method must include interruption of the protective
current or measurement of the potential when there is no current flowing, to guarantee
the removal of all IR drop and anode gradient errors. There are four different equipment
technologies that are used and several ways to accomplish the current interruption
(sometimes depending on the type of equipment being used). Types of equipment
include:
7-3.5.1
with conventional current interrupters, manually synchronizable, or advanced
7-11
Previous Page
