SYSTEM CHECKOUT AND INITIAL ADJUSTMENTS
Introduction. After a cathodic protection system is installed, it
must be checked out to determine if protective potentials have been achieved
without interference to other structures in the vicinity. Initial testing
should be considered to be part of the system design and installation and
should be the responsibility of the designer of the system. The structure-to-
electrolyte potential measurement is the basic measurement that is used to
determine if proper levels of protection have been achieved. The -850 mV or
100 mV negative polarization shift criteria (refer to para. 3.3.1) are
recommended for evaluation of the effectiveness of cathodic protection systems
on steel structures. Problems with interference can be identified during the
initial system checkout and should be corrected as soon as possible to prevent
Initial Potential Survey. Structure-to-electrolyte potentials
should be measured at each test station or test point. Due to polarization
effects, these potentials may change substantially within the first year of
installation, and should be checked monthly for the first 3 months, then
quarterly for the remainder of the first year. Low potential readings may be
due to inadequate protective current flow, coating damage, or interference.
Sacrificial anode output currents should be measured at each potential current
test station since anode current measurements can be used to determine the
cause of low potential readings and to better estimate sacrificial anode
consumption rates. Anode currents should also be read monthly for the first 3
months and then quarterly for the duration of the first year.
Detection and Correction of Interference. Interference is normally
detected by analysis of structure-to-electrolyte potentials made during
initial system checkout. Unusually high or low potential readings are found
over points where current is either entering or leaving the structure.
Methods of detecting and correcting interference problems in cathodic
protection systems are described in para. 5.2.1.
Adjustment of Impressed Current Systems. Adjustment of rectifier
output is the most common adjustment made in impressed current cathodic
protection systems. Underprotection or overprotection can be corrected by
adjusting rectifier output if the structure-to-electrolyte potentials are
fairly uniform over the structure and the required output is within the
capacity of the rectifier. Rectifier output should not require frequent
adjustment as system changes that can be corrected by rectifier adjustment
occur slowly. Improper system potentials may also be the result of unusual
seasonal conditions and may be self correcting.
Uneven Structure-To-Electrolyte Potentials. If the structure-to-
electrolyte potentials are vastly uneven, overprotection or underprotection in
some areas in order to achieve proper potentials in other areas may result.
In this case, if interference is not present, output of anodes at the areas of
underprotection will have to be increased or anodes added. The output of
anodes in the areas of over protection will have to be reduced. If the anodes
are connected through resistors, resistor adjustment may be adequate. If the
structure is protected by impressed systems with point ground beds,
underprotected areas may have to be improved by the addition of impressed