MAINTAINING CATHODIC PROTECTION SYSTEMS
Introduction. In order to provide the increased structural
lifetime and reliability intended, cathodic protection systems must be
monitored and maintained. Economic analysis, made at the time when cathodic
protection was selected as a means of corrosion control, should have included
the cost of periodic monitoring and maintenance.
Required Periodic Monitoring and Maintenance. The effectiveness of
cathodic protection systems usually changes with time. The consumption of
both sacrificial and impressed current anodes can result in decreased anode
output which results in inadequate protection. Deterioration of cable
insulation or connections can result in increased circuit resistance with
similar effects. Rectifier output may be reduced by aging of the stacks, or
may be completely interrupted by electrical failure. The corrosion
environment may change if there is a change in drainage patterns or the area
around an anode is paved reducing local soil moisture content. Construction
of additional structures or modification to existing structures in the area
Design Data Required for System Maintenance. In order for a
cathodic protection system to be effectively monitored and maintained, the
parameters used in the design of the system and the "as built" configuration
of the system must be known.
Drawings. "As built" drawings of the cathodic protection system
and the structure being protected should be available as well as drawings of
other structures in the area which might cause interference problems. The
cathodic protection system drawings should include, as a minimum, the location
and configuration of all test stations, the location and type of all anodes
and rectifiers, and the location of all connections and insulating joints.
These drawings should be periodically updated to show any changes made to the
cathodic protection system, the structure being protected, or nearby
System Data. The following system design parameters should be
recorded and kept with the system drawings in order to properly monitor and
maintain the cathodic protection system.
Design Potentials. The desired potentials used in the design of
the cathodic protection system should be indicated. In some cases, different
criteria may be used to establish minimum protective potentials at different
locations of the same structure.
Current Output. The design current outputs of the rectifiers or
sacrificial anodes in the system should be recorded. This data is most
important in the initial system checkout but may also be used to evaluate
discrepancies in structure-to-electrolyte potential readings.
System Settings and Potential Readings. The initial system
settings and potential readings should be recorded. Changes to the system,
such as rectifier adjustment, should be periodically recorded as described in
paras. 12.4 and 12.5. Potential readings taken both at the time of initial