JANUARY 31 2003
Review all potential readings. Annotate the three lowest potential
measurements and the highest potential measurement to re-evaluate those specific
locations when performing the impressed current system check.
For all structures, compare the potential measurements to those previously
taken at the same locations to identify changes.
If the potential measurements reveal current output does not satisfy criteria in
Chapter 6, adjust or supplement the system as necessary. After 30 days, accomplish
the survey again (paragraph 4-3.1).
WATER TANK CALIBRATION. The water tank calibration is a
comprehensive and thorough survey to ensure that cathodic protection is maintained
over the entire surface of the tank to be protected in accordance with Chapter 6 criteria,
and there are no excessive voltages on any part of the tank interior that could damage
the coating. Water tank calibration comprises an interrupted potential survey on
impressed current systems and a non-interrupted potential survey on galvanic systems.
The interruption cycle must have an ON cycle that is a minimum of four times longer
than the OFF cycle where the OFF cycle is normally one second. On a galvanic
system, measurement errors must be accounted for using sound engineering practices,
including reference cell placement, anode positions, and coating condition. If the
system design permits, this may also include an interrupted potential survey.
Maintenance Intervals. Recommended intervals for conducting water tank
Thirty days after the cathodic protection system is installed, modified, or
Inspect water tanks in accordance with Tables 4-5 and 4-6.