5 Jan 91
Cathodic protection complements the protective coat-
ing system. A good coating system substantially
reduces the amount of cathodic protection current
required. The coating efficiency has to be
All short circuits must be eliminated from both new
and existing structures for which a cathodic
protection system is being designed.
Calculate surface area to be protected.
The overall current requirement of a cathodic protection
system is directly proportional to the surface area to be
protected. This includes underground or submerged pipes,
buried tanks, and wetted surfaces (up to high
water(level) of watertanks (including risers).
Determine current requirement.
For existing structures, a current requirement test will
provide the actual current requirement at the time of the
test. Allowance should be made in the design for future
degradation of coatings or structure additions that will
increase the current requirement.
For new structures not yet installed, the amount of
current needed to provide protection as defined in Na-
tional Association of Corrosion Engineers (NACE) RP-0l-69
(reference 22) will be dependent on a number of
variables. Table 3-1 gives guidelines for current
requirements in various soil and water conditions.
The efficiency of the coating
system, both when new and
at the end of design life, is
a determining factor in the
range of current that will be
required over the lifetime
of the system. Total current
required is given by the
I = (A)(I')(l.0 - CE)
where I is the total current requirement, A is the total
surface area to be protected, I' is the estimated current
density, and CE is the efficiency of the coating system.
This procedure should always be followed, even when a