JANUARY 31 2003
the structure-to-electrolyte boundary must be considered for valid interpretation of this
voltage measurement. Note: Consideration is understood to mean the application of
sound engineering practice in determining the significance of voltage drops by methods
Measuring or calculating the voltage drop(s);
Reviewing the historical performance of the cathodic protection system;
Evaluating the physical and electrical characteristics of the pipe and its
Determining whether or not there is physical evidence of corrosion.
A negative polarized potential (the potential across the structure/electrolyte
interface that is the sum of the corrosion potential and the cathodic polarization) of at
least 850 mV relative to a saturated copper/copper sulfate reference electrode.
A minimum of -100 mV of cathodic polarization between the structure surface
and a stable reference electrode contacting the electrolyte. The formation or decay of
polarization can be measured to satisfy this criterion. This criterion is not valid when bi-
metallic corrosion, such as when connected to copper grounding, is present.
On bare or ineffectively coated pipelines where long line corrosion activity is
of primary concern, the measurement of a net protective current at predetermined
current discharge points from the electrolyte to the pipe surface, as measured by an
earth current technique, may be sufficient.
In some situations, such as the presence of sulfides, bacteria, elevated
temperatures, acid environments, and dissimilar metals, the criteria in paragraph 6-3
may not be sufficient.
When a pipeline is encased in concrete or buried in dry or aerated high
resistivity soil, values less negative than the criteria listed in paragraph 6-3 may be
CAUTION: Using polarized potentials less negative than -850 mV is not recommended
for cathodic protection of pipelines when operating pressures and conditions are
conducive to stress corrosion cracking (see references on stress corrosion cracking in
CAUTION: Use of excessive polarized potentials on coated pipelines should be
avoided to minimize cathodic disbondment of the coating.