UFC 3-570-06
JANUARY 31 2003
cathodic protection systems are first installed but is sometimes detected through routine
field measurements. Good record keeping is very useful in preventing cathodic
interference problems, as any system changes, particularly additions of new buried
structures, can be more easily determined when proper records are kept. Interference
tests must be made on all structures adjacent to a cathodic protection system to
determine effects and to allow design of mitigation measures.
Cathodic interference can be detected by measuring structure-to-soil
potentials, potential gradients and current flow (IR drop) with cathodic protection current
or resistance bonds on and/or cycled on and off. Structure-to-soil potentials give
indications of interference only when measured in an area of current discharge or
pickup on the foreign structure. Abnormal or unusual current distribution on a protected
structure indicates possible interference on a foreign structure. Current flow (IR drop)
readings show the relationship between pickup and discharge areas on a foreign
structure. A cathodic protection rectifier output contains a waveform, which results in a
pulsating DC signal. Presence of this pulsating DC on foreign structures indicates
interference from a rectifier. When conducting current requirement tests or initially
energizing impressed current cathodic protection systems, all companies owning
underground structures in the area should be notified and coordination tests made with
those interested. Current drainage requirements for each structure, from tests at
various anode locations, can be determined.
7-14.1.1 The best method to locate interference is to perform a pipe-to-soil potential
survey of the foreign pipeline with the source of the interference cycled on and off at
specific intervals. The algebraic difference between the "on" and "off" reading (potential
shift) gives the interference effect on the foreign structure. The location showing
greatest pipe-to-soil potential change in the positive ("unprotected") direction is called
the "critical" or "control" point. This is often at the point where protected and
unprotected pipelines cross. The areas showing pipe-to-soil potential change in the
negative ("protected") direction are called "pickup" areas. Presence of a pickup area on
a foreign structure indicates that interference is present, and a discharge area exists
somewhere on that structure. If metallic continuity exists between the foreign structure
and the negative terminal of the rectifier, this is not interference, it is protection, and no
discharge area exists (and therefore, by definition is not a foreign structure).
7-14.1.2 If the source of the cathodic interference is not known, it can be detected by
measuring structure-to-soil potentials with the cathodic protection current on and by
measuring potential gradients. Structure-to-soil potentials give indications of
interference only when measured in an area of current discharge or pickup on the
foreign structure.
7-14.1.3 Potential gradients are measured by the cell-to-cell test procedures in
paragraph 7-5. Taking these measurements along the foreign pipeline may locate the
discharge point and pickup areas. The polarity must be ascertained to determine the
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