UFC 3-570-06
JANUARY 31 2003
Table 4-2. Close-Interval Survey Potential Measurement Locations
STRUCTURE TYPE
POTENTIAL MEASUREMENT LOCATIONS
PIPELINES
Locate the reference cell over the pipeline at intervals not to
exceed the depth of the pipeline, normally every (1 to 1.5 meters
(3 to 5 feet).
ON GRADE STORAGE
Locate the reference cell:
Next to the tank every 1.8 meters (6 feet) around the tank
TANKS
circumference.
At a distance one tank radius away from the tank at eight equally
spaced locations around the tank circumference.
UNDERGROUND
Locate the reference cell:
STORAGE TANKS
Every 1 meter (3 feet) over the tank.
At least every 1M over feed and return piping.
Over the manhole, fill pipe, and vent pipe.
Over all metallic structures in the area if readings indicate an
isolated system is shorted to a foreign structure.
ISOLATED
Take one structure-to-electrolyte (S/E) potential measurement on
STRUCTURES
each side of all dielectric couplings without moving the reference
electrode.
Note: If the potential difference between measurements on each
side of a dielectric coupling is < 10 millivolts, verify its integrity
using an isolation flange tester
ALL STRUCTURES
Locate the reference cell:
WITH FOREIGN LINE
Over the foreign line at all points where it crosses the protected
structure.
Over the foreign line where it passes near the anode bed.
ALL STRUCTURES
Locate the reference cell:
WITH CASED
Over each end of the casing on all casings.
Note: If the casing is shorted or partially shorted to the pipeline,
and the potentials over the pipeline are depressed below criteria
described in Chapter 6, take immediate action to clear the short.
ALL STRUCTURES IN
Annotate the soil condition for comparison of past/future potential
SOIL
and current measurements.
4-3
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