UFC 3-570-06
JANUARY 31 2003
7-4.4
Uncoated Structures. For uncoated structures, there are no theoretical
potential limits. Instant-OFF readings over -1.00 generally waste power and anode
material. Instant-OFF measurements that are over approximately -1.22 volts DC are
not theoretically possible. If instant-OFF readings are significantly over -1.22 volts DC,
other DC current sources are present. Synchronous interruption of all current sources
must be accomplished.
Table 7-1. Potential Limits for Underground Coated Structures
Coating Damage
Average Soil Resistivity
Suspected
Expected
2,000
-1.20
-1.80
3,000
-1.30
-2.20
5,000
-1.40
-2.50
10,000
-1.60
-2.70
15,000
-1.75
-2.75
20,000
-1.90
-3.00
30,000
-2.05
-3.30
40,000
-2.20
-3.60
50,000
-2.35
-3.90
100,000
-2.60
-4.40
7-5
CELL-TO-CELL POTENTIAL TESTING PROCEDURES
7-5.1
Performing Test. Cell-to-cell potential testing is performed to determine the
direction of current flow in the earth. This is especially useful on unprotected pipelines
to locate the anodic areas on the pipeline. These procedures are not used on protected
structures. On unprotected pipelines when cathodic protection of the complete line is
not feasible or economical, hot spot protection is sometimes used. This test procedure
is used to identify the anodic areas of the pipeline for application of cathodic protection
7-19
Previous Page
