UFC 3-570-06
JANUARY 31 2003
Figure 7-16. Testing for a Shorted Dielectric with Power Supply
V oltm et er
+ -
1
T em po ra ry
T em po ra ry
Po w er
A no des
2
Su pp ly
-+
R eference
E lect rod e
Ov er 5 0 Feet
7-7.4
Using a Temporary Local Cathodic Protection System. Install a
temporary local cathodic protection system to increase the current to the street side of
the dielectric (paragraph 7-10); or if possible, merely increase the current level of the
existing system. Note that the temporary system should be installed where the current
should distribute to the location being tested. Repeat the potential measurement of
both structures. If the potential of the house side of the dielectric remains approximately
the same or changes in a positive direction (less negative), when the potential of the
street side of the dielectric changes in a negative direction, they are not shorted. If both
potential measurements change more negative as current is increased, the two
structures are shorted together.
7-8
CASING TESTS. Casings present a unique and sometimes very challenging
problem to corrosion control. Although they are required in some cases, they present a
serious problem to the application of cathodic protection to the carrier pipe. If not
shorted, they may shield adequate protection; and if shorted, they totally shield the
carrier pipeline and steal the cathodic protection, often for a large area of the pipeline.
The preferred method of corrosion control is to isolate and seal the casing so there is no
electrolyte in the space between the casing and the carrier pipe, or fill that area with a
nonconductive sealant. Casings are normally bare, while carrier pipelines are normally
very well coated. Casings normally have vent pipes at one or both ends and a test
station for corrosion control testing. This test station usually has four wires, two to the
7-27
Previous Page
