JANUARY 31 2003
casing and two to the carrier pipeline. If there is not a test station already installed, one
should be installed prior to testing. At a minimum, there must be a metallic connection
made to the carrier pipeline and a vent pipe that is connected metallically to the casing.
If there is no vent pipe or carrier pipe test point in the vicinity of the casing, you must
excavate to the carrier pipeline or the casing, as required, and test connections. Again,
a test station should be installed.
Figure 7-17. Typical Casing Installation
V E NT PIPE
T E ST ST A TI O N
R O A D OR R AI LW AY
C A S IN G
C A R R IE R P IP E L IN E
pipeline and the casing. If the isolation is good, current will flow through the meter and
damage could result. If that current does not damage the meter, the measurement
would not indicate a resistance value. The voltage would be interpreted by the meter as
coming from the internal battery instead of the external electrical circuit being
Testing a Casing with Cathodic Protection on the Carrier Pipeline. Take
a potential measurement of the carrier pipeline and the casing by changing only the
structure connection without moving the copper/copper sulfate reference electrode.