Leaders in Pipelin
e Survey Systems
C
C
C
-
-
-
S
S
S
C
C
C
A
A
A
N
N
N
2
2
2
0
0
0
1
1
1
0
0
0
SYSTEM MANUAL Version 6.03i
21
DISCONNECT TR station from
Ground Bed and Pipeline
Fig 4.1 – Disconnecting ground bed
Although it is likely to be the best connection, it is incorrect to assume that the TR station
has a perfect connection to the pipeline, as the cables connection the TR station to both
the pipeline and ground bed may themselves be suffering corrosion or wear that is masked
by high CP currents/voltages. The impedance indication given by the Signal Generator
(see 3.2) may help to provide information about this, but if in doubt always perform
resistance/impedance checks independently.
If a TR station has been selected as the signal injection point, the ground bed lead
(rectifier positive lead) and the lead connecting the rectifier to ‘pipeline under survey’
(rectifier negative) must be disconnected from the rectifier terminals. This completely
isolates the pipeline under survey not only from the CP system but also other pipelines
that may be protected by the same rectifier from a common buss. The Signal Generator
Ground
connection can now be safely connected to the rectifier’s ground bed, and the
Signal Generator
Pipe
connection can be attached to the ‘pipeline under survey’ lead.
Connecting the Signal Generator in this way not only provides the best connection to the
pipeline, but it will also provide significant information as to the electrical integrity (loop
impedance) of the rectifier’s ground bed and pipe connections.
If a CP test post or valve is being used, the Signal Generator
Ground
lead should be
clipped to one end of the
Earth Extension Lead
, and this in turn should be taken to a
suitable grounding point as far away as possible from the pipeline – and at right angles to
it. One or more of the
Spikes
should be driven into the ground at this earth point and the
Earth Extension Lead
should be attached to them (using the
Earth Spike Jump
cables
provided, as necessary).
Fig 4.2 – Connection at CP test post