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
20
•
Set the multi-meter to DC volts and re-connect between the
Pipe
and
Ground
leads as
before – and again, before they are connected to the Signal Generator. If the DC
voltage is greater than +/-10v – DO NOT CONNECT SIGNAL GENERATOR
The source of either foreign signal must be found and isolated before a survey can be
started.
Failure to check the above could result in permanent damage to the Signal
Generator
4.3.3. Signal Interference
Other points to consider when selecting the signal injection point is the availability of a
good ground or earth connection, and the fact that a section of line 30-50ft either side of
the Injection Point cannot be surveyed because of mutual interference between the fields
radiating from the
Pipe
lead connecting the Signal Generator to the pipeline. Thus, if it is
intended to survey a road crossing or river etc, it is better not to use a signal Injection Point
that is positioned at, or close to, the crossing to be checked. It must also be noted that
when connecting to a pipeline via a remote connection such as a CP test post, TR station
etc, the mutual interference experienced from the injected signal could be greater than 30-
50ft. The link between the CP test post/TR station and pipeline under survey may not be
as direct as possible and may even cross the pipeline before it is bonded to the pipeline.
In this instance the surveyor may experience initial rising current readings due to the anti-
phase signal on the bonding cable. When current readings stop rising, the interference
has subsided.
4.4. Connection Methods
Methods of connecting to the pipeline can differ slightly but all require the same basic
principle; a good, low-resistance connection to the pipeline and a good, low-resistance
earth to complete the electrical circuit. Many surveys are compromised before they even
start by a poor connection to a rusty valve.
Once the signal injection point has been chosen, the Signal Generator should be placed
close to it and connected to it using one of the
Earth/Pipe
leads plugged into the
Pipe
socket. The other
Earth/Pipe
lead should be plugged into the
Ground
socket and
connected to a suitable earth.
Arguably, the best connection point to use is the TR station used for Cathodic Protection,
as this has a direct connection to the pipeline and its own ground bed for a good earth
connection. If the TR station is to be used as a connection then it must be switched off
(de-energised) and the positive and negative leads disconnected from their relevant
busses. The Signal Generator can then be connected to these positive and negative
leads. Failure to shut down or disconnect the TR station before connecting the Signal
Generator may permanently damage the Signal Generator.
If connecting using CP test posts it is still imperative to disconnect active TR stations
within 3000ft while carrying out a survey.
In all situations, the tests detailed in section 4.3.2 should always be carried out before
connecting the Signal Generator.
