INSTRUMENTATION

High resistance voltmeter

2 Cu/CuSO4 standard electrodes.

1 holder with at least 100m of conductor wire.(for roving electrode)

Two lengths of flexible cable, each fitted with a voltmeter connector and a crocodile clip.

Field notes

Report forms

METHOD

2.1. Cause the closest cathodic protection installation to be switched on for 12 seconds and off for 3 seconds for the duration of this procedure.

NOTE This can be done manually or automatically, using a current interrupter.

2.2. Place the electrode firmly in the ground, close to the test post.

2.3. Connect the negative pole of the voltmeter to the pipeline cathodic protection test point.

2.4 Connect the positive pole of the meter to a standard Cu/CuSO4 electrode.

2.5. Make a note of the highest reading that appears on the meter.

2.6. Make a note of the lowest reading that appears on the meter.

These readings will be caused by the cathodic protection current causing alterations in the potential of the ground at the point of contact of the electrode.

2.7. Disconnect the negative pole of the meter from the pipeline test facility.

2.8. Connect the negative pole of the meter to the fixed half-cell through the trailing conductor.

2.9. Secure the electrode and connection so that it does not pull out of the ground as the trailing conductor unreels.

2.10. Connect the second (roving) electrode to the positive pole of the meter.

2.11. Place the roving electrode beside the fixed electrode and make sure that the reading on the meter is less than 20 mv.

NOTE . If it is not, then check the connecting leads and metering circuit by short circuiting each section. If there is a consistent but very small voltage between the half cells, then they should be cleaned and recharged. If the voltage persists and cannot be remedied, then this voltage and polarity should be noted, so that the error can be allowed for during the remainder of the procedure.

2.12. The roving electrode should then be stepped, at one meter intervals, away from the pipeline and away from the cathodic protection groundbed.

2.13. Mark the ground where the maximum voltage is shown.

NOTE The voltages will then be the same for each step, or the difference between each ground contact will change to a different polarity.

2.14. If the readings remain constant, then the exact location of the remote half-cell should be marked as the position to set the reference electrode for other procedures.

2.15. The fixed electrode should be moved to the remote reference position.

2.16. The roving electrode should then be stepped in a circle of about 3m radius around the remote reference electrode.

NOTE. The readings should not reflect and regular switching of the pipeline CP.