Recording changes in the ground potential that occur during the time which it takes to conduct any type of DC voltage survey.


Many locations are subject to changes in the IR drop in the ground, during the day, caused by such influences as radio transmissions, AC generator surges and magnetic phenomena. Some of these changes can effect pipelines and some merely effect readings on the meter. This procedure is designed to allow the engineer to eliminate the errors in the readings and to assess the probability of accelerated corrosion due to this type of electrical activity. It is based on the work carried out in the regions of British Gas for the Experimental Research Station.


Chart recorder with a range of -1.0v to =1.0v with 3 channels capable of simultaneous recording with distinctive traces.

4 Cu/CuSO4 electrodes.

3 lengths of at least 100m of conductor wire.

High resistance voltmeter.


3.1.1. Procedure 2 should be used to establish two separate locations for remote reference electrodes.

3.1.2. The first is used as the reference and connected to the positive terminal of channel 1 of the chart recorder.

3.1.3. The second remote electrode is connected to the negative terminal of channel 1 of the recorder.

3.2.1. The positive poles of channels 1, 2, and 3 of the recorder are connected to each other as they will then all refer to the common remote reference electrode.

3.3.1 Using the remote reference electrode, Procedure 4 is used to identify a location which is directly over a coating fault in the pipeline.

3.3.2. The third electrode is placed in this location and connected to the negative pole of channel 2 on the recorder.

3.4.1. Using the remote reference electrode and Procedure 4, an area of good coating is identified for the position of the fourth half-cell.

3.4.2. The fourth half-cell is then connected to the positive pole of channel 3.

3.5.1. The CP current is then switched to its normal operating mode and the recorder is switched on.

3.5.2. Recording continues for the duration of the other surveys which should be recorded on the other channels of the same instrument.


The voltage on channel 1, between the two remote locations, will show any variations due to outside influences such as radio transmissions, rectified AC earthing faults etc.

The voltage on channel 2 will show any variations caused to the ground due to the presence of the coating fault.

The voltage on channel 3 will show voltage changes in the immediate vicinity of the pipeline but which are not necessarily associated with our own CP system.

This procedure can be carried out using a data logging computer, which can be used to analyse the readings.

The 'Dynamic' software is ideal to store analyse and display the results of this procedure. It will be available soon and will be installed and commissioned by software engineers who have been through the Cathodic Protection Network training courses.

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