Computerizing of DCVG

At present DCVG is merely presented as graphs of voltages

Computers are adding machines

• We can use them to make extremely big calculations.• Computers can make trillions of floating point

calculations per second.• We need to put in real scientific data to allow computers

to calculate the results of any adjustment that we make to our cathodic protection systems.

• If we can do this we can use the computer to trigger actions in response to any event.

• In this way we can program computers to control corrosion to networks of pipelines.

• The present ‘remote monitoring’ systems are producing data that cannot be computed.

DCVG simulation.• Two Cu/Cuso4 electrodes

are connected through the centre multi-meter

• This is connected to the computer display that records the voltages.

• This measuring circuit is NOT connected to the pipeline or the cathodic protection system.

• The meter on the right shows the corrosion current in the Alexander Cell.

DCVG at Guararema training centre

Note the exact positions of the two electrodes

In the frame above.

• One Cu/CuSO4 electrode is on remote earth near the Alexander Cell.

• The other is positioned in the ‘shells of resistance’ that create potential zones as the charges approach a coating fault on the pipeline.

• This allows real measurements to be seen and recorded.

Positions of electrodes

The previous slide shows the reaction current.

• It also shows the voltage between the Cu/CuSO4 electrode immediately close to the anode of a corrosion cell as specified in DIN50918.

• This electrode is in a circuit that is embedded in the circuit containing other electrical influences.

• The other electrode is in contact with the main circuit in the same way as is found in corrosion control field work.

Anode reaction potential.

DCVG 128.7 mv positive

11.7 micro-amps corrosion current

All readings visible

Measurements at this point of time.

• Dry cell battery corrosion cell 1.3205 potential difference between the positive and negative breadboard rails.

• DCVG potential difference between the points of contact of the two Cu/CuSO4 electrodes.

• 11.6 micro amps passing between the anode and the cathode of the Alexander Cell (corrosion cell)

Complete circuits can be examined• We can compare the circuits

on the Technotoy to the equivalent circuits that we experience in cathodic protection field work.

• The DCVG measuring circuit is separate from the cathodic protection circuit and the corrosion circuits of any corrosion cells.

• DCVG is NOT measuring corrosion or the pipeline circuit.

• DCVG is measuring ground potential variations.

Oscilloscope and logged voltages

• You can see in this picture that the voltages through the breadboard at the black and the yellow terminals are being recorded on the oscilloscope.

• You can also see the voltages on the data logged and presented in graphic format at the same time.

Note the electrode positions and DCVG voltage

Cu/CuSO4 electrode on anode

DIN50918

Replication of DIN50918• Note that contact with the

electrolyte/metal interface is through a tooth pick that is damp and conductive.

• This is the Luggin capillary and does not disturb the corrosion reaction.

• However, we cannot replicate the closed circuit conditions required with the return electrode in contact with the other circuits.

• This illustrates why we cannot use Cu/CuSO4 electrodes as reference potentials for the purpose of our calculations.

DCVG is a voltage between two electrodes.

• It can be seen in this picture that the slightest change of position of either of the electrodes causes a change in the recorded values.

Cu/CuSO4 electrode on cathode• Moving one electrode from the

anode of the Alexander cell to the cathode has changed the DCVG voltage to 10.95 mv

• This is only possible to measure if the electrode is positioned at the interface and cannot be measured in the field.

• Some people try to say that we can measure ‘anodic anodic’ ‘cathodic cathodic’ but this is nonsense with no scientific foundation.

3.6 micro-amps reaction current

DCVG 123.0 mv positive.

This series was without cathodic protection.

• The next series will include measurements with impressed current and switching.

• I would like to see any presentations or written information from others who claim that they invented DCVG.

• It is not sufficient to say that Mr X or Ms Y invented it and has now died.

This is where I first used DCVG in 1974

Oscilloscope

Sample of data logger capability.

Circuit sketch.

Data acquisition. • The DCVG measuring circuit is between two Cu/CuSO4

electrodes as in field work.• The base of the Alexander Cell is in contact with remote

earth, but corrosion has not been activated by cleaning the anode on top.

• The Alexander cell is connected to the pipeline and so the current measurement is influenced by the whole circuit, as in real life. The meter is set to micro-amps and these are not logged.

• The Oscilloscope is connected to the whole circuit through the breadboard.

• The left hand multimeter is not in logging mode and is just displaying the breadboard voltages.

‘Natural’ pipe-to-soil potentials. • The measurements that we have recorded have not

been subject to impressed current or sacrificial anode cathodic protection.

• The term ‘natural’ is sometimes used to describe this status but the correct term is ‘as found’ because the equilibrium between the structure and the electrolyte is not natural as soon as the structure is constructed.

• Technotoy includes some of the influences that are in play everywhere that cathodic protection systems are designed, constructed and commissioned.

• We can now examine the effects of both impressed current and sacrificial anode systems on the recorded measurements.