technotoy6

Technotoy stage 6

DCVG with impressed current switching

Setting up for stage 6

Cu/CuSO4 electrodes stored.

Power supply to timer

Timer set to 5 sec on 1 sec off

Measurements at 20:35 on 7th July 2016

• Oscilloscope flat line at 1.35 volts

• Left hand meter 1.3552 volts

• Centre meter 448.3 mv• Right hand meter unclear

in picture.• Data logger showing

dynamic graph of DCVG voltages.

• TR set a 3 volts and very little current due to resistances in CP circuit.

DCVG voltages fluctuating.• Corrosion current 46.4

micro-amps being protected during the switched on phase.

• The graphic log of the DCVG voltages are easily seen.

• The left hand meter is measuring the voltage at the blue and green terminals on the breadboard. This is the voltage of the dry cell battery.

In the same minute

• Dry cell battery 1.3551 volts

• Centre meter 484.6mv• Left meter -50.7 micro-

amps corrosion current• Data logger graph visible.• Display response shown

by different voltages through RS232c connection. 482.2 mv.

In the same minute• The electrodes are in the same

positions so the displayed measurements have altered with time

• There are recordings of slight corrosion noise on the oscilloscope.

• The data logger shows the variations in voltages between the two DCVG electrodes during this minute

• The corrosion current has been reversed by the CP and shows negative 52.3 micro-amps

During the next minute

DCVG voltages changing with time

During second minute

Immediate after off.

During 3rd minute

Showing breadboard circuit

Positions of DCVG electrodes

During 3rd minute

During 4th minute

Corrosion current is negative

Corrosion current is negative.

Corrosion current is positive

Corrosion current is negative

Corrosion current is positive.

DCVG logged data

Voltage between two electrodes

• This voltage is 000.4 mv when the porous tips are together.

• The values are positive because of the way the probes are plugged into the voltmeter.

• The top graph shows all the values recorded a1 second intervals for 1065 seconds.

• The lower graph shows the first 100 seconds.• Neither graph shows wave forms for the

purposes of determining the ‘polarized potential’.

This stage proves that DCVG cannot possibly determine the corrosion status.

• Remember that we must see a kick on the waveform immediately the CP current is switched off.

DCVG

• Is very good at accurately positioning coating faults.

• It is also good for plotting ground potentials if used properly.

• A copper/copper-sulphate electrode cannot be used as a reference potential to determine if corrosion has been controlled.

Resetting Technotoy

Electrolyte added to Orac

• Two layers of absorbent cloth have been added to the copper plate that represents remote earth.

• Some features have been added between the layers to demonstrate some readings that are often misinterpreted.

•

Connections

Groundbed and pipelines

• The yellow jumper connect Orac groundbed to the breadboard.

• The black leads seen coming round the front of the case are connected to the pipeline test posts.

Details of breadboard

Details of Orac

Connections to oscilloscope• These are doubled up

with the micro-ammeter.• The anode of the

Alexander cell has been polished to make it react to the electrolyte that will be added to the absorbent cloth.

• The two Cu/CuSO4 electrodes can be seen in their store container.

The Alexander Cell is a corrosion cell in which the corrosion current can be measured

• NACE has not got a method to measure actual corrosion current.

• ICorr has not got a criterion for the achievement of protection or control.

• No university has produced a definitive criterion.

• Using the Alexander Cell in Technotoy we can actually computerize corrosion control.

DCVG measurement record.• The first reading will be

logged at the near zero mv between the tips of the two electrodes.

• The electrodes will then be moved in the same way that DCVG walking sticks are moved during a survey.

• These measurements will be recorded on the data logger in the computer.

Ready to rumble

Start corrosion

• Polish the anode of the Alexander Cell.• Wet the absorbent cloth covering remote

earth on Orac• Switch on the meters and the Oscilloscope• Position the two DCVG probes.• Wet the absorbent ‘bridge’ between the

anode and the cathode on top of the Alexander cell.

Alexander Cell primed and CP ‘On’

DCVG probes same position

CP switching and probes moved• Oscilloscope shows

disturbance plus switching.

• Data logger shows -172.2 volts between the two electrodes.

• Left hand meter 1.3383 volts of battery

• Middle meter -172.4 mv• Left meter -74.6 micro

amps corrosion current reversal.

DCVG probes not moved• Oscilloscope shows

disturbance plus switching.

• Data logger shows -172.2 volts between the two electrodes.

• Left hand meter 1.3383 volts of battery

• Middle meter -172.4 mv• Left meter -74.6 micro

amps corrosion current reversal.

Displayed measurements changed

• Left hand meter 1.3383 volts

• DCVG meter -112.1 volts

• Corrosion current on left hand meter 4.0 micro-amps

Technotoy

Corrosion cell measurement• The DCVG probes placed

on the anode and cathode of the Alexander corrosion cell and displayed 046.7 mv difference.

• Left hand meter 1.3382• DCVG meter 0.428 mv• Protection curent -32.2

micro-amps• 046.7 logged

DCVG probes on corrosion cell

• Left hand meter 1.3382

• DCVG meter 010.9 mv

• Cathodic protection reverse corrosion current on right hand meter.-35.9 micro-amps

Anode corrosion visible.

Visible corrosion

We have demonstrated• It is possible to gather and record data from a

DCVG survey.• This data is not related to the corrosion status of

any structure or pipeline.• We can plot ground potentials in voltages related

to ground potentials at other locations.• A Cu/CuSO4 electrode is a ground contact only.• The electrolyte potential at the interface of

anode in a corrosion cell is the only place that we can make a meaningful measurement for electrochemical calculations.

technotoy6

Engineering