The document describes an experiment using Technotoy to demonstrate that direct current voltage gradient (DCVG) measurements alone cannot determine corrosion status. Electrodes, a data logger, and other equipment were set up and connected. Measurements of voltage, current, and DCVG readings were taken over several minutes as the cathodic protection system switched on and off. The experiment showed that DCVG readings changed with time and probe position but were not related to corrosion levels. It concluded that only measurements using a reference electrode directly on a corrosion cell anode provide meaningful data for electrochemical calculations.

1. Technotoy stage 6
DCVG with impressed current
switching

2. Setting up for stage 6

3. Cu/CuSO4 electrodes stored.

4. Power supply to timer

5. Timer set to 5 sec on 1 sec off

6. 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.

7. 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.

8. 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.

9. 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

10. During the next minute

11. DCVG voltages changing with time

12. During second minute

13. During second minute

14. Immediate after off.

15. During 3rd
minute

16. During 3rd
minute

17. Showing breadboard circuit

18. Positions of DCVG electrodes

19. During 3rd
minute

20. During 4th
minute

21. Corrosion current is negative

22. Corrosion current is negative.

23. Corrosion current is positive

24. Corrosion current is negative

25. Corrosion current is negative

26. Corrosion current is negative

27. Corrosion current is positive.

28. Corrosion current is positive.

29. DCVG logged data

30. 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’.

31. 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.

32. 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.

33. Resetting Technotoy

34. 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.
•

35. Connections

36. 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.

37. Details of breadboard

38. Details of Orac

39. 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.

40. 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.

41. 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.

42. Ready to rumble

43. 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.

44. Alexander Cell primed and CP ‘On’

45. DCVG probes same position

46. 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.

47. 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.

48. Displayed measurements changed
• Left hand meter
1.3383 volts
• DCVG meter -112.1
volts
• Corrosion current on
left hand meter 4.0
micro-amps

49. Technotoy

50. 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

51. 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

52. Anode corrosion visible.

53. Visible corrosion

54. 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.