Cathodic Protection Interactive Experiment/Demonstration.



The practical application of cathodic protection
including Cathodic Shielding and Disbondment.
This on line experiment is now being followed by a number of cathodic protection professionals who have asked questions that can be answered by repeated observation during this experiment/demonstration.

The following statement is included in a scientific paper by a highly qualified corrosion control specialist and does not seem to reflect field experience or electrical logic. As it refers to matters that can only be measured by electrical instruments it deserves examination with experiments to repeatedly observe the claims.

"If the failed coating does not impede the flow of CP current onto the pipe steel then normal CP monitoring will ensure continued pipeline integrity.
When a PE based coating loses adhesion from the metal substrate then a condition of CP shielding can be created."


This statement means that a highly resistant layer over the metal is now described as 'CP shielding'.

There have been questions raised about cathodic protection in association with metalic sleeve crossings and this is being included in the second run of this experiment.

The following drawings might help to explain my rational behind the set up.



This drawing shows a section of a length of steel pipe with coating that has not stuck to the steel but has not included any reacting chemicals in the space.



This picture shows the transformer rectifier 'pumping charges' into the groundbed and they are diffusing to remote earth through shells of resistance.



This drawing shows the potential gradient that can be plotted and the path of the cathodic protection current. It cannot pass into the pipeline metal due to the resistance of the coating.



It is possible to measure the voltage across the coating and the resistance of the coating itself at this location to get the amount of current flowing onto the pipe metal.



The total current output of the transformer rectifier is the sum of the current passing through each of the coating faults minus the amount passing through the coating itself (and that must be considered as the number of resistances in parallel given by the coating manufacturer as the specified resistance per square meter divided by the total area of pipeline metal separated from the electrolyte).



The voltages measured using Cu/CuSO4 electrodes are the potentials of the ground at the location off contact. The potential of the pipe metal is zero, as that is connected to the common pole of the meter, and that is how the meter works. Reversing the connections merely changes the polarity sign.



This is known in electrical terms as 'insulation' and is a condition whereby a conductor is coated with a highly resistant material ranging from shellac through to a wide variety of plastics that prevent electrical current from entering the metal.

If the current can enter the conductor it is called a 'short circuit' and sometimes occurs when age reduces the electrical resistance of the coating material and there are charges in the environment that complete their circuit through the coating fault.

It occurs on pipelines where bio-degradible materials such as natural bitumen have been used. Such pipelines require lots of current to achieve cathodic protection, and in some circumstances this current will not spread sufficiently without extensive re-wrapping of the pipeline in the immediate area of influence of the groundbed.

If the insulation on a pipeline is complete then no curent will reach the metal and corrosion can only take place in the 'blister' formed by the lack of adhesion.



The amount of corrosion possible within this confined space is limited to the reactions possible dependent on the content. If there is no cyclic microbial activity then the corrosion will use up all the agressive chemicals and stop. It is easy to see where this has happenned as you will see a thin layer of corrosion products at the anodic areas and discoloration at the cathodic areas.



If there are sulphate reducing bacteria encapsulated with water and sulphates, then they have a micro-environment that is self-sustaining by reducing the sulphates to sulphides that with water make sulphuric acid that disolves the metal leaving sulphates for the bacteria to eat all over again.

The only way that these microbes can get into the blister is during the wrapping of the pipe as the coating is waterproof and electrically insulating.



The energy released by this life cycle is in the region of 1.2volts when measured in closed circuit condition in relation to a Cu/CuSO4 electrode and Lugin capillary to the anodic interface of the reaction. This can be replicated in a laboratory and in the field using the Alexander Cell.



The result of these animals is a carbunkle that smells of rotten eggs and to test for these you must gather samples under water and add distilled water to the test tubes to observe the discoloration over time.

If the coating has the slightest hole in it then the whole of the blister will be charged to the same level as the ground. This is confirmed by the recommendations of the 'Isopotential Cell' as suggested by Dr's Baekmann, Prinz, Schwenk and others (who all filed patents based on this principle).



Electricity does not 'flow' in the same way as fluids or gasses but distributes itself according to the laws of physics as codified by Newton, Einstein, Kirchoff, Gibbs etc.



It can therefore be seen that the potential outside of the blister is equal to that inside the blister and if there are sufficient charges to balance the corrosion reaction outside of the blister they will certainly balance the electro-motive force at the anode of any corrosion cell within the blister.



Scientists express themselves using Greek letters to represent their reasoning and I find it difficult to explain what they mean to my students. That is one reason that I use demonstrations and diagrams in my publications as I would like to enable people to UNDERSTAND cathodic protection and not just to be able to reproduce scientific notation.








The following demonstration is set up to measure the effects of cathodic protection on corrosion cells and coatings.
1. A short piece of steel pipe is coated with insulation tape and four coating faults are cut out. Corrosion will not take place under the coating of a pipeline as manufacturers have designed the material to prevent this.



Each fault is treated in a different way to replicate conditions found on pipelines.



Fault 1. Is left clean and bright but the tape is not stuck to the metal. This represents a 'void' as seen where coating is not applied properly.

Fault 2. Is coated with masking tape that is electrically conductive and through which water and chemicals can permeate.

Fault 3. Is treated with acid electrolyte on half of it's area and the other half left bright and clean.

Fault 4. Is treated with acid electrolyte on half of it's area and the other half left bright and clean. This is then wrapped with insulation tape to replicate pipeline coating that includes active electrolyte that might be subject to 'cathodic shielding'.



Lugin Capillaries are prepared to be in contact with the metal-to-electrolyte interface at each of the faults. These are necessary to make measurements at the reaction interface between the metal and the electrolyte It should be made clear that this is the reaction potential or electro-motive force caused by the metal going into solution. Any measurement away from this reaction is subject to the IR drop due to the charges travelling through the electrolyte towards the cathodic electrode of the system.



These Lugin capillaries are fitted to each interface to enable true potential measurements to be made. These consist of drinking straws filled with conductive non-reactive gell that will become charged to the same potential as the EMF but will carry no current once charged.



This drawing shows the measuring circuit in compliance with DIN50918. It will be seen that the 'reference electrode' is in a position similar to that described by many scientists in cathodic protection papers.








The pipe is placed on a bed of sharp sand in the first section of a tray.





A fully coated pipe is placed in the second section of the tray, the bare steel anode pipe is placed in the third section of the tray and a pipe wrapped in masking tape is placed in the fourth. The bare steel anode is the eqivalent of an anode bed or groundbed in an impressed current cothodic protection system. The Charges are 'pumped' or impressed into the ground rising it's electrical pressure or potential. This is measured during this experiment as will be seen.



The straws that serve as lugin capillaries are fed through the lid of the tray that is supported on two plastic clamps.



The subject pipe in the first section is connected to the negative terminal of the power supply.This is the same as any pipe or structure that is being subject to any impressed current cathodic protection.
The fully wrapped pipe in the second section is also connected to the negative terminal of the power supply.
The pipe in the third section is the anode of this impressed current cathodic protection system and is connected to the positive terminal of the power supply.
The pipe in the fourth section is not connected to anything and is wrapped in masking tape that is not insulating or water resistant. It might tell us something.



Anyone wishing to set up an experiment outside can use a short length of 2" dia steel pipe.



This should be coated with tape or shrink sleeve and provided with connection points in the same way as cross country or service pipelines.



A transformer rectifier or a battery charger/DC power supply should be set up to pump charges to a steel grounding facility or even use manufactured impressed current anodes.



Steel coupons or off cuts from the pipe should be buried at intervals with 'tails' to be brought up to test posts. This will allow manipulation of the distribution of current that will enable testing of automatic control systems, ground potential profile plotting and other monitoring techniques.



A coupon with a 'reference electrode' should be buried close to the pipe and the tails brought up to a junction box and labelled.



The whole area should be reinstated as a buried pipeline would be seen in service.








There are several national and international cathodic protection disbondment tests that are recommended to coating manufacturers. This is a schematic representation of the UK code of practice written by Prof Les Woolf for the British Standards Institute.



A steel coupon (coloured green) is suspended in a tank of water at a specific pH value with a coating fault of specific dimensions exactly 10mm from a reference electrode. A controlled amount of charge and current is passed from an anode in the tank that is a specific distance from the reference electrode and the coating fault.



This picture shows the reasons for the specific distances as the voltage drop in the electrolyte create zones of potential that are crucial to the measurements.



This drawing shows the effect of moving the reference electrode out of it's specified position.



This drawing shows the result of trying to conduct the test with no coating fault. No current would flow and there would be a uniform potential throughout the tank.



This drawing shows current flowing to the metal from the whole of the tank. We must remember that this is in three dimensions and the lines follow the inverse square law of radiation and not the flow behaviour of liquids.



The flow of charges to the coating fault through 'shells of resistance' (described by Dr's Prinz, Baekmann and Baaltz) form the potential profile that we are familiar with in cathodic protection field work and on which DCVG and CIPS depend.

The following statement appears in a scientific paper on cathodic shielding and is considered during this experimental demonstration.

The electrochemical process of cathodic protection causes the environment around the cathode (pipe, tank, etc.) to become alkaline, especially at the surface of the metal being protected. The pH of typical pipeline surfaces with adequate CP would be in a range of 9 to 13. In this range steel is protected and corrosion is significantly reduced or eliminated.



We need to test this statement and pH measurements will be included as this experiment develops.



The position of reference potentials is crucial to Cathodic protection measurements and this is studied in detail in this demonstration by using many independent voltmeters and lugin capillaries to the positions recommended by science.



'Salt bridges' are made using gelatine and plastic drinking straws to electrically connect the sections of the tray without introducing the possibility of intrusive electrochemical reaction. this is the same principle as using agar agar in Lugin capillaries.... conductive but not disturbing the reaction.



It is good to have expensive laboratory equipment for experiments such as this, but the cost is one reason why many cathodic protection engineers and field workers do not test theories when they see their field results.



'Salt bridges' made with straws and gelatine. These are included to test the conductivity of such items and relate to the use of lugin capillaries and such like.



The lid of the tray is used as platform for the reference potential containers.



All materials and instruments used in these experiments are available from retail sources as a deliberate intent to make the results repeatable by anyone anywhere.



The mechanical clamp used to support the lid is plastic with a metal spring that is not in contact in any way that can effect this experiment.



The negative terminal of the power supply is connected to two pipes and the positive connected to a bare steel pipe as the anode of the system.

This view through the top of the tray shows the way that charges can travel from the shiny bare pipe into the electrolyte and then through the gelatine in the straws to each of the sections of the tray.



You can see the red connector and the two black connectors and that they are insulated from the electrolyte to prevent bi-metalic couplings in the system.



These pictures show the setting up using things like tooth pick containers and stripped copper wire.



It is hoped that others will examine these pictures make suggestion of improvement.







The copper sulphate solution has been added to the containers and the voltages are shown on the multimeters.



The multimeters show the 'natural potentials' referred to by many corrosion engineers.



The power supply has not yet been switched on.



The red meter on the right is connected between the standard 'half-cell' and the subject pipe. The pipe-to-soil potential difference is 0.729 volts.



The grey multimeter is connected between another half-cell and the subject pipe and shows 0.15volts.



The four multimeters at the bottom of the picture are connected to the subject pipe and each of the four reference electrodes.



Each of these reference electrodes is connected to the interface between the metal and the electrolyte by a Lugin capillary.


In the case of the large multimeter on the right it is in fully enclosed 'blister' with no inclusions except the conductive gelatine to complete the measuring circuit.



The second meter from the left is connected to the Lugin capillary that runs to the interface between the metal and the conductive permeable coating.



The third Lugin capillary runs to the anodic interface on the coating fault that is covered by the conductive coating.



The right hand Lugin capillary runs to the anodic interface of the coating fault that is contained in a sealed 'blister in the coating.














04 ?April ?2012, ??23:07:04



Voltages of 0.661, 0.63,0.62 and 0.61 on respective voltmeters



In the picture below you can see that the grey voltmeter reads 3.92 volts and is connected to the half cell that is in the section with the pipe that is being used as the anode of this cathodic protection system.



The red multimeter is showing 0.661volts and is connected to the half cell that is in the section containing the subject pipe. Both this and the grey meter have their common connections to the subject pipe.



In this picture you can read 0.63, 0.62 and 0.61 volts on the meters and see that they are all connected to the reference electrodes and the common connection to the subject pipe. The individual Lugin capillaries run to three of the metal-to-electrolyte interfaces.



This picture shows the status and setting of the power supply for this group of pictures.



These pictures show the voltmeter readings at the new settings.



The power supply was adjusted upwards through this next group of pictures.



At this stage I had not adopted a disciplined method and was simply adjusting and watching the results in the way that I do in the field.


I realised that I must get this sorted for the benefit of those reviewing these experiments.



You will notice that later I include a clock in the pictures, but at this stage the pictures were taken in sequence on the same camera and pasted straight into this report.



I hope that readers will comment and suggest improvements to techniques and display.



This picture shows the setting for the next batch of pictures.



Viewers should note that the meters all have a common connection to the subject pipe as in field application of cathodic protection. A mile of welded 36" dia pipeline has no significantly more resistance that the piece of pipe in this experiment.



We can only obtain data using electrical instruments as sophisticated electrochemical methods are not practical for extensive field use.



In this picture you can see the two hald-cells that I made using copper wire and small plastic containers with plaster porous plugs. For those who argue about the accuracy and calibration of half-cells it can be seen that the voltages we are measuring will not be rendered useless by the fraction of a percent inaccuracy between two half-cells.



It can be seen that the grey meter and the red meter have a common connection to the pipe and are each connected to a similar half cell in a different location. This replicates the status found in cathodic protection field work.



There is a potential difference between the half cell in the anode section and the subject pipe of 18.03 volts. The power supply is at it's maximum setting of 12 volts. There is no other source of charges in this closed circuit system.



It can be seen that the copper sulphate solution is leaking from the reference electrode containers into the subject pipe section of the tray.







At last I thought of including a clock in the picture showing the time to be 1737.







Taken at 1738pm.........



At 1812 I had arranged the multimeters to be standing up so that all readings could be seen on the same picture.























































At 2000hrs it became obvious that the salt bridges were not carrying enough charges to the subject pipe section of electrolyte to satisfy the normal requirement of -0.85 volts potential difference between a half cell and the pipe line metal. This is shown on the meter on the right as 0.660 volts and the half cell is placed in the subject section of the tray but with the insulating coating making it electrically remote as in the case of normal field pipe to soil readings.



A copper wire is connected between the anode section and the subject section to carry the charges completing their circuit. This would be considered as cathodic shielding in real life as it would deprive remote earth of charges and restrict the spread of current. We are dealing with a contained system, so this does not apply.



The readings were affected by the contact of the copper wire with the electrolyte.



Moving the wire improved the contact and altered the readings.



Good contact was established with the results seen.



This picture was taken at 803pm on wednesday 4th April 2012.

The grey meter at the top of the picture is connected to a half-cell in the immediate area of influence of the anode and therefore shows avoltage of 17.86v as this is the potential difference between the Cu/CuSO4 electrode and the pipe metal.

The red meter beside the tray is connected to a half-cell in the sectionof the pipe but in what might be called 'remote earth' by comparison to field work. This shows a reading of 1.279volts and is typical of voltages recorded on 'pipe-to-soil' surveys.

The next meter, going clockwise, is connected to the pipe metal and a reference electrode with a Lugin capillary to the anodic interface of a corrosion cell on the pipe that has been coated over the active electrolyte to mimic a blister on a pipeline that has inclusions but no access to cathodic protection current.

The next meter has a similar arrangement but is coated with a permiablematerial.

The next meter is connected to a bare piece of the pipe that represents a coating fault on a pipeline in the field.

The final big meter on the left is connected through a Lugin capillary to an interface where there is no adhesion but no inclusion.























































This picture was taken at 1327 on thursday 5th april 2012




This picture was taken at 1328 on thursday 5th april 2012




This picture was taken at 1327 on thursday 5th april 2012




This picture was taken at 1327 on thursday 5th april 2012








There is a copper bridge between the anode section and the subject pipe section.







This picture was taken at 1330 on thursday 5th april 2012
here is a copper bridge between the section containing the anode and the section containing the subject pipe.
Salt bridges are in place as originally set up.The grey meter is connected between the subiect pipe and the half-cell in the anode section.




This picture was taken at 1330 on thursday 5th april 2012



This picture was taken at 1330 on thursday 5th april 2012
There is a copper bridge between the section containing the anode and the section containing the subject pipe.
Salt bridges are in place as originally set up.The grey meter is connected between the subiect pipe and the half-cell in the anode section.




This picture was taken at 1335 on thursday 5th april 2012




This picture was taken at 1336 on thursday 5th april 2012
There is a copper connection between the anode section and the subject pipe section.
The grey meter is now connected between the two half-cells in the anode section and the subject pipe section.



This picture shows the copper connection between the electrolyte in the anode section and the electrolyte in the subject pipe section.
It shows that the salt bridges are still in place between all sections.



this picture shows the copper connection between the anode section and the subject pipe section.
It also shows that the grey meter is connected between the two half-cells and the salt bridges in place.



This picture was taken at 1337 0n thursday 5th april 2012




This picture shows the two copper connections between the anode section and the subject pipe section.
The salt bridges are still in place between all sections.







this picture was taken at 1339 on thursday 5th april 2012.



This picture was taken at 1340 on thursday 5th april 2012.



This picture shows that the three copper connections have been removedand the following pictures show the effect of these removals.



This picture was taken at 1342 on 5th april 2012. It shows that the three copper connections are removed and the salt bridges are still in place.



This picture was taken 1342 on 5th april 2012.



This picture was taken 1342 on 5th april 2012.



This picture was taken 1342 on 5th april 2012.



This picture was taken 1342 on 5th april 2012.



This picture shows the 7 salt bridges have ben removed from between the anode section and the section with the pipe that is coated with permeable conductive tape.



This picture was taken 1345 on 5th april 2012.
06 ?April ?2012, ??02:04:32



This picture shows that the salt bridges have been removed between the anode section and the section with the pipe with the conductive, permeable coating.



This picture was taken at 1345 pm on 5th april 2012. 06 ?April ?2012, ??02:05:54



This shows that the second row of salt bridges have been removed from between the anode section and the disconnected, well coated pipe.



This picture was taken at 1538 on 5th april 2012. 06 ?April ?2012, ??02:07:19



This picture was taken at 1538 on 5th april 2012.
it shows the salt bridges that have been removed from the division.



This shows that all the salt bridges have been removed from the dividing walls.



This picture was taken at 1351pm on 5th april 2012.
















This picture was taken at 1352 on 5th april 2012.



This picture was taken at 1352 on 5th april 2012.



This picture shows the setting and status of the DC power supply, taken at 1353 on 5th april 2012.



This picture was taken at 1354 on 5th april 2012.



This picture was taken at 1354 on 5th april 2012.



This picture shows that the setting of the power supply has been changed to 7.5 volts output.



This picture was taken at 1355 on 5th april 2012.



This picture was taken at 1355 on 5th april 2012.



This picture was taken at 1355 on 5th april 2012.



This shows that the power supply has been set at 6 volts.



This picture was taken at 1355 on 5th april 2012.



This picture was taken at 1355 on 5th april 2012.



This shows that the power supply has been set at 4.5 volts.



This picture was taken at 1356 on 5th april 2012.



This picture was taken at 1356 on 5th april 2012.



This shows that the power supply has been set at 3 volts.



This picture was taken at 1356 on 5th april 2012. 06 ?April ?2012, ??13:03:00



This picture was taken at 1357 on 5th april 2012.



This shows that the power supply has been switched off.



This shows that the power supply has been switched off.



This picture was taken at 1358 on 5th april 2012.



This picture was taken at 1358 on 5th april 2012.



This picture was taken at 1358 on 5th april 2012.



This picture was taken at 1912 on 5th april 2012.



This picture was taken at 1912 on 5th april 2012.



This picture was taken at 1912 on 5th april 2012.



This picture was taken at 1914 on 5th april 2012.



This picture was taken at 1914 on 5th april 2012.





This picture was taken at 1914 on 5th april 2012.



This picture was taken at 1921 on 5th april 2012.



This picture was taken at 1922 on 5th april 2012.



This picture was taken at 1935 on 5th april 2012.



This shows the power supply now on set to 12 volts



This picture was taken at 1935 on 5th april 2012.
The power is on and the copper bridges are in place between the section with the anode and the section with the subject pipe.



Close up of four meters.



Copper bridges in place.



Pipe-to-soil 1.718 volts



This picture was taken at 1937 with the copper bridges in place



Close up of four meters.



This picture was taken at 1937 with the copper bridges in place



This picture was taken at 1937 with the copper bridges in place



This picture was taken at 1937 with the copper bridges in place



This picture was taken at 1938 with the copper bridges in place



This shows the power supply on at 12 volts.



This shows the time at 2043 on 5th april 2012



This shows the copper bridges in place between the anode section and the subject pipe section



This shows the time being 2045 on 5th april 2012.



This shows the time being 2045 on 5th april 2012.



Close up of the four meters



Close up of the four meters



Pipe-to-soil and half cell to half cell voltages.



All voltages at 2045 5th april 2012.



Power supply setting 12 volts.



Time 0022 on 6th april2012.



Time 0022 6th april 2012, ppe-to-soil 1.715 volts, half cell to half cell 9.5 volts.



All voltages shown.















Shows the copper bridges in place.



Time 0024 6th april 2012 pipe-to-soil 1.709 volts.



Time 1115 am 6th april 2012,



Power supply still on and set at 12 volts output.



Half cell to half cell 8.2volts on grey meter,
pipe-to-soil 2.3 volts,
front row (clockwise) 1.07 volts,
0.66 volts,
0.79 volts,
and the big meter on the left 0.99 volts.


06 ?April ?2012, ??13:47:18
Another view showing copper section connection on left of tray and two half-cells.



Showing copper connections between sections on the left of the tray.half-cells.



This picture was taken at 1506 on the 6th april 2012.
08 ?April ?2012, ??17:15:33

08 ?April ?2012, ??17:17:28
The power supply is on at 12 volts setting..



This picture was taken at 1507 on the 6th april 2012.



This picture was taken at 1507 on the 6th april 2012.



This picture was taken at 1514 on the 6th april 2012. after the solution had been changed in the reference cells.



This picture was taken at 1515 on the 6th april 2012.



This picture was taken at 1515 on the 6th april 2012.



This picture was taken at 1515 on the 6th april 2012.



The power supply was on set at 12 volts during this group of photos.



This picture was taken at 1515 on the 6th april 2012.



This picture was taken at 1515 on the 6th april 2012.



This picture was taken at 1515 on the 6th april 2012.



This picture was taken at 2005 on the 6th april 2012.



The power supply was on at 12 volts.



The time was 2005 6th april 2012.



The time was 2005 6th april 2012.



The time is 1937 7th april 2012.



The power supply is on at 12 volts.



The time is 1937 7th april 2012.



The time is 1937 7th april 2012.



The time is 1937 7th april 2012.



The time is 1937 7th april 2012.



The time is 1948 7th april 2012 after changing 9 volt battery on the pipe to soil meter.



This shows the settings and status of the power supply at the time of this group of pictures.



This picture shows the copper connections between the anode section and the subject pipe section. They are seen to be in place but might have corroded away. To be inspected later.



This picture shows voltages that have changed dramatically in the past few minutes and must be investigated.



This picture shows the half-cell to half-cell voltage being 9.7v.



This picture was taken at 1949 on 07 april 2012.

click here for dismantling and results.