Cathodic Protection Course

Dynamic Cathodic Protection

Applying circuit analysis to Cathodic Protection.

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Cathodic Protection Training Course

SYLLABUS

The content of all modules is drawn from personal experience and field experimentation backed up by years of research into the theory and application of cathodic protection in field conditions. Each module is supported by documentation including pictures and data from actual field activities. The cost of each module includes on-line, real time discussion period at the end of each module. We can supply the instruments needed for this course, but will require payment plus shipping costs prior to dispatch. Your organisation may already have the required instruments or chose to obtain them locally.

Module 01

� Introduction to cathodic protection. � Foundation of C.P. � Examples of traditional data � Practical appraisal the voltmeters used in CP work. � Two practical bench studies, requiring a report. � First field visit, requiring a report. � On-line real time discussion.

Module 02

� Technical history of C.P.

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� Explanation of the reasons behind current trends in C.P. � Financial and operational benefits of CP. � Academic and scientific views of CP. � Commercial aspects for and against CP. � Introduction to measuring and monitoring � Theory behind the 'immediate off potential'. � Practical, make two reference electrodes (half-cells) � Field trip with simple exercise in CP measurment requiring a report. � On-line real time discussion.

Module 03

� Thermodynamic theory of CP simplified. � The significance of the Pourbaix diagrams. � The Daniel Cell in laboratory work. � The importance of the reference potential. � Codes of practice. � Standard laboratory techniques � The development of standard techniques in field work. � Open circuit measurements. � Errors and their causes. � Interference. � Practical bench experiments. � Field trip with experiments requiring a report. � On-line real time discussion.

Module 04

� Equivalent circuits � Physical modelling of CP measurement techniques. � Practical construction of 8 measurment models. � Simulation of field conditions on the bench. � Field trip to confirm theoretical and model integrity requiring a report. � On-line real time discussion.

Module 05

� Significance of the paper presented at the � Australasian Corrosion Conference of 1982 � Practical bench work to confirm this paper. � Field trip to confirm theoretical and benchwork integrity requiring a report. � On-line real time discussion.

Module 06

� Introduction continuous potential surveys � Recording voltmeters and data-loggers. � Monitoring techniques which are presently used to establish

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C.P. criteria. � The Prinz Cell. The Baekmann Cell, � The Alexander Cell and arrangement suggested by Jim Gosden of the British Standards Institute. � Summary of the present status of the criteria for 'protection'. � Practical bench construction of an 'isopotential cell' and an Alexander Cell. � Field trip to use both types of cell requiring a report. � On-line real time discussion.

Module 07 (under construction)

� Proximity of foreign structures. � Interference possibilities. � Basic interference testing and resolution � Monitoring interference and interpretation of data. � Practical bench experiment simulating interference. � Field work to set up temporary interference readings. � Computer modelling of interference. � Report and on-line real-time discussion.

Module 08 (not compiled yet)

� Ground resistivities. � Resistivity measurements. � Temperature and pressure effects. � Effects on corrosion. � Spread of protective currents. � Effects on monitoring measurements. � Groundbed siting. � Practical work with Mega, soil boxes, resistivity cells etc.

� Report and on-line real-time discussion.


� Groundbed design. � Sacrificial anodes. � Impressed current anodes, materials conductors, volts drops, header cables, ring mains, insulation, jointing systems. � Groundbed potential profile plotting. � Closeness of anodes. � Horizontal, vertical, borehole and disused-used oil-wells. � Scrap metal groundbeds. � Practical bench experiments relating to groundbeds. � Field work with survey to locate a groundbed and plot it's profile.

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� Report and on-line real-time discussion.


� Transformer rectifier design and specification. � Output requirements for land and swamp applications compared. � Safety in design. � Safety in operation and maintenance. � Practical bench work with small transformer/rectifier. � Field visit to identify anf define a transformer recifier. � Report and on-line real-time discussion.


� Polarisation and de-polarisation. � CIPS surveys. � CIPS with switching. � Potential Gradient surveys. � Potential Gradient surveys with switching. � Practical bench demonstration of polarisation. � Field work to set up and monitor an example of polarisation and de-polarisation. � Report and on-line real-time discussion.


� Long term monitoring using coupons. � Installed monitoring using Isopotential cells. � Installed monitoring using anodes. � Installed monitoring using the Alexander Cell. � Maintenance and care of instruments, tools and equipment. � Old instruments and the advantages of hi-tech, solid state, digital instruments. � Analogue and digital recording compared. � Advantages over manual records and metering. � Test facilities, test post locations, electrode position, plastic insulation tube theory. � Students will be required to provide a summary and examples. for on-line real-time discussion.


� Current readings, shunts, multi-meters, magnetic filed meters, current direction detection systems. � Current paths and C.P. circuits. � Measurable and immeasurable electrolytic paths. � Current density. � Current requirements for protection. � Design, theoretical vs practical.

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� Demonstration on models and practice setting up and testing. � Field work to measure cathodic protection current. � Report and on-line real-time discussion.


� Tank farms and storage facilities. � Refineries and congested areas. � Pipes under concrete. � Isolation joints. � Pipeline manifolds. � Internal cathodic protection. � Ribbon anodes and line anodes. � Practical bench experiments. � Field visit with test measurements and report. � On-line real-time discussion.


� Computerisation of CP � The Dynamic Project � History of CP computer analysis. � Some software tools for analysis.


� Coatings and surface treatment. � Cathodic disbondment. � Hydrogen embrittlement and overprotection. � Anaerobic bacterial corrosion. � Leak investigation. � Corrosion damage reporting, imaging and castings. � Practical bench work. � Field visit with report, on-line real time discussion.


� Ground potential fluctuations. � Teluric effects, sunspots and earth magnetic turbulance. � Other identifiable metering disturbances � Field procedures (interpretation of 21 procedures on the web site) � Practical bench simulation of procedures and disturbances. � Field practice of each procedure with report. � On-line real time discussion.


� Offshore cathodic protection.

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� Sacrificial anodes offshore. � Impressed current systems offshore. � Isolation joints, flexible hose connections and safety. � Monitoring of offshore pipelines. � Monitoring of offshore platforms and structures. � Practical bench modelling of offshore pipeline CP � Report and on-line real time discussion.

Return to front page

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Introduction to this course

This course is for everyone involved with the application of cathodic protection. Cathodic Protection has always been divided between the science of electro-chemistry and the application of cathodic protection technology in the field. Since the 1980's cathodic protection data has been stored on computers but the gap between the electro-chemists and the most basic field practices has made it difficult to achieve computer analysis. This course includes practical work that is designed to enable the student to understand applied cathodic protection from the very basic principles. It is important that each student understands each module as a basis on which they can move forward to the next. At the end of the course each student will be required to present a paper for publication on the CPN website. The merits of each paper will be assessed by the membership of the CPN. Experienced corrosion engineers and scientists will be able to check the validity of each step and are encouraged to express their opinions.

Module 1

An introduction to cathodic

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protection

What is cathodic protection?

Cathodic protection is an electrical way of stopping corrosion. It is crucial that a Cathodic Protection engineer can visualise 'electrical pressures'.

This is a typical illustration of a corrosion cell with the arrows showing the direction of the current. This current is driven by the 'pressure' (EMF) of the corrosion reaction on the surface of the metal.



This pressure drives electrical current through the electrolyte to a point with a lower electrical pressure. We should imagine the 'electrical pressures' as we use the instruments to measure electrical values.

This meter is showing that there is a voltage of 0.530



between it's negative and positive poles. An electrical pressure is known as a 'potential' - not be confused with a voltage. A voltage is the difference in potential between two points, measured in volts. The relationship between voltage, current (measured by ammeters) and resistance (measured in ohms) is defined by Ohm's Law. When measuring voltages any potential can be regarded as zero for the purpose of graphic display and calculations.

This potential can then be compared to another potential using a voltmeter so that the potential



difference can be expressed in volts. The graph above only shows the difference between the two potentials at each point of measurement. There is no reason to suppose that any two voltages are related. This fact is dealt with in depth during this course, including practical experiments.

The above experiment will confirm that the graph base line is a 'floating zero'.

Corrosion produces 'electro-motive-force', which drives current into the electrolyte, causing the



potential of the electrolyte to increase and the corrosion current to radiate out into the surrounding electrolyte. Corrosion is a chemical reaction that discharges electricity from an anode to a cathode through the electrolyte. Metal is changed into rust at the anode and the metal at the cathode remains undamaged. The current generated at a coating defect takes the least line of resistance to return to the pipeline metal

The point where current enters the metal is known as the cathode. No corrosion reaction is possible at this site as the potential of the electrolyte is greater than that of the metal at this immediate interface. The reaction can continue until equilibrium is reached between the chemicals and the electrical energy. The chemicals have 'eaten away' all the metal and have run out of 'food'. No current is produced and so the whole coating fault is 'at rest'. Corrosion product builds up on the metal blocking the path of the current.



Batteries work on this principle. When batteries reach equilibrium we have to re- charge or discard them.



The public are not generally aware that our gas and oil comes to us through pipes that are inclined to rust but are protected by 'Cathodic Protection'.



Pipelines are 'out of sight and out of mind' so little attention is given to the fact that metal dissolves in some solutions and gives off electricity. It is left to the corrosion engineers to worry about such things until a pipeline fails, causing loss of life, environmental damage and massive financial consequences. Consultants are then asked why the pipeline failed and the debate about the criterion for cathodic protection receives attention for a little while. Ship and boat owners are constantly aware of the damage caused by corrosion and consequently metal



boats are protected by cathodic protection. They have lumps of metal attached to hulls for this purpose. These lumps of metal disolve in the water and give off electricity which prevents the hull from corroding. Sir Humphrey Davy first introduced this system by attaching 'pig iron' to the copper clad hulls of ships. There is a considerable amount of information and computer modelling advertised on the internet in this respect. A search will reveal a number of specialised companies offering services and the CPN is not competing in this market. We are concerned with the analysis of data gathered relating to the cathodic protection of buried and submerged, coated, steel pipelines that carry most of the worlds energy supplies from source to the consumer. This is a very specialised study that must begin with at the interface between the pipeline metal and the electrolyte in which it is submerged or buried.

This old photograph was taken during the construction of the network of gas pipelines that have been buried



in the UK for over 30 years. This particular stretch was coated with coal tar enamel and was handled by heavy construction machines. The coating was often damaged and repaired before back-fill. It is clear that coating faults were sometimes missed. The pipe metal at these coating faults is in contact with the ground (the 'electrolyte') , which gets 'charged up' with electricity. The electrical potential' of this bit of ground is increased to a higher electrical 'pressure' than the metal surrounding ground and so the electricity 'radiates' into the earth. The metal that is disolving is the 'anode' from which the electrical current passes into the electrolyte.

The other metal is the 'cathode' into which the current passes from the 'charged up' eletrolyte, because the electrical pressure must be balanced out. (everything tries to equalise it's electrical potential with everything around it). The disolving metal is sacrificed to prevent the subject metal from corrosion, and this fact is harnessed by providing a less noble metal in the corrosion circuit... a system known as 'sacrificial cathodic protection'. There are limits to which sacifical cathodic protection can be used but the same principle can be used by causing a manufactured electrical pressure which is 'impressed' into the electrolyte. The electricity is then 'drained' out of the subject metal....... boat hull or pipeline.... and this interfers with the natural tendency



of the metal to disolve....or rust! Students should try to form a mental image of electrical potential (pressure) and the resulting flow of 'charges'. Do not get confused by the flow of electrons as we cannot see this on our meters. It might be important to the academics but it is irrelevant to field engineers

Impressed current cathodic protection

Alternating Current Electricity is generated by a sort of pumping action which causes it to flow backwards and forwards in 'waves', but this is no use for our purposes so we have to get it going in one direction through a circuit known as a 'rectifier'. At the same time we can control the amount of current by transforming it, so the apparatus is know as a transformer-rectifier.



A transformer-rectifier can be regarded as an electrical pump which is sucking the electricity out of the pipeline (etc) and pumping it into the ground (or sea ... or swamp... or wherever else you want to pump it). The effect of this is amazing. It stops rust! And it's cheap! But there are some snags. Because it's so good, it gets installed .... then ignored...... well most people don't even know it exists... and because it's cheap some people don't think it's important.



THE BASIC CONCEPT OF PIPELINE CATHODIC

PROTECTION

As stated before, everything has a 'potential', which has an effect on it's relationship with it's environment. Corrosion is effected by this relationship, as it is an electro-chemical reaction. The basic concept of cathodic protection is that the electrical potential of the subject metal is reduced below its corrosion potential, and that it will then be incapable of going into solution, or corroding. The reasons for this are given in thermo-dynamic theory but these will not be discussed at this stage.

The corrosion reaction and cathodic protection mechanism has been defined by many scientists and has become established beyond dispute. Many books and papers have been published, giving details of the scientific background of corrosion and corrosion control, as a result of many years of research by respected and sincere specialists. It is not intended to dispute any of this work or the conclusions drawn.

Battery technology can be



compared to corrosion control technology

The principles of corrosion reactions are used in the design and construction of expendable and re-chargeable batteries and accumulators, which play such a major part in modern life. A battery is designed to allow a chemical reaction to cause an electrical current to pass through a desired path, giving energy to the appliance. The battery has a very carefully composed electrolyte which has qualities to ensure a predictable reaction with the other components of the battery.

Corrosion within a battery can be controlled by external electrical techniques which are in common use. Some batteries have a reversible reaction which enables them to be recharged by adjusting the electrical 'pressure' at the terminals. Many appliances are nowadays controlled by computers to balance the reaction equilibrium to suit their own power demands.



All this is possible because the battery is a manufactured unit, designed for the purpose of receiving and supplying electrical current.

CATHODIC PROTECTION IS DIFFERENT Unfortunately, cathodic protection is not a unit composed of simple elements in the way that batteries are, because the electrolyte is the ground itself. This is an uncontrollable feature with an almost infinite variety of qualities.



The picture above is an equivalent circuit diagram of the cathodic protection systems that were preventing corrosion over an area of tens of thousands of square miles of pipelines serving a major oil and gas production company.



The chemical composition and electrical conductivity of the ground can span a vast range and can include environments such as sea water, deserts, freshwater swamps, arable (fertilised) land, etc. etc. Climatic effects cause variations in the temperature, and depth of cover causes pressure variations which effect the reaction, adding yet more indeterminable factors in the reaction.



Cathodic protection of such subjects as gathering stations (shown above) and storage tank bases is relatively simple but as the size of the structure increases, it extends through electrolytes of different nature and the reaction at each interface varies. Offshore oil rigs, for example have different temperatures and pressures at the sea bed to those at the surface, and studies of these conditions have shown that they have substantial influences on corrosion.

UNDEFINABLE ELEMENTS

Pipelines are more complex, and can be regarded as many interface reactions connected together, in parallel.



The metal element, of the reaction, can be well defined, as this is specified to a high degree by the designers. The coating material is carefully designed but it is generally accepted that no coating can be perfect, and the faults (or 'Holidays') introduce the first indefinable element to the system. During the construction of a pipeline, all possible measures are taken to detect and repair coating faults, so it follows that the location and size of those remaining are unknown and not definable. It is possible to calculate the theoretical resistance of a perfectly coated pipeline, given the specification of the coating and dimensions of the pipeline, but it is not possible to calculate the resistance of the coating of an actual pipeline. The electrical current measurements, taken during routine cathodic protection monitoring, show that there is little resistance in the total coating of a pipeline and this can be explained by the difficulty in quality control during coating operations and preventing damage during the construction period. Perfect coating would prevent any output from the CP system but undetected coating faults provide paths for cathodic protection current. We, therefore, know that



there are many unspecified metal-to-electrolyte interfaces present on an average pipeline. The electrical resistance of the pipeline metal itself can be calculated, and is found to be very low. The effect that the pipeline resistance has on the complex current paths and variation in potentials, is found to be so small that it can almost be ignored.

FURTHER COMPLEXITY Each coating fault is a metal-to-electrolyte interface which is capable of a different reaction, electro-motive-force (EMF) which cannot be measured as it is in parallel with all other EMFs on the same section of pipeline.

The magnitude of the current from each of these is dependent on the earth resistance immediately adjacent to the interface, and the current direction is the result of the combined effects of all the resistances and electrical pressures caused by all the other EMF's. Although it is simple to understand each corrosion cell and the mechanism of corrosion itself, the reality of applying the science, to the field, becomes immensely complex. This becomes more obvious when the circuit has been subject to computer modeling as discussed later. To be effective, cathodic protection must reduce the metal at each single interface, to below it's corrosion potential. This is not too difficult to achieve, as each interface is part of the same structure, which has a very low electrical resistance. The difficulty is knowing when all the interfaces have been reduced to below their corrosion potential in relation to the electrolyte in their reaction vicinity.



OVER PROTECTION

There are several other problems, however, as too much current passing onto a steel surface can cause embrittlement, which under certain circumstances can be as detrimental as corrosion itself. This is manifest in such applications as the protection of the external surfaces of drill pipe casings, where a considerable amount of cathodic protection current is used. Another fear of 'over-protection' is that of cathodic disbondment of the coating. This happens when the coating manufacturers specifications are exceeded. Cathodic protection current passing onto the metal causes the release of hydrogen which disbonds the coating. In reality this is rarely a problem. The current will only pass onto the metal at a coating fault, and the density of the current will depend on the size of the coating fault and the current locally available. As the current blows the coating from the metal, the volts drop at the interface will decrease, and equilibrium will be reached with a very small increase in additional disbondment. If there is no coating fault, then no cathodic disbondment will occur, as recognised in the British Standard Code of Practice for testing the coating manufacturers specification. This requires a specific size of coating fault on a steel coupon, to be subjected to an increasing voltage over a specified period. The test cannot be carried out on a coupon with perfect coating as the disbondment is observed under the coating at the edge of the fault. These matters will be covered in detail later in the course THEORY V PRACTICE We simply want to stop corrosion but we need to know when we have succeeded. Cathodic protection is immensely successful, and cost effective, but every leak is a demonstration that we have not applied it correctly. Link to page on Cathodic Protection Measurements



Before going any further it is necessary to imagine electricity and this has been likened to water pressure, with containers connected by pipes to allow current to flow.

However, it can be seen that the levels would equalise as soon as enough water had run from one container to the other. No current would then flow. If water was added to the higher container at the same rate that it is passing through the connecting tube, then the current will continue.



This is similar to a dry cell battery which is, infact a corrosion cell. The current will flow through a conductor when the two poles are connected in the same way that water flows through the connecting tube at the bottom of the two containers. When the reaction energy has run out, the battery is dead and the potential levels are the same at each pole.



A corroding nail is similar in that the corrosion current flows from the anode of the nail, into the damp cloth and then goes back through the cloth to the cathode of the nail. The corrosion reaction on the nail can be forced in a variety of ways to be defined in this course. refering back to the water analogy, it is important to understand that the pressure is caused by the height of the water in each container and not the weight. The water will fill any connecting tube and then the pressure downwards will be greater in the vessel which has the highest level. The reason for this is obviously due to the imbalance between the pressures in the two containers and electrical potentials have the same tendency when connected by conductors. This is fine when visualising a simple circuit such as a single corrosion cell or a dry cell battery connected through a light bulb, but in a cathodic protection circuit, or when corrosion takes place on a pipeline we have no means of measuring each separate cell in this way.



If we examine the technique that is used in the laboratory then it becomes clear that provision has been made to eliminate outside influences in this 'open circuit measurement'.

This is not possible in cathodic protection field work, and yet laboratory derived theories are applied to readings obtained in the field. The situation on pipelines is that there are many corrosion cells, all connected to the same metal and



yet each having it's own corrosion reaction. This can be imagined like this.

It can be seen that it is impossible to measure the pressure differences in each cell by making a single connection to the common reservoir at the bottom. However it would be possible to stop the flow of water in each of the cells by continuously making the water level equal in each pair of containers.



However, it can be seen that the pressure measurement in such a system would need to be between the lowest water level and the highest water level in the whole system.



This is achieved in cathodic protection by flooding all the containers as shown in green. The current then stops flowing between each pair. Because of the nature of electricity this requires that current is drained from the pipeline and pumped into the ground in sufficient quantity to 'fill all the containers' or overcome the corrosion reaction potential (EMF).

link to page showing water containers to demonstrate electrical potentials and in relation to pipeline cathodic protection The difficulty in making this voltage measurement is shown in the demonstration with water holders buried in sand.



We can measure the level of the water against the level of the sand. We cannot see the bottom of the containers but in this case some are connected to others by a glass tube through which the water can pass. Water can pass between some of the visible containers to others in the same way as corrosion current. We can never know if the corrosion current has been stopped when (whole system is in equilibrium) as we have no reference to zero potential. It is out of sight and reach! In the same way, we cannot know the EMF (water level) of each corrosion cell. We can only measure the voltage between the potential of the ground and the potential of ALL OF THE METAL. That is the equivalent of the level of all of the water in the containers. We do not know how deep each containers is and we do not know which are connected.



The established method of measuring the effectiveness of cathodic protection is by recording the voltage between two variables. This cannot determine if corrosion has stopped.

Open circuit measurements

The term 'open cuircuit measurements' was acknowledged by Dr Peabody of NACE when recognising the problem that was termed 'the IR drop in the soil'

Natural corrosion cells are much different from those set up in a laboratory, as they can be physically minute or large. Large corrosion cells can contain micro-cells within the same area where anodic areas completely surround cathodes or vice-versa. When studying such cells, we are not able to separate the component parts, and the measurements have come to be known as 'open circuit measurements'. This type of measurement involves connections to the



electrolyte as well as the metal and this requires the use of an electrode. There is a danger that this will introduce another EMF into the circuit, by the reaction between the electrode and the electrolyte. We therefore use an electrode in a solution of its own salts, which has a known reaction EMF. We can then make a connection between the electrolyte in the cell and the earth electrolyte, in the hopes that there will be no electrical disturbance to the measuring circuit.

In the laboratory, this disturbance is prevented by the use of a glass capillary filled with inert gel, which is used as a conductor from the reaction interface to the reference electrode. The reference electrode is a metal in a saturated solution of its own salts, as this has a known reaction potential. Reference electrodes are related to each other by known voltages and are used as international standards.



Without this consistency it would be impossible to evaluate the reaction, develop theories or design cathodic protection systems etc. Unfortunately, it became the practice to apply laboratory principles in cathodic protection field work. This subject can now be studied in greater detail by computer modeling which makes it clear that the fixed potential is normally that of the pipeline metal, and the variation in the measured voltage is due to the different potentials elsewhere in the measuring circuit.



Imagine that we require to know the voltage of two dry cell batteries which are arranged in parallel. That is to say that each is in connection with a common conductor to the positive pole and another common conductor (the ground)to their negative poles.

Both conductors would carry equilibrium current according to the reaction within each battery and the voltage between the two conductors could be measured by connecting a meter between the two. Unless the two cells are separated, it is impossible to evaluate the voltage of each battery. Even this is not as complex as the expectancies of cathodic protection monitors. If we take two batteries and half bury them in an electrolyte with their positive poles exposed and connected, we have two corrosion cells in closer condition to those found on a pipeline.



A circuit drawing of this arrangement will show that current will pass through the ground to equalise the pressures caused by the interface reactions within each battery. We must now try to evaluate the reaction within each battery using a high resistance voltmeter and an electrode. We cannot break the circuit or separate the batteries but connections can be made to the metal or the electrolyte or both. It will be seen that we are only capable of measuring voltages across various spans of the circuit, and cannot establish a reference within that circuit. The laboratory techniques cannot be applied to these conditions as there are too many variables which are impossible to evaluate. If we increase the number of half buried batteries connected together, we improve the similarity to a pipeline, but in order to be more realistic, we must include some which have their positive poles buried. This has been shown earlier in this page.

The complexity of the situation is now apparent and what seemed to be a simple measurement, now seems almost impossible. A circuit diagram of the complex arrangement will show that a different voltage will be measured with every new position of the electrode, and this is born out in cathodic protection field practice. It is especially obvious on pipelines which are not connected to cathodic protection systems and which have poor coating. The different voltages are due to the variety of potentials at each pole of the voltmeter. These can be caused in many ways, as described later, but it is important to realise that they are all components of the voltage shown on the meter. It is possible to eliminate them in the laboratory but not in the field, therefore they must be evaluated and considered in the analysis of survey results.



The problem is even more complex when cathodic protection is introduced as this is an additional voltage which is superimposed over all the others. Being designed to drain charges from the whole of the

pipeline, it has an effect on the equilibrium of all the other electrical influences. However, the dynamic effects of an impressed current system can be removed by taking voltage measurements immediately after the system has been switched off.



This cannot be achieved where sacrificial anodes are used, unless they have a special facility designed for this purpose at construction stage. The voltages obtained between the pipeline metal and a randomly placed electrode have a certain amount of value when compared to others obtained from connections to the same pipeline. This is because of the very low electrical resistance in this part of the corrosion and cathodic protection circuits. link to page about electrical potentials and in relation to pipeline cathodic protection Students are now required to read Procedure 1a Students are required to understand the instruments they will be using. Students are required to carry out experiments and submit a report. Link to some old report forms dating back to before



the original CIPS survey Go to field trip




Introduction to the second module

Students will by now realise that this course is very practical and based on the experience of Roger Alexander over a 30 year period. In order that Cathodic Protection knowledge is transferred to many, it is now up to all students to share their knowledge through the Cathodic Protection Network. The first section of this module is the history of cathodic protection as experienced by Roger Alexander. Student are now required to add their own experience of this history in response This will be circulated to all students as they continue with the course and it is therefore essential that we do not allow any CPN information out of the network or it will diminish the commercial value of being a member of CPN. From this module onwards each student will be accumulating increasing ability to stop corrosion and earning capability. Each student will be required to review the reports of the students taking the preceding module. CPN is often asked for Cathodic Protection engineers but will not recommend anyone on other qualification than completing this course successfully. This module includes information about the business side of cathodic protection and corrosion control because this has had a greater effect on

Page 1 of 2Cathodic Protection Module 2


corrosion than the technical and scientific progress that makes control possible.

Module 2

� Technical history of Cathodic Protection � Explanation of the reasons behind current trends in C.P. � Financial and operational benefits of CP. � Academic and scientific views of CP. � Introduction to measuring and monitoring � Theory behind the 'immediate off potential' � Practical, make two reference electrodes (half-cells) � Field trip with simple exercise in CP measurment requiring a report. � On-line real time discussion using MSN IM or Skype

Page 2 of 2Cathodic Protection Module 2


History of development of the Cathodic Protection Network

Pipelines are mainly made of steel and coated with material that protects them from chemical reaction with their backfill. This coating must be electrically resistant and is inspected immediately before the pipeline is buried or submerged.

Steel pipes leave the factory in lengths of about 40 feet which are welded together into continuous lengths before lowering into the ditch. Each length has been factory coated but the gaps left for welding are coated in the field.

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The coating inspection is known as 'holiday detection' from the old expression of paint inspectors that the painter had taken a holiday when leaving a bare patch. The primary inspection is visual plus a continuous spring ring is wrapped round the pipe and rolled along using an insulated handle which connects the spring to a very high voltage coil. The voltage is set so that an arc occurs at a coating defect and rings a bell in the detector box. The inspector marks the fault which is repaired and re-checked.

The detection and repair of coating faults delays the work of pipe laying which involves using heavy plant and equipment in difficult circumstances, all of which make it very easy to damage the coating further.



It is not surprising that coating faults are not uncommon. The back-fill operation is inspected but often includes metalic and hard objects that can effect the cathodic protection measurements and physical condition of the pipeline when covered.

Cathodic Protection

Cathodic protection test leads are connected to the pipeline metal at intervals varying from half kilometer to one mile, depending on the country and operators specification. Additional test points are provided at locations where the pipeline passes beneath roads, railways, canals and rivers. The test leads are very well insulated because they are copper and would tend



to form a 'bi-metalic coupling' reaction causing accelerated corrosion to the steel pipe.

The test leads are bought to the surface through a pipe or concrete post set in the ground. The ends are normally attached to brass nuts and bolts which protrude giving access for electrical connection to instruments. Vandals often damage these test posts so it is sometimes necessary to simply use a steel post and set the lead in concrete or epoxy compound to the top of the post. Cathodic protection Inspectors were required to connect the test lead to the negative terminal of a voltmeter, connect the positive terminal to an electrode described as a 'half-cell' which was placed on the ground directly above the pipeline.



It was thought that the half-cell was a reference potential against which it was possible to measure the voltage which would give an indication of the corrosion status of the pipeline metal.



Field workers found that moving the half-cell would produce a significantly different result and when they reported this the data was altered to suit the expectations of the clients consultant engineers. From the 1950's to the 1970's, the source of scientific excellence and engineering guidance was a publication known as 'Peabodies' published by the National Association Of Corrosion Engineers.



Scientists believed that the works of Pourbaix substantiated the use of a standard voltage -0.850v when measured between the pipeline metal and a copper/copper sulphate electrode as the criterion for achievement of cathodic protection. Although cathodic protection had been a very cost effective success there continued to be disastrous corrosion related pipeline failures world wide and in the mid 1970's the method of making the field measurements was closely examined. In 1974 I was appointed to the position of Corrosion Engineer for the Eastern Division of Shell-BP Development Corporation of Nigeria.



It was very clear that corrosion control was not effective as leaks were increasing alarmingly. I was allowed to utilise some of my unique survey procedures to build an overview of the corrosion status of the region. I specified the 'two half-cell' survey to a contractor Mark Derefaka in early 1975 at Bomu Manifold which had been bombed during the Biafran war.



Another manifold had been quickly built over the old one, to get the oil flowing, but there were no drawings of the old buried pipework as they had been lost in the destruction of some of the head office buildings. This contract proved the value of mapping the potential profile of the ground and showed the exact position of all the old pipework prior to exacavation.



By regarding the whole network of pipelines as a massive electronic circuit, I was able to draw an equivalent circuit with impressed current systems and sacrificial anodes.



Pocket calculators had just become available so I was able work out the likely locations of corrosion using electrical laws and reconciling each part of the system. My survey teams would enter their readings on wall graphs using map pins linked with cotton.



Direct Current readings were shown on cardboard strips on a wall mounted schematic of the pipeline layout of the whole region.





The picture above shows a very small section of the layout. By comparing data from the files with present field data I was able to predict, with a fair degree of accuracy, the likely locations of corrosion failure in the immediate future. On one occasion Steve Mayaki returned from an investigative survey having found that a predicted location had actually started to leak. This was immediately remedied with a leak clamp having lost only a few gallons of oil and virtually no environmental damage. I was able to bring the whole corrosion crisis under control in a couple of years and reduce the incidence of external corrosion leaks to zero in four years. This extensive period of investigation and prevention of corrosion confirmed that there is no way that the 'half-cell' can be used to establish a reference potential but that it is very useful as a probe to contact the electrolyte in which the pipeline or structure is burried or submerged. If a bare metal contact is made then that metal reacts to the salts disolved in the electrolyte, thus adding yet another EMF to the measuring circuit. In 1978 I realised that the only way forward was to try to devise a method of measuring the actual corrosion current and the effect of cathodic protection on the corrosion reaction itself.



I used an assortment of metal coupons and sensitive meters but the problem was that the current must be measured without disturbing the reaction. The effect of the cathodic protection must be measured without disturbing the passage of that current onto either the anodic or cathodic interface. The only way to do this is to create a real corrosion cell in such a way that the corrosion current can be observed in any state of equilibrium.

Return to the UK

During a period of independant research and development in the UK I designed the Alexander Cell into a working unit.













I had a solicitor witness the document above to substantiate that I had indeed invented and constructed the device myself at that time. I then spent four years as a cathodic protection technician working first for Atkins Inspection and later with Global Cathodic Protection on contract to North Thames Gas. Before I took the position I was interviewed by Mike Foskett, Chief Corrosion Engineer for North Thames Gas who was based at Staines. We discussed my experience in Nigeria and he agreed that I could conduct field trials of the Alexander Cell (in my own time) at North Thames Gas pipeline locations.

The project was to conduct a condition audit of many thousands of miles of high pressure gas pipelines delivering North Sea Gas to the north London area. A mainframe computer had just been installed in Staines Head Office of North Thames Gas and the project was guided by Bob Greenwood of the Gas Council ERS. The procedure being developed was known as OLI1 (Over Line Inspection) and was developed in stages to OLI4 which is now known internationally as CIPS (Close Interval Potential Survey)



The reason for its development was the corrosion failures of pipelines that had been operated in compliance with the British Standards Institute Code Of Practice (CP1021) on which the pipeline licencing in the UK was based. I joined one of four teams of technicians who were making notes of each voltage as the cathodic protection current was switched off and on at the nearest transformer rectifier. Mike Fosket told me that they used the computer to plot the voltages in both states and that they had started by plotting the difference until they realised that this plot did not show the coating faults as they had hoped.



The theory had been that they could use the difference between the on and off readings to work out if the corrosion had been stopped. In fact, they had found the principles that I had used several years before of plotting the ground potential profile. I described the 'two half-cell' procedure that I used extensively in Nigeria and it was adopted as and additional check to locate the exact position of coating faults before excavation. I was then required to carry out the final overline procedures, including the Alexander Cell, to produce a written report for each location before excavation. The use of OLI4 procedures alone produced 7% accuracy and the complete Alexander Technology procedures produced 97% accuracy. The sampling was 100 excavations that I attended personally. My success was such that Bob Greenwood visited site and saw the my



procedures in action. He later authorised the purchase of an Alexander Cell, which prompted the Corrosion Engineer from South East Gas to buy one. Mike Fosket asked me if I would like to write a paper about my view of cathodic protection which was radically different from mainsteam science at the time. The paper was sent for technical editing to Dr Vic Ashworth of Ashton University, who rejected it completely with the comments that it did not fall within the concepts of known science. Because of the success of my work in the field, Mike Foskette arranged for me to make a presentation to the London branch of the Institute of Corrosion Science and Technology.link to copy of the notes of that presentation This was attended by over 100 qualified , practicing corrosion engineers 64 of whom signed the register.













The presentation included demonstration models and videos of field work to support the content of the talk. The Chairman of the BSI Committee for CP1021 attended and addressed the meeting after the presentation. He said that he supported everything he had heard and as a result was withdrawing the BSI Code of Practice 1021 for review.









John Tiratsoo published my paper in his journal Corrosion Prevention and Control and was then asked by readers to publish it in Pipes and Pipelines International, a journal that had 10 times the circulation. I received positive response from all over the world and requests for the Alexander Cell.

Back to module02 index




Module 2

Explanation of the reasons behind current trends in C.P. Technology.

� Cathodic protection theory dictates that the metal must be reduced to below its corrosion potential IN RELATION TO A STANDARD REFERENCE POTENTIAL. � Top corrosion scientists regard the copper/copper sulphate electrode as a 'reference' electrode, capable of rendering a potential to which all C.P. work can be related. � Standard reference electrodes have a recognised and known potential which can be used as an electrical datum point against which to measure other potentials. � Complete cathodic protection is totally achievable but the problem is to measure the effectiveness of cathodic protection when applied in the field.

The illustration below shows the traditional method of making the voltage measurement that

has been the basis of all cathodic protection design and monitoring since the 1950's

Page 1 of 12Latest trends in Cathodic Protection Industry

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Typical test posts at a road crossing in the UK



As a general guide the value of -.850v in relation to a copper/copper-sulphate electrode was chosen as a criterion for the achievement of cathodic protection. It was felt that this was substantiated by the Pourbaix diagrams and since then all attempts at monitoring the effectiveness of cathodic protection been based on this value and the use of this electrode. Cathodic protection has been very cost effective and successful and consequently has become required as a maintenace technique for pipelines world wide. Being so cost effective has resulted in it being very lucrative for those offering it as a service. It is very simple to install and commission and the equipment and parts are readily available from many sources.



Almost anyone with a rudimentary understanding can design a system that will reduce corrosion by about 90% and so we have a situation now that there are many 'cathodic protection experts' in positions of authority, world wide who cannot explain why pipelines fail due to corrosion that should be prevented.



Our instruments are capable of measuring VOLTAGES which are the differences between two potentials. Cathodic protection salesmen refer to measurements as POTENTIALS...... they are NOT. They are potential differences..... VOLTAGES. The potential at either pole of the meter can be regarded as zero and the other pole will be either charged higher or lower. The meter will show positive or negative values according to the polarity of the connecting conductors but the value displayed will be a voltage. Even when displayed on a 'scope' type of instrument. It is this misunderstanding that has caused the delay in the fruition of cathodic protection as a science and engineering technology. Top scientists are anxious to sustain their present concept as this affects their very livelihood. Their 'consultancy advice' has been taken by organisations such as NACE and various pipeline standards authorities world wide. It is very difficult for them to explain that the standards and criterion that they recommend cannot be applied in the field of pipeline cathodic protection. They have sold this criterion as an axiom on which they can base scientific calculations for the purposes of design of cathodic protection systems.

The effect of 'business competition' on cathodic protection.

In a world where money rules, it should be recognised that all those who have the job of preventing corrosion to pipelines have the priority objective to sustain their position and to earn as much personal money as they can. The pursuit of personal money has overridden the desire to stop corrosion and this has been a greater impact than any other cause on the useful life of pipelines, world wide. This is the most important fact in each corrosion engineers life. There are two questions that are regularly directed at CPN. "If CPN technolgy is so good then why is it not adopted world wide?" The answer is that the market place economy makes it impossible to implicate changes that do not have financial benefit to those who hold the money. Considerable investment had already been made into



The other re-occuring question is 'Where is CPN technology installed so that we can see it's success?' The answer is nowhere! The question is simply an attempt to gather information without paying for it. If the pipeline industry could see a working example of a new technology they would simply coppy it. The most recent people to ask this question of the CPN were the Iranians. The energy industry is multi-national and the pipeline industry has a pool of experts who work wherever they can get paid. When any technology is successful it will be copied and in the 'competitive market' work will be given to the company submitting the lowest tender. A presentation of CPN technology was given to the Iranians who are now looking for 'another source' as they do not want to pay Cathodic Protection Network International Ltd. This ignors the fact that their pipelines are corroding because they are using technology from those 'other sources' and it simply does not work. I can be seen that the commercial situation throughout the world has resulted in the scientific establishment controlling the only advances in technology and resisting changes that will damage their established work. This is not greed, selfishness or meglomania but a natural result of money being the basis of society. Everyone needs money to survive and the work ethic dictates that those who do not work are not even deserving of survival. 'Work' has come to mean 'employed' and that infers that each individual must perform some defined task. Those that are defining the task are performing work that gives them power and money. In the case of cathodic protection the top line definition is the work of scientists. It was a proposal by Sir Humphry Davy that resulted in the definition of the work to be done to stop corrosion to the copper cladding of wooden war ships. This successful application of the scientific principles resulted in the proposal that this science could be applied to steel pipelines that were corroding in a very short time. This type of cathodic protection was defined by scientists and applied by engineers very successfully resulting in those scientists and engineers being employed to stop corrosion on other pipelines. Other scientists studying corrosion found that coatings separated the electrolyte from the metal and stopped the reaction. Various wax and oil based coatings were reinforced with cloth and wrapped round the pipelines. These were conductive (Denso tape is an example) and the protective current from the CP systems could pass onto the pipeline metal without achieving its purpose. Electrically resistant bitumen coating was then used successfully but this was found to be bio-degradable and lost it's effect after a few years. Coal tar enamel was found to be very effective and durable especially when



combined with glass fibre re-inforcement. All these steps resulted in specialised consultants becoming more significant in the fields of corrosion control, coating manufacture and application. Companies were formed for the manufacture of these coatings under the scientific guidance of the specialists who were paid to research better products. It was found that some products were so electrically resistant that they could be applied very thinly. Some had sufficient tensile strength and impact resistance that they could be applied without re-inforcement. Present day coatings are very efficient but none can be applied without faults because of the nature of pipeline construction. It is because of these coating faults that cathodic protection is required by law in most countries of the world. Cathodic protection is only needed at these coating faults but their location is not known. Industry has developed a variety of methods to detect the location of coating faults and these will be studied later in this course. Pipelines continue to fail through external corrosion and there is a need to monitor the effectiveness of cathodic protection. However most big pipeline operating companies only take those measures that are required by law governing the issue of their pipeline operating licences. There is no commercial incentive to try to enhance the effectiveness of their cathodic protection systems as the failures are covered by insurance. The insurance companies can easily raise their premiums and the value of oil and gas are such that the enormous profits can assimilate the cost of repair and replacement of the damaged pipelines. The majority of rich people world wide are best served by the present status of corrosion control and cathodic protection and that is why CPN technology has not been adopted world wide.

The Emperors new suit

There is a famous story of the Emperors new 'invisible' suit and the little boy who sees him nude because he has not been told of the 'magic suit'. This story is common to many countries and the principle must be known world wide. Tricksters had convinced the whole nation of this suit and the little boy wass



the only person who had not received the message. His simple logic and the evidence of his eyes showed him that the suit did not exist. His exclamations to this effect werwe well received in the story but in real life the little boys comments would not be popular. He was a 'whistle blower' who upset the 'establishment'. The fable seems to end there, but in real life there remains the problem of the Empeorors pride and 'entrepreneurs' money.

The purpose of this chapter is to allow the student to realise that commercial pressures have a bigger effect on pipeline corrosion than the natural effects of the corrosion reaction. The technology contained in this course will not please many in the cathodic protection industry as it challenges the very foundation of much of their work. NACE and the rest of the cathodic protection industry have based all their efforts on the fact that the copper/copper-sulphate or silver/silver-chloride electrodes renders a reference potential on which it is possible to base cathodic protection design and monitoring. That is the 'invisible suit' that they sold to pipeline operators who wanted a criterion so that they would know when cathodic protection was effective and had indeed stopped corrosion. Sir Humphrey Davy had proved that cathodic protection actually worked when applied to copper cladding on ships and pipeline operators found that leak frequencies dropped off dramatically when cathodic protection was applied to pipelines but no one could say when the application was complete and to what extent it had been achieved. When it was recognised that there were errors in the measurements these were, at first, blamed on inaccurate instrumentation and poor field work. With the availability of digital instruments and some laboratory studies it was possible to identify that there were real errors in field measurements that are not present in laboratory techniques. These errors were all described as 'the IR drop in the soil'. It is significant that the 'experts' did not use the simple world 'voltage'. This would have made it simple for any electrician to see the error and recognise the way the mistake had come about. It would clarify the route to a simple solution such as the Alexander Cell. However, this would not sell the 'invisible suit'. It was necessary to cloud the issue with new terminology. Scientists thought that they could eliminate the errors by taking the required voltage with the cathodic protection current switched off. It seemed that the error was caused by the measuring circuit alone and that by removing the



current that was causing the voltage error, the measurement would be equivalent to the actual reading at the interface, as required by Pourbaix. The very first lagre scale attempt to utilise the 'off potential' theory was carried out by North Thames Gas in the UK. It was then realised that most pipelines were affected by more than one transformer rectifier and that the current had not actually been switched off but had been reduced by an unquantifiable amount. Attempts were then made to sychronise the switching of all the transformer rectifiers that affected each length of pipeline. This was difficult in the 1980's as the technology was not available. Instrument manufacturers and cathodic protection providers came out with more and more sophisticated sychronised switching systems in an attempt to achieve the required 'immediate off' potential. In 2001 Roger Alexander (the little boy who saw the Emperor was nude) was requested by NASA to submit a report for consideration by the American Standards Authority relating to the Immediate Off Potential Survey.

Click here to see the paper sent to NASA



Cathodic protection is required by law in most countries as a condition for a pipeline operating licence. However, there is no internationally agreed criterion for the achievement of complete protection. Pipeline operators are required to report leaks but it is very difficult to compile information about this. The use of the CIPS survey is an attempt to apply the Pourbaix theory based on the voltage between the metal potential and the electrolyte potential but the DCVG survey shows that the same electrode renders a different value in each location. This makes it possible to accurately identify the position of coating faults using the difference in ground potentials touched by copper/copper-sulphate electrodes but proves that the CIPS survey CANNOT determin the corrosion status of the pipeline metal. Faced with this problem, the cathodic protection industry has no scientific point of excellence that can answer the simplest questions levied by the most fundamental electrical and electronic engineers. CIPS and DCVG are being used world-wide despite the limitations of DCVG and the complete failure of CIPS to determine the corrosion status. Mainstream scientists still insist on trying to use the Cu/CuSO4 electrode as a reference potential and consequently the CPN is the only organisation that can offer the computerisation of pipeline cathodic protection, The adoption of CPN technology in Iran is currently being delayed by financial and business considerations but it is significant that this technology would save the country money that is being spent on unsuccessful methods of applying cathodic protection. Less money spent on CPN technology would stop most of the corrosion that is causing massive financial losses and ecological damage. This is the same situation that pertains in the rest of the world but Iran has at least had the sense to examine cathodic protection and look for better ways of applying it. No doubt the people of Iran will apply the same sense when looking at the financial situation surrounding their massive corrosion related losses.

Money and esteem

Those who are not good at making money are seen as failures and their work is not respected. It is similar in principle to qualifications... if a person has no qualifications, he



cannot know about the subject under discussion. It then follows that a persons word is a valuable as his apparent wealth. The notion is that if a person is not rich, he/she is not intelligent or wise. The logic is that everyone knows that money = success and if you have no money you are a failure. What has this got to do with corrosion control and cathodic protection in particular? All of the above have directly affected the present status of corrosion control and cathodic protection. Pipelines continue to fail and are repaired or replaced at enormous expense and loss of money, energy and sometimes life. If one of these failures reaches the general public there is an investigation and enquiry that takes enough time for the public to lose interest. In the event of the incident becoming politically important, many lawyers and polititians make a lot of money. The first reaction of the investigators is to ascertain the cause of the failure. These investigators normally are people involved with the maintenance of safety standards and are keen to find taht the cause is not with themselves or their immediate friends and associates. The most convenient cause is local activity at a low social level. In the case of a developing nation this is usually found to be people trying to steal the product or clumsy behaviour of a mechanical device such as a digger or tractor. It is very rarely blamed on corrosion as this is preventable by people in positions of power and wealth, but if that is the conclusion of the inquiry then the consultants have a ready excuse in that they claim that there are matters beyond the control of science and that they can never guarantee total success of cathodic protection. The British Standards Institute Code of Practice CP1021 was withdrawn by Jim Gosden when it was proved in public that the recommendations could not be practiced. It has been replaced by a very loose document that carefully avoids any specific procedure. The National Association of Corrosion Engineers based in the USA (NACE) has gained world wide authority over the years as no other national or international body has come forward with a workable criterion for cathodic protection. They publish a standard for cathodic protection of pipelines that is available on the internet at a cost of $83. I am the founder and owner of CPN and cannot afford this as no businessman or entrepreneur is prepared to pay any money to me. NACE will not answer any correspondence from CPN and it is proving impossible to arrange an official meeting with UK authorities. It would seem that financial and commercial considerations are more important than stopping corrosion. CPN is not a commercial success but CPN technology has prevented and halted corrosion in every challenge that has been faced during the past 30 years.



The Alexander Cell is still the only clear method of indicating the effectiveness of cathodic protection and yet nobody is using it for purely commercial and business reasons. I am at present considering giving away the home made Alexander Cells that I have in my posession so that they will prove that CPN technology really works in the field.





Module 2

Financial and operational benefits of CP.

We must examine the finances of cathodic protection as a number of facts Pipelines are a method of transportation and storage in competition with trucks, trains and tank farms. They are therefore a threat to the livelihoods of those who sell their skills in these competitive industries. Pipelines themselves require little maintenance and are only replaced on a contingency basis. Good maintenance is not in the interest of the pipeline construction industry. The pipeline construction industry has a vested interest in pipelines needing replacement. Corrosion is a major contingency issue in the maintenance of pipelines and is prevented by coatings to separate the metal from the environment. The coating industry has a vested interest in pipelines failing so that they can sell more advanced coating systems that they can claim will reduce the cost of pipeline replacement. Cathodic protection enhances the purpose of coatings and is therefore in competition with the transport industry, the pipeline construction industry and the pipeline coating industry. These three industries have a financial hold on the energy industry.

Page 1 of 4Cathodic Protection Finance

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They also have a significant presence at the top financial levels in world energy based societies. Cathodic Protection is so cost effective that it directly threatens the livelihood of a small section of the very rich.

Insurance

As the energy industry gains importance in any social structure, contingencies become an issue of high finance and political power. When energy is dominant there is enough money to insure against corrosion leaks and insurance companies simply put their premiums at a level where they can make a healthy profit. During these periods they are not interested in Cathodic Protection as the frequency of leaks is not an issue in their balance books. However, when the financial clout of energy is low the industry looks at financial efficiency and it is found better to cut out the insurance companies and take on the contingency risks in house. All of the above affect decisions at the top level of finance and government policy in relation to Cathodic Protection.

Political advantages of corrosion leaks

Action groups and political activists seize on danger to life and environmental hazard of every pipeline failure that hits the headlines. Every successful method of corrosion control weakens their case against energy producing companies by depriving them of the events that lead to publicity for their cause. Cathodic protection is therefore a powerful tool against local unrest and terrorism. It removes a substantial amount of agravation from local communities and if organised correctly can actually involve them in simple low cost activities that benefit industry. CPN technology is based on simple procedures that can be learned at local level for the locally based activities. This is not only the most cost effective way to organise Cathodic Protection but has immense local social benefits. This would seem to be a benefit to all but in fact it is not. If local workers hold the technical ability to save millions of dollars then they hold the power over that money and demand a disproportionate reward for their services. If the local Chiefs sieze this amount of power then they elevate themselves to the realms of those who control the energy rescources of the world. They then become interested in money and world power so that they can live to the standard the see their contemperaries enjoying. This is not wrong, but it leads to a situation where scientific and technical facts are ignored and financial considerations are dominant.



Unfortunately finance cannot stop corrosion and science can. Scientists have developed a system of working together to enhance the understanding of science and broaden their knowledge.

Professional Bodies

Specialists have grouped together in Universities and professional bodies for the purpose of exchanging knowledge. As each speciality develops into practical value, these groups take advantage of that to enrich themselves privately. With the introduction of 'healthy competition' it becomes advantageous to restrict the knowledge to within the group. In an ideal world this would not be necessary but in the real world, the intellectual property of each group has a value that is now traded as a commodity. The mass of knowledge that is possessed by each group represents each individual's 'equity' in that group and so each must pay to enter the group to buy that 'equity'. It is now possible to obtain the consent of a group by simply paying without aquiring the necessary expertise. Degrees and memberships can be bought and their ownership does not necessarily mean that the person is competent. However, membership of a particular group gives the right to contribute to the group judgements that influence the commercial value of the group 'product'. It is this process of power that has restricted the control of corrosion for at least 30 years.

Patents laws and all that stuff

Protection of the individual's equity is a problem that has resulted in the Patents system. In order to launch CPN technology into the world of cathodic protection it is necessary to make it financially attractive. On the invention of the Alexander Cell I was told that the only way that it would be accepted would be if I had the 'patent' which would give me the monopoly on commercial exploitation supported by the law of the UK. If anyone was to copy the device and sell it I could then sue them for financial damages.



I found that the cost of a patents agent was not within my ability to pay so I spent three weeks learning the requirements and filed my own patent application that would give me the monopoly for a period of 18 months. This cost a relatively small fee to the UK patents office. In the process of doing this I found that a friend had tried to patent the Alexander Cell in our joint names using the services of a patents agent. I succeeded in having this patent application annulled by the patents office and then tried to market the device. I then found that the Alexander Cell simplified cathodic protection monitoring to a extent that it undermined the complications that had been introduced by the 'professional bodies and universities. It is these complications that support the need for their expertise in advising the industry and charging very high consultancy fees. I recently attended a meeting at a university where the leading professor asked me why my technology was not successful and then went on to explain to the meeting that the only way to monitor the effects of cathodic protection is by the use of an electrode system identical to the Alexander cell ... which he drew on the flip chart. I suggested that he had just drawn the Alexander Cell and he agreed. He had on the table copies of many of my published papers yet the business professionals representing my interests at that meeting refused to arrange any payment to me for the transfer of my knowledge to the professor. Without any financial support I have been unable to progress CPN technology further through that route.

This is a statement of fact not a comment on the system used by the UK





Module 2

Academic and Scientific history of Cathodic Protection.

There are many facets of the development of cathodic protection not covered in this history and students are invited to add any information they have for the benefit of the CPN. Theoretical understanding of the corrosion reaction is supported by thermodynamic theories such as the Nernst Equations.Link to a typical scientific explanation A text book on cathodic protection was published in 1953, by the National Association of Corrosion Engineers (NACE) and was known as 'Peabodies' by the engineers and technicians working in the field until at least 1973. It was regarded as 'the Bible fo Cathodic Protection', and was the reference book that set the standards of the day. The technology advocated in this book was utilised over the whole of the natural gas pipeline network in the UK that was under the control of The Gas Council. The Gas Council Engineering Reseach Station (ERS) in the north east of the UK examined and ratified the science of cathodic protection and advised regional corrosion engineers on matters of field implementation. In the very early 1970's a group of practicing field engineers formed the Institute of Corrosion Science and Technology in the UK.


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One of the founding members was Tim ffrench-Mullens of Solus Schall, an international oil service company supplying pipeline inspection services. Other companies included MAPEL, a branch of William Press (pipeline construction and maintenance company in the UK. Roxby Engineering (CWE) a similar company, Spencer and Partners, a specialised corrosion consultancy and 'body shop' for corrosion engineers. There were many others and the 'experts' seemed to move between companies and form their own companies according to financial opportunities. Cathodic Protection field technicians were recruited from the public and given very brief instructions before being set to work. The only qualification that was insisted upon was the ERS certificate of a 'Coat and Wrap Inspector'. This qualification required an examination at the British Gas ERS and was recognised world wide. There was no such qualification for cathodic protection technicians but some were invited by NACE to become members if they gained a reputation for their work. There was a requirement of a recognised degree in engineering to become a member of the Institution of Corrosion Science and Technology but this was contentious among the founders and eventually that organisation fell apart and re-named itself into different organisations. The National Physical Laboratory, at Teddington in the UK, formed the 'Corrosion Club' under Dr Peter Francis, as a co-ordinating advisory body for matters concerning cathodic protection who were referred to by such organisations as the UK Patent Office, The British Broadcasting Corporation and the leaders in industry. They co-operated with the Univesity of Manchester Institute of Science and Technology (UMIST), corrosion studies headed up by Dr David Scantlebury. Prof. Schrier of Middlesex Polytechnic wrote the definitive scientific guide to cathodic protection published by the National Physical Laboratory. The British Council arranged for overseas scientists to visit the UK on fact finding arrangements and the field element of these visits were arranged by private companies. The basis of all the theoretical work remains based on the equations of thermodynamics and it is assumed that the values that can be derived from laboratory experiments can also be applied in field work. These values depend on the 'half-cell' being a 'reference electrode' with a known potential (EMF) that can be compared to the EMF of the corrosion reaction at the interface between the subject metal and the electrolyte. It will be seen that other values must be considered when applying these



equations. These include temperature and pressure as well as the pH of the electrolyte. Field data, gathered in the present way contains errors as great as 300% and this is readilly demonstrated using sand trays, in the field and now using computer modelling. This was acknowledged by the British Standards Institute in 1985 and shown to be so by scientists form Nederlands and Germany. However, the UK and US organisations and scientists did not acknowledge that this invalidated all cathodic protection design and applied theory. The measurment of the metal to electrolyte EMF by comparison to a reference potential is a component of ALL CATHODIC PROTECTION DESIGN. Academia is still trying to devise ways of applying a reference electrode to field work and the isopotential cell has been patented in various shapes and forms. This is favoured by many scientists but does not render the anticipated results when used in the field. Many leading scientific papers have been ignored as has a major guide to cathodic protection field work. Handbook of Cathodic Corrosion Protection, by Walter von Baeckmann (Author), Wilhelm Schwenk (Author), Werner Prinz (Author). This book was in the UMIST library in 1980's and was translated with the help of Bryan Wyatt, Managing Director of Global Cathodic Protection Ltd. In 1973 cathodic protection technicians were issued with analogue galvanometers with a measuring circuit resistance of 10,000ohms per volt and their duties were to record voltage measurements between the steel of the pipeline and a copper/copper-sulphate electrode placed on the ground near to the 'test lead' which the contractors had 'cad-welded' to the pipeline.





Technicians found that many of the techniques recommended in Peabodies did not render the results predicted. Some of the information it contained, simply did not work when applied in the field. However, they believed that technology in industry was well established and that anything that had been widely adopted and standardised throughout the world was soundly based on scientific principles that seemlessly interfaced between academia and the technicians who were puting that science into practice. This was wrong! Research in available publications of the time revealed that most of the recommended procedures did not produce the predicted results. After many months of field experimentation by the founder of CPN it became apparent that the measurement that was being taking was recorded relative to a



floating zero. The copper/copper-sulphate electrode (known as a 'half-cell) was not a 'reference potential' when used in the manner defined in the cathodic protection industry. Tim ffrench-Mullens and Jim Gosden, the head of corrosion engineering for the Central Electricity Board of the UK, were aware of this problem and scientists in Europe were working on an acceptable solution that fitted in with the practices of the day. Technicians and field engineers were told that the problem was with the instruments that were available in the field. Digital voltmeters were not widely available at this time. Peabody produce a table and formulae for correcting readings taken on a low resistance volt meter and this will be explained fully in this course. The validity of pipe-to-soil potentials, taken in the traditional way was recognised some years later when the measurment was described (in a paper by DR.Peabody himself and published published by NACE,) as an 'open circuit measurement', and this renders it impossible to eliminate errors which are not present in normal closed circuit electrical measurements. The traditional technique for making the standard CP 'pipe-to-soil' measurement had became open to question when pipelines began to fail in spite of having been theoretically 'protected. Some 'experts' had blamed operator error and then poor instrumentation for the anomalies in the readings but it was then recognised that there is another voltage included in the traditional 'pipe-to-soil potential measurement' and this was named the 'IR drop in the soil'. It was thought that improved instrumentation could remedy this problem and a whole range of new meters were offered onto the market. Methods were then proposed to overcome the problem which had been identified. In the late 1970's a theory was developed that it would be possible to eliminate the error in pipe-to-soil potential readings by removing the CP current flowing onto the pipeline. It was reasoned that it would be possible to measure the 'protected potential' after the CP current is switched off and before the pipe 'de-polarised'.

















Prof. Walshe of Southampton University http://www.southampton.ac.uk/ses/people/staff/WalshFC.html acknowledged to a meeting that the only way to establish if a corrosion reaction has stopped it by using an arrangement of electrodes such as the Alexander Cell. Minutes of meeting

It is therefore true to say that CPN can measure the effects of cathodic protection and NACE cannot.




Module 2

Measuring the effect of corrosion control

Corrosion failures occur in spite of the use of cathodic protection. This shows that there is an error in measuring the effectiveness of cathodic protection. Corrosion is electro-chemical and this suggests that electrical metering can be used for short term monitoring. The simplicity of the circuit of a single corrosion cell would tend to suggest that there is a simple means available to make the required measurement. Standard reference electrodes have a recognised and known potential which can be used as an electrical datum point against which to measure other potentials, in a laboratory. We normally measure VOLTAGES which are the differences between two potentials. This causes confusion because the readings are commonly called "potentials", where in fact, either of the two potentials can be regarded as zero and the other will be either higher or lower. The meter will show positive or negative values according to the polarity of the connecting conductors. Cathodic protection theory dictates that the metal must be reduced to below its corrosion potential IN RELATION TO A STANDARD REFERENCE

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POTENTIAL. These potentials can be measured in a laboratory where it is possible to control all elements of the circuit, but it has proved impossible, so far, to measure the required potential in field work. The problem with field measurements, is that the earth at one location has never exactly the same potential as the earth at another location. In a laboratory, the electrolyte is contained in an electrically insulated container and the currents are all in closed circuit and related to the corrosion reaction. The potential of the electrolyte can be measured at the reaction interface by the use of a glass capillary containing an inert, but conductive, electrolyte such as agar-agar gel. This cannot be achieved in field work, although a close approximation has been achieved by Dr Prinz of Rhurgas, in Germany.

BR> Field readings taken and analysed in the established way are not related to each other, except through the low resistance of the pipeline itself. This is easily demonstrated by a simple calculation base on Ohms law as follows. Take any sample readings from a typical pipe-to-soil "potential" cathodic protection survey and work out the amount of current that must be passing through the pipeline between any two cathodic protection test facilities. It will



be found to be ridiculously high, to the extent of being unbelievable. For example, a span of 24"diameter steel pipeline ten miles long will have a resistance of about 0.001 Ohms, depending on the wall thickness, and the readings at either end of the span might be -0.950 volts and -1.250volts. This would not cause alarm, and would be plotted on an 'attenuation curve', without too much comment. However, calculation shows that, if the 'half-cell' (electrode) is truly a reference, then there is a volts drop of 0.300 over the ten mile span. This seems reasonable until it is realised that with such a low resistance there must be 300 amps passing through the pipeline. Something is quite clearly wrong with the measuring system or the theories. This has not been seen as a major problem until pipelines became so widespread and numerous that reliability became a major industrial consideration. Even now there seems to be little concern with this subject until a failure causes financial losses. The public at large are not even aware that the inadequacy of present technology could result in an unforeseen disaster.



Before going any further it is necessary to imagine electricity and this has been likened to water pressure, with containers connected by pipes to allow current to flow. The pressure is caused by the height of the water in each container and not the weight. The water will fill any connecting tube and then the pressure downwards will be greater in the vessel which has the highest level. The reason for this is obviously due to the imbalance between the pressures in the two containers and electrical potentials have the same tendency when connected by conductors. This is fine when visualising a simple circuit such as a single corrosion cell or a dry cell battery connected through a light bulb, but in a cathodic protection circuit, or when corrosion takes place on a pipeline we have no means of measuring each separate cell in this way. If we examine the technique that is used in the laboratory then it becomes clear that provision has been made to eliminate outside influences in this 'open circuit measurement'. This is not possible in cathodic protection field work, and yet laboratory derived theories are applied to readings obtained in the field. It can be seen that it is impossible to measure the pressure differences in each cell by making a single connection to the common reservoir at the bottom. However it would be possible to stop the flow of water from the highest level in the small vessels by adding a supply of water from a higher level. However, it can be seen that the pressure measurement in such a system would need to be between the lowest water level and the highest water level in the whole system. This would be a much greater voltage (Vp in the drawing) than that required to stop the flow in the single cell with the biggest differential. Comparing electrical pressure with that of water is a good starting point, but it is better to imagine electricity as simply a pressure which can pass through conductors, and is restricted by resistances. Imagine trying to measure the gas pressure within a cylinder. We must allow that pressure to act on a meter which will guage the pressure. This action will consume some of the gas within the cylinder and it is the passage of the gas which makes it possible to measure the pressure itself. The same rule applies to electrical pressure and this used to cause considerable inaccuracy in voltage measurements until the digital meters made it possible to measure voltages while drawing very little current. Back to the gas cylinder and imagine measuring the pressure with a guage which draws very little gas. We still have the problem that this pressure has to be compared to something. In the case of gases, we can related this pressure to



atmospheric pressure, displayed in such a way that we can imagine its effect on our senses. We are aware that we are all subject to atmospheric pressure and the effect of increasing the pressure on the human body can be felt, when swimming under water, for example. We use our muscles to compress stale air which is then exhaled and can feel the current of air through our nose and mouth. Gas pressure is therefore part of our lives with which we are familiar. We can use this experience to imagine electrical pressure, which has similar qualities. Everything has an electrical potential (pressure) which has the tendency to equalise on contact with another item of a different potential. It is this tendency which causes current to flow and allows us to make. In the same way that chemical reactions can give off gas, and increase the pressure within a cylinder, for example, chemical reactions can cause an electro-motive-force (EMF) which increases the electrical pressure, or potential, on one side of the reaction. In order to measure the electrical pressure of this reaction we must complete a measuring circuit with a low resistant electrically conductive path. The whole measuring circuit reaches equilibrium with a small amount of current flowing depending on the requirement of the meter.(in the case of digital meters, the current required to make the measurement is very small). In the case of measuring the voltage of a dry cell battery, we connect a voltmeter between the poles of the battery and the voltage is the difference in electrical pressure caused by the chemical reaction at the interface between the electrolytic paste and the inner surface of the metal container and the electrode which serves as the positive pole of the battery. The technique is simple because it is possible to confine the path of the current to that of the measuring circuit and each element of this circuit can be evaluated. Voltage drops can be measured around the circuit, using independent meters and measuring current can be detected by magnetic field and other techniques. Natural corrosion cells are much different, as they can be physically minute or large. Large corrosion cells can contain micro-cells within the same area where anodic areas completely surround cathodes or vice-versa. When studying such cells, we are not able to separate the component parts, and the measurements have come to be known as 'open circuit measurements'. This type of measurement involves connections to the electrolyte as well as the metal and this requires the use of an electrode. There is a danger that this will introduce another EMF into the circuit, by the reaction between the electrode and the electrolyte. We therefore use an electrode in a solution of its own salts, which has a known reaction EMF. We can then make a connection between the electrolyte in the cell and the earth electrolyte, in the hopes that there will be no electrical disturbance to the measuring circuit. In the laboratory, this disturbance is prevented by the use of a glass capillary



filled with inert gel, which is used as a conductor from the reaction interface to the reference electrode. The reference electrode is a metal in a saturated solution of its own salts, as this has a known reaction potential. Reference electrodes are related to each other by known voltages and are used as international standards. Without this consistency it would be impossible to evaluate the reaction, develop theories or design cathodic protection systems etc. Unfortunately, it became the practice to apply the same principles in cathodic protection field work. It seems that many thought that the electrode could be regarded as a reference against which other potentials can be established. They thought that pipe to soil voltages were pipeline metal potentials which could be plotted against a fixed potential supplied by the use of the 'reference electrode'. There are still remnants of this concept in cathodic protection practice today, which are manifest in 'attenuation curves' etc., which are used by some in the design of CP systems. This subject can now be studied in greater detail by computer modeling which makes it much clearer that the fixed potential is normally that of the pipeline metal, and the variation in the measured voltage is due to the different potentials elsewhere in the measuring circuit. Imagine that we require to know the voltage of two dry cell batteries which are arranged in parallel. That is to say that each is in connection with a common conductor to the positive pole and another common conductor to their negative poles. Both conductors would carry equilibrium current according to the reaction within each battery and the voltage between the two conductors could be measured by connecting a meter between the two. Unless the two cells are separated, it is impossible to evaluate the voltage of each battery. Even this is not as complex as the expectancies of cathodic protection monitors. If we take two batteries and half bury them in an electrolyte with their positive poles exposed and connected, we have two corrosion cells in closer condition to those found on a pipeline. A circuit drawing of this arrangement will show that current will pass through the ground to equalise the pressures caused by the interface reactions within each battery. We must now try to evaluate the reaction within each battery using a high resistance voltmeter and an electrode. We cannot break the circuit or separate the batteries but connections can be made to the metal or the electrolyte or both. It will be seen that we are only capable of measuring voltages across various spans of the circuit, and cannot establish a reference within that circuit. The laboratory techniques cannot be applied to these conditions as there are too many variables which are impossible to evaluate. If we increase the number of half buried batteries connected together, we improve the similarity to a pipeline, but in order to be more realistic, we must include some which have their positive poles buried. The complexity of the situation is now apparent and what seemed to be a simple measurement, now seems almost impossible.



A circuit diagram of the complex arrangement will show that a different voltage will be measured with every new position of the electrode, and this is born out in cathodic protection field practice. It is especially obvious on pipelines which are not connected to cathodic protection systems and which have poor coating. The different voltages are due to the variety of potentials at each pole of the voltmeter. These can be caused in many ways, as described later, but it is important to realise that they are all components of the voltage shown on the meter. It is possible to eliminate them in the laboratory but not in the field, therefore they must be evaluated and considered in the analysis of survey results. The problem is even more complex when cathodic protection is introduced as this is an additional voltage which is superimposed over all the others. Being designed to drain charges from the whole of the pipeline, it has an effect on the equilibrium of all the other electrical influences. However, the dynamic effects of an impressed current system can be removed by taking voltage measurements immediately after the system has been switched off. This cannot be achieved where sacrificial anodes are used, unless they have a special facility designed for this purpose at construction stage. The voltages obtained between the pipeline metal and a randomly placed electrode have a certain amount of value when compared to others obtained from connections to the same pipeline. This is because of the very low electrical resistance in this part of the corrosion and cathodic protection circuits.




Instant off Potentials for Cathodic Protection of Buried Steel Structures

Roger Alexander

Organization Mailing address

Including postal code and COUNTRY

[email protected]

ABSTRACT Steel pipelines transport the world’s energy supplies from their natural reservoirs to the consumers. These pipelines pass under ground which is sometimes densely populated or where the public would be threatened by an explosive failure. The integrity of these pipelines is therefore of huge financial and public safety consequence, and yet there is no international standard criterion for cathodic protection of these pipelines. . This is the problem that is addressed by this paper.

INTRODUCTION Steel naturally corrodes when in contact with an electrolyte, such as the ground in which it is buried or the water in which it is submerged. The first line of defense against corrosion is a coating of inert material which chemically separates and electrically isolates the pipeline metal from its environment. However, a perfect coating is impossible in practice and the electro-chemical reaction is concentrated at coating faults. Cathodic protection has been developed as an extremely cost effective method of extending the life of metal structures by an order of magnitude. Unfortunately it has proved very difficult to monitor the effects of cathodic protection and there are frequent disastrous corrosion failures at locations where it was thought that corrosion had been prevented. In 1974 two oil pipelines in West Africa leaked 6 weeks after being constructed. They continued to develop further leaks until the author diagnosed and corrected 'interference' current from another CP system. They have not leaked since. ROGER—IS THERE A REFERENCE FOR THIS? Bob …. The pipelines concerned were Ekulama 14 and Ekulama 17 which were 6” diameter steel pipelines coated with Napco thin film coating each from the repective oil well to the gathering station at Ekulama which is in the Eastern division of Shell Nigeria. There are records of these events but I do not know if they would be considered to be in commercial confidence. Cathodic Protection requires scientific knowledge and engineering discipline to apply. In 1978 a wrong connection at an oilfield installation caused 20 pipelines to leak within 3 weeks due to the accelerated corrosion caused by the direct electric current leaving the pipe metal.

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Despite cathodic protection being required by law in most countries there is no internationally agreed criterion at present.

MEASURES OF EFFECTIVENESS OF CATHODIC PROTECTION

Many failures of cathodic protection demonstrate the need for a better understanding and a clear benchmark for pipeline operators in respect of this method of corrosion control. The most definite method of monitoring the performance of corrosion control is by physical examination by excavation. The development of the 'intelligent pig' has allowed excavations to be carried out at locations suspected of damage before the pipeline actually fails but this method does not indicate the measures that must be taken to stop the progress of any damage that is found. The next most certain way of measuring the actual progress of corrosion is to install a series of “weight loss coupons” which will reflect the performance of the pipeline metal, but this is a long-term exercise with practical difficulties. It requires expert and highly trained technicians to apply the technique and is not commonly practiced. The electrical element of corrosion can be controlled and it would seem that a simple electrical measurement would suffice to establish when corrosion has stopped. After all Faraday determined that the amount of metal that goes into solution in the corrosion reaction is directly proportional to the amount of DC current which results from that reaction. The problems in making field measurements are discussed later in this paper but until the early 1970's it was generally believed that a standard reference electrode could be used in cathodic protection field work and the instructions were that it should be placed as close as possible to the pipeline or structure. The traditional '-0.850v' criterion: It was believed that if the pipeline became negative relative to a copper/copper-sulfate reference electrode in excess of 0.85 volts with the CP system operating, then corrosion had been halted. The academics supported this notion and Codes of Practice have been published. (CP 1021 B.S.I. Code of Practice for Cathodic Protection of Pipelines)

Fig. 1. The standard method of monitoring cathodic protection.



The 'Pourbaix' diagram was published in the 1950's and was hailed as validation of the -0.850v criterion in relation to a copper/copper sulfate electrode.

Fig. 2. The Pourbaix diagram of Iron in water.

Problems Pipelines have continued to leak, even when this criterion has been reached, and new criteria have been proposed, but none have been adopted internationally. In 1982 the paper ' New Developments in Measuring the Effectiveness of Cathodic Protection' was presented to the Conference of the Australasian Corrosion Association, Hobart, Tasmania discussing the problems involved in establishing when corrosion has stopped. This author made a presentation on this subject to the London Branch of the Institute of Corrosion Science and Technology on the 10th of January 1984 and had a paper published in the International Journal 'Corrosion Prevention and Control' in October 1984 entitled “An Examination of CP Monitoring using the half-cell and voltmeter which disputes the present interpretation.” Much research has been carried out, resulting in a number of techniques being suggested, and devices patented. None of these devices have achieved international acceptance, and there is still no reliable criterion for cathodic protection. The papers rely on the reader being conversant with details of corrosion science whereas the aim is to find a criterion, which is easy to understand, and achievable with instruments that are



rugged enough for field use.

Instant off potentials In the late 1970's worldwide experience was showing that the methods of ascertaining the corrosion status of buried, steel pipelines were inadequate as pipelines were subject to corrosion failure at locations where they were thought to be cathodically protected. The traditional method of monitoring a CP system was to make a voltage measurement between the pipeline metal and an electrode placed as close as possible to the pipeline in the ground in which it was buried (or in the water in which it was submerged). Field experience had revealed that such CP voltages were subject to an “IR drop in the soil'” which was of indeterminate value. The “IR” drop in the soil is another way of expressing the potential difference (voltage) between two places in the soil. The effect of these variations in voltage is to alter the reading shown on the meter.

Fig. 3. The IR Drop in the soil

A laboratory in Holland had shown that this error could be removed by using an analogue recording voltmeter while the current was switched off to show a 'kick' in the downward curve at a value at which it was thought the metal was 'polarized' by the cathodic protection system.



Fig 4. Kick in the downward curve. The theory is that the 'IR drop' is caused by the flow of the current from the cathodic protection anodes to the pipeline metal, and that this current could be switched off to eliminate the voltage drop. It is known that the pipeline holds its voltage due to “polarization,” and it was thought that it would be possible to measure the “polarized potential'” immediately after the current was switched off. Trials were carried out for an international oil company in Africa, but it was found that the “Instant off Potential” measurement was impractical and would be too expensive to be viable in field conditions. This was due to the cathodic protection systems being integrated into a complex electrical circuit being affected by at least 43 transformer/rectifiers with a variety of output voltages and currents. It was also found that there were many other influences on the voltage readings that could not be removed by switching the cathodic protection transformer/rectifiers off. Attempts to isolate each section of pipeline for the purpose of switching proved that the electrical equilibrium is altered by such activity and results do not, therefore, show the normal corrosion status of the pipeline. The 'two half-cell' survey was developed and used successfully in West Africa during this period confirming the variable potential of two copper/copper-sulfate electrodes when placed in contact with the ground. Potential gradients were plotted and used to identify coating faults, ground bed profiles and active corrosion. These techniques are mentioned later in this paper.



Close Interval Potential Survey (Switching) (CIPS) In the early 1980's a survey was devised to take 'Instant off' voltage readings at close intervals over all pipelines in a major network that included urban and rural, high-pressure gas mains. The author was a participant of this most significant CIPS survey that was carried out between 1980 and 1984 in the following way. Disconnecting the cathodic protection “bonds” at insulation joints and isolation flanges isolated sections of the pipeline network.

Fig 5. A Cathodic Protection Bond Wire The position of the pipeline was marked using “Pearson type” instruments. The transformer/rectifier for this section was switched on for 5 seconds and off for 2 seconds. The pipeline metal was contacted through CP test points and a trailing wire was connected to the negative pole of a digital voltmeter, carried by the technician. The positive pole of the voltmeter was connected to a copper rod suspended in a saturated solution of copper sulfate that was put in contact with the ground.



Fig 6. Close interval potential survey. The technician noted the highest and the lowest readings on the meter as the switching occurred at each point of ground contact. This was repeated at 10-meter intervals over the pipeline.



Fig 7. The form on which the technician entered the voltage readings. Millions of 'on' and 'off' readings were fed into the computer during a four-year period by four teams of technicians and two engineers engaged on the survey. The computer plotted the 'on readings', the 'off readings' and the difference between the two, which was anticipated to show the results of corrosive activity. The third plot was abandoned after a few months as it was then thought to be insignificant.

Fig 8. Computer generated plot of readings supplied by technician.



During the four-year condition audit, several 'Pearson type' techniques were used to identify the position of the pipeline and to pinpoint coating faults. A method was devised to record the 'Pearson' signal and make a permanent, graduated record that could be compared to physical examination, following excavation.

Fig. 9 Permanent graduated record of a 'Pearson Style' survey. The 'two-half-cell' method of survey [ref 2] was used extensively to identify exact locations for excavation, and the Alexander Cell was field tested with permission of the pipeline operating company.



Fig 10 One example of a 'two-half-cell' plot showing potential gradients in the soil. Further refinements were made to the original survey and the format entirely changed to determine the locations to excavate for physical examination.



Fig. 11. The final report format for excavation at locations suspected as having active corrosion.

At total of 102 excavations showed less than 10% success in predicting the condition of the coating and pipeline metal by the CIPS survey. The operating organization developed 'the intelligent pig' concurrently with this over line audit, but cathodic protection monitoring has the advantage of indicating the cause of corrosion damage as well as suggesting remedial measures by adjusting the cathodic protection system. It is also possible to monitor the success of remedial measures inexpensively.

Observations The survey did not meet the requirements of the laboratory recommendations for making the 'polarized potential' measurement that should be made on an analogue recording voltmeter capable of showing the 'kick' in the downward curve. Attempts were made to find a satisfactory way to conduct a recorded CIPS and they clearly



demonstrated that the “polarized” potential could not be readily identified as required by the laboratory test and that other influences would have to be evaluated to obtain a true potential for the purposes of applying the principles of the Pourbaix Diagram.

Fig 12. Analog recording voltmeter with stepped electrode showing the difficulty of identifying

the 'kick' in the downward curve. Attempts were made to correct readings using analog recording voltmeters with static electrodes to evaluate the voltage differences over a period of time at a single location. This would also be necessary in order to apply the principles of Pourbaix and Faraday.



Fig 13 Recording voltmeter with static electrode showing how the on and off potentials varying during a period of several minutes.

All cathodic protection systems work in an environment influenced by other cathodic protection systems. By isolating one section we alter the equilibrium, which we wish to measure, in the act of making the measurement. (See also later note) Synchronized switching of TR's was attempted and found to be impossible to achieve. Several techniques have been suggested since this audit but successful results do not seem widely available despite the marketing of sophisticated and expensive instrumentation. No attempt was made to switch the sacrificial anodes that were influencing the sections under test although some of these were temporarily disconnected. The exact position of each reading would have to be recorded and repeatable for the survey to have any value.

Comments on this type of survey. Cathodic protection systems are switched on while in service, and the current flowing from the cathodic protection anode is a significant part of the electrical equilibrium. It is a powerful electro-motive force within the integrated circuits of both the corrosion reactions and the measuring system and to remove this force from the corrosion reaction is to falsify the results of any measurement. Removing the 'IR drop' in the measuring circuit can easily and cheaply be achieved using an “isopotential cell” as suggested by many reputable and leading scientists. There are two versions patented and a simple unpatented version of the same principle can easily and cheaply be made by anyone. “Instant off” and CIPS readings cannot be analyzed using either Ohms Law or Kirchoff's Laws but are traditionally interpreted by the informed guesswork of specialists. We should aim to determine whether corrosion has stopped by non-intrusive techniques that can be confirmed by physical inspection at coating faults that are detected to be corroding.




Module 2

Students are required to make two 'half-cells'.

This is necessary to make it clear that a copper/copper-sulphate electrode is a very simple article with no mystical powers or scientific properties that are difficult to understand. It is simply a copper rod immersed in a saturated solution of copper sulphate. Copper sulphate is the result of disolving copper in sulphuric acid and therefore the scientific description 'in a saturated solution of it's own salts' is correct. Copper sulphate crystals can be obtained from Ebay and Distilled water can be obtained from any garage.

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Any clear plastic material can be used as the tube in which to place the copper sulphate crystals and the porous plug can be made from wood or gypson (plaster of Paris). Other domestic fillers can be used but they must be porous when they have set.

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Scientists would have us believe that it is crucial to have pure copper and a pure saturated solution solution, but in fact you will be able to check this out when you have made the two electrodes.

You will be able to alter the purity of one cell and make a voltage measurement against the potential of the other.

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Experimenting on a damp cloth or in a tray of wet sand will help you understand the function of the electrode.

The two Cu/CuSO4 electrodes will be used extensively during the remainder of this course.

The real purpose of the 'half-cell' is that of a convenient ground contact for buried pipelines and as a contact with the water in the case of submerged pipelines or structures.

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Standard pipe-to-soil voltage measurement at a test post,

with the Cathodic Protection installation switched on.

INSTRUMENTATION. AND EQUIPMENT

� High resistance voltmeter.

� Cu/CuSO4 electrode.

� Two lengths of flexible cable, each fitted with a voltmeter

connector and a crocadile clip.

� Field notes

� Report forms

METHOD

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1.1 Place the electrode firmly in the ground.

1.2 Connect the electrode to the positive pole of the voltmeter.

1.3. Connect the negative pole of the voltmeter to the pipeline test point connection.

1.4. Record the voltage reading on the record sheet.

Notes.

This is the standard type of measurement that has been recorded over many years by most operating organisations.

The reading will indicate that the CP is functioning and connected in the correct polarity.

Such records can be related to corrected readings where the errors have been identified by using other procedures.

click to return to Module 02 index page


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Pipe-to-soil voltage measurement at a test post

where there is a standard position for placing the half-cell,

with the Cathodic Protection installation switched on.

INSTRUMENTATION. AND EQUIPMENT

� High resistance voltmeter.

� Cu/CuSO4 electrode.

� Two lengths of flexible cable, each fitted with a voltmeter

connector and a crocadile clip.

� Field notes

� Report forms

METHOD


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1.1 Place the electrode firmly in the standard ground position.

1.2 Connect the electrode to the positive pole of the voltmeter.

1.3. Connect the negative pole of the voltmeter to the pipeline test point connection.

1.4. Record the voltage reading on the record sheet under the heading 'P'.

Notes.

This is the standard type of measurement that has been recorded over many years by most operating organisations.

The reading will indicate that the CP is functioning and connected in the correct polarity.

Such records can be related to corrected readings where the errors have been identified by using other procedures.

click to return to Module 02 index page


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Module 2

Field trip with simple exercise in CP measurment requiring a report.

Return to the test post that you identified in module 01. You will need your digital multi-meter and one of the half-cells that you have made. You will need a sheet of paper and a permanent water-resistant pen of some sort. This is necessary so that you can relate to the historical data that you will be looking at during this course. Carry out Procedure 1 Carry out Procedure 1a Carry out Procedure 1c Carry out procedure 1d


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Module 3

Thermo-dynamic theory of CP simplified.

It is necessary to address this subject as I once received a letter from Dr David Scantleberry of the University of Manchester Institute of Science and Technology saying "You should get yourself a good book on electro-chemistry". Such books always refer to thermodynamics, the behaviour of electrons and energy. In another instance, at the end of my presentation to the Institute of Corrosion Science and Technology in London in the 1980's, one of the delegates stood up and said that I had ignored the thermo-dynamic aspects of cathodic protection.

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(Happily, another delegate stood up, announced himself as having a PhD in the subject, and stated that I had satisfied him in all aspects. The other 100 delegates glared at my critic so he sat down red-faced.) However, these two incidents show that you will always be faced by someone who cannot rebutt your presentation of the facts, and who will resort to trying to confuse everyone with long words. It is for this reason that I have developed the ability to demonstrate and repeatedly confirm everything that I know about cathodic protection and corrosion. Thermo-dynamics deals with energy and corrosion releases energy in the form of electrons. These electrons flow in the opposite direction to that shown on a voltmeter as the direction of Direct Electrical Current (DC) You will find some who want to show their superior knowledge by pointing this out. The answer is to agree and then ask if this is shown on any of the meters that have ever been used in the field by corrosion engineers. The direction of the electron flow only confuses the matter and should be ignored. This will only receive further attention when we can see an electron and see that it makes a difference to the practical application or measurement of cathodic protection. There are more complications that are already present in the study and practice of cathodic protection engineering. The main point of the laws of thermodynamics, relating to corrosion and cathodic protection, is that the energy released by the chemical reaction between metals and their environments must complete a circuit to reach equilibrium. Everything must balance out. The metal disolves, giving off energy, which we can measure using a digital voltmeter. We can 'see' this corrosion using and Alexander Cell.



This energy can be called Electric Motive Force or EMF. This adds to the property known as 'electrical potential'of the eletrolyte which has disolved the metal. This is at the anode on top of the Alexander Cell.



This electrolyte is then charged to a higher potential than the surrounding electrolyte to which the energy is radiated. In the case of the Alexander Cell, the sample of electrolyte with which the cell is 'fired up'is isolated from the ground and the only conductive path to complete the circuit is through the cathode on top of the device. We therefore have the only method to make the measurements that are necessary to use the Pourbaix Diagram or the Nerst Equations for in practical application of cathodic protection. The use of the half-cell or any other reference electrode CANNOT render the data required by all of the theories used in cathodic protection! We will study the whole of the circuit in detail later in this course.The thermodynamics and all the science is important in that it is the law by which the whole world works. In this case we have a law that applies to each corrosion cell and we are dealing with millions of individual cells on every length of pipeline. This will include micro-corrosion cells on a single coating fault, long line corrosion cells that can have their anodes separated from their cathodes by several meters and complex



combinations of corrosion reactions. It is all very well knowing how to control each individual corrosion reaction if we are in a laboratory or trying to design a battery charger but we have to define a system that will stop all corrosion reactions on a variety of structures made from a variety of metals in a variety of environments. Each of these reactions has a direct effect on all of the others. The application of simple rules like the Nerst Equations and Gibbs free energy etc are only relevant if we have a method of measuring the values that are incorporated in them.





In practical work the measurement is complicated by the fact that the electrical balance of the circuit formed by connections between all the metalic structure must be measured in 'open circuit' as they are all submerged in common electrolyte of infinitely variable conductivity. We therefore need the skills of electronic engineers and considerable computer power to analyse the true status of each corrosion reaction.

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Module 3

� Thermodynamic theory of CP simplified. � The significance of the Pourbaix diagrams. � The Daniel Cell in laboratory work. � The importance of the reference potential. � Codes of practice. � Standard laboratory techniques � The development of standard techniques in field work. � Open circuit measurements. � Errors and their causes. � Practical bench experiments. � Field trip with experiments requiring a report.

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Module 3

The significance of the Pourbaix diagrams.

People will refer to the Pourbaix Diagrams and scientific papers by Pourbaix and Evans because they are recognised as having explained how cathodic protecion works in thermo-dynamic terms. That is what I have been told by qualified scientists and I am not about to argue with them... they have been paid a lot more than me for their conclusions!

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I have reproduced the Pourbaix Diagrams several times and believe that they show a state of equilibrium in which metal has not got the energy to disolve. It does not matter what equations etc he used to prove this as everyone believes him ... so that's OK. It is VERY IMPORTANT to understand how the measurements were made to obtain the values included in these equations.

In plain words this drawing shows a piece of steel called 'the working electrode' corroding in an electrolyte. The corrosion current passes through the electrolyte to the other piece of steel called the 'counter electrode'. The potential of each piece of steel is regulated by a device called a

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'potentiostat'. The 'reference electrode' is shown to look like a half-cell with a copper rod 'reference electrode' in a saturated solution of copper sulphate 'reference well'. The Lugin Capillary is a fine glass tube filled with conductive gell that provides a chemically inert conductive path to an exact position in the active region of the interface between the working electrode and the electrolyte. Even this sophisticated arrangement leaves some sceptisism due to the fact that making the measurement disturbs the value of the data it yields. There have been some attempts to apply the principles of this type of measurement in the field by Global Cathodic Protection in Libya for example. A plastic tube is provided to represent the lugin capillary but of course this tube finishes at the coating and not at the bare metal interface that would be present at a coating fault. Such arrangements are of no technical or scientific value. There are several arrangements of electrodes patented by scientists in an attempt to resolve this problem. CPN has one such device available known as the Isopotential Cell and will be described in detail elsewhere in this course. If we cannot make the same measurements in our work then we cannot apply the equations. The Alexander Cell is the only available method to obtain the correct values in field work, to apply to the Pourbaix Diagrams. This will be made clear during this course.

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Module 3

The Daniel cell and such measuring techniques

The main point of the laws of thermodynamics relating to corrosion and cathodic protection is that the energy released by the chemical reaction between metals and their environments must complete a circuit to reach equilibrium. Everything must balance out. The metal disolves, giving off energy, which we can measure using a digital voltmeter. This energy can be called Electric Motive Force or EMF. This adds to the property known as 'electrical potential'of the eletrolyte which has disolved the metal. This electrolyte is then charged to a higher potential than the surrounding electrolyte to which the energy is radiated. It is VERY IMPORTANT to understand how the measurements were made to obtain the values included in the equations used by scientists. If we cannot make the same measurements in our work then we cannot apply the equations and the Pourgaix diagrams, the Nerst equations, ohms law, Kirchoff's laws etc cannot be applied to establish the corrosion status.

Page 1 of 3Cathodic Protection Network, training course, Daniell Cell

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The Daniel Cell is a glass module that allows absolute electrical potentials to be measured. The Daniel Cell is used to establish the relative potentials between metals in saturated solutions of their own salts. you can see a steel coupon in acid connected to a voltmeter and the meter connected to a copper coupon in acid.The glass loop connecting the two is filled with porous material.... rolled up paper will do...and that provides a conductive path for the current to pass through In this way they can assign numerical values to electro-chemical reactions. Scientists can then work out theories to explain the behaviour of corrosion. Our job is to see if these theories can be seen to work in the field.

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Module 3

The importance of the reference potential.

A voltmeter can only display the difference between two potentials. To display a voltage of 3 the meter must assign the value of zero to the pole of the meter we shall call 'A' and measure the potential difference between that value and the value we shall call 'B' which is connected to the other pole of the meter.

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A+B=3. Everyone knows this but DO NOT THINK ABOUT IT! In the illustration we see that the meter will displayed the value as negative because that it has been programmed to display it. the software has told it that B is zero. If we need to know the relationship between three potentials using a single voltmeter, we must take two readings. A-B=3 and A-C=9



or we can take the readings A-B=3 and B-C=6 in which case the meter has assigned the value of zero first to A and then to B. It is clearly better that we relate both readings to one zero as this avoids calculations and confusion. This becomes more obvious if we need to know the relationship between four potentials using a single voltmeter. We need only to take three readings providing we establish our own reference potential. A=0 therefore A+B+-3, A+C=-9 and A+D=3. being able to think this way is essential to the cathodic protection field engineer and technician. It is the only way to picture what is actually going on with regard to corrosion and CP currents. It is possible to calculate the relationships if we take different readings but it is unnecessary and confusing... so let's not do it. Unfortunately traditional cathodic protection readings do not have a common zero but it is possible to establish the common zero using standard CPN Procedures.

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Module 3

Codes of Practice

There are numerous codes of practice that have been published

and revised over the years but none of them have been based on scientific principles as outlined in this course. I would suggest that all students try to follow all written codes of practice and carry out a detailed examination and report of the results.

The first module of this course is in fact such a critique and CPN has received no answer from the many communications sent to

those issuing those codes of practice. We, therefore, cannot say that they are wrong but we can definitely prove that we are correct. It is a fact that the British Standards Code of practice CP1021 was withdrawn by the chairman of the BSI committee as a result of the presentation made by Roger Alexander to the London Branch of Inst Corr Sc and Tech

I got no response from the Institute relating to this presentation

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and sent the following letter.

Still no response from the Institute





They then responded.

J.H.Morgan was an established consultant with many published papers based on the use of the half-cell as a reference. I received the following letter from Jim Gosden.

Many years later I was requested by a University in the USA to contribute to an appraisal of the American standards with reference to this whole subject. NACE have no single criterion for the achievement of cathodic

protection.





Module 3

Standard laboratory techniques

Standard Laboratory Techniques allow scientists all over the world to co-operate in the general advance of science and understanding. Standard tests are carried out to ensure accurate product data can be published and that the quality of products conform to the specification required by the consumer. However, we should not rely on the scientific establishment to provide absolute solutions to pratical problems The following is my reason for doubt. During a visit to UMIST I was shown a glass tank that was set up to conduct a 'cathodic disbondment test' intended to conform to the BSI code of practice. Specified positioning of the test coupons in relation to the reference electrode had been ignored and readings were being adjusted by controlling the anode potential level. The test was ineffective, but the reported results would contain enough of the right numbers to keep the client (a major paint manufacturer) happy and to convince the paint users that the BSI standard had been met. Prof. Les Wolff wrote this particular BSI code of practice and had supported me (in writing) relating to my publication about the problems that are inherent in cathodic protection field work. He was specific about the positioning of the

Page 1 of 2Cathodic protection network Module 03

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reference electrode which should have been EXACTLY 10mm from the metal/electrolyte interface. There is much more to this matter than is apparent from a purely scientific point of view. UMIST were busy 'selling the king his new coat'. Dr Scantlebury was the tailor who convinced the King of Paint that the new suit would serve the purpose and he was believed because of his reputation and qualifications. It is vitally important for corrosion engineers to understand that field conditions are not readily mirrored in the laboratory The purpose of CPN is to stop corrosion. If our custommers want corrosion stopped they will have to come to us as all competition is interested in is making money. During my travels as a corrosion engineer all of my client have said that what they have learnt at university has not worked in the field.


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Module 3

The development of standard techniques in field work. The best way that I can cover this topic is from a personal point of view, as there have been a flood of suggestions and hypotheses from many sources. Engineers in other specialities have consistantly refered to cathodic protection as a 'black art' and 'something of a mystery'. I have even heard an engineer saying that 'cathodic protection deals with a 'different form of electricity'. This is nonsense! Cathodic Protection is an exact engineering practice based on an exact science which can produce predictable results based on repeatable demonstration of the observations on which it is based. It is for this reason that no-one will be allowed to bullshit in the name of the Cathodic Protection Network.

Link to Procedures index page

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Module 3

Open circuit measurements

This is a name used by Peabody of NACE to describe an electrical measurement made when one pole of the meter is connected to the electrolyte rather than a definitive point on a metalic circuit. A normal electrical measurment is made by contacting metal conductors Such measurements can be studied in the confines of a laborarory or on a bench, using trays and containers with sufficient space to allow the movement of the contact point within the electrolyte.

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It will be seen that the measuring circuit of the standard cathodic protection measurement consists of a conductor from the negative pole of the meter to a conductor in a pipeline test post that is directly connected to the pipeline metal. The pipeline metal is then in contact with the ground/water at undefined coating faults. The positive pole of the meter is connected to a conductor to a copper rod in a saturated solution of copper-sulphate. The solution soaks through a porous plug and makes contact with the ground/water. It is realised that a silver/silver chloride electrode is traditionally used in sea water measurements but this does no make any difference to the measuring principles. There is a volume of electrolyte between the pipeline metal and the point where the electrode contacts the mass of the electrolyte.

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This electrolyte is conductive and can be perceived as a number of resistances in parallel. The point at which the current to be measured passes through a deminishing number of resistances from the mass of the electrolyte to the point of contact of the electrode is recognised as 'shells of resistance'.

The effect of these shells of resistance can be measured using a galvanometer and a digintal meter as shown in the drawing below.

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This can be carried out in the field or on a bench in a tray of wet sand. It can also be replicated on a mathmatical model using a computer.

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Each feature of open circuit measurements can be described mathmatically and tested on bench models and in the field. It is obvious that these studies involve Ohms Law and that this can be used to determin the resistances in the immediate area of the corrosion reaction and the cathodic protection current paths.

The electrolytic path. Attempts are often made to ascertain the resistance of the earth along the path of the pipeline. There are several methods used but all miss the point

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that the 'average resistance' of the wayleave is corrupted by the presence of coating faults. It is necessary to study this as an electrical problem rather than an electro-chemical problem. One difficulty is that the unit of measurement is ohm-meters or ohm-centimeters. this is NOT Ohms per centimeter or Ohms per meter! This is not a value that you can say the further the distance the greater the resistance! The reason for this is that the quality of resistance is subject to the laws of resistances in parallel. The 'charges' radiate out from a point to an area where there are an infinite number of resistances in parallel... and therefore there is an infinitely low resistance. click to return to Module03 index page

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Module 3

'Errors' or mistakes made by people using instruments

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It has long been recognised that there are errors in the data that has been recorded relating to cathodic protection field work. These errors have all been refered to as 'the IR drop in the soil' NACE has recognised that there are difficulties in making 'open circuit measurements'. CPN has always recognised the inherent errors in conventional CP measurements and has developed a suit of procedures to take advantage of the features that cause them. Two papers in this course define the errors in practical and scientific terms. The drawing above is intended to draw the attention of the field corrosion engineer to the circuit that he is engaging with every time he makes a cathodic



protection field measurement. CPN has exact technology based on exact science and a member of CPN must always work in a disciplined way that renders high quality data that is capable of being computer analysed. By following the exact steps defined in CPN procedures we can be sire that we are following engineering and valid scientific practices that evaluate the conditions surrounding corrosion.





Module 3

Bench Work

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The purpose of the bench work in this course it to help the student visualise electricity. Cathodic protection engineers must be able to use their instruments to 'see' what is happening as a result of

corrosion and to 'see' the results of the cathodic protection systems that they install, commission and adjust.

We need a plastic tray of earth or sand which we can keep dry or damp and saturate with different

purities of water. We need steel nails, batteries a multi-meter and an assortment of connectors.

The pictures on this page give you and idea of how you 'play around' to prove to yourself the contents of Module 03 and to start you visualising the content of the whole course.

















You will see that the half cell is not used in the above pictures and that the results of sticking the nichol plated copper probes into the sand yield useful data.

In the next picutures you will see that we use super absorbant cloth instead of sand.

This is because it is easier to transport and can more readily show the stains fom corrosion product.















Module 3

Field work

The field work for this section is to replicate the bench experiments at the test post with which you are now familiar. Your should be now have the 'feel' of what is going on and be able to use your meter to 'see' the electrical effects. By connecting a crocodile clip to the stud on the test post (that is connected to the pipeline) you will be able to make a steel coupon represent a coating fault. It is convenient to us a 1" broad, wood chisel as a coupon as this is easily stuck in the ground and can the depth can be readily adjusted to give an assortment of metal to electrolyte areas of contact. You can then use the meter probes to plot the depression caused in the ground potential profile around the chisel.


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Module 4

� Equivalent circuits � Physical modelling of CP measurement techniques. � Practical construction of 8 measurment models. � Field trip to confirm theoretical and model integrity requiring a report. � On-line real time discussion.

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Module 4

Equivalent circuits.

Many books on cathodic protection try to substantiate theories by showing electrical drawings of equivalent circuits. This is fine for the parts of the cathodic protection circuits that pass through conductors that are designed for the purpose. Cathodic Protection Network is different.... we not only draw equivalent circuits... we make them. Our equivalent circuits have to work!


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Equivalent Circuit of a groundbed and three pipelines.



Equivalent Circuit of three CP test posts and a coating fault.

The drawing of equivalent circuits fails to be useful when the circuits do not function as described when actually constructed.



The problem is that the path of the electrical current passes through 'mass earth' and that cannot be accurately expressed by the

symbolism used by convention in the electrical industry.

A dry cell battery is a corrosion cell and can be incorporated into a working model of an equivalent circuit.



Corrosion cells can happen to be in parallel or in series and the equivalent circuits of these situations can be achieved

very simply using battery holders as shown.



By using a length of steel pipe and a thick copper wire, we can pruduce an equivalent circuit of several corrosion cells on a pipeline.

We then balance the battery outputs with a transformer rectifier and we have

the equivalent circuit of a single cathodic protection system applied to a single pipeline.



This is a useful aid to study cathodic protection in the field as we can now visualise the electrical balance.





Module 4

Physical modelling of CP measurement techniques.

It is very useful for students to actually model the cathodic protection that they are studying. This helps them to visualise the electrical paths and effects that they are dealing with. It allows them to understand that potentials are electrical pressures that are similar to water pressure and gas pressure, but have other qualities that must be taken into consideration. Water pressure is often shown in drawings but CPN uses actual models with real water to show some of the aspects of the application of cathodic protection.


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We have four glass flower vases, each being three tubes joined so that water can level out in each tube. We have placed these vases in compartments of a transparent container, each supported at a different level and the fourth section being filled with sand so that we cannot see the bottom part of the flower vase. This shows that we are limited in the information that we can gather about the status of each tube and each vase. Our meter allows us to 'see' the potential of one tube by comparison



to each of the other tubes. In the case of our model, our eyes allow us to evaluate the water levels in each of the tubes but not in the parts buried in sand.

Each glass flower vase represents a coating fault, with the water level in each tube being the electrical potential (or EMF) of that particular surface reaction. If the 'circuit' of each tube is completed through the connecting glass tube and atmospheric pressure, then the water will reach equilibrium and the surfaces will be level.



If the 'potential' of each tube is too low then the water will not flow between them .... no current will flow and there is no metal or energy lost.



We can use the whole model to show the difficulties in measuring the relative potentials of all of the coating faults on a length of pipeline. A side view of the water model shows that the level of each main compartment is different and the level of each of the tubes might be different in relation to the bottom of that tube.



Now look at the sand filled partition and we cannot know anything about the botoms of the tubes or the water levels that are out of our sight. All we can see is the water level that is visible above the sand. This is exactly the situation we are in when measuring the voltage between a half-cell and the pipeline in cathodic protection work.



It is necessary to play around with this model or the notion of this model so that you understand that all 'potentials' have to be related to other potentials to be significant. It is no good puting a potential value into a formula if it is not related to a common zero value within that formula. You can apply Ohms Law to a single corrosion cell because that is a single circuit but you cannot apply it to two corrosion cells unless they are integrated. You can relate this notion of modeling to that of using dry cell batteries. A dry cell battery has a potential difference from one pole to the other and can be compared to the tubes in each of the flower vases.

return to Module 04 index page




Module 4

8 cathodic protection models

3 nails to show corrosion resulting from direct electrical current. Coated pipe with coating faults. Two coated pipes with coating faults Dry cell battery as a corrosion cell. Dry cell battery with one end submerged. Two dry cell batteries in parallel and series. Multiple dry cell batteries with ends submerged. TR with steel pipe and groundbed.


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Module 5

Significance of the paper presented at the Australasian Corrosion Conference of 1982

This paper was an attempt to address the problems inherent in the monitoring of cathodic protection. It confirms everything found in field practice and was followed up by a book by the same authors. This book is in the library of UMIST and was lent to me for a short period by a student who attended a course I ran under the manpower services commission in the UK. Unfortunately, the practices recommended in the book are very expensive as they required qualified engineers and a van load of instruments. I believe some surveys were carried out to these specifications but I have no knowledge of the effectiveness. I have not had the time or opportunity to research this matter but would be pleased to get any information from anyone. Students should write their own version of this paper in their own words. This will be published on the CPN website together with my own version. The intention is to have everyone in the CPN 'singing to the same songsheet'.





The front page makes it clear that significant errors exist in the 'immediate off' voltage measurements that are still the mainstay of cathodic protection measurements.





These scientist have missed one practical point. Before the advent of digital multimeters there was a depression in the potential of the ground caused by the cathodic protection current that was necessary to drive the mechanism of the meter itself. This is described in detail in the Module dealing with instrumentation. Up until the 1980's there was a huge effort to get the cathodic protection readings to a level that was virtually impossible. On the wide spread use of digital meters it was found that 'protected' readings were achievable at locations where they had been impossible. There is no way of establishing which of these measurements indicates the true achievement of cathodic protection.





The formulae above are a complex way of explaining that the voltage on the meter is the sum of several potentials. We need to know one of them to discover if the metal is corroding.





Now THAT page seems to me deliberately confusing. If you wade through the strange letters used to express quite ordinary things it is quite clear that there are a lot of approximations and uncertainties in the rational. Read it again and again whilst visualising each symbol meaning something with which you are familiar. Question all assumptions that you do not regard as proven. In real life you will find that the voltage drops for days after switching off the TR. What the above formulae does not even consider is that we are dealing with an unknown number of corrosion cells in parallel. The Pourbaix diagrams make it plain that you must know the pH of the electrolyte to determine the value they describe as Ep. Do not let this sort of scientific expression cloud the issue. We need to know when the CP has stopped corrosion at each location.





The statement at the top of the above page is not correct in real life. Try it and see for yourself. I have ..... many times.





The above page has given a simplified equivalent circuit drawing of two coating faults. In fact there might be two corrosion cells on a single coating fault or a single corrosion cell consisting of an anode 500 meters from the cathode.





The page above shows 3 coating faults and makes assumptions that are not necessarily correct.





At this point of reasoning there is the assumption that 10 M perpendicular is not only remote from the influence of the pipeline





The page above shows 3 coating faults and makes assumptions that are not necessarily correct.





Students will now realise how the facts shown in Module01 are important when reading the above page.



It must be put into perspective that this paper quotes the results for surveys



conducted over a very limited mileage of pipelines. The formulae rely on assumptions that can be questioned, if not rebutted.





The above page is very important as it says clearly that CIPS is useless. CPN Procedures are designed to overcome these problems and can render data that can be computer analysed including the effects of all electrical flux.





The above effects have been described as 'teluric effects..... this is a missnomer.





I was engaged by British Gas ERS to carry out the field tests in response to the studies of magnetic fluctuations and am very familiar with the results. It is quite amusing as I got the job as no-one else understood how to do it. They were all too busy using long words and spouting off at meetings.





I have similar data and copies of chart recordings in the CPN archives.





The above refers to a device that has since been patented individually by each of the authors. We can easily manufacture our own device called the Isopotential Cell and not be in breach of the patents.





I have used isopotential cells in the field and in fact they have many problems other than those described above.





CPN have conducted the above tests in the field.





results available in the CPN archives





This is proof of the value of the Alexander Cell





This paper is an acknowledgement that all monitoring used by other companies world wide is seriously questionable. CPN Technology has resolved all of the problems described above and can prove it by demonstration and computerisation.



� Practical bench work to confirm this paper. � Field trip to confirm theoretical and benchwork integrity requiring a report. � On-line real time discussion.




Module 6

Practical application of available science and technology

� Introduction continuous potential surveys � Recording voltmeters and data-loggers. � Monitoring techniques which are presently used to establish C.P. criteria. � The Prinz Cell. The Baekmann Cell � The Alexander Cell and arrangement suggested by Jim Gosden of the British Standards Institute. � Summary of the present status of the criteria for 'protection'. � Field trip to use both types of cell requiring a report. � Case study at Rapelli- Nigeria 1992 � On-line real time discussion.



Instant off potentials

The traditional method of monitoring a CP system was to make a voltage measurement between the pipeline metal and an electrode placed as close as possible to the pipeline in the ground in which it was buried (or in the water in which it was submerged).


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Field experience had revealed that such CP voltages were subject to an “IR drop

in the soil'” which was of indeterminate value.



The “IR” drop in the soil is another way of expressing the potential difference

(voltage) between two places in the soil. The effect of these variations in voltage is to alter the reading shown on the meter.

The IR Drop in the soil

The theory is that the 'IR drop' is caused by the flow of the current from the cathodic protection anodes to the pipeline metal, and that this current could be switched off to eliminate the voltage drop. It is known that the pipeline holds

its voltage due to “polarization,” and it was thought that it would be possible to

measure the “polarized potential'” immediately after the current was switched

off.

A laboratory in Holland had shown that this error could be removed by using an analogue recording voltmeter while the current was switched off to show a 'kick' in the downward curve at a value at which it was thought the metal was 'polarized' by the cathodic protection system.



Trials were carried out for an international oil company in Africa, but it was

found that the “Instant off Potential” measurement was impractical and would

be too expensive to be viable in field conditions.

This was due to the cathodic protection systems being integrated into a complex electrical circuit being affected by at least 43 transformer/rectifiers with a variety of output voltages and currents.



It was also found that there were many other influences on the voltage readings that could not be removed by switching the cathodic protection transformer/rectifiers off. Attempts to isolate each section of pipeline for the purpose of switching proved that the electrical equilibrium is altered by such activity and results do not, therefore, show the normal corrosion status of the pipeline.

The 'two half-cell' survey was developed and used successfully in West Africa

during this period confirming the variable potential of two copper/copper-

sulfate electrodes when placed in contact with the ground. Potential gradients were plotted and used to identify coating faults, ground bed profiles and active corrosion. These techniques are mentioned later in this paper.

Close Interval Potential Survey (Switching) (CIPS)

In the early 1980's a survey was devised to take 'Instant off' voltage readings at close intervals over all pipelines in a major network that included urban and

rural, high-pressure gas mains.



The author was a participant in this most significant CIPS survey that was carried out between 1980 and 1984. At no time was it possible to measure the kick in the volts drop as the current was switched off, as described by the scientists in Holand on whose advice this type of survey was devised.

The survey was carried out in the following way

The position of the pipeline was marked using “Pearson type” instruments.

( Made by Simtec in the UK)

The transformer/rectifier for this section ofpipeline was switched on for 5 seconds and off for 2 seconds.

The pipeline metal was contacted through CP test points and a trailing wire that was connected to the negative pole of a digital voltmeter, carried by the technician.

The positive pole of the voltmeter was connected to a 'half-cell'which is in fact



a copper rod suspended in a saturated solution of copper sulfate that was used to contact the ground.

The technician noted the highest and the lowest vontage readings on the meter as the switching occurred at each point of ground contact. This was repeated at

10-meter intervals over the pipeline.

Millions of 'on' and 'off' readings were fed into a mainframe computer during a

four-year period by four teams of technicians and two engineers engaged on

the survey. The computer plotted the 'on readings', the 'off readings' and the difference between the two, which was anticipated to show the results of corrosive activity.

The third plot showing the difference between 'on' and 'off' was abandoned after a few months as it was then thought to be insignificant.





During the four-year 'condition audit', several 'Pearson' type techniques were

used to identify the position of the pipeline and to pinpoint coating faults.

A method was devised to record the 'Pearson' signal and make a permanent, graduated record that could be compared to physical examination, following excavation.



The 'two-half-cell' method of survey [ref 2] was used extensively to identify

Page 10 of 21Cathodic Protection Network, cathodic protection, corrosion control, pipelines, energy ...


exact locations for excavation.





Further refinements were made to the original survey and the format entirely changed to determine the locations to excavate for physical examination.



The Alexander Cell was field tested with permission of the pipeline operating company.



At total of 102 excavations showed less than 10% success in predicting the condition of the coating and pipeline metal by the CIPS survey.

The survey enhanced by the two half cell grid survey and the use of the Alexander Cell proved to be successful and accurate in it's predictions at 97% of the excavations.

The operating organization developed 'the intelligent pig' concurrently with this over line audit, but cathodic protection monitoring has the advantage of indicating the cause of corrosion damage as well as suggesting remedial measures by adjusting the cathodic protection system. It is also possible to monitor the success of remedial measures inexpensively.

Observations



The survey did not meet the requirements of the laboratory recommendations for making the 'polarized potential' measurement that should be made on an analogue recording voltmeter capable of showing the 'kick' in the downward curve.

Attempts were made to find a satisfactory way to conduct a recorded CIPS and

they clearly demonstrated that the “polarized” potential could not be readily

identified as required by the laboratory test and that other influences would have to be evaluated to obtain a true potential for the purposes of applying the principles of the Pourbaix Diagram.

Attempts were made to correct readings using analog recording voltmeters with static electrodes to evaluate the voltage differences over a period of time at a single location. This would also be necessary in order to apply the principles of Pourbaix and Faraday.

All cathodic protection systems work in an environment influenced by other cathodic protection systems. By isolating one section we alter the equilibrium, which we wish to measure, in the act of making the measurement. (See also later note)

Synchronized switching of TR's was attempted and found to be impossible to achieve. Several techniques have been suggested since this audit but successful results do not seem widely available despite the marketing of sophisticated and expensive instrumentation.

No attempt was made to switch the sacrificial anodes that were influencing the sections under test although some of these were temporarily disconnected.

The exact position of each reading would have to be recorded and repeatable for the survey to have any value.

Comments on this type of survey.

Cathodic protection systems are switched on while in service, and the current flowing from the cathodic protection anode is a significant part of the electrical

equilibrium. It is a powerful electro-motive force within the integrated circuits

of both the corrosion reactions and the measuring system and to remove this force from the corrosion reaction is to falsify the results of any measurement.



Removing the 'IR drop' in the measuring circuit can easily and cheaply be

achieved using an “isopotential cell” as suggested by many reputable and

leading scientists. There are two versions patented and a simple unpatented version of the same principle can easily and cheaply be made by anyone.

This is possible by combining existing technology with later developments, which should be adopted as the international criterion for cathodic protection. This would utilize the records and hard work of established cathodic protection engineers and incorporate additional techniques that allow mathematical analysis by computer.

“Instant off” and CIPS readings cannot be analyzed using either Ohms Law or

Kirchoff's Laws but are traditionally interpreted by the informed guesswork of specialists.

We should aim to determine whether corrosion has stopped by non-intrusive

techniques that can be confirmed by physical inspection at coating faults that are detected to be corroding.

A considerable amount of effort was made to draw attention to improvements that were available to the CIPS type of survey but these improvements were rejected as seen in the following correspondence.







British Gas is now influential in the maintenance of pipelines world wide and



has still not adressed this inherent error in it's maintenance procedures with the consequence that pipelines are failing unneccesarily throughout the world.

Many of the scientists and engineers involved with this original survey are in high advisory positions and were on a list of advisors to Prof Walsh of the University of Southampton in the UK who stated that the Alexander Cell is the only available method that satisfies the science behind the measurement of the corrosion reaction under the influence of cathodic protection.

back to Module 06 index page




Module 6

Instrumentation for Close Interval Potential Surveys

The history of electrical measuring instruments affected the development of cathodic protection monitoring and it is worth examining how this was perceived by engineers.


07/02/2010http://www.dynamic-cathodic-protection.com/module06/dataloggers.htm

This picture shows a data logger made specifically for conducting cathodic protection monitoring surveys. Several manufacturers are supplying such equipment and making all sorts of claims about it. It should be remembered that all these instrumenst measure voltages. They cannot measure a potential..... they measure the difference between two potentials. They sample voltages and store them digitally, using computer technology that is standard throughout the world in all industries. There are millions of people who understand this technology and it is based on the laws of electricity. Present instruments and software are not capable of analysing the data rendered from a CIPS or DCVG survey as the input probes are gathering data in open circuit. All they are capable of rendering is graphic displays of the voltages between two floating potentials.



The Isopotential cell is an attempt to resolve this problem but it does not work according to the theory behind it. This is the link to the page about the Isopotential Cell. The Alexander Cell can provide a base datum to which other values can be related and then CIPS and digital DCVG can be used to ascertain the criterion for the achievement of cathodic protection. This will be dealt with in detail in Module 15 which describes the Dynamic software that calculates where corrosion is located by applying the laws of electricity to the data. THE GALVANOMETER Up until the 1970s, digital instruments were not readily available and cathodic protection measurements were carried out with a variety of electrical meters which were based on the galvanometer.



These instruments work on the reaction of a magnet in an electric field against the elastic effect of a hair spring. They are less rugged than digital instruments and more difficult to manufacture. They also require a considerable amount of current to move the indicator needle.



The amount of current drawn by this type of instrument is sufficient to cause a depression in the potential of the soil in which the electrode is placed. It can be said that the current flowing through the measuring circuit causes its own IR drop.



This potential depression can be measured using two electrodes and a digital voltmeter.



This 'volts drop' in the measuring circuit caused substantial inaccuracies in the measurement, and the readings were shown to be lower than the true voltage. This is the opposite effect to that of the 'IR drop in the soil' which is caused by the passage of the cathodic protection current.



During the period in which these meters were used, the fact that the readings were less than the criteria, encouraged operators to blame instrument inaccuracy when protected criteria could not be achieved. All the time that a needle was moved against a hair spring, at any time in the measuring process, this required sufficient current to be effected by any resistance in the measuring circuit. Instruments which were extremely sensitive had to have extremely fragile mechanisms which were unsuitable for rough field use.



The error in the measuring system tended to give the impression that sections of pipeline were not protected and engineers worked to increase the protection on these sections. They found that many sections of pipeline could not be 'protected' as it proved impossible to increase the output of the cathodic protection system enough to show the required voltage on the meter.

A formula was recommended to correct readings to an increased value, in proportion to the internal resistance of the voltmeter. This formula corrected the readings upwards towards the required criteria, whereas the correction to present readings, which is obtained by switching the CP current off, is a correction



downwards.

NUL-BALANCE METERS Attempts were made to design specialised instruments which balanced out this error with an opposition EMF supplied from an internal battery. The idea was that if they worked on a balancing process when the actual measurement was made, then they would draw no current. Some of these instruments became quite complex but they all drew current during the original balancing operation, and hence none reached the accuracy which is possible with a digital meter.



The designers seemed to have missed the point that the current drawn, to set up the balance, created an error which was carried through the whole measuring operation.

The complexity of operation of the balancing meters required more care and understanding by the operators, and the instruments were not as rugged as the simpler ones of the day.



Instruments appeared with more and more dials, switches and adjustments but this resulted in less and less personnel who understood how to use them. It also had the adverse effect that the amount of time to take a single reading with such an instrument, precluded the possibility of taking 'immediate off potentials'.

There was then the problem of measuring the EMF which had balanced the measuring circuit. This had to come from a dry cell battery which would not have a constant potential as the current drawn, to balance the circuit, would drain the battery each time of use.



Some instruments were then marketed with a more constant (laboratory tested) battery built in, with which to balance the, commercially available, dry cell.

The problem that still remained, was to establish a potential value, within the meter, against which a reliable voltage could be measured. Sophisticated variable resistors were built into some instruments and it was claimed that an error free voltage could be measured by a complex procedure of balancing potentials using two galvanometers, two sources of DC charge and a variety of switches, variable resistances and a component called a "potentiometer". On examination, the "potentiometer" turned out to be a variable resistor which had been calibrated to give a reading on a mechanically driven digital dial. This did not make any difference in reality....... the problem had not been solved. DIGITAL METERS The availability of digital instruments removed the downward error which had been caused by the volts drop in the measuring circuit and allowed increased voltages to be obtained, because they dramatically reduced the amount of current flowing. The solid state



electronics of today's meters only require a tiny amount of current to make a reading and the resistance in the measuring circuit is greater by an order of magnitude than the resistance in the circuit to be measured. Using a digital voltmeter with an impedance of 7 to 10 mega-ohms per volt ensures that the current flowing through the measuring circuit is not sufficient to cause a potential depression in the earth in which the electrode is placed.

Using galvanometers, the error in measuring had helped to balance out the IR drop in the soil which, at present, causes optimistic readings. In fact it was the advent of digital metering which bought the question of the cathodic protection criteria sharply into focus.



Pipelines began to fail in areas where digital voltmeters had shown that the pipeline had achieved a voltage difference of -0.850 mv with respect to an electrode placed immediately above the pipeline on the ground surface. It is doubtful if this value would have shown on a galvanometer which often required the ground contact to be watered to allow sufficient current to pass through the metering circuit to activate the magnet against the hairspring.



This inaccuracy was not an advantage, but did have some tendency to balance the inherent error in the measuring technique.





Module 6

Monitoring

Pipe to soil voltages are the main routine measurements that are made and recorded at regular time intervals at cathodic protection test facilities along every pipeline and in refineries, tank farms and other compounds where underground pipework is located. A full survey at every test point is normally specified every six months but it can be easily seen by the condition of many test posts in public places that this is not carried out.

Page 1 of 6Cathodic Protection Course Module 04 2 batteries

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It can be seen in this picture that the test post has not been disturbed for at least one year as the plant growth of all four seasons is in tact.



In this picture we can see that the contact stud on the side of the test post bears no mark resulting from an electrical connection to a meter. The bright metal remains shiny for several months before oxidation cases slight dulling. This particular studd has not been properly contacted for several years. However, the maintenance records for this particular location will probably show that it has been visited.



Easily accessible test posts are usually chosen for more frequent monitoring as often as one month intervals on a regular basis.





Monitoring and record keeping is very important as corrosion is normally a very slow and sometimes seasonal activity. Records will show changes in the environment that will have a direct effect on the pipeline metal strength. If the monitoring data is accurate and meaningful it is possible to predict corrosion failure well in advance and make adjustments to the CP system to stop the reaction between the electrolyte and the metal. Properly applied cathodic protection can prolong the life of a pipeline indefinitely.





Module 6

The isopotential Cell

The problem of the error caused by the IR drop in the soil was reconised in the paper that you studied in Module 05 and each of the scientists who wrote that paper registered a patent to overcome the problem. Each of the designs was similar in concept that an isolated container full of conductive material will hold a number of charges and that number can be measured and evaluated as an electrical potential. If that potential can be measured without a current flowing through it, then it has the same qualities as measurements made in laboratory conditions. The Isopotential cell is an attempt to resolve the problem of the IR drop in the soil caused by the currents passing from the cathodic protection anode to the metal exposed at a coating fault.

Page 1 of 6Cathodic Protection Course Module 06 isopotential cell by Dr Prinz

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The idea of the isopotential cell is to make a potential measurement without the effects of the cathodic protection current creating a potential gradient in the ground. We have already examined the act of making 'pipe to soil' measurements and seen that the very act of measuring must draw current from the soil to activate an analogue meter We have already seen attempts to overcome this problem by charging up a battery in a complicated instrument using a potentiometer. We have also seen that a digital meter has such a high internal resistance that it draws very little current to make the measurement. In the system proposed by these three scientists a tube of inert but conductive material is isolated from the ground except by contact through a porous plug set in the centre of the base plate. The reaction of the base plate to the earth electrolyte charges up the inert but conductive content of the container but no further current flows.



The whole of the content of the container becomes of one potential with no gradient. It is at one potential throughout and can be correctly described as an isopotential cell. The ground surrounding the underside of the base plate is subject to the potential gradients caused by the cathodic protection current and other electrical flux.



Isopotential contours in the ground can be defined to show the regions of differing potential and that is how DCVG works.

As the inert but conductive content of the cell is equal to the potential caused by the reaction of the base of the cell to the electrolyte, it is the equivalent to a potential measurement made at the interface between the pipeline metal and a similar electrolyte in close proximity to the test.



The base of the isopotential cell is a steel coupon of the pipeline metal and is put in contact with the ground as close as possible to the pipeline. This subjects it to the same corrosion reaction as a coating fault.



The base plate is connected directly to the pipeline so that it serves the same purpose as a weight loss coupon or other form of measuring electrode.

Rapelli index





Module 6

The Alexander Cell

The Alexander Cell was developed in the early 1980's when I found that there was no way of seeing that corrosion had been stopped by cathodic protection. All available monitoring theory and practice were questioned and discussed with experts and scientists who were praticing at that time. They could not prove that corrosion had stopped outside of the laboratory and their advice was being applied as best it could in the field. We needed a method to make closed circuit measurements in the field, similar to those that are made by scientists in the laboratory and I applied for a patent for an arranement that does exactly this.

Page 1 of 6Cathodic Protection Course Module 06 the Alexander Cell

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I then worked for a contractor on the development of the very first CIPS in the world that was being carried out by North Thames Gas and the British Gas



Council in the UK. The engineer in charge was Mike Foskett who gave permission for the Alexander Cell to be trialed during the four year project. The results of the trials were passed to Bob Greenwood who was a scientist at the Gas Council Experimental and Reseach Station and who later bought an Alexander Cell for scientific appraisal.

The Alexander Cell, DCVG and CIPS were closely examined at 100 excavations and it was found that DCVG is an accurate method of locating coating faults but the predictions of the corrosion state by CIPS was 7%.



but the predictions of the corrosion state by CIPS was 7%.



The Alexander Cell was accurate at 97 excavations and could be seen to be correct at the other 3 excavations when all conditions and data was taken into consideration.



The Alexander Cell is simply a corrosion cell in which the corrosion current can be measured in closed circuit. This allows the true corrosion potential at the active electrode to be calculated exactly including the effects of the pH of the electrolyte and the corrosion circuit resistance. The Alexander Cell is used as set out in the formal CPN procedure at this link





Module 6

The Cathodic Protection Criterion


07/02/2010http://www.dynamic-cathodic-protection.com/module06/criterion.htm

The criterion for cathodic protection was changed by the presentation of a scientific paper at two conferences in Brazil in 2009. This links to the actual presentation of the paper 'A definitive criterion for cathodic protection' by Roger Alexander Students can also read the documents that were accepted by both conference committees prior to the conferences. Abstract Introduction



Problem Extrapolation Solution





Module 6

Field trip



Students should go to the nearest pipeline test post with an Alexander Cell, an isopotential cell, two half-cells and a digital multi-meter. They should carry out each of the tests and report with comments and draw their own conclusions.




INTRODUCTION

The activities described in this report have a direct bearing on all cathodic protection work and design,

Criteria presently being used for cathodic protection are now recognised to contain inherent errors, and we are advised to make measurements in a different way. However there is no internationally agreed criterion, that will guarantee that corrosion has been halted.

Much research has been carried out, resulting in a number of techniques being suggested, and devices patented.

The activities at this particular pipeline were intended to test a number of procedures to determine the condition the pipe, and help to improve the survey techniques which can be used to ascertain the condition of all pipelines within the pipeline operation.

Many staff were instructed in these techniques when they visited the site during the weeks of these activities.

Some of the data was gathered using a recording voltmeter but temperatures were above the permitted level for the data logger that was then available. However all data was gathered very critically and cross checked very carefully. The arrival of specialised instruments will ensure that future data is of similar high quality and the procedures used at this site are being prepared for use during the forthcoming condition monitoring project.

CONCLUSIONS

This report proves that the ground itself is a complex mass of different electrical potentials, causing or caused by currents from any sources.

Conventional measuring techniques include the effects of these potentials in the measuring circuit, causing significant errors.

Complex techniques can evaluate the errors, but in this instance the corrected voltage did not indicate the true condition of the pipeline.

The potentials, detectable at the surface, can be reliably used to detect the exact

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position of coating faults.

The established method of taking voltage readings with the cathodic protection on, and the electrode placed at the ground surface, has given a more accurate indication, of the status, than the 'immediate off potential' method that has been recommended to replace it.

next

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Module 6

Real time chat

roger.alexander5 is the Skype name for [email protected] Just tell me which Module you want to discuss and we will take it from there.



07/02/2010http://www.dynamic-cathodic-protection.com/module06/chat.htm


Module 7 (under construction 26:01:2010)

Interference

� Looking for possible interference. � Causes of interference � Basic interference testing. � Long term monitoring of interference. � Practical bench experiment simulating interference. � Computer modelling of interference. � Field work to set up temporary interference readings. � On-line real time discussion.

Back to itinery index




Module 7

Interference

� Proximity of foreign structures. The very first activity of a corrosion control engineer is to conduct an overview of the problem area as described by the client. The problem can be that an existing pipeline has an increasing incidence of corrosion leaks or that they want to construct a new pipeline.


07/02/2010http://www.dynamic-cathodic-protection.com/module07/foreign.htm

Useful information can be obtained from Google Earth, aerial photographs and existing maps as well as any plans and 'as built' drawings available from the client and other utilities in the area. All structures should be mapped and examined to ascertain the electrical disturbances that they cause in the ground that they occupy. Concrete and brick constructions invariably contain some metal that causes a footprint in the electrical potential at surface level. This can be detected and plotted using the two half-cell procedure. This is not possible using DCVG equipment as the nature of the instrumentation is inadequate.



Structures such as water towers, pylons, wind turbines, church spires etc will all have earthing systems to conduct lightning strikes to the ground. These will be earthed using copper or bronze alloys that will be in electrical flux with their surroundings. Generators will be earthed and there can be an inbalance of the three phases. This can cause surges that can be rectified by the layer of oxides on a pipeline surface at a coating fault. This in turn causes a build up of charge in that length of the pipeline which leaks back to earth at other coating faults..... the metal will disolve at these places.



The purpose of this overview is to relate reality to an electrical circuit on a vast scale that includes the cathodic protection systems and all other causes of electrical flux. These can then be modelled using the mathmatical power of computer analysis.



This screen shot shows an spreadsheet model of a complete oil and gas production area with all the delivery pipelines from the gathering stations to the manifolds. The formulae that drive this model are all based on the laws of electricity and for that reason the data that is used must be accurate and related to a common base.





Module 7

Interference

Interference is the influence to the corrosion reaction by causes outside of the natural corrosion process and the intended result of the cathodic protection system. The effect of interference is to alter the potential of the electrolyte in the immediate area of the corrosion reaction. This can accellerate the corrosion or dampen it.


07/02/2010http://www.dynamic-cathodic-protection.com/module07/interf.htm

In the picture above, the nail on the left was charged to a higher potential than the nail on the right. The current flowed into the damp cloth and distributed itself in all directions according to kirchoffs laws which describe it following the paths of inverse resistance. It can be seen by the distribution of corrosion products that the current then passed onto the nail in the centre and from that nail towards the nail on the right. The central nail is an example of interference preventing corrosion where current enters and accellerating corrosion where it leaves the metal and passes onto the electrolyte. Interference should be considered from the very first stages of design for every cathodic protection system. This is because every metal pipeline is part of an electrical circuit composed of every other pipeline and all other electrical influences. Before considering interference it is necessary to have a complete overview of the pipeline system and to superimpose all known cathodic protection systems over the pipeline network. This is the reason that the schematic/equivalent circuit was drawn in 1977 as shown below.



Proximity of foreign structures. Foreign structures include pipelines, and anything that can cause a disturbance to the natural electrical equilibrium of the ground itself.



The most commonly quoted is railways which are driven by DC charges. These are carried in overhead cables and return via the rails which are earthed. This means that there are surges of DC charges in the ground itself which will take the least line of electrical resistance to complete their particular circuit.



Remote earth is a resistanceless conductor and the charges in remote earth will not cause a detectable surge. However, the charges are drawn from the rails and the energy drained from these will cause a momentary potential gradient in the electrical path from remote earth. If there is a steel pipeline in this path then it will offer a lower resistance path to the returning current, but if the coating is perfect then it will not.



In order to affect the corrosion status of the pipeline there must be a point or points of entry to the pipeline metal and point or points of discharge from the metal into the ground. Where the current enters the pipe metal it will stop corrosion but where it leaves it will accelerate corrosion. However, it will cause errors in the voltage measurements whether or not it is detrimental to the pipeline corrosion performance. Accellerated corrosion is readily prevented by the exact placement of sacrificial anodes which must be provided with a method of monitoring.

This is simple to carry out providing you have a clear perception of the 'electrical picture'. The picture above was taken at a pipeline crossing in West

Africa where two sacrificial anodes were installed successfully in 1976.



We can construct a computer model of each situation and simple add the data gathered by our specialised survey methods.

This will show the exact paths of the various currents and the exact position in which to place the sacrificial anode in each case.

It will allow us to see the performance of each anode and to balance the impressed current cathodic protection systems to reach a 'protected'

equilibrium. It will allow us to recocile voltage measurements which might otherwise be

taken to indicate problems. It is sometimes advantageous to use recording voltmeters and osciliscopes to

examine the causes and likely effects of some of these ground surges. It is now possible that we can control the effects of this 'noise' very efficiently

using electronic means, which have been developed by NASA and are available to us through our members in Italy, Sobrel.

The Alexander Cell certainly displays the effect of these features on the corrosion reaction and is therefore the only known method of short term

monitoring for electronic corrosion control.

Other Interference possibilities.

The generation of AC electricity by mechanical means requires that energy is applied to rotating magnets which induce a potential into coils of

conductor wire. These coils discharge current through carbon brushes into cables which then are at a higher electrical potential than the metal to

which they are connected.

The magnet then charges the next coil in turn and the first returns to it's basic potential value.

In countries such as the UK, generating companies are required by law to supply electrical energy at exactly 50 cycles per second. That means that each conductor is charged and discharges it's energy 50 times per second.

The amount of energy carried by each conductor depends on how far



apart the 'potential' of each conductor is forced away from 'zero'by the engine supplying the energy.

For a 50th of a second this is DC charge. There is then a mechanical

arrangement that forces the current to flow in the other direction until the cable is charged negatively in relation to original 'zero'.

The whole generator system is balanced to maintain the zero at an equal

potential to the ground on which the generator is based.

Field generators are sometimes unbalanced and cause the potential of the ground to alter. This can be manifest as a steady fixed potential increase of decrease which can be plotted around the earthing system of the generator itself or it can be in a waveform the effects of which can be detected up to

half a mile away in high resistance grounds.

Overhead high energy conductors (high tension wires) opperate in the UK at a potential difference of 400,000 volts and have a field of of influence

that can effect buried pipeline that run parallel to them. This can be seen in fluctuations in the voltages measured in pipe-to-soil

surveys. In one such instance the voltages on the meter swung from 0.600v to

2.13volts in an irregular pattern over a period of 20 minutes. This was in a location where three pipelines ran parallel to two high tension pylon runs

rated at 400,000 and 232,000 respectively for lengths of several miles.

I reported this matter to the operators of the pipelines but learned that sections of each of the pipelines had been replaced as they took no action.

I was unable to offer assistance in this matter as I had no money to set up a

business. I was shut out in the cold by established service companies despite a letter from the chief executive of one of the operators instructing

that my services be engaged.

Basic interference testing and resolution

The first step is to acquire all available drawings and maps of the area. Local planning authorities, electricity suppliers, gas and water suppliers

an the national survey authorities are usefull starting points. Satelite imaging is now a valuable rescource to give a factual picture on

which to base all the information (in the abscence of the dynamic project which incorporates all this information)

The second step is to add all of the historical data available from cathodic

protection records to a schematic of the area in the form of a circuit diagram.

The areas of high ground potential should be shaded in various degrees of

green allowing for areas in which corrosion might be found should be shaded in various degrees of red. It is convenient to relate all of these



voltages to to the pipeline metal being zero.(deep red) It follows that a groundbed area of 5 volts or more would be deep green

and that any metal in this area would be protected by the current tending to enter at every interface.

This metal would then be charged and shown as an equal voltage to the part of the groundbed profile through which it passed.

If this is the subject pipeline it would be immediately drained of charges by the negative connection to the transformer-rectifier, thus being at zero

volts. Any sacrificial anode attached to the subject pipeline in the area of influence of the impressed current ground bed would be protected

depending on it's nobility in relation to the pipeline metal. It is important to recognise that in an area of over 1.6 volts the ground potential would

show a depression in potential with the impressed current switched on and this would reverse to a peak when the current is on. This feature is easily

recognised in a two-half-cell survey grid plot with the TR switching.

A foreign conductor passing through the subject groundbed area(very green) will pick up charges and discharge in areas where the ground

potential is lower(shaded red) Their presence will cause the ground potential to be higher (greener or less red) than surrounding ground. This will be detectable on a CIPS or DCVG

survey but the cause might not be apparent until a proper two-half-cell survey is conducted with that particular groundbed switching.

It is best practice to notify all services in the area of interference testing and to invite their representation. However, it is never essential to have

their co-operation, which is just as well because you will find that most of them have no idea what it is all about. Even worse is that some of them

pretend to know what they are doing but their procedures are not logical and are unproductive.

Don't let them confuse you! Keep a clear electrical picure in your head based on the data that you gather. Believe your meters and trust your own

expertise. Electricity does bullshit! If you haven't established all the facts then your electrical picture will be unclear. Gather more facts!!! Add more data to the schematic circuit and

the real picture will become clear. If you can get the co-operation of other operators in the area then it will be very useful to get them to switch their own equipment at certain stages of

your investigation. You should only do this when you want to confirm your own picture and

can predict the likely outcome of their switching. You should explain your reasoning to them, before the switching begins. If the results are not as

expected you will look a fool if you do not have alternative paths of enquiry, so make sure that have covered everything.

At this stage you should have remedial action in mind.

� Monitoring interference and interpretation of data.







Module 7

Interference

Basic interference testing and resolution



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Module 7

Interference

� Proximity of foreign structures. � Interference possibilities. � Basic interference testing and resolution � Monitoring interference and interpretation of data. � Practical bench experiment simulating interference. � Computer modelling of interference. � Field work to set up temporary interference readings. � On-line real time discussion.



07/02/2010http://www.dynamic-cathodic-protection.com/module07/monitinterf.htm


Module 7

Interference

Practical bench experiment simulating interference.


07/02/2010http://www.dynamic-cathodic-protection.com/module07/benchinterf.htm

In the above demonstration we can undeniably see the effects of interference current on the nail in the centre. The current passes onto the left end of the nail in the centre and off at the right end. This how interference works on a pipeline.

There are more charges in the electrolyte at the left end of the nail which is then a less resistant path to the electrolyte at the right end. It is very important that students experiment themselves in order to confirm



their concepts of how corrosion and cathodic protection work in reality. Your will need some 6" nails and a length of pipe with some insulation tape, two half-cells, a dry cell battery, some wet cloth, a multimeter and some 'jumper leads'.

Set the experiment up as in the picture and note the positions of both half-cells and the reading on the meter. The purpose of these bench experiments is to allow students to understand the nature of 'currents' and 'potentials' in relation to the recognition of interference.

















Module 07

Computer modelling of interference.


07/02/2010http://www.dynamic-cathodic-protection.com/module07/compinterf.htm

The above spreadsheet shows the measurable values where interference influences the earth above a buried pipeline. The potential of the pipeline is considered to be zero as the resistance of the metal is extremely low, as discussed extensively in this course. The source of each interference current is shown as an anode output in amps and each current passes to a negative terminal or cathode in it's own circuit labelled 'Path A', 'Path B' etc. The result of each current flowing through the resistance of the ground is a potential gradient that we can measure with two half-cells. The values entered into the spread sheet are the each current in amps and the resistance of the earth from which the potential of each cell can be calculated



using Ohms Law. Each path is calculated on the assumption that it is linear so that the concept is manageable at this stage of reasoning. This model assumes that there are no coating faults on the pipeline and therefore the 'interference' has no effect on the corrosion status of the pipeline. Using this simplistic spreadsheet will help the engineer to visualise that pipe to soil voltages have errors that do not necessarily affect the performance of the cathodic protection system, but that must be extrapolated for the purpose of computer analysis. These soil potentials can be measured with a voltmeter referring to another (but static) half-cell. It shows that we need a zero potential on which to base all cathodic protection calculations. This zero is the datum on which we have to base all our calculations in the same way that the height of a person is regarded as the distance from the top of his head to the ground. If he is standing on a step and has high heels on his shoes these introduce errors into the measurement of his height. In the case of potential comparisons with respect to interference we can conveniently use the pipe metal as one reference potential. This has the advantage that we can use historical data to test computer models and to simulate the electrical balance of all the integrated electrical circuits formed by the cathodic protection systems and pipeline networks.



In this model we can see that the point at which the half cell touches the ground has been related to all of the other points at which the half cell touched the ground. This is very important as the cathodic protection current passes from the impressed current anode to remote earth at which stage there are an infinite number of resistances in parallel. According to Kirchoff there is an infinite conductor from this point until the current is approaching the locations at which it can pass into the pipeline metal. The resistance of the pipeline metal can be computed as we have the 'as built'



specifications of each part of the metal network. We can measure the output of all cathodic protection current sources but we cannot measure the amount of current going into the pipeline at any point. Some engineers try to assess this value and call it current density. At this stage of monitoring we can measure the ground potentials in relation to other ground potentials or in relation to the potential of the pipeline at the nearest connection point. This potential is likely to be the average potential as influenced by all of the corrosion reactions and electrical flux along the nearby span. If there is a coating fault then the cathodic protection current will cause an 'IR drop in the soil' that muat be evaluated as well as the interference currents. This voltage drop decays over a period of time that cannot be accurately determined.





Module 7

Interference

Field work to set up temporary interference readings.



07/02/2010http://www.dynamic-cathodic-protection.com/module07/fieldinterf.htm


Module 6

Real time chat

roger.alexander5 is the Skype name for [email protected] Just tell me which Module you want to discuss and we will take it from there.



07/02/2010http://www.dynamic-cathodic-protection.com/module07/chat.htm

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Cathodic Protection Course