Cathodic Protection Training Course
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.
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.