I have been told by highly qualified scientists that is it not even a half-cell
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http://www.rogeralexander1938.webspace.virginmedia.com/cpn/halfcell/halfcell.htm
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Monday, 28 January 2013
The half-cell is not a reference electrode.
I have been told by highly qualified scientists that is it not even a half-cell
...
http://www.rogeralexander1938.webspace.virginmedia.com/cpn/halfcell/halfcell.htm
...
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This discussion is avoided by NACE and the Institution of Corrosion Engineers whose elite have been wrestling with the problem without success. The history of cathodic protection is littered with failed proposals to overcome this problem and is now cluttered up with instruments that claim to measure 'potentials' where in fact they measure voltages with reference to a floating zero.
ReplyDeleteIf established cathodic protection service providers accept that the 'half-cell' cannot be used as a reference potential in maintenance and CIPS work it leaves them with little to substantiate their claims that these services are worth the money that is being paid.
ReplyDeleteHowever, if the voltages are regarded as having a floating zero, then a true interface potential can be used to set the level for achieving 'protection' at each location. We can do this using a closed circuit measurement of a corrosion cell such as the arrangement known as the Alexander Cell
ReplyDeleteIt is apparent that established cathodic protection practitioners realize that the marketing and use of such a system not only proves that the half-cell is not a reference electrode when used in the way they specify and that the Alexander Cell is detrimental to their commercial interests.
ReplyDeleteThe first step in blocking this innovation into te market was an attempt to buy the rights to the sell and include the monopoly right not to market it. This proposal was rejected and then a report on the Alexander Cell was published by the National Physical Laboratory in the UK saying that the contemporary methods of monitoring cathodic protection was satisfactory and that there was no need for the Alexander Cell. This report contained 17 technical errors identified by Jim Gosden of the BSI committee CP1021 and was withdrawn, but after it had been circulated to several parties with vested interests in suppressing the Alexander Cell
ReplyDeleteAttempts are still being made to justify the half-cell as a reference potential starting off with the 'immediate off' measurement. It was suggested by a laboratory in Holland that the true 'polarized potential' of cathodically protected metal could be seen on a graph made by a recording voltmeter in their laboratory.
ReplyDeleteThis was tried in Shell-BP Development Corporation in Nigeria and found to be impossible due to the limitations of the pH in which it is effective, and the problem of switching off all of the CP systems that affected every location of each test.
ReplyDeleteBritish Gas Council scientists developed the CIPS survey to include the on and off voltages and it was found that these could not be applied in field work.
The trailing wire technique of the CIPS survey was started by British Gas and subject to an IP infringement claim by an American company. This case establishes the principles of using the 'roving half-cell' and plotting the resulting voltages as if they are made using a fixed potential against which to measure the voltage between that and the variable potential.