Chemistry: electrical and wave energy – Apparatus – Electrolytic
Patent
1996-08-06
1998-03-24
Bell, Bruce F.
Chemistry: electrical and wave energy
Apparatus
Electrolytic
204404, 204290F, 204292, 204293, G01N 2726
Patent
active
057308489
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
This application is a 371 of PCT/GB92/01724 filed on Sep. 18, 1992.
The invention concerns a continuous-action reference electrode for the cathodic protection of metallic structures.
The invention relates to the field of techniques for the protection of underground and underwater plants from electrochemical corrosion.
The reference electrode is predisposed for the measurement of the polarised potential of the plant and can be used for the measurement of the corrosion and also for the automatic control of the cathodic protection station.
Some prior art continuous-action reference electrodes are composed of two metallic pivots of different metals having high chemical purity, placed in mutual contact at a point where the connection cable is also connected, which cable leads to the cathodic protection station.
The said pivots are generally made of antimony and bismuth and are covered with the oxides of the above metals.
Another type of reference electrode in the prior art is composed of two magnesium cylinders with an iron, copper of nickel pivot inside.
The cylinder and the pivot are mutually insulated with insulator compound and their point of mutual contact is on a surface of the head, where they both also contact the connection cable.
Common defects of the reference electrodes described above are high metal consumption and low internal conductivity which prevents use in dry environments with high impedance.
In such cases, in order to increase the conductivity of the electrode, it is necessary to increase its size, leading to a high consumption of metal as well as to high costs.
A further type of prior art reference electrode comprises a ceramic box element, filled with high-viscosity electrolyte, in which a copper pivot-shaped electrode is inserted.
The connection cable is welded to the copper pivot.
On the external surface of the ceramic element an electrochemical potentiometric end instrument is attached, consisting of a steel plate with a surface of 625 mm, to which plate another connection cable is welded.
This type of reference electrode also has several drawbacks, such as a high specific consumption of metal and the need for periodic maintenance for filling the ceramic element with new electrolyte due to the inevitable consumption of the said electrolyte.
Furthermore, the measurement precision of the electrochemical potential by means of the relative steel end instrument is not high due to the difference of the chemical composition of the steel plate in the end instrument and of the material of the underground metal plant to be protected.
The reference electrode can be installed only in a vertical position and thus its field of application is limited particularly with regard to large-diameter piping.
Still further, the said reference electrode can be used only when the ground temperature is above 0.degree..
A principal aim of the present invention is to perfect the precision of electrochemical potential measurement and to reduce the maintenance costs of the plant.
A further aim is to economise on the costs of the reference electrode with regard to the specific consumption of metal.
These and other are all at least partially attained by a continuous-action reference electrode for the cathodic protection of metallic structures, object of the present invention characterised in that the electrode: comprises a support (1) substantially plate-shaped and made of ceramic material porous to electrolyte having the function of a base for a copper plate (2) having the function of an electrode, situated on both flat faces of the said ceramic support (1) and of a titanium plate (3) having the function of an electrode, isolated from the said copper plate (2) on both flat faces; the electric connection for both said plates (2), (3) being realised by means of connection to a further copper plate applied on a lateral face of the said support (1), the arrangement of the said copper and titanium plate (2), (3) on the first surface of the said support (1) in such a way that a copper plate (2) on a flat surfa
REFERENCES:
patent: 4994159 (1991-02-01), Agarwala et al.
patent: 5216370 (1993-06-01), Bushman et al.
Bell Bruce F.
Chameleon Investments Limited
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