CATHODIC PROTECTED INSTALLATIONS

Abstract: A metal item in the ground, such as a lamp post, is cathodically protected from corrosion by a system comprising at least one anode, a reference electrode and an electrically powered control system connected to the power supply of the lamp post.

Description: CATHODIC PROTECTED INSTALLATIONS Metallic lighting columns and lamp standards and like devices suffer corrosion generally at or about ground level due to the presence of salts (from road de-icing, from sea-spray and from animal urine) and also due to differential aeration between the metal near the surface and the metal lower down, thus setting up galvanic cells. The area just at or below ground level becomes anodic with respect to the rest of the column and the metal therefore corrodes and ultimately causes the structural failure of the column. It is an object of this invention to reduce or eliminate this problem. According to the invention in one aspect there is provided a system for the cathodic protection of lighting columns and other electrically powered devices which are partly buried in the ground, which comprises at least one anode, a reference (or pseudo-reference) electrode and an electrical power control system connected to the power supply for the lighting column or other device. The electrically powered devices may be highway lamp posts, traffic bollards, traffic lights, sea defence installations; and the like. The cathodic protection is particularly conveniently carried out in the case of lighting columns using the source of electric power in every column so that the cost of an impressed current system for each column is reasonable. The installation costs are low as all the relevant parts of a system (anodes, reference electrode, rectifier and power control system) can be supplied and installed as one unit. The unit can be attached to the column to be protected, in a shallow hole dug adjacent to the column with a single power feed wire introduced into the column interior and connected to the electrical power supply. The hole is then backfilled burying the device, and any appropriate surface (asphalt, Flagstone, concrete) reinstated. In one embodiment the system includes a carrier or frame adapted to hold the anode(s) and electrode. While the carrier may take a variety of shapes, in one embodiment the carrier is shaped roughly like a coat-hanger, for the anode and reference electrode, preferably with two impressed current anodes one mounted at each of the extremities. It is an advantage of the invention that one can locate the reference electrode at the line of equipotential between two (or more) anodes. It can be advantageous to interpose barrier means between the anode and the reference electrode means for splitting the electrical current passing in between, thereby to create one or more virtual anodes. The barrier means may take the shape of a simple cross member, typically like a baffle, made of a non-electrically conductive material, typically a plastics. The shape and location of the baffle will determine the number of virtual electrodes. The location of the reference electrode is preferably determined by the lines of equal potential formed by the real and virtual anodes, and should be as close as possible to the lighting column itself. The reference electrode is preferably not on the same side of the barrier means as the "real" anode otherwise its output would be affected by the anode voltage. The anode material can be a conductive ceramic or an electrocatalytic coated titanium metal, lead metal, or any of the materials which are commonly used in the industry for long lived, corrosion resistant anodes. For small columns, a single working anode would be sufficient and for larger columns it may be necessary to have more than 2, say up to 4. The barrier means will be dimensioned so that it diverts the current flow appropriately. Typically it may be 500mm long so that the virtual anodes appear to be spaced about 250mm on each side of the column to give a substantially uniform current density to the entire column surface. The height of the barrier means is selected to ensure that minimal current leakage occurs above and below the barrier instead of at the ends. The height of the barrier preferably approaches twice the width (in this example 500mm) so that the distance from the anode to the column around the top and the bottom is at least similar to the distance around the end. The reference electrode may be mounted in the carrier in any convenient place to measure the potential in the region of the column in the centre of the frame and thus close to the column. This electrode can be of a high accuracy type of thermodynamic equilibrium, such as Ag/AgCl , or calomel, or Cu/CuSO or any of those electrodes well known to the electrochemical industry. It is not necessary in all cases to have such a highly accurate and thereby expensive electrode and in order to reduce costs, a "pseudo-" reference electrode made out of a short length of platinum wire, or of titanium metal coated with a suitable electrocatalyst (such as Ta/lr oxides or others well known in the electrochemical industry). The reference electrode may also be made of zinc. In another aspect the invention provides a method of installing a cathodic protection system for a lighting column or like device, the method comprising burying the anode(s) and electrode in a hole adjacent the column, connecting the electrodes in circuit with the power supply of the column, and then covering the buried anode(s) and electrode. The method preferably includes the step of mounting the anode(s) and electrode in a common carrier. The method preferably includes the step of locating a barrier means between the reference electrode and a real electrode to divert electric current and create a virtual anode. It is preferred that the barrier means is shaped so as to create a plurality of virtual electrodes. In order that the invention may be well understood it will now be described by way of example only with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a side elevation of one carrier of the invention; and Figure 2 is a horizontal section through an installation; and Figures 3A, 3B and 3C each show a transverse sectional view of another embodiment of the invention. The same reference numerals are used where convenient in describing the different embodiments. The carrier 1 comprises a coat hanger shaped plastics moulding generally triangular as seen in elevation. The moulding is hollow and each corner has a socket 2 to receive an electrode E. Two anodes Ea are present at the lower corners; a reference electrode Er is present at the apex. A wire 3 extends between the electrodes and exits from an outlet 4 at the top to pass via a hole in the wall 5 of the light column 6 to a PLC7 in the interior. (The lamp column is mounted in the ground, or other substrate such as concrete, with the lower portion buried therein. The usual power supply for the lamp is located within the column). In use, a shallow hole is dug near the light column. The device is installed and the single power feed wire 5 introduced into the column interior and connected to the electrical power supply. The hole is then backfilled burying the device, and any appropriate surface material (asphalt, Flagstone, concrete) is reinstated. The wire 5 is connected directly or in the PLC7 to the lamp electrical supply. The PLC is arranged to periodically or continually assess the potential as registered by the reference electrode and adjust the current to the working anodes in order to control the potential at the reference electrode at/near a preferred value. This value would be chosen to ensure that the column is cathodically polarised, but not to too high a voltage to induce significant amounts of hydrogen to be generated on the buried metal of the column. Because the anodes and reference electrode are mounted in a common frame not only are these parts properly spaced apart but the installation procedure is quick and efficient. In the embodiment of Figure 3 A a baffle 10A is present between the reference electrode Er adjacent to column 6 and the single real anode Ea. (Note that two alternative positions for the reference electrode are shown). The baffle is a planar sheet of plastics material measuring about 500 mm wide and about 500 mm deep which diverts the electrical current flow to go round the edges and in the process creates two virtual electrodes Ev. The benefit of doing this is to increase the number of effective anodes without aggravating the costs of specialised components or installation charges. In the embodiment of Figure 3B the baffle 10B is of V section and is present on one side of the reference electrode Er, between that electrode and two anodes Ea. This has the effect of creating four virtual anodes Ev. In the embodiment of Figure 3C there are generally V section baffles IOC, each between the column 6 and a real anode Ea. As a result four virtual anodes Ev are created. The installation of Figures 3 A, 3B and 3C works in the same way as that of Figures 1 and 2 with the added advantages of providing all round cathodic protection to the light column. The invention is not limited to the embodiment shown.

Claims: CLAIMS 1. A system for the cathodic protection of lighting columns and other electrically powered devices which are partly buried in the ground, which comprises at least one anode, a reference (or pseudo-) reference electrode and an electrical power control system which is connected to the power supply for the lighting column or other device. 2. A system according to Claim 1, wherein the electrical power and the control system are mounted independently inside the lighting column. 3. A system according to Claim 1 or 2, wherein the anodes(s) and reference electrode are mounted in a common carrier. 4. A system according to any preceding Claim, incorporating up to 4 anodes. 5. A system according to any preceding Claim, wherein at least one anode is made of an electrically conductive ceramic material, electrocatalytically coated titanium metal, or lead. 6. A system according to any preceding Claim, wherein the reference electrode is a thermodynamic equilibrium electrode. 7. A system according to any of Claims 1 to 5, wherein the reference electrode is made of platinum or other noble metal, or titanium metal with an electrocatalytic coating. 8. A system according to any preceding Claim, wherein the power supply and control system is equipped with means for read-out of the operation of the system. 9. A system according to any preceding Claim, wherein the electrical power and control system incorporates a PLC arranged to adjust the electric current to the anode(s) to bring the potential as measured by the reference electrode below the level at which significant volumes of hydrogen are generated. 10. A method of installing a cathodic protection system for a lighting column or like device, the method comprising burying the anode(s) and electrode in a hole adjacent the column, connecting the electrodes in circuit with the power supply of the column, and then covering the buried anode(s) and electrode. 11. A method according to Claim 10, including mounting the anode(s) and electrode in a common carrier. 12. A method according to Claim 10, including the step of locating a barrier means between the reference electrode and a real electrode to divert electric current and create a virtual anode. 13. A method according to Claim 12, including shaping the barrier means so as to create a plurality of virtual electrodes. 14. A method according to Claim 10 or 11, wherein the hole is shallow.

Inventors: HILL ANDREW, HILL, ANDREW
Applicants: ATRAVERDA LTD, HILL ANDREW, ATRAVERDA LIMITED, HILL, ANDREW
Application year: 1999
Main classification: C23F13
IPC codes: C23F13