EA024024B1 - Method for manufacturing anode for cathodic protection - Google Patents

Abstract

It is described a metal anode for cathodic protection in form of mesh ribbon having meshes whose holes are of rhomboidal shape, characterised by having such holes of rhomboidal shape arranged with the major diagonal oriented along the direction of the ribbon length and by the fact that the side edges along the ribbon length are free from cutting protrusions. It is also described a method for obtaining such anode.

Description

Field of Invention

The invention relates to the field of cathodic protection of structures made of reinforced concrete (reinforced concrete structures) and, in particular, to the construction of the anode, which is particularly effective in terms of electrical resistance per unit length and flexibility and is especially safe when installing and handling it.

The invention also relates to a method for manufacturing such an anode.

BACKGROUND OF THE INVENTION

Corrosion phenomena affecting reinforced concrete structures are well known in the art. Steel reinforcement inserted into cement structures in order to increase their mechanical properties usually operates in a passivation mode caused by the alkaline environment of concrete; however, after some time, the migration of ions through the porous surface of the concrete leads to a localized aggressive effect on the protective passivation film. Of particular concern is the aggressive effect of chlorides, which are present in almost all types of environments where reinforced concrete structures are used, and even more so where there is exposure to hard or brackish water (bridges, columns, pylons, pillers, buildings located in coastal areas ), salts of anti-icing agents (bridges and road structures in cold climatic zones) or even sea water, for example, in the case of piers and docks. A critical value when exposed to chlorides is considered to be approximately 0.6 kg per 1 cubic meter of concrete, above which the passivation state of reinforcing steel is not guaranteed. Another form of concrete destruction is represented by the phenomenon of carbonization, that is, the formation of calcium carbonate during the reaction of lime from a cementitious mixture with atmospheric carbon dioxide. Calcium carbonate reduces the alkali content in concrete (from pH 13.5 to 9), converting iron to an unprotected state. The presence of chlorides and simultaneous carbonization are the worst conditions for the protection of reinforcing bars in structures. Corrosion products of steel are more voluminous than steel itself, and mechanical stresses resulting from their formation can lead to delamination and cracking of concrete, which translate into huge losses from an economic point of view, in addition to damage to safety. For this reason, it is known in the art that the most effective way to extend the service life of reinforced concrete structures exposed to atmospheric phenomena, even in the case of appropriate salt concentrations, is to cathodically polarize steel reinforcement. With this technique, the latter becomes the site of cathodic oxygen reduction, inhibiting the anodic reactions of corrosion and dissolution. Such a system, known as the cathodic protection of reinforced concrete, is implemented in practice by connecting various types of anode structures with concrete, for which the protected reinforcement acts as a cathode counter electrode; the resulting electric currents supported by an external rectifier flow through an electrolyte consisting of porous concrete, partially impregnated with saline.

Anodes commonly used for the cathodic protection of reinforced concrete consist of a titanium substrate coated with transition metal oxides or other types of oxygen anode evolution catalysts. Other valve metals, whether pure or alloyed, can be used as the substrate, however, pure titanium is the most preferred choice in terms of cost.

European patent EP458951 describes an electrode design of a trellised type for cathodic protection, consisting of a plurality of metal tapes with an electrocatalytic coating having voids of various geometries.

This type of tapes can be made by punching solid metal tapes or, more generally, by traditional methods of metal stretching, in which the metal sheet is stretched by pressing and punching through a series of knives located perpendicular to the direction of advancement of the tape itself. This first step makes it possible to obtain a stretched metal sheet. Such a sheet is then subjected to a second cutting step suitable for producing tapes of the required size. These stretched metal tapes have cells with rhomboid-shaped voids, the large diagonal of which is oriented perpendicular to the length of the tape.

This manufacturing method has the disadvantage of producing metal tapes with cells having sharp lateral protrusions that automatically form during the cutting operation, which makes such anodes difficult to handle, and the phase of their installation is accordingly dangerous.

Canadian Patent Application CA 2078616 A1 discloses metal bands (stripes) with smooth side edges; with the method described in this document, the obtained tapes have a continuous longitudinally extending continuous section of a certain width, which is necessarily formed during the manufacturing process and which can be used only for spot welding. In existing cathodic protection systems, however, it is preferable not to weld the tape anodes at all, but instead to lay them directly on the armature with the installation of plastic spacers between them. In this case, the longitudinally extending continuous section is only a loss of material, especially since this continuous section necessarily becomes covered

- 1 024024 expensive metals during the deposition of the catalytic layer. However, such a catalytic layer cannot work properly on a non-perforated structure and affects the calculation of the real current density created in the anode structure, thereby complicating the development of the entire cathodic protection system as a whole.

SUMMARY OF THE INVENTION

Various aspects of the invention are set forth in the appended claims.

According to one aspect, the invention relates to a mesh tape anode for cathodic protection systems, for example, cathodic protection of reinforced concrete structures (reinforced concrete structures), overcoming the drawbacks of the prior art, the edges of which essentially have no discontinuities in the form of sharp protrusions and have a sinusoidal form.

Although in the context of this description, for the sake of simplicity, the cathodic protection of reinforced concrete structures is considered, it is understood that the invention can be practiced in the field of cathodic protection in general, for example, including cathodic protection of the bottom of metal containers.

According to another aspect, the invention relates to a method for manufacturing said anode.

According to another aspect, the invention relates to a cathodic protection system containing at least one anode in the form of a mesh tape, the edges of which, essentially, do not have sharp protrusions.

Some of the most significant results obtained by the inventors are presented in the following description, which is given merely as an example, without the desire to limit the invention.

The anode according to the invention is a tape of a stretched metal, characterized by cells with voids of a rhomboid shape, a large diagonal of which is oriented in the direction of the length of the tape. In one embodiment, the lateral edges of the tape have a sinusoidal profile and do not have sharp protrusions.

The inventors were surprised to find that the anode for cathodic protection described above exhibits a markedly reduced ohmic (active) resistance per unit length, for example, reduced by 4 times, compared with the prior art anodes.

Lower electrical resistance reduces the number of electrical connections, for example, in a grid system with tangible savings in material and installation time.

In one embodiment, the metal mesh tape is made of titanium.

In another embodiment, the metal mesh tape is coated with a catalytic coating containing noble metals or their oxides.

In one embodiment, the dimensions of the tape may vary in width from 3 to 100 mm with a thickness of 0.25 to 2.5 mm and a length of 1 to 150 m.

Brief Description of the Drawings

For a better understanding of the invention, it will be discussed with reference to the following drawings, the purpose of which is to illustrate some preferred embodiments of the invention without limiting its scope.

FIG. 1A shows a top view of a conventional stretched metal anode; FIG. 1B shows a top view of a tensile metal anode according to the invention.

Detailed Description of Drawings

Speaking in detail, FIG. 1A shows a top view of a traditional anode in which sharp (cutting) protrusions 1 are clearly visible due to a manufacturing method including a cutting step, rhomboid geometry with a large diagonal of 3 rhomboid voids located in the direction of the width of the tape and their small diagonal of 4 located in the direction tape lengths.

FIG. 1B shows a top view of the anode of the invention, in which the non-sharp, rounded side edges 2, rhomboid geometry with a large diagonal 3 of rhomboid voids located in the direction of the length of the tape and their small diagonal 4, located in the direction of the width of the tape are clearly visible.

Example.

Some of the most significant results obtained by the inventors are shown in the table, where the ohmic resistance data of representative anodes according to the invention are compared with traditional anodes. The anodes, designated A and B, are anodes with rhomboid geometry with a large diagonal of rhomboids oriented perpendicular to the length of the tape, similar to those shown in FIG. 1A, conventionally obtained by longitudinal extension with respect to the direction of movement of a continuous metal strip. The anodes, designated as C and Ό, are anodes with rhomboid geometry according to one embodiment of the invention, similar to that depicted in FIG. 1B.

Anodes C and Ό were prepared by stretching perpendicularly with respect to the direction of movement of a continuous metal tape, which is passed through a parallel row of knives in the apparatus, which leads to stretching of a continuous tape in a perpendicular direction by pressing and punching. The manufacture of the tape is completed by means of the last series of knives having blades of a given length greater than the blades of the previous knives, which, when applied, are suitable for modeling the lateral edge of the tape shown in FIG. 1B. In addition to the properties already explained, from the point of view of conductivity due to the geometry of the anode, this method has the advantage of providing a stretched metal strip without longitudinally extending solid sections, which, without being subjected to subsequent cutting, has no sharp edges and is therefore much safer and easier handling it during installation. Moreover, this method makes it possible in an advantageous manner to obtain a metal strip of the required length immediately after completion of the stretching. This method of production, in addition, allows to obtain tapes of greater length than the traditional method, which facilitates the installation of large sizes, which would require the connection of multiple tapes, with a lower continuity of the anode system as a whole.

From the data given in the table, it can be seen that with a certain given width, the anodes of the invention exhibit ohmic resistance approximately 60% lower.

Anodes in accordance with FIG. 1A E - Ohmic resistance A - 20 mm wide 0.22 ohm / m B - 10 mm wide 0.43 ohm / m Anodes in accordance with FIG. 1B E - Ohmic resistance C - 2 0 mm wide 0.088 ohm / m ϋ - 10 mm wide 0.177 Ohm / m

The above description is not intended to limit the invention, which can be applied according to other variants of implementation without going beyond it and the scope of which is determined solely by the attached claims.

Throughout the description and claims of this application, the term contain and its word forms, such as containing and contains, do not exclude the presence of other elements or additives.

Discussion of documents, regulations, materials, devices, products, etc. included in this description solely for the purpose of providing context for the present invention. This does not imply and is not evidence that any or all of these objects formed the basis of the prior art or were well-known information in the field to which the present invention relates, prior to the priority date of each claim of the present invention.

Claims (5)

CLAIM 1. A method of manufacturing an anode for cathodic protection in the form of a stretched metal tape with rhomboid cells without longitudinally extending solid sections geometrically made with a large diagonal parallel to the direction of the length of the tape, comprising the following steps: passing a metal tape through a stretching device provided with at least one row of knives of a first predetermined length parallel to the direction of movement of the tape; stretching the metal tape by pressing and punching the action of the at least one row of knives; the formation of the profiles of the lateral edges of the stretched metal tape by pressing and punching the action of the last row of knives having blades of a second predetermined length exceeding said first length. 2. The method according to claim 1, moreover, in the said anode, the profiles of the side edges along the length of the said metal tape have no discontinuities. 3. The method of claim 1 or 2, wherein said metal is titanium. 4. The method according to any one of claims 1 to 3, wherein said metal is coated with a catalytic layer. 5. The method according to claim 4, wherein said catalytic layer contains noble metals or their oxides.