DK2616568T3

DK2616568T3 - ANOTHES FOR CATHODIC PROTECTION AND PROCEDURES FOR PRODUCING THEM

Info

Publication number: DK2616568T3
Application number: DK11757856.7T
Authority: DK
Inventors: Corrado Mojana; Simone Tremolada
Original assignee: Industrie De Nora Spa
Priority date: 2010-09-17
Filing date: 2011-09-15
Publication date: 2019-02-18
Also published as: PL2616568T3; US20130168261A1; AU2011303882A1; MA34596B1; ITMI20101689A1; EP2616568B1; CN103119201A; JP6068343B2; CN103119201B; US20160040302A1; MX2013002844A; PE20140396A1; JP2013537261A; BR112013006334B1; AR084116A1; HK1185386A1; NZ606985A; SG188189A1; MY159927A; WO2012035107A1

Description

DESCRIPTION

FIELD OF THE INVENTION

[0001] The invention relates to the field of cathodic protection of reinforced concrete structures, and in particular to a design of anode particularly efficient in terms of electrical resistance per unit length and of flexibility, and particularly safe to install and handle.

The invention also relates to the method of production of such anode.

BACKGROUND OF THE INVENTION

[0002] Corrosion phenomena affecting reinforced concrete structures are well known in the art. The steel reinforcement inserted in the cementitious structures to improve the mechanical properties thereof normally works in a passivation regime induced by the alkaline concrete environment; however, after some time, the ion migration across the porous surface of the concrete causes a localised attack to the protective passivation film. Particularly worrying is the attack by chlorides, which are virtually present in all kinds of environments where the reinforced concrete structures are employed, and to an even higher extent where an exposure to brackish water (bridges, pillars, buildings located in marine zones), antifreeze salts (bridges and road structures in cold climate zones) or even seawater, such as for instance in the case of piers and docks, takes place. The critical value of chloride exposure has been esteemed around 0.6 kg per cubic metre of concrete, beyond which the passivation state of the reinforcing steel is not guaranteed. Another form of concrete decay is represented by the carbonatation phenomenon, that is the formation of calcium carbonate by reaction of the lime of the cementitious mixture with atmospheric carbon dioxide. Calcium carbonate lowers the concrete alkali content (from pH 13.5 to pH 9) bringing iron in an unprotected state. The presence of chlorides and the simultaneous carbonatation represents the worst of conditions for the preservation of the reinforcing bar of the structures. The corrosion products of steel are more voluminous than steel itself, and the mechanical stress resulting from their formation may lead to concrete delamination and fracturing phenomena, which translate into huge damages from the point of view of economics besides the one of safety. For this reason, it is known in the art that the most effective method for indefinitely prolonging the lifetime of reinforced concrete structures exposed to the atmospheric agents, even in the case of relevant salt concentrations, consists of cathodically polarising the steel reinforcement. In this way, the latter becomes the site of an oxygen cathodic reduction, suppressing the anodic corrosion and dissolution reactions. Such system, known as cathodic protection of reinforced concrete, is practised by coupling anodic structures of various kinds to the concrete, respect to which the reinforcement to be protected acts as a cathodic counterelectrode; the electrical currents involved supported by an external rectifier transit across the electrolyte consisting of the porous concrete partially soaked with a salty solution.

[0003] The anodes commonly used for the cathodic protection of reinforced concrete consist of a titanium substrate coated with transition metal oxides or other types of catalysts for anodic oxygen evolution. As the substrate it is possible to make use of other valve metals, either pure or alloyed; pure titanium is however the largely preferred choice for the sake of cost.

[0004] European Patent EP458951 discloses a grid-type electrodic structure for cathodic protection consisting of a plurality of metal ribbons having an electrocatalytic coating, said metal ribbons having voids of different geometries.

[0005] This type of ribbons can be manufactured by punching of solid metal ribbons or more commonly by the traditional methods of metal expansion wherein a metal sheet is expanded by pressuring and punching through a series of knives arranged orthogonal to the advancement direction of the ribbon itself. This first step allows obtaining an expanded metal sheet. Such sheet is then subjected to a second step of cutting suitable for obtaining ribbons of the required dimensions. Said expanded metal ribbons present meshes having voids of rhomboidal shape with the major diagonal oriented orthogonal to the ribbon length.

[0006] This method of manufacturing has the inconvenience of producing metal ribbons with meshes having cutting side protrusions automatically formed during the operation of cutting, making these anodes difficult to handle and the installation phase accordingly dangerous.

[0007] Metal ribbons with smooth lateral edges are disclosed in Canadian Patent Application CA 2078616 A1; by the method described this document, the ribbons obtained present a continuous longitudinally-extending solid section of a certain width, which is invariably formed in the manufacturing process and which can only be used for spot-welding. In present-day cathodic protection systems, however, it is preferred not to weld ribbon anodes at all, but rather to overlay them directly to the reinforcement with plastic spacers arranged in-between. In such case, the longitudinally-extending solid section is just a loss of material, especially because this solid section invariably gets coated with precious metals during the application of the catalytic layer. Such catalytic layer however cannot work properly on a non-foraminous structure and affects the calculation of the actual current density impressed to the anodic structure, thereby complicating the design of the overall cathodic protection system.

SUMMARY OF THE INVENTION

[0008] Various aspects of the invention are set out in the accompanying claims.

[0009] Under one aspect, the invention relates to an anode in form of mesh ribbon for systems of cathodic protection, for instance of cathodic protection of reinforced concrete structures, overcoming the inconveniences of the prior art, whose edges are substantially free of discontinuities in form of cutting protrusions and have a sinusoidal shape.

[0010] In the context of the present description reference is made, for the sake of simplicity, to cathodic protection of reinforced concrete structures; it is understood that the invention may be practised in the field of cathodic protection in general, for instance comprising the cathodic protection of metal tank bottoms.

[0011] Under another aspect, the invention relates to a method for manufacturing said anode.

[0012] Under a further aspect, the invention relates to a cathodic protection system comprising at least one anode in form of mesh ribbon whose edges are substantially free of cutting protrusions.

[0013] Some of the most significant results obtained by the inventors are presented in the following description, which is merely provided by way of example without wishing to limit the invention.

[0014] The anode according to the invention consists of a ribbon of expanded metal characterised by meshes with rhomboidal shaped voids with the major diagonal oriented along the direction of the ribbon length. In one embodiment, the lateral edges of the ribbon have a sinusoidal profile and are free of cutting protrusions.

[0015] The inventors have surprisingly noticed that an anode for cathodic protection as hereinbefore described displays a remarkably reduced ohmic resistance per unit length, for instance up to 4-fold reduced, with respect to the anodes of the prior art.

[0016] The lower electrical resistance makes possible to reduce the number of electrical connections, for instance in a grid system, with sensible savings of material and installation time.

[0017] In one embodiment, the metal mesh ribbon is made of titanium.

[0018] In another embodiment, the metal mesh ribbon is coated with a catalytic coating containing noble metals or oxides thereof.

[0019] In one embodiment, the dimensions of the ribbon can have a width ranging from 3 mm to 100 mm with a thickness of 0.25 mm to 2.5 mm and a length of 1 m to 150 m.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] For the sake of a better understanding of the invention, reference will be made to the following drawings, having the purpose of depicting some preferred embodiments thereof without limiting its extent. • Fig. 1A shows a top-view of a traditional expanded metal anode. • Fig. 1B shows a top-view of an expanded metal anode according to the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0021] In detail, Fig. 1A shows a top view of the traditional anode in which are distinguishable cutting protrusions 1 due to the manufacturing method including a cutting step, the rhomboidal geometry with major diagonal 3 of rhomboidal voids arranged in the direction of the ribbon width and the minor diagonal 4 of the same arranged in the direction of the ribbon length.

[0022] Fig. 1B shows a top-view of the anode according to the invention in which are distinguishable non-cutting blunt lateral edges 2, the rhomboidal geometry with major diagonal 3 of rhomboidal voids arranged in the direction of the ribbon length and the minor diagonal 4 of the same arranged in the direction of the ribbon width.

EXAMPLE

[0023] Some of the most significant results obtained by the inventors are reported in Table 1, wherein ohmic resistance data of representative anodes of the invention are compared to traditional anodes. Anodes labelled A and B are anodes of rhomboidal geometry with the major diagonal of rhomboids oriented orthogonal to the ribbon length likewise depicted in Fig. 1A, traditionally obtained by longitudinal expansion with respect to the displacement direction of a solid metal ribbon. Anodes labelled C and D are anodes of rhomboidal geometry according to one embodiment of the invention, likewise depicted in Fig. 1B.

[0024] Anodes C and D were prepared by orthogonal expansion with respect to the displacement direction of a solid metal ribbon allowed to run in an apparatus along a parallel row of knives which expand the solid ribbon in an orthogonal direction by pressuring and punching. The ribbon manufacturing is completed by means of a last series of knives, having blades of predefined length higher than the blades of previous knives, which upon applying a pressure are suitable for modelling the lateral edge of the ribbon as depicted in Fig. 1B. Besides the advantages already explained in terms of conductivity due to the anode geometry, this method has the advantage of providing an expanded metal ribbon free of longitudinally-extending solid sections which, being not subsequently cut, does not present any cutting edge and is therefore much safer and easy to handle during the installation. This method moreover allows to advantageously obtain a metal ribbon of the desired length directly upon completion of the expansion. Such method of production furthermore allows obtaining ribbons of higher length than the traditional method thereby facilitating big size installation which would require connections of multiple ribbons, with a lower solidity of the overall anodic system.

[0025] From the data reported in the table it can be noticed that for a given width, the anodes of the invention display an ohmic resistance about 60% lower.

Table 1

[0026] The previous description is not intended to limit the invention, which may be used according to different embodiments without departing from the scopes thereof, and whose extent is univocally defined by the appended claims.

[0027] Throughout the description and claims of the present application, the term "comprise" and variations thereof such as "comprising" and "comprises" are not intended to exclude the presence of other elements or additives.

[0028] The discussion of documents, acts, materials, devices, articles and the like is included in this specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention before the priority date of each claim of this application.

REFERENCES CITED IN THE DESCRIPTION

This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

Patent documents cited in the description • EP458951A [00041 • CA2078616A1 [00071

Claims

Anode for cathodic protection in the form of an expanded metal band with rhombic meshes without fixed, non-perforated sections extending longitudinally, characterized in that the rhombic meshes are geometrically arranged with the main diagonal parallel to the direction of the length of the band which masks are obtained by driving the metal belt through an extension device provided with at least a series of knives having blades of a first predetermined length arranged parallel to the direction of the belt displacement, and extending the metal belt by means of a pressing and punching action thereof. at least one row of blades, and the side edge profiles along the length of the band are without discontinuities, which side edge profiles are obtained by forming side edge profiles of the expanded metal band by pressing and punching the last row of knives with blades of another predetermined length, which is larger than the first length.

Anode according to claim 1, wherein the metal is titanium.

Anode according to any one of claims 1 or 2, wherein the metal is coated with a catalytic layer.

Anode according to claim 3, wherein the catalytic layer comprises precious metals or oxides thereof.

A method of producing an anode for cathodic protection in the form of an expanded metal band with rhombic meshes without fixed, non-perforated sections extending longitudinally, comprising the following steps: - running a metal band through an extension device provided with at least one row of blades having blades of a first predetermined length arranged parallel to the direction of the belt displacement, - expanding the metal band by a pressing and punching action of the at least one row of blades so that the rhombic meshes are placed geometrically with the main diagonal parallel to the direction of the length of the metal band, - forming side edge profiles of the expanded metal band by a pressing and punching action of a last row of knives with blades of a second predetermined length greater than the first length, so that the rhombic masks rhombic masks are placed geometrically with the main diagonal parallel to the direction of the metal band ts length, and so that the side edge profiles along the length of the expanded metal band are without discontinuities.

A cathodic protection system comprising at least one anode according to any one of claims 4 to embedded in a cementitious structure provided with metal reinforcing rods.

A method of cathodic protection of a reinforced concrete structure comprising applying an anodic potential to the anodes of the cathodic protection system of claim 6.