WO2021111314A1

WO2021111314A1 - Cathodic protection anode for an offshore structure and cathodic protection device comprising same

Info

Publication number: WO2021111314A1
Application number: PCT/IB2020/061359
Authority: WO
Inventors: Denis MONDIERE; Olivier VANACKERE
Original assignee: Controle Et Maintenance
Priority date: 2019-12-04
Filing date: 2020-12-02
Publication date: 2021-06-10
Also published as: EP4069887A1; FR3104177A1; FR3104177B1

Abstract

The invention relates to a cathodic protection anode (1) and to a cathodic protection device comprising same. The cathodic protection anode (1) with a current determined by a rectifier (R) for an offshore structure (2) is characterized in that it comprises a cartridge comprising a sealed peripheral frame, two parallel external perforated plates extending on either side of the peripheral frame, the plates thus defining an upper face of the cartridge and a lower face of the cartridge, respectively, the upper and lower faces of the cartridge and the peripheral frame together delimiting an interior space for receiving a flat anode in the cartridge.

Description

CATHODIC PROTECTION ANODE FOR MEr STRUCTURE and Cathodic protection device INCLUDING IT

The present invention relates to the field of corrosion protection equipment, in particular to a cathodic protection anode for an offshore structure and to a cathodic protection device comprising it.

Cathodic protection is a technique of "active protection" against the corrosion of a metallic material in contact with an electrolyte (an ionically conductive aqueous medium such as water, soil, concrete). It is an electrochemical prevention system based on reducing the potential of the metal to a level where the corrosion rate of the metal is significantly reduced. Cathodic protection is achieved by applying a voltage capable of delivering sufficient cathodic current to a metal surface to decrease its potential to a level corresponding to a sufficiently low residual corrosion rate for the application concerned.

The variation in potential under the effect of current is called "polarization". When it is in the negative direction, it is called "cathodic polarization". The decrease in the corrosion potential of the metal results in a reduction in the rate of oxidation (anodic) of the metal and an increase in the reduction reaction (s) (cathodic) of the oxidizing species present in the electrolyte. The metal work to be protected is placed at a potential such that the corrosion rate becomes acceptable over the entire surface of the metal in contact with the electrolyte. For industrial structures such as pipelines or underground tanks, a residual corrosion rate of less than 10 μm / year is generally achieved using a perfectly efficient cathodic protection system.

For this, a direct electric current is circulated between one or more anode (s) and the material to be protected, which constitutes the cathode. The effectiveness of the method requires intimate contact of the electrolyte with the material to be protected at all points thereof. The current, which flows through the electrolyte to the metal, is adjusted so as to provide a cathodic current density allowing a potential value to be reached at which the rate of corrosion of the metal becomes very low. The variation in the potential of the structure as a function of the cathodic current density that it receives follows a cathodic polarization curve, or intensity - potential curve, characteristic of the electrochemical behavior of a given metal in a given electrolytic medium. This curve quantifies the current exchanges, therefore in particular the corrosion rate and the need for cathodic protection current.

An anode, by definition, is in contact with an electrolyte and seeks to transmit as much current as possible so that a structure does not corrode. When the electrolyte is seawater, the anodes at sea are generally always in direct contact with the external environment.

Today, along with environmental concerns, more and more structures, such as wind turbines, are being installed at sea, called offshore structures, in order to produce renewable energy. However, one of the disadvantages of installing a structure at sea is the risk of corrosion of the latter. There is therefore a real concern for the protection of structures at sea, in particular because of the cost of such a structure.

At present, a first solution to protect most offshore platforms is to equip them with sacrificial anodes made from aluminum. In fact, given that this technique does not require an imposed current, it has been widely favored.

A second solution used in a few rare cases of protection by impressed current at sea consists in using anodes based on TiMMo (Titanium - mixed metal oxides), however generally on surfaces of a few square centimeters and always in a very visible manner when the anodes are placed in the electrolyte.

The drawbacks of the first solution are the need for many tonnes of aluminum oxide (weight, handling, installation, efficiency, etc.), as well as the dilution of these tonnes of aluminum in sea water. given that the principle of a sacrificial anode is to allow the corrosion of an anode instead of the structure to be protected, it appears clearly, in the case of protection by means of an aluminum sacrificial anode , that the aluminum consumed from the sacrificial anode will end up in seawater, which will result in a strong release of aluminum oxide in seawater.

The drawbacks of the second solution are the small anode surface (high current density, proximity to the structure, strong local diffusion of chlorides, risk of erosion of oxidizing metals, etc.), the small distance from the structure (no more of 1 meter, in general,…).

There is therefore a need for a solution as less visible as possible, having a low ecological impact, having a small footprint and a low weight, more robust and making it possible to easily position the new anode, further from the structure, while protecting it from problems. erosion, and other incidents that may occur at sea. The anodic part will therefore be protected from its deposit of oxidizing materials, during its design and assembly until it leaves the factory and especially in all stages. from the life of the anode assembly until its end of use at 5, 10, 20 or 50 years from its installation, according to the demands and the calculation of its oxidizing part. It will ensure that certain disruptors can be kept at a distance which may short-circuit it and render it inoperative.

The applicant company has taken into account the existing drawbacks and proposed the use of an invisible anode, preferably bagged or encapsulated. It appears that encapsulating the anode has the effect of protecting it from all possible attacks at sea, such as erosion. Thus, the invention consists in being able to have anodes having a surface, generally large, necessary according to the calculations and the design, advantageously ballasted enough to be able to lay them on the seabed or suspend them, while protecting them from direct contact with flora and fauna, various and varied attacks, such as erosion, and also own attacks linked to its own emissions of chlorides.

The subject of the present invention is therefore a cathodic protection anode with current imposed by a rectifier for an offshore structure, characterized in that it comprises a planar anode and a cartridge comprising a peripheral frame sealed against particles of a predefined diameter of which at least one part forms a ballast, the structure of the peripheral frame being held by spacers extending in two parallel planes, the cartridge also comprising two parallel external perforated plates extending on either side of the peripheral frame, the perforated plates external being fixed to the spacers and thus defining respectively an upper face of the cartridge and a lower face of the cartridge, the upper and lower faces of the cartridge and the peripheral frame together delimiting an internal space for receiving the planar anode in the cartridge , the planar anode being configured to be electrically connected to a rectifier by means of 'at least one connection cable and having respectively an upper face facing the upper face of the cartridge and a lower face facing the underside of the cartridge, the cartridge further comprising, in the space delimited by a on the one hand by the upper face of the cartridge and the upper face of the flat anode, and on the other hand by the lower face of the cartridge and the lower face of the flat anode, a support element configured to hold the anode planar in a plane parallel to the top and bottom faces of the cartridge.

In the above configuration, the function of the cartridge is to enclose the planar anode in order to protect it both from possible attacks at sea, such as erosion, and possible attacks during transport of the anode. cathodic protection up to sea, such as shocks. The ballast part or parts allow the cathodic protection anode to be placed on the seabed, or to be suspended at sea from a structure at sea.

The structure of the cartridge is made up of two external perforated plates making it possible to filter particles beyond a certain diameter, an internal space for receiving a flat anode in the cartridge making it possible to receive the flat anode in order to limit the movements of the latter, and of spacers making it possible to maintain a certain distance between the part or parts forming ballast. The cartridge is then electrically connected to a rectifier for offshore structures via a connection cable.

With the above configuration, the cathodic protection anode has a robust and easily assembled structure. In addition, the cathodic protection anode is protected during its transport from the factory outlet to the offshore structures by the presence of support elements making it possible to keep the flat anode in place inside the cartridge. and thus avoiding any possible degradation of this flat anode due, for example, to shocks occurring during its transport to sea.

It should be noted that the perforated plates filter particles beyond a certain diameter, thus making it possible to filter most of the particles liable to come into contact with the anode once it is at sea. the anodic protection anode is, because of its structure, impermeable to particles of a certain diameter.

In addition, each connection cable electrically connecting the plane anode to a rectifier for an offshore structure is electrically insulated to prevent corrosion and a possible risk of short-circuiting.

In addition, with the above configuration, any shape of the sealed peripheral frame of the cartridge could be envisaged. Preferably, the peripheral frame is rectangular. However, a peripheral frame of toroidal or even polygonal shape could be envisaged in the context of the present invention.

According to a particular embodiment, the cartridge of the cathodic protection anode further comprises two internal perforated plates parallel to the external perforated plates, the two internal perforated plates being located in the internal space of the cartridge between each face of the cartridge. flat anode and the corresponding external perforated plate opposite.

The two internal perforated plates located in the interior space of the cartridge double the effectiveness of the protection and facilitate the insertion of the planar anode into the cartridge.

It should be noted that the external and internal perforated plates can have the same degree of filtering, or have different degrees of filtering. Thus, the internal and external perforated plates make it possible to obtain a double level of filtering. Therefore, it could be envisaged that the internal and external perforated plates each have different spacings between their perforations, different perforation diameters, a different perforation density, as well as different distribution patterns of the perforations, for example a distribution. staggered, a distribution with perforations of one plate overlapping with perforations of the other plate, a distribution in which the perforations of one plate lie behind the perforations of the other plate, or a combination of these this.

According to a particular embodiment, the external perforated plates and, where appropriate the internal perforated plates, are made of a material resistant to seawater, preferably polyethylene (PE).

Of course, any material resistant to chloride emissions could be considered in the context of the present invention for the production of the external and internal perforated plates.

The realization of the external and internal perforated plates in a water-resistant material allows them to resist the chloride emissions that appear especially when the anode is in operation. The cathodic protection anode is then protected by means of the external perforated plates from contacts and external aggressions, such as chloride emissions.

Thus, the sandwich formed by the planar anode and the internal perforated plates is closed peripherally by external perforated PE plates to form a tight assembly against particles of a certain diameter. Thus, the electrolyte can only come into contact with the planar anode through the perforations of the internal and external PE plates.

According to a particular embodiment, the cartridge further comprises, between each face of the planar anode and the facing perforated plate, one of a permeable material and a water-soluble material.

In the above configuration, the planar anode located in the cartridge of the anode protection anode is bagged or encapsulated with a thin layer from its design in order to protect it as soon as possible from possible shocks that may occur during its transport from the factory outlet to offshore structures. In other words, the planar anode is sandwiched between two layers of one of a permeable material and a water-soluble material.

Preferably, when the material is a water-soluble material, the latter is a non-polluting material consisting of one of a gel, cardboard, "hardboard" (registered trademark), or a combination thereof. this.

The water-soluble material is a non-polluting material configured to disappear once the anode is installed at sea, so that the anode is protected during manufacture, transport and installation.

Alternatively, a cardboard plate and / or a "hardboard" (registered trademark) plate is inserted between the flat anode and the internal perforated PE plate, to form an additional layer. According to this variant, the anode may not be covered with a water-soluble material.

According to the above configuration, the water-soluble material covering the anode and / or the layers formed between the planar anode and the spacers serve to protect the anode during its manufacture, its transport and its installation: it is about a spacer element preventing the anode from being damaged against the PE plates. This spacer element is intended to disappear in contact with the electrolyte once the anode is installed.

Preferably, the planar anode is made of titanium coated with a coating based on mixed metal oxides, MMo.

It should be noted that any coating of the anode making it possible to protect the latter is envisaged within the framework of the present invention.

Preferably, the planar anode is one of a plate, a stretched plate, a grid or a wire wound in a plane.

Thus, the size of the cartridge forming the cathodic protection anode is reduced, thus making it possible to produce a compact cathodic protection anode.

According to a particular embodiment, the peripheral frame is rectangular, at least two of the sides of said peripheral frame being constituted by ballast elements, each ballast element being formed by one of a single piece block made in a material having a density greater than that of sea water, preferably a concrete block, and a fastening device configured to be connected to an element at sea.

Note that the density of each weight element is such that it allows the cartridge to be weighted and to be below sea level.

In the above configuration, according to one of the variants, the ends of the spacers are inserted, or even embedded, in a ballast element, for example a concrete block, thus ensuring the integrity of the anode.

Preferably, the spacers have an elongated shape, in particular in the form of a tube, and are fixed to the peripheral frame. As indicated above, the ends of the spacers can be embedded in the material constituting the ballast element.

Preferably, the support elements consist of cleats.

According to a particular embodiment, the anode further comprises means for handling the assembled anode.

According to this particular embodiment, the anode may have hooks, or equivalent members, to hang in the manner of a pallet, in order to allow its transport, its hooking, in particular its suspension to the structure at sea and to facilitate also its palletization and storage.

The present invention also relates to a cathodic protection device, characterized in that it comprises a cathodic protection anode as defined above and a rectifier connected to the cathodic protection anode by at least one connection cable. .

Thus, according to the above configuration, the cathodic protection anode as well as the rectifier for an offshore structure are envisaged within the scope of the present invention.

To better illustrate the object of the present invention, several particular embodiments will be described below, by way of illustration and not by way of limitation, with reference to the accompanying drawings.

On these drawings:

is a general view of a structure at sea connected to two cathodic protection anodes located at sea.

is a perspective view of the cathodic protection anode with partial cut away of each layer composing it.

is a cross-sectional view of the cathodic protection anode.

is an enlarged view of one side of the anode protection anode according to the .

If we refer to the , we can see two cathodic protection anodes 1 placed at sea M and each connected to a rectifier R of the structure at sea 2, here a wind turbine, via a connection cable 3, the rectifier R being located in the emerged electrical circuit part of the offshore structure 2. The offshore structure 2 shown in comprises a mast 2a extending between a foundation 2b in the lower part and a nacelle 2c in the upper part connected to three blades 2d.

Referring to Figures 1 and 2, it can be seen that the cathodic protection anode 1 according to a particular embodiment of the present invention is rectangular in shape. However, a cathodic protection anode 1 of toric shape or other polygonal shape could be envisaged within the framework of the present invention.

If we refer to the , it can be seen that the cathodic protection anode 1 according to a particular embodiment of the present invention is composed of several layers which are visible by virtue of the partial tearing shown in this Figure.

The cathodic protection anode 1 according to a particular embodiment of the present invention comprises a cartridge 4 comprising a peripheral frame of which two parts form a ballast 5. The parts forming a ballast 5 of the peripheral frame each consist of a cylindrical block of. in one piece. However, a toroidal shaped ballast portion 5 extending around the cartridge 4 could be envisioned in another embodiment of the invention.

The cartridge 4 comprises at its upper and

lower faces

4a, 4b, an external perforated plate 6 comprising perforations 6a distributed over the surface of each external perforated plate 6. The perforations 6a of the external perforated plates 6 have a defined diameter which allows filtering particles with a diameter greater than the diameter of the perforations.

The upper and

lower faces

4a, 4b of the cartridge 4 defined by the external perforated plates 6 together delimit an internal reception space 12 of a planar anode 10 in the cartridge 4. Inside this reception space 12 is housed said. planar anode 10 which is configured to be electrically connected to a rectifier for an offshore structure 2 by means of at least one connection cable 3, preferably a single connection cable.

The layers of the cartridge lying respectively below the external perforated plate 6 at the level of the upper face of the cartridge 4 and above the external perforated plate 6 at the level of the lower surface of the cartridge 4 consists of spacers 7 maintaining the structure of the peripheral frame of the cartridge 4 and on which the external perforated plates 6 are fixed.

The spacers 7 have according to a particular embodiment of the invention an elongated shape, preferably in the form of tubes spaced apart from one another and extend from one part forming a ballast 5 to another part forming a ballast 5.

The layer located respectively immediately under the layer formed by the spacers 7 at the level of the upper face 4a of the cartridge 4 and immediately on the layer formed by the spacers 7 at the level of the lower face 4b of the cartridge 4 is composed of an internal perforated plate 8 provided at its surface with perforations 8a having a predefined diameter.

The two internal perforated plates 8 located in the interior space 12 of the cartridge 4 make it possible to double the effectiveness of the protection and facilitate the insertion of the planar anode 10 into the cartridge 4.

According to a particular embodiment of the invention, the diameter of the perforations 8a of the internal perforated plates 8 is less than the diameter of the perforations 6a of the external perforated plates 6 in order to allow a distinct degree of filtering of particles. However, according to an alternative embodiment of the invention, the diameter of the perforations 8a of the internal perforated plates 8 may be equal or even greater than the diameter of the perforations 6a of the external perforated plates 6 in order to have a double degree of particle filtering.

The perforations 6a of the outer perforated plates 6 and the perforations 8a of the internal perforated plates 8 are distributed in a regular pattern in which the spacing between the perforations is the same and the density of the perforations is the same. However, according to another embodiment of the invention, the distribution patterns of the perforations of the internal and

external plates

8, 6 are different. Thus, a staggered distribution (the perforations of one plate are completely offset from the perforations of the other plate), a distribution in which the perforations of one plate overlap with perforations of the other plate (the perforations of the other plate). one plate are partially aligned with the perforations of the other plate), a distribution in which the perforations of one plate are aligned with the perforations of the other plate (the perforations of one plate are directly aligned with the perforations of the (other plate), or a combination thereof are contemplated.

According to a particular embodiment, the external perforated plates 6 and, where appropriate the internal perforated plates 8, are made of a material resistant to seawater, preferably polyethylene (PE).

Of course, any material resistant to chloride emissions could be considered in the context of the present invention for the production of the external and internal

perforated plates

6, 8.

The realization of the external and internal

perforated plates

6, 8 in a water-resistant material allows the latter to resist the chloride emissions which appear in particular when the anode is in operation. The cathodic protection anode 1 is then protected by means of the external perforated plates 6 from contacts and external attacks, such as chloride emissions.

Thus, the sandwich formed by the planar anode 10 and the internal perforated plates 8 is closed peripherally by external perforated plates 6 made of PE to form a tight assembly to particles of a predefined diameter. Thus, the electrolyte can only come into contact with the planar anode 10 through the

perforations

6a, 8a of the inner and

outer plates

6, 8 of PE.

If we continue to refer to the , one can see a layer 9 located respectively above and below the planar anode 10. This layer 9 is composed of one of a water-soluble material, and a permeable material. The planar anode 10 located in the cartridge 4 of the anode protection anode 1 is then encapsulated with a thin layer from its design in order to protect it as soon as possible from any shocks that may occur during its transport from the outlet. from factory to offshore structures 2. In other words, the planar anode 10 is sandwiched between two layers 9 of one of a permeable material and a water-soluble material.

The water-soluble material is a non-polluting material configured to disappear once the cathodic protection anode 1 is installed at sea, so that the anode 10 is protected during its manufacture, transport and installation.

According to an alternative embodiment of the invention, a cardboard plate and / or a "hardboard" (registered trademark) plate is inserted between the flat anode 10 and the internal perforated plate 8, to form an additional layer. According to this variant, the anode 10 may not be covered with a water-soluble material.

According to the above configuration, the water-soluble material covering the planar anode 10 and / or the layers formed between the planar anode 10 and the spacers 7 serves to protect the anode 10 during its manufacture, its transport and its installation: it This is a spacer element preventing the anode 10 from being damaged against the internal 8 or external 6 plates. This spacer element is intended to disappear in contact with the electrolyte once the anode 1 has been installed.

Referring to Figures 3 and 3A, one can see a cross section of the cathodic protection anode 1 allowing to see the superposition of all the layers forming the cartridge 4 of the cathodic protection anode 1. Thus, it can be seen that the cartridge 4 further comprises, respectively, in the space delimited by the upper face 4a of the cartridge 4 and the upper face of the anode, and the lower face 4b of the cartridge and the lower face of the anode, two support elements 11, preferably cleats, configured to hold the planar anode 10 in a plane parallel to the upper and

lower faces

4a, 4b of the cartridge 4 while remaining inside the anode. space 12 delimited by the two parallel planes of the spacers 7.

If we refer more particularly to the , it can be seen that the ends of the spacers 7 are located inside the parts forming ballast 5 of the cartridge 4, which makes it possible to guarantee the integrity of the anode 1. In addition, we can see rods 13 s 'extending transversely to the spacers 7 and longitudinally with respect to the parts forming ballast 5 of the cartridge 4. These rods 13 allow the spacers 7 to be held in place during the formation of the parts forming the ballast 5 of the cartridge 4 at the level of the ends of the spacers 7.

According to the embodiment of the invention described with reference to Figures 2 to 3A, the planar anode 10 is a plate. However, according to another embodiment of the invention, the planar anode 10 is one of a plate, a stretched plate, a grid or a wire wound in a plane. Thus, the size of the cartridge forming the cathodic protection anode is reduced, thus making it possible to produce a compact cathodic protection anode.

In addition, the anode is made of titanium coated with a coating of mixed metal oxides, MMo. However, any coating of the anode making it possible to protect the latter is envisaged within the scope of the present invention.

According to the embodiment of the invention shown in Figures 1 to 3A, the peripheral frame is rectangular, and at least two of the sides of the peripheral frame are formed by ballast elements 5. Each ballast element 5 consists of a single piece block made of a material having a density greater than that of sea water, preferably a concrete block. However, according to another embodiment of the invention, each ballast element 5 may consist of a fixing device configured to be connected to an offshore element 2.

It should be noted that the density of each ballast element 5 is such that it allows the anode 1 to be ballasted and to be located below sea level M.

According to an alternative embodiment of the invention (only shown in ), the anode 1 further comprises handling members 14 of the assembled cartridge. According to this variant embodiment, the anode 1 has hooks 14, or equivalent members, to hang in the manner of a pallet, in order to allow its transport, its attachment, in particular its suspension to the structure at sea. 2 and also facilitate its palletization and storage.

Claims

- Anode (1) for cathodic protection with current imposed by a rectifier (R) for an offshore structure (2), characterized in that it comprises a planar anode (10) and a cartridge (4) comprising a sealed peripheral frame particles of a predefined diameter, at least part of which forms ballast (5), the structure of the peripheral frame being held by spacers (7) extending in two parallel planes, the cartridge (4) also comprising two external perforated plates (6) parallel extending on either side of the peripheral frame, the external perforated plates (6) being fixed to the spacers (7) and thus defining respectively an upper face (4a) of the cartridge (4) and a face lower (4b) of the cartridge (4), the upper (4a) and lower (4b) faces of the cartridge (4) and the peripheral frame together delimiting an interior space (12) for receiving the planar anode (10) in the cartridge (4), the planar anode (10) being configured to be connected e electrically to a rectifier via at least one connection cable (3) and having respectively an upper face facing the upper face (4a) of the cartridge (4) and a lower face facing the face lower part of the cartridge (4b), the cartridge (4) further comprising, in the space delimited on the one hand by the upper face (4a) of the cartridge (4) and the upper face of the planar anode (10 ), and on the other hand by the lower face (4b) of the cartridge (4) and the lower face of the planar anode (10), a support element (11) configured to hold the planar anode (10) in a plane parallel to the upper and lower faces of the cartridge (4).
- Anode (1) for cathodic protection according to claim 1, characterized in that the cartridge (4) further comprises two internal perforated plates (8) parallel to the external perforated plates (6), the two internal perforated plates (8) being located in the internal space of the cartridge (4) between each face of the planar anode (10) and the corresponding external perforated plate (8).
- Anode (1) for cathodic protection according to claim 1 or claim 2, characterized in that the external perforated plates (6) and, where appropriate the internal perforated plates (6), are made of a material resistant to l seawater, preferably polyethylene (PE).
- Anode (1) for cathodic protection according to one of claims 1 to 3, characterized in that the cartridge (4) further comprises between each face of the planar anode (10) and the perforated plate facing the one of a permeable material and a water soluble material.
- Anode (1) of cathodic protection according to claim 4, characterized in that the water-soluble material is a non-polluting material consisting of one of a gel, cardboard, "hardboard" (registered trademark), or of a combination of these.
- Anode (1) for cathodic protection according to one of claims 1 to 5, characterized in that the planar anode (10) is made of titanium coated with a coating based on mixed metal oxides, MMo.
- Anode (1) for cathodic protection according to one of claims 1 to 6, characterized in that the planar anode (10) is one of a plate, a drawn plate, a grid or a wire wound in a plan.
- Anode (1) for cathodic protection according to one of claims 1 to 7, characterized in that the peripheral frame is rectangular, at least two of the sides of said peripheral frame being constituted by ballast elements (5), each element ballast (5) consisting of one of a one-piece block made of a material having a density greater than that of sea water, preferably a concrete block, and a configured fastening device to be connected to an element at sea.
- Anode (1) for cathodic protection according to one of claims 1 to 8, characterized in that the spacers (7) have an elongated shape, preferably in the form of a tube, and are fixed to the peripheral frame.
- Anode (1) for cathodic protection according to one of claims 1 to 9, characterized in that the support elements (11) consist of cleats.
- Anode (1) for cathodic protection according to one of claims 1 to 10, characterized in that the anode (1) further comprises handling members (14) of the assembled anode.
- Cathodic protection device, characterized in that it comprises an anode (1) of cathodic protection according to one of claims 1 to 11 and a rectifier (R) connected to the cathodic protection anode by at least one cable connection (3).