WO2010089457A1

WO2010089457A1 - Electrode element and a method for connecting the electrode element and an arrangement for electrochemical protection

Info

Publication number: WO2010089457A1
Application number: PCT/FI2010/050073
Authority: WO
Inventors: Jouko Elfving
Original assignee: Leion Oy
Priority date: 2009-02-05
Filing date: 2010-02-05
Publication date: 2010-08-12
Also published as: FI20095105A0; FI20095105A; EP2393962A1; FI124416B

Abstract

The invention relates to an electrode element for electrochemical protection. The electrode element is prefabricated and adapted to be tightly connected to a structure (10) to be protected located in a medium. The electrode element includes electrode components (12), extending to the medium, which are arranged in the electrode element non-destructively and detachably. The invention also relates to a method for connecting an electrode element and an arrangement in electrochemical protection.

Description

ELECTRODE ELEMENT AND A METHOD FOR CONNECTING THE ELECTRODE ELEMENT AND AN ARRANGEMENT FOR ELECTROCHEMICAL PROTECTION

The invention relates to an electrode element for electrochemi- cal protection, which is prefabricated and adapted to be tightly connected to a structure to be protected located in a medium and includes electrode components that extend to the medium. The invention also relates to a method for connecting the electrode element as well as an arrangement in electrochem- ical protection.

Electrochemical protection, such as cathodic protection, can prevent corrosion of a metal in an electrically conducting medium, such as sea water, earth or concrete. In active cath- odic protection (ICCP, Impressed Current Cathodic Protection) , a power source is connected between the structure to be protected and an anode to supply direct current from the anode to the surface of the structure to be protected, via a medium. Thus the structure to be protected forms the provided cathode. Protective current decreases the corrosion potential of the surface to be protected to a so called immunity range preventing thus corrosion of this surface. The anode can be separate from the structure to be protected or it can be connected to said structure. US patent No. 5416314 discloses an example of cathodic protection of a ship.

FI patent No. 70260 proposes a prefabricated anode or reference electrode element wherein electrodes are preconnected to the insulating material. The element is welded to an opening made in a ship frame. However, problems appear in the utilization of the element. Firstly, each. wall thickness and metal quality requires a specific element. Furthermore, the manufacturing costs of the element are high. Replacing a damaged anode requires the ship to be drydocked during which the element is cut off and replaced with a new similar element. Welding a prefabricated element to a structure to be protected is also diffi- cult. The element is sensitive to damage, which is due to the different thermal expansion coefficients of steel and insulating material. The element is also unnecessarily large because of the safety distance required by tacking.

The object of the invention is to provide a novel electrode element which is more resistant than before and more user-friendly than previously. Another object of the invention is to provide a novel method of connecting an electrode element the method being quicker than before and lower in costs than previously. Still another object of the invention is to provide a novel arrangement for electrochemical protection said arrangement being more compact than before but easier to service than previously. The characteristic features of the electrode element according to this invention become evident from the appended claim 1. Correspondingly, the characteristic features of the method according to the invention become evident from the appended claim 10 and the characteristic features of the arrangement according to the invention become evident from the appended claim 14. The electrode element according to the invention is compact and it has a simple and sealed construction. In addition, the maintenance and particularly the replacement of the electrode element are extremely easy. The electrode element is suitable for installation in various applications and its resistance is good. The method brings significant savings and the arrangement is suitable for various structures to be protected.

The invention is described below in detail by making reference to the enclosed drawings which illustrate some of the embodiments of the invention, in which

Figure 1 is a partial cross-sectional view of an arrangement according to the invention, Figure 2a shows the cross-section of a structure to be protected, Figure 2b Shows the parts of en electrode element according to the invention separated from one another,

Figure 3 shows one step of a method according to the invention, Figure 4a is a partial cross-sectional view of a second embodiment of the arrangement according to the inven- tion,

Figure 4b is a partial cross-sectional view of a third embodiment of the arrangement according to the invention, Figure 4c is a partial cross-sectional view of a fourth embodiment of the arrangement according to the invention,

Figure 5 is a partial cross-sectional view of a fifth embodiment of the arrangement according to the invention,

Figure 1 illustrates an arrangement which is used in electrochemical protection. In the arrangement, one or more prefabricated electrode elements 11 are joined, for example by welding to the structure 10 to be protected located in a medium. The structure can be a side of a ship, an underground pipe or a steel container, for example. A large ship can have as many as several tens of electrode elements. Figure 1 shows a power supply electrode application which is used to supply direct current. In potentiostatic electrochemical protection, a refer- ence electrode is also used, the design principle of which can be similar to that of a power supply electrode. Instead of supplying power, a reference electrode measures the corrosion potential of a structure. Regardless of the embodiment, the electrode element 11 includes electrode components 12 that extend to water. The electrode component can supply current or measure the corrosion potential. Here the electrode element 11 according to the invention includes a holding block 13 which is tightly joined to the structure 10 by welding, for example, and the electrode components 12 are arranged in contact with the holding block 13 non-destructively and detachably. Various advantages are achieved with this construction. Firstly, the holding block can be welded to the structure without a fear of the electrode components getting damaged due to heating up. In addition, the electrode components can be replaced without welding and even without drydocking. For example, in case of a container, emptying of the container is avoided. The electrode element is advantageously prefabricated and it is adapted to be connected to a structure to be protected located in a medium. According to the invention, the electrode element advantageously includes a holding block adapted to be tightly joined to the structure, advantageously by welding. Along with or in addition to welding, a threaded connection, for example, can be used. Additional embodiments of the invention are shown in Figures 4a-c and in Figure 5. In addition, the electrode components are arranged in contact with the holding block non-destructively and detachably. That is, the electrode components can be easily detached from the holding block without breaking the electrode element. Thus a connection method that forms the material, such as welding, is required only in the initial installation, after which the maintenance of the elec- trode element can be done from one side of the structure using conventional tools.

Figure 2a shows the cross-section of a structure 10 to be protected. A circular opening 14 is made in the structure 10, such as a side of a ship, for the electrode element. Figure 2b shows the parts of an electrode element according to the invention separated from one another. The holding block 13 is advantageously a metallic body of revolution and its material is classified steel. Advantageously, high-quality steel is used in which case one type of a holding block is suitable for use in a variety of structures. On the outer periphery of the holding block 13 there is additionally a protrusion 15 to provide a sufficient extension in case a weld joint 16 is used for joining. At the same time, an opening with straight edges can be made in the structure. The holding block is also clearly thicker compared to the material thickness of the structure,, which increases the resistance of the electrode element. Moreover, a holding block provided with a protrusion is suitable for constructions with different thicknesses. In practice, only steel parts are present during joining that takes place by welding, for example.

In the electrode element according to the invention, the electrode components 12 are also advantageously adapted as a prefabricated electrode pack 17, the construction of which is described in more detail later. An opening 18 corresponding to the external dimensions of the electrode pack 17 is arranged in the holding block 13. Thus the electrode pack 17 is securely supported to the holding block 13. In addition, the opening 18 is advantageously at least partly conical. The conical shape opens toward the installation side of the structure. Thus it is prevented that the electrode pack 17 comes to the other side of the structure 10 through the opening 18. At the same time, the electrode pack 17 is sealed to the holding block 13. Tightness is additionally secured with an elastic material. Besides the conical shape, a suitable shoulder, for example, can be used.

Advantageously, the thickness of the electrode pack is substantially the same as or smaller than the thickness of the holding block. Then the whole electrode pack fits inside the holding block and sealing of the electrode element is easy and secure. More generally, the thickness of the electrode pack is substantially the same as or smaller than the space formed between the outer surface of the holding block and the inner surface of a mounting flange. Thus, in practice, the empty space formed by the mounting flange and the holding block is filled for ensuring sealing and the resistance of the structure. The arrangement further includes a mounting flange 19 for connecting the electrode pack 17 to the holding block 13. Between the mounting flange 19 and the holding block 13, a flange seal 20 is addi- tionally used and the mounting flange 19 is connected with a suitable number of bolts 21. The electrode components 12 in- elude a cabling arrangement 22 for which the mounting flange 19 includes double-sealed lead-throughs 23. Firstly, a seamless pipe 21, closed with a threaded plug 26, is welded to the mounting flange 19, at the bore 24 arranged for the cabling 22. In addition, nipples 27 provided with sealing flanges 28 are welded to both the bore 24 and the pipe 25.

Figure 2b shows an electrode pack 17 both as a whole and with the main parts disassembled. According to the invention, the electrode pack 17 includes a plate electrode 29 which is here cast as an integral part of the electrode pack 17. Figure 2b shows an insulating sleeve 30, inside which the plate electrode 29 is cast using an electrically non-conductive material. Alternatively, the plate electrode can be cast directly to an electrically non-conductive material in which case a separate insulating sleeve is not necessary. Advantageously, the plate electrode has stiffening ribs 31 which ensure secure adhesion. A titan plate with an oxide or platinum coating is advantageously used. For example, an MMO coating (Mixed Metal Oxide) is resistant and forms a catalyst bed. Then the electrode is not sacrificial, which means that it. is non-wearing. The insulating sleeve 30 has also a groove 32, which ensures the adhesion of the material. In addition, the insulating sleeve isolates the plate electrode from the holding block. Instead of a circular plate electrode, an oval plate electrode, for example, can be used. In the reference electrode, the titan plate is replaced with a clearly thicker cylinder, which is made of zinc, for example.

When performing an exemplary application, such as cathodic protection of a ship, the ship is drydocked and an opening is made on its side below the water line by flame cutting, for example. The holding block included in the electrode element is first welded to the opening, after which the electrode compo- nents are connected detachably to the holding block. A required number of electrode elements are installed both as anodes and reference electrodes and the electrode elements are connected to a power supply. A significant benefit is achieved particularly when servicing and replacing the electrode element later without the need of drydocking. According to the invention, 5 when removing the electrode element 11, a flexible membrane 33 is adapted outside the structure 10 at the electrode element 11, after which the electrode components 12 are removed from the holding block 13. This step is illustrated in Figure 3, wherein a so called diver's tarpaulin is spread as the membrane

10 33 at the holding block 13. Water 34 surrounding the structure presses the tarpaulin tightly against the structure. The tarpaulin can be maintained securely in place using magnets 35, for example. The tarpaulin may slightly collapse at the opening 18, but the electrode pack will push the tarpaulin ahead of it

15 during the installation. Using the solution according to the invention, the electrode pack can be replaced almost anywhere without drydocking. At the same time, it is unlikely that the electrode components get damaged.

20 Figure 1 shows an arrangement according to the invention as a whole, however without a power supply and controls. The arrangement is compact and smaller in size than previously. Thus the electrode component can be installed even on a curved part of a ship. Moreover, the parts of the electrode component 11

25 are arranged substantially on the same level with the structure 10. Thus the surface is plane and smooth, which reduces the fuel consumption of the ship. In addition, the ice stress is smaller than in embodiments in which the electrode element protrudes from the surface of the structure. In one dimensio-

30 ning example, the outer diameter of the holding block is 455 mm and it has an opening of 310 mm for the electrode pack. The thickness of both the holding block and the electrode pack is 50 mm and the mounting flange 19 is connected with twelve bolts 21.

35 In Figure 4a, a threaded connection is provided between the holding block 13 and the electrode pack 17. In other words, the holding block 13 has an internal thread 36 and the corresponding external thread 37 is in the insulating sleeve 30 of the electrode pack 17. In addition, particularly in smaller applications subjected to low loads, even the holding block can be joined to the structure with a threaded connection (not shown) . For ensuring tightness, a suitable seal 38 can be used between the holding block 13 and the electrode pack 17. In addition, Figures 4a-c show a design, such as the groove 39, which locks the insulating sleeve 30 to the casting material 41. A corresponding design, such as the groove 40, can be adapted to lock the plate electrode 29 to the casting material 41. In the embodiments shown in Figures 4a-c, besides plastic, also steel can be used as the material for the insulating sleeve 30.

In Figure 4b the electrode pack 17 has a similar construction as in Figure 4a. Here the electrode pack 17 is adapted to an opening 18 formed in the structure 10 and an excessive protru- sion of the electrode pack 17 is prevented with a shoulder 42. In addition, the mounting flange 19 is connected with stud bolts 43 connected to the holding block 13. In the embodiment shown in Figure 4c, the stud bolts 43 are connected to the structure 10 in which case a separate holding block is com- pletely missing.

The embodiment of Figure 5 corresponds greatly to the embodiment of Figure 1. However, here the electrode pack 17 and its installation are different. The plate electrode 29 has a plate-like design with a conical collar that also functions as a stiffener. Then the plate electrode 29 creates a form-fitting connection with the inner hole of the insulating sleeve 30. During the installation, the plate electrode 29 is pressed in place using the mounting flange 19 and the flange seal 20. In this embodiment, the flange seal 20 substantially covers the entire holding block 13 and it also functions as insulation. Thus the form-fitting connection becomes tightly sealed . The plate electrode can thus be a mere plate-like component with an insulated conductor 22 ' attached at it s center . The plate electrode can be installed as such or it is f illed up with casting material up to the edges during the installation . In other words , a current supply plate electrode can be separate without other insulators , in which case forming of the electrode pack is delayed until to the installation . Then a suitable arrangement can be formed out of suitable components at the installation site . A plate-l i ke plate e lect rode can of course be used in prefabricated electrode packs as well .

Regardless of the construction, all embodiments of the invention obviate drydocking that was previously required in the maintenance work. After the initial installation, the electrode pack and the constructions required for holding it in place can be replaced by disassembling the arrangement only on the so called dry side of the structure . In demanding applications , the structure to be protected is a metal ship or a pressure vessel . Specific characteristics are demanded from these, such as the strength of the structures used compared to the strength of the original structure without an opening . Then the ship endures the ice conditions and meets the strength requirements . The strength is increased by the holding block, connected by welding, which is clearly thicker than the thickness of the structure . The electrode element is resistant even as such .

Claims

1. Electrode element for electrochemical protection which is prefabricated and adapted to be tightly connected to a structure (10) to be protected located in a medium and which includes electrode components (12) extending to the medium, characterized in that the electrode components (12) are arranged in the electrode element non-destructively and detach- ably.

2. Electrode element according to claim 1, characterized in that the electrode element (11) includes a holding block (13) adapted to be tightly connected to the structure (10) and that the electrode components (12) are arranged in contact with the holding block (13) non-destructively and detachably.

3. Electrode element according to claim 1 or 2, characterized in that the electrode components (12) are adapted as a prefabricated electrode pack (17), an opening (18) correspond- ing to the external dimensions thereof being arranged in the holding block (13).

4. Electrode element according to claim 3, characterized in that the opening (18) is at least partly conical.

5. Electrode element according to claim 3, characterized in that the opening (18) or the electrode pack (17) is provided with a shoulder (42) .

6. Electrode element according to any of claims 3 - 5, characterized in that the thickness of the electrode pack (17) is substantially the same as or smaller than the thickness of the holding block (13) .

7. Electrode element according to any of claims 3 - 6, characterized in that the electrode element further includes a mounting flange (19) for fastening the electrode pack (17) to the holding block (13) .

8. Electrode element according to claim 7, characterized in that the mounting flange (19) includes double- sea led lead-throughs (23) for a cabling arrangement (22) included in the electrode components (12) .

9. Electrode element according to any of claims 3 - 8, characterized in that the electrode pack (17) includes a plate electrode (29) which is cast as an integral part of the electrode pack (17 ) .

10. Method for connecting an electrode element, wherein one or more prefabricated electrode elements (11) including electrode components (12) that extend to a medium for arranging electrochemical protection are tightly connected to a structure (10) to be protected located in the medium, characterized in that the electrode components (12) are connected to the elec- trode element (11) non-destructively and detachably.

11. Method according to claim 10, characterized in that, before connecting the electrode components (12) , a holding block (13) included in the electrode element (11) is tightly connected to the structure (10) , after which the electrode components (12) are connected to the holding block (13) non-destructively and detachably.

12. Method according to claim 10 or 11, characterized in that, when removing the electrode element (11) , a flexible membrane (33) is adapted outside the structure (10) at the electrode element (11) , after which the electrode components (12) are removed.

13. Method according to any of claims 10 - 12, characterized in that the holding block (13) is welded to an opening (14) made in the structure (10) to be protected.

14. Arrangement in electrochemical protection, wherein one or more prefabricated electrode elements (11) including electrode components (12) that extend to a medium are tightly connected to a structure (10) to be protected located in the medium, characterized in that the electrode components (12) are arranged in contact with the electrode element (11) non-destructively and detachably.

15. Arrangement according to claim 14, characterized in that the electrode element (11) includes a holding block (13) that is tightly connected to the structure (10), and that the electrode components (12) are arranged in contact with the holding block (13) non-destructively and detachably.

16. Arrangement according to claim 14 or 15, characterized in that the electrode element (11) included in the arrangement is according to any of claims 3 - 9.

17. Arrangement according to any of claims 14 - 16, characterized in that the parts of the electrode element (11) are arranged substantially on the same level with the structure (10).

18. Arrangement according to any of claims 14 - 17, characterized in that the structure (10) to be protected is a metal ship.

19. Arrangement according to any of claims 14 - 17, characterized in that the structure (10) to be protected is a metal pressure vessel.