JP5402177B2 - The galvanic anode body and the galvanic anode method - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a galvanic anode body and a galvanic anode method for sacrificial corrosion protection of structures built on the sea, in harbors or brackish waters.

  In the corrosive environment such as offshore, harbor and brackish water area, it is necessary to apply appropriate anti-corrosion means when constructing a structure with a material such as steel that is susceptible to corrosion. As an anticorrosion means, an anticorrosion method for supplying an anticorrosion current to a structure using an external power source or a sacrificial metal, or a method using an anticorrosion film such as painting is often employed.

  Among the cathodic protection methods, the galvanic anode method in which a galvanic anode body made of a sacrificial metal is attached to the structure has been widely adopted for ease of maintenance. FIG. 1 is a conceptual diagram of the galvanic anode method. By sacrificing the sacrificial metal having a lower corrosion potential than that of steel, the anticorrosion current I is supplied from the galvanic anode body 1 to the steel structure 3, and thus the elution (corrosion) of the steel structure 3. Is prevented. FIGS. 8A and 8B show an example 101 of a galvanic anode body, which includes a polyhedral galvanic anode 105 and a pair of tabs 109. The galvanic anode body 101 is fixed to the structure using the tab 109 and is also electrically connected. Patent Documents 1 and 2 and Non-Patent Document 1 disclose related technologies related to cathodic protection.

  Patent document 3 is disclosing the related technique which protects a structure with a membrane | film | coat.

Japanese Examined Patent Publication No. 2-54421 JP-A-6-235081 JP 2005-320602 A

Japan Society for the Promotion of Science: Handbook of Metal Corrosion Protection Technology (Nikkan Kogyo Shimbun) (1978)

  As pointed out in Patent Document 2, it is frequently observed that the anticorrosion current changes after the galvanic anode body is installed. Non-Patent Document 1 conceptually shows changes in anticorrosion current as shown in FIG. 9 (Japan Society for the Promotion of Science: Metal Anticorrosion Technology Handbook, Nikkan Kogyo Shimbun (1978), page 595) As shown. If the number and arrangement of the galvanic anodes are designed based on the initial current density, it is expected that the corrosion protection will be insufficient when the current density decreases. Therefore, usually, the number and arrangement of the galvanic anodes are designed by taking into account the empirical knowledge and the like and expecting a steady value after the decrease. However, according to the study by the inventors, the anticorrosion current can still change even after reaching a steady state. Under such circumstances, it is not easy to guarantee the anticorrosion performance for a very long time.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a galvanic anode body and a galvanic anode method capable of supplying a stable anticorrosion current over a long period of time even after installation. is there.

According to the first aspect of the present invention, the galvanic anode body includes a tab made of a metal for fixedly connecting to a metal structure to be protected against corrosion, and a corrosive potential lower than that of the metal structure. The sacrificial metal is electrically and structurally connected to the tub and has two or more surfaces, and at least one surface selected from the surfaces is prevented from being eluted. And a covering body that restricts elution of the sacrificial metal only to the remaining surface, and the galvanic anode has a facing surface facing the metal structure, a facing surface opposite to the facing surface , And the covering body covers only the opposite surface or only the side surface.

  Alternatively, preferably, the sacrificial metal is made of any one selected from the group consisting of aluminum, zinc, magnesium, an aluminum alloy, a zinc alloy, and a magnesium alloy.

According to the second aspect of the present invention, the galvanic anode method includes a tab made of metal for fixedly connecting to a metal structure to be protected against corrosion, and a corrosive potential lower than that of the metal structure. A galvanic anode body comprising a sacrificial metal and electrically and structurally connected to the tub and having two or more surfaces, and having at least one surface selected from the surfaces Covering the sacrificial metal to prevent elution of the sacrificial metal and restricting the elution of the sacrificial metal only to the remaining surface, and connecting the galvanic anode body to the metal structure fixedly and electrically by the tab. The galvanic anode comprises six surfaces including a facing surface facing the metal structure, a facing surface opposite to the facing surface, and a side surface, and the covering includes only the facing surface or the Cover only the sides.

Preferably, in the galvanic anode method, before the galvanic anode body is fixedly and electrically connected to the metal structure, an anode is installed to face the metal structure in seawater or brackish water, The method further includes electrolyzing the seawater or brackish water with the metal structure as a cathode to electrodeposit the product onto the structure.

  Provided are an galvanic anode body and an galvanic anode method capable of supplying a stable anticorrosion current over a long period of time even after installation.

FIG. 1 is a conceptual diagram showing an aspect of anticorrosion by the galvanic anode. FIG. 2 is a three-side view of a galvanic anode body according to an embodiment of the present invention. FIG. 3 is a cross-sectional view of the galvanic anode body. FIG. 4 is a plan view of a galvanic anode body according to a modification. FIG. 5 is a cross-sectional view of a galvanic anode body according to another modification. FIG. 6 is a cross-sectional view of a galvanic anode body according to still another modification. FIG. 7 is a cross-sectional view of a galvanic anode body according to another modification. FIG. 8 is a three-side view and a cross-sectional view of a galvanic anode body according to a conventional example. FIG. 9 is an example of a graph showing a change in current density supplied by the galvanic anode body according to the conventional example.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  Referring to FIG. 8C, which is a cross-sectional view of the galvanic anode body 101 according to the conventional example, the initial sacrificial metal 105 usually has a clearly trapezoidal trapezoidal or rectangular cross section. The sacrificial metal 105 ′ after a lapse of a certain period changes to an irregular cross section with rounded corners as shown in FIG. In the figure, the alternate long and short dash line represents the initial surface. According to what the present inventors have clarified by comparing the potential before and after the change, and further by analyzing the potential distribution around the galvanic anode body, the electric field is concentrated around the corner, and further to the ocean current. Since it was most strongly affected, it was estimated that the elution from the corner became the most active and the corner disappeared quickly. It was also estimated that the reduction in surface area caused by such a shape change and the disappearance of the corner that supplies the largest anticorrosion current would result in a long-term change in the anticorrosion current.

  Considering based on the above-mentioned knowledge, if the surface of the sacrificial metal is appropriately coated to remove the influence of corners and only a specific surface is exposed, uniform elution can be expected from this surface. If it elutes uniformly, the shape of such a surface does not change and the area is almost unchanged, so that it can be expected that a stable anticorrosive current can be supplied over a long period of time.

  Therefore, according to one embodiment of the present invention, as shown in FIG. 2, the galvanic anode body 1 includes a tab 9 made of metal for fixedly connecting to a metal structure to be protected against corrosion, and the metal structure. A galvanic anode 5 made of any sacrificial metal having a more corrosive corrosion potential, electrically and structurally connected to the tub 9 and having two or more surfaces, and the galvanic anode One or more surfaces of 5 are covered with a covering 7. Such a covering 7 prevents elution of the sacrificial metal from the coated surface, and restricts the elution of the sacrificial metal only to the remaining uncoated surface 5A.

  The galvanic anode 5 is preferably an elongated hexahedron, and the hexahedron usually includes an opposing surface facing the metal structure and an opposing surface on the opposite side. The covering 7 covers two or more surfaces selected from the six surfaces. In the example of FIG. 3, the opposing surface and the opposite surface are left exposed and a pair of side surfaces are covered. Since the upper and lower exposed surfaces 5A do not have corners, the upper and lower exposed surfaces 5A are eluted uniformly to supply the anticorrosion current I to the metal structure. Preferably, the covering body 7 has a mode in which the covering body 7 protrudes slightly above and below the exposed surface 5A in order to reduce the influence of both side ends of the exposed surface 5A.

  The material of the covering 7 needs to be kept in close contact with the galvanic anode 5 for a sufficiently long period. Examples of such materials include tar epoxy, modified epoxy, FRP, and glass flake paint, but of course not limited thereto.

  As the sacrificial metal, when the structure to be protected against corrosion is made of steel, any metal or alloy having a lower corrosion potential than iron can be applied. Examples of such metals or alloys include aluminum, zinc, magnesium, and alloys thereof, but of course not limited thereto.

  In order to further reduce the influence of the corners, both end faces to which the tab 9 is connected may be further covered with a covering 7 'as shown in FIG.

  Or as shown in FIG. 5, it is good also as an exposed surface 25A to cover also the opposing surface which opposes a metal structure, and only an opposite surface. Since the opposing surface is very close to the target structure, the anticorrosion current is preferentially supplied only to the vicinity thereof. Since only the opposite surface is exposed, the anticorrosion current can be supplied uniformly over a longer distance.

  The cross-sectional shape of the galvanic anode is not limited to the trapezoid as shown in FIGS. 3 and 5, but may be a rectangle as shown in FIG. 6 or another shape. The rectangular galvanic anode 35 as shown in FIG. 6 can supply a more stable anticorrosion current because the surface area of the exposed surface 35A is not changed even if wear progresses.

  Furthermore, the covering may cover other surfaces instead of the both side surfaces. FIG. 7 shows such an example, and the covering 47 covers the opposing surface and the opposite surface, and both side surfaces are exposed surfaces 45A. Since the opposing surface and the opposite surface have different current densities compared to the other surfaces, uniform elution is difficult. That is, the opposing surface tends to elute more quickly and the opposite surface tends to elute more slowly. Since both sides can be eluted more uniformly than these, the galvanic anode 45 can supply a more stable anticorrosion current.

  Although the galvanic anode body 1 by each above-mentioned embodiment can be applied to steel structures, such as a floating structure, a steel sheet pile quay, a caisson, etc. constructed in the sea, a harbor, or a brackish water area, it is not restricted to these. The galvanic anode body 1 is fixed to the steel structure through a tab 9 by an appropriate method such as welding. Fixing can be used not only by welding but by any method suitable for electrical and structural connections. In any embodiment, at the beginning of installing the galvanic anode body, a rapid change in the anticorrosion current as illustrated in FIG. 9 can occur. However, since there is no change in the anticorrosion current caused by the change in shape and surface area, when the steady state is reached after a certain period, the subsequent anticorrosion current has a very small fluctuation. Therefore, the galvanic anode body can supply a stable anticorrosion current over a long period of time, thereby extending the life of the steel structure from the viewpoint of anticorrosion.

  The galvanic anode body 1 according to each embodiment can be applied to a structure provided with an anticorrosion film. For example, the anticorrosion film can be applied in advance by the following method. First, in seawater or brackish water, an anode is installed to face the installed structure, and the structure is used as a cathode, and current is supplied using an external power source to electrolyze the seawater or brackish water. The product is electrodeposited onto the structure. Alternatively, further, the supply of current is stopped for a period of time to at least partially replace such products with insoluble components in seawater or brackish water. The structure having the anticorrosive film thus obtained is anticorrosive by fixing the galvanic anode 1 by the same method as described above.

  When applied to a structure provided with an anticorrosion film, the galvanic anode body 1 according to each embodiment not only protects the structure, but also prevents the anticorrosion film from deteriorating and peeling off, and thus has an extremely long period of time. Has the anticorrosive effect.

  Although the present invention has been described with reference to preferred embodiments, the present invention is not limited to the above-described embodiments. Based on the above disclosure, a person having ordinary skill in the art can implement the present invention by modifying or modifying the embodiment.

  Provided are an galvanic anode body and an galvanic anode method capable of supplying a stable anticorrosion current over a long period of time even after installation.

1 Current-flow anode body 5, 25, 35, 45 Current-flow anode 5A, 25A, 35A, 45A Exposed surface 7, 7 ', 27, 37, 47 Cover 9 Tab

Claims (4)

A tab made of metal for fixed connection with a metal structure to be protected against corrosion;
An galvanic anode made of any sacrificial metal having a lower corrosion potential than the metal structure, electrically and structurally connected to the tab, and having two or more faces;
One or more surfaces selected from the surfaces are coated to prevent the elution of the sacrificial metal, and a covering for restricting the elution of the sacrificial metal only to the remaining surface;
In a galvanic anode body with
The galvanic anode is composed of six surfaces including an opposing surface facing the metal structure, an opposing surface opposite to the opposing surface, and a side surface, and the covering is only the opposite surface or only the side surface. A galvanic anode body, characterized in that it is coated while leaving   The galvanic anode body according to claim 1, wherein the sacrificial metal is selected from the group consisting of aluminum, zinc, magnesium, an aluminum alloy, a zinc alloy, and a magnesium alloy. A tab made of metal for fixed connection with a metal structure to be protected against corrosion, and any sacrificial metal having a lower corrosion potential than the metal structure, and is electrically and structurally connected to the tab. A galvanic anode body comprising a galvanic anode having two or more surfaces and covering at least one surface selected from the surfaces to prevent the sacrificial metal from eluting. Regulate only the remaining surface,
Connecting the galvanic anode body to the metal structure fixedly and electrically by the tab;
In galvanic anode method consists in,
The galvanic anode is composed of six surfaces including an opposing surface facing the metal structure, an opposing surface opposite to the opposing surface, and a side surface, and the covering is only the opposite surface or only the side surface. The galvanic anode method, characterized in that the coating is carried out leaving behind. Before the galvanic anode body is fixedly and electrically connected to the metal structure, an anode is installed to face the metal structure in seawater or brackish water, and the seawater is used as the cathode. Or electrolyze the brackish water to electrodeposit the product onto the structure,
The galvanic anode method according to claim 3 , further comprising:

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