Method for preventing crevice corrosion and corrosion-proof structure of flange connection part

Abstract

To provide: a method for preventing crevice corrosion applicable to a large diameter flange; and a corrosion-proof structure of a flange connection part.SOLUTION: A method for preventing crevice corrosion includes: disposing an anode 20 on a surface of the flange 10 so as to store the surface of the flange 10 in a potential gradient formed by the anode 20; and degrading a potential of the flange 10 so as to extinguish a potential difference between portions in the flange 10. A plurality of anodes 20 are placed at intervals along a circumferential direction of the flange 10.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for preventing crevice corrosion and a corrosion-resistant structure for flange connections. [Background technology]

[0002] Crevice corrosion may occur at flange connections of stainless steel piping. For example, the proximity anode method described in Non-Patent Document 1 is a method for preventing crevice corrosion. For example, the anode material used in the proximity anode method is "Saskett (registered trademark)" manufactured by Softem Co., Ltd. described in Non-Patent Document 2. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Katsumune Okamoto, “Corrosion Prevention Technology for Buried Pipes Using the Proximity Anode Method”, [online], May 20, 1985, Nakagawa Anticorrosion Technical Report, No. 28, p. 8-12, [Retrieved November 18, 2022], Internet<URL:https: / / jglobal.jst.go.jp / detail?JGLOBAL_ID=200902036997323250> [Non-Patent Document 2] Softem Co., Ltd., "High-purity zinc anode "Saskett"", [online], [searched on November 18, 2022], Internet<URL:https: / / premium.ipros.jp / softem / catalog / detail / 468339 / > Summary of the Invention [Problem to be solved by the invention]

[0004] The conventional "Sasket (registered trademark)" is formed by coating the back side of a foil of high-purity zinc anode material with a conductive adhesive, and then processing it into a shape that meets the gasket specifications. However, depending on the width of the raw material, foil-shaped high-purity zinc anode material, there is an issue that it is not possible to supply products that can be used for large diameter flanges (for example, outer diameter of 200 mm or more).

[0005] The present invention has been made in consideration of the above-mentioned circumstances, and has an object to provide a method for preventing crevice corrosion that is applicable to large-diameter flanges, and a corrosion-resistant structure for flange connections. [Means for solving the problem]

[0006] <1> A method for preventing crevice corrosion according to a first aspect of the present invention is a method for preventing crevice corrosion by arranging an anode on a surface of a flange, absorbing the surface of the flange in a potential gradient formed by the anode, thereby making the potential of the flange less noble, thereby eliminating the potential difference between each portion of the flange, and the anodes are arranged at intervals along the circumferential direction of the flange.

[0007] According to the present invention, anodes are arranged on the surface of the flange to prevent crevice corrosion, and are arranged at intervals along the circumferential direction of the flange. This allows the size of each anode to be smaller than when an anode integrally formed to match the size of the flange is used. Even when the size of the anode is reduced in this way, a sufficient number of anodes can be arranged for the flange by appropriately changing the intervals and number of anodes. Therefore, even when the width of the raw material of the anode (e.g., foil-shaped high-purity zinc anode material) is insufficient and an anode integrally formed for a large-diameter flange cannot be supplied, the anode can be applied by the method according to the present invention.

[0008] <2> A method for preventing crevice corrosion according to a second aspect of the present invention is a method for preventing crevice corrosion by placing an anode on a surface of a flange, immersing the surface of the flange in a potential gradient formed by the anode, thereby making the potential of the flange less noble, thereby eliminating the potential difference between each portion of the flange, wherein the flange is annular and has a plurality of bolt holes spaced circumferentially, and the anode is arranged in an annular shape between an inner peripheral edge of the flange and a plurality of the bolt holes.

[0009] According to this invention, the anode arranged on the surface of the flange to prevent crevice corrosion is arranged in an annular shape between the inner peripheral edge of the annular flange and a plurality of bolt holes provided in the flange. This allows, for example, the diameter of the anode to be made smaller than the diameter of the flange. Therefore, for example, it is possible to reduce the number of cases where the width of the raw material for the anode is insufficient for a flange with a large diameter. Even if the width of the raw material for the anode is insufficient, an anode of an appropriate size can be formed by processing a strip-shaped or linear raw material into an annular shape. Therefore, for example, even if the width of the raw material for the anode is insufficient and an anode formed integrally with a flange with a large diameter cannot be supplied, the anode can be applied by the method according to the present invention.

[0010] <3> A method for preventing crevice corrosion according to a third aspect of the present invention is the method for preventing crevice corrosion according to the first or second aspect, wherein the anode is a foil- or plate-shaped high-purity zinc anode.

[0011] According to the present invention, the anode used for preventing crevice corrosion is a foil or plate-shaped high-purity zinc anode, which can effectively prevent crevice corrosion.

[0012] <4> A method for preventing crevice corrosion according to a fourth aspect of the present invention is the method for preventing crevice corrosion according to any one of the first to third aspects, wherein the anode is a composite zinc anode, and the composite zinc anode comprises a foil-shaped zinc tape or a plate-shaped zinc anode and an anode paste.

[0013] According to this invention, the anode used to prevent crevice corrosion is a composite zinc anode. The composite zinc anode includes a foil-shaped zinc tape or a plate-shaped zinc anode, and an anode paste. By using the anode paste in addition to the foil-shaped zinc tape or plate-shaped zinc anode, it becomes easier to maintain the anode potential in the gap between the zinc anodes. In addition, the anode paste can be used to fill the gap between the zinc anodes when small pieces of zinc anodes are used, and to eliminate the step with the flange surface, so that the composite zinc anode can be flexibly adapted to the shape of the flange. Furthermore, it is possible to suppress the occurrence of gaps on the surface of the flange. Therefore, it is possible to effectively prevent crevice corrosion.

[0014] <5> The corrosion protection structure for a flange connection according to aspect 5 of the present invention is a structure for preventing crevice corrosion of the flange, the flange having a plurality of recesses spaced apart along a circumferential direction of the flange, and an anode is disposed in the recess.

[0015] According to the present invention, the flange includes a plurality of recesses spaced apart from each other along the circumferential direction, and an anode is disposed in the recess. This allows, for example, the flange connection portion to have a structure that easily prevents crevice corrosion. In addition, the size of each anode can be made smaller than when an anode integrally formed to match the size of the flange is used. Even when the size of the anode is reduced in this way, a sufficient number of anodes can be disposed on the flange by appropriately changing the interval and number of recesses. Therefore, for example, even when the width of the raw material of the anode (for example, foil-shaped high-purity zinc anode material) is insufficient and an anode integrally formed on a large-diameter flange cannot be supplied, the anode can be applied by the method according to the present invention. Furthermore, by reducing the size of each anode, the anode can be easily disposed on the flange. Therefore, the workability at the construction site can be improved.

[0016] <6> A corrosion protection structure for a flange connection part according to aspect 6 of the present invention is a corrosion protection structure for a flange connection part according to aspect 5, wherein the flange is annular and has a plurality of bolt holes spaced circumferentially, and the recess is arranged 5.0 mm away from the bolt hole, has a flat bottom, and has a depth of 1.0 mm or more and 3.0 mm or less.

[0017] According to this invention, the recess is provided 5.0 mm away from the bolt hole of the flange. This prevents the recess and the anode placed in the recess from interfering with the mounting when the flange is mounted to another component with a bolt. The recess has a flat bottom and a depth of 1.0 mm to 3.0 mm. This allows the recess to have a shape and size sufficient for disposing the anode.

[0018] <7> A corrosion protection structure for a flange connection according to a seventh aspect of the present invention is the corrosion protection structure for a flange connection according to the fifth or sixth aspect, in which the recess is formed in a flat shape, and the anode is plate-shaped or foil-shaped.

[0019] According to this invention, the depressions are formed in a planar shape, and the anodes are plate-shaped or foil-shaped. This allows the anodes to be placed in the depressions one by one. This makes it easy to align the depressions and the anodes, improving workability.

[0020] <8> The corrosion protection structure for a flange connection part of aspect 8 of the present invention is the corrosion protection structure for a flange connection part of aspect 7, wherein the recess is circular and the center of the recess is positioned so as to be located on an imaginary circle centered on the center of the flange.

[0021] According to this invention, the recesses are circular. As a result, when the anodes are placed in the recesses, the anodes can be placed in the recesses one by one. This makes it easy to align the recesses with the anodes, improving workability. In addition, the centers of the recesses are arranged to be located on a virtual circle centered on the center of the flange. In this way, by aligning the distance from the center of the flange to the center of the recesses, the anodes can be evenly arranged along the circumferential direction of the flange.

[0022] <9> The corrosion protection structure for a flange connection according to aspect 9 of the present invention is a structure for preventing crevice corrosion of the flange, wherein the flange is annular and has a plurality of bolt holes spaced circumferentially, and has annular recesses between the inner peripheral edge of the flange and the bolt holes, and an anode is disposed in the recess.

[0023] According to this invention, the flange has a recess, and an anode is disposed in the recess. This makes it easier to dispose the anode on the flange. This improves workability at the construction site. The recess is also provided between the inner peripheral edge of the flange and the plurality of bolt holes. This makes it possible to prevent, for example, the anode from shifting position after the flange is attached to another component with bolts, causing the anode to come out from between the flange and the other component. This makes it possible to provide the flange connection portion with a structure that makes it easier to prevent crevice corrosion.

[0024] The recess is provided in an annular shape between the inner peripheral edge of the annular flange and a plurality of bolt holes provided in the flange. This allows the diameter of the anode to be reduced, for example, by making the diameter of the recess smaller than the diameter of the flange. This reduces the number of cases where the width of the raw material for the anode is insufficient for a large-diameter flange. Even if the width of the raw material for the anode is insufficient, an anode of an appropriate size can be formed by processing a strip-shaped or linear raw material into an annular shape. Therefore, even if the width of the raw material for the anode is insufficient and an anode formed integrally with a large-diameter flange cannot be supplied, the anode can be applied by the method according to the present invention.

[0025] <10> The corrosion protection structure for a flange connection part of aspect 10 of the present invention is the corrosion protection structure for a flange connection part of aspect 9, in which the recess is arranged 5.0 mm away from the bolt hole, has a flat bottom surface, and has a depth of 1.0 mm or more and 3.0 mm or less.

[0026] According to this invention, the recess is provided 5.0 mm away from the bolt hole of the flange. This prevents the recess and the anode placed in the recess from interfering with the mounting when the flange is mounted to another component with a bolt. The recess also has a flat bottom and a depth of 1.0 mm to 3.0 mm. This allows the recess to have a shape and size sufficient for disposing the anode.

[0027] <11> The corrosion protection structure for a flange connection part of aspect 11 of the present invention is a corrosion protection structure for a flange connection part of any one of aspects 5 to 10, in which the recess and the anode have the same shape and dimensions, and the part of the flange other than the recess and the anode are flush with each other.

[0028] According to this invention, the recess and the anode have the same shape and the same dimensions. This makes it possible, for example, to prevent the waterproof function of the flange from being impaired. The part of the flange other than the recess and the anode are flush with each other. This makes it possible to prevent the waterproof function of the flange from being impaired.

[0029] <12> A corrosion protection structure for a flange connection according to a twelfth aspect of the present invention is the corrosion protection structure for a flange connection according to any one of the fifth to eleventh aspects, in which an anode paste is disposed on the contact surface between the anode and the recess.

[0030] According to this invention, the anode paste is disposed on the contact surface between the anode and the recess, whereby the gap between the anode and the recess can be filled with the anode paste, thereby strengthening the electrical connection between the flange and the anode. Effect of the Invention

[0031] According to the present invention, it is possible to provide a method for preventing crevice corrosion that is applicable to large diameter flanges and a corrosion-resistant structure for flange connections. [Brief description of the drawings]

[0032] [Figure 1] This is the first example of a flange connection. [Diagram 2] This is a second example of a flange connection. [Diagram 3] This is a diagram showing the potential gradient (anode effect range) formed when a magnesium anode is installed in a part of a pipeline placed in a high resistivity electrolyte (soil). [Figure 4] FIG. 1 is a diagram showing the potential gradient (anode effect range) formed when a zinc anode is placed on a flange surface. [Diagram 5] FIG. 2 is a diagram showing the state of the connection between the zinc anode and the anode paste in a composite zinc anode. [Figure 6] FIG. 1 is a diagram showing a conventional example in which an annular, integrally molded zinc anode is disposed on a flange surface. [Figure 7]1 is a conventional zinc anode integrally molded into an annular shape. [Figure 8] This is an example in which multiple flat recesses are formed on the flange surface. [Figure 9] This is an example in which multiple circular depressions are formed on the flange surface. [Figure 10] This is an example in which an annular recess is formed on the flange surface. [Figure 11] FIG. 13 is a diagram showing a state in which anode paste has been applied to the contact surface between the recess on the flange surface and the zinc anode placed in the recess in order to strengthen the electrical connection. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] Hereinafter, a corrosion prevention structure for a flange connection portion 100 and a method for preventing crevice corrosion of the flange connection portion 100 according to one embodiment of the present invention will be described with reference to the drawings. The structure and method according to the present invention are used to prevent crevice corrosion that occurs, for example, at a flange connection 100 of a stainless steel pipe S as shown in Fig. 1 or 2. The structure and method according to the present invention use a proximity anode method, which is a type of cathodic protection using a galvanic anode method.

[0034] (How to prevent crevice corrosion) In this embodiment, crevice corrosion is prevented by eliminating the potential difference between each portion of the flange 10. Figure 3 is a graph showing the relationship between the distance from the magnesium anode to the pipeline and the potential when the magnesium anode is disposed in a portion of the pipeline disposed in a high resistivity electrolyte (soil). As shown in Figure 3, the potential of the portion of the pipeline where the magnesium anode is disposed is -1600 mV. The potential changes to approach 0 mV with increasing distance from the magnesium anode along the pipeline.

[0035] In this embodiment, by disposing the anode 20 on the surface of the flange 10, the surface of the flange 10 is contained within the potential gradient (anode effect range) formed by the anode 20, that is, within a region in the pipeline where the potential has a more negative value than other parts. This makes the potential of the flange 10 less noble, thereby eliminating the potential difference between each part of the flange 10. Note that, in order to prevent crevice corrosion of the flange 10, it is preferable that the potential at the location where the flange 10 is disposed is, for example, -1000 mV or less.

[0036] Fig. 4 is a graph showing the relationship between the distance from the zinc anode on the flange 10 and the potential when the zinc anode is placed on the surface of the flange 10. As shown in Fig. 4, even if the zinc anode is placed only on a part of the flange 10, it is possible to set the potential to -900 mV over the entire surface of the flange 10. Therefore, it is understood that even if the zinc anode is placed discretely on the surface of the flange 10, it is possible to prevent crevice corrosion over the entire flange 10 as long as the entire flange 10 is within the anode effect range. The following describes several examples of the form of the anode 20.

[0037] (First form of anode 20) In this embodiment, the anode 20 is, for example, a high-purity zinc anode. That is, the anode 20 is made of high-purity zinc (Zn≧99.995% or more). The high-purity zinc anode is, for example, formed in a foil or plate shape. In this embodiment, the term "foil" refers to a member having a thickness of 200 μm or less. The term "plate" refers to a member having a thickness of more than 200 μm. Hereinafter, the foil-shaped or plate-shaped high-purity zinc anode will be referred to as the foil-shaped zinc anode 20F and the plate-shaped zinc anode 20B, respectively. In the first form of the anode 20, the foil-shaped zinc anode 20F or the plate-shaped zinc anode 20B is placed in a recess 10d formed in the flange 10, for example, as shown in FIG. 1 (details will be described later).

[0038] (Second Form of Anode 20) As described above, instead of disposing the foil-shaped zinc anode 20F or the plate-shaped zinc anode 20B in the recess 10d, a composite zinc anode 30 may be provided on the surface of the flange 10. That is, the anode 20 according to the second embodiment is the composite zinc anode 30. When the composite zinc anode 30 is provided, the recess 10d may not be provided in the flange 10 as shown in FIG. The composite zinc anode 30 includes, for example, a foil-shaped zinc tape 30T and an anode paste 30P. Alternatively, the composite zinc anode 30 may include a plate-shaped zinc anode 20B and an anode paste 30P.

[0039] The zinc tape 30T is, for example, a foil-shaped zinc anode 20F coated with an adhesive. For example, "Saskette (registered trademark)" manufactured by Softem Co., Ltd. is preferably used as the zinc tape 30T. The plate-shaped zinc anode 20B used in the composite zinc anode 30 is, for example, a plate-shaped zinc anode 20B punched into a disk shape or other shape. The anode paste 30P is, for example, a mixture of zinc powder and an adhesive, etc. As the anode paste 30P, for example, "Metal Guard (registered trademark) Paste" manufactured by Softem Co., Ltd. is suitably used.

[0040] 2 and 5, the composite zinc anode 30 is formed by applying anode paste 30P around zinc tape 30T, foil-shaped zinc anode 20F or plate-shaped zinc anode 20B arranged on the surface of flange 10. At this time, as shown in FIG. 5, it is preferable that the zinc tape 30T, foil-shaped zinc anode 20F or plate-shaped zinc anode 20B and the anode paste 30P are flush with each other in the composite zinc anode 30.

[0041] Here, as shown in Figures 6 and 7, the anode 20 according to the conventional example is a foil-shaped zinc anode 20F or a plate-shaped zinc anode 20B integrally formed in the same annular shape as the joint surface of the flange. In this case, depending on the width of the high-purity zinc anode material used as the raw material, it was not possible to supply a product applicable to a large-diameter flange 10 (for example, an outer diameter of 200 mm or more).

[0042] To address the above-mentioned issues, in the first and second forms of the anode 20, the amount of the anode 20 placed on the flange 10 is appropriately adjusted according to the size of the flange 10. Note that the anode 20 here includes the foil-shaped zinc anode 20F, the plate-shaped zinc anode 20B, and the zinc tape 30T, but does not include the anode paste 30P. For example, as shown in Fig. 8 or 9, a plurality of anodes 20 are arranged at intervals along the circumferential direction of the flange 10. In this case, the amount of anodes 20 is adjusted by appropriately changing the intervals and number of the anodes 20. This form is suitably used in both the first and second forms of the anode 20 described above. Alternatively, the amount of anode 20 may be adjusted by using a strip-shaped or linear foil zinc anode 20F, a plate-shaped zinc anode 20B, or a zinc tape 30T as shown in Fig. 10, and determining the length of the anode 20 in accordance with the circumferential length of the flange 10. This form is particularly suitable for use in the first form of anode 20 described above, but may also be used in the second form.

[0043] (Regarding the corrosion-resistant structure of the flange connection portion 100) Next, a description will be given of the corrosion prevention structure of the flange connection portion 100 according to this embodiment. The corrosion prevention structure described below is a structure applied to the first embodiment of the anode 20 described above. As shown in FIG. 1, the flange connection portion 100 includes a flange 10 and an anode 20 . The flange 10 is provided at the end of the stainless steel pipe S. In this embodiment, the flange 10 is, for example, annular. The stainless steel pipes S are connected to each other by fastening the flanges 10 to each other with a bolt B and a nut N. Therefore, as shown in Figs. 8, 9, and 10, the flange 10 in this embodiment has a plurality of bolt holes 10h spaced apart along the circumferential direction of the flange 10. In addition, the surface of the flange 10 is provided with a recess 10d in which the anode 20 is placed. With the anode 20 placed in the recess 10d, the flanges 10 are fastened to each other with the bolt B and the nut N. In this way, the anode 20 is placed between the flanges 10, and the potential around the flanges 10 is made lower.

[0044] In this embodiment, a foil-shaped zinc anode 20F or a plate-shaped zinc anode 20B is used as the anode 20. The recess 10d and the anode 20 preferably have the same shape and dimensions. When the anode 20 is placed in the recess 10d, the anode 20 is preferably flush with the part of the flange 10 other than the recess 10d as shown in FIG. 11. In addition, an anode paste 30P may be placed on the contact surface between the anode 20 and the recess 10d. This is preferable to fill the gap between the anode 20 and the recess 10d. The following describes several examples of the shape of the recess 10d and the anode 20.

[0045] (First Form of Recess 10d and Anode 20) The recess 10d according to the first embodiment is provided between the outer peripheral edge and the inner peripheral edge of the flange 10, as shown in Fig. 8. The recess 10d is provided so as to be spaced 5.0 mm away from the bolt hole 10h. The recess 10d has a flat bottom surface and a depth of 1.0 mm to 3.0 mm. The recesses 10d according to the first embodiment are formed in a planar shape, and a plurality of recesses 10d are provided at intervals along the circumferential direction of the flange 10. The recesses 10d according to the first embodiment make it possible to adjust the amount of anodes 20 disposed in the recesses 10d by adjusting the size and intervals. In the recess 10d according to the first embodiment, the anode 20 is plate-shaped or foil-shaped. That is, in the recess 10d according to the first embodiment, the anode 20 is a planar foil-shaped zinc anode 20F, a plate-shaped zinc anode 20B, or a zinc tape 30T.

[0046] (Second Form of Recess 10d and Anode 20) The recess 10d according to the second embodiment is annular, as shown in FIG. 10. The recess 10d is provided between the inner peripheral edge of the flange 10 and the plurality of bolt holes 10h. The recess 10d is provided so as to be spaced 5.0 mm away from the bolt holes 10h. The recess 10d has a flat bottom surface and a depth of 1.0 mm to 3.0 mm. The length of the recess 10d according to the second embodiment in the circumferential direction of the flange 10 is determined by the size of the flange 10. This makes it possible to adjust the amount of anodes 20 disposed in the recess 10d. In the recess 10d according to the second embodiment, the anode 20 is a plurality of strip-shaped plate materials or annular wire materials. That is, in the recess 10d according to the second embodiment, a strip-shaped or wire-shaped foil zinc anode 20F, a plate-shaped zinc anode 20B, or a zinc tape 30T is disposed in the anode 20. That is, the length of the anode 20 disposed in the recess 10d according to the second embodiment is determined according to the circumferential length of the flange 10.

[0047] (Third Form of Recess 10d and Anode 20) 9, the recesses 10d according to the third embodiment are circular and provided at intervals in the circumferential direction of the flange 10. The recesses 10d are each provided 5.0 mm away from the bolt hole 10h. The recesses 10d are arranged such that their centers are located on an imaginary circle centered on the center of the flange 10. The amount of anode 20 disposed in the recess 10d according to the third embodiment can be adjusted by adjusting the size and interval of the recess 10d. In the recess 10d according to the third embodiment, the anode 20 is plate-shaped or foil-shaped. That is, in the recess 10d according to the third embodiment, the anode 20 is a foil-shaped zinc anode 20F, a plate-shaped zinc anode 20B, or a zinc tape 30T formed in a circular shape. By appropriately combining the above-described embodiments, a corrosion protection structure for a flange connection according to this embodiment is formed.

[0048] As described above, according to the method for preventing crevice corrosion of the present embodiment, the anodes 20 arranged on the surface of the flange 10 to prevent crevice corrosion are arranged at intervals along the circumferential direction of the flange 10. This allows the size of each anode 20 to be smaller than when, for example, an anode 20 formed integrally to match the size of the flange 10 is used. Even if the size of the anodes 20 is reduced in this way, a sufficient number of anodes 20 can be arranged on the flange 10 by appropriately changing the intervals and number of the anodes 20. Therefore, for example, even if the width of the raw material of the anodes 20 (for example, foil-shaped high-purity zinc anode material) is insufficient and an anode 20 formed integrally with a large-diameter flange 10 cannot be supplied, the anodes 20 can be applied by the method according to the present invention.

[0049] In addition, the anode 20 arranged on the surface of the flange 10 to prevent crevice corrosion is arranged in an annular shape between the inner peripheral edge of the annular flange 10 and the multiple bolt holes 10h of the flange 10. This allows, for example, the diameter of the anode 20 to be made smaller than the diameter of the flange 10. Therefore, for example, it is possible to reduce the number of cases where the width of the raw material of the anode 20 is insufficient for a large-diameter flange 10. Even if the width of the raw material of the anode 20 is insufficient, the anode 20 of an appropriate size can be formed by processing a strip-shaped or linear raw material into an annular shape. Therefore, for example, even if the width of the raw material of the anode 20 is insufficient and the anode 20 formed integrally with the large-diameter flange 10 cannot be supplied, the anode 20 can be applied by the method according to the present invention.

[0050] The anode 20 used to prevent crevice corrosion is a foil or plate-shaped high-purity zinc anode, which can effectively prevent crevice corrosion.

[0051] The anode 20 used to prevent crevice corrosion is a composite zinc anode 30. The composite zinc anode 30 includes a foil-shaped zinc tape 30T or a plate-shaped zinc anode 20B, and an anode paste 30P. By using the anode paste 30P in addition to the foil-shaped zinc tape 30T or the plate-shaped zinc anode 20B, it becomes easier to maintain the anode potential in the gap between the zinc anodes. In addition, the anode paste can be used to fill the gap between the zinc anodes when small pieces of zinc anodes are used, and to eliminate the step with the flange surface, so that the composite zinc anode 30 can flexibly respond to the shape of the flange 10. Furthermore, it is possible to suppress the occurrence of gaps on the surface of the flange 10. Therefore, it is possible to effectively prevent crevice corrosion.

[0052] According to the corrosion prevention structure of the flange connection part 100 of the present embodiment, the flange 10 includes a plurality of recesses 10d spaced apart from each other along the circumferential direction, and the anodes 20 are disposed in the recesses 10d. This allows the flange connection part 100 to have a structure that is easy to prevent crevice corrosion. In addition, the size of each anode 20 can be made smaller than when the anodes 20 are formed integrally with the flange 10 in accordance with its size. Even when the size of the anodes 20 is reduced in this manner, a sufficient amount of the anodes 20 can be disposed on the flange 10 by appropriately changing the interval and number of the recesses 10d. Therefore, even when the width of the raw material of the anodes 20 (for example, foil-shaped high-purity zinc anode material) is insufficient and the anodes 20 formed integrally with the flange 10 having a large diameter cannot be supplied, the anodes 20 can be applied by the method according to the present invention. Furthermore, by reducing the size of each anode 20, the anodes 20 can be easily disposed on the flange 10. This improves the workability at the construction site.

[0053] Moreover, the recess 10d is provided so as to be spaced 5.0 mm from the bolt hole 10h of the flange 10. This makes it possible to prevent the recess 10d and the anode 20 placed in the recess 10d from interfering with the attachment when the flange 10 is attached to another component with the bolt B. The recess 10d has a flat bottom surface and a depth of 1.0 mm or more and 3.0 mm or less. This makes it possible to provide a shape and size sufficient for placing the anode 20.

[0054] Moreover, the recess 10d is formed in a flat shape, and the anode 20 is in a plate or foil shape. This allows the anode 20 to be placed in the recess 10d, so that the anode 20 is placed in each of the recesses 10d. This makes it easy to align the recess 10d with the anode 20, improving workability.

[0055] Moreover, the recess 10d is circular. As a result, when the anode 20 is placed in the recess 10d, the anode 20 can be placed in each of the recesses 10d. This makes it easy to align the recess 10d with the anode 20, improving workability. Furthermore, the center of the recess 10d is arranged to be located on a virtual circle centered on the center of the flange 10. In this way, by aligning the distance from the center of the flange 10 to the center of the recess 10d, the anode 20 can be evenly arranged along the circumferential direction of the flange 10.

[0056] Moreover, the flange 10 has a recess 10d, and the anode 20 is disposed in the recess 10d. This allows the anode 20 to be easily disposed in the flange 10. This improves workability at the construction site. The recess 10d is provided between the inner peripheral edge of the flange 10 and the bolt holes 10h. This prevents the anode 20 from being displaced and coming out from between the flange 10 and the other component after the flange 10 is attached to the other component with the bolt B, for example. This allows the flange connection portion 100 to have a structure that easily prevents crevice corrosion.

[0057] The recess 10d is annularly provided between the inner peripheral edge of the annular flange 10 and the plurality of bolt holes 10h of the flange 10. This allows the diameter of the anode 20 to be reduced by, for example, reducing the diameter of the recess 10d relative to the diameter of the flange 10. This reduces the number of cases where the width of the raw material of the anode 20 is insufficient for a large-diameter flange 10. Even if the width of the raw material of the anode 20 is insufficient, the anode 20 of an appropriate size can be formed by processing a strip-shaped or linear raw material into a ring. Therefore, even if the width of the raw material of the anode 20 is insufficient and the anode 20 formed integrally with the large-diameter flange 10 cannot be supplied, the anode 20 can be applied by the method according to the present invention.

[0058] Moreover, the recess 10d is provided so as to be spaced 5.0 mm from the bolt hole 10h of the flange 10. This makes it possible to prevent the recess 10d and the anode 20 placed in the recess 10d from interfering with the attachment when the flange 10 is attached to another component with the bolt B. Moreover, the recess 10d has a flat bottom surface and a depth of 1.0 mm or more and 3.0 mm or less. This makes it possible to provide a shape and size sufficient for placing the anode 20.

[0059] Moreover, the recess 10d and the anode 20 have the same shape and the same dimensions. This can make it difficult to impair the waterproof function of the flange 10, for example. The portion of the flange 10 other than the recess 10d and the anode 20 are flush with each other. This can make it even difficult to impair the waterproof function of the flange 10.

[0060] Furthermore, anode paste 30P is placed on the contact surface between anode 20 and depression 10d. This allows anode paste 30P to fill the gap between anode 20 and depression 10d. This allows the electrical connection between flange 10 and anode 20 to be strengthened.

[0061] The technical scope of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, the flanges 10 do not have to have the bolt holes 10h. In this case, the flanges 10 may be connected to each other by a clamp member (not shown).

[0062] In addition, within the scope of the invention, the components in the above-described embodiments may be replaced with well-known components, and the above-described modified examples may be combined as appropriate. [Explanation of symbols]

[0063] 10 Flange 10d recess 10h Bolt hole 20 Anode 20B Plate-shaped zinc anode 20F Foil zinc anode 30 Composite zinc anode 30P Anode Paste 30T Zinc Tape 100 Flange connection B Bolt N Nut S Stainless steel piping

Claims

1. A method for preventing crevice corrosion, comprising the steps of: placing an anode on a surface of a flange, accommodating the surface of the flange in a potential gradient formed by the anode, and lowering the potential of the flange, thereby eliminating a potential difference between each portion of the flange, comprising: The anode is disposed at intervals along the circumferential direction of the flange. How to prevent crevice corrosion.

2. A method for preventing crevice corrosion, comprising the steps of: placing an anode on a surface of a flange, accommodating the surface of the flange in a potential gradient formed by the anode, and lowering the potential of the flange, thereby eliminating a potential difference between each portion of the flange, comprising: The flange is annular and includes a plurality of circumferentially spaced bolt holes; the anode is annularly disposed between an inner peripheral edge of the flange and the bolt holes; How to prevent crevice corrosion.

3. The anode is a foil or plate-shaped high-purity zinc anode; The method for preventing crevice corrosion according to claim 1 or 2.

4. the anode is a composite zinc anode, The composite zinc anode comprises: A zinc foil tape or a zinc plate anode; Anode paste; Equipped with The method for preventing crevice corrosion according to claim 1 or 2.

5. A structure for preventing crevice corrosion of a flange, The flange includes a plurality of recesses spaced apart along a circumferential direction of the flange, An anode is disposed in the recess. Corrosion-resistant structure at flange connection.

6. the flange is annular and includes a plurality of circumferentially spaced bolt holes; The depression is The bolt hole is spaced 5.0 mm from the bolt hole. The bottom surface is flat, The depth is 1.0 mm or more and 3.0 mm or less. The corrosion-resistant structure for a flange connection according to claim 5.

7. The recess is formed in a planar shape, The anode is in the form of a plate or foil. The corrosion-resistant structure for a flange connection according to claim 6.

8. The recess is circular, and the center of the recess is disposed so as to be located on an imaginary circle having a center at the center of the flange. The corrosion-resistant structure for a flange connection according to claim 7.

9. A structure for preventing crevice corrosion of a flange, The flange is annular and includes a plurality of circumferentially spaced bolt holes; a recess provided annularly between an inner peripheral edge of the flange and the bolt holes; An anode is disposed in the recess. Corrosion-resistant structure at flange connection.

10. The depression is The bolt hole is spaced 5.0 mm from the bolt hole. The bottom surface is flat, The depth is 1.0 mm or more and 3.0 mm or less. The corrosion-resistant structure for a flange connection according to claim 9.

11. the recess and the anode have the same shape and size; The portion of the flange other than the recess and the anode are flush with each other. The corrosion protection structure for a flange connection according to any one of claims 5 to 10.

12. An anode paste is disposed on the contact surface between the anode and the recess. The corrosion protection structure for a flange connection according to any one of claims 5 to 10.

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