Method for preventing crevice corrosion and corrosion-resistant structure for flange connections

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-protective structure for flange connections. [Background technology]

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

[0003] [Non-Patent Document 1] Okamoto Katsun, "Corrosion Protection Technology for Buried Pipes Using the Proximity Anode Method," [online], May 20, 1985, Nakagawa Anti-Corrosion Technical Report, No. 28, pp. 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 "Sasket"," [online], [searched 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 applying a conductive adhesive to the backside of a foil-shaped high-purity zinc anode material, and then processing it into a shape that meets the gasket specifications. However, depending on the width of the foil-shaped high-purity zinc anode material used as the raw material, there is an issue in that it is not possible to supply products that are suitable for large-diameter flanges (for example, outer diameters of 200 mm or more).

[0005] The present invention has been made in consideration of the above-mentioned circumstances, and an object of the present invention is to provide a method for preventing crevice corrosion that can be applied to large-diameter flanges, and a corrosion-protective 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 the 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 this invention, anodes are placed on the surface of a flange to prevent crevice corrosion, and multiple anodes are arranged at intervals along the circumferential direction of the flange. This allows the size of each anode to be smaller than, for example, when anodes integrally formed to fit the flange size are used. Even when the anode size is reduced in this way, a sufficient number of anodes can be arranged for the flange by appropriately adjusting the spacing and number of anodes. Therefore, even when the width of the anode raw material (e.g., foil-shaped high-purity zinc anode material) is insufficient and anodes integrally formed for a large-diameter flange cannot be supplied, anodes can be applied using the method of 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 the 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 annularly placed between the inner peripheral edge of the flange and the plurality of bolt holes.

[0009] According to this invention, an anode placed on the surface of a flange to prevent crevice corrosion is annularly arranged 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. This reduces the number of cases where the width of the anode raw material is insufficient for a large-diameter flange, for example. Even if the width of the anode raw material is insufficient, an anode of appropriate size can be formed by processing a strip-shaped or linear raw material into an annular shape. Therefore, even if, for example, the width of the anode raw material is insufficient and an anode integrally formed with a large-diameter flange cannot be supplied, the anode can be applied using the method of 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-shaped or plate-shaped high-purity zinc anode.

[0011] According to the present invention, the anode used to prevent crevice corrosion is a foil or plate-shaped high-purity zinc anode, which effectively prevents 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 gaps between the zinc anodes. Furthermore, the anode paste can be used to fill the gaps between the zinc anodes when small pieces of zinc anodes are used and to eliminate any unevenness with the flange surface, allowing the composite zinc anode to flexibly adapt to the shape of the flange. Furthermore, it is possible to prevent gaps from forming on the flange surface. Therefore, crevice corrosion can be effectively prevented.

[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, wherein the flange has a plurality of recesses spaced apart along the circumferential direction of the flange, and an anode is disposed in the recess.

[0015] According to this invention, the flange has a plurality of recesses spaced apart along the circumferential direction, and anodes are disposed in the recesses. This allows, for example, the flange connection portion to have a structure that is more likely to prevent crevice corrosion. Furthermore, the size of each anode can be reduced compared to, for example, when anodes integrally formed to match the size of the flange are used. Even when the size of the anodes is reduced in this way, a sufficient number of anodes can be disposed on the flange by appropriately adjusting the spacing and number of recesses. Therefore, for example, even when the width of the anode raw material (e.g., foil-shaped high-purity zinc anode material) is insufficient and anodes integrally formed on a large-diameter flange cannot be supplied, the anodes can be applied using the method of the present invention. Furthermore, by reducing the size of each anode, anodes can be more easily disposed on the flange. This improves workability at the construction site.

[0016] <6> A corrosion protection structure for a flange connection part according to aspect 6 of the present invention is the 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 is 1.0 mm or more and 3.0 mm or less in depth.

[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 installation when the flange is attached 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 placing 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 recesses are formed in a planar shape, and the anodes are plate-shaped or foil-shaped. This allows the anodes to be placed in the recesses one by one. This makes it easy to align the recesses 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. This allows anodes to be placed in the recesses by placing one anode in each of the recesses. This facilitates alignment of the recesses with the anodes, improving workability. Furthermore, the centers of the recesses are positioned on an imaginary circle centered on the center of the flange. By aligning the distances from the center of the flange to the centers of the recesses in this way, anodes can be evenly arranged around the circumference 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 plurality of bolt holes, and an anode is disposed in the recesses.

[0023] According to this invention, the flange has a recess, and an anode is placed in the recess. This makes it easier to place 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 the anode from shifting position and coming out from between the flange and the other component, for example, after the flange is attached to another component with bolts. This allows the flange connection portion to have a structure that makes it easier to prevent crevice corrosion.

[0024] The recess is formed annularly 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 relative to the diameter of the flange. This reduces the likelihood of the width of the anode raw material being insufficient for a large-diameter flange. Even if the width of the anode raw material is insufficient, an anode of 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 anode raw material is insufficient and an anode integrally formed with a large-diameter flange cannot be supplied, the anode can be produced using the method of 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, wherein the recess is arranged 5.0 mm away from the bolt hole, has a flat bottom surface, and is 1.0 mm or more and 3.0 mm or less in depth.

[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 installation when the flange is attached 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 placing the anode.

[0027] <11> The corrosion protection structure for a flange connection part according to aspect 11 of the present invention is a corrosion protection structure for a flange connection part according to 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 dimensions. This makes it possible, for example, to prevent the watertight 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 even more possible to prevent the watertight 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, anode paste is applied to the contact surface between the anode and the recess, thereby filling the gap between the anode and the recess and strengthening the electrical connection between the flange and the anode. [Effects of the Invention]

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

[0032] [Figure 1] This is the first example of a flange connection. [Figure 2] This is a second example of a flange connection. [Figure 3] FIG. 1 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 the flange surface. [Figure 5] FIG. 2 is a diagram showing the state of the connection between the zinc anode and the anode paste in the composite zinc anode. [Figure 6] FIG. 10 is a diagram showing a conventional example in which an annular, integrally molded zinc anode is disposed on a flange surface. [Figure 7]This is a conventional zinc anode that is integrally molded into a ring 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. 10 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 to strengthen the electrical connection. DETAILED DESCRIPTION OF THE INVENTION

[0033] Hereinafter, a corrosion prevention structure for a flange connection portion 100 and a method for preventing crevice corrosion of a 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 Figure 1 or Figure 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. FIG. 3 is a graph showing the relationship between the distance from the magnesium anode and the potential of a pipeline in a high-resistivity electrolyte (soil) where the magnesium anode is located. As shown in FIG. 3, the potential of the pipeline at the location of the magnesium anode is −1600 mV. The potential approaches 0 mV as the distance from the magnesium anode increases along the pipeline.

[0035] In this embodiment, by placing 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 of the pipeline where the negative potential value is greater than that of 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 placed be, for example, −1000 mV or less.

[0036] Figure 4 is a graph showing the relationship between the distance from the zinc anode on the flange 10 and the potential when a zinc anode is placed on the surface of the flange 10. As shown in Figure 4, even when zinc anodes are placed only on a portion of the flange 10, it is possible to set the potential to -900 mV over the entire surface of the flange 10. Therefore, even if zinc anodes are 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. Hereinafter, several examples of the form of the anode 20 will be described.

[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, "foil-shaped" refers to a member having a thickness of 200 μm or less. "Plate-shaped" refers to a member having a thickness of more than 200 μm. Hereinafter, the foil-shaped and plate-shaped high-purity zinc anodes 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 zinc anode 20F or the plate 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 does not need to be provided in the flange 10, as shown in FIG. Composite zinc anode 30 includes, for example, foil-shaped zinc tape 30T and anode paste 30P, or may include plate-shaped zinc anode 20B and anode paste 30P.

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

[0040] 2 and 5, the composite zinc anode 30 is formed by applying anode paste 30P to the periphery of zinc tape 30T, foil 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 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 flange joint surface. 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 that could be applied 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 adjusted appropriately 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 configuration is preferably used in both the first and second configurations of the anode 20 described above. Alternatively, the amount of anode 20 may be adjusted by using a strip-shaped or wire-shaped 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 anode 20 to match the circumferential length of flange 10. This embodiment is particularly suitable for use in the first embodiment of anode 20 described above, but may also be used in the second embodiment.

[0043] (Regarding the corrosion prevention 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 that is 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 flanges 10 are provided at the ends of the stainless steel pipes S. In this embodiment, the flanges 10 are, for example, annular. The stainless steel pipes S are connected to each other by fastening the flanges 10 together with bolts B and nuts N. Therefore, as shown in Figures 8, 9, and 10, the flanges 10 in this embodiment have a plurality of bolt holes 10h spaced apart along the circumferential direction of the flanges 10. The surfaces of the flanges 10 also have recesses 10d into which the anodes 20 are placed. With the anodes 20 placed in the recesses 10d, the flanges 10 are fastened together with the bolts B and nuts N. In this way, the anodes 20 are placed between the flanges 10, making the potential around the flanges 10 less noble.

[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 portion of the flange 10 other than the recess 10d, as shown in FIG. 11 . An anode paste 30P may be placed on the contact surface between the anode 20 and the recess 10d. This preferably fills the gap between the anode 20 and the recess 10d. The following describes several examples of the shapes of the recess 10d and the anode 20.

[0045] (First Form of Recess 10d and Anode 20) As shown in Fig. 8, the recess 10d according to the first embodiment is provided between the outer peripheral edge and the inner peripheral edge of the flange 10. The recess 10d is provided 5.0 mm away from the bolt hole 10h. The recess 10d has a flat bottom 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 can adjust the amount of anode 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 the Recess 10d and the Anode 20) As shown in FIG. 10 , the recess 10d according to the second embodiment is annular. 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 5.0 mm away from the bolt holes 10h. The recess 10d has a flat bottom 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 anode 20 placed 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 placed as the anode 20. That is, the length of the anode 20 placed 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 a plurality of recesses 10d are provided at intervals around the circumference of the flange 10. Each of the recesses 10d is provided 5.0 mm away from the bolt hole 10h. The recesses 10d are arranged so that their centers are located on an imaginary circle whose center is the center of the flange 10. The depressions 10d according to the third embodiment can adjust the amount of anode 20 disposed in the depressions 10d by adjusting the size and spacing thereof. 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, the corrosion prevention structure for the flange connection portion according to this embodiment is formed.

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

[0049] Furthermore, the anode 20, which is placed on the surface of the flange 10 to prevent crevice corrosion, is annularly arranged between the inner peripheral edge of the annular flange 10 and the multiple bolt holes 10h provided in the flange 10. This allows, for example, the diameter of the anode 20 to be smaller than the diameter of the flange 10. This reduces the likelihood that the width of the raw material for the anode 20 is insufficient for a large-diameter flange 10, for example. Even if the width of the raw material for the anode 20 is insufficient, an anode 20 of an appropriate size can be formed by processing a strip-shaped or linear raw material into an annular shape. Therefore, even if the raw material for the anode 20 is insufficient in width and an anode 20 integrally formed with the large-diameter flange 10 cannot be supplied, the anode 20 can be applied using the method of the present invention.

[0050] The anode 20 used to prevent crevice corrosion is a foil or plate-shaped high-purity zinc anode, which effectively prevents 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. The use of the anode paste 30P in addition to the foil-shaped zinc tape 30T or the plate-shaped zinc anode 20B facilitates maintaining the anode potential in the gaps between the zinc anodes. Furthermore, the anode paste can be used to fill gaps between the zinc anodes when small pieces of zinc anodes are used and to eliminate unevenness with the flange surface, allowing the composite zinc anode 30 to flexibly adapt to the shape of the flange 10. Furthermore, the formation of gaps on the surface of the flange 10 can be suppressed. This effectively prevents crevice corrosion.

[0052] Furthermore, according to the corrosion prevention structure of the flange connection portion 100 of this embodiment, the flange 10 includes a plurality of recesses 10d spaced apart along the circumferential direction, and anodes 20 are disposed in the recesses 10d. This allows the flange connection portion 100 to have a structure that is more resistant to crevice corrosion, for example. Furthermore, the size of each anode 20 can be reduced compared to when anodes 20 integrally formed to match the size of the flange 10 are used. Even when the size of the anodes 20 is reduced in this manner, a sufficient number of anodes 20 can be disposed on the flange 10 by appropriately adjusting the spacing and number of the recesses 10d. Therefore, for example, even when the width of the raw material for the anodes 20 (e.g., foil-shaped high-purity zinc anode material) is insufficient and anodes 20 integrally formed on a large-diameter flange 10 cannot be supplied, the anodes 20 can be applied by the method of the present invention. Furthermore, by reducing the size of each anode 20, it is easier to dispose the anodes 20 on the flange 10. This improves workability at the construction site.

[0053] Furthermore, the recess 10d is provided 5.0 mm away from the bolt hole 10h of the flange 10. This prevents the recess 10d and the anode 20 placed in the recess 10d from interfering with the mounting of the flange 10 to another component with the bolt B. The recess 10d has a flat bottom and a depth of 1.0 mm to 3.0 mm. This allows the recess 10d to have a shape and size sufficient for mounting the anode 20.

[0054] Furthermore, the recesses 10d are formed in a planar shape, and the anodes 20 are plate-shaped or foil-shaped. This allows the anodes 20 to be placed in the recesses 10d by placing one anode 20 in each of the multiple recesses 10d. This makes it easy to align the recesses 10d with the anodes 20, improving workability.

[0055] Furthermore, the recesses 10d are circular. This allows the anodes 20 to be placed in the recesses 10d by placing one anode 20 in each of the multiple recesses 10d. This facilitates alignment of the recesses 10d with the anodes 20, improving workability. Furthermore, the centers of the recesses 10d are positioned on an imaginary circle centered on the center of the flange 10. In this way, by aligning the distances from the center of the flange 10 to the centers of the recesses 10d, the anodes 20 can be evenly arranged around the circumferential direction of the flange 10.

[0056] The flange 10 also has a recess 10d, in which the anode 20 is placed. This makes it easier to place the anode 20 on the flange 10. This improves workability at the construction site. The recess 10d is also provided between the inner peripheral edge of the flange 10 and the plurality of bolt holes 10h. This prevents the anode 20 from shifting position 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] Furthermore, the recess 10d is annularly formed between the inner peripheral edge of the annular flange 10 and the plurality of bolt holes 10h provided in the flange 10. As a result, for example, by making the diameter of the recess 10d smaller relative to the diameter of the flange 10, the diameter of the anode 20 can be reduced. This reduces the number of cases where the width of the raw material for the anode 20 is insufficient for a large-diameter flange 10. Even if the width of the raw material for the anode 20 is insufficient, an 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 for the anode 20 is insufficient and an anode 20 integrally formed with a large-diameter flange 10 cannot be supplied, the anode 20 can be applied using the method according to the present invention.

[0058] Furthermore, the recess 10d is provided 5.0 mm away from the bolt hole 10h of the flange 10. This prevents the recess 10d and the anode 20 placed in the recess 10d from interfering with the mounting of the flange 10 to another component with the bolt B. The recess 10d has a flat bottom and a depth of 1.0 mm to 3.0 mm. This allows the recess 10d to have a shape and size sufficient for mounting the anode 20.

[0059] Furthermore, the recess 10d and the anode 20 have the same shape and dimensions. This makes it possible, for example, to prevent the watertight function of the flange 10 from being impaired. The portion of the flange 10 other than the recess 10d and the anode 20 are flush with each other. This makes it even more possible to prevent the watertight function of the flange 10 from being impaired.

[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, thereby strengthening the electrical connection between flange 10 and anode 20.

[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 may not have bolt holes 10h. In this case, the flanges 10 may be connected to each other by clamp members (not shown).

[0062] In addition, within the scope of the spirit of the present invention, the components in the above-described embodiments may be replaced with well-known components as appropriate, and the above-described modifications 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 by placing an anode on a surface of a flange, accommodating the surface of the flange in a potential gradient formed by the anode, and thereby making the potential of the flange less noble, thereby eliminating the potential difference between each portion of the flange, comprising: A plurality of the anodes are arranged at intervals along the circumferential direction of the flange. How to prevent crevice corrosion.

2. A method for preventing crevice corrosion by placing an anode on a surface of a flange, accommodating the surface of the flange in a potential gradient formed by the anode, and thereby making the potential of the flange less noble, thereby eliminating the potential difference between each portion of the flange, comprising: the flange is annular and has a plurality of circumferentially spaced bolt holes; The anode is disposed in an annular shape between an inner peripheral edge of the flange and the plurality of bolt holes, and the anode is a foil-shaped zinc tape or a plate-shaped zinc anode. An anode paste is disposed around the anode. 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.

4. the anode is a zinc foil tape or a zinc plate anode; An anode paste is disposed around the anode. The method for preventing crevice corrosion according to claim 1.

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 bolt holes spaced apart in a circumferential direction, and the recess 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 flange connections according to claim 5.

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

9. A structure for preventing crevice corrosion of a flange, the flange is annular and has a plurality of circumferentially spaced bolt holes; a recess provided annularly between an inner peripheral edge of the flange and the plurality of bolt holes, and an anode is disposed in the recess; An anode paste is disposed on the contact surface between the anode and the depression. 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 depression. The corrosion protection structure for a flange connection according to any one of claims 5 to 8.

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