Corrosion inhibition method

Abstract

To inhibit the corrosion of metal members.SOLUTION: In a corrosion inhibition method that inhibits the corrosion of a support metal fitting 30 and a cleat 21 made of a metal having a higher ionization tendency than the support metal fitting 30, an insulation sheet 40 is inserted between the support fitting 30 and cleat 21 to avoid contact between the different metals of the support metal fitting 30 and the cleats 21. As the insulating sheet 40 is larger than a pedestal base 22B of the cleat 21, a sheet outer edge 40A protruding from the outer peripheral part of the pedestal base 22B suppresses a bypass current that flows by bypassing the outer edge of the sheet 40A from the support metal fitting 30 to the cleat 21.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a method for inhibiting corrosion. [Background technology]

[0002] As disclosed in Patent Document 1, when fixing a cable inside a manhole, a support member (cleat) that restrains the cable and a support stand (support bracket) that supports the cleat are used. If the support member and the support stand are made of dissimilar metals, corrosion occurs due to dissimilar metal contact.

[0003] Patent Document 1 describes a method for preventing corrosion inside a manhole, which includes a step of cutting off at least one of the areas where the members made of different metals come into contact with each other and between the members made of different metals that have a relatively small ionization tendency when two or more members made of different metals are placed inside the manhole. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2007-205026 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the corrosion prevention method of Patent Document 1, if water flows into a manhole and each component is submerged, current may flow between the components via the water, causing corrosion to progress.

[0006] The present invention was completed in view of the above circumstances, and an object of the present invention is to provide a corrosion inhibition method for inhibiting corrosion of a member made of metal. [Means for solving the problem]

[0007] (1) A corrosion suppression method for suppressing corrosion of a first metal member and a second metal member made of a metal having a greater ionization tendency than the first metal member, comprises interposing an insulating sheet between the first metal member and the second metal member to prevent dissimilar metal contact between the first metal member and the second metal member, and the insulating sheet is larger than the second metal member and has an outer edge portion protruding from the outer periphery of the second metal member to suppress a bypass current that flows from the first metal member to the second metal member, bypassing the outer edge portion of the sheet.

[0008] In the above (1), the sheet outer edge protruding from the outer periphery of the second metal member lengthens the detour path of the current (current flowing due to differences in ionization tendency) flowing from the first metal member to the second metal member when submerged, and the resistance of the detour path increases. Increasing the resistance of the detour path makes it more difficult for the detour current to flow, and corrosion caused by the detour current can be suppressed.

[0009] In this specification, the term "detour path" refers to a path of current flowing from the first metal member to the second metal member other than the contact point between the metal members, and the term "detour current" refers to current flowing from the first metal member to the second metal member via the detour path.

[0010] (2) In the corrosion suppression method described in (1) above, the first metal member and the second metal member may be fixed by a bolt penetrating both the first metal member and the second metal member and a nut screwed onto the bolt, and at least one of a first current flowing through a first interface between the head of the bolt and the first metal member and a second current flowing through a second interface between the nut and the second metal member may be blocked by an insulating washer inserted between at least one of "between the head of the bolt and the first metal member" and "between the nut and the second metal member."

[0011] By adopting the above-mentioned (2), the current passing from the first metal member to the second metal member via the bolt and the nut is interrupted, thereby making it possible to suppress corrosion.

[0012] (3) In the corrosion suppression method described above in (2), a third current passing through the shaft portion from the first metal member to the second metal member may be blocked by an insulating sleeve covering the shaft portion of the bolt.

[0013] By adopting the above-mentioned (3), the current from the first metal member to the second metal member via the shaft portion is interrupted, thereby making it possible to suppress corrosion.

[0014] (4) In the corrosion suppression method described in any one of (1) to (3) above, the second metal member may be protected from corrosion by a sacrificial anode having a higher ionization tendency than the second metal member.

[0015] By adopting the above method (4), the sacrificial anode, which has the greatest ionization tendency, corrodes first among the first metal member, the second metal member, and the sacrificial anode, so that corrosion of the first metal member and the second metal member can be suppressed. Effect of the Invention

[0016] According to the present invention, corrosion of metal members can be suppressed. [Brief description of the drawings]

[0017] [Figure 1] Side view of cable fixture [Diagram 2] Top view of cable fixture [Diagram 3] Exploded view of bolts and nuts [Figure 4] Enlarged view of the cable fastener DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] 1. Mode for Carrying Out the Invention Fig. 1 is a side view showing the inside of a manhole MH to which a corrosion inhibition method according to an embodiment of the present invention is applied. A standing metal fitting 11 is erected inside the manhole MH, which is provided underground. A cable fixing device 20 for fixing a cable 10 is attached to the standing metal fitting 11. The up-down direction in Fig. 1 indicates the up-down direction inside the manhole MH. Furthermore, the cable 10 extends in a direction perpendicular to the plane of the paper on which Fig. 1 is drawn.

[0019] The cable 10 is an underground cable laid underground and in a manhole MH. The cable fixing device 20 has a cleat (an example of a "second metal member" in the claims) 21 that restrains the cable 10, a support bracket (an example of a "first metal member" in the claims) 30 that supports the cleat 21 from below, and an insulating sheet 40 interposed between the cleat 21 and the support bracket 30.

[0020] The cleat 21 has a lower frame 22 and an upper frame 23. The lower frame 22 and the upper frame 23 are fixed in a conductive state by fastening bolts 24. The lower frame 22 has a base 22B and a semicircular recess 22A with an upper end opening upward above the base 22B. The upper frame 23 has a semicircular recess 23A with a lower end opening downward. The cable 10 is restrained by the cleat 21 by being sandwiched between the recess 22A and the recess 23A.

[0021] Pedestal 22B has a generally hexagonal plate shape in plan view (see Figs. 1 and 2). Pedestal 22B contacts insulating sheet 40 at seat surface 22C. Lower frame 22 and upper frame 23 constituting cleat 21 are made of the same material, for example, aluminum or an aluminum alloy. The shape of pedestal 22B in plan view may be generally hexagonal, or may be any other shape such as a polygon other than a hexagon, a circle, an ellipse, or the like.

[0022] The support fitting 30 has a rectangular plate shape overall. The support fitting 30 is fixed to the side of the upright metal fitting 11 with the plate surface facing the up-down direction. The upper surface 30A, which is the upper plate surface of the support fitting 30, is formed in a flat shape without any irregularities, and faces the seat surface 22C of the lower frame 22 with an insulating sheet 40 sandwiched between them. The support fitting 30 is made of a different type of metal from the cleat 21, and has a smaller ionization tendency than the cleat 21. Examples of the material of the support fitting 30 include stainless steel or zinc-plated steel.

[0023] An L-shaped mounting bracket 61 is fastened to one of the two bolts 24 that secure the lower frame 22 and the upper frame 23. A sacrificial anode 60 is attached to the mounting bracket 61, and the lower frame 22 and the sacrificial anode 60 are electrically connected via the mounting bracket 61. The sacrificial anode 60 is made of a metal that has a higher ionization tendency than the lower frame 22. An example of the material for the sacrificial anode 60 is a magnesium alloy.

[0024] Of the three components, the cleat 21, the support bracket 30, and the sacrificial anode 60, the component with the greatest ionization tendency is the sacrificial anode 60. The component with the second greatest ionization tendency is the cleat 21. The component with the least ionization tendency is the support bracket 30. Because the cleat 21 is electrically connected to the sacrificial anode 60, the sacrificial anode 60, which has the greatest ionization tendency, corrodes first between the cleat 21 and the sacrificial anode 60. This makes it possible to protect the cleat 21 from corrosion and suppress corrosion.

[0025] The insulating sheet 40 is provided between the seat surface 22C of the lower frame 22 and the upper surface 30A of the support metal fitting 30. The insulating sheet 40 is a rectangular sheet in a plan view made of an insulating material such as resin. Specific examples of the material of the insulating sheet 40 include PTFE (polytetrafluoroethylene) and FRP (Fiber Reinforced Plastics). The upper surface of the insulating sheet 40 contacts the seat surface 22C, and the lower surface of the insulating sheet 40 contacts the upper surface 30A of the support metal fitting 30. The insulating sheet 40 is interposed between the cleat 21 and the support metal fitting 30, thereby preventing dissimilar metal contact between the cleat 21 and the support metal fitting 30.

[0026] Fig. 2 is a plan view showing the relative sizes and positional relationship between insulating sheet 40 and base 22B. In Fig. 2, structures above base 22B, bolts 50, nuts 51, etc., which will be described later, are not shown.

[0027] 2, the upper surface 30A of the support bracket 30 is substantially rectangular in plan view. The insulating sheet 40 is disposed so as to cover the vicinity of the center of the upper surface 30A from above. Parts of the surface of the support bracket 30 (including not only the upper surface 30A but also the side and lower surfaces) that are not covered with the insulating sheet 40 are exposed metal.

[0028] 2, the insulating sheet 40 is formed to be larger than the base 22B. The base 22B is placed inside a sheet outer edge portion 40A, which is the outer edge of the insulating sheet 40, so as not to protrude outward beyond the insulating sheet 40. The sheet outer edge portion 40A protrudes outward further than any part of the outer periphery of the base 22B. The insulating sheet 40 covers the area between the outer periphery of the base 22B and the portion of the surface of the support bracket 30 where metal is exposed.

[0029] Since the insulating sheet 40 is interposed between the upper surface 30A of the support bracket 30 and the base 22B (cleat 21), dissimilar metal contact can be avoided. However, even if there is no dissimilar metal contact, if water infiltrates into the manhole MH, for example, a bypass current may flow from the support bracket 30 to the cleat 21 via the water, which may corrode the cleat 21. In particular, if the infiltrating water is seawater, which has high electrical conductivity, there is a heightened concern that a bypass current may flow.

[0030] In the configuration of this embodiment, there is a possibility that a detour path A1 shown in Fig. 4 may be formed between the support bracket 30 and the base 22B. The detour path A1 is a path that connects a portion of the upper surface 30A of the support bracket 30 that is not covered with the insulating sheet 40 and the base 22B. The detour path A1 is a path that crosses the sheet outer edge portion 40A that protrudes from the outer periphery of the base 22B.

[0031] When the sheet outer edge 40A of the insulating sheet 40 does not protrude beyond the outer periphery of the base 22B, in other words, when the end of the insulating sheet 40 is located directly below the outer periphery of the base 22B, the path of the detouring current is the detouring path A2. The detouring path A1 has a longer path length than the detouring path A2 by an amount that exceeds the sheet outer edge 40A, and therefore has a higher resistance value than the detouring path A2. If the resistance value of the detouring path A1 is high, the detouring current is less likely to flow, and corrosion caused by the detouring current can be suppressed.

[0032] 2, the base 22B, the insulating sheet 40, and the support fitting 30 each have a hole penetrating in the vertical direction at a position where they overlap in a plan view, and when the holes overlap, they form a single through hole 52. As shown in FIG 1, the cleat 21 is fixed to the support fitting 30 by a bolt (an example of a "bolt" in the claims) 50 inserted into the through hole 52 and a nut (an example of a "nut" in the claims) 51 screwed onto the bolt 50.

[0033] The bolt 50 that fixes the cleat 21 to the support bracket 30 and its surrounding structure will be described with reference to Fig. 3 and Fig. 4. Fig. 3 is an exploded view showing the arrangement of the bolt 50, the nut 51, and the members arranged between them. Fig. 4 is an enlarged view of the bolt 50 and its surroundings in Fig. 1.

[0034] 3, a cylindrical insulating sleeve 62 is attached to the shaft portion 50A of the bolt 50 to cover the side surface of the shaft portion 50A. The insulating sleeve 62 is made of an insulating material that does not allow current to pass through. Examples of materials for the insulating sleeve 62 include PTFE and nylon.

[0035] 4, when the base 22B is fixed to the support bracket 30 with the bolt 50, the insulating sleeve 62 is interposed between the shaft portion 50A and the inner wall of the through hole 52. The insulating sleeve 62 electrically insulates, within the through hole 52, between the shaft portion 50A and the base 22B, and between the shaft portion 50A and the support bracket 30.

[0036] The insulating sleeve 62 can block the third current I3 from the support bracket 30 to the base 22B (the cleat 21) via the shaft portion 50A. This can suppress corrosion of the cleat 21.

[0037] 3, a first insulating washer (an example of an "insulating washer" in the claims) 64 and metal washers 63 and 65 are inserted into the shaft portion 50A on which the insulating sleeve 62 is attached, so as to sandwich the first insulating washer 64. The first insulating washer 64 is a washer made of an insulating material. Examples of materials for the first insulating washer 64 include PTFE and FRP.

[0038] 4, when the support bracket 30 and the cleat 21 are fixed, the washer group 63-65 is sandwiched between the head 50B of the bolt 50 and the support bracket 30. A first insulating washer 64 is inserted between the head 50B and the support bracket 30, and a first current I1 flowing through a first interface 71 between the head 50B and the support bracket 30 is blocked.

[0039] 3, a second insulating washer (an example of an "insulating washer" in the claims) 66 and a metal washer 67 are inserted into the shaft portion 50A between the nut 51 and the base 22B. The second insulating washer 66, like the first insulating washer 64, is made of an insulating material such as PTFE or FRP.

[0040] 4, when the support bracket 30 and the cleat 21 are fixed, the washer group 66-67 is sandwiched between the nut 51 and the base 22B. The second current I2 flowing through the second interface 72 between the nut 51 and the base 22B is blocked by the second insulating washer 66 interposed between the nut 51 and the base 22B.

[0041] By blocking at least one of the first current I1 and the second current I2, the current flowing from the support fitting 30 to the cleat 21 can be suppressed, thereby suppressing corrosion.

[0042] The metal washers 63, 65 are disposed above and below the first insulating washer 64. Moreover, the metal washer 67 is disposed between the nut 51 and the second insulating washer 66. The metal washers 63, 65, 67 are made of, for example, stainless steel, and in addition to fulfilling the role of a general washer (preventing jamming, preventing loosening, etc.), they also serve to protect the insulating washers 64, 66 from scratches and deformation.

[0043] 2.Effects According to the present invention, the sheet outer edge 40A protruding from the outer periphery of the base 22B of the cleat 21 lengthens the detour path A1 for the current (current that flows due to differences in ionization tendency) that flows from the support bracket 30 to the cleat 21 when submerged, and increases the resistance of the detour path A1. By increasing the resistance of the detour path A1, it becomes more difficult for the detour current to flow, and corrosion caused by the detour current can be suppressed.

[0044] <Other embodiments> (1) In the above embodiment, the case where the sacrificial anode 60 for corrosion prevention is attached to the cleat 21 is illustrated. However, the sacrificial anode 60 does not have to be attached.

[0045] (2) In the above embodiment, the cable fixing device 20 inside the manhole MH has been described as an example, but the cable fixing device 20 may be attached to a location other than the manhole MH.

[0046] (3) In the above embodiment, a case was described in which the second member (the cleat 21) had a greater ionization tendency than the first member (the support metal fitting 30), but the magnitude of the ionization tendency may be reversed.

[0047] (4) In the above embodiment, the head 50B of the bolt 50 is on the support bracket 30 side and the nut 51 is on the base 22B side. However, the positions of the bolt 50 and the nut 51 may be interchanged.

[0048] (5) In the above embodiment, the case where both the first insulating washer 64 and the second insulating washer 66 are inserted is illustrated. However, it is also possible to insert only one of the insulating washers.

[0049] (6) In the above embodiment, the insulating sheet 40 is rectangular, but the shape of the insulating sheet 40 is not limited to rectangular. For example, the insulating sheet 40 may be circular, elliptical, or a polygon other than rectangular, or may be a shape similar to the base 22B. [Explanation of symbols]

[0050] 21: cleat, 22B: base, 22C: seat, 30: support bracket, 30A: upper surface, 40: insulating sheet, 40A: outer edge of sheet, 50: bolt, 50A: shaft, 50B: head, 51: nut, 52: through hole, 62: insulating sleeve, 63, 65, 67: metal washer, 64: first insulating washer, 66: second insulating washer, 71: first interface, 72: second interface, A1: bypass path, A2: bypass path, I1: first current, I2: second current, I3: third current

Claims

1. A corrosion suppression method for suppressing corrosion of a first metal member and a second metal member made of a metal having a higher ionization tendency than the first metal member, comprising: An insulating sheet is interposed between the first metal member and the second metal member to prevent dissimilar metal contact between the first metal member and the second metal member, A corrosion suppression method in which the insulating sheet is larger than the second metal member, and the sheet outer edge portion protrudes from the outer periphery of the second metal member to suppress a bypass current flowing from the first metal member to the second metal member, bypassing the sheet outer edge portion.

2. The corrosion inhibition method according to claim 1, The first metal member and the second metal member are fixed together by a bolt passing through both the first metal member and the second metal member and a nut screwed onto the bolt; A corrosion suppression method in which an insulating washer is inserted between at least one of "the head of the bolt and the first metal member" and "the nut and the second metal member", thereby blocking at least one of a first current flowing through a first interface between the head of the bolt and the first metal member and a second current flowing through a second interface between the nut and the second metal member.

3. The corrosion inhibition method according to claim 2, A corrosion suppression method comprising: blocking a third current from the first metal member to the second metal member via the shaft portion by an insulating sleeve covering the shaft portion of the bolt.

4. The corrosion inhibition method according to any one of claims 1 to 3, The second metal member is protected from corrosion by a sacrificial anode having a higher ionization tendency than the second metal member.

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