JP5105899B2 - Anticorrosion method for underground piping - Google Patents

Description

The present invention relates to a corrosion prevention method for underground pipes.

  Conventionally, in order to prevent corrosion of underground underground pipes, anticorrosion coating has been used to insulate from the underground environment. However, with anticorrosion coating alone, damage and defects have occurred over time, and sufficient anticorrosion has been achieved. Absent. In particular, in underground penetration pipes penetrating reinforced concrete structures such as manholes, common grooves or bridges, underground pipes come into contact with the reinforcement of reinforced concrete structures, resulting in concrete / soil macrocell corrosion (C / S macrocells). Corrosion) is known to occur. For example, in an embedded agricultural water pipe, C / S macrocell corrosion occurs in a reinforced concrete structure penetrating part such as a valve chamber.

  In this way, when the underground pipe causes C / S macrocell corrosion, a corrosion hole is generated in the underground pipe and causes problems such as water leakage and water pollution.

  In order to prevent the C / S macrocell corrosion of underground piping in such a reinforced concrete structure penetrating portion, an galvanic anode method or an external power supply method, which is an anticorrosion method, is employed.

  In order to perform such anticorrosion in underground underground piping, excavate the soil near the outer wall of the reinforced concrete structure from the ground surface, and embed a galvanic anode or embed an insoluble anode (external power electrode). Then, anti-corrosion is performed by energizing.

  However, there are many existing trees in mountainous areas and upland fields, private fields and orchards, or steep slopes. And equipment cannot be carried in and out, and excavation from the ground surface is difficult, so that insoluble anodes and galvanic anodes cannot be buried. In urban areas, there are the same problems as described above when there are structures such as buildings and apartment houses and paved roads. Furthermore, even when excavation from the ground surface is possible, it is necessary to lay roads and the like for carrying materials and equipment to and from the planned excavation point.

  As a proposal for solving such a problem, Patent Document 1 (Japanese Patent Publication No. 6-53940) and Patent Document 2 (Japanese Patent Application Laid-Open No. 7-26389) describe that a concrete wall is penetrated from the inside of a concrete structure. There has been proposed an anti-corrosion construction method in which an energizing electrode or an anti-corrosion assembly protrudes from a drilled external soil hole and is fixed to the concrete wall. And such an underground hole is supposed to be drilled by a concrete cutter or the like. According to this cathodic protection method, it is not necessary to excavate the soil from the surface of the earth, so the above problems are solved temporarily.

Japanese Examined Patent Publication No. 6-53940 JP-A-7-26389

  However, in the anticorrosion construction method as disclosed in Patent Documents 1 and 2, since the earth and sand falls from the upper part and fills in the drilled hole, it is possible to push the current-carrying electrode or the anticorrosion assembly into a predetermined position. It is difficult, and the anticorrosion effect of underground underground piping may not be fully demonstrated, so it is not practical. Further, when the energizing electrode is pushed into the soil hole, it is necessary to project the energizing electrode and the cable so as not to be damaged, so that the workability is extremely inferior. Furthermore, since a narrow gap is formed between the energizing electrode and the earth hole in the earth hole, this space has been filled with mortar in the past. In particular, it is necessary to press-fit a lateral gap, and there is a risk that a space may be generated.

  Thus, the anticorrosion method which can fully exhibit the anticorrosion effect of the penetration part of the reinforced concrete structure of underground piping, and was excellent in workability and economical efficiency is not obtained.

  Accordingly, an object of the present invention is to provide an anticorrosion method for a penetration portion of a reinforced concrete structure in a buried underground pipe that is excellent in workability and economical efficiency and can exhibit a sufficient anticorrosion effect, and a cylindrical electrode for cathodic protection used in the method. It is to provide an apparatus and a conductive filler.

  As a result of the study, the inventor formed a cutting hole in a concrete wall and soil from the inside of a reinforced concrete structure using a cylindrical core bit of a core drill, and the cylindrical core bit in the cutting hole and a casing connected to the core bit. A cylindrical electrode device for cathodic protection, in which a plurality of bearings are attached to the outer peripheral surface of the tube, is slid and installed at a predetermined position of the cutting hole, and then the cylindrical core bit and the casing tube are connected to the cutting hole. The inventors have found that the above object can be achieved by a corrosion prevention method in which a conductive filler is drawn into a narrow space in the cutting hole and then injected into a narrow space.

That is, the present invention provides the following steps (1) to (4):
(1) A step of forming a cutting hole in a horizontal direction or an oblique direction in a concrete wall and soil from the inside of a reinforced concrete structure using a cylindrical core bit of a core drill in the vicinity of a reinforced concrete wall penetrating portion of an underground pipe.
(2) A cylindrical electrode device for cathodic protection having a plurality of bearings attached to the outer peripheral surface is slid into the cylindrical core bit in the cutting hole and a casing tube connected to the core bit, and the cutting hole is Installing at a predetermined position in
(3) a step of pulling out the cylindrical core bit and the casing tube from the cutting hole;
(4) Injecting a conductive filler into the space in the cutting hole,
It is intended to provide an anticorrosion method for underground underground pipes characterized in that

Moreover, this invention is the process of following (1)-(5);
(1) Install a cylindrical electrode device for cathodic protection in the horizontal or diagonal direction on the concrete wall and soil from the inside of the reinforced concrete structure using the cylindrical core bit of the core drill near the reinforced concrete wall penetration of the underground pipe. A step of forming a cutting hole for installing a corrosion prevention and detection unit composed of at least one of a cutting hole and a reference electrode separate from the cutting hole or a corrosion prevention detection probe;
(2) An anti-corrosion cylinder in which a plurality of bearings are attached to the outer peripheral surface in the cylindrical core bit in the cutting hole in which the cylindrical electrode device for anti-corrosion is installed and a casing tube connected to the core bit. Sliding the electrode device and installing it at a predetermined position in the cutting hole,
(3) Corrosion composed of at least one of a reference electrode or a corrosion protection detection probe in the cylindrical core bit in the cutting hole in which the corrosion protection detection unit is installed and a casing tube connected to the core bit. Inserting the anticorrosion detection unit and installing it at a predetermined position in the cutting hole;
(4) A step of pulling out the cylindrical core bit and the casing tube from the respective cutting holes,
(5) A step of injecting a conductive filler into the space in each cutting hole in which the cylindrical electrode device for corrosion protection and the corrosion protection detection unit are installed,
It is intended to provide an anticorrosion method for underground underground pipes characterized in that

  In the anticorrosion method of the underground pipe according to the present invention, the cylindrical electrode device for cathodic protection has an electrode body composed of an insoluble anode or a flowing anode, and a plurality of through holes on a peripheral side surface protecting the electrode body. It is desirable to have an insulating synthetic resin protective tube having an anticorrosive backfill filled in the protective tube and a plurality of bearings attached to the outer peripheral surface.

  The anticorrosion method for underground underground pipes according to the present invention, even when it is difficult to embed electrodes on the outer periphery of a reinforced concrete structure by excavating from the ground surface, near the penetration part of the reinforced concrete structure of the underground underground pipe, The electrode device can be easily placed at the required position, and damage to the electrode and the cable connected to the electrode can be prevented. Also, the equipment, tools, and materials used can be transported manually, making field work easier and reducing costs. it can.

  Moreover, the cylindrical electrode device for cathodic protection according to the present invention can be easily installed in the cutting hole, and can prevent C / S macrocell corrosion of the reinforced concrete structure penetrating portion of the underground pipe. Moreover, the space part of the cutting hole provided in the vicinity of the reinforced concrete structure penetration part can be efficiently filled with the conductive filler according to the present invention.

Hereinafter, the best mode for carrying out the present invention will be described in detail.
FIGS. 1-2 and FIGS. 4-5 are process drawings which show 1st Embodiment of the anticorrosion construction method of underground underground piping which concerns on this invention, and show process (1)-(4), respectively. In this embodiment, the insoluble anode of the external power source system shown in FIG. 3 is used as the cylindrical electrode device for cathodic protection.

[Step (1)]
As shown in FIG. 1, a cutting hole 6 is formed in the concrete wall 2 and the soil 5 from the inside of the reinforced concrete structure using the cylindrical core pit 4 of the core drill 3 in the vicinity of the reinforced concrete wall 2 penetrating portion of the underground pipe 1. .

  The underground underground pipe 1 used here is not particularly limited, and examples thereof include an agricultural water underground pipe and a tap water underground pipe. Reinforced concrete structures include valve chambers, buildings, bridges, and common grooves.

  The diameter of the cutting hole 6 formed by the cylindrical core pit 4 of the core drill 3 needs to be larger than the diameter of the cylindrical electrode device for cathodic protection. In view of facilitating the removal of gravel that falls away from the base rock and falls into the cutting hole, it is desirable to form a cutting hole of about φ300 mm, for example. Moreover, the cutting hole 6 is formed in a horizontal direction or a diagonal direction with respect to a concrete wall and soil.

[Step (2)]
Next, as shown in FIG. 2, a cylindrical core for cathodic protection in which a plurality of bearings are attached to the outer peripheral surface in a cylindrical core bit 4 in the cutting hole 6 and a casing tube 7 connected to the core bit. The electrode device 8 is slid and the cylindrical electrode device 8 for anticorrosion is installed at a predetermined position in the cutting hole 6.

  An example of the cylindrical electrode device 8 for cathodic protection according to the present invention is shown in FIG. FIG. 3 uses an insoluble anode 9 of an external power source system, and is electrically connected to an external power source via a lead wire 10. As the insoluble anode 9, magnetic iron oxide, platinum group metal oxide-coated electrode (MMO electrode), high silicon cast iron or the like is used. When the galvanic anode method is used, magnesium, zinc, and alloys thereof are used as the galvanic anode.

  By performing such anticorrosion, C / S macrocell corrosion of the concrete structure penetration part of underground piping is prevented.

In the cylindrical electrode device 8 for cathodic protection according to the present invention, the insoluble anode 9 is protected by an insulating synthetic resin protective tube 11 having a plurality of through holes on the peripheral side surface. A backfill 12 for cathodic protection is filled. The synthetic resin protective tube 11 is made of polyvinyl chloride or the like. The anticorrosion backfill used for the insoluble anode is made of, for example, coke or graphite, and the anticorrosion backfill used for the galvanic anode is a mixture of gypsum, bentonite and anhydrous sodium sulfate (Na ₂ SO ₄ ). The ratio is 30:60:10 or 70: 25: 5).

  The cylindrical electrode device 8 for cathodic protection according to the present invention has a plurality of bearings 13 attached to the outer peripheral surface. By attaching the bearing 13 in this manner, it becomes easy to slide the cathodic protection cylindrical electrode device 8.

[Step (3)]
After the cylindrical electrode device 8 for cathodic protection is disposed at a predetermined position of the cutting hole 6, the cylindrical core bit 4 and the casing tube 7 are pulled out from the cutting hole 6 using a pipe wrench 14 as shown in FIG. 4.

[Step (4)]
Finally, the space of the cutting hole 6 is filled with the conductive filler 16 using the pressure pump 15, and the cutting hole 6 provided in the concrete wall 2 and the soil 5 is sealed.

  The conductive filler 16 according to the present invention contains at least bentonite powder and a water-soluble thickener, and further contains a preservative or the like as necessary. By adding such a water-soluble thickener, a high thickening effect can be imparted to the conductive filler, and the filling and sealing of the cutting holes provided in the horizontal direction or oblique direction should be performed efficiently. Can do.

  As the bentonite powder, both calcium type and sodium type can be used, but sodium type bentonite having a higher degree of swelling than calcium type is advantageous. This sodium-type bentonite is bentonite in which alkali metals such as sodium ions and potassium ions are adsorbed between layers of montmorillonite sheet-like crystals.

  Examples of the water-soluble thickener include at least one selected from the group consisting of carboxymethylcellulose, carboxyvinyl polymer, polyacrylamide polymer, sodium polyacrylate, methylcellulose, polyvinyl alcohol, hydroxyethylcellulose, hydroxypropylcellulose, and xanthan gum. However, carboxymethyl cellulose is particularly preferably used.

  The addition ratio of bentonite powder and water-soluble thickener is preferably 0.05 to 20 parts by weight, more preferably 0.1 to 5 parts by weight, based on 100 parts by weight of bentonite powder. Is added to water such as fresh water and tap water, it gives high viscosity and gelation. When added in the above ratio, proper thixotropy is obtained by their interaction, and the filling operation is stabilized, which is preferable.

  Next, 2nd Embodiment of the anticorrosion construction method of underground underground piping which concerns on this invention is described. In this embodiment, in addition to the cylindrical electrode device for corrosion protection, a corrosion protection detection unit including at least one of a reference electrode and a corrosion protection detection probe is provided. By arranging a reference electrode such as zinc, the anti-corrosion effect can be confirmed by measuring the ground potential of the underground buried pipe. In addition, by locating a corrosion / corrosion detection probe, the current between the probe and the underground pipe can be measured, the magnitude and direction of the current can be confirmed, and the anticorrosion status of the underground pipe can be monitored. .

[Step (1)]
In the step (1) of the present embodiment, for corrosion protection detection, which comprises at least one of a cutting hole in which a cylindrical electrode device for corrosion protection is installed and a reference electrode separate from the cutting hole or a probe for corrosion protection detection. A cutting hole for forming the unit is formed. Although the corrosion protection detection unit may be installed in the cutting hole where the cylindrical electrode device for cathodic protection is installed, the electrode device is formed by forming a cutting hole separate from this cutting hole and installing the corrosion protection detection unit. The underground piping can be monitored accurately because it is away from the ground. The method for forming the cutting hole is the same as in the first embodiment.

  FIG. 6 is a perspective view showing a state in which the cutting holes 61 and 62 are formed. In FIG. 6, cutting holes 61 and 62 are formed in the concrete wall 2 and the soil 5 from the inside of the reinforced concrete structure using the cylindrical core pit 4 of the core drill 3 in the vicinity of the reinforced concrete wall 2 penetrating portion of the underground pipe 1.

[Step (2)]
As shown in FIG. 7, a plurality of bearings are attached to the outer peripheral surface in the cylindrical core bit 4 in the cutting hole 61 in which the cylindrical electrode device for cathodic protection is installed and the casing tube 7 connected to the core bit. The cylindrical electrode device 8 for cathodic protection is slid, and the cylindrical electrode device 8 for cathodic protection is installed at a predetermined position in the cutting hole 61. This is the same step as the step (2) of the first embodiment.

[Step (3)]
As shown in FIG. 7, a cylindrical core bit 4 in a cutting hole 62 in which a corrosion / corrosion protection detection unit is installed and a casing tube 7 connected to the core bit are constituted by a verification electrode 17 and a corrosion / corrosion protection detection probe 18. The corrosion / corrosion detection unit to be used is inserted and installed at a predetermined position in the cutting hole 62. Since the verification electrode 17 and the corrosion / corrosion protection detection probe 18 are small and lightweight, they can be easily installed at predetermined positions without attaching bearings to their outer peripheral surfaces. For example, it can be installed using a zinc reference electrode size φ40 mm × L250 mm and a corrosion protection detection probe size φ38 mm × L126 mm.

[Step (4)]
Using the pipe wrench 14, the cylindrical core bit 4 and the casing tube 7 are pulled out from the cutting holes 61 and 62. This is the same step as step (3) of the first embodiment.

[Step (5)]
The space between the cutting holes 61 and 62 is filled with the conductive filler 16 using the pressure pump 15, and the cutting holes 61 and 62 provided in the concrete wall 2 and the soil 5 are sealed. If the surroundings of the reference electrode 17 or the corrosion protection detection probe 18 are filled with mortar, the corrosion protection status of the underground piping may not be accurately monitored. Therefore, the cutting hole 62 provided with the corrosion protection detection unit is also conductive. Filler 16 is injected. This is the same step as the step (4) of the first embodiment.

  Hereinafter, the present invention will be specifically described based on examples and the like.

<Examples 1a to 1c (production of conductive filler)>
To 300 ml of tap water, 30 g (9.09% by mass) of bentonite “Asama” from Kunimine Co., Ltd. was added and stirred vigorously with a spoon to prepare a bentonite suspension. To 100 ml of this bentonite suspension, 0.05 g (0.045 mass%), 0.1 g (0.09 mass%) of sodium carboxymethylcellulose (CMC-Na) “Serogen BSH-10” from Daiichi Kogyo Seiyaku Co., Ltd. (Mass%) or 0.15 g (0.135 mass%) and the amount added was changed, and Examples 1a to 1c were prepared by stirring vigorously with a spoon.

Comparative example

<Comparative Examples 1a to 1f (production of bentonite suspension)>
To the tap water, Kunimine Co., Ltd. bentonite “Asama” was added and stirred vigorously with a spoonful of 8%, 9.09%, 10%, 11%, 12% and 13%. Comparative Examples 1a to 1f were prepared by changing the blending amount of mass%.

(Viscosity measurement)
For each of Examples 1a to 1c and Comparative Examples 1a to 1f, after vigorously stirring with a spoonful for 30 seconds, the rotor of a B-type viscometer (TV-10M from Toki Sangyo Co., Ltd.) was immersed for 2 minutes. Left to stand. Using a B-type viscometer, it was rotated at an M4 rotor at 20 ° C. and 12 rpm, and the viscosity after 15 seconds was measured.

[Viscosity measurement evaluation results]
As is apparent from Table 1, Examples 1a to 1c showed higher viscosities at the same bentonite addition amount as compared with Comparative Example 1b in the case where CMC-Na was not added. That is, it was found that if CMC-Na was added to the bentonite suspension, a thickening action was exhibited.

[Hardness test]
For each of Example 1b and Comparative Examples 1c to 1f, after vigorously stirring with a spoon for 30 seconds, 30 g was sucked using a syringe (35 ml) 19 and, as shown in FIG. Then, the sample 21 was discharged from a height of 5 cm in 10 seconds. Next, with respect to the sample 21 of Example 1b and Comparative Examples 1c to 1f on the measurement plate, the tactile sensation was recognized with the fingertip, and the diameter immediately after the syringe was discharged and the diameter after being left until the next day were measured. Indicated.

[Evaluation results of hardness test]
As is clear from Table 2, it was found that the hardness of Example 1b increased with the addition of a small amount of CMC-Na, as compared with Comparative Examples 1c to 1f in the case where CMC-Na was not added. Further, Comparative Examples 1c to 1f are gels having viscosity, whereas Example 1b is a gel having elasticity. That is, when the fluidity is lost even with a low addition amount of CMC-Na as compared with the bentonite suspension, the gel is changed to an elastic gel, so that the filling of the space portion of the cutting hole provided in the vicinity of the reinforced concrete structure penetration portion It is also excellent for sealing and practical.

<Production of Comparative Example 2 (Mortar)>
A commercially available premix mortar (trade name “DENKA PRETASCON-type 1” manufactured by Denki Kagaku Kogyo Co., Ltd.) was mixed with water based on the catalog and kneaded to prepare a mortar.

[Leakage test for gaps]
A transparent cylindrical container 22 (φ350 mm × L1,500 mm) having an opening on the top is placed vertically, and a cylindrical electrode device 8 (φ230 mm × L1,420 mm) for cathodic protection to which 12 bearings are attached is formed in this cylindrical shape. Three things each prepared in the container were prepared. After each sample (conductive filler 16) of Example 1b and Comparative Example 1f and 2 is vigorously stirred, a narrow gap between the cylindrical container 22 and the cylindrical electrode device 8 for cathodic protection is used by using a pump. The liquid was sufficiently injected into the cylinder and adjusted to the opening end face of the cylindrical container. And this cylindrical container 22 was gently rolled over.

Next, the degree of leakage in Example 1b and Comparative Example 1f, 2 after standing for 10 minutes and after standing for 20 minutes was evaluated in the following three stages.
A: Almost no leakage and stable in a stationary state.
○: There was some leakage, but it was stable in the stationary state.
X: Almost out of the gap, no practicality.

  These results are shown in Table 3. FIG. 9 shows a state immediately after rollover, and FIG. 10 shows a state after standing still.

[Evaluation result of leak test]
As is clear from Table 3, it was found that the conductive filler according to Example 1b was non-fluid and could be filled without voids even when the surface had irregularities.

  The anticorrosion method for underground underground pipes according to the present invention, even when it is difficult to embed electrodes on the outer periphery of a reinforced concrete structure by excavating from the ground surface, near the penetration part of the reinforced concrete structure of the underground underground pipe, The electrode device can be easily arranged at a required position, and the electrode device can be prevented from being damaged. Also, the equipment used can be transported manually, and the work at the site can be facilitated and the cost can be reduced. The cylindrical electrode device for anticorrosion according to the present invention can be easily moved in the cutting hole and can prevent C / S macrocell corrosion of the reinforced concrete structure penetrating portion of the underground pipe. In addition, the conductive filler according to the present invention can efficiently fill the space portion of the cutting hole provided in the vicinity of the reinforced concrete structure penetration portion.

  Therefore, this invention is used suitably for corrosion prevention of the reinforced concrete structure penetration part of underground piping.

FIG. 1: is process drawing which shows 1st Embodiment of the anticorrosion construction method of underground underground piping which concerns on this invention, and shows a process (1). FIG. 2: is process drawing which shows 1st Embodiment of the anticorrosion construction method of underground underground piping which concerns on this invention, and shows a process (2). FIG. 3 is a cross-sectional view showing an example of a cylindrical electrode device for cathodic protection according to the present invention. FIG. 4: is process drawing which shows 1st Embodiment of the anticorrosion construction method of underground underground piping which concerns on this invention, and shows a process (3). FIG. 5: is process drawing which shows 1st Embodiment of the anticorrosion construction method of underground underground piping which concerns on this invention, and shows a process (4). FIG. 6: is a perspective view which shows 2nd Embodiment of the anticorrosion construction method of underground underground piping which concerns on this invention, and shows a process (1). FIG. 7: is a perspective view which shows 2nd Embodiment of the anticorrosion construction method of underground underground piping which concerns on this invention, and shows process (2) and (3). FIG. 8 is a diagram illustrating a measurement method of a hardness test. FIG. 9 is a diagram for explaining a conductive filler leakage test, and shows a state immediately after rollover. FIG. 10 is a diagram for explaining a leakage test of the conductive filler, and shows a state after standing.

Explanation of symbols

1: Underground piping 2: Concrete wall 3: Core drill 4: Cylindrical core bit 5: Soil 6, 61, 62: Cutting hole 7: Casing tube 8: Cylindrical electrode device 9 for insulative protection 9: Insoluble anode 10: Lead wire 11: Synthetic resin protective pipe 12: Electrocorrosion backfill 13: Bearing 14: Pipe wrench 15: Pressure feed pump 16: Conductive filler 17: Reference electrode 18: Corrosion protection probe 19: Syringe 20: Measuring plate 21: Sample 22: Cylindrical container

Claims (3)

The following steps (1) to (4);
(1) A step of forming a cutting hole in a horizontal direction or an oblique direction in a concrete wall and soil from the inside of a reinforced concrete structure using a cylindrical core bit of a core drill in the vicinity of a reinforced concrete wall penetrating portion of an underground pipe.
(2) A cylindrical electrode device for cathodic protection having a plurality of bearings attached to the outer peripheral surface is slid into the cylindrical core bit in the cutting hole and a casing tube connected to the core bit, and the cutting hole is Installing at a predetermined position in
(3) a step of pulling out the cylindrical core bit and the casing tube from the cutting hole;
(4) Injecting a conductive filler into the space in the cutting hole,
The anticorrosion method for underground pipes, characterized in that The following steps (1) to (5);
(1) Install a cylindrical electrode device for cathodic protection in the horizontal or diagonal direction on the concrete wall and soil from the inside of the reinforced concrete structure using the cylindrical core bit of the core drill near the reinforced concrete wall penetration of the underground pipe. A step of forming a cutting hole for installing a corrosion prevention and detection unit composed of at least one of a cutting hole and a reference electrode separate from the cutting hole or a corrosion prevention detection probe;
(2) An anti-corrosion cylinder in which a plurality of bearings are attached to the outer peripheral surface in the cylindrical core bit in the cutting hole in which the cylindrical electrode device for anti-corrosion is installed and a casing tube connected to the core bit. Sliding the electrode device and installing it at a predetermined position in the cutting hole,
(3) Corrosion composed of at least one of a reference electrode or a corrosion protection detection probe in the cylindrical core bit in the cutting hole in which the corrosion protection detection unit is installed and a casing tube connected to the core bit. Inserting the anticorrosion detection unit and installing it at a predetermined position in the cutting hole;
(4) A step of pulling out the cylindrical core bit and the casing tube from the respective cutting holes,
(5) A step of injecting a conductive filler into the space in each cutting hole in which the cylindrical electrode device for corrosion protection and the corrosion protection detection unit are installed,
The anticorrosion method for underground pipes, characterized in that   The cylindrical electrode device for cathodic protection includes an electrode main body made of an insoluble anode or a galvanic anode, an insulating synthetic resin protective tube having a plurality of through holes in a peripheral side surface for protecting the electrode main body, and the protective tube. The anticorrosion method for underground pipes according to claim 1 or 2, comprising a backfill for cathodic protection to be filled and a plurality of bearings attached to the outer peripheral surface.

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