JPH09108624A - Method for protecting metallic tube-connecting part from corrosion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for protecting the metallic tube-connecting part from corrosion, capable of forming a hard anticorrosive protective layer excellent in corrosion preventiveness on the weld zone of clad metallic tubes without using a die in a short time. SOLUTION: A cylindrical body 4 consisting of thermoplastic resin is arranged to cover the connecting part A including the weld zone of metallic tubes 1 and 2 and the exposed surfaces 1a and 2a of the tubes on both sides of the weld zone. A liq. reactant contg. a norbornene-base monomer, a metathesis catalyst and an activator is injected into a cavity B formed by the connecting part A and the cylindrical body 4 and then cured to form an anticorrosive protective layer covering the connecting part A.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anticorrosion protection method for a metal pipe connecting portion, and more specifically, a connection portion formed by welding metal pipes to each other at a construction site has excellent anticorrosion performance and high hardness. The present invention relates to an anticorrosion protection method for a metal pipe connecting portion, which can be covered with an anticorrosion protection layer in a short time.

[0002]

2. Description of the Related Art When metal pipes such as steel pipes and stainless steel pipes are coated with polyethylene or polyurethane on the outer peripheral surface, when connecting metal pipes to each other at the construction site, the coating is the desired length from the pipe end. The pipe ends of the peeled and removed metal pipes are butted, and the butted parts are welded.

Therefore, after welding, at the connecting portion, there is a welded portion and the surface portion of the metal pipe which is bare at a desired length on both sides of the welded portion. It is necessary to apply anticorrosion treatment to the connection part. Conventionally, as the above-mentioned anticorrosion treatment, prior to the welding of the metal tubes to each other, a heat shrinkable tube is placed on one of the metal tubes,
After welding, the heat-shrinkable tube is moved to the welded part to cover the welded part and the bare exposed surface parts of the metal pipes on both sides of the welded part, and then the heat-shrinkable tube is sealed using, for example, a propane gas burner. A method in which a heat-shrinkable tube is brought into close contact with the outer periphery of the connection portion by heating and shrinking to cover the connection portion is widely adopted.

However, the commonly used heat-shrinkable tube is relatively soft and has excellent strength characteristics because its base material is composed of cross-linked medium density polyethylene. Therefore, if the metal pipe is buried in the ground, the heat-shrinkable tube after anticorrosion work may be damaged by the impact of the earth and sand applied during burial. The tubing may tear and lose its ability to protect the connection from corrosion.

Further, the outside of the connecting portion of the metal tube is covered with, for example, a metal mold having a split structure, and a liquid reactive resin is filled in a void portion formed between the metal mold and the connecting portion. Inject and
A method is also employed in which the reactive resin is thermoset and then the mold is removed to form an anticorrosion protective layer with a desired thickness that covers the connection portion. For example, a method is known in which a two-liquid mixed type urethane resin whose curing reaction is completed in about 0.5 to 1 hour is pressed into the cavity of the above-mentioned mold to cure.

[0006]

In the latter method using a mold, when a reactive resin whose hardened product has a high hardness is used, the anticorrosion protective layer of the anticorrosion protective layer is more than that when a heat shrinkable tube is used. The strength can be increased and the anticorrosion ability can be increased. However, in the case of this construction method, it is necessary to prepare various types of dies having different diameters according to the outer diameter of the connection portion to be subjected to anticorrosion treatment. However, since the mold is expensive, the cost at the time of construction using the mold is increased.

Further, when the outer diameter of the connecting portion is increased, the diameter of the die used is correspondingly increased. However, since such a die having a large diameter becomes a considerable weight, it can be used as a metal pipe. The work for arranging at the connection part also becomes large in scale, for example, by using a crane, and actual construction becomes considerably difficult. Further, depending on the type of reactive resin to be injected, the pressure during injection may be high. Therefore, when the mold is arranged at the connecting portion of the metal pipe, it must be arranged so that liquid leakage does not occur, and the work is considerably complicated.

The present invention solves the above-mentioned problems in the method of forming an anticorrosion protective layer by using a mold, and moreover, by using the reaction solution described later, the connection portion of the metal tube has high hardness and anticorrosion ability. It is an object of the present invention to provide an anticorrosion protection method for a connecting portion of a metal pipe, which is capable of forming an excellent anticorrosion protection layer in a short time and at low cost.

[0009]

In order to achieve the above object, in the present invention, there is provided a metal pipe including a welded portion of the metal pipe and a bare exposed surface portion of the metal pipe located on both sides of the welded portion. A tubular body made of a thermoplastic resin is disposed so as to cover the connecting portion, and a reaction liquid containing a norbornene-based monomer, a metathesis catalyst, and an activator in the void formed by the connecting portion and the tubular body. Is provided, and then the reaction solution is cured to form an anticorrosion protective layer that covers the connection portion.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, as shown in the partial cross-sectional view of FIG. 1, the anticorrosion coating (not shown) on the pipe end of the metal pipe 1 is removed to remove the surface portion 1a of the metal pipe 1. Naked
Further, the anticorrosion coating (also not shown) on the end of the metal pipe 2 to be welded is removed to expose the surface 2a of the metal pipe.
The ends of each metal pipe are butted against each other and welded together.

Therefore, the welded portion 3 and the bare exposed surface portions 1a and 2a located on both sides of the welded portion 3 are formed at the connecting portion A of the metal pipes 1 and 2 after the welding is completed. Then, as shown in FIG. 2, the tubular body 4 made of a thermoplastic resin is arranged so as to cover the outer peripheral surface of the connection portion A. Examples of the thermoplastic resin forming the tubular body 4 include polyethylene,
Ethylene / vinyl acetate copolymer resin, polypropylene, polystyrene, acrylonitrile / styrene resin, acrylonitrile / butadiene / styrene resin, methacrylic resin, polyvinyl chloride, polyamine, polycarbonate,
Polyethylene terephthalate, polybutylene terephthalate, cellulose acetate, diallyl phthalate,
Examples thereof include polybutadiene, chlorinated polyolefin, polyvinylidene chloride, polyacetal, polymethylpentene, butadiene / styrene resin, thermoplastic polyurethane, and polytetrafluoroethylene.

The tubular body 4 may be either a pipe or a tube formed by using any of the above-mentioned thermoplastic resins, and either of them can be used. Among them, the tube is highly flexible. It is preferable. Depending on the type of resin, a tube that is stretch-molded to have heat-shrinkability is more preferable. An inlet 4a for injecting a reaction solution described later and an air hole 4d for venting air are attached to the cylindrical body 4. The inner diameter of the tubular body 4 is larger than the outer diameter of the connecting portion A, the total length of the tubular body 4 is longer than that of the connecting portion A, and both end portions 4b and 4c thereof are
Coating layer 1b of metal tube 1 and coating layer 2 of metal tube 2, respectively
It has such a length that it surely overlaps a part of b.
The air holes 4d are usually mounted above so that the gas in the voids easily escapes when the reaction solution is injected and the reaction solution does not easily leak. On the other hand, the inlet 4a is
In order to prevent gas from remaining in the void, it is preferable to install it downward, while it is preferable to install it upward in terms of workability at the site. Just decide.

Both ends 4 of the cylindrical body 4 arranged
b and 4c are coating layers 1b and 2b of the metal tubes 1 and 2, respectively.
It is in close contact with. It should be noted that, prior to the formation of the above-mentioned connecting portion A, the tubular body 4 is attached to one of the metal pipes.
After the connection portion A is formed, the connection portion A may be moved and arranged so as to cover the connection portion A.

Thus, in the longitudinal direction of the tubular body 4, the coating layers 1b and 2b and the connecting portion A are provided between both ends 4b and 4c thereof.
A void portion B is formed so as to surround the. Tubular body 4
In order to make the structure in which gas and liquid do not leak by closely adhering both end portions 4b, 4c of the coating layer to the coating layers 1b, 2b, the coating layer 1
At a desired position on the surface of b, 2b, for example, a butyl rubber mastic is wound to form pressure-sensitive adhesive layers 5a, 5b, and the pressure-sensitive adhesive layers 5a, 5b and both ends 4b, 4c of the tubular body 4 are bonded together. Good.

In this case, a heat-shrinkable tube is used as the tubular body 4, both ends of the heat-shrinkable tube are brought into contact with the adhesive layer, and the contact point is selectively heated, so that only the heated point shrinks. Since it adheres to the pressure-sensitive adhesive layer, a more reliable liquid-tight structure can be formed, which is preferable. In this state, the reaction liquid is injected into the void B from the injection port 4a of the tubular body 4.

The reaction liquid used in the method of the present invention contains a norbornene-based monomer, a metathesis catalyst, an activator, and, if necessary, an optional component described later, and the norbornene-based monomer is It opens the ring to cause bulk polymerization. That is, in order to prevent bulk polymerization of the norbornene-based monomer with only one liquid, the above-mentioned components are divided into two or more liquids to prepare a reaction stock solution, and these are prepared immediately before injection into the mold. Each reaction stock solution is mixed.

The reaction solution has a low viscosity of about 300 cps immediately after mixing the reaction stock solution and has a very high fluidity. Therefore, when injecting the reaction liquid into the void B of the tubular body 4, it is not necessary to apply a large pressure to the reaction liquid, and the reaction liquid is promptly injected into the corner of the void B as the injection work is started. It flows into various parts and is injected in a homogeneous state without involving air.

When it is heated to a temperature of about 60 ° C., it is rapidly exothermicly cured and solidified within 5 minutes.
Since the process of this curing reaction is ring-opening polymerization, no decomposition gas is generated, and the mechanical strength characteristics such as compression hardness, elongation, flexural modulus, etc. begin to develop reliably from the initial stage of the curing reaction. The value of 50% or more of the final characteristic value is reached within about 10 minutes after the initiation of the curing reaction.

Here, as the norbornene-based monomer,
It may be anything as long as it has a norbornene ring, for example, a bicyclic compound such as norbornene or norbornadiene; a tricyclic compound such as dicyclopentadiene or dihydrodicyclopentadiene; a tetracyclododecene such as tetracyclododecene. Tetracycles; pentacycles such as tricyclopentadiene; heptcycles such as tetracyclopentadiene; alkyls such as methyl, ethyl, propyl, butyl, alkenyls such as vinyl, alkylidene such as ethylidene, phenyl. , Tolyl, naphthyl and the like substituted with an aryl; further, a substituent having a polar group such as an ester group, an ether group, a cyano group and a halogen atom.

These monomers may be used alone or in a suitable mixture of two or more kinds.
Among these, tricyclic, tetracyclic or pentacyclic are preferred because they are easily available, have excellent reactivity, and have excellent heat resistance of the cured product after the reaction. You can The norbornene-based monomer is ring-opening polymerized to be resinified and solidified. At this time, the ring-opening polymer to be formed is preferably thermosetting. For that purpose, 10% by weight or more, preferably 30% by weight or more, of the norbornene-based monomer to be used may be a crosslinkable monomer. This crosslinkable monomer has a reactivity of 2
A polycyclic norbornene-based monomer having two or more heavy bonds in one molecule, specifically, dicyclopentadiene,
Examples thereof include tricyclopentadiene and tetracyclopentadiene.

The metathesis catalyst is a catalyst for promoting the ring-opening polymerization of the norbornene-based monomer, and the kind thereof is not particularly limited, and metathesis is carried out to cause the ring-opening polymerization of the norbornene-based monomer. Any material may be used, and examples thereof include halides such as tungsten, molybdenum and tantalum, oxyhalides, oxides and ammonium salts.

The amount of the metathesis catalyst used is usually set to 0.01 to 50 mmol, preferably 0.1 to 20 mmol, per 1 mol of the norbornene-based monomer in the reaction solution used. If the amount used is too small, the activity for ring-opening polymerization of the norbornene-based monomer is too low and the ring-opening polymerization takes a lot of time, so that curing in the tubular body does not proceed rapidly, and However, if the amount used is too large, the ring-opening polymerization will proceed rapidly, and the reaction solution will cure in the process of being injected into the voids of the tubular body, or the metathesis catalyst will precipitate and the reaction solution will be homogeneous. It becomes difficult to save in the state.

An activator capable of enhancing the catalytic activity of the metathesis catalyst is further added to such a reaction solution. Any activator may be used as long as it can activate the metathesis catalyst, and examples thereof include alkylaluminum, alkylaluminum halides, alkoxyalkylaluminum halides, aryloxyalkylaluminum halides and organic tin compounds. .

The amount of the activator used is not particularly limited, but it is usually the metathesis catalyst 1 in the reaction solution.
It is set to 1 to 10 moles per mole. This is because if the amount used is too small or too large, the same disadvantages as in the case of the metathesis catalyst occur. Furthermore,
Other optional components such as known antioxidants, fillers, pigments, colorants, foaming agents, flame retardants, and solid lubricants such as graphite may be added to the reaction liquid.

In addition, polybutadiene, styrene-butadiene copolymer, styrene-butadiene-
When a diene elastomer such as a styrene copolymer or a styrene-isoprene-styrene copolymer, natural rubber, polyisoprene, or ethylene-propylene-diene terpolymer is blended, the impact resistance of the obtained cured product is improved. Therefore, it is preferable. When the diene-based elastomer is blended, the blending amount is set to 15% by weight or less, preferably 10% by weight or less, based on the weight of the norbornene-based monomer in the reaction solution. This is because if the blending amount becomes too large, the reaction liquid becomes highly viscous, and it becomes difficult to inject it into the tubular body, and at the same time, the heat resistance and rigidity of the cured product begin to decrease.

As described above, the reaction solution comprising the above components is prepared by dividing the reaction solution into two or more solutions so that the ring-opening polymerization reaction of the norbornene-based monomer does not occur with only one solution. It is prepared and mixed immediately before the injection work into the tubular body, at which time the ring-opening polymerization reaction of the norbornene-based monomer occurs and the curing reaction proceeds.

For example, a reaction stock solution A containing a norbornene-based monomer, a metathesis catalyst, and other optional components, and a reaction stock solution B containing a norbornene-based monomer, an activator, and other optional components are each used alone. Does not cause a curing reaction. However, when the reaction stock solution A and the reaction stock solution B are mixed,
At that time, a component necessary for the ring-opening polymerization reaction, that is,
A reaction solution in which all of the norbornene-based monomer, the metathesis catalyst, and the activator are prepared, and the ring-opening polymerization reaction of the norbornene-based monomer starts. In the present invention, the reaction stock solution is mixed to form a reaction solution, which is immediately poured into the void portion of the cylindrical body to be cured.

Usually, a mixing head of a reaction injection molding machine is attached to the injection port of a tubular body, and two or more kinds of the above-mentioned reaction stock solutions are simultaneously injected into the mixing head to cause collision and mixing, thereby producing a reaction solution. Is prepared and poured into the void portion of the tubular body as it is. Since the method of the present invention is applied at a construction site, considering the workability thereof, it is preferable to prepare a reaction solution using two types of reaction stock solutions.
The reaction solution may be prepared using more than one kind of reaction stock solution.

In this case, since the norbornene-based monomer and the respective components are sufficiently mixed with each other after the reaction stock solutions are mixed and the ring-opening polymerization proceeds, the reaction stock solutions before mixing are
In both cases, it is preferable to contain a norbornene-based monomer. However, when the norbornene-based monomer, the metathesis catalyst, and the activator are contained in the reaction stock solution before mixing, ring-opening polymerization of the norbornene-based monomer starts before mixing, and therefore, normally, The metathesis catalyst and the activator do not coexist in one reaction stock solution.

The viscosity of the reaction stock solution to be used is not particularly limited, but if the viscosity is too high or too low, it becomes difficult to mix the reaction stock solutions and inject it into the cylindrical body. Is usually 50 to 2000 cps, preferably 10
It is set within the range of 0 to 1000 cps. When the reaction solution prepared by mixing the above-mentioned reaction stock solution is injected into the void B of the tubular body 5 shown in FIG. 2, the ring-opening polymerization reaction of the norbornene-based monomer proceeds in the void B to generate heat. Then, the injected reaction liquid becomes a cured product.

As a result, as shown in FIG.
On the outer peripheral surface of, the anticorrosion protective layer 6 is formed by covering the connection portion A and the coating layers 1b and 2b. Thereafter, the outermost tubular body 4 may be peeled and removed. Even if it is left as it is, it does not cause any inconvenience to the anticorrosion ability of the anticorrosion protective layer. As the constituent resin of the tubular body 4, a thermoplastic resin that melts by the reaction heat generated by the ring-opening polymerization of the reaction solution, for example, polyolefin such as polyethylene or polystyrene is used. During the thermosetting process of the reaction solution, the inner surface of the tubular body melts and mixes with the reaction solution, and after cooling, it comes into close contact with the formed anticorrosion protective layer, thereby further improving the anticorrosion ability. This is preferable because it can be improved.

Further, in the method of the present invention, prior to disposing the tubular body on the outside of the connecting portion, the following treatment may be applied to the connecting portion because the anticorrosion protection effect can be further enhanced. is there. That is, in the connection portion A shown in FIG. 2, after applying a conventional anticorrosion brimer to the outer peripheral surfaces of the welded portion 3, the bare surface portions 1a and 2a, and the coating layers 1b and 2b, for example, butyl Adhesive sheet or tape consisting of adhesive rubber mixture containing tackifier (tackifier), softening agent, and cross-linking agent as main component of system rubber, or wound directly, or directly used anticorrosion tape After winding, or after closely covering the heat-shrinkable tube in the same manner as in the past, place a tubular body on the outside,
When the anticorrosion protective layer made of a polymer of norbornene-based monomer is formed, the hot melt adhesive is softened by the heat generated during the curing reaction of the reaction liquid and firmly adheres to the connection portion, and the formed cured layer is formed. Firmly adhere to the inner surface of
A more excellent anticorrosion protective layer is formed.

[0033]

【Example】

Example 1 The connection portion of the coated steel pipes 1 and 2 shown in FIG. 1 (outer diameter 216.3 m)
m, length 450 mm), a heat-shrinkable tube 4 having an inner diameter of 265 mm and a length of 600 mm was arranged. Therefore, the both ends 4b and 4c of the heat-shrinkable tube 4 have a thickness
It overlaps with the coating layers 1b and 2b of 2.5 mm with a length of 75 mm.

Prior to the arrangement of the heat shrink tube 4,
The surface of the connection portion A was subjected to a surface treatment of about SIS St-3 with a disk sander, and the surfaces of the coating layers 1b and 2b were roughened with sandpaper having a grain size of about 80. This heat-shrinkable tube 4 is made of cross-linked polyethylene,
It was a tube having a heat shrinkage of%.

Then, both ends 4b of the heat shrinkable tube 4 are
Butyl rubber mastics 5a and 5b are wound around the surfaces of the plastic coatings 1a and 1b corresponding to the position 4c, and the ends 4b and 4b are wrapped with the butyl rubber mastics 5a and 5b, and then the ends 4b and 4c are heated by a propane gas burner. Heat-shrink and adhere to the mastics 5a and 5b, and then heat-shrink tube 4
As shown in FIG. 2, the void B was formed.

On the other hand, 75 parts by weight of dicyclopentadiene and 25 parts by weight of asymmetric cyclopentadiene trimer were mixed,
Here, 5 parts by weight of a styrene-isoprene-styrene block copolymer (trade name, Kraton 1170, manufactured by Ciel) and 2 parts by weight of a phenolic antioxidant (trade name, Irganox 1010, manufactured by Ciba Geigy) are dissolved. , The obtained solution is divided into two liquids, one of which is
40 millimoles of diethylene aluminum chloride (activator), 44 millimoles of n-propanol per liter,
Reaction active ingredient A was prepared by blending 20 mmol of tetrasilicon.
To the other solution, 10 mmol of tri (tridecyl) ammonium molybdate (metathesis catalyst) was added per liter to prepare a reaction active material B. Both reaction actives A and B were kept on standby at a temperature of 30 ° C.

Then, the above-mentioned reaction stock solution A and reaction stock solution B were prepared.
The same volume was mixed using a reaction injection molding machine to form a reaction liquid, which was immediately injected into the void B from the injection port 4a of the heat shrinkable tube 4. After 5 minutes, a very hard anticorrosion protective layer having an Izod impact strength of 40 kg · cm / cm was formed on the outside of the connection portion A and the polyethylene coating layers 1b and 2b.

Then, the place where the anticorrosion protective layer is formed is immersed in an outdoor water tank for one month and then taken out, and the insulation resistance of the anticorrosion protective layer is measured using a mega ohm meter.
Then, the anticorrosion protective layer was peeled off to expose the connection part A, and the presence or absence of rust on the exposed surface was visually observed. The insulation resistance was very large at 10 ¹⁰ Ω · m ^2, and no rusting was observed.

Example 2 The outside of the connecting portion A and the polyethylene coating layers 1b and 2b was 450 mm in length, 265 mm in inner diameter, and 0.6 mm in thickness on the inner surface.
The anticorrosion protective layer was formed in the same manner as in Example 1 except that the polyethylene heat-shrinkable tube (thickness: 1.2 mm) on which the butyl rubber-based pressure-sensitive adhesive layer was adhered was coated.

In this case, the insulation resistance and the rusting condition were examined by the same use as in Example 1. The insulation resistance was about 10 ¹⁰ Ω · m ² , and no rusting was observed.

[0041]

According to the method of the present invention, when the anticorrosion protective layer is formed on the connection portion of the metal pipe, the connection portion of the metal pipe is arranged by the tubular body of thermoplastic resin instead of the conventional mold. The work of transporting, arranging, removing, and cleaning heavy dies is no longer required as in the prior art, and the construction efficiency at the site is extremely high. Further, since the reaction liquid is composed of the norbornene-based monomer, the metathesis catalyst and the activator, it takes a very short time,
It is possible to form an anticorrosion protective layer having excellent anticorrosion ability.

In the case of the methods of claims 2 and 6, since the formed anticorrosion protective layers are a plurality of layers in close contact with each other, the overall anticorrosion ability is further improved. In the method of claim 3, since the heat-shrinkable tube is used as the cylindrical body, the force for constantly tightening the anticorrosion protective layer that is being formed continues to act during the curing process of the reaction solution, so that the leakage of the injected reaction solution is prevented. It is possible to prevent it and improve the adhesion between the anticorrosion protective layer and the connecting portion.

In the method of the fourth aspect, only the both ends of the heat-shrinkable tube shrink and come into close contact with the connecting portion of the metal tube, so that liquid leakage does not occur when the reaction solution is injected into the tubular body. . In the case of the method of claim 5, since both ends of the tubular body and the adhesive layer are liquid-tightly adhered to each other, liquid leakage of the reaction liquid can be reliably prevented.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view showing a state in which coated metal pipes are welded to each other at their pipe ends.

FIG. 2 is a partial cross-sectional view showing a state in which a tubular body is arranged outside the connection portion of FIG.

FIG. 3 is a partial cross-sectional view showing a state in which an anticorrosion protective layer is formed on a connection portion.

[Explanation of symbols]

 1, 2 Coated metal pipe 1a, 2a Bare metal surface 1b, 2b Coated metal pipe 1, 2b Coating layer 3 Welded portion 4 Thermoplastic resin cylinder 4a Reactant injection port 4b, 4c Cylindrical body 4 Both ends 4d Air holes 5a, 5b Adhesive layer 6 Corrosion protection layer A Connection part B Void part

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kazuo Toho 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Zeon Co., Ltd. (72) Inventor Makoto Yamamoto 1-2-1, Yokou, Kawasaki-ku, Kanagawa No. ZEON Corporation, R & D Center (72) Inventor Hirotoshi Tanimoto 1-2-1, Yokou, Kawasaki-ku, Kawasaki-shi, Kanagawa ZEON Corporation, R & D Center

Claims (6)

[Claims] 1. A tubular body made of a thermoplastic resin is disposed so as to cover a welded portion of a metal pipe and a connecting portion of the metal pipe including a bare exposed surface portion of the metal pipe located on both sides of the welded portion. , An anticorrosion coating the connection portion by injecting a reaction liquid containing a norbornene-based monomer, a metathesis catalyst, and an activator into the void formed by the connection portion and the tubular body, and then curing the reaction liquid. A method for protecting a metal pipe connecting portion from corrosion by forming a protective layer. 2. The anticorrosion protection method for a metal pipe connecting portion according to claim 1, wherein the anticorrosion protection layer comprises a layer of a cured product of the reaction solution and a layer of the tubular body fused to the surface thereof. 3. The anticorrosion protection method for a metal pipe connecting portion according to claim 1, wherein the tubular body is a heat-shrinkable tube. 4. A heat-shrinkable tube is used as the tubular body, and the heat-shrinkable tube is arranged at the connection portion,
The anticorrosion protection method for a metal pipe connecting portion according to claim 1, wherein only both end portions of the heat shrinkable tube are selectively heated to cause heat shrinkage, and only both end portions of the heat shrinkable tube are brought into close contact with the connecting portion. 5. The metal pipe connecting portion according to claim 1, wherein an adhesive layer is provided at a portion of the connecting portion where both ends of the tubular body come into contact when the tubular body is arranged in the connecting portion. Anticorrosion protection method. 6. The winding treatment of the pressure-sensitive adhesive sheet, which is performed after applying an anticorrosive primer to at least the outer periphery of the connecting portion prior to disposing the tubular body on the connecting portion of the metal tube according to claim 1. 1. A method for preventing corrosion of a metal pipe connecting portion, wherein any one of a winding treatment of an anticorrosion tape and an adhesion coating treatment of a heat-shrinkable tube is performed.