JPH10329216A - Self-heating type heat shrinkable tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a body to be protected from being corroded even when the body to be protected comes into contact with a heating body, by a method wherein for a heat shrinkable tube which covers the body to be protected, the heating body is provided in the heat shrinkable tube, and the heating body is formed of a metal body having a lower electric potential than the metal body which forms the body to be protected. SOLUTION: This self-heating type heat shrinkable tube is constituted by providing a heat shrinkable tube 1, an adhesive layer 2 and a heating body 3. The heating body 3 is a heating wire comprising an aluminum wire, and when a body P to be protected is made a steel pipe, for the material of the heating body 3, a metal having a lower electric potential than steel is used. For the adhesive layer 2, e.g. a mixture of asphalt and rubber to which various kinds of additives are mixed is used. Thus, by using a metal body having a lower electric potential than steel after applying the heat shrinkable tube, even if the heat shrinkable tube is damaged and the steel electrically comes into contact with the heating body 3, the heating body 3 becomes an anode, and the steel becomes a cathode, and even if the heating body 3 is corroded, the steel can be prevented from being corroded.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a self-heating type heat-shrinkable tube for covering a welding joint of a pipe such as a gas pipe, a water pipe, an electric power pipe and the like for corrosion protection.

[0002]

2. Description of the Related Art Generally, steel pipes used for gas pipes, water pipes, electric power pipes and the like are coated with a synthetic resin material such as polyethylene in a corrosion preventing coating in a manufacturing process. Since the pipe joint is welded at the piping site, the end of the pipe body is not provided with an anticorrosion coating, and it is necessary to perform the anticorrosion coating process at the piping site each time.

[0003] As a method of this anti-corrosion coating, as shown in FIG. 2, a steel pipe P is connected at a welding beat portion a, and the pipe joint portion is made of a heat-shrinkable synthetic resin material such as cross-linked polyethylene. The coating is performed by covering the heat-shrinkable tube c and heating and shrinking it manually by a burner or the like. However, in places where the use of open flames is restricted, such as joint ditch, etc., in order to automate the process of shrinking the heat-shrinkable tube, a heating wire is previously built in the heat-shrinkable tube in a bellows shape. A self-heating type heat-shrinkable tube which shrinks and coats the heat-shrinkable tube by energizing a heating wire made of a copper wire to generate heat has been proposed.

[0004]

However, when the heat-shrinkable heat-shrinkable tube with the heating wire is used to protect the pipe joint from corrosion, the heat-shrinkable tube is damaged by the external mechanical force after the heat-shrinkable tube is installed. As a result, the steel and the heating wire may come into electrical contact. A copper wire is used as a conventional heating wire material. Since copper is a metal having a redox potential higher than that of steel, there is a concern that steel serves as an anode, and a copper heating wire serves as a cathode, iron ions of the steel are dissolved, and the steel pipe is corroded.

When the pipe joint is covered with a heat-shrinkable tube, as shown in FIG.
Also, when a step is generated between the steel pipe surface and the factory coating part b, and the pipe joint is covered with a heat-shrinkable tube containing a heating wire made of copper wire, the copper wire has high rigidity and is hardly deformed. However, there is a drawback that it is difficult to conform to the shape of the above, and it is difficult to follow the deformation of the contracted portion. Therefore, heat shrink tube c
In the stepped portion between the factory coating portion b and the surface of the steel pipe, or at the stepped portion between the welding beat portion a and the surface of the steel tube, a gap d is generated because the exposed steel tube surface cannot be sufficiently contacted. When the gap d is generated, air enters, so-called air voids are generated, and a portion where the heat-shrinkable tube and the surface of the steel tube are not bonded is generated.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and can prevent corrosion of a protected object even when the protected object and a heating element are in electrical contact with each other. It is an object of the present invention to provide a self-heating type heat-shrinkable tube having a built-in heating element made of a material that does not impair the adhesion to a step portion or the like.

[0007]

In order to achieve the above object, according to the present invention, there is provided a heat-shrinkable tube for covering an object to be protected, wherein the heat-shrinkable tube has a heating element inside the heat-shrinkable tube. A self-heating type heat-shrinkable tube made of a metal having a lower potential than a metal forming a protected body. According to the present invention, a heating element is provided inside the heat-shrinkable tube, and after the heat-shrinkable tube is constructed, the heating element is exposed by a mechanical external force, and the heating element and the protected object (for example, a steel pipe) are electrically connected. Even if it comes into contact with the heating element, since the heating element becomes the anode and the protected body (steel pipe) becomes the cathode, even if the metal of the heating element corrodes, the protected body (steel pipe) does not corrode.

The invention according to claim 2 is the self-heating type heat-shrinkable tube according to claim 1, wherein the heating element is made of an aluminum wire. According to the present invention, the heating element is an aluminum wire, and even if the heating element is built in the heat-shrinkable tube, it is a material having good adhesion to the stepped portion, it is difficult to form a gap, and it is hard to generate an air void.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a self-heating type heat-shrinkable tube according to the present invention will be described below with reference to the drawings. 1 (a) and 1 (b) are views showing one embodiment of the present invention, and FIG. 1 (a) is a partial cross-sectional view showing a self-heating type heat-shrinkable tube which covers a pipe joint of a steel pipe. FIG. 1B is a cross-sectional view showing a steel pipe covered with a self-heating type heat-shrinkable tube.

FIG. 1 shows a self-heating type heat-shrinkable tube of the present invention, which covers a pipe joint to prevent corrosion. As shown in FIG. 1 (a), a heat-shrinkable tube 1
The heat-shrinkable tube 1 includes an adhesive layer 2 formed on the inner surface of the heat-shrinkable tube 1 and a heating element 3 buried in the heat-shrinkable tube 1 by a heating wire. The heat-shrinkable tube 1 in which the heating element 3 is embedded is referred to as a self-heating type heat-shrinkable tube.

The heat-shrinkable tube 1 is a tube made of a thermoplastic resin such as a polyethylene tube or a cross-linked polyethylene tube. The heat-shrinkable tube 1 is made of a thermoplastic resin other than polyethylene, such as denatured polyethylene, vinyl chloride, polypropylene, ethylene vinyl acetate copolymer, polytetrafluoroethylene or tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer, etc. Ethylene / propylene copolymers, silicone rubber, and the like and crosslinked resins thereof are used.

The heating element 3 is a heating wire made of an aluminum wire, and may have a circular cross section or a ribbon shape. The heating element 3 is made of a metal having a potential lower than that of steel, and has a bellows shape, as shown in FIG. 1B, and has both ends as end electrodes 3a. An adhesive layer 2 is formed on the inner surface of the heat-shrinkable tube 1. The pressure-sensitive adhesive layer 2 is, for example, a mixture of asphalt and rubber mixed with various additives.

On the other hand, FIG. 1 (b) shows a steel pipe covered with a self-heating type heat-shrinkable tube 1, in which a factory coated part b of a coated steel pipe p near a pipe joint is peeled off, and an end thereof is provided. Is welded, and then the exposed surface of the steel pipe between the factory coating portions b and the welding beat portions a are coated with a heat-shrinkable tube. As described above, the ends of the weld beet portion a and the factory covering portion b of the coated steel pipe are covered with the heat-shrinkable tube 1.

By using a metal body having a potential lower than that of steel as the heating element, the heat-shrinkable tube is damaged by external mechanical force after the heat-shrinkable tube is constructed, and the steel and the heating element which is a heating wire are separated. Even in electrical contact, the heating element becomes the anode, the steel becomes the cathode, and even if the heating element is corroded, the steel is not corroded.

Next, experimental results of an example of the self-heating type heat-shrinkable tube of this embodiment and a comparative example will be described. The results of this comparative experiment show average results.

In this embodiment, referring to FIG. 1, a cross-linked polyethylene tube 1 is used as a heat-shrinkable tube, an adhesive layer 2 is formed on an inner surface thereof, and a heating element 3 made of aluminum wire is a bellows. It is built in the shape. This self-heating type heat-shrinkable tube has a tube diameter of 2
The heat-generating element 3 was energized to thermally shrink it over the welded joint portion of the steel pipe of 00A, and was subjected to roller cling to coat the pipe joint portion. Thereafter, the heat-shrinkable tube was peeled off, and voids were detected. As a result, no air void having a diameter of 5 mm or more could be confirmed between the steel pipe and the self-heating type heat-shrinkable tube.

On the other hand, in the comparative example, the material of the heating element was different from that of the example. A cross-linked polyethylene tube was used for the heat-shrinkable tube, an adhesive layer was formed on the inner surface thereof, and a copper wire was used. A heating element (heating wire) is built in bellows. The heat-generating type heat-shrinkable tube was put on a welded joint portion of a steel pipe having a diameter of 200 A, a heat-generating body was energized to thermally shrink, and a roller was applied to coat the tube-joint portion. Thereafter, the heat-shrinkable tube was peeled off in the same manner as in the example, and a void was detected. as a result,
5mm in diameter between steel pipe and self-heating type heat shrink tube
There were six air voids. As is clear from this result, when the heating element is a copper wire, it has become clear that the copper wire has an effect of inhibiting adhesion to the pipe joint when the heat-shrinkable tube shrinks.

In this embodiment, a steel pipe is described as a pipe to be protected. However, a pipe of another material may be used, and the material of the pipe is not limited to a steel pipe. The heating element may be a metal having a lower potential than the metal of the tube.

[0019]

As described above, according to the present invention, a metal body having a potential lower than that of steel, which is a protected object, is used as a heating element. Even if the shrink tube is damaged and the steel and the heating element come into electrical contact, even if the heating element becomes an anode and the steel becomes a cathode and the heating element is corroded, the steel is not corroded.

Further, according to the present invention, since a heating element made of an aluminum wire softer than a copper wire is used, the degree of adhesion at a stepped portion such as a steel pipe is good, and the stepped portion is formed when the heat-shrinkable tube shrinks. Close contact with the part,
Adhesion defects (gaps) are less likely to occur, and this has the effect of reducing the occurrence of air voids. Further, according to the present invention, there is an advantage that the surface shape of the heat-shrinkable tube after heat-shrinkage is smooth by using an aluminum wire as the heating element incorporated in the heat-shrinkable tube.

[Brief description of the drawings]

FIG. 1 (a) is a partial cross-sectional view showing one embodiment of a self-heating type heat-shrinkable tube according to the present invention, and FIG. 1 (b) is a cross-sectional view showing a construction state thereof.

FIG. 2 is a cross-sectional view showing a construction state of a conventional heat-shrinkable tube.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heat shrink tube 2 Adhesive layer 3 Heating element 3a End electrode

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Ryoichi Ikeda 1-2-1, Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation

Claims (2)

[Claims] 1. A heat-shrinkable tube for covering an object to be protected, wherein the heat-shrinkable tube has a heat-generating element inside the heat-shrinkable tube, and the heat-generating element has a lower electric potential than the metal body forming the object to be protected. A self-heating type heat-shrinkable tube characterized in that: 2. The self-heating type heat-shrinkable tube according to claim 1, wherein said heating element is made of an aluminum wire.