JP2000185353A - Method for partial anticorrosion of outer surface anticorrosive metal tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To recycle an electric heating mat and to conduct a method for heat shrinking a heat shrinkable anticorrosive material by heating the mat by energizing by guaranteeing good anticorrosive performance by covering a part to be anticorrosive of an outer surface anticorrosive metal tube with a heat shrinkable anticorrosive material and enclosing the material with the mat. SOLUTION: The method for partly anticorroding an outer surface anticorrosive metal tube comprises the steps of covering the tube with a heat shrinkable anticorrosive material 3, covering the material 3 with an electric heating mat 1 divided in a predetermined width with a circumferential direction of the tube set to the width direction, and covering the mat 1 with a heat shrinkable temporary retaining material 4. The method further comprises the steps of heating the mat 1 by energizing to radially shrink the mat 1 by heat shrinkage of the material 4 to bring it into pressure contact with the material 3, heat shrinking the material 3, finally removing the material 4 and removing the mat 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a partial corrosion protection method for an external corrosion-resistant metal pipe, and is useful for preventing corrosion of a welded joint of the external corrosion-resistant metal pipe and for repairing an existing external corrosion-resistant metal pipe.

[0002]

2. Description of the Related Art When a city gas pipeline, a water pipeline, a pipeline for transporting oil and steam, and the like are constructed by welding and joining external corrosion-resistant metal pipes that have been corrosion-protected at a factory, the welded joints are protected from heat shrinkage. It may be coated with foodstuffs, such as heat shrinkable plastic tubes. In this heat-shrinkable plastic tube, uniform heating is difficult with burner heating because the dimensions are considerably large.

Therefore, (1) a heat-shrinkable anticorrosive material is wound around a portion to be protected, and the above-mentioned anticorrosion material-wound layer is covered with a heat-shrinkable sheet containing a heating wire. A method in which the built-in heat-shrinkable sheet is heat-shrinked and pressed against the heat-shrinkable anticorrosion material, and the heat-shrinkable anticorrosion material is heat-shrinked (Japanese Patent Laid-Open No. 6-182872). (2) As shown in FIG. Wrap the heat-shrinkable anticorrosion material 3 'around the portion to be protected,
A heating jig 1 'having a heating wire attached to a heat-resistant sheet 11' and a spring-type band 12 'attached to an end thereof is wound around the heat-shrinkable anticorrosion material 3', and its winding end is formed by a spring-type band 1.
2 ', the heat shrinkable anticorrosive material 3' is thermally contracted by the heat generated by the heating jig 1 ', and the heat of the heat shrinkable anticorrosive material 3' is shrunk. The heating jig 1 'is reduced in diameter by the compression reaction force, and the heat shrinkage of the heat-shrinkable anticorrosion material 3' is advanced while the pressure-contact state between the heating jig 1 'and the heat-shrinkable anticorrosion material 3' is maintained. (For example, Japanese Utility Model Laid-Open No. 57-128791) and the like have been proposed.

[0004]

However, in the above method (1), the heat-shrinkable sheet with a built-in heating wire is deformed by heat shrinkage, and the heat-shrinkable sheet with a built-in heating wire is reused. It is difficult and uneconomical.

In the above method (2), the sheet jig provided with a heating wire can be reused, but the diameter of the jig is reduced when the sheet provided with a heating wire is tightened by the spring stress of a spring band. Since the sliding is performed, the outer surface of the anticorrosion material is roughened by friction with the sheet jig provided with the heating wire, and there is a concern that the anticorrosion performance may be deteriorated. As the pressure contact force is increased and the tightness between them is increased to improve the heat transfer efficiency, the friction becomes stronger and the outer surface of the heat-shrinkable anticorrosion material becomes more prominent). In addition, since the lap portion of the sheet provided with the heating wire is concentrated at one location where both ends are overlapped in the circumferential direction of the pipe, work defects due to uneven heating, for example, local burning of the anticorrosive coating are likely to occur.

An object of the present invention is to cover a portion to be protected of an external corrosion-resistant metal tube with a heat-shrinkable anticorrosion material, surround the heat-shrinkable anticorrosion material with a current-carrying heating mat, and generate heat with the current-carrying heating mat. It is an object of the present invention to provide a method for thermally shrinking a heat-shrinkable anticorrosive material, in which a current-carrying heating mat can be reused, and a partial anti-corrosion method for an outer anti-corrosion metal pipe that can be performed with assurance of good anti-corrosion performance. .

[0007]

According to the present invention, there is provided a partial corrosion protection method for an external corrosion-resistant metal pipe according to the present invention, in which a portion to be protected of the external corrosion-resistant metal pipe is covered with a heat-shrinkable corrosion-resistant material, and the circumferential direction of the pipe is set to a predetermined width. Cover the anticorrosion material with an energizing heating mat divided by
The energized heating mat is covered with a heat-shrinkable temporary holding material, and the energized heating mat is energized to generate heat so that the heat-shrinkage of the temporary holding material reduces the diameter of the mat cover so that the mat can be pressed against the anticorrosion material and prevented. It is characterized by heat shrinking the food material, finally removing the temporary holding material, and removing the energizing heating mat.After covering the energizing heating mat with the heat shrinking temporary holding material, it is protected from corrosion. The portion may be surrounded by a decompression chamber, and the heating mat may be energized and heated under reduced pressure.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of a current-carrying heating mat 1 used in the present invention, which is divided by a predetermined width with the circumferential direction of the portion to be wound protected being a width direction (Y direction). 11 are connected by a flexible insulated wire 12, and the mat unit has flexibility and sufficient heat generation uniformity that can be easily deformed corresponding to the circular surface of the tube outer surface. Any suitable one can be used.

For example, FIGS. 2A and 2B
As shown in the cross-sectional view of FIG.
Insulating heating wires 13 are arranged in a meandering shape (the direction X of the linear portion and the Y direction are orthogonal to each other), and these meandering heating wires are sandwiched between heat-resistant plastic films 14, 14, and FIG. ) And (b) of FIG. 3 (a cross-sectional view of FIG. 3 (a)), opposed electrodes 16 are provided on an insulating base plastic film 15. It is possible to use a material in which a heat-generating conductive film 17 is provided therebetween and these are covered with an insulating cover plastic film 18.

The above-mentioned energizing heating mat 1 is shown in FIG.
As shown in the figure, the coil is used by being wound on the portion to be protected, the overlap margin a between the mat units 11 is increased at the time of diameter reduction, and the final diameter of the diameter reduction is substantially equal to the outer diameter of the portion to be protected. A sufficient extra length is provided to the flexible insulated wires [12 in FIG. 1] for connecting the mat units so that the diameter can be reduced. It is preferable that the mat units are connected in a blind manner on condition that the final diameter can be reduced.

FIGS. 4 (a) to 4 (c) are drawings showing the working procedure of the method for partial corrosion protection of the external corrosion-resistant metal pipe according to the present invention. In FIG. 4, reference numeral 2 denotes an external corrosion-resistant metal tube,
In the factory, steel pipes are subjected to external corrosion protection except for the pipe ends (for example, coating of asphalt, coal enamel, polyethylene, epoxy resin, urethane resin, etc.), and welding and joining the pipe ends to each other on site I have.

In order to prevent the above-mentioned welded joint from being corroded according to the present invention, first, as shown in FIG. 4A, the welded joint 20 is covered with the heat-shrinkable anticorrosive material 3 so as to cover the end portion 21 of the anticorrosion layer of the factory. I do. In order to surround the heat-shrinkable anticorrosive material, a previously drawn heat-shrinkable plastic tube is pulled back onto the welded joint, and a heat-shrinkable plastic sheet is wound around the welded joint once. A method of binding both ends with a fastener or the like can be used. The heat-shrinkable plastic tube or the plastic sheet having an inner surface coated with an adhesive can be used.

After the welded joint is thus surrounded by the heat-shrinkable anticorrosive material, as shown in FIG. Once, and the mat units 11 are wrapped so as to leave no gap between them. This heating type heating mat 1
The mat 1 is longer than the heat-shrinkable anticorrosive material 3 so that the heat-shrinkable anticorrosive material 3 can be completely surrounded by the mat.

Further, as shown in FIG. 4C, the electrically conductive heating mat 1 is surrounded by a heat-shrinkable temporary holding member 4. In order to surround the temporary holding member, a heat-shrinkable plastic tube previously drawn in is pulled back onto the welded joint, a heat-shrinkable plastic sheet is wound once around the welded joint, and both ends thereof are wound. A method of binding with a fastener, a method of winding a heat-shrinkable plastic sheet a plurality of times, and the like can be used. The length of the temporary holding member 4 is longer than the length of the heat-shrinkable anticorrosion material.

After being surrounded by the temporary holding member in this way, the above-mentioned energizing heating mat 1 is energized and heated. The heat-shrinkable temporary holding member 4 is thermally contracted by the heat generated by the current-carrying heating mat 1.
Slip occurs on the lap surface between the mat units 11 and 11, and the lap allowance a is increased, the mat 1 is reduced in diameter, and the mat 1 and the heat-shrinkable anticorrosion material 3 are pressed against each other to reduce the heat generated by the mat. The heat transfer to the heat-shrinkable anticorrosive material is efficiently performed, and the heat-shrinkable anticorrosive material 3 is thermally contracted. At this time, the frictional force f of the lap surface sliding between the mat units 11 and 11 acts as a compressive force on the mat unit in the width direction (the above-described Y direction). The diameter of the heating mat 1 can be reduced smoothly without buckling of the mat unit 11.

In the above, the diameter of the heat-shrinkable temporary holding material 4, the diameter of the electrically conductive heating mat 1, and the diameter of the heat-shrinkable anticorrosion material 3 are simultaneously reduced, and the inner peripheral surface of the electrically conductive heating mat 1 is reduced. Since no slippage occurs between the outer peripheral surfaces of the heat-shrinkable anticorrosive material 3, the outer surface of the heat-shrinkable anticorrosive material 3 can be held on a smooth surface without roughness.

In the above description, if the number of mat units of the energizing heating mat is n and the outer diameter of the portion to be protected is d, the wrap portions of the mat units are present at intervals of approximately πd / n in the circumferential direction. The heavy heating spots of the heating mat are present at intervals of approximately πd / n in the circumferential direction. However, if n is made sufficiently large and the spacing between the heavy heating spots is shortened, the location of the heavy heating spot and its heavy heating The temperature difference from the spot intermediate point can be suppressed to a small value, so that heating can be performed sufficiently uniformly. Therefore, as compared with the method disclosed in Japanese Utility Model Application Laid-Open No. 57-128791, in which only one overlapping portion of both ends of the electric heating mat is wrapped, unreasonableness due to uneven heating, for example, burnout at the wrapped portion can be eliminated well. The division number n of the current-carrying heating mat satisfies n ≧ 2. In particular, it is preferable that n = 4 to 16.

After the heat-shrinkable anticorrosive material 3 has been sufficiently heat-shrinked as described above, the heating of the current-carrying heating mat 1 is stopped, and after cooling to normal temperature, the temporary holding material 4 is removed. Then, the electric heating mat 1 is removed, and the anticorrosion treatment according to the present invention is completed. Thus, according to the present invention, the energizing heating mat can be reused, and in spite of the use of the energizing heating mat, the surface of the heat-shrinkable anticorrosion material at the time of mat diameter reduction or mat unit wrap is used. The resulting uneven heating can be prevented well, and the corrosion can be prevented with good appearance and good anticorrosion performance.

In the present invention, the heat-shrinkable anticorrosive material and the heat-shrinkable plastic tube or the heat-shrinkable plastic sheet as the temporary holding material include heat-shrinkable polyethylene, heat-shrinkable polypropylene and heat-shrinkable polypropylene. Vinyl chloride, heat-shrinkable polyamide, preferably an electron beam crosslinked gel fraction of 30 to
Tubes or sheets of 60% cross-linked polyethylene can be used. As the adhesive applied to the inner surface of the heat-shrinkable plastic tube or heat-shrinkable plastic sheet, a hot melt adhesive (for example, ethylene vinyl acetate copolymer) or a pressure-sensitive adhesive can be used. , For pressure sensitive adhesives,
It is preferable to attach a separator to the surface of the adhesive layer.

The heating wire of the mat unit may be, for example, an enamel-coated copper wire, an enamel-coated copper alloy wire, an enamel-coated nickel alloy wire, an enamel-coated chromium alloy wire having a wire diameter of 0.1 to 1.0 mm. As the heat resistant film of the unit, for example, a crosslinked polyethylene film or a silicone rubber sheet can be used.

As shown in FIG. 5, in the method for partially protecting an external corrosion-resistant metal pipe according to the present invention, a portion to be protected of the external corrosion-resistant metal pipe is covered with a heat-shrinkable anticorrosion material 3, and the pipe circumferential direction is defined as a width direction. The anticorrosion material 3 is formed by an electric heating mat 1 divided by width.
, And the energized heating mat 1 is covered with a heat-shrinkable temporary holding member 4, and then the decompression chamber 5 is airtightly mounted.
It can also be implemented by reducing the pressure in the chamber 6 with a vacuum pump and causing the heating mat 1 to conduct heat under this reduced pressure atmosphere. The reduced pressure chamber is provided with a two-piece container made of steel, aluminum, or the like. Alternatively, a two-piece container made of fiber reinforced resin can be used (a rubber packing is used for the seal between the split and the metal pipe anticorrosion layer). According to this method, it is possible to suppress the heat release from the outer surface of the temporary holding member, in addition to the partially anticorrosion void dress, which is advantageous in terms of thermal efficiency.

Examples of the anticorrosion metal pipes to be subjected to the partial anticorrosion of the present invention include city gas pipes, water pipes, oil transportation pipes, district cooling pipes, and the like. The partial protection method according to the present invention can be used for not only corrosion protection at a welded joint after welding and welding a metal pipe protected at a factory, but also partial repair of a corrosion protection layer of an existing external corrosion-resistant metal pipe.

[0023]

EXAMPLE A polyethylene core was used except for the 150 mm end of the pipe.
The welded joint of a steel pipe with an outer diameter of 600 mmφ, which was corrosion-protected at the factory by pitting, was used as a portion to be protected. Heat-shrinkable anticorrosion materials include
Internal pressure-sensitive adhesive layer thickness 1.5mm, with separator, wall thickness 1.5mm, radial heat shrinkage 50%, length 600mm
Was used. An enameled copper wire for a heater having a wire diameter of 0.7 mm is arranged in a meandering shape at a pitch of 9.3 mm on a current-carrying heating mat, which is sandwiched and insulated with a cross-linked polyethylene film.
12 mat units with a length of 170 mm, connected in a mat style (electrical connection between mat units in series)
It was used. The heat-shrinkable temporary holding material has a thickness of 0.2 mm,
A heat-shrinkable polyethylene sheet having a width of 650 mm and a lengthwise heat shrinkage of 50% was used, and was wound three times. After passing the heat-shrinkable anticorrosive material through one of the outer corrosion-resistant steel pipes, the ends of the steel pipes are welded together, and then the heat-shrinkable anticorrosive material is pulled back to the welded joint. The heating mat was wound with the mat units wrapped around each other, the heat-shrinkable temporary holding material was wound three times around the winding mat, and the wound end was fixed with an adhesive tape.

After the outer surface temperature of the steel pipe was kept at 200 ° C. for 20 minutes by the heat generated by the electric heating mat, the electric current was cut off and the temperature was cooled to room temperature, the temporary holding material was removed, and the electric heating mat was removed. The current-carrying heating mat was not deformed, and the current-carrying heating mat could be reused. The outer surface of the partial anticorrosion layer was smooth and had a good appearance.

[0025]

According to the method for partial corrosion protection of an external corrosion-resistant metal pipe according to the present invention, a heat-shrinkable anticorrosive material is coated on a portion to be protected of the external corrosion-resistant metal pipe by heat shrinking by heating with an electric heating mat. Since the energizing heating mat can be used in a detachable state while preventing deformation, it is possible to reuse the energizing heating mat. In addition, since the split type energizing heating mat and the heat-shrinkable anticorrosive material can be simultaneously reduced in diameter without slippage, the heat-shrinkable anticorrosive material can be heat-shrinked without rubbing the outer surface. Since the laps between the mat units of the heating mat are dispersed and the heating is sufficiently uniform along the circumferential direction of the pipe, uneven heating of the heat-shrinkable anticorrosive material can be prevented well. Therefore, according to the present invention, it is possible to guarantee the economy by reusing the energized heating mat, and achieve partial corrosion protection with good appearance and corrosion protection performance.

[Brief description of the drawings]

FIG. 1 is a drawing showing an example of a current-carrying heating mat used in the present invention.

FIG. 2 is a drawing showing an example of a mat unit in the above-mentioned electric heating mat.

FIG. 3 is a drawing showing another example of a mat unit in the above-mentioned electric heating mat.

FIG. 4 is a view showing an example of a method for partially protecting an external corrosion-resistant metal pipe according to the present invention.

FIG. 5 is a view showing an example of a method for partial corrosion protection of an external corrosion-resistant metal pipe according to the present invention.

FIG. 6 is a view showing a conventional method of partially protecting an external corrosion-resistant metal pipe.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electric heating mat 11 Mat unit 2 External corrosion-resistant metal pipe 20 Protected part 3 Heat-shrinkable anticorrosive material 4 Temporary heat-shrinkable material 5 Decompression chamber

Continued on the front page (72) Inventor Ryoichi Ikeda 1-8-5 Hara-cho, Fukaya-shi, Saitama Saitama Nitto Denko Corporation (72) Inventor Reiji Heita 1-8-8 Harara-cho, Fukaya-shi, Saitama Saitama Nitto Denko Inside (72) Inventor Takashi Nakano 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Within Nihon Kokan Co., Ltd. (72) Inventor Toshiyuki Namioka 88 Ono-cho, Tsurumi-ku, Yokohama-shi, Kanagawa Japan Japan Steel Pipe Construction Co., Ltd. (72) Inventor Toshio Nakano 88, Ono-cho, Tsurumi-ku, Yokohama-shi, Kanagawa Prefecture F-term in Japan Steel Pipe Works Co., Ltd. (Reference) AM28 SA04 SA11 SC01 SD01 SD04 SD18 SG07 SH06 SJ01 SJ22 SN08 SN13 SP13 SP17 SP22 SP34

Claims (2)

[Claims] An anti-corrosion material is covered by a heat-shrinkable anti-corrosion material, and the anti-corrosion material is covered by an electric heating mat which is divided by a predetermined width with the circumferential direction of the pipe being a width direction. Is covered with a heat-shrinkable temporary holding material, and the energized heating mat is energized to generate heat so that the heat-shrinkage of the temporary holding material reduces the diameter of the mat cover so that the mat is pressed against the anticorrosion material and heat-shrinks the anticorrosion material. And finally removing the temporary holding member and removing the energized heating mat. 2. The outer surface according to claim 1, wherein after the energized heating mat is covered with a heat-shrinkable temporary holding material, the portion to be protected is surrounded by a decompression chamber, and the energized heating mat is energized and heated under reduced pressure. Partial anticorrosion method for anticorrosion metal tubes.