JPH10311493A - Corrosion protective covering method of corrosion protective covering steel pipe joint part - Google Patents

Abstract

PROBLEM TO BE SOLVED: To hold corrosion resistance of a welding joint part, and prevent winding and separation in a boundary part between the welding joint part and pipe body corrosion protective covering parts by covering it by injecting a tar urethane resin into a form to cover the welding joint part and pipe body corrosion protective covering end parts after joint parts are welded together. SOLUTION: Corrosion protective covering steel pipes 1a and 1b where pipe body corrosion protective covering parts 3a and 3b are formed on a pipe body outer periphery by a polyethylene resin except for joint parts 2a and 2b, are used as buried pipes, and the joint parts are welded together. After welding, a main agent of a tar urethane resin and a hardening agent are injected into a form installed so as to cover the whole surface periphery of a welding joint part 2 and pipe body corrosion protective covering end parts 3c and 3d, and it is covered with the tar urethane resin. At this time, front and rear parts of the form are narrowed, and a cross section is formed in a smooth curve shape so that a step difference is not generated on a surface of a tar urethane resin covering part 7. Therefore, corrosion resistance of the welding joint part is held, and burr and separation in a boundary part between the welding joint part and the pipe body corrosion protective covering parts can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anticorrosion coating method for an anticorrosion coated steel pipe joint.

[0002]

2. Description of the Related Art Generally, gas pipes, water supply pipes, electric power pipes and the like are installed as buried pipes by underground buried pipe work. In the above-mentioned plumbing work, a straight-line propulsion method of directly propelling a steel pipe into the soil without digging a trench and sequentially welding and embedding the steel pipes has been implemented.

[0003] Compared with the open-cutting method (a method of digging a groove at the site of a steel pipe, installing a steel pipe, and welding and burying the pipe), the above-described construction method receives resistance to earth and sand during propulsion, so that the anticorrosion coating of the steel pipe is applied to the steel pipe. Abrasion resistance is required.

[0004] For this purpose, a factory is previously thickly coated with a polyolefin resin such as polyethylene or polypropylene having excellent wear resistance. If necessary, a protective coating such as polymer cement is applied to the surface of the polyolefin resin coating.

[0005] However, at a construction site, a joint portion welded and joined has to be covered on the spot, and a heat-shrinkable tube is generally covered after welding.

FIG. 5 is a cross-sectional view of the anticorrosion coating portion of the anticorrosion coating steel pipe joint by the heat-shrinkable tube. At the construction site, the anticorrosion coated steel pipe 1a and the anticorrosion coated steel pipe 1b are welded to form a welded joint 2
Is formed. Anticorrosion coated steel pipe 1a and anticorrosion coated steel pipe 1b
Are joints 2a, 2b at the factory
Except for the above, pipe anticorrosion coating portions 3a and 3b made of polyolefin resin such as polyethylene and polypropylene are formed. Reference numeral 4 denotes a weld.

After welding the joints 2a and 2b, the welded joint 2 and the end portions 3c and 3d of the pipe anticorrosion coating are covered with a heat-shrinkable tube to form a heat-shrinkable tube coating 5.
The heat-shrinkable tube is made of a heat-shrinkable synthetic resin material such as cross-linked polyethylene that shrinks when heated.

[0008]

However, the above-described conventional welded joint portion 2 and the end portions 3c, 3d of the pipe anticorrosion coating are described above.
When the anticorrosion-coated steel pipe coated with a heat-shrinkable tube is propelled straight under the ground, the heat-shrinkable tube-coated end 5a is stepped and rolled up. This part increases the resistance due to propulsion and develops a defect reaching the steel pipe surface. May be.

When such a defect occurs, the defect can be found by inspection after burying, but it is very difficult to repair the defect.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and the corrosion resistance of a welded joint portion is maintained by a simple covering means at a construction site, so that the welded joint portion and a tubular body corrosion-resistant coating portion can be formed. An object of the present invention is to provide an anticorrosion coating method for a buried pipe joint which is excellent in wear resistance and does not cause winding or peeling at a boundary portion.

[0011]

A first aspect of the present invention is an anticorrosion coating for a steel pipe joint when a steel pipe having an anticorrosion coating made of a polyolefin resin except for a joint on the outer periphery of a pipe body is sequentially welded and buried. In the method, after welding the joint portion, a formwork is attached so as to cover the welded joint portion and the end portion of the tube corrosion protection coating, tar urethane resin is injected into the formwork, and the welded joint portion and the tube body corrosion protection coating end are provided. A corrosion protection method for a corrosion-resistant coated steel pipe joint, characterized in that a portion is coated with a tar urethane resin.

In a second aspect of the present invention, in the first aspect, the joint portion is welded, a special polyolefin adhesive is applied to the surface of the end portion of the pipe anticorrosion coating and hardened. A method of attaching a mold so as to cover it, injecting a tar urethane resin into the mold, and covering a weld joint portion and an end portion of the tubular body with a corrosion protection coating with a tar urethane resin. It is.

The tar urethane resin used in the first and second inventions is a combination of a urethane resin excellent in curability and a coal tar excellent in water resistance, and has a quick-curing, thick-film type coating having long-term corrosion protection. It has good adhesion to steel, is hard, and has extremely excellent damage resistance. Therefore, a primer used for coating a known urethane resin is generally unnecessary.

As the special polyolefin adhesive used in the second invention, chlorinated polyolefin, polyolefin or ethylene-vinyl acetate copolymer obtained by imparting polarity with an unsaturated dicarboxylic acid or the like, or a graft polymer of an unsaturated dicarboxylic acid A material obtained by blending two or more chlorinated products of an unsaturated dicarboxylic acid graft polymer is used.

The above adhesive has good adhesion to polyolefin resin and tar urethane resin.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of an anticorrosion-coated steel pipe showing one embodiment of the anticorrosion-coated steel pipe of the first invention. The same reference numerals are used for the portions common to FIG. 5 described above.

In FIG. 1, a corrosion-resistant coated steel pipe 1a and a corrosion-resistant coated steel pipe 1b are welded to form a welded joint 2.
The anti-corrosion coated steel pipe 1a and the anti-corrosion coated steel pipe 1b are preliminarily formed at the factory on the outer periphery of the pipe except for the joints 2a and 2b, with the pipe anti-corrosion coating parts 3a and 3b made of polyethylene resin having excellent impact resistance and wear resistance. It is. Reference numeral 4 denotes a weld. Reference numeral 7 denotes a tar urethane resin coating portion, and a boundary portion between the welded joint portion 2 and the pipe anticorrosion coating ends 3c and 3d is formed by the tar urethane resin coating portion 7.

The tar urethane resin is a combination of a urethane resin having excellent curability and a coal tar having excellent water resistance.
It is a fast-curing, thick-film type coating material having long-term anticorrosion properties, has good adhesion to steel, is hard, and has extremely excellent damage resistance. Therefore, a primer used for coating a known urethane resin is generally unnecessary.

As shown in FIG. 1, the cross-sectional shape of the tar urethane resin coating 7 is thick at the welded joint portion 2 and thin and smooth at the surfaces of the tubular anticorrosion coating ends 3c and 3d. .

Thus, the anticorrosion-coated steel pipes 1a, 1
b, the tar urethane resin coating 7 and the pipe anticorrosion coating 3
Since the boundary between a and 3b has a smooth surface shape,
No curling or peeling of the tar urethane resin coating 7 occurs.

Next, the anticorrosion coating method of the first invention will be described with reference to FIG. At the factory, joints 2a, 2
Except for b, polyethylene resin is applied and the pipe anticorrosion coating 3
The anticorrosion-coated steel pipes 1a and 1b on which a and 3b are formed are manufactured. As a coating method, an extrusion coating method using a die or the like is employed. Here, about 100 mm of the end of the steel pipe is exposed as a joint 2a, 2b.

The anticorrosion coated steel pipes 1a and 1b are transported to the site where they are buried. At the construction site, the anticorrosion-coated steel pipes 1a and 1b are buried in the starting shaft, starting yard, and the like, and the joints are welded. After welding, FIGS. 2 and 3 are attached so as to cover the surfaces of the weld joint portion 2 and the end portions 3c and 3d of the pipe anticorrosion coating.
Is applied with a tar urethane resin coating in which a main agent and a curing agent of a tar urethane resin are injected into the mold frame 6.

FIG. 2 is a perspective view showing an embodiment of a mold used in the present invention, and FIG. 3 is a longitudinal sectional view of FIG.

In FIG. 2 and FIG. 3, the main body of the mold 6 is divided into two vertically divided bodies 6a and 6b.
a and 8b are fixed with bolts and nuts 12 or the like. The front and rear portions of the mold 6 are narrowed, and the surface of the tar urethane resin coating (not shown) is smoothed so as not to generate a step.
The cross-sectional shape is curved.

Here, the main agent and the curing agent made of the tar urethane resin are pressure-injected into the mold 6 from the inlet 9 provided in the upper divided body 6a, and the material overflowing from the outlet 10 is caused to flow out of the mold 6 Stop filling when is filled.

FIG. 4 is a sectional view of an anticorrosion-coated steel pipe joint according to an embodiment of the second invention. 1 are denoted by the same reference numerals, and description thereof is omitted.

In FIG. 4, reference numerals 11a and 11b denote chlorinated polyethylene coating portions, and the tubular anticorrosion coating ends 3c and 3d.
Applied and cured on the surface.

The chlorinated polyethylene coating portions 11a, 11b of the surface of the welded joint portion 2 and the end portions 3c, 3d of the pipe anticorrosion coating are provided.
Is formed with a tar urethane resin coating 7. The tar urethane resin coating 7 is similarly formed using the mold 6 shown in FIGS.

Chlorinated polyethylene is one of the special adhesives for coated polyolefin used in the second invention, and chlorinated polyolefins, polyolefins and ethylene-vinyl acetate copolymers are polarized with unsaturated dicarboxylic acids and the like. A substance obtained by blending two or more kinds of a given substance, a graft polymer of an unsaturated dicarboxylic acid, and a chlorinated product of a graft polymer of an unsaturated dicarboxylic acid is used.

The above adhesive makes the adhesion to polyolefin resin and tar urethane resin very good.

[0032]

Embodiments of the present invention will be described below.

At a factory, a 750A steel pipe coated with polyethylene resin to an average thickness of 3 mm is welded and joined, and a formwork is attached so as to cover the welded joint part and the end of the pipe corrosion protection coating.
A tar urethane resin [Nippon Paint Protegal 32-10] was injected into the mold to cover the weld joint portion and the end surface of the anticorrosive coating of the tube. It was set to 1.

At a factory, a 750A steel pipe coated with a polyethylene resin to an average thickness of 3 mm is welded and joined, and a special polyolefin adhesive commercially available on the surface of the pipe corrosion protection coating end [Thermo-Tac E300 manufactured by China Paint Co., Ltd.] Then, a mold is attached so as to cover the welded joint portion and the end portion of the pipe anticorrosion coating, and a tar urethane resin [Nippon Paint Protegal 32-10] is injected into the mold to form a welded joint portion. And 5 mm thick test material No. 5 at the center of the welded joint. And 2.

At a factory, a 750A steel pipe coated with a polyethylene resin to an average thickness of 4 mm is welded and joined, and a special polyolefin adhesive commercially available on the surface of the anticorrosion coating end of the pipe [Thermo-Tac E300 manufactured by China Paint Co., Ltd.] Then, a mold is attached so as to cover the welded joint portion and the end portion of the pipe corrosion protection coating, and a tar urethane resin [Nippon Paint Protegal 32-10R] is injected into the mold to form a welded joint portion. And a 6 mm-thick test material No. having a thickness of 6 mm at the center of the welded joint. It was set to 3.

At a factory, a 750A steel pipe coated with a polyethylene resin to an average thickness of 6 mm is welded and joined, and a special polyolefin adhesive commercially available on the surface of the anticorrosion coating end of the pipe [Thermo-Tac E300 manufactured by China Paint Co., Ltd.] Then, a mold is attached so as to cover the welded joint portion and the end portion of the pipe anticorrosion coating, and a tar urethane resin [Nippon Paint Protegor 32-10RR] is injected into the mold to form a welded joint portion. And an 8 mm-thick test material No. having a thickness of 8 mm at the center of the welded joint. And 4.

At a factory, a 750A steel pipe coated with a polyethylene resin to an average thickness of 3 mm was welded and joined, and a heat-shrinkable tube was coated on the welded joint portion and the end of the anticorrosion coating of the tube. . It was set to 1.

Test material No. of the present invention example. 1 to No. 4 and Comparative Material No. of Comparative Example. 1 in soil mixed with crushed stone
Table 1 shows the test results after propulsion of 0 m.

The following items were visually judged, and the overall evaluation was evaluated in three grades: ◎: very good, ○: good, and x: bad.

(1) Occurrence of scratches on the surface of the welded joint coating (2) Adhesion at the interface between the steel pipe surface and the tar urethane resin coating, and the interface between the tar urethane resin coating and the pipe corrosion protection coating end (Comparative Example) Boundary surface between the heat-shrinkable tube coating and the steel pipe surface and the end of the pipe corrosion protection coating)

[0041]

[Table 1]

As is clear from Table 1, Example No.
1, No. 2, No. 3, No. In No. 4, there was no particular problem to the extent that a slight scratch was produced on the surface of the coated portion of the anticorrosion coated steel pipe joint. Example N for coating adhesion
o. 2, No. 3, No. In Example No. 4, although the adhesion between the steel pipe surface of the welded joint portion and the boundary portion between the tar urethane resin coating portion and the tar urethane resin coating portion and the pipe corrosion protection coating portion was very good, Example No. In No. 1, a slight decrease in adhesion occurred at the boundary portion between the tar urethane resin coating portion and the tubular corrosion protection coating portion.

On the other hand, in Comparative Example No. In No. 1, curling occurred from the heat-shrinkable tube coating end, and a part of the steel pipe surface was exposed.

[0044]

As described above, according to the present invention, the corrosion resistance of the welded joint portion is maintained by the simple covering means at the construction site, and the winding at the boundary between the welded joint portion and the pipe anticorrosion coating portion is prevented. The anticorrosion coating of the anticorrosion-coated steel pipe joint having excellent abrasion resistance without peeling can be applied.

[Brief description of the drawings]

FIG. 1 is a sectional view of an anticorrosion-coated steel pipe joint according to an embodiment of the first invention.

FIG. 2 is a perspective view showing an embodiment of a mold used in the present invention.

FIG. 3 is a longitudinal sectional view of FIG. 2;

FIG. 4 is a sectional view of an anticorrosion-coated steel pipe joint according to an embodiment of the second invention.

FIG. 5 is a cross-sectional view of a conventional anticorrosion-coated steel pipe joint using a heat-shrinkable tube.

[Explanation of symbols]

 1a, 1b anticorrosion coated steel pipe 2 welded joint 2a, 2b joint 3a, 3b pipe anticorrosion coating 3c, 3d pipe anticorrosion coating end 4 welded part 5 heat shrinkable tube coating 6 formwork 7 tar urethane resin coating 8a, 8b Flange 9 Inlet 10 Outlet 11a, 11b Chlorinated polyethylene coating 12 Bolt and nut

Claims (2)

[Claims] In a method for anticorrosion coating of a steel pipe joint portion when welding and burying a steel pipe having a corrosion prevention coating made of a polyolefin resin except for a joint portion on an outer periphery of a pipe body, the joint portion is welded. Later, a mold is attached so as to cover the welded joint and the end of the pipe corrosion protection coating, tar urethane resin is injected into the formwork, and the welded joint and the end of the pipe corrosion protection coating are covered with the tar urethane resin. An anticorrosion coating method for a corrosion-resistant coated steel pipe joint. 2. A method according to claim 1, wherein the steel pipe is provided with an anticorrosion coating made of a polyolefin resin except for a joint on the outer periphery of the pipe body. After applying and curing a special polyolefin adhesive on the surface of the pipe corrosion protection coating end, a mold is attached so as to cover the weld joint part and the pipe corrosion protection coating end,
A corrosion-resistant coating method for a corrosion-resistant coated steel pipe joint, which comprises injecting a tar urethane resin into a mold, and coating a welded joint portion and a pipe corrosion-resistant coating end portion with the tar urethane resin.