JPH10311492A - Corrosion protection coating method for steel pipe joints - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an anticorrosive covering method of anticorrosive cover steel pipe joint which maintains the anticorrosive property of a welded joint by a simple covering means at an execution site, generates no burr even through a thermal contraction tube is used, and has an excellent wear resistance. SOLUTION: On the surfaces of a welded joint 2 and pipe body anticorrosive cover ends 3c and 3d, a cover by a thermal contraction tube 5 is applied. To the surfaces of the border parts of the pipe body anticorrosive covers 3a and 3b between the surface of a thermal contraction tube cover 5 and the thermal contraction tube cover 5, a tar urethane resin cover 6 is formed. Since the thermal contraction tube cover 5 is made built in the tar urethane resin cover 6, a burr of the thermal contraction cover 5 is prevented perfectly.

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 In general, anticorrosion coated steel pipes are used for gas pipes, water pipes, electric power pipes, and the like, and are installed as buried pipes by burying pipes in soil. 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 a resin such as polyethylene or polypropylene having excellent wear resistance. If necessary, a protective coating such as a polymer cement is applied to the surface of the olefin 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. 2 is a cross-sectional view of the anticorrosion-coated steel pipe joint portion formed 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 provided. 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.

When an anticorrosion-coated steel pipe in which a heat-shrinkable tube is coated on a welded joint portion 2 is propelled straight in soil, the heat-shrinkable tube-coated end portion 5a is stepped up, so that it is turned up. May develop into defects that reach the surface. When such a defect occurs, the defect can be found by inspection after embedding, but it is very difficult to repair the defect. For this purpose, various countermeasures are being studied.

As an example of the above countermeasures, Japanese Patent Laid-Open No.
JP-87-248-A discloses the following corrosion protection coating method for a steel pipe joint.

In this anticorrosion coating method, a heat-shrinkable tube is coated on the outer periphery of a joint portion of a steel pipe whose outer periphery is coated with a polyolefin resin as an anticorrosion coating, and includes a boundary portion between the anticorrosion coating portion and the heat-shrinkable tube coating portion. After applying an adhesive primer on the surface, the paint is applied, and a metal having a higher ionization tendency than Fe is sprayed before the paint is completely cured. As the primer, a urethane primer having adhesiveness to a polyolefin resin is used. After the primer is applied, a paint such as urethane paint, acrylic urethane paint, acrylic paint, alkyd paint, acrylic emulsion paint, vinyl chloride paint, etc. is applied. , Zn and the like are sprayed smoothly.

[0011]

However, the technique disclosed in Japanese Patent Laid-Open Publication No. 3-87248 has the following problems.

When the above-described corrosion protection is performed on the joint portion of the corrosion-resistant coated steel pipe at the construction site, it is necessary to consider timing for spraying a metal having a higher ionization tendency than Fe before the paint is completely hardened. The operation is complicated.

[0013] The present invention has been made to solve the above-mentioned problems, and the corrosion resistance of the welded joint portion is maintained by a simple covering means at a construction site, and the winding is obtained even when a heat-shrinkable tube is used. An object of the present invention is to provide an anticorrosion coating method for a corrosion-resistant coated steel pipe joint part which does not generate and has excellent wear resistance.

[0014]

SUMMARY OF THE INVENTION The present invention relates to an anticorrosion coating method for steel pipe joints when welding and embedding steel pipes coated with a polyolefin resin except for the joints around the outer periphery of the pipe body. The joint portion is welded, and the welded joint portion and the end portion of the tubular corrosion protection coating are covered with a heat-shrinkable tube, and the boundary between the surface of the heat-shrinkable tube coating portion and the heat-shrinkable tube coating portion. The method of claim 1, wherein the surface of the steel pipe is coated with a tar urethane resin.

The tar urethane resin used in the present invention is a combination of a urethane resin having excellent curability and a coal tar having excellent water resistance to form a coating material having a fast curing property and a long-term corrosion resistance of a thick film type. It has good adhesion to steel and is very hard and very resistant to damage. for that reason,
No primer such as ordinary urethane resin is required.

[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 joint according to an embodiment of the present invention. The same parts as those in FIG. 2 are denoted by the same reference numerals.

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 anticorrosion-coated steel pipe 1a and the anticorrosion-coated steel pipe 1b are provided with pipe anticorrosion coating parts 3a, 3b made of polyethylene resin having excellent impact resistance and wear resistance except for the joint parts 2a, 2b in the factory in advance at the factory. . Reference numeral 4 denotes a weld.

Examples of the tubular anticorrosive coating material include the above-mentioned polyethylene resin and other olefin resins such as polypropylene.

The welded joint 2 and the end portions 3c, 3c
The heat-shrinkable tube coating 5 is formed on the surface of d.

The heat-shrinkable tube is made of a heat-shrinkable synthetic resin material such as crosslinked polyethylene which is shrunk by heating.

A tar urethane resin coating 6 is provided on the surface of the heat-shrinkable tube coating 5 and the surface of the boundary between the anticorrosion coatings 3a and 3b between the heat-shrinkable tube coating 5. Here, it is necessary that the heat-shrinkable tube coating portion 5 be incorporated in the tar urethane resin coating portion 6. This completely prevents the heat-shrinkable tube coating end 5a from being turned up.

The method of coating the tar urethane resin is not particularly limited, but spray coating, ironing, a method of mounting a mold and injecting the resin are preferred.

Next, the method of the present invention will be described with reference to FIG. At the factory, the anticorrosion coated steel pipes 1a and 1b are manufactured by forming the anticorrosion coating portions 3a and 3b of polyethylene resin on the outer periphery of the pipe except for the joint portions 2a and 2b. 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
The tubes are exposed as a and 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. In this case, the heat-shrinkable tube is penetrated by one of the anticorrosion-coated steel pipes 1a and is moved toward the anticorrosion-coated portion so as not to be affected by welding.

After welding, the heat-shrinkable tube is connected to the joints 2a, 2a
b and the tubular body anticorrosion coating ends 3c and 3d, and are heated and shrunk by a burner, a heater, or the like, and brought into close contact.

Next, a tar urethane resin coating 6 is formed on the surface of the heat-shrinkable tube coating 5 and a boundary between the heat-shrinkable tube coating 5 and the pipe anticorrosion coating 3a, 3b. The coating method is spray coating, ironing, a method of mounting a mold and injecting.

[0028]

Embodiments of the present invention will be described below.

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 having an average thickness of 3 mm was coated on the welded joint and the end of the anticorrosion coating of the tube. A tar urethane resin [Nippon Paint Protegal 32-10] is applied to the surface of the heat-shrinkable tube coating on the surface of the heat-shrinkable tube coating and on the surface of the boundary between the heat-shrinkable tube coating and the heat-shrinkable tube coating. Part), spray coating was applied smoothly so that the average thickness was 2 mm thicker than the thickness from the steel pipe surface at the end of the heat-shrinkable tube coating part. It was set to 1.

At a factory, a 750A steel pipe coated with polyethylene resin to an average thickness of 4 mm was welded and joined, and a heat-shrinkable tube having an average thickness of 3 mm was coated on the joint portion and the end of the anticorrosive coating of the tube. On the surface of the boundary between the tube coating and the heat-shrinkable tube coating and the pipe corrosion protection coating,
Tar urethane resin [Nippon Paint Protegor 32-
10RR] is the test material No. As in the case of 1, the average thickness is 2 mm at the center (weld joint) of the heat shrinkable tube coating.
Test iron No. And 2.

At a factory, a 750A steel pipe coated with polyethylene resin to an average thickness of 6 mm was welded and joined, and a heat-shrinkable tube having an average thickness of 3 mm was coated on the joint portion and the end of the anticorrosion coating of the tube. On the surface of the boundary between the tube coating and the heat-shrinkable tube coating and the pipe corrosion protection coating,
Tar urethane resin [Nippon Paint Protegor 32-
10R] is the test material No. As in the case of No. 2, the material was injected into the mold so that the average thickness was 3 mm thick at the center (weld joint) of the heat-shrinkable tube. It was set to 3.

In a factory, a 750A steel pipe coated with polyethylene resin to an average thickness of 3 mm was welded and joined, and a heat-shrinkable tube having an average thickness of 3 mm was coated on the joint and the end of the anticorrosion coating of the tube. Comparative material No. It was set to 1.

Test material No. 1 to No. 3 and comparative material N
o. Table 1 shows the test results after propelling No. 1 in soil mixed with crushed stone for about 500 m.

The following items were visually judged, and as a comprehensive evaluation, a circle was evaluated as good and a cross was evaluated as bad.

(1) The state of the occurrence of scratches on the surface of the welded joint coating (2) The steel pipe surface and the heat-shrinkable tube coating, the heat-shrinkable tube coating and the tar urethane resin coating, the heat-shrinkable tube coating end and the pipe corrosion protection coating Contact state of the boundary surface of the part

[0036]

[Table 1]

As is clear from Table 1, Example No.
1, No. 2, No. In No. 3, there is no particular problem to the extent that a slight scratch is generated on the surface of the tar urethane resin coating portion of the welded joint portion, and the steel pipe surface and the heat shrink tube coating portion, the heat shrink tube coating portion and the tar urethane resin coating portion, The state of adhesion at the boundary between the shrinkable tube coating end and the tubular body corrosion protection coating was good.

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

[0039]

As described above, according to the present invention, the corrosion resistance of the welded joint portion is maintained by a simple covering means at the construction site, and even if a heat shrinkable tube is used, the welded joint portion coating portion and the pipe corrosion protection can be prevented. The anticorrosion coating of the anticorrosion-coated steel pipe joint with excellent abrasion resistance that does not cause winding or peeling at the boundary with the coating 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 present invention.

FIG. 2 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, 1b joint 3a, 3b pipe anticorrosion coating 3c, 3d pipe anticorrosion coating end 4 welded part 5 heat-shrinkable tube coating 5a heat-shrinkable tube coating end 6 tar Urethane resin coating

Claims (1)

[Claims] An anticorrosion coating method for a steel pipe joint portion when a steel pipe coated with a polyolefin resin except for a joint portion on the outer periphery of a pipe body is sequentially welded and buried.
The joint portion is welded, and the welded joint portion and the end portion of the tubular corrosion protection coating are covered with a heat-shrinkable tube, and the boundary between the surface of the heat-shrinkable tube coating portion and the heat-shrinkable tube coating portion. A method for coating a corrosion-resistant steel pipe joint part by coating the surface of the steel pipe with a tar urethane resin.