JPH10311494A - Anticorrosive covering method of anticorrosive cover steel pipe joint - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an anticorrosive covering method of an 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 and no peeling at the border part of the welded joint and a pipe body anticorrosive cover, and has an excellent wear resistance. SOLUTION: An anticorrosive cover steel pipe 1a and an anticorrosive cover steel pipe 1b are welded to form a welded joint 2. A tar urethane resin cover 6 is formed on the surfaces of the welded joint 2, and the pipe body anticorrosive cover ends 3c and 3d. The cross-sectional form of the tar urethane resin cover 6 is made thick on the welded joint 2, and thin on the surface of the pipe body anticorrosive cover ends 3c and 3d, so as to form a smooth surface with no difference in level. Consequently, even though the above anticorrosive cover steel pipes 1a and 1b are advanced straightly under the ground as the embedded pipes, a burr and a peeling of the tar urethane resin cover 6 at the border part between the tar urethane resin cover 6 and the pipe body anticorrosive covers 3a and 3b are never generated.

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 mainly used as an underground pipe for gas pipelines, water pipes, electric power pipes and the like.

[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 piping work, a straight propulsion method is often practiced in which a steel pipe is directly propelled into the soil without digging a groove, and the steel pipes are sequentially welded and buried.

[0004] The above-mentioned construction method is more resistant to soil and sand during propulsion than the open-cutting method (a method of digging a groove at a site of a steel pipe, installing a steel pipe, and burying the steel pipe), so that the steel pipe has a corrosion-resistant coating. Abrasion resistance is required.

[0005] To this end, a factory is previously thickly coated with a polyolefin resin such as polyethylene or polypropylene having excellent abrasion resistance.

[0006] If necessary, a protective coating such as a polymer cement is applied to the surface of the anticorrosion coating.

[0007] However, at the construction site, the joint portion welded and joined has to be covered on the spot, and a heat-shrinkable tube is generally covered after welding.

FIG. 3 is a cross-sectional view of the anticorrosion-coated steel pipe joint part 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, the anticorrosion coating portions 3a and 3b made of a 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 anticorrosion coating are covered with a heat-shrinkable tube to form a heat collection 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.

[0010]

However, according to the prior art described above, when a corrosion-resistant coated steel pipe in which a heat-shrinkable tube is coated on a welded joint portion 2 is propelled straight in the ground, the heat-shrinkable tube-coated end 5a is formed. Since it is stepped, it turns up, and the resistance due to propulsion increases at that part, and it may develop into a defect reaching the steel surface.

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 is maintained by a simple covering means at a construction site. It is an object of the present invention to provide a corrosion-resistant coating method for a corrosion-resistant coated steel pipe joint which is excellent in abrasion resistance and does not cause winding or peeling at a boundary portion of the steel pipe joint.

[0013]

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. Welding the joint,
A corrosion protection method for a corrosion protection coated steel pipe joint characterized by covering a welded joint portion and a pipe corrosion protection coated end portion with tar urethane resin.

In the second invention, the joint of the first invention is welded, and a special polyolefin adhesive is applied and hardened on the surface of the pipe corrosion-proof coating end. A corrosion protection method for a corrosion-resistant coated steel pipe joint, characterized in that a portion is coated with a tar urethane resin.

[0015] The tar urethane resin used in the first and second inventions is a combination of a urethane resin having excellent curability and a coal tar having excellent water resistance to form a coating having a fast curing property and a long-term anticorrosion property of a thick film type. 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 unsaturated dicarboxylic acid or the like, or graft polymer of 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 adhesiveness with polyolefin resin and tar urethane resin.

[0018]

FIG. 1 is a sectional view showing an embodiment of a corrosion-resistant coated steel pipe joint according to an embodiment of the first invention. The same reference numerals are used for the portions common to FIG. 3 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 anticorrosion-coated steel pipe 1a and the anticorrosion-coated steel pipe 1b are made of a polyolefin resin having excellent impact resistance and abrasion resistance at the factory except for the joints 2a and 2b on the outer periphery of the pipe in advance at the factory. Is formed. 4
Is a weld.

The tubular anticorrosion coating portions 3a and 3b are coated with polyethylene resin at a factory.

Reference numeral 6 denotes a tar urethane resin coating portion, which is formed by coating the surfaces of the welded joint portion 2 and the end portions 3c and 3d of the pipe anticorrosion coating.

The tar urethane resin is a combination of a urethane resin excellent in curability and a coal tar excellent in 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.

The cross-sectional shape of the tar urethane resin coating 6 is thick at the welded joint 2 and the pipe anticorrosion coating ends 3c, 3d
The surface is thin and smooth with no steps.
Thereby, even if the above-mentioned anticorrosion-coated steel pipes 1a and 1b are buried pipes and are propelled straight through the soil, the tar-urethane resin coating 6 at the boundary between the tar urethane resin coating 6 and the pipe anticorrosion coatings 3a and 3b can be obtained. No peeling or peeling occurs.

Next, the anticorrosion method of the first invention will be described with reference to FIG. At the factory, the pipe anticorrosion coating 3a made of polyethylene resin except for the joints 2a and 2b on the outer circumference of the pipe,
The anticorrosion coated steel pipes 1a and 1b on which 3b are formed are manufactured.

As a coating method, an extrusion coating method using a die or the like is employed. Here, the end of the steel pipe is about 100m
Approximately m is used as the joints 2a and 2b to expose the tubular body.

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, the surface of the weld joint part 2 and the end surfaces 3c and 3d of the pipe anticorrosion coating are spray-coated with tar urethane using a two-component hot airless spray coating device or the like, or the tar urethane resin coating 6 is coated with a trowel or brush. Form.

FIG. 2 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. 2, the pipe corrosion protection coating ends 3c, 3c
Chlorinated polyethylene resin coating portions 7a and 7b formed by applying and curing a chlorinated polyethylene resin adhesive on the surface of d. The chlorinated polyethylene resin adhesive is one of the special polyolefin adhesives used in the second invention. Other special polyolefin adhesives include chlorinated polyolefins other than the chlorinated polyethylene resin adhesive, polyolefin and ethylene vinyl acetate copolymer. A substance obtained by blending two or more of a substance obtained by imparting a polarity to the union with an unsaturated dicarboxylic acid, a graft polymer of an unsaturated dicarboxylic acid, and a chlorinated product of a graft polymer of an unsaturated dicarboxylic acid is exemplified.

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

The cross-sectional shape of the tar urethane resin coating portion is thick at the welded joint portion 2 and thin at the surfaces of the pipe anticorrosion coating ends 3c and 3d, and has a smooth surface shape with no step. Thereby, even if the above-mentioned anticorrosion-coated steel pipe is buried and straight-propelled in the soil, winding of the tar-urethane-resin coating 6 at the boundary between the tar-urethane resin coating 6 and the pipe anticorrosion coatings 3a, 3b is performed. And peeling do not occur.

(Example) In a factory, a 750A steel pipe coated with polyethylene resin to an average thickness of 3 mm was welded and joined, and a tar urethane resin [Nippon Paint Pre-Tegole] was applied to the surface of the welded joint and the end of the pipe anticorrosion coating. 32-10]
Was applied to the center of the welded joint by ironing to a thickness of 4 mm, and the test material No. It was set to 1.

At a factory, a 750A steel pipe coated with polyethylene resin to an average thickness of 3 mm is welded, and a special polyethylene adhesive [China Paint Co., Ltd. Thermotack E300] is applied to the surface of the pipe corrosion-resistant coating end. Let it cure,
A tar urethane resin [Nippon Paint Protegal 32-10] was applied to the surface of the welded joint and the special polyethylene coating by spray coating three times at the center of the welded joint to a thickness of 4 mm, and the test material No. And 2.

At the factory, a 750A steel pipe coated with polyethylene resin to an average thickness of 4 mm is welded, and a special polyethylene adhesive [China Paint Co., Ltd. Thermotack E300] is applied to the surface of the pipe anticorrosion coating end. Let it cure,
A tar urethane resin [Nippon Paint Protegor 32-10R] was applied to the center of the welded joint portion by spray coating twice to a thickness of 5 mm on the surface of the welded joint portion and the special polyethylene coating film portion. It was set to 3.

At a factory, a 750A steel pipe coated with polyethylene resin to an average thickness of 6 mm is welded, and a special polyethylene adhesive [China Paint Co., Ltd., Thermotack E300] is applied to the surface of the pipe anticorrosion coating end. Let it cure,
A test urethane resin (Nippon Paint Protegal 32-10RR) is applied to the weld joint and the surface of the special polyethylene coating film to a thickness of 7 mm by a single spray coating.
o. 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 joint portion and the end of the pipe corrosion protection coating. It was set to 1.

Test material No. 1 to No. 4 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 three-point scale of の was very good, ○ was good, and X was 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 boundary surface 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)

[0039]

[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.

[0042]

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 curling at the boundary between the jointed 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 sectional view of an anticorrosion-coated steel pipe joint according to an embodiment of the second invention.

FIG. 3 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 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 7a, 7b Chlorinated polyethylene coating

Claims (2)

[Claims] In a method for anticorrosion coating of a steel pipe joint part in which a steel pipe coated with anticorrosion coating with a polyolefin resin except for a joint part on the outer periphery of a pipe body is sequentially welded and buried, the joint part is welded. And a method for coating a corrosion-resistant steel pipe joint part by coating a welded joint part and a pipe corrosion-resistant coating end part with tar urethane resin. 2. A method according to claim 1, wherein the steel pipe is provided with an anticorrosion coating of a polyolefin resin except for the joint on the outer periphery of the pipe body. After applying and curing a special polyolefin adhesive on the surface of the tubular corrosion protection coating end, the corrosion protection coated steel pipe fitting is characterized in that the welded joint and the corrosion protection coating end are coated with tar urethane resin. Anticorrosion coating method.