JP2691026B2 - Corrosion protection coating method for steel pipe joints - Google Patents

Description

The present invention relates to an anticorrosion coating method for welded joints when constructing an anticorrosion coated steel pipe.

[Conventional technology]

In recent years, excavation method (method of digging a groove in a place where a steel pipe is laid to place a steel pipe, welding and burying it) cannot be performed due to ground conditions and environmental conditions in the underground burial work, and the steel pipe is not digged into the soil. A direct propelling method in which direct propelling is performed and steel pipes are sequentially welded and buried is often carried out.

Since the direct propulsion method is a method of directly propelling the steel pipe into the soil, the anticorrosion coating of the steel pipe is required to have impact resistance and wear resistance because it is subjected to the resistance of earth and sand at the time of propulsion as compared with the excavation method. For this reason, the factory has thickly coated these excellent resins such as polyethylene and polyurethane in advance. However, the joints welded together at the construction site have to be coated locally, and after welding, they are covered with heat-shrinkable tubes or coated with polyurethane paint.
For example, as disclosures of known patents, there are JP-A-60-12234 and JP-A-59-144042.

[Problems to be solved by the invention]

However, when coating the heat-shrinkable tubing on the welded joint at the construction site on-site, the heat-shrinkable tubing coating at the site is different from the steel surface in comparison with the coating pre-coated at the factory due to the restrictions of the field coating. Poor adhesion. Generally, the impact resistance of a coating obtained by covering a certain coating with the same material is higher as the adhesion between the coating and the material is stronger. The same applies to the impact resistance of the factory pre-coated and the local heat-shrinkable tube coating, and the impact resistance of the heat-shrinkable tube coating is inferior to the factory pre-coated coating. For this reason, in the direct propulsion method that has been often implemented in recent years, the heat-shrinkable tube coating of the joint part, which is inferior in adhesion and impact resistance to the coating pre-coated at the factory, is partially destroyed by the resistance of earth and sand during propulsion. was there.
When such a defect occurs, the defect can be found by an inspection after embedding, but it is very difficult to repair the defect. Therefore, we are currently taking new measures such as anticorrosion.

Further, even in the case of burying in the usual excavation method, if the joint part welded and joined at the construction site is painted locally, due to the poor adhesion of the joint anticorrosion part, penetration flaws due to backfilling sand may occur, There is a surface that is not well managed like factory coating, and the factory coating surface and the local joint are buried without sufficient sea surface adhesion, and corrosion may proceed from there.

The present invention has been made to solve the above problems, and has a coating hardness that can withstand the resistance of earth and sand during propulsion, and in the unlikely event that the coating partially breaks or has a pinhole. However, the purpose is to obtain a coating capable of sufficiently exhibiting anticorrosion ability.

[Means for solving the problem]

That is, the present invention is: (1) In a pipe construction in which a steel pipe having a corrosion-resistant coating formed on the outer periphery of the pipe is sequentially welded and embedded, the pipe outer periphery is coated with a polyolefin resin as the corrosion-resistant coating on the outer periphery of the joint. After coating a heat-shrinkable tube, and then applying an adhesive primer to the surface including the boundary portion between the anticorrosion coating and the heat-shrinkable tube coating, paint is applied,
An anticorrosion coating method for an anticorrosion coated steel pipe joint, comprising spraying a metal having a greater ionization tendency than Fe before the coating material is completely cured.

(2) In a pipe construction in which steel pipes having an anticorrosion coating formed on the outer periphery of the pipe are welded one after another and buried, a polyurethane resin is coated on the outer periphery of the joint of a steel pipe having a polyurethane resin coating on the outer periphery as the anticorrosion coating. A method for anticorrosion coating of an anticorrosion coated steel pipe joint, comprising spraying a metal having a greater ionization tendency than Fe before the polyurethane resin is completely cured.

It is.

The method of anticorrosion coated steel pipe of the anticorrosion coated steel pipe joint portion of the present invention will be specifically described below.

When applying the anticorrosion coating to the joint part of the steel pipe coated with polyolefin resin as an anticorrosion coating excluding the joint part on the outer circumference of the pipe,
Generally, a polyolefin resin used as an anticorrosion coating has very few polar groups in the molecule and thus has very weak adhesion to other materials. Therefore, a urethane primer having adhesiveness with these polyolefin resins is applied in advance. The urethane primer is obtained by polyaddition of a compound having two or more hydroxyl groups or amino groups in the molecule (hereinafter referred to as polyol) and a compound having two or more isocyanate groups in the molecule (hereinafter referred to as polyisocyanate). A terminal isocyanate group-containing urethane prepolymer obtained by polymerization. When the molecular weight of the polyol is low, the coating film of the primer tends to be hard, so that the coating film does not extend, and when the coated object is bent, the coating film tends to crack. On the contrary, when the molecular weight of the polyol is large, the concentration of the urethane bond having a large cohesive force becomes low, so that the adhesiveness with the polyolefin resin is likely to deteriorate. Therefore, it is preferable to use a polyol having a molecular weight of 400 to 2000. The polyol and polyisocyanate are not particularly limited, but as the polyol, it is preferable to select a polyether polyol that is difficult to hydrolyze from the viewpoint of water resistance. Also, as the polyisocyanate, aromatic ones,
Particularly, diphenylmethane diisocyanate is excellent in adhesiveness. It is considered that this is because the cohesive force of the aromatic ring contributes to the improvement of the adhesiveness.

After applying the urethane primer, then apply a paint such as urethane paint, acrylic urethane paint, acrylic paint, alkyd paint, acrylic emulsion paint, vinyl chloride paint, etc., and have a greater ionization tendency than Fe before these paints are completely cured. Smoothly sprays metals such as Al and Zn. This metal sprayed layer increases the hardness of the anticorrosion coating,
The factory coating film and the on-site coating film can be smoothly bonded to each other, and can withstand the resistance of the earth and sand when propelling the pipe in the burying work. Moreover, the reason why a metal such as Al or Zn, which has a higher ionization tendency than Fe, is used as the sprayed metal is that the metal sprayed layer serves as a sacrificial anode to provide an electrolytic protection effect should the corrosion-resistant coating be partially destroyed. Since the coating film and the sprayed metal are attached by mechanical adhesion, the metal is sprayed onto the coating film in a semi-cured state, the metal is hard to coat the coating film, and the cohesive force of the coating film strengthens the adhesive force between the coating film and the sprayed metal. There is a need to. Hereinafter, the present invention will be specifically described with reference to Examples, but it goes without saying that the scope of the present invention is not limited to these Examples.

A 200 A (216.3 mmφ) steel pipe was previously coated with polyethylene resin or polyurethane resin to a thickness of 3 mm at the factory, and then welded, and the joint portion was subjected to anticorrosion coating. The coating method will be described below with reference to the drawings.

〔Example〕

Example 1 A cross-sectional view of a joint portion anticorrosion coating in the present invention of a steel pipe previously coated with a polyethylene resin in a factory is shown in FIG. 1, a cross section of a joint portion after welding joining and before anticorrosion coating is shown in FIG. FIG. 3 shows a cross section of the joint portion in which only the post-heat shrinkage tube is covered. Reference numeral 1 is a steel pipe, 2 is a welded portion, and 3 is a polyethylene resin coating previously coated in a factory. The joint portion is cut in steps, and both ends of the heat-shrinkable tube 4 are placed on the steps as shown in FIG. And heat to shrink and coat. Then, after subjecting the surface of polyethylene to flame treatment, a primer 5 having adhesiveness with polyolefin resin and polyurethane resin is applied as shown in FIG. This time, we used MacFlex350U manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd. as the adhesive primer. Urethane paint after application of adhesive primer (Daiichi Kogyo Seiyaku Co., Ltd. Ma
cFlex210) is applied to form the urethane coating 6. While the urethane coating is in a semi-cured state, a metal having a higher ionization tendency than Fe is sprayed to form a metal sprayed coating 7. The curing time of the urethane film is preferably 30 minutes to 1 hour in the case of MacFlex210 manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd. The thermal spray machine is not particularly limited, but this time PME manufactured by Pan Metal Engineering Co., Ltd.
Using arc sprayer PA-101, 1.1mmφ wire at room temperature, current 100A, voltage 13V, air pressure 7.5kg / cm ²
Zn spraying was performed.

Example-2 PME arc sprayer PA manufactured by Panmetal Engineering Co., Ltd. after coating with polyurethane resin as in Example 1
Using -101, a 1.1 mmφ wire was used at room temperature, and Al was sprayed at a working current of 200 A, a voltage of 14 V, and an air pressure of 5.5 kg / cm ² .

Example 3 FIG. 4 shows a cross-sectional view of the joint portion anticorrosion coating in the present invention of a steel pipe previously coated with polyurethane resin in a factory, and FIG. 5 shows a cross-sectional view of the joint portion after welding and before anticorrosion coating. Reference numeral 1 is a steel pipe, 2 is a welded portion, and 8 is a polyurethane coating that has been pre-painted at the factory. As shown in Fig. 4, the surface of the welded joint is cleaned with a wire brush or a glider, and a primer (this time using MacFlex320 manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) is applied to form the primer coating 9. . Urethane paint after applying primer (MacFle manufactured by Daiichi Kogyo Seiyaku Co., Ltd.)
x210) is applied to form a urethane coating 6. As in the above example, Zn was sprayed while the urethane coating was in a semi-cured state to form a metal sprayed coating 7.

Example-4 After forming the urethane coating 6 in the same manner as in Example 3, Al was sprayed to form the metal sprayed coating 7 while the urethane coating was in a semi-cured state as in the above example.

The coating obtained as described above is protected by the metal sprayed layer and the impact resistance of the coating is improved. Also, by freely controlling the thickness of the coating such as urethane paint and the metal spray coating on the joint, the boundary between the factory coating and the joint coating and the surface of the joint coating can be made extremely smooth, External force such as friction received during propulsion can be reduced. The stronger the coating is, the stronger the coating strength against external force during propulsion is. Table 1 shows the adhesion test results of the coating.

The adhesion was measured by measuring the vertical adhesion with an adhesion tester manufactured by UK Elcometer.

The coating obtained in the above example was actually subjected to a soil propulsion test. Underground propulsion test is a test that assumes actual construction conditions and simulates the actual construction by pushing the steel pipe against the sand by vertical pressure to promote it, and estimates how the coating will actually change during construction. Is. The propulsion speed is set as follows in the standard steps of the Ministry of Construction. The propulsion method includes a blade tip propulsion method in which a pipe tip with a sharp end is attached to the tip of the pipe for propulsion, and a muddy water propulsion method in which mud is poured to reduce friction on the peripheral surface of the pipe.

(1) Blade promotion (2) Muddy water propulsion Table 2 shows the setting values of the standard rate of construction of the Ministry of Construction for the propulsion speed during muddy water propulsion.

Considering the values of blade propulsion and muddy water propulsion as described above, a safety factor of 2 was selected for a blade tip propulsion speed of 3.1 cm / min that causes severe friction on the pipe circumferential surface, and a propulsion speed of 6.2 cm / min was selected in the test. It is. The pressure of the sediment as calculated by loosening the height of the soil by WSP-018, a 7.4t / m ² in a steel pipe of 2.2 T / m ^2, 3000A in steel pipe 800A. The steel pipe used in this test is 200A, but 7.4t / m ² , which is a sufficiently severe condition, was selected as the earth and sand pressure (vertical pressure). Table 3 shows the test results.

It was confirmed that the coating obtained according to the present invention has considerably high durability as compared with the case where the coating by the conventional method blisters.

〔The invention's effect〕

As shown in the above examples, the anticorrosion coating method of the joint portion according to the present invention is a method of directly spraying a metal having an anticorrosion property, protecting the resin layer coated for the purpose of anticorrosion, and directly propelling it in a burial work. Also, in the above, a durable coating can be formed without causing defects such as coating blistering.

[Brief description of the drawings]

Fig. 1 shows a cross-sectional view of the joint portion anticorrosion coating of the present invention of a steel pipe previously coated with polyethylene resin at the factory, Fig. 2 shows a cross-section of the joint portion after the welding joint and before the anticorrosion coating, only the weld joint heat shrinkable tube A cross section of the coated joint portion is shown in FIG. In addition, FIG. 4 shows a cross-sectional view of the joint portion anticorrosion coating in the present invention of a steel pipe previously coated with polyurethane resin at the factory, and FIG. 5 shows a cross-sectional view of the joint portion after welding and before the anticorrosion coating. 1 ... Steel pipe, 2 ... Welded part 3 ... Polyethylene resin pre-coated at the factory 4 ... Heat-shrinkable tube 5 ... Primer layer that adheres to polyolefin resin and polyurethane resin 6 ... Polyurethane coating 7 ... … Metal sprayed coating with greater ionization tendency than Fe 8 …… Polyurethane resin pre-coated at factory 9 …… Adhesive primer coating

Claims (2)

(57) [Claims] 1. In a pipe construction in which a steel pipe having an anticorrosive coating formed on the outer periphery of the pipe is welded and buried in order, the outer periphery of a steel pipe coated with a polyolefin resin as the anticorrosive coating is heat-shrinkable on the outer periphery of the joint. After coating the tube, and then applying an adhesive primer on the surface including the boundary portion between the anticorrosion coating and the heat-shrinkable tube coating, paint is applied, and the ionization tendency of Fe before Fe is completely cured before the coating is completely cured. Corrosion-proof coating method for corrosion-prevention-coated steel pipe joints, characterized by spraying a metal with a large 2. A pipe construction in which a steel pipe having an anticorrosion coating formed on the outer periphery of the pipe is welded one after another and embedded therein, a polyurethane resin is provided on the outer periphery of the joint of a steel pipe having a polyurethane resin coating on the outer periphery as the anticorrosion coating. An anticorrosion coating method for an anticorrosion coated steel pipe joint, which comprises coating and spraying a metal having a greater ionization tendency than Fe before the polyurethane resin is completely cured.