JPH0387248A - Method for applying anti-corrosion coating to anti-corrosion coated steel pipe joint part - Google Patents

Abstract

PURPOSE:To obtain coating having film hardness withstanding the resistance of earth and sand at the time of propelling and capable of sufficiently developing anti-corrosion capacity by applying a primer to the surface containing the boundary part of the anti-corrosion film of a steel pipe and the heat-shrinkable tube film of a joint part to apply paint to the primer layer and subsequently applying a specific metal to the paint layer by flame spraying. CONSTITUTION:A polyethylene resin is preliminarily applied to the outer periphery of a steel pipe 1 in a factory to form a film 3 and a joint part is cut in a stepped state. Both ends of a heat-shrinkable tube 4 are placed to the stepped part to cover the same and heated to be shrunk to coat said stepped part. Subsequently, a polyethylene surface 3 is treated with flame and a primer 5 having adhesiveness to a polyolefin resin and a polyurethane resin is applied to the treated surface. After the coating of the adhesive primer, urethane paint is applied to the primer layer to form an urethane film 6. When the urethane film is in a semicured state, a metal higher than Fe in an ionization tendency is applied by flame spraying to form a metal flame spraying film 7. The ageing period of the urethane film is pref. 30min - 1hr.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for anticorrosion coating a welded joint during construction of an anticorrosion coated steel pipe.

[Conventional technology]

In recent years, due to ground and environmental conditions in underground piping work, it has become impossible to use the open cut method (a method in which a trench is dug where the #4 pipe is to be installed, the steel pipe is installed, welded and buried), A direct propulsion method is often implemented in which steel pipes are directly propelled and then sequentially welded and buried.

Since the direct propulsion method is a construction method in which steel pipes are propelled directly into the soil, the anticorrosive coating on the steel pipes is required to have impact resistance and abrasion resistance because it is subject to more resistance from earth and sand during propulsion than in the open cut method. For this reason, at the factory, they are coated with a thick layer of resin such as polyethylene or polyurethane, which have excellent performance in these areas. However, joints that are welded together at the construction site must be covered on-site, such as by covering them with heat-shrinkable tubes or painting them with polyurethane paint after welding. For example, disclosures of known patents include JP-A No. 60-12234 and Utility Model Application No. 59-144042.

(Problem to be solved by the invention) However, when a heat-shrinkable tube is applied on-site to a joint that has been welded at a construction site, due to the constraints of on-site coating, the on-site heat shrinkage is lower than that of a pre-coated coating at a factory. Shrinkable tube coating has poor adhesion to steel surfaces. Generally, the impact resistance of a coating obtained by covering a coating with the same material increases as the adhesion between the coating and the material becomes stronger. The same goes for the impact resistance of factory pre-coated and on-site heat-shrinkable tube coatings, with the impact resistance of heat-shrinkable tube coatings being inferior to factory pre-coated coatings.

Therefore, in the direct propulsion method that has been frequently implemented in recent years, the heat-shrinkable tube coating at the joint part, which has inferior adhesion and impact resistance than the coating pre-coated at the factory, is partially destroyed due to resistance from earth and sand during propulsion. was there. If such a defect occurs, it can be discovered through post-burying inspection, but it is very difficult to repair the defect. Therefore, we are currently taking new measures such as electrolytic protection.

In addition, when the joints welded and joined at the construction site are painted on-site even when buried using the normal open-cut construction method, the adhesion of the corrosion-protected parts of the joints is weak, resulting in through-holes caused by backfilling earth and sand. There are surfaces, such as factory paint, that are not well managed, and the interfacial adhesion between the factory paint surface and the anti-corrosion coating for on-site joints may be insufficient and buried, allowing corrosion to progress from there.

The present invention was made to solve the above-mentioned 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 is partially destroyed or has pinholes. The government's objective is to obtain a coating that can exhibit sufficient anticorrosion ability even when exposed to corrosion.

[Means to solve the problem]

That is, the present invention provides the following features: (1) In piping construction in which steel pipes with an anticorrosive coating formed on the outer periphery of the pipe except for the joint part are sequentially welded and buried, the outer periphery of the joint part of the steel pipe whose outer periphery is coated with a polyolefin resin as the anticorrosive coating is Coating a heat-shrinkable tube, then applying an adhesive primer to the surface including the boundary between the anti-corrosion coating and the heat-shrinkable tube coating, and then applying a paint;
A method for coating a pipe joint with an anticorrosive liquid Mm, characterized in that a metal having a higher ionization tendency than Fe is thermally sprayed before the paint is completely cured.

(2) In piping construction in which steel pipes with an anti-corrosion coating formed on the outer periphery of the pipe are sequentially welded and buried except for the joint part, polyurethane resin is applied to the outer periphery of the joint part of the steel pipe that has a polyurethane resin coating on the outer periphery as the anti-corrosion coating. A method for anti-corrosion coating of a joint of an anti-corrosion coated steel pipe, characterized in that, before the polyurethane resin is completely cured, a metal having a higher ionization tendency than Fe is thermally sprayed.

It is.

The following is the anticorrosive liquid T! of the present invention! 1. A method of anti-corrosion coating for steel pipe joints will be specifically explained.

When applying anti-corrosion coating to the joints of steel pipes where the outer periphery of the pipe is coated with polyolefin resin as an anti-corrosive coating, the outer periphery of the pipe is coated with polyolefin resin as an anti-corrosion coating. Adhesion with these materials is extremely weak, so a urethane primer that has adhesive properties with these polyolefin resins is applied in advance. Urethane primer is a compound that has two or more hydroxyl or amino groups in its molecule (hereinafter referred to as polyol) and a compound that has two or more isocyanate groups in its molecule (hereinafter referred to as polyisocyanate). It is a urethane bleb polymer containing terminal isocyanate groups obtained by polymerization. If the molecular weight of the polyol is low, the primer coating tends to become hard, resulting in no elongation, and the coating tends to crack when the object to be coated is bent. On the other hand, when the molecular weight of the polyol is large, the concentration of urethane bonds with large cohesive force becomes low, so that the adhesiveness with the polyolefin resin tends to deteriorate. Therefore, it is preferable to use a polyol with a molecular weight of 400 to 2000. There are no particular limitations on the polyol and polyisocyanate, but from the viewpoint of water resistance, it is recommended to select a polyether polyol that is difficult to hydrolyze. preferable. Furthermore, aromatic polyisocyanates, particularly diphenylmethane diisocyanate, are excellent in terms of adhesiveness. This is thought to be because the cohesive force of the aromatic ring contributes to the improvement of adhesion.

After applying the urethane primer, paints such as urethane paints, acrylic urethane paints, acrylic paints, alkyd paints, acrylic emulsion paints, and vinyl chloride paints are applied, and before these paints are completely cured, the ionization tendency is greater than that of Fe. Smoothly spray metals such as AM and Zn. This metal sprayed layer increases the hardness of the anti-corrosion coating, allows smooth coating bonding between the factory coating and the on-site coating, and can withstand the resistance of earth and sand during propulsion of the vibrator during burial work. Furthermore, the reason why metals such as AJj and Zn, which have a higher ionization tendency than Fe, are used as the sprayed metal is to provide an electrolytic protection effect by using the metal sprayed layer as a sacrificial anode in the event that a portion of the anticorrosion coating should be destroyed.

Since the paint film and the sprayed metal are attached by mechanical adhesion, the metal is sprayed onto the semi-cured paint film, the metal is embedded in the paint film, and the cohesive force of the paint film strengthens the adhesion between the paint film and the sprayed metal. There is a need to. EXAMPLES The present invention will be specifically described below with reference to Examples, but it goes without saying that the scope of the present invention is not limited to these Examples.

A 200A (216.3 mmφ) steel pipe was coated with polyethylene resin or polyurethane resin to a thickness of 3 mm in advance at a factory, and then welded and joined, and an anticorrosive coating was applied to the joint. The coating method will be explained below according to the figures.

〔Example〕

Example-1 Fig. 1 shows a cross-sectional view of the anti-corrosion coating of a joint in the present invention of a steel pipe coated with polyethylene resin in advance at a factory, and Fig. 2 shows a cross-section of the joint after welding and before anti-corrosion coating. FIG. 3 shows a cross section of the joint portion covered only with the post-heat shrink tube. 1 is a steel pipe, 2 is a welded part, 3 is a polyethylene resin coating coated in advance at the factory, and the joint part is cut into a step shape.
As shown in FIG. 3, both ends of the heat-shrinkable tube 4 are placed and covered on the stairs, and heated to cover the stairs with shrinkage. Next, after flame-treating the polyethylene surface, a primer 5 that is adhesive to polyolefin resin and polyurethane resin is applied as shown in FIG.
Apply. This time, Dai-Kogyo Yakuhin Ajibu MacF1ex3SOIJ was used as the adhesive primer. Urethane bonding after application of adhesive primer (M made by Daiichi Kogyo Seiyaku ■)
acF1ex210) to form a urethane coating 6. While the urethane coating is in a semi-hardened state, a metal having a higher ionization tendency than Fe is thermally sprayed to form a metal sprayed coating 7. The curing time for the urethane coating is Mac manufactured by Daiichi Kogyo Seiyaku ■.
In the case of FLex21Q, 30 minutes to 1 hour is preferable. There are no particular restrictions on the thermal spraying machine, but this time we used a PME arc spraying machine PA-101 manufactured by Panmetal Engineering ■, using a wire of l, Lmmφ at room temperature, using a current of IQOA, a voltage of 13V, and an air pressure of 7. 5kg/c
Zn thermal spraying was carried out in Bo.

Example-2 After painting the polyurethane resin in the same manner as in Example 1, use the PME arc spraying machine P A manufactured by Pan Metal Engineering ■.
-101, a 1.1 mmφ wire at room temperature, and a working current of 200 A.

An thermal spraying was performed at a voltage of 14 V and a z-ar pressure of 5.5 kg/cm'.

Example 3 FIG. 4 shows a cross-sectional view of the anti-corrosion coating of a joint in the present invention of a steel pipe coated with polyurethane resin in advance at a factory, and FIG. 5 shows a cross-sectional view of the joint after welding and before anti-corrosion coating. 1 is a steel pipe, 2 is a welded part, and 8 is a polyurethane coating that has been previously painted at a factory. As shown in Figure 4, clean the surface of the welded joint using a wire brush or grinder, and then use a brush to clean the surface of the welded joint.
20) to form a primer coat M9.

After applying the primer, urethane paint (Ma manufactured by Daiichi Kogyo Seiyaku ■)
cFlex210) to form a urethane coating 6. As in the previous example, Zn was added while the urethane coating was in a semi-cured state.
was thermally sprayed to form a metal sprayed coating 7.

Example 4 After forming up to the urethane coating 6 in the same manner as in Example 3, AX was thermally sprayed while the urethane coating was in a semi-hardened state to form the metal sprayed coating 7, as in the previous example.

The coating obtained as described above is protected by the metal spray layer, and the impact resistance of the coating is improved. In addition, 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 forces such as friction received during propulsion can be reduced. The tighter the coating, the stronger the coating strength against external forces during propulsion. Table 1 shows the results of the coating adhesion test.

The vertical adhesion was measured using an adhesion tester manufactured by Elcometer, UK.

The coating obtained in the above example was actually subjected to an underground propulsion test. Underground propulsion testing is a test that simulates actual construction by pushing a steel pipe against earth and sand using vertical pressure under actual construction conditions, and estimates how the coating will change during actual construction. It is. The propulsion speed is set as follows in the Ministry of Construction standard rate. There are two types of propulsion methods: the blade propulsion method, which attaches a sharp tip to the tip of the vibrator to propel the vibrator, and the muddy water propulsion method, which reduces friction on the pipe circumferential surface by flushing muddy water away.

(1) Blade propulsion 800-3000φ 2.43m 2.43m v-0m O,031m/m1n-3,1cm/ff1
in1.3hrs 78mxn (2) Muddy water propulsion Table 2 shows the setting values set by the Ministry of Construction standard rate for propulsion speed during muddy water propulsion.

Considering the values of blade propulsion and muddy water propulsion as described above, the blade tip propulsion speed is 3.1 cta/■, which causes severe friction on the pipe circumferential surface.
With a safety factor of 2 for in, the propulsion speed in the test is fi,
2cm/win was selected, and the earth and sand pressure was WSP-
According to Gill's calculation of soil loosening height, ao
aAtf) 2.2t/rn', 30GOA for 111 tube
CF) Steel pipe is 7.4t/d. The steel pipe used in this test was 20OA, but the conditions were sufficiently severe1.
4t/d was selected as the soil pressure (vertical pressure).

The test results are shown in Table 's3.

Table N3 It was confirmed that the coating obtained by the present invention was considerably more durable than the coating obtained by the conventional method, which caused blistering.

〔Effect of the invention〕

As shown in the examples above, the method of anti-corrosion coating of a joint according to the present invention involves smooth thermal spraying of a metal having cathodic protection,
It protects the resin layer coated for the purpose of corrosion prevention, and can form a durable coating without causing defects such as coating blistering even in the direct propulsion method for buried construction.

[Brief explanation of drawings]

Figure 2 is a cross-sectional view of the anti-corrosion coating of the joint in the present invention using steel that has been previously coated with polyethylene resin at the factory, Figure 2 is a cross-sectional view of the joint after welding and before the anti-corrosion coating, and welded heat-shrinkable tube. FIG. 3 shows a cross section of the joint portion covered with a chisel. Further, FIG. 4 shows a cross-sectional view of the joint part of the steel pipe coated with polyurethane resin in advance at the factory in the present invention, and FIG. 5 shows a cross-sectional view of the joint part before the corrosion-proof coating after welding. 1... Steel pipe 2... Welded part 3... Polyethylene resin coated in advance at the factory 4... Heat shrinkable tube 5... Primer layer 6 with adhesive properties to polyolefin resin and polyurethane resin...・Polyurethane coating 7...Metal sprayed coating 8 with a greater tendency to ionize than Fe
...Polyurethane resin 9 coated in advance at the factory...
・Adhesive primer coating 4 people! ：Steel Pipe Diagram Diagram Diagram Diagram Diagram Diagram Diagram Diagram Diagram Diagram Diagram Diagram Diagram Diagram

Claims (1)

[Scope of Claims] 1. In piping construction in which steel pipes with an anticorrosive coating formed on the outer periphery of the pipe except for the joint portion are sequentially welded and buried, heat is applied to the outer periphery of the joint portion of the steel pipe whose outer periphery is coated with a polyolefin resin as the anticorrosive coating. After coating the shrinkable tube and then applying an adhesive primer to the surface including the boundary between the anti-corrosion coating and the heat-shrinkable tube coating, a paint is applied, and before the paint is completely cured, it is coated with Fe. A method for anti-corrosion coating of a joint of an anti-corrosion coated steel pipe, characterized by thermal spraying a metal with a high ionization tendency. 2. In piping construction in which steel pipes with an anticorrosion coating formed on the outer periphery of the pipe except for the joint are sequentially welded and buried, the outer periphery of the joint of the steel pipe that has a polyurethane resin coating on the outer periphery as the anticorrosive coating is coated with polyurethane resin, A method for anti-corrosion coating of a joint of an anti-corrosion coated steel pipe, characterized in that a metal having a higher ionization tendency than Fe is thermally sprayed before the polyurethane resin is completely cured.