JPH07276560A - Heavy corrosionproof coated steel pipe and its production - Google Patents

Abstract

PURPOSE:To obtain a heavy corrosionproof coated steel pipe keeping a sufficient adhesion even during transport or installation by a method wherein a thermosetting resin corrosionproof coating layer and a thermoplastic resin protective coating layer each having a specific layer thickness are laminated on a surface of a steel pipe, and a shear release strength and a peel release strength are specified between the layers. CONSTITUTION:In a heavy corrosionproof coated steel pipe, a coating layer 3 made of a thermosetting resin with a layer thickness of 0.05-1.0mm is provided on a steel pipe 1, and thereon a thermoplastic resin 5 of 0.1-10mm layer thickness is laminated through an adhesive layer 4 of 0.05-1.0mm layer thickness. A shear release strength between the corrosionproof coating layer 3 and the adhesive layer 4 is not lower than 20kgf/cm<2> but lower than a shear release strength between the steel pipe 1 and the corrosionproof coating layer 3. A 90 deg. peel release strength between the corrosionproof coating layer 3 and the adhesive layer 4 is not higher than 10kgf/cm<2>. In addition, the release strength between the steel pipe 1 and the corrosionproof coating layer 3 and that between the corrosionproof coating layer 3 and the adhesive layer 4 are the most important constitutional requirements.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heavy-duty anticorrosion coated steel pipe in which a steel pipe is coated with a thermosetting resin, and a protective layer of a thermoplastic resin is further coated on the steel pipe with an adhesive, and a method for producing the same.

[0002]

2. Description of the Related Art Steel pipes whose surfaces are coated with resin are widely used for pipelines for transporting crude oil and natural gas and for offshore structures such as steel pipe pile plates.

Among such resin-coated steel pipes, particularly heavy-corrosion steel pipes are required to have both the function of preventing corrosion of the steel pipe and the function of protecting the corrosion-preventing layer from impact. Therefore, various resin-coated steel pipes have been proposed in which a thermosetting resin such as an epoxy resin is first coated to form an anticorrosion layer, and a thermoplastic resin such as polyethylene or polypropylene is coated thereon as a protective layer.

For example, Japanese Unexamined Patent Publication No. 59-7038 discloses a steel pipe in which a powder epoxy resin is coated on the outer surface of the steel pipe, and a protective layer of a polyolefin resin is coated thereon.

In Japanese Patent Laid-Open No. 1-127085, a powder epoxy layer is applied to the outer surface of a steel pipe, and a polyolefin layer is immediately laminated with a modified polyolefin adhesive.

[0006]

In the case of the coated steel pipe having the anticorrosion layer and the protective layer on the surface of the steel pipe as described above, if the adhesion is insufficient, the protective layer peels off during transportation or installation, May not be done.

On the other hand, when the anticorrosion layer and the coating layer are firmly adhered to each other by the adhesive agent and the binding force between the layers is strong, the protective layer and the adhesive layer around the joint portion when the coated steel pipes are joined together. It is not easy to peel off and it takes time to work. In addition, when the coated steel pipe is installed or after installation, if the protective layer shifts from the steel pipe due to external force or internal stress of the protective layer itself, the anticorrosive layer also follows it and the anticorrosive layer peels off from the steel pipe surface. Or, if a crack is formed in the protective layer, the crack propagates to the anticorrosion layer.

An object of the present invention is to provide a heavy-duty anticorrosion coated steel pipe and a method for producing the same, which solves the above problems.

[0009]

The coated steel pipe for heavy anticorrosion of the present invention has a coating layer made of a thermosetting resin having a layer thickness of 0.05 to 1.0 mm on the steel pipe, and the layer thickness on the coating layer. 0.05 ~
The layer thickness is 0.1 to 10 mm through the 1.0 mm adhesive layer.
It is a coated steel pipe for heavy anticorrosion in which the thermoplastic resin of is laminated, and the shear peel strength between the anticorrosion coating layer and the adhesive layer is 20 kgf /
cm ² or more, lower than the shear peel strength between the steel pipe and the anticorrosion coating layer, and 90 ° between the anticorrosion coating layer and the adhesive layer
The peel peel strength is 10 kgf / cm ² or less.

In the above heavy-duty anticorrosion coated steel pipe, the open time from the time when the thermosetting resin is applied to the time when the adhesive layer and the thermoplastic resin protective layer are coated is at least twice as long as the gel time of the thermosetting resin. , 100 times or less.

[0011]

In the present invention, a coating layer made of a thermosetting resin is provided in a layer thickness of 0.05 to 1.0 mm as a layer for preventing corrosion of the steel pipe. As the thermosetting resin, epoxy resin is advantageous in terms of anticorrosion performance. If the layer thickness is less than 0.05 mm, it is difficult to obtain a uniform layer thickness by the powder coating method.
Even if it exceeds 1.0 mm, there is no difference in anticorrosion performance. 0.
A layer thickness of 07 to 0.4 mm is desirable. When coating the above-mentioned thermosetting resin on the steel pipe, it is usually preferable to perform chromate treatment as a base treatment for forming a strong anticorrosion layer thickness.

An adhesive layer is provided on the thermosetting resin. The resin as the adhesive is preferably a modified polyethylene resin. The layer thickness of the adhesive is preferably 0.05 to 1.0 mm. If the layer thickness is less than 0.05 mm, it is difficult to uniformly form the adhesive layer, and if the layer thickness exceeds 1.0 mm, the adhesive resin is more expensive than the anticorrosion thermoplastic resin, which is disadvantageous in terms of cost.

A layer thickness of 0.1 to 10 mm is provided on the adhesive layer.
The thermoplastic resin of is provided as a protective layer. As the thermoplastic resin, a polyolefin resin such as polyethylene or polypropylene is preferable. Since the polyolefin resin is relatively inexpensive, it is economical to increase the layer thickness for the purpose of protection. If the layer thickness is less than 0.1 mm, the impact resistance is poor, and if it exceeds 10 mm, the protective effect is saturated.

Next, the most important constituent factor in the present invention is the peel strength between the steel pipe and the anticorrosion coating layer and between the anticorrosion coating layer and the adhesive layer.

In the heavy-duty anticorrosion coated steel pipe of the present invention, it is necessary to maintain the protective function as it is without peeling off the entire coating layer during transportation or storage. Therefore, the tensile shear strength between the steel pipe and the anticorrosion coating layer is 40 kgf / cm ²
That is all. Next, when welding and joining the coated steel pipe, it is necessary that the coating around the joint can be easily removed. Therefore, the 90 ° peel peel strength is set to 10 kgf / c so that the anticorrosion coating layer and the adhesive layer can be peeled manually.
m ² or less. Furthermore, after the coated steel pipe is used as a line pipe or an offshore structure, even if stress from inside or outside acts on the protective layer, the stress does not propagate to the anticorrosion layer and it is necessary to maintain the anticorrosion function. For that purpose, it is necessary that the deviation caused when a shearing force is applied to the adhesive surface of the coating is limited between the anticorrosion coating layer and the protective layer. Therefore, the shear peel strength between the anticorrosion coating layer and the adhesive layer is made lower than the shear strength between the steel pipe and the anticorrosion coating layer.

A manufacturing method satisfying the above required characteristics will be described.

The powder coating of the thermosetting resin is sprayed on the preheated steel material, then once melted into a high-viscosity liquid state as the temperature rises, and then cured to form an anticorrosion coating layer. As shown in FIG. 1, the longer the elapsed time (open time) until the powder coating of the thermosetting resin is sprayed and the protective layer is covered with the adhesive layer, the longer the thermosetting resin anticorrosion layer. The peel strength between the adhesive layer and the adhesive layer decreases. Therefore, by manipulating this open time, it is possible to set the strength targeted by the present invention.

In the coating layer defined in the present invention, the open time is preferably in the range of 2 times or more and less than 100 times the gel time of the thermosetting powder coating material at the preheating temperature of the steel material. The gel time here is a value measured by the hot plate method.

[0019]

EXAMPLE As shown in FIG. 2, a coated steel pipe in which a chromate layer 2, a powder epoxy resin anticorrosion layer 3, a modified polyethylene adhesive layer 4, and a polyethylene resin protective layer 5 were sequentially laminated on a steel pipe 1 was manufactured. did.

After adjusting the base material of the steel pipe by blasting and subjecting it to chromate treatment, the temperature is raised to 190 ° C., and then the powdered epoxy resin is sprinkled so that the formed anticorrosion layer of the epoxy resin has a layer thickness of 0.2 mm. Following this, after a lapse of a certain open time, a polyethylene resin in a molten state was coated with an adhesive layer of maleic anhydride-modified polyethylene having a layer thickness of 0.2 mm so as to have a layer thickness of 3 mm, and then cooled with water. .

Regarding the sample produced as described above,
The following items were tested.

(1) Adhesion of coating layer The shear bond strength when the steel pipe and the coating were pulled to opposite sides in the pipe length direction was evaluated according to the measuring method of JIS-K6850, and the result was evaluated as ○ / △ / ×. It was expressed in three stages. ○
Indicates that the shear adhesive strength is 40 kgf / cm ² or more. △ indicates a shear adhesive strength of 20 kgf / cm ²
It is above 40 kgf / cm ² . × is
The shear bond strength is less than 20 kgf / cm ² .

(2) Workability of coating peeling work on pipe end The workability of coating peeling was evaluated by peeling strength in a 90 ° peel test, and the results were expressed in three grades of ⊚ / ◯ / Δ. ◎
Indicates that the peeling strength is less than 1 kgf / cm ² , the coating peels off without applying any particular force, and the peeling work is very easy. ◯ indicates a peel strength of 1 kgf / cm ² or more 10
When it is less than kgf / cm ^2, it means that the peeling work can be carried out manually by heating below the melting point of the polyethylene protective layer. Δ indicates that the peel strength is 10 kgf / cm ² or more, and that heating to reach a temperature exceeding the melting point of the polyethylene protective layer is required to perform the peeling operation manually.

(3) Shear peeling position of the coating layer In the measurement of the tensile shear strength in (1) above, the position where shearing occurred during shear peeling was observed.

In order to prevent the anticorrosion layer of the epoxy resin from falling off from the steel when the coated steel pipe is installed, the deviation is limited to the anticorrosion layer / protection, and shear peeling is required between them.

Table 1 shows the evaluation results. From the test results, in Example 2, desirable performances were shown for all three items. That is, in the coated steel pipe manufactured under the conditions according to Example 2, the coating does not fall off during transportation and construction, but it is easy to remove the excess coating on the pipe end during welding and the like. Even if a stress is applied, the stress is absorbed by the shift of the polyolefin protective layer, and the epoxy resin anticorrosion layer does not peel off.

The priorities of the above items differ depending on the environment in which the steel pipe is used. For example, in some cases, it may be more important that the coating adheres firmly than the ease of joining the steel pipes together. In that case, the open time at the time of forming the anticorrosion layer of the present invention may be further shortened and the production may be performed under the conditions of Example 1. On the contrary, if the ease of joining the steel pipes is more important than the firm adhesion of the coating, the open time may be made longer and the production may be performed under the conditions of Example 3.

[0028]

[Table 1]

[0029]

INDUSTRIAL APPLICABILITY In a heavy-corrosion coated steel pipe in which a protective coating layer made of a thermoplastic resin is laminated on an anticorrosion coating layer made of a thermosetting resin via an adhesive layer, the anticorrosion coating is performed as described above. The following effects are obtained by defining the shear peel strength between the layer and the adhesive layer and the 90 ° peel peel strength, and by making the shear peel strength between the both layers lower than the shear peel strength between the steel pipe and the anticorrosion coating layer. To be

1) The protective function is maintained without peeling the entire coating during transportation or storage of the coated steel pipe.

2) When welding a coated steel pipe by welding, the coating around the joint can be easily removed.

3) Even if stress acts on the protective layer from inside and outside during installation of the coated steel pipe, it does not propagate to the anticorrosion layer and the anticorrosion performance can be maintained.

[Brief description of drawings]

FIG. 1 is a diagram showing a flow of a coating process of the present invention.

FIG. 2 is a diagram showing a coating structure of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Steel pipe 2 ... Chromate processing layer 3 ... Epoxy resin anticorrosion layer 4 ... Modified polyolefin adhesive layer 5 ... Polyolefin resin protective layer

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B05D 7/24 P 7717-4D 302 U 7717-4D G 7717-4D

Claims (3)

[Claims] 1. A layer thickness of 0.05 to 1.0 mm on the surface of a steel pipe.
Protective coating made of a thermoplastic resin having a layer thickness of 0.1 to 10 mm with an anticorrosion coating layer made of a thermosetting resin on which an adhesive layer having a layer thickness of 0.05 to 1.0 mm is interposed. A coated steel pipe for heavy anticorrosion in which layers are laminated, the shear peel strength between the anticorrosion coating layer and the adhesive layer is 20 kgf / cm ² or more, and the shear peel strength between the steel pipe and the anticorrosion coating layer is lower, and the anticorrosion coating layer And 90 ° peel peel strength between the adhesive layer and the adhesive layer is 10 kgf / cm ² or less. 2. The coated steel pipe for heavy corrosion prevention according to claim 1, wherein the thermosetting resin is a powdered epoxy resin, the adhesive is an unsaturated organic acid- or unsaturated anhydride-modified polyolefin, and the thermoplastic resin is a polyolefin. 3. The open time from the time when the thermosetting resin is applied to the steel pipe to the time when the adhesive layer and the thermoplastic resin protective layer are coated is at least twice and less than 100 times the gel time of the thermosetting resin. The method for producing a coated steel pipe for heavy corrosion protection according to claim 1 or 2, wherein