JPS5874336A - Manufacture of coated steel pipe - Google Patents

Abstract

PURPOSE:To provide a polyolefin-coated steel pipe which has no problem on adhesiveness even in a very cold or a very hot region, by a method wherein three resins of a thermosetting epoxy series adhesive, a denatured polyolefin, and olefin are used in a given line constitution. CONSTITUTION:Solventless thermosetting epoxy series adhesives 3 and 4 are coated by squeeze on a steel pipe 1, on which a pretreatment has been made, by means of a coating vessel 2. Immediately after said coating is made, the work is rapidly heated by an induction heater 6 to cure the adhesives, and the temperature of the steel pipe is maintained at a range of a melting point-a melting point +60 deg.C, the steel pipe is coated with an adherent denatured polyolefin 8 and polyolefin 9 with the aid of a co-extruding dice 7, and the resultant work is rapidly cooled by a water cooling device 11.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing coated steel pipes, and more specifically to a method for in-line manufacturing polyolefin-coated steel pipes that have excellent adhesion to the surface of steel pipes and can be used in extremely cold and extremely hot regions. It is.

Polyolefins not only exhibit excellent corrosion resistance against acids, alkalis, and certain organic solvents, but also have electrical insulation properties and are easy to process, so they are used as linings for buds, covering electric wires, and electrical appliances. It is widely used for J-te, F-ng, etc.

As a specific example of how coated steel pipes can be used, polyolefin coated steel pipes are highly anticipated for use in gas pipelines, crude oil or petroleum transfer pipes, cable preservation pipes, etc., laid on the ground or buried. It is something that exists.

In this type of polyolefin-coated steel pipe, an adhesive substance such as asphalt and a rubber component is applied to the outside of the steel pipe, and the outer periphery thereof is coated with polyolefin by an extrusion method. However, since such conventional polyolein-coated steel pipes use the above-mentioned adhesive, when the temperature at which they are used increases, the adhesive softens and begins to flow easily. Therefore, the adhesion between the polyolefin layer and the polyolefin layer begins to deteriorate, and if some external force is applied during or after the polyolefin-coated steel pipe is laid (for example, during suspension by a crane or soil disproportionation), the steel pipe and the polyolefin layer will begin to deteriorate. On the other hand, if the operating temperature is extremely low, the adhesive will lose its viscosity and the adhesive function between the steel pipe and the coating layer will be impaired.
It also becomes brittle and causes the coating layer to flake or peel during installation. The relationship between temperature and peel adhesion force in conventional adhesive polyolefin coated steel pipes is as shown by the broken line in FIG.

Therefore, when using polyolefin-coated steel pipes in extremely cold or extremely hot regions, or when transporting high-temperature fluids, adhesives have higher adhesive strength and are stable over a wider temperature range than the adhesives mentioned above. It has been desired to develop polyolefin-coated steel pipes manufactured from materials that maintain the same strength.

When coating a metal surface such as a steel pipe with polyTolefin, a layer of modified polyolefin modified with an unsaturated carboxylic acid such as maleic anhydride or its anhydride is interposed to increase the adhesion between the two. It is known to do so. Also known is a method in which a thermosetting epoxy resin film is formed on a metal surface, the film is cured, and then a modified polyolefin modified with an unsaturated carboxylic acid is coated.

However, in either method, when coating with modified polyolenoin, it is necessary to maintain the temperature of the surface of the metal, which is the base material, above the melting point of the resin, and if this preheating is insufficient, it is necessary to coat with modified polyolenoin. When the resin comes into contact with the metal surface, the resin is cooled down to a single point and cannot be fused.

Therefore, sufficient adhesive strength may not be obtained, but to avoid this, it is said that preheating, that is, increasing the temperature of the steel pipe, is necessary, for example, a temperature of 200° C. or higher is required. However, in order to obtain such a high temperature in-line, actual 1"1 scale 1 consideration 11 insects and pole "5"
It's not a stupid idea that requires zero equipment.
The cooling time after the polyolefin coating is carried out becomes long, and the productivity is extremely low, as for example, the resin cannot be placed on the conveying table until the temperature reaches the melting point or the softening point of the resin on the coated steel pipe.

The inventors of the present invention have conducted various studies on how to manufacture polyolefin-coated steel pipes on a factory production line that do not have any risk of adhesion even when exposed to extremely cold or harsh conditions. By skillfully utilizing the six functions of modified polyolein and polyolefin, and making various considerations for the line configuration, we were able to produce polyolefin-coated steel pipes that have high adhesion and guarantee high quality in-line, while also sufficiently increasing productivity. We have discovered a manufacturing method that

That is, in the present invention, when coating the outer surface of the steel pipe with a polyolefin resin using a cylindrical molding die, a non-malted thermosetting poxy adhesive is applied to the Kurayagi steel pipe after the pretreatment. Immediately after applying the iron coat, the coated steel pipe is rapidly heated with an induction heating machine to harden the adhesive, and the temperature of the adhesive-coated steel pipe is maintained within a temperature range that is equal to or higher than the melting point of the adhesive-modified polyolefin and does not exceed its melting point +60°C. keep it to
The present invention relates to a method for manufacturing a coated steel pipe, which comprises coating the adhesive-coated steel pipe by overlapping adhesive modified polyolefin and polyolefin by coextrusion, and then rapidly cooling the coating.

In carrying out the present invention, the steel pipes to be provided are those in the small to medium diameter size range that can be manufactured using cylindrical forming. It is necessary that pickling and blasting are carried out sufficiently and uniformly. If, for example, oil or dirt remains on the surface of the steel pipe as a result of this pretreatment, the adhesive may be repelled during application of the adhesive or the surface of the steel pipe may not be sufficiently wetted.

As the adhesive, a solvent-free thermosetting epoxy adhesive is used, which has the advantage of being able to increase the line speed because it cures more quickly than solvent-based adhesives. In addition, there is no need to take measures against residual solvent in the epoxy resin after curing, and the adhesive strength between the steel pipe surface and the polyolefin coating layer is greater.

Therefore, the usable temperature range of the coated steel pipe as a finished product is also wide.

Furthermore, in the case of containing a solvent, rapid heating is applied during induction heating in the next step, resulting in rapid volatilization of the solvent, which is disadvantageous because pinholes are formed in the coating film.

In addition to the above-mentioned advantages, solvent-free adhesives do not require measures against solvents in the working environment, and are also very advantageous from the viewpoint of resource conservation.

This solvent-free thermosetting epoxy adhesive naturally needs to be in liquid form because the object to be coated is moving in the manufacturing process line and uniform coating is to be achieved under these conditions.

As a result of various studies, the epoxy adhesive was determined to be epichlorohydrin-bisphenol A, which is most suitable for the purpose of the present invention. Its molecular weight is approximately 300
~650m11, it is a fluid adhesive. In addition, when a curing agent is required to cure this adhesive, common curing agents such as diethylenetriamine, triethylenetetramine, and fatty acid amides can be used, but due to performance and environmental concerns, For these reasons, it is advantageous to use a heterocyclic amine or a modified product thereof.The above-mentioned solvent-free thermosetting epoxy adhesive is applied to the outer surface of a steel pipe in an adhesive coating tank. It is preferable to adjust the viscosity of the solution to a viscosity that can be applied by squeezing, specifically, approximately 10 to 2 x 10'cps0.As a result, a coating of around 25μ, for example, can be obtained.If the viscosity is too low, the steel pipe The adhesive will penetrate faithfully into the minute rough areas on the surface, making it impossible to obtain a smooth coating surface, and conversely, if it is too high, the adhesive coating tank's diaphragm 0.
- Even with the ring, the adhesive could not be squeezed out and the coating film became thicker than necessary, so instead of using the uneconomical Bakasho method, it was rapidly heated in the next process, an induction heating machine (however, the curing reaction was still slow. An inconvenient phenomenon occurs in which the adhesive suddenly drops in viscosity and drips into the heating machine during a minute period when the heating is not occurring.

This thermosetting epoxy adhesive must already be cured when the adhesive modified polyolefin and polyolefin are superimposed and coated on the extruded steel pipe. If the coating is applied before the adhesive has sufficiently hardened, the polyolefin layer will migrate, making it difficult to obtain an even coating (not only will it be difficult to obtain a uniform coating, but in the case of steel pipes with peads, it will be difficult to obtain a uniform coating by pressing with a roll. In our case, even if the coating appears to be uniform, the coating separates from the sides of the pead in a relatively short period of time, resulting in a coating with non-adhesive areas.We want to avoid this inconvenience. For this reason, in the present invention, rapid heating is performed using an induction heating machine, but even if conventionally known heating means such as burner heating or radiant heating are used in place of this, sufficient results cannot be obtained.

That is, when burner heating or radiant heating methods are used, their thermal efficiency is low, so it takes a long time to heat the steel pipe above the melting point of the adhesive-modified polyolefin, resulting in a long heating zone on the production line. In fact, it becomes impossible to apply the highly efficient inline method.

At this time, it is possible to process the process in an apparently short time by increasing the firepower and radiation intensity of the burner, but the surface of the adhesive layer will be extremely heated and the adhesive will deteriorate due to heating. This is undesirable.

When heating the surface rapidly by passing through the induction heating machine, the surface to be heated is heated at least 10°C/sec, preferably the type of steel pipe,
Although it varies depending on the line speed, it is approximately 4~b The temperature of the adhesive-coated steel pipe when the adhesive-modified polyolefin is extruded after curing is completed while the adhesive layer is on the surface and comes into contact with the adhesive layer is equal to or higher than the melting point of the adhesive-modified polyolefin. Set the temperature of the induction heating machine so that the temperature is maintained at a temperature that does not exceed the cough melting point +60°C. If the temperature of the adhesive-coated steel pipe exceeds the above range, it will not be cooled sufficiently and roll marks will occur on the outermost polyolefin layer when the steel pipe is drawn out.

Under these temperature conditions, if the adhesive modified polyolefin and the polyolefin are extruded using a coextrusion die so that the former is in contact with the adhesive layer, the adhesive layer and the adhesive modified polyolefin are Since the polyolefin forming the outermost layer is also compatible with the adhesive modified polyolefin forming the intermediate layer, the coating layer is tightly fixed as a whole. The steel pipe that has been coated as described above is immediately passed through a ring-shaped cooler to prevent uneven thickness, and then passed through a separate ordinary shower-shaped cooler to cool it below its softening point and then rolled. We will take over.

The adhesive modified polyolefin used in this invention is
It includes polyolefins with unsaturated carboxylic acids or their acid anhydrides, or blends of unmodified polyolefins with this modified polyolefin, and the base polyolefins include polyethylene (low to high density), polyglopylene, poly-1-butene, poly-4-
Examples include methyl□41□11°-1-pentene, ethylene-propylene copolymer, ethylene-1-butene copolymer, propylene-1-butene copolymer, and mixtures thereof. Examples of the unsaturated carboxylic acid or its acid anhydride include acrylic acid, methacrylic acid, maleic acid, maleic anhydride, citraconic acid, citraconic anhydride, itaconic acid, and the like.

This adhesive modified polyolefin layer is provided to increase the tightness between the thermosetting epoxy adhesive and the polyolefin, so the thickness of the film is not necessary and is approximately 0.
．． A length of about 0.6 to 0.6 m is sufficient.

The polyolefin forming the outermost layer is usually formed to have a thickness of about 1 to 4 W since it serves as an anti-corrosion layer and a reflection layer.This polyolefin may be appropriately selected from the polyolefins listed above.

By carrying out the present invention having the configuration as described above, it becomes possible to coat polyoleain in-line while adhering it to the steel pipe, which is clear from the behavior shown by the solid line in Figure 1. The nine-coated steel pipes obtained through this process can withstand use under harsh conditions that were previously unimaginable.

The effects of the present invention will be explained below with reference to Examples and FIG.

The steel pipe 1 with an outer diameter of 406.4 after the pretreatment is heated to t at room temperature.
Primer coating is carried out through a thermosetting epoxy adhesive coating tank 2 at a line speed of 4.1 m/min. This application tank 2 includes an adhesive main agent tank 6 and a curing agent tank 4.
A main agent and a curing agent are supplied from each pump p by a pump p. The coating tank 2 is a round coating tank with an O-ring for uniformly applying the primer to the curved surface of the steel pipe 1, and the thickness of the coating film is adjusted by drawing with a Q-IJ ring.

The steel pipe 5 on which the primer has been applied passes through a ring-shaped induction heater 6, which is set to have a heating rate of 4°C/sec until it reaches 150°C, where it is rapidly heated, and the surface is coated with the primer. The curing reaction of the adhesive is completed before it reaches the coextrusion die 7. The primer-coated steel pipe 5, which is still at a sufficiently high temperature, is sent from an extruder 8 for adhesive modified polyolefin and an extruder 9 for polyolenoin, which will be the outermost layer, and passed through a die 7 for coextruding the molten resin. The double-coated metal receiver is then cooled by a ring-shaped water cooler 11 so that it can be transferred to the product depot without any changes to the manufacturing twin speed. - In the figure, reference numeral 12 indicates a cooling water injection device that must be installed separately so that cooling can be performed as required.

When we coated a steel pipe with an outer diameter of 406.4 rtts over a length of 12 m with polyolefin, the time required was 2.9 minutes, which was inferior to the line speed of conventional adhesive coated steel pipe. It was recognized that there was no productivity in processing.

The polyethylene film thickness at this time was 6 m, and its peel adhesion was 15:9/crl, and no film damage such as row marks or skid marks during transportation was observed.

[Brief explanation of drawings]

Claims (1)

[Claims] When coating the outer surface of a steel pipe with polyolefin resin using a cylindrical molding die, a solvent-free thermosetting epoxy adhesive is applied to the steel pipe after pretreatment, and then the steel pipe is immediately guided. The adhesive is cured by rapid heating with a heating machine, and the temperature of the adhesive-coated steel pipe is raised to a temperature equal to or higher than the melting point of the adhesive-modified polyolefin and its melting point +60.
An in-line coated steel pipe characterized in that the adhesive-coated steel pipe is maintained at a temperature range not exceeding °C, and the adhesive-coated steel pipe is coated with adhesive modified polyolefin and polyolefin by co-extrusion, and then the coating is rapidly cooled. Production method.