JPH06182872A - Preventing method for partial corrosion of steel tube - Google Patents

Abstract

PURPOSE:To provide a method for heating a hat shrinkable coating material to form an excellent corrosion preventing coating having no burning deterioration and no unadhering part to an outer surface of the tube at a joint or a damaged part of the coating of a steel tube. CONSTITUTION:A heat shrinkable coating material 4 is wound on an outer surface 1 of a tube and a factory coating part 3, and its periphery is coated with a heat generator 5 made of a heat shrinkable sheet in which an electric heating wire 6 is sealed. The wire of the generator is energized to the coating material thereby to adhere the coating material to the outer surface of the tube.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anticorrosion method for coating the outer surface of a pipe with a heat-shrinkable coating material in a joint portion such as a gas pipe, a water pipe, an electric power pipe or a damaged portion of the anticorrosion coating.

[0002]

2. Description of the Related Art Steel pipes used for gas pipes, water pipes, electric power pipes, etc. are anticorrosion coated with polyethylene or epoxy resin in a factory, but since the joints are welded at the pipe installation site, they are coated with welding heat. To avoid damage
No coating is applied to the pipe end, and it is necessary to perform anticorrosion coating on the welded part on site.

In addition to the joint portion, if the coating material is damaged during pipe laying work or due to some factor, it is necessary to repair this portion with an anticorrosion coating.

Conventionally, in order to perform these coatings, the outer surface of the tube to be coated is preheated by a burner using propane gas, and then the outer surface of the tube is provided with a heat-meltable adhesive layer or pressure-sensitive adhesive layer on the outer surface of the tube. Wrap a covering material (for example, heat-shrinkable sheet, heat-shrinkable tube, heat-shrinkable tape), and heat and shrink the covering material from the outer surface with a burner by a direct fire method to bring it into contact with the outer surface of the pipe, and then heat it up. A method of melting and coating an adhesive layer or an adhesive layer in contact with the outer circumference of a pipe has been used.

However, in this method, since a burner which is easily heated locally by a high temperature flame is used for heating for heat shrinkage of the coating material, it is extremely difficult to uniformly heat shrink the whole material, and the surface of the coating material is extremely difficult. Since it is liable to be burnt and deteriorated, or air entrapment is likely to occur, there is a problem that skill is required for the work and at the same time the work time is long and the work efficiency is poor.

Further, there is a security problem that construction cannot be performed in a place where direct fire is prohibited (for example, narrow space for gas pipes or pipes in tunnels).

In order to solve these problems, for example, the heat-shrinkable covering material is surrounded by a sheet-shaped electric heater, and power is supplied to the heater to heat-shrink the heat-shrinkable covering material wound around the outer surface of the tube. A method of coating the outer surface of the pipe has been proposed and partially put into practical use.

For the sheet-like electric heater, a sheet-like silicone rubber having a heating resistance wire inside is used.

Besides, a stainless steel plate having a sheathed heater wired on the outside is also used.

[0010]

In the joint portion around which the heat-shrinkable coating material is wound, there is a step between the steel pipe surface, the weld bead portion, and the factory coating portion.

Therefore, when the heat-shrinkable coating material is wound around the joint, the heat-shrinkable coating material comes into contact with the factory coating portion, the weld bead portion, and a part of the steel pipe surface, but at the step portion, the heat shrinkable coating material contacts the steel pipe surface. It cannot be contacted and a gap is created.

When a conventional sheet-shaped electric heater (for example, the above-mentioned silicon rubber heater. The conventional sheet-shaped electric heater is hereinafter referred to as a silicon rubber heater) is wound around the heat-shrinkable covering material, the silicon rubber is wound. The heater will contact the heat-shrinkable coating on the factory coating and weld bead and not the heat-shrinkable coating on the steel pipe surface.

When the silicon rubber heater is energized in the above state, the portion of the heat-shrinkable coating material which is in contact with the silicon rubber heater has good heat transfer from the heater and relatively quickly undergoes heat shrinkage, so that the inner adhesive layer When the melting is sufficient, it adheres or adheres to the outer surface of the tube.

On the other hand, heat transfer is not sufficient at the portion of the heat-shrinkable coating material that is not in contact with the silicon rubber heater,
The heat shrinkage requires a relatively long time. Further, it cannot be said that the adhesive layer on the inner side is sufficiently melted, and the heat-shrinkable coating material is only in contact with the outer surface of the tube, and neither adhesion nor adhesion is caused.

Therefore, the inside of the heat-shrinkable covering material should be
A portion that is simply in contact with a portion that adheres or adheres to the outer surface of the tube occurs.

It is necessary to energize for a long time in order to sufficiently melt the adhesive layer inside the heat-shrinkable coating material that is not in contact with the silicon rubber heater to adhere or adhere to the outer surface of the pipe. Therefore, heat input to the heat-shrinkable coating material in contact with the silicon rubber heater is more than necessary, and the surface of the heat-shrinkable coating material is burned.

As a countermeasure against this problem, a method has been used in which a copper plate having a high thermal conductivity is inserted into the step portion to fill the gap so that the heat transfer from the silicon rubber heater to the heat-shrinkable covering material is uniform. It was

However, this method is not effective because the work is complicated and the height of the weld bead portion is not constant and the gap cannot be completely eliminated.

Alternatively, the silicon rubber heater may be divided into three or four, and the electric circuit may be independent.
There is also a method of energizing, but the equipment becomes large-scale,
Equipment costs are high.

Further, the operation becomes complicated.

The present invention provides a method for heating a heat-shrinkable coating material which solves the non-uniformity of heat transfer from the heating body to the heat-shrinkable coating material without using any complicated device, and a steel pipe joint. The present invention aims to form a good anticorrosion coating on a damaged part or a damaged part.

[0022]

SUMMARY OF THE INVENTION The present invention, which has been made to achieve the above-mentioned object, has the following structures.

That is, a heat-shrinkable covering material is wound around the outer surface of the steel pipe in a portion requiring anticorrosion, and the surrounding area is a heating member made of a heat-shrinkable sheet material in which a conventional sheet-shaped electric heater has a heat-shrinkable function. By heating the heating wire of the heating body by supplying electric power to the heating wire of the heating body, first, the heating body itself contracts heat and comes into contact with the heat-shrinkable coating material to transfer heat from the heating body to the heat-shrinkable coating material. It is a partial corrosion protection for a steel pipe, characterized in that the heat-shrinkable coating is heat-shrinked by uniform heating and then the heat-shrinkable coating is adhered or adhered to the outer surface of the pipe.

[0024]

The point of the present invention resides in the method of heat-shrinking the heat-shrinkable covering material using the heating body made of the heat-shrinkable sheet material enclosing the heating wire.

When the heat-shrinkable covering material wound around the steel pipe is covered with this heating element and electric power is supplied to the heating wire, first, the heating element itself causes heat shrinkage along the surface shape of the joint portion to completely complete the heat-shrinkable covering material. Contact.

After that, the heat-shrinkable covering material is uniformly heated from the outer surface by the heat transfer action from the heating element to cause shrinkage and adhere to the joint surface.

The heat-shrinkable coating material having an adhesive layer or a pressure-sensitive adhesive layer on its inner surface can be further adhered to the outer surface of the tube evenly by the subsequent heating so that the contact layer or the pressure-sensitive adhesive layer is sufficiently melted.

[0028]

The present invention will be described in detail below based on preferred embodiments.

As shown in FIG. 1, after the heat-shrinkable covering material 4 is wound around the joint welding portion 2 of the steel pipe 1 so as not to wrinkle, the heating element 5 is attached around the heat-shrinkable covering material.

The heating element is a heat-shrinkable sheet material (for example, polyethylene or polyvinyl chloride) in which a heating wire is enclosed, and has a tubular shape slightly larger than the outer diameter of the steel pipe. There is a method of fixing the same with a fastener 8, a method of wrapping and adhering and fixing, or a method of forming into a tubular shape in advance.

FIG. 2 is a cross sectional view.

As for the wiring shape of the heating wire enclosed in the heating element, it is preferable that the wiring pattern is formed by folding back the extension wire in the direction perpendicular to the shrinking direction of the heat shrinkable sheet material as shown in FIG.

This is because when the heating wire is extended in the shrinking direction, wrinkles are likely to occur due to the difference in shrinkage between the heat shrinkable sheet material and the heating wire.

When a fastener type heating element is used, the attachment is performed by tightening a fastener provided at the end of the heating element.

The fastener should be brought to a position where it is easy to work, depending on the pipe diameter and working space.

Next, the lead wire from the power supply device 9 connected to the power supply 10 is connected to the heating wire power supply terminal 7 of the heating body, and power is supplied for a predetermined time according to the pipe diameter and the pipe wall thickness.

Then, as described above, the heat generated by the heating wire 6 first causes the heating element itself to shrink along the shape of the tube, and comes into contact with the heat-shrinkable covering material without any gap.

After that, the heat-shrinkable covering material gradually shrinks due to heat transfer from the heating element, and comes into contact with the outer surface of the tube.

When the adhesive layer or pressure-sensitive adhesive layer on the inner surface of the heat-shrinkable covering material is sufficiently melted, the outer surface of the tube is uniformly adhered.

FIGS. 4, 5, and 6 show the state of heat shrinkage after the start of power supply.

FIG. 4 shows immediately after the start of power supply.

FIG. 5 shows a state in which the heating element contracts heat due to the heat generated by the heating wire and is in contact with the heat-shrinkable covering material without any gap.

FIG. 6 shows a situation in which the heat transfer from the heating wire progresses and the heat-shrinkable coating material adheres to the outer surface of the pipe to complete the anticorrosion coating.

After the adhesion of the heat-shrinkable coating material to the outer surface of the tube is completed, it is desirable to open the fastener of the heating element and remove the heating element around the heat-shrinkable coating material.

This is because if the heating element is buried or left with the outer surface of the heat-shrinkable covering material left, the heating wire enclosed in the heating element will be heated if it is damaged due to some external force. This is because there is a possibility that the contractible coating material may be broken and contact with the steel pipe, contact corrosion of dissimilar metals may occur due to the difference in corrosion potential between the heating wire and the steel pipe, and corrosion of the steel pipe may be accelerated.

[0046]

According to the present invention described above, the following effects can be obtained.

(1) Since the heat-shrinkable covering material can be uniformly heat-shrinked by using the sheet-shaped heating body having heat-shrinkability for the adhesion of the heat-shrinkable covering material, The surface is not burnt at all, the adhesive layer or the adhesive layer on the inner surface of the heat-shrinkable covering material is sufficiently melted, and an anticorrosion coating having excellent adhesion or adhesion to the outer surface of the pipe can be formed.

(2) After the heat-shrinkable coating material is wound on the outer surface of the tube and the heating element is mounted thereon, the heating wire energizing terminal is simply supplied with power for a predetermined time according to the tube thickness. As it is a method that does not require complicated operations, no special training is required for workers.

(3) The only device required is a power supply device for supplying power to the heating wire in addition to the sheet-shaped heating body, and a place where the construction space is limited or a place where a lot of labor is required for movement (for example, It is most suitable for construction in narrow places of gas pipes or pipes in tunnels.

[Brief description of drawings]

FIG. 1 is a schematic view of a heating body attached around a heat-shrinkable covering material for adhering the heat-shrinkable covering material to an outer surface of a pipe in an embodiment of the present invention.

FIG. 2 is a view of FIG. 1 viewed from the AA direction.

FIG. 3 is a plan view of a fastener type heating element developed on a plane.

FIG. 4 is a diagram of FIG. 1 viewed from the BB direction immediately after power supply to the heating body is started.

FIG. 5 is a diagram showing a state where the heating element is in contact with the heat-shrinkable covering material during the power feeding.

FIG. 6 is a diagram showing a situation in which the heat-shrinkable covering material is adhered to the outer surface of the pipe after the power supply is finished for a predetermined time, and the anticorrosion covering is completed.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Steel pipe 2 ... Joint welding bead part 3 ... Factory coating part 4 ... Heat-shrinkable coating material 5 ... Heat-shrinkable sheet-shaped heating body 6 ... Heating wire 7 ... Power supply terminal 8 ... Fastener 9 ... Power supply device 10 ... Power supply

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Takaji Chikada 5-9-1 Nishihashimoto, Sagamihara-shi, Nippon Steel & Steel Co., Ltd., Steel Construction & Marine Division (72) Nobuhiro Sasaki 5-9 Nishihashimoto, Sagamihara -1 Nippon Steel Co., Ltd. Steel Construction & Marine Division (72) Inventor Shoji Suzuki 2-6-3 Otemachi, Chiyoda-ku, Tokyo Inside Nippon Steel Corporation

Claims (1)

[Claims] 1. A heat-shrinkable covering material is wound around an outer surface of a steel pipe in a portion requiring corrosion protection, and the periphery thereof is covered with a heating body made of a heat-shrinkable sheet material enclosing a heating wire. A partial anticorrosion method for a steel pipe, characterized in that the heat-shrinkable coating material is heated and shrunk by supplying power, and the heat-shrinkable coating material is adhered or adhered to the outer surface of the pipe.