JPH0791589A - Method for coating welded joint part for pipe - Google Patents

Abstract

PURPOSE:To facilitate a joint part coating operation on the spot by using a coating having an adhesive layer to which hot melt adhesives are applied for the inner surface of a crosslinked polyethylene tube to radiate far infrared ray from a far infrared ray radiation body to melt hot melt adhesives. CONSTITUTION:When a welded joint part 5 such as a gas conduit, oil transportation pipe 4, etc., is coated, a coating tube 1 having an outer layer 2 formed of a thermal contraction property polyester tube for irradiating radiation to give crosslink to the molecular structure and an adhesive layer 3 applied to the outer layer 2 and an adhesive layer 3 applied to the outer layer 2 is outside fitted on the peripheral part of the welded joint part 5 for the pipe 4. Next, a heating device 6 including a cylindrical far infrared ray radiation body 7 and heater 8 is disposed around the coating tube 1 to heat the far infrared ray radiation body 7 with the heat of the heater 8 and to irradiate the coating tube 1 with the far infrared ray so that crosslinked polythylene forming the outer layer 2, hot melt adhesives forming the coating layer 3 and polyethylene forming a coating layer 4b of a coated steel pipe 4 are subjected to self-heat generation and adapted to adhere to each other through melted adhesives.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pipe welding joint portion coating method for coating welded joint portions of various pipes such as gas pipes and oil feed pipes.

[0002]

2. Description of the Related Art Steel pipes used for underground pipes such as gas pipes are coated with an outer surface for the purpose of anticorrosion and chemical resistance. The coating of joints such as steel pipe single pipes and elbows used for this underground pipe is performed in a factory with thorough quality control,
Welded joints that are welded circumferentially to connect steel pipes at the burial site need to be coated on site. In order to prevent corrosion in the welded joint on-site, a shrink tube in which an asphalt / butyl rubber adhesive is applied to the inner surface of a radiation-crosslinked heat-shrinkable polyethylene tube is used. After covering the factory coating layer end of the steel pipe welded and welded at the site and the welded joint with a shrink tube, it is heated by a burner to shrink the crosslinked polyethylene by the memory effect,
The asphalt / butyl rubber adhesive adheres to the welded joint to form a corrosion-resistant coating layer. Since this shrink tube is tube-shaped and seamless, water channels are unlikely to occur and the reliability of anticorrosion is high.

On the other hand, when burying a gas conduit or the like in the ground, the cutting method has become difficult in recent years due to traffic conditions and construction pollution. Therefore, a method of burying the pipe by a non-open cutting method such as a shield method or a propulsion method is often adopted.

[0004]

However, the adhesive strength of the asphalt / butyl rubber adhesive of the shrink tube covering the welded joint portion of the steel pipe can be expected to be 3 kg / cm or less with respect to the surface of the polyethylene steel pipe factory coating layer. .
For this reason, there is no particular problem when using the open-cut construction method, but when laying for a long distance by the direct push propulsion method, due to the shear resistance with the surrounding soil that the end of the shrink tube covering the welded joint contacts during propulsion. There was a risk of peeling or slipping.

In order to eliminate such a danger, a shrink tube in which a hot melt adhesive is applied to crosslinked polyethylene is used instead of the asphalt / butyl rubber adhesive, but in this case, the adhesive is used. In order to keep the adhesive strength of the adhesive at a predetermined value, it is necessary to heat the adhesive to a temperature above the melting point of the adhesive, for example, to a temperature above 110 ° C. However, when heated by a burner, it is difficult to uniformly heat the adhesive, it is difficult to obtain an adhesive strength with uniform strength, and a lot of working time is required. .

The present invention has been made in order to solve the above disadvantages, and the coating can be easily performed on site, and a stable coating layer can be maintained even when laid for a long distance by the direct thrusting method. It is an object of the present invention to provide a pipe welded joint portion coating method capable of achieving the above.

[0007]

A method for coating a pipe welded joint portion according to the present invention is an adhesive layer in which a hot melt adhesive is applied to the inner surface of a crosslinked polyethylene tube or one surface of a crosslinked polyethylene sheet. Covering the welded joint portion of the pipe and the coating portion in the vicinity thereof with the adhesive layer of the coating material having
The outer peripheral portion of the covering material is covered with a heating device having a heater attached to the outer surface of the far-infrared radiator formed into a cylindrical shape, and the far-infrared radiator emits far-infrared rays to energize the heater to emit far-infrared rays. It is characterized in that the hot-melt adhesive is melted while heating the welded joint portion and the coating portion in the vicinity thereof to integrate the crosslinked polyethylene with the welded joint portion and the coating portion in the vicinity thereof.

Further, the current flowing through the heater of the above heating device can be increased stepwise to increase the heating intensity of far-infrared rays of the welded joint portion between the coating material and the pipe and the coating portion in the vicinity thereof stepwise. preferable.

[0009]

In the present invention, a crosslinked polyethylene tube is used.
Or a state where the outer layer of the crosslinked polyethylene tube or sheet is heat-shrinked after the welded joint portion of the pipe is covered with a coating material having an adhesive layer in which a hot-melt adhesive is applied to the crosslinked polyethylene sheet or A heating device having a far-infrared radiator formed in a cylindrical shape is arranged on the outer peripheral portion of the covering material in a state where the cross-linked polyethylene tube or sheet of the outer layer is not heated and shrunk. Then, electric power is supplied to the heater of the heating device to raise the temperature of the far-infrared radiator, and the far-infrared radiator irradiates the covering material with far-infrared rays. Since the cross-linked polyethylene tube irradiated with the far infrared rays, the hot-melt adhesive and the polyethylene coating layer of the welded pipe have an absorption band at a wavelength farther than 3 μm, they absorb the far infrared rays and generate heat. Therefore, the electric power supplied to the heating device is adjusted to adjust the heating intensity of the radiated far infrared rays to heat and melt the hot-melt adhesive, and at the same time, the cross-linked polyethylene tube and the pipe in the vicinity of the welded joint and the coating layer of the pipe. Is heated and a crosslinked polyethylene tube or sheet is adhered to the pipe and its coating layer near the welded joint to seal the welded joint.

When sealing the welded joint, the electric power supplied to the heating device is adjusted to heat and shrink the crosslinked polyethylene tube or sheet, and then the hot melt adhesive is heated so as to be melted. When the strength is adjusted stepwise, the heat shrinking step of the crosslinked polyethylene tube or the like and the bonding step can be performed only with the far infrared rays emitted from the far infrared ray radiator of the heating device.

[0011]

1 is a perspective view showing a coating tube for coating an outer surface of a steel pipe according to an embodiment of the present invention. As shown, the coating tube 1 has an outer layer 2 and an adhesive layer 3 applied to the outer layer 2. The outer layer 2 is formed of a heat-shrinkable polyethylene tube having a molecular structure crosslinked by irradiation with radiation and having enhanced hardness and heat resistance. The adhesive layer 3 is formed of, for example, a modified polyolefin-based hot melt adhesive that can adhere even non-adhesive polyethylene, which is a non-polar molecule, and is difficult to adhere to.

In a polyethylene-coated steel pipe (hereinafter referred to as a coated steel pipe) used for transporting gas, oil, water, etc., the pipe end shape is a bevel end because it is joined by welding, as shown in the sectional view of FIG. The coated steel pipe 4 has a steel pipe exposed surface 4a of 130 to 150 mm at the pipe end. When the coated steel pipe 4 is joined by welding at the laying site for anticorrosion treatment, it is necessary to cover both ends of the factory coating layer 4b with the coating tube 1 by 50 mm or more in addition to the exposed surface 4a of the steel pipe. Therefore, the coating tube 1 usually has a total length of 450 mm or more.

When the welded joint portion of the coated steel pipe 4 is subjected to anticorrosion treatment with this coated tube 1, the coated tube 1 is inserted into one of the coated steel pipes 4 before welding of the coated steel pipe 4. After circumferentially welding the end portion of the coated steel pipe 4 as shown in the sectional view of FIG. 3, the coated tube 1 is moved so that the center of the coated tube 1 is located at the position of the welded joint 5, and the coated tube 1 is heat-shrinked. Enter the process. In the heat shrinking step, a flame is applied from the position of the welded joint 5 of the coated tube 1 to the left and right by a burner to uniformly heat and shrink the outer layer 2 made of a crosslinked polyethylene tube in the circumferential direction. The heat shrinkage of the coating tube 1 is such that the coating tube 1 is circumferentially shrunk so as to expel air from the center of the coating tube 1 toward one end, and then is shrunk circumferentially toward the other end.
The coating tube 1 is brought into close contact with the exposed surface 4a of the steel pipe and the end of the factory coating layer as shown in the sectional view of FIG. This coating tu
When shrinking the outer layer 2 of the bush 1, the cross-linked polyethylene is 100
It shrinks rapidly at a temperature of about ℃ within 30 seconds.

The heat applied to the adhesive layer 3 through the outer layer 2 when the coating tube 1 is heated and shrunk is blocked to some extent by the outer layer 2 which is also a heat insulating layer, so that the adhesive layer 3 and the coated steel pipe 4 are heated by the outer layer 2. Shrinkage temperature is around 100 ° C or lower. Therefore, for example, the adhesive layer 3 of a modified polyolefin hot melt adhesive having a melting point of 110 ° C. or higher
Does not melt and maintains a solid state.

Next, the step of adhering the heat-shrinkable coating tube 1 is started. In the step of adhering the coating tube 1, a heating device 6 as shown in the sectional view of FIG. 5 is used. Heating device 6
Is a cylindrical far infrared radiator 7, a heater 8, and a heat insulating material 9.
And a cover 10. The far-infrared radiator 7 is made of ceramics such as zirconia, titania, and alumina, and stainless steel whose surface is oxidized.
The emissivity of far-infrared rays having a wavelength longer than m increases. Heater 8
Is wound around the outer peripheral surface of the cylindrical far-infrared radiator 7 to heat the far-infrared radiator 7.

In the step of adhering the coating tube 1, as shown in FIG. 5, the coating tube heat-shrinked by the heating device 6 is used.
Cover the outer circumference of the bu 1. Next, electric power is supplied from a power supply device (not shown) to the heater 8 of the heating device 6, and the far infrared radiator 7 is heated by the heat of the heater 8. Far infrared rays are radiated from the heated far infrared radiator 7 to irradiate the coating tube 1. Outer layer 2 of coating tube 1 irradiated with this far infrared ray
The cross-linked polyethylene that forms the adhesive, the hot-melt adhesive that forms the adhesive layer 3, and the polyethylene that forms the factory coating layer 4b of the coated steel pipe 4 have an absorption band at a wavelength of 3 μm or more, and therefore absorb the irradiated far infrared rays. Self-heating. On the other hand, the heating intensity of the far-infrared radiator 7 can be easily adjusted by adjusting the electric power supplied to the heater 8. Therefore, the electric power supplied to the heater 8 of the heating device 6 is adjusted so that the heating temperature by the far infrared rays emitted is equal to or higher than the melting point of the hot melt adhesive, for example, 110 ° C. or more, and the heating intensity of the far infrared radiator 7 is adjusted. Adjust.

When the coating tube 1 is irradiated with far infrared rays so that the heating intensity of the far infrared radiator 7 becomes higher than the melting point of the hot melt adhesive, the hot melt adhesive of the adhesive layer 3 is heated. , The polyethylene pipe and the steel pipe of the coated steel pipe 4 in the vicinity of the welded joint portion that melts and forms the cross-linked polyethylene of the outer layer 2 and the factory coating layer 4b of the coated steel pipe 4 are heated to the same temperature as the hot melt adhesive, and the welded joint portion is heated. The coating tube 1 is adhered to the steel pipe and the welded joint 5 of the factory coating layer 4b and the coated steel pipe 4 in the vicinity to seal the welded joint.

As described above, when the coated tube 1 is bonded to the coated steel pipe 4, the coating tube 1 and the coated steel pipe 4 are bonded by utilizing the self-heating of the far infrared rays. can do. Also, a factory coating layer 4b made of polyethylene of the coated steel pipe 4 and an outer layer 2 made of polyethylene tube of the coated tube 1 are provided as an adhesive layer 3.
Since it is heated and bonded with the hot melt adhesive of No. 3, it is possible to enhance the adhesive strength between the factory coating layer 4b and the outer layer 2 of the coating tube 1, and even when the coated steel pipe 4 is laid by the direct push propulsion method, a welded joint is used. It is possible to prevent the end portion of the anticorrosion tube coated on the part from peeling or shifting due to the shear resistance with the surrounding soil that comes into contact with it during propulsion. Therefore, the corrosion resistance of the buried coated steel pipe 4 can be improved.

In the above embodiment, the case where the heating tube 6 having the far-infrared radiator 7 is used only for the step of adhering the coating tube 1 has been described. -It is also possible to perform both the heat shrinking step and the bonding step of the sleeve 1. That is, in heating using far infrared rays emitted from the far infrared radiator 7, it is easy to control the heating intensity. Therefore, as shown in the heating strength characteristic diagram of FIG. 6, the temperature of the coating tube 1 is 10
The electric power supplied to the heater 8 of the heating device 6 is adjusted so as to be about 0 ° C., and the heater 8 of the heating device 6 is controlled so that the temperature of the coating tube 1 becomes 110 ° C. or more in the next bonding step. It is advisable to change the supplied power in stages.

In this way, by utilizing the far infrared rays emitted from the far infrared ray radiator 7 also in the heat shrinking step of the coating tube 1, the coating tube 1 is heat shrinked without using the burner. Therefore, the corrosion prevention treatment of the welded joint portion of the coated steel pipe 4 can be performed more easily.

[0021]

As described above, according to the present invention, a covering material having an adhesive layer in which a hot melt adhesive is applied to a crosslinked polyethylene tube or a crosslinked polyethylene sheet is provided far from a far infrared radiator of a heating device. Irradiates infrared rays, and uses the self-heating of the coating material due to the far infrared rays emitted to melt the hot-melt adhesive and bond the coating material near the welded joint of the pipe. The covering can be adhered to the pipe near the welded joint.

Further, since the factory coating layer made of polyethylene of the pipe and the polyethylene of the coating tube or sheet are heat-bonded with a hot-melt adhesive, the factory coating layer and the coating tube or sheet are joined together. Adhesive strength can be increased, and even when pipes are laid by the direct push propulsion method, peeling occurs due to shear resistance with the surrounding soil with which the end of the anticorrosion tube coated on the welded joint contacts during propulsion. It is possible to prevent the occurrence of slippage and displacement, and it is possible to further improve the corrosion resistance of the buried pipe.

Further, when the welded joint is sealed, the electric power supplied to the heating device is adjusted to heat and shrink the crosslinked polyethylene tube or sheet, and then the hot melt adhesive is melted. If you adjust the heating intensity stepwise,
It is possible to perform the heat shrinking process and the bonding process of the cross-linked polyethylene tube etc. only with the far infrared rays emitted from the far infrared radiator of the heating device, and to perform the corrosion prevention treatment of the welded joint part of the pipe in a shorter time and easily. Therefore, the working efficiency can be greatly increased.

[Brief description of drawings]

FIG. 1 is a perspective view showing a covering tube according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing an end portion of a coated steel pipe.

FIG. 3 is a cross-sectional view showing a state in which a welded joint portion of a coated steel pipe is covered with a coated tube.

FIG. 4 is a cross-sectional view showing a state in which the coating tube is heated and shrunk.

FIG. 5 is a cross-sectional view showing a step of adhering the covering tube.

FIG. 6 is a heating strength characteristic diagram of the heating device.

[Explanation of symbols]

 1 coating tube 2 outer layer 3 adhesive layer 4 coating steel pipe 4b factory coating layer 5 welding joint 6 heating device 7 far-infrared radiator 8 heater

Claims (2)

[Claims] 1. A welded joint portion of a pipe having an inner surface of a crosslinked polyethylene tube or one surface of a crosslinked polyethylene sheet as an inner surface of an adhesive layer of a coating material having an adhesive layer coated with a hot melt adhesive. And the covering portion in the vicinity thereof, and the outer peripheral portion of the covering material is covered with a heating device having a heater attached to the outer surface of the far-infrared radiator formed into a tubular shape, and the far-infrared radiator is energized to the heater. Far-infrared rays are emitted from the pipe to heat the hot-melt adhesive while heating the welded joint portion of the pipe and the coating portion in the vicinity thereof, and the cross-linked polyethylene is integrated with the welded joint portion and the coating portion in the vicinity thereof. And method for coating pipe weld joints. 2. The method for coating a pipe welded joint portion according to claim 1, wherein the current supplied to the heater of the heating device is increased stepwise.