JP7627642B2 - Double Tube - Google Patents

Description

The present invention relates to a double pipe having an outer pipe and an inner pipe disposed inside the outer pipe with a gap therebetween.

When transporting cryogenic fluids such as liquid nitrogen, double pipes that utilize vacuum insulation are used to prevent the temperature of the cryogenic fluid inside the pipe from rising. Such double pipes include an outer pipe and an inner pipe that is spaced apart from the outer pipe and is placed inside the outer pipe, and the cryogenic fluid flows inside the inner pipe. Insulation is also achieved between the outer pipe and the inner pipe by forming an insulating layer such as a vacuum space between the outer pipe and the inner pipe. For example, one disclosed in Patent Document 1 is known as an example of such a double pipe.

International Publication No. 2018/021509 (WO2018/021509A1)

When a conventional double-walled pipe is placed outdoors where it is exposed to direct sunlight, the temperature of the surface of the outer pipe rises. If the double-walled pipe is bent or becomes misaligned due to sagging under its own weight, the outer pipe and the inner pipe may come into contact, and the heat from the surface of the outer pipe may be transferred to the inner pipe, heating the cryogenic fluid flowing inside the inner pipe.

The present invention was made in consideration of these points, and aims to provide a double pipe that can prevent the fluid flowing inside the inner pipe from being heated.

The double pipe of the present invention is
an outer tube and an inner tube disposed inside the outer tube with a gap therebetween;
A heat insulating layer is formed between the outer pipe and the inner pipe,
The outermost layer of the outer tube is coated with a resin as an anticorrosive layer, and the resin contains a white material.

The double pipe of the present invention can suppress the temperature rise of the surface of the outer pipe due to direct sunlight, and can prevent the fluid flowing inside the inner pipe from being heated by the heat of the surface of the outer pipe being transferred to the inner pipe.

1 is a perspective view showing a double pipe according to an embodiment of the present invention; 2 is a cross-sectional view of the double pipe shown in FIG. 1 taken along the line AA. 3 is a cross-sectional view of the double pipe shown in FIG. 2 taken along the line BB. 1 is a graph showing the change in temperature over time of the outer and inner surfaces of an outer tube when the outermost layer of the outer tube is coated with a white anticorrosion layer and a black anticorrosion layer, respectively. 1 is a graph showing the relationship between the wavelength of visible light and reflectance when the titanium oxide content in a sheet formed by compression molding a resin used in a corrosion protection layer that coats the outermost layer of an outer tube is 0 mass%, 0.25 mass%, 0.5 mass%, or 2 mass%. 1 is a graph showing the relationship between elongation and stress in a tensile test when the titanium oxide content in a sheet obtained by compression molding a resin used in a corrosion protection layer that coats the outermost layer of an outer tube is 5 mass %, 10 mass %, or 25 mass %.

The following describes an embodiment of the present invention with reference to the drawings. Figures 1 to 3 are perspective and cross-sectional views showing a double pipe according to an embodiment of the present invention.

As shown in Figs. 1 to 3, the double pipe 2 according to this embodiment includes an outer pipe 10 and an inner pipe 20, and a vacuum space 30 is formed between the outer pipe 10 and the inner pipe 20. The inner pipe 20 is disposed inside the outer pipe 10 with a gap therebetween. The outermost layer of the outer pipe 10 is coated with resin as a corrosion protection layer 12. The outermost layer of the inner pipe 20 is coated with a heat insulating member 22. The heat insulating member 22 and the vacuum space 30 form a heat insulating layer. A fluid (specifically, a cryogenic fluid such as liquid nitrogen) flows inside the inner pipe 20. Each component of the double pipe 2 is described below.

The material of the outer tube 10 is a metal, and is selected from the group consisting of aluminum, aluminum alloy, iron, steel, stainless steel, Ni-based alloy, and Co-based alloy. It is more preferable to use stainless steel as the material of the outer tube 10. In addition, as shown in Figures 1 and 3, the outer tube 10 has a corrugated shape along the longitudinal direction and is flexible.

As shown in Figs. 1 to 3, the outermost layer of the outer pipe 10 is coated with a resin as a corrosion protection layer 12. There is no particular limitation on the material of such a resin, and any resin can be used. Here, the resin is preferably selected from the group consisting of polyethylene resin, urethane resin, epoxy resin, fluorine-based resin, and mixtures thereof, and it is particularly preferable to use low-density polyethylene resin of polyethylene resin. The thickness of such a resin is within a range of 10% to 100% of the depth of the waves on the inner surface of the outer pipe 10, preferably within a range of 30% to 70%, and particularly preferably within a range of 40% to 60%. If the thickness of the resin as the corrosion protection layer 12 is less than 10% of the depth of the waves on the inner surface of the outer pipe 10, the corrosion protection layer 12 is too thin and easily torn, which causes a problem that the outer pipe 10 is easily worn and corroded. On the other hand, if the thickness of the resin as the corrosion protection layer 12 is greater than 100% of the depth of the waves on the inner surface of the outer pipe 10, the corrosion protection layer 12 is too thick and easily torn, which causes a problem that the outer pipe 10 is easily worn and corroded. The outer surface of the anticorrosion layer 12 may have projections and recesses corresponding to the corrugated shape of the outer pipe 10, or the outer surface of the anticorrosion layer 12 may be a circular surface. Such an anticorrosion layer 12 can protect the outer pipe 10 from external factors such as damage, wear, corrosion, and ultraviolet degradation, and can also identify the use of the double pipe 2 and harmonize with the surrounding environment.

In this embodiment, the resin as the anticorrosive layer 12 contains a white material. The white material contains a pigment, and this pigment contains a material selected from the group consisting of C.I. Pigment White, sulfates of alkaline earth metals such as barium sulfate, carbonates of alkaline earth metals such as calcium carbonate, silicas such as fine powdered silicic acid and synthetic silicates, calcium silicate, alumina, alumina hydrate, metal compounds such as titanium oxide and zinc oxide, talc, clay, and the like. Here, it is particularly preferable that the pigment contains titanium oxide. Titanium oxide has characteristics such as a high refractive index, chemical stability, and high safety, and is therefore particularly suitable as a pigment as a white material. More specifically, titanium oxide has a small particle diameter of 0.2 to 0.3 μm and can increase the scattering of visible light, so that the reflectance of light on the outer surface of the anticorrosive layer 12 can be increased. Titanium oxide is also widely distributed and easy to obtain. In this way, titanium oxide has various advantages as a pigment for a white material.

In this embodiment, the anticorrosion layer 12 contains a resin containing a white material, so that the outer surface of the anticorrosion layer 12 can be made white. Therefore, even if the double pipe 2 is placed outdoors where it is exposed to direct sunlight, the outer surface of the anticorrosion layer 12 is white and has a high light reflectance, so that the temperature rise of the surface of the outer pipe 10 is suppressed. Therefore, even if the double pipe 2 is bent or the double pipe 2 is misaligned due to sagging due to its own weight, the temperature rise of the outer pipe 10 is suppressed even if the outer pipe 10 and the inner pipe 20 come into contact, so that the cryogenic fluid flowing inside the inner pipe 20 can be prevented from being significantly heated.

The pigment content in the resin is 25% by mass or less. The pigment content in the resin is preferably in the range of 0.25% by mass to 25% by mass, more preferably in the range of 0.25% by mass to 10% by mass, and particularly preferably in the range of 0.5% by mass to 10% by mass. If the pigment content in the resin is greater than 25% by mass, the dispersion of the pigment in the resin will vary, and the elongation of the anticorrosive layer 12 will vary, especially when the external temperature is low, and the anticorrosive layer 12 may break when the outer pipe 10 is bent. If the pigment content in the resin is less than 0.25% by mass, the visible light irradiated to the anticorrosive layer 12 cannot be sufficiently scattered due to the small pigment content, and the light reflectance on the surface of the anticorrosive layer 12 will decrease, so that the surface of the outer pipe 10 may heat up when the double pipe 2 is exposed to direct sunlight.

The material of the inner pipe 20 is a metal, and the material of the inner pipe 20 is selected from the group consisting of aluminum, aluminum alloy, iron, steel, stainless steel, stainless steel, Ni-based alloy, and Co-based alloy. It is more preferable to use stainless steel as the material of the inner pipe 20. The material of the inner pipe 20 may be the same as the material of the outer pipe 10, or the material of the inner pipe 20 may be different from the material of the outer pipe 10. Also, as shown in Figures 1 and 3, the inner pipe 20 has a corrugated shape along the longitudinal direction and is flexible. In this way, when the outer pipe 10 and the inner pipe 20 each have a corrugated shape along the longitudinal direction and are flexible, the double pipe 2 can be laid according to the external environment, and the double pipe 2 can be bent to avoid pillars and beams of a building or to lay along corners.

As shown in Figures 1 to 3, the outermost layer of the inner tube 20 is covered with a heat insulating material 22. More specifically, the heat insulating material 22 may be a super insulation (specifically, a metal foil or a metal-plated plastic film, etc.) that cuts heat transfer by radiation, or a spacer (specifically, a rod-shaped resin, etc.) with low thermal conductivity that reduces the amount of heat transferred when the outer tube 10 and the inner tube 20 come into contact, which is wrapped around the outermost layer of the inner tube 20.

As described above, a vacuum space 30 is formed between the outer tube 10 and the insulating member 22 of the inner tube 20. The vacuum space 30 does not mean a complete vacuum state, but by discharging most of the air present in the vacuum space 30 to the outside, the insulating member 22 cuts off heat transfer by radiation, and prevents heat transfer via the air. In this way, the insulating layer consisting of the insulating member 22 and the vacuum space 30 provides insulation between the outer tube 10 and the inner tube 20, suppressing the rise in temperature of the fluid flowing through the inner tube 20 caused by the rise in temperature of the outer tube 10.

According to the double pipe 2 of the present embodiment configured as described above, a heat insulating layer is formed between the outer pipe 10 and the inner pipe 20, and the outermost layer of the outer pipe 10 is coated with resin as the anticorrosive layer 12, and the resin contains a white material. In this case, since the resin as the anticorrosive layer 12 coated on the outermost layer of the outer pipe 10 contains a white material, even if the double pipe 2 is placed outdoors where it is exposed to direct sunlight, the light reflectance of the outer surface of the anticorrosive layer 12 is high. Therefore, the rise in temperature of the surface of the outer pipe 10 is suppressed. Therefore, even if the double pipe 2 is bent or the double pipe 2 is misaligned due to sagging due to its own weight, even if the outer pipe 10 and the inner pipe 20 come into contact, the rise in temperature of the outer pipe 10 is suppressed, so that it is possible to prevent the cryogenic fluid flowing inside the inner pipe 20 from being significantly heated.

In the double pipe 2 of this embodiment, the outer pipe 10 and the inner pipe 20 each have a wave shape along the longitudinal direction. In this case, the double pipe 2 can be laid out in accordance with the external environment, for example, the double pipe 2 can be bent to avoid pillars and beams of a building or to lay out along corners. Even if the outer pipe 10 and the inner pipe 20 come into contact by bending the double pipe 2, the resin as the corrosion protection layer 12 contains a white material, so that the rise in temperature of the outer pipe 10 is suppressed, and therefore the cryogenic fluid flowing inside the inner pipe 20 can be prevented from being significantly heated.

In the double pipe 2 of this embodiment, when the outer pipe 10 is corrugated, the thickness of the resin is within a range of 10% to 100% of the depth of the waves in the outer pipe 10. In this case, the thickness of the resin is 10% or more of the depth of the waves on the inner surface of the outer pipe 10, so that the wear and corrosion of the outer pipe 10 can be suppressed, and the thickness of the resin is 100% or less of the depth of the waves on the inner surface of the outer pipe 10, so that the outer pipe 10 can be prevented from becoming difficult to bend.

In the double pipe 2 of this embodiment, the white material contains a pigment. The pigment also contains titanium oxide. As described above, titanium oxide has a small particle diameter of 0.2 to 0.3 μm and can increase the scattering of visible light, thereby increasing the light reflectance on the outer surface of the anticorrosive layer 12. Titanium oxide is also widely distributed and easy to obtain. Thus, titanium oxide has various advantages as a pigment for a white material. The pigment content is 25% by mass or less. By having the pigment content in the resin be 25% by mass or less, the occurrence of variation in the elongation of the anticorrosive layer 12 is suppressed even when the external temperature is low, and therefore the anticorrosive layer 12 can be prevented from breaking.

The double pipe of the present invention is not limited to the above-mentioned configuration, and various modifications can be made.

For example, in the double pipe according to the present invention, the outer pipe and the inner pipe are not limited to those that are corrugated along the longitudinal direction and have flexibility. In another embodiment, the outer pipe and the inner pipe may each be straight pipe. When the outer pipe and the inner pipe are corrugated, they have flexibility and can be laid according to the external environment, but the present invention can be applied even when the outer pipe and the inner pipe are each straight pipe. Specifically, even when the outer pipe and the inner pipe are each straight pipe, the outermost layer of the outer pipe is coated with resin as a corrosion prevention layer, and when the resin contains a white material, it is possible to prevent the temperature of the outer pipe from rising even when the double pipe is placed outdoors where it is exposed to direct sunlight. In particular, when the outer pipe and the inner pipe are straight pipes, there is a risk that the outer pipe and the inner pipe will come into contact with each other due to misalignment caused by sagging due to their own weight, and the heat on the surface of the outer pipe will be transferred to the inner pipe. Furthermore, if a spacer is provided between the inner surface of the outer tube and the outer surface of the inner tube to support the inner tube, there is a risk that heat from the surface of the outer tube will be transferred to the inner tube via this spacer. To address these issues, the temperature of the outer tube can be prevented from rising by including a white material in the resin that coats the outermost layer of the outer tube. Note that if the outer tube and the inner tube are both straight tubes, the outer tube will not have flexibility but will have a smaller surface area, which will further prevent the temperature of the outer tube from rising.

In addition, when the outer tube has a straight shape, the thickness of the resin as the anticorrosive layer is preferably within the range of 0.05% to 15% of the outer diameter of the outer tube. If the thickness of the resin is less than 0.05% of the outer diameter of the outer tube, the anticorrosive layer is too thin and easily torn, which causes a problem that the outer tube is easily worn or corroded. On the other hand, if the thickness of the resin is more than 15% of the outer diameter of the outer tube, the weight of the outer tube becomes large, which makes it inconvenient to carry. In addition, in this case, there is a problem that an excessive amount of resin material is used. In contrast, if the thickness of the resin as the anticorrosive layer is within the range of 0.05% to 15% of the outer diameter of the outer tube, the above-mentioned problems can be suppressed.

The pigment contained in the anticorrosion layer is not limited to titanium oxide. Any pigment other than titanium oxide may be used as the pigment contained in the anticorrosion layer as long as it can make the outer surface of the anticorrosion layer white.

Example 1
An outer pipe (1000 mm long, 150 mm outer diameter, 0.7 mm thick, 5.8 mm wave depth) was produced, in which the metal material was cold-rolled steel (SPCD) and the corrugated shape was formed along the longitudinal direction. In addition, the outer pipe was covered with a resin containing a white material to a thickness of 2.9 mm (50% of the wave depth) as a corrosion protection layer. Polyethylene resin (NUCG-7641) manufactured by ENEOS NUC Corporation was used as the resin. In addition, a master batch (PE-M 20N3127C WH) manufactured by Dainichiseika Chemicals Mfg. Co., Ltd., which contains titanium oxide as a pigment, was used as the resin, and the titanium oxide concentration of the molded product was mixed to 1.56 to 2.19 mass%, and extrusion molding was performed. Such an outer pipe was placed in a place exposed to direct sunlight, and the temperature of the outer surface and the temperature of the inner surface of the outer pipe 10 were measured over time from 11:00 a.m. to 3:00 p.m. The average outside air temperature was 28.4°C. The line designated by reference number 50 in FIG. 4 indicates the change in temperature of the outer surface of the outer tube, and the line designated by reference number 52 in FIG. 4 indicates the change in temperature of the inner surface of the outer tube.

Comparative Example 1
An outer pipe (1000 mm long, 150 mm outer diameter, 0.7 mm thick, 5.8 mm wave depth) was produced, in which the metal material was cold-rolled steel (SPCD) and the corrugated shape was formed along the longitudinal direction. The outer pipe was coated with a resin containing a black material to a thickness of 2.9 mm (50% of the wave depth) as a corrosion protection layer. Polyethylene resin (NUCG-7641) was used as the resin. A master batch (M-1535) manufactured by ENEOS NUC Co., Ltd., which contained carbon as a pigment, was used as the resin, and the titanium oxide concentration of the molded product was mixed to 0.8 to 2.5 mass%, and extrusion molding was performed. Such an outer pipe was placed in a place exposed to direct sunlight, and the temperature of the outer surface and the temperature of the inner surface of the outer pipe 10 were measured over time from 11:00 a.m. to 3:00 p.m. The average outside air temperature was 28.4°C. In the graph of FIG. 4, the line indicated by reference number 54 shows the change in temperature of the outer surface of the outer tube, and the line indicated by reference number 56 shows the change in temperature of the inner surface of the outer tube.

In the outer tube of Comparative Example 1, the temperature of the outer and inner surfaces of the outer tube rose to 45°C to 60°C due to direct sunlight hitting the outer surface. In this case, when the outer tube and the inner tube come into contact, the inner tube is heated, which may heat the fluid flowing inside the inner tube as well. In contrast, in the outer tube of Example 1, even when direct sunlight hits the outer surface, the temperature of the outer and inner surfaces of the outer tube was maintained within the range of 30°C to 40°C. In particular, the temperature of the inner surface of the outer tube was maintained within the range of 30°C to 35°C, and did not rise significantly from the average outside air temperature of 28.4°C. In this case, it is believed that even if the outer tube comes into contact with the inner tube, a large rise in the temperature of the fluid flowing inside the inner tube is suppressed.

[Examples 2 to 4]
A sheet (length 168 mm, width 187 mm, thickness 2 mm) was produced by compression molding a resin containing a white material into a plate shape. A polyethylene resin (NUCG-7641) manufactured by ENEOS NUC Corporation was used as the resin. In addition, titanium oxide contained in a master batch (PE-M 20N3127C WH) manufactured by Dainichiseika Chemicals Mfg. Co., Ltd. was used as a pigment in the resin, and was mixed to 0.25 mass% (Example 2), 0.5 mass% (Example 3), and 2 mass% (Example 4), respectively. Using a Shimadzu ultraviolet-visible-near infrared spectrometer (SolidSpec-3700) manufactured by Shimadzu Corporation, the reflectance was measured when visible light with a wavelength of 400 nm to 700 nm was irradiated onto the surface of such a sheet. In the graph of Figure 5, the line indicated by reference number 62 shows the relationship between wavelength and reflectance when the titanium oxide content is 0.25 mass%, the line indicated by reference number 64 shows the relationship between wavelength and reflectance when the titanium oxide content is 0.5 mass%, and the line indicated by reference number 66 shows the relationship between wavelength and reflectance when the titanium oxide content is 2 mass%.

Comparative Example 2
A sheet (length 168 mm, width 187 mm, thickness 2 mm) was produced by compression molding a resin not containing a white material into a plate shape. A polyethylene resin (NUCG-7641) manufactured by ENEOS NUC Corporation was used as the resin. The titanium oxide content in the resin was 0 mass%. Using a Shimadzu Corporation ultraviolet-visible-near infrared spectrometer (SolidSpec-3700), the reflectance was measured when visible light with a wavelength of 400 nm to 700 nm was irradiated onto the surface of such a sheet. In the graph of FIG. 5, the line indicated by reference number 60 shows the relationship between wavelength and reflectance when the titanium oxide content is 0 mass%.

In the sheet according to Comparative Example 2, the reflectance was in the range of 15% to 30% when visible light with a wavelength of 400 nm to 700 nm was irradiated onto the surface of the sheet. Therefore, when direct sunlight hits the outer surface of the sheet according to Comparative Example 2, there is a risk that the temperature of the sheet will rise due to the low reflectance. In contrast, in the sheets according to Examples 2 to 4, the reflectance was in the range of 70% to 100% when visible light with a wavelength of 400 nm to 700 nm was irradiated onto the surface of the sheet. Therefore, it is believed that even if direct sunlight hits the outer surface of the sheets according to Examples 2 to 4, a large rise in the temperature of the sheet is suppressed.

[Examples 5 to 7]
A sheet (length 168 mm, width 187 mm, thickness 2 mm) was prepared by compression molding a resin containing a white material into a plate shape. A polyethylene resin (NUCG-7641) manufactured by ENEOS NUC Corporation was used as the resin. Titanium oxide contained in a master batch (PE-M 20N3127C WH) manufactured by Dainichiseika Chemicals Mfg. Co., Ltd. was used as a pigment in the resin, and was mixed to 5 mass% (Example 5), 10 mass% (Example 6), and 25 mass% (Example 7). From such a sheet, a dumbbell-shaped tensile test piece based on "JIS K 7161-2 Plastics - Determination of tensile properties - Part 2, Appendix A, Small test piece, Figure A.1 and Table A.1" was prepared, and three tests were performed for each example at a tensile speed of 500 mm/min and a test temperature of 0°C based on the test method of "JIS K 7161-1 Plastics - Determination of tensile properties - Part 1". In the graph of Figure 6, the lines indicated by reference numbers 71, 72, and 73 show the relationship between elongation and stress when the titanium oxide content is 5 mass%, the lines indicated by reference numbers 74, 75, and 76 show the relationship between elongation and stress when the titanium oxide content is 10 mass%, and the lines indicated by reference numbers 77, 78, and 79 show the relationship between elongation and stress when the titanium oxide content is 25 mass%.

As shown in the graph of FIG. 6, when the titanium oxide content was 5%, 10%, or 25% by mass, there was no significant variation in the results of the three tensile tests. When the titanium oxide content is too high, the dispersion of titanium oxide in the resin varies, which can cause variations in the elongation of the corrosion protection layer, particularly when the external temperature is low, and there is a problem that the corrosion protection layer may break when the sheet is bent. However, when the titanium oxide content was 5%, 10%, or 25% by mass, there was no significant variation in the results of the three tensile tests, so it is thought that there is no significant variation in the dispersion of titanium oxide in the resin at these contents, and therefore it is thought that there is a low possibility that the corrosion protection layer will break when the sheet is bent.

2 Double pipe 10 Outer pipe 12 Anticorrosive layer 20 Inner pipe 22 Insulation member 30 Vacuum space

Claims (7)

an outer tube and an inner tube disposed inside the outer tube with a gap therebetween;
A heat insulating layer is formed between the outer pipe and the inner pipe,
an outermost layer of the outer pipe is coated with a resin as a corrosion protection layer, the resin containing a white material makes an outer surface of the corrosion protection layer white;
The outer pipe and the inner pipe are made of metal . an outer tube and an inner tube disposed inside the outer tube with a gap therebetween;
A heat insulating layer is formed between the outer pipe and the inner pipe,
an outermost layer of the outer pipe is coated with a resin as a corrosion protection layer, the resin containing a white material makes an outer surface of the corrosion protection layer white;
The outer pipe and the inner pipe each have a corrugated shape along a longitudinal direction . 3. The double pipe according to claim 1 , wherein when the outer pipe is corrugated, the thickness of the resin is within a range of 10% to 100% of the depth of the waves of the outer pipe. 2. The double pipe according to claim 1 , wherein the thickness of the resin when the outer pipe has a straight shape is within a range of 0.05% to 15% of the outer diameter of the outer pipe. The double pipe according to any one of claims 1 to 4, wherein the white material includes a pigment. The double pipe of claim 5, wherein the pigment includes titanium oxide. The double-walled pipe according to claim 5 or 6, wherein the pigment content is 25% by mass or less.

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