JP6791016B2 - Double pipe insulation structure - Google Patents

Description

The present invention relates to a double tube insulation structure.

A double pipe heat insulating structure is known in which an inner pipe and an outer pipe opened at both ends are connected at both ends, and the space formed between the inner pipe and the outer pipe is decompressed. Patent Document 1 describes a double-tube heat insulating structure in which an inner tube and an outer tube are connected by bellows at both ends.

Japanese Unexamined Patent Publication No. 2011-080719

In the double pipe heat insulating structure described in Patent Document 1, since the inner pipe and the outer pipe are connected by bellows at both ends, the deformation of the inner pipe becomes bellows even when the inner pipe is heated and thermally expanded. Since it is absorbed, it is possible to suppress the deformation of the inner pipe from being transmitted to the outer pipe. However, the double pipe heat insulating structure described in Patent Document 1 is not preferable in terms of cost because bellows, which is a relatively expensive member, is used at both ends of the double pipe, that is, at two places.

The present invention has been made in view of the above background, and is capable of suppressing the transmission of deformation of the inner tube to the outer tube when the inner tube is thermally expanded while suppressing an increase in cost. The purpose is to provide a structure.

In the double pipe heat insulating structure according to one aspect of the present invention, the inner pipe and the outer pipe having both ends are connected at both ends, and the space between the inner pipe and the outer pipe is depressurized. In the pipe heat insulating structure, thin-walled portions having a tube wall thickness thinner than the other portions are provided at both end portions of either the inner pipe or the outer pipe, and the inner pipe and the outer pipe are provided with thin-walled portions. In either one, a bellows portion capable of absorbing the deformation of the inner tube due to thermal expansion is arranged at one place, and even when the inner tube is maximally expanded in a temperature range that can be heated in actual use. The bellows portion is arranged in a compressed or stretched state so as to suppress the generation of compressive stress in the thin-walled portion.

According to the present invention, it is possible to suppress the deformation of the inner tube from being transmitted to the outer tube when the inner tube is thermally expanded, while suppressing the increase in cost.

It is a schematic diagram explaining the structure of the double pipe insulation structure which concerns on Embodiment 1. FIG. It is a schematic diagram which shows the state before and after connecting the inner pipe and the outer pipe in the manufacture of the double pipe insulation structure which concerns on Embodiment 1. FIG. It is a schematic diagram which shows the state before and after the inner pipe is heated in the double pipe insulation structure which concerns on Embodiment 1. FIG. It is sectional drawing which shows typically about the structure of the double pipe insulation structure which concerns on Embodiment 2. FIG. It is a schematic diagram which shows the state before and after connecting the inner pipe and the outer pipe in the manufacture of the double pipe insulation structure which concerns on Embodiment 2. FIG. It is a schematic diagram which shows the state before and after the inner pipe is heated in the double pipe insulation structure which concerns on Embodiment 2. FIG. It is sectional drawing which shows typically about the structure of the double pipe insulation structure which concerns on Embodiment 3. FIG. It is a schematic diagram which shows the state before and after connecting the inner pipe and the outer pipe in the manufacture of the double pipe insulation structure which concerns on Embodiment 3. FIG. It is a schematic diagram which shows the state before and after the inner pipe is heated in the double pipe insulation structure which concerns on Embodiment 3. FIG. It is sectional drawing which shows typically about the structure of the double tube insulation structure which concerns on Embodiment 4. It is a schematic diagram which shows the state before and after connecting the inner pipe and the outer pipe in the manufacture of the double pipe insulation structure which concerns on Embodiment 4. FIG. It is a schematic diagram which shows the state before and after the inner pipe is heated in the double pipe insulation structure which concerns on Embodiment 4. FIG.

Embodiment 1
Hereinafter, Embodiment 1 of the present invention will be described with reference to the drawings.

First, the configuration of the double pipe heat insulating structure 1 according to the present embodiment will be described with reference to FIG.
FIG. 1 is a cross-sectional view schematically showing the configuration of the double pipe heat insulating structure 1. As shown in FIG. 1, the double pipe heat insulating structure 1 includes an outer pipe 2 and an inner pipe 3. The inner pipe 3 and the outer pipe 2 are cylindrical pipes having both ends open. The inner pipe 3 is coaxially arranged inside the outer pipe 2. The material of the outer pipe 2 and the inner pipe 3 is, for example, stainless steel or steel. The inner pipe 3 and the outer pipe 2 are connected at both end portions.

Thin-walled portions 3a having a thinner tube wall than the other portions 3b are provided at both ends of the inner tube 3. That is, the thickness t2 of the pipe wall of the thin portion 3a is thinner than the thickness t1 of the pipe wall of the other portion 3b (t1> t2). In the outer tube 2, one bellows portion 5 capable of absorbing the deformation of the inner tube 3 due to thermal expansion is arranged at one place. That is, the bellows portion 5 acts as a flexible elastic member. At both ends of the outer pipe 2, annular walls 2a extending inward along the opening surface of the outer pipe 2 are formed.

The inner pipe 3 and the outer pipe 2 are connected at both end portions. Specifically, the tips of the thin-walled portions 3a at both ends of the inner tube 3 and the tips of the annular walls 2a at both ends of the outer tube 2 are connected. This bonding may be performed, for example, by welding.

A closed space 8 is formed between the outer pipe 2 and the inner pipe 3. Space 8 is a decompressed vacuum space. That is, the outer tube 2 and the inner tube 3 are insulated by a vacuum space. The outside of the outer pipe 2 is the outside air. The inside of the inner pipe 3 is a storage space 113. A process of heating is performed in the accommodation space 113, whereby the inner tube 3 is heated.

FIG. 2 is a schematic view showing a state before and after connecting the inner pipe 3 and the outer pipe 2 in the manufacture of the double pipe heat insulating structure 1. Here, the upper figure shows the state before the inner tube 3 and the outer tube 2 are connected, and the lower figure shows the state after the inner tube 3 and the outer tube 2 are connected. In FIG. 2, for convenience, only the upper half of the double pipe heat insulating structure 1 is shown. As shown in FIG. 2, the bellows portion 5 is in the state of natural length Lc1 in the state before the inner tube 3 and the outer tube 2 are connected.

On the other hand, in the state after the inner tube 3 and the outer tube 2 are combined, the bellows portion 5 is in a state of being compressed (shrinked) to a length Lc2 shorter than the natural length Lc1 (Lc2 <Lc1). That is, the restoring force F1 from the compressed state of the bellows portion 5 acts in the direction of stretching the inner tube 3 in the axial direction. Therefore, in the state after the inner pipe 3 and the outer pipe 2 are connected, the thin-walled portion 3a is pulled by the restoring force F1 of the bellows portion 5, so that the thin-walled portion 3a is in a state where a predetermined tensile stress is applied. ing. Since the thin-walled portion 3a is relatively strong against tensile stress, no particular problem occurs even when a predetermined tensile stress is applied to the thin-walled portion 3a.

FIG. 3 is a schematic view showing the state before and after the inner pipe 3 is heated in the double pipe heat insulating structure 1. Here, the upper figure is a state before the inner tube 3 is heated, and the middle and lower figures are a state after the inner tube 3 is heated. In FIG. 3, for convenience, only the upper half of the double pipe heat insulating structure 1 is shown.

As shown in the upper part of FIG. 3, the length Lc2 of the bellows portion 5 is shorter than the natural length Lc1 (Lc2 <Lc1) before the inner tube 3 is heated. As shown in the middle part of FIG. 3, when the inner tube 3 is heated, the length of the other portion 3b extends from La1 to La2 due to thermal expansion, and accordingly, the length of the bellows portion 5 increases from Lc2 to Lc3. Suppose it grows to. At this time, it is assumed that the length Lc3 of the bellows portion 5 after the inner tube 3 is heated is equal to or less than the natural length Lc1 of the bellows portion 5 (Lc3 ≦ Lc1). That is, the bellows portion 5 is in a compressed state. When Lc3 ≦ Lc1, the restoring force F2 from the compressed state of the bellows portion 5 acts in the direction of extending the inner tube 3 in the axial direction. Therefore, since the thin-walled portion 3a is pulled by the restoring force F2 of the bellows portion 5, the thin-walled portion 3a is in a state where a predetermined tensile stress is applied. Since the thin-walled portion 3a is relatively strong against tensile stress, no particular problem occurs even when a predetermined tensile stress is applied to the thin-walled portion 3a.

As shown in the lower part of FIG. 3, when the inner tube 3 is heated, the length of the other portion 3b extends from La1 to La3 due to thermal expansion, and accordingly, the length of the bellows portion 5 increases from Lc2 to Lc4. Suppose it grows to. At this time, it is assumed that the length Lc4 of the bellows portion 5 after the inner tube 3 is heated is longer than the natural length Lc1 of the bellows portion 5 (Lc4> Lc1). That is, the bellows portion 5 is in an elongated state. That is, when Lc4> Lc1, the thin-walled portion 3a is compressed by the restoring force F3 of the bellows portion 5, so that the thin-walled portion 3a is in a state where a predetermined compressive stress is applied. The thin-walled portion 3a is relatively strong against tensile stress but relatively weak against compressive stress.

Therefore, even when the other portion 3b of the inner pipe 3 is maximized by thermal expansion in the temperature range in which the inner pipe 3 can be heated in actual use in the double pipe heat insulating structure 1, the thin-walled portion It is necessary that the length of the bellows portion 5 is not longer than the natural length Lc1 so that compressive stress is not generated in 3a. In the double pipe heat insulating structure 1 according to the present embodiment, even when the inner pipe 3 is maximally thermally expanded in a temperature range that can be heated in actual use, it is possible to suppress the generation of compressive stress in the thin portion 3a. As described above, the bellows portion 5 is arranged in a compressed state. Specifically, the restoring force F1 (see FIG. 2) from the compressed state of the bellows portion 5 when the inner tube 3 and the outer tube 2 are connected is maximized in the temperature range in which the inner tube 3 can be heated in actual use. It is set to a predetermined value or more so that the generation of compressive stress in the thin portion 3a can be suppressed even when the thermal expansion is limited to the limit.

From the above, according to the double pipe heat insulating structure 1 according to the present embodiment, it is possible to suppress the action of compressive stress on the thin portion 3a when the inner pipe 3 is thermally expanded.

Embodiment 2
Hereinafter, a second embodiment of the present invention will be described with reference to the drawings. The parts common to those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted.

First, the configuration of the double pipe heat insulating structure 101 according to the present embodiment will be described with reference to FIG.
FIG. 4 is a cross-sectional view schematically showing the configuration of the double pipe heat insulating structure 101. As shown in FIG. 4, the double pipe heat insulating structure 101 includes an outer pipe 102 and an inner pipe 103. The inner pipe 103 and the outer pipe 102 are cylindrical pipes having both ends open. The inner pipe 103 is coaxially arranged inside the outer pipe 102. The material of the outer pipe 102 and the inner pipe 103 is, for example, stainless steel or steel. The inner pipe 103 and the outer pipe 102 are connected at both end portions.

Thin-walled portions 102a having a thinner tube wall than the other portions 102b are provided at both ends of the outer tube 102. That is, the thickness t2 of the pipe wall of the thin portion 102a is thinner than the thickness t1 of the pipe wall of the other portion 102b (t1> t2). In the inner pipe 103, one bellows portion 5 capable of absorbing the deformation of the inner pipe 103 due to thermal expansion is arranged at one place. Specifically, in the inner pipe 103, the bellows portion 5 is arranged between the left side portion 103a and the right side portion 103b. At both ends of the inner pipe 103, annular walls 103c extending outward along the opening surface of the inner pipe 103 are formed.

The inner pipe 103 and the outer pipe 102 are connected at both end portions. Specifically, the tips of the thin-walled portions 102a at both ends of the outer tube 102 and the tips of the annular walls 103c at both ends of the inner tube 103 are connected. This bonding may be performed, for example, by welding.

A space 8 which is a vacuum space is formed between the outer pipe 102 and the inner pipe 103. As a result, the outer pipe 102 and the inner pipe 103 are insulated from each other. The inside of the inner pipe 103 is a storage space 113. A process of heating is performed in the accommodation space 113, whereby the inner tube 103 is heated.

FIG. 5 is a schematic view showing a state before and after connecting the inner pipe 103 and the outer pipe 102 in the manufacture of the double pipe heat insulating structure 101. Here, the upper figure shows the state before the inner pipe 103 and the outer pipe 102 are connected, and the lower figure shows the state after the inner pipe 103 and the outer pipe 102 are connected. In FIG. 5, for convenience, only the upper half of the double pipe heat insulating structure 101 is shown. As shown in FIG. 5, the bellows portion 5 is in the state of natural length Lc1 in the state before connecting the inner pipe 103 and the outer pipe 102.

On the other hand, in the state after the inner tube 103 and the outer tube 102 are combined, the bellows portion 5 is in a state of being compressed (shrinked) to a length Lc2 shorter than the natural length Lc1. That is, the restoring force F1 from the compressed state of the bellows portion 5 acts in the direction of stretching the outer tube 102. Therefore, in the state after the inner pipe 103 and the outer pipe 102 are connected, the thin-walled portion 102a is pulled by the restoring force F1 of the bellows portion 5, so that the thin-walled portion 102a is in a state where a predetermined tensile stress is applied. ing. Since the thin-walled portion 102a is relatively strong against tensile stress, no particular problem occurs even when a predetermined tensile stress is applied to the thin-walled portion 3a.

FIG. 6 is a schematic view showing the state before and after the inner pipe 103 is heated in the double pipe heat insulating structure 101. Here, the upper figure is a state before the inner tube 103 is heated, and the lower figure is a state after the inner tube 103 is heated. In FIG. 6, for convenience, only the upper half of the double pipe heat insulating structure 101 is shown.

As shown in the upper part of FIG. 6, the length Lc2 of the bellows portion 5 is shorter than the natural length Lc1 (Lc2 <Lc1) before the inner tube 103 is heated. As shown in the lower part of FIG. 6, when the inner tube 103 is heated, the length of the left side portion 103a of the inner tube 103 extends from Lal1 to Lal2 due to thermal expansion, and the length of the right side portion 103b extends to Lar1 due to thermal expansion. Extends from to Lar2. Along with this, the length of the bellows portion 5 further shrinks from Lc2, which is shorter than the natural length Lc1, to Lc5 (Lc5 <Lc2 <Lc1). The restoring force F5 from the compressed state of the bellows portion 5 acts in the direction of extending the outer tube 102 in the axial direction. Therefore, since the thin-walled portion 102a is pulled by the restoring force F5 of the bellows portion 5, the thin-walled portion 102a is in a state where a predetermined tensile stress is applied. Since the thin-walled portion 102a is relatively strong against tensile stress, no particular problem occurs even when a predetermined tensile stress is applied to the thin-walled portion 102a.

From the above, according to the double pipe heat insulating structure 1 according to the present embodiment, it is possible to suppress the action of compressive stress on the thin portion 102a when the inner pipe 103 is thermally expanded.

Embodiment 3
Hereinafter, a third embodiment of the present invention will be described with reference to the drawings. The parts common to those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted.

First, the configuration of the double pipe heat insulating structure 201 according to the present embodiment will be described with reference to FIG. 7.
FIG. 7 is a cross-sectional view schematically showing the configuration of the double pipe heat insulating structure 201. As shown in FIG. 7, the double pipe heat insulating structure 201 includes an outer pipe 202 and an inner pipe 203. The inner pipe 203 and the outer pipe 202 are cylindrical pipes having both ends open. The inner pipe 203 is coaxially arranged inside the outer pipe 202. The material of the outer pipe 202 and the inner pipe 203 is, for example, stainless steel or steel. The inner pipe 203 and the outer pipe 202 are connected at both end portions.

Thin-walled portions 203a having a thinner tube wall than the other portions 203b are provided at both ends of the inner pipe 203. That is, the thickness t2 of the pipe wall of the thin portion 203a is thinner than the thickness t1 of the pipe wall of the other portion 203b (t1> t2). Further, in the inner pipe 203, one bellows portion 5 capable of absorbing the deformation of the inner pipe 203 due to thermal expansion is arranged at one place. At both ends of the outer tube 202, annular walls 202a extending inward along the opening surface of the outer tube 202 are formed.

The inner pipe 203 and the outer pipe 202 are connected at both end portions. Specifically, the tips of the thin-walled portions 203a at both ends of the inner tube 203 and the tips of the annular walls 202a at both ends of the outer tube 202 are connected. This bonding may be performed, for example, by welding.

A space 8 which is a vacuum space is formed between the outer pipe 202 and the inner pipe 203. That is, the outer pipe 202 and the inner pipe 203 are insulated by a vacuum space. The inside of the inner pipe 203 is a storage space 113. A process of heating is performed in the accommodation space 113, whereby the inner tube 203 is heated.

FIG. 8 is a schematic view showing a state before and after connecting the inner pipe 203 and the outer pipe 202 in the manufacture of the double pipe heat insulating structure 201. Here, the upper figure shows the state before the inner pipe 203 and the outer pipe 202 are connected, and the lower figure shows the state after the inner pipe 203 and the outer pipe 202 are connected. In FIG. 8, for convenience, only the upper half of the double pipe heat insulating structure 201 is shown. As shown in FIG. 8, the bellows portion 5 is in a state of natural length Lc1 in the state before the inner pipe 203 and the outer pipe 202 are connected.

On the other hand, in the state after the inner tube 203 and the outer tube 202 are combined, the bellows portion 5 is in a state of being extended (extended) to a length Lc6 longer than the natural length Lc1 (Lc6> Lc1). In the state after the inner pipe 203 and the outer pipe 202 are connected, the thin-walled portion 203a is pulled by the restoring force F6 from the stretched state of the bellows portion 5 and is in a state where a predetermined tensile stress is applied. Since the thin-walled portion 203a is relatively strong against tensile stress, no particular problem occurs even when a predetermined tensile stress is applied to the thin-walled portion 203a.

FIG. 9 is a schematic view showing the state before and after the inner pipe 203 is heated in the double pipe heat insulating structure 201. Here, the upper figure is a state before the inner pipe 203 is heated, and the middle and lower figures are a state after the inner pipe 203 is heated. In FIG. 9, for convenience, only the upper half of the double pipe heat insulating structure 201 is shown.

As shown in the upper part of FIG. 9, the length Lc6 of the bellows portion 5 is longer than the natural length Lc1 (Lc6> Lc1) before the inner tube 203 is heated. As shown in the middle part of FIG. 9, when the other portion 203b of the inner pipe 203 is expanded by heating the inner pipe 203, the bellows portion 5 is expanded by the amount of the other portion 203b of the inner pipe 203 being expanded. Shrinks. Along with this, it is assumed that the length of the bellows portion 5 is shortened from Lc6 to Lc7. Here, it is assumed that the length Lc7 of the bellows portion 5 after the inner tube 203 is heated is equal to or greater than the natural length Lc1 of the bellows portion 5 (Lc6> Lc7 ≧ Lc1). That is, the bellows portion 5 is in an stretched state. When Lc7 ≧ Lc1, the thin-walled portion 203a is pulled by the restoring force F7 of the bellows portion 5, so that the thin-walled portion 203a is in a state where a predetermined tensile stress is applied. Since the thin-walled portion 203a is relatively strong against tensile stress, no particular problem occurs even when a predetermined tensile stress is applied to the thin-walled portion 203a.

As shown in the lower part of FIG. 9, the length of the bellows portion 5 was shortened from Lc6 to Lc8 as the other portion 203b of the inner pipe 203 was expanded by thermal expansion due to the heating of the inner pipe 203. And. Here, it is assumed that the length Lc8 of the bellows portion 5 after the inner tube 203 is heated is shorter than the natural length Lc1 of the bellows portion 5 (L6c> Lc1> Lc8). That is, the bellows portion 5 is in a shrunk state. When Lc8 <Lc1, the restoring force F8 from the compressed state of the bellows portion 5 acts in the direction of axially compressing the outer tube 202 and the inner tube 203. That is, when Lc8 <Lc1, the thin-walled portion 203a is compressed by the restoring force F8 of the bellows portion 5, so that the thin-walled portion 203a is in a state where compressive stress is applied. The thin-walled portion 3a is relatively strong against tensile stress but relatively weak against compressive stress.

Therefore, even when the other portion 203b of the inner pipe 203 is maximized by thermal expansion in the temperature range in which the inner pipe 203 can be heated in actual use in the double pipe heat insulating structure 201, the thin-walled portion It is necessary that the length of the bellows portion 5 is not shorter than the natural length Lc1 so that compressive stress is not generated in 203a. In the double pipe heat insulating structure 201 according to the present embodiment, even when the inner pipe 203 is maximally thermally expanded in a temperature range that can be heated in actual use, it is possible to suppress the generation of compressive stress in the thin portion 203a. As described above, the bellows portion 5 is arranged in a stretched state. Specifically, the restoring force F6 (see FIG. 8) from the stretched state of the bellows portion 5 when the inner tube 203 and the outer tube 202 are connected is maximized in the temperature range in which the inner tube 203 can be heated in actual use. The value is set to a predetermined value or more so that the generation of compressive stress in the thin portion 203a can be suppressed even when the thermal expansion is limited to the limit.

From the above, according to the double pipe heat insulating structure 201 according to the present embodiment, it is possible to suppress the action of compressive stress on the thin portion 203a when the inner pipe 203 is thermally expanded.

Embodiment 4
Hereinafter, a fourth embodiment of the present invention will be described with reference to the drawings. The parts common to those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted.

First, the configuration of the double pipe heat insulating structure 301 according to the present embodiment will be described with reference to FIG.
FIG. 10 is a cross-sectional view schematically showing the configuration of the double pipe heat insulating structure 301. As shown in FIG. 10, the double pipe heat insulating structure 301 includes an outer pipe 302 and an inner pipe 303. The inner pipe 303 and the outer pipe 302 are cylindrical pipes having both ends open. The inner pipe 303 is coaxially arranged inside the outer pipe 302. The material of the outer pipe 302 and the inner pipe 303 is, for example, stainless steel or steel. The inner pipe 303 and the outer pipe 302 are connected at both end portions.

Thin-walled portions 302a having a thinner tube wall than the other portions 302b are provided at both ends of the outer tube 302. That is, the thickness t2 of the pipe wall of the thin portion 302a is thinner than the thickness t1 of the pipe wall of the other portion 203b (t1> t2). Further, in the outer pipe 302, one bellows portion 5 capable of absorbing the deformation of the inner pipe 303 due to thermal expansion is arranged at one place. At both ends of the inner pipe 303, annular walls 303a extending outward along the opening surface of the inner pipe 303 are formed.

The inner pipe 303 and the outer pipe 302 are connected at both end portions. Specifically, the tips of the thin-walled portions 302a at both ends of the outer tube 302 and the tips of the annular walls 303a at both ends of the inner tube 303 are connected. This bonding may be performed, for example, by welding.

A space 8 which is a vacuum space is formed between the outer pipe 302 and the inner pipe 303. That is, the outer pipe 302 and the inner pipe 303 are insulated by a vacuum space. The inside of the inner pipe 303 is a storage space 113. A process of heating is performed in the accommodation space 113, whereby the inner tube 303 is heated.

FIG. 11 is a schematic view showing a state before and after connecting the inner pipe 303 and the outer pipe 302 in the manufacture of the double pipe heat insulating structure 301. Here, the upper figure shows the state before the inner pipe 303 and the outer pipe 302 are connected, and the lower figure shows the state after the inner pipe 303 and the outer pipe 302 are connected. In FIG. 11, for convenience, only the upper half of the double pipe heat insulating structure 301 is shown. As shown in FIG. 11, in the state before connecting the inner pipe 303 and the outer pipe 302, the bellows portion 5 is in a state of natural length Lc1.

On the other hand, in the state after the inner tube 303 and the outer tube 302 are combined, the bellows portion 5 is in a state of being extended (extended) to a length Lc6 longer than the natural length Lc1 (Lc6> Lc1). In the state after the inner pipe 303 and the outer pipe 302 are connected, the thin-walled portion 302a is pulled by the restoring force F6 from the stretched state of the bellows portion 5 and is in a state where a predetermined tensile stress is applied. Since the thin-walled portion 302a is relatively strong against tensile stress, no particular problem occurs even when a predetermined tensile stress is applied to the thin-walled portion 302a.

FIG. 12 is a schematic view showing the state before and after the inner pipe 303 is heated in the double pipe heat insulating structure 301. Here, the upper figure is a state before the inner pipe 303 is heated, and the lower figure is a state after the inner pipe 303 is heated. In FIG. 12, for convenience, only the upper half of the double pipe heat insulating structure 301 is shown.

As shown in the upper part of FIG. 12, the length Lc6 of the bellows portion 5 is longer than the natural length Lc1 (Lc6> Lc1) before the inner tube 303 is heated. As shown in the lower part of FIG. 12, when the inner pipe 303 is heated and the inner pipe 303 is stretched due to thermal expansion, the bellows portion 5 is also stretched by the amount that the inner pipe 303 is stretched. When the length of the bellows portion 5 further extends from Lc6 longer than the natural length Lc1 to Lc9 (Lc9> Lc6> Lc1), the thin-walled portion 302a is pulled by the restoring force F9 of the bellows portion 5, so that the thin-walled portion 302a is predetermined. It is in a state where tensile stress is applied. Since the thin-walled portion 302a is relatively strong against tensile stress, no particular problem occurs even when a predetermined tensile stress is applied to the thin-walled portion 302a.

From the above, according to the double pipe heat insulating structure 301 according to the present embodiment, it is possible to suppress the action of compressive stress on the thin portion 302a when the inner pipe 303 is thermally expanded.

The present invention is not limited to the above embodiment, and can be appropriately modified without departing from the spirit.

1, 101, 201, 301 Double pipe insulation structure 2, 102, 202, 302 Outer pipe 3, 103, 203, 303 Inner pipe 3a, 102a, 203a, 302a Thin wall part 5 Bellows part 8 Space 113 Storage space

Claims (1)

A double pipe heat insulating structure in which an inner pipe and an outer pipe having both ends opened are connected at both ends, and the space between the inner pipe and the outer pipe is decompressed.
At both ends of either the inner pipe or the outer pipe, thin-walled portions having a thinner tube wall than the other portions are provided.
In either the inner pipe or the outer pipe, a bellows portion capable of absorbing the deformation of the inner pipe due to thermal expansion is arranged at only one place.
Both ends of the bellows portion are connected to either the inner pipe or the outer pipe.
The bellows portion is arranged in a compressed or stretched state so as to suppress the generation of compressive stress in the thin-walled portion even when the inner tube is maximally expanded in a temperature range that can be heated in actual use. Double pipe insulation structure installed.

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