JPH0364757B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to liquid natural gas, liquid nitrogen, etc.
This invention relates to improvements in heat-insulating pipes for low-temperature fluids that constitute pipes for flowing low-temperature fluids at temperatures below 100°C.

[Conventional technology]

Conventionally, insulated pipes for low-temperature fluids constituting pipelines for flowing low-temperature fluids have been made by connecting unit-length steel pipes with each other using bellows, and by using thick-walled porous materials on the outside of the steel pipes. Insulated pipes wrapped with insulation material were used.

Such insulated pipes for low-temperature fluids require a great deal of labor and time to insulate when constructing pipelines spanning several kilometers, and the initial cost is also enormous.

Therefore, in the past, an outer tube of the same length was provided outside an inner tube of unit length constituting a pipe line for low-temperature fluid, with a heat insulating space in between, and these inner and outer tubes were connected and fixed together at both ends. At the same time, bellows are provided near both ends of the inner tube that comes into contact with the low-temperature fluid, allowing the inner tube to contract due to contact with the low-temperature fluid.
The idea was to improve construction efficiency by allowing the inner and outer tubes to be treated as a single unit with a heat insulating function.

[Problem to be solved by the invention]

As mentioned above, if the insulated pipe is composed of an inner and outer double pipe with a heat-insulating cavity, it is effective in improving the workability when constructing a low-temperature fluid pipeline. Although it is possible to reduce the cost of the pipe, on the other hand, it is inevitable that the cost of manufacturing the unit length of the heat insulating pipe itself will increase. In other words, since the inner tube is equipped with bellows near both ends to allow contraction due to contact with low-temperature fluid, in addition to the material cost including the bellows, there is also a cost for the joint between the inner tube and the bellows. There is an increase in cost associated with the production of the insulated pipe itself, such as an increase in cost due to an increase in the number of weld lines, and an increase in cost due to an increase in the support structure for the outer tube in the tube section between the bellows.

The present invention improves workability by allowing a heat insulating pipe for low temperature fluid to be handled as an integral piece with a heat insulating function for each unit length, and also makes it possible to easily manufacture the heat insulating pipe itself. The purpose is to reduce manufacturing costs.

[Means to solve the problem]

The technical means of the present invention taken to achieve the above object forms a heat insulating space between the inner tube and the outer tube, and has the configurations described in [A] to [C] below. That's true.

[B] Hollow cover plates are provided near both ends of both the inner and outer tubes to connect and fix both the inner and outer tubes together.

[B] The insulation space between the inner tube and the outer tube is a vacuum layer.

[C] In the inner tube, the tube portion between the hollow cover plates at both ends becomes longer than the distance between the two hollow cover plates when stretched at room temperature, and is bent. In order to maintain a straight line in the contracted state when it comes into contact with the tube, a permanent strain is caused in the tube portion due to heat contraction, and the length of the tube at room temperature is set to be longer than the distance between the hollow lid plates by the amount of permanent strain. It has been done.

[Effect]

The effects of taking the above technical measures are as follows.

The inner and outer tubes are separated by a heat insulating cavity,
The inner and outer pipes are connected and fixed together through the hollow cover plate, so when constructing the pipeline, the inner and outer pipes can be easily connected.
Each unit length can be handled as a single piece with a heat insulating function.

The inner tube that comes into contact with the low-temperature fluid has a permanent strain due to thermal contraction between the hollow cover plates at both ends, and is configured to be longer than the distance between the cover plates at room temperature by the amount of permanent strain. Therefore, even if the piping comes into contact with a low-temperature fluid after piping, the amount of contraction is small after subtracting the above-mentioned permanent strain, so the inner tube can be adjusted without using special expansion/contraction adjustment means such as bellows. can be allowed to shrink.

Furthermore, at room temperature, the length of the outer tube is maintained constant by bending the stretched tube between the lid plates at both ends, so when constructing a long pipeline, The design dimensions of the entire unit length of the insulated pipe do not change significantly. Also,
During contraction, the bending part of the pipe section mainly contracts, so for example, compared to the case where two insulated double pipes of similar structure without this bending part are connected, the contact points between adjacent inner pipes are ,
It is possible to avoid leakage of low-temperature fluid due to a large gap caused by contraction.

〔Effect of the invention〕

(b) Due to the above-mentioned effects, it is possible to perform piping with good workability without the need for separate insulation construction after piping.

(b) Although the workability of the insulated piping is good as described in (a) above, due to the effect of A simple and low-cost insulated tube was obtained.

〔Example〕

Examples of the present invention will be described below, together with a method of manufacturing the same.

Both the inner and outer tubes are made of SUS304, and the sizes are as follows:
The inner pipe is 2B x 2t, and the outer pipe is 4B x 2t. As a heat insulating material, five layers of polyester film with aluminum deposited on one side are wrapped around the outer circumferential surface of the inner tube.
The cavities of both the inner and outer tubes are closed off with a SUS304 cover plate, and the vicinity of both ends of the inner tube is fixed to the vicinity of both ends of the outer tube via this cover plate by welding. A vacuum is applied to the heat insulating cavity between the two tubes and the cover plates thus constructed. The time required for evacuation was 170 hours, including heating and evacuation for 36 hours at 100°C, and the degree of vacuum was set to 1 x 10 ^-4 Torr when liquefied nitrogen was flowed through the inner tube.

Liquid nitrogen is flowed through the inner tubes of the two unit tubes thus manufactured to cool them once.

Thereafter, the liquefied nitrogen is removed to return the temperature of the inner tube to room temperature, and such cooling and heating to room temperature are repeated.

With this temperature change, SUS304 shrinks by 0.28% at -196°C as described above, but when it is returned to room temperature, about 0.17% remains as permanent strain. In other words, in a unit tube, the length of the outer tube does not change whether it is at room temperature or when it is cooled, but if a SUS304 tube is used for the inner tube, when it is cooled to the temperature of liquefied nitrogen (-196℃), the length of the outer tube will change at room temperature. It shrinks by 0.28% compared to the time. Conversely, in the case of a tube with both ends fixed, the same tensile stress was applied as when the tube was stretched by 0.28%. Therefore, at room temperature, the inner tube is longer than the outer tube by a permanent strain of 0.17%, so it may bend or meander within the outer tube.
Furthermore, a portion remains as compressive stress.
However, since it contracts again and becomes a straight tube when cooled, there is no problem in practical use. As described above, if the tensile stress caused by the contraction of the inner tube is less than the proof stress of the inner tube material, the tube will not break due to the contraction even if a bellows is not used as in the conventional case.

In the above embodiment, a vacuum layer having a layer made of a polyester film with aluminum vapor deposition on one side or a layer made of alternating layers of aluminum foil and paper-like glass fiber is used as the heat insulating layer. A simple vacuum layer or a vacuum layer filled with other insulation material (e.g. perlite) can also be used.

Claims (1)

[Scope of Claims] 1. A heat insulating pipe for low temperature fluid, which forms a heat insulating space between an inner pipe and an outer pipe, and has the configurations described in [A] to [C] below. [B] Hollow cover plates are provided near both ends of both the inner and outer tubes to connect and fix both the inner and outer tubes together. [B] The insulation space between the inner tube and the outer tube is a vacuum layer. [C] In the inner tube, the tube portion between the hollow cover plates at both ends becomes longer than the distance between the two hollow cover plates when stretched at room temperature, and is bent. In order to maintain a straight line in the contracted state when it comes into contact with the tube, a permanent strain is caused in the tube portion due to heat contraction, and the length of the tube at room temperature is set to be longer than the distance between the hollow lid plates by the amount of permanent strain. It has been done. 2. The insulated pipe for low temperature fluid according to claim 1, wherein the inner pipe is made of stainless steel pipe. 3. On the outer circumferential surface of the inner pipe in the heat insulating space,
The insulating pipe for low temperature fluid according to claim 1, wherein a polyester film is wound. 4. The heat-insulating pipe for low-temperature fluid according to claim 1, wherein the heat-insulating cavity is a pearlite-filled vacuum layer.