JPH06307595A - Corrosion preventing structure for vacuum insulating pipe - Google Patents

Abstract

PURPOSE:To prevent the occurrence of corrosion and the stress corrosion crack of a membrane, in a vacuum insulating pipe having a vacuum insulating layer the end part of which is sealed by welding it to a thermal expandable membrane. CONSTITUTION:A membrane 1 is previously solidified and annealed and a silicone coating material film 12 is formed on the membrane 1 and weld parts 10 and 11 between the membrane 1 and inner and outer pipes 2 and 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anticorrosive structure for a vacuum heat insulating tube used for heat insulation and cold insulation.

[0002]

2. Description of the Related Art Conventionally, this type of vacuum heat insulating pipe is constructed by joining heat insulating pipes 1 as shown in the longitudinal sectional view of FIG. The heat insulation pipe 1 is composed of an outer pipe 2 and an inner pipe 3.
The membrane 4 is disposed between and, and these are airtightly welded to form the vacuum heat insulating layer 5 inside the inner and outer double structure. The vacuum heat insulating layer 5 is filled with a heat insulating material 6 such as inorganic fine powder or fiber. At the end of the heat insulating pipe 1, the inner pipe 3 is formed longer than the outer pipe 2, and the inner pipes 1 are welded to each other as shown in the figure to prevent the fluid flowing in the pipe from leaking. Therefore, since the region 7 where the heat insulating material is not applied is formed at the end of the heat insulating pipe 1, the atmospheric pressure heat insulating material 8 such as rock wool or glass wool is applied to the entire outer periphery of this region 7 after the pipe joining. Then, for the purpose of protecting the heat insulating material 8 and preventing moisture absorption, a cover material 9 is attached to the outside thereof.

[0003]

However, in the conventional vacuum heat insulating tube as described above, the thin stainless steel plate such as SUS304 having a small thermal conductivity is used in the state of being pressed or spun on the membrane 4. ing. Therefore, when the heat insulating material 8 absorbs rainwater or the like to bring the joint portion into a wet state, the membrane 4 may be corroded and fine holes may be formed. Then, this causes a vacuum break, which impairs the heat insulating performance of the pipe.

Further, as shown in FIG. 3, the inner pipe 3 has a ΔL
Since the membrane 4 is deformed and absorbs this thermal elongation ΔL when it is thermally expanded, a relatively large stress acts on the membrane 4. Therefore, there is a problem that stress corrosion cracking occurs in the membrane 4 when it becomes wet.

Further, the membrane 4 is often annealed at a high temperature of 550 ° C. or higher in the forming process, and at this time, Cr is precipitated in the grain boundaries and intergranular corrosion occurs in a wet state. There's a problem.

Further, since the inner and outer pipes 2 and 3 are usually made of steel, there is a problem that they are welded between dissimilar metals with the membrane 4 made of stainless steel, which causes electrical corrosion.

The present invention solves the above problems, and an object of the present invention is to prevent the corrosion and stress corrosion cracking of the membrane and to maintain the heat insulating performance of the vacuum heat insulating tube.

[0008]

In order to solve the above-mentioned problems, the anticorrosion structure for a vacuum heat insulating pipe of the present invention forms a vacuum heat insulating layer between an inner pipe and an outer pipe, and the end of the vacuum heat insulating layer is formed. In a vacuum heat insulation tube whose part is sealed by welding a heat-expandable membrane, the membrane has been solution-annealed in advance, and this membrane and the welded part of the membrane with the inner tube and the outer tube are coated with silicone. The material coating film is formed.

Further, the anticorrosion structure of the vacuum heat insulating tube of the present invention is
It is characterized in that the coating film of silicone coating material is formed thick at the welded portions of the membrane and the inner tube and the outer tube, and thinly formed at the central portion of the membrane.

[0010]

With the above structure, it is possible to prevent intergranular corrosion and stress corrosion cracking of the membrane by previously subjecting the membrane to solution annealing.

Further, since the silicone coating material coating film is formed on the membrane and the weld portion of the membrane and the inner pipe and the outer pipe, the corrosion resistance of the membrane portion and the weld portion of the membrane and the pipe can be improved. .

Further, a silicone coating material coating film,
By forming a thick film at the welded part of the membrane and the inner and outer pipes and a thin film at the central part of the membrane, the anticorrosion effect at the welded part can be improved and the central part of the membrane due to the thermal expansion and contraction of the pipe It is possible to prevent peeling of the coating film due to deformation of the coating film.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the anticorrosion structure for a vacuum heat insulating tube of the present invention will be described below with reference to the enlarged cross-sectional view of the main part of FIG.
The construction of the vacuum insulation tube of this embodiment is shown in FIGS. 2 and 3 above.
Since it is almost the same as that described by using, the same members will be described with the same reference numerals.

The vacuum heat insulating tube 1 has a vacuum heat insulating layer 5 formed between a steel inner tube 3 and an outer tube 2, and the end of the vacuum heat insulating layer 5 is sealed by a heat-expandable membrane 4. Has been done. This membrane 4 is made of SUS30 having a thickness of 1 mm.
It is made of 4 stainless steel and is previously solution-annealed by heating at 1050 ° C. for a predetermined time and then rapidly cooling.

The membrane 4 and the inner pipe 3 and the membrane 4 and the outer pipe 2 are connected by welding, respectively, and a portion of the membrane 4 and a welded portion 10 between the membrane and the inner pipe and a membrane and the outer pipe are connected. At the atmosphere side of the welded portion 11 with the pipe, the silicone coating material coating film 12
Are formed. The silicone coating material coating film 12 is thickly formed at the welded portions 10 and 11 and thinly formed at the central portion 13 of the membrane.

In the vacuum heat insulating tube having the above-mentioned structure, since the membrane 4 is solution-annealed in advance, Cr is prevented from precipitating at grain boundaries during the forming process of the membrane 4,
The intergranular corrosion is prevented. Further, the residual stress in the membrane 4 is removed and the stress corrosion cracking is prevented.

Further, by forming the silicone coating material coating film 12 on the welded portions 10 and 11 of the membrane portion 4 and the membrane and the inner pipe and the outer pipe, the membrane portion 4 and the membrane and the inner pipe and the outer pipe are different from each other. Corrosion resistance can be improved in the welded portions 10 and 11 with the metal. At this time, the silicone coating material has excellent cold resistance and heat resistance, and has excellent adhesiveness to metal regardless of whether the fluid medium inside the pipe is at high temperature or low temperature. The coating film 12 can be maintained.

Further, the silicone coating material coating film 1
2 is a welded portion 10, 1 between the membrane and the inner pipe and the outer pipe.
1 is formed thick and the central portion 13 of the membrane is formed thin, so that the welded portion 10 between dissimilar metals is
The anticorrosion effect in 11 can be improved. Further, when the membrane 4 is deformed due to the thermal expansion and contraction of the inner tube 3, a large deformation is generated especially in the central portion 13,
Since the coating film 12 is formed thin at that portion, peeling of the coating film 12 during deformation can be prevented.

The anticorrosion structure of the membrane can be applied to a vacuum heat insulating container.

[0020]

As described above, according to the present invention, by pre-solution-annealing the membrane, it is possible to prevent the precipitation of Cr at the grain boundaries during the forming process of the commonly used stainless steel membrane, and to prevent the residue. Since the stress can be removed, the intergranular corrosion and stress corrosion cracking can be prevented.

Further, since the silicone coating material coating film is formed on the membrane and the welded portions of the membrane and the inner tube and the outer tube, the corrosion resistance can be improved.

Further, since the silicone coating material coating film is formed thick at the welded portion of the membrane and the inner tube and outer tube and thinly formed at the central portion of the membrane, the welded portion between different metals between the membrane and the tube is formed. The anticorrosion effect can be improved, and peeling of the coating film due to deformation of the membrane due to thermal expansion and contraction of the inner pipe can be prevented.

As a result of the above, it is possible to obtain a vacuum heat insulation tube having stable heat insulation performance for a long period of time.

[Brief description of drawings]

FIG. 1 is an enlarged cross-sectional view of a main part showing an anticorrosive structure for a vacuum heat insulating tube according to an embodiment of the present invention.

FIG. 2 is a vertical cross-sectional view showing a joint portion of a vacuum heat insulating tube.

FIG. 3 is an enlarged sectional view of an essential part for explaining thermal expansion and contraction of a conventional vacuum heat insulating tube.

[Explanation of symbols]

 1 Vacuum Insulation Pipe 2 Outer Pipe 3 Inner Pipe 4 Membrane 5 Vacuum Insulation Layer 10 Welding Part 11 Welding Part 12 Silicone Coating Material Coating 13 Central Part

Claims (2)

[Claims] 1. A vacuum heat insulation tube in which a vacuum heat insulation layer is formed between an inner tube and an outer tube, and an end portion of the vacuum heat insulation layer is sealed by welding a heat-expandable membrane, wherein the membrane is An anticorrosion structure for a vacuum heat insulation tube, which has been solution-annealed in advance, and a coating film of silicone coating material is formed on this membrane and a welded portion of the membrane and the inner tube and the outer tube. 2. The vacuum heat insulating tube according to claim 1, wherein the silicone coating material coating film is formed thick at a welded portion of the membrane and the inner tube and the outer tube and thinly formed at a central portion of the membrane. Anti-corrosion structure.