JPS61262295A - Vacuum heat-insulating pipe - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to improvements in vacuum insulated pipes used in power plants, chemical plants, aircraft, submarines, and the like.

(Prior Art) In nuclear power plants, aircraft, submarines, etc., pipes are required to have a high degree of insulation, but the insulation space is often limited. In such a case,
It is best to use so-called vacuum insulated pipes, but vacuum insulated pipes made of stainless steel actually have many problems that need to be solved in terms of manufacturing costs, insulation properties, maintaining the degree of vacuum, etc.

For example, in order to further improve the heat insulation properties, it is necessary to form a silver mirror film on at least one of the inner and outer surfaces of the heat insulation space to prevent heat loss due to radiation.

However, it is difficult to evenly and firmly adhere a silver mirror film directly to the surface of stainless steel, and in reality, after forming an intermediate layer of nickel or chromium, a silver mirror film is formed on top of it. There is. As a result, the plating process becomes complicated and manufacturing costs increase.

In addition, in order to maintain insulation performance over a long period of time, it is necessary to maintain a high degree of vacuum in the insulated space, and usually a getter is placed in the insulated space to adsorb the generated gas to reduce the vacuum. I try to keep it.

However, since the gas adsorption performance of the getter decreases when it comes into contact with moisture etc., it is impossible to form a silver mirror film with the getter installed in a heat insulating space. Therefore, it is necessary to attach the getter after forming a silver mirror film on the inner surface of the heat insulating space, which complicates the assembly process and makes it difficult to reduce manufacturing costs. There is a problem that the silver mirror film is easily damaged and the heat insulation performance is deteriorated.

(Problems to be Solved by the Invention) The present invention solves the above-mentioned problems in vacuum insulated pipes using stainless steel, namely: ■ The process of forming the silver mirror film is complicated, so it is difficult to reduce manufacturing costs. *This method attempts to solve the problems of complicating the manufacturing process and unavoidable damage to the silver mirror film due to welding, etc., since the getter must be installed in the vacuum insulation space after forming the silver mirror film. The purpose of the present invention is to provide a vacuum insulated pipe made of stainless steel that can maintain excellent heat insulating properties over a long period of time and significantly reduce manufacturing costs.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention includes forming a silver mirror film directly on the outer surface of stainless steel, and forming a silver mirror film after attaching a getter. As a subject, we carried out tests to directly form a silver mirror film on the outer surface of a large number of stainless steels, and also tested the effects of the silver mirror film formation treatment on the adsorption performance of various getters.

In addition, based on the above test results, the inventor of the present application has found that: (1) If the outer surface of stainless steel is appropriately oxidized to form a film mainly composed of ferric oxide on the outer surface, The silver mirror film can be formed by so-called electroless plating, and the gas adsorption performance of the Zr-V-Fe ternary alloy non-evaporable getter is not impaired by electroless silver plating solution, cleaning water, etc. They each learned the following.

The present invention was invented based on the above-mentioned knowledge, and provides a vacuum insulated pipe in which at least one of the inner tube and the outer tube is made of stainless steel, and the insulated space is evacuated through the chip tube. In this case, the inner tube and the outer tube;
end plates on both sides for forming a heat insulating space; a chip tube that communicates with the heat insulating space and whose opening is sealed after the heat insulating space is evacuated; an oxide film; a Zr-V-Fe ternary alloy non-evaporable getter disposed within the heat insulating space;
The basic structure of the invention is to supply a silver plating solution through a chip tube into the heat insulating space in which the getter is arranged, and directly form a silver mirror film on all or a part of the surface of the stainless steel tube by an electroless plating method. That is.

(Function) By appropriately oxidizing the surface of stainless steel, the surface contains a relatively small proportion of chromic oxide, which is expected to inhibit the progress of the silver mirror reaction, and which has a positive effect on the silver mirror reaction. An oxide film whose main component is assumed to be ferric oxide is formed. As a result, the so-called silver mirror reaction is promoted by contacting the silver plating solution, and a silver mirror film is directly formed on the surface of the stainless steel.

Furthermore, even if a silver plating liquid or the like is allowed to flow into the heat insulating space where the getter is installed in advance, there is almost no change in the gas adsorption performance of the getter, so the silver plating liquid is discharged after the silver mirror film is formed. By heating and activating the getter after the adiabatic space is evacuated, the degree of vacuum in the adiabatic space is maintained at a high degree of vacuum for a long period of time.

(Example) Hereinafter, the details will be explained based on the example of the present invention shown in the drawings. Figure 1 is a longitudinal cross-sectional view of a vacuum insulated pipe, and in the figure, 1 is an inner tube made of stainless steel (SUS304) (outer diameter 60.5 fins, length 4000 mm, wall thickness 3.5 mm). , 2 is an outer tube made of stainless steel (SUS304) (outer diameter 89.1 mm, expanded diameter part outer diameter 139.8 mm, length 3868 mm, wall thickness 2.1 + m), 3 and 4 are insulated space A. 5 is a chip tube communicating with inside the insulation space A, 6 and 7 are flanges attached to both ends of the inner tube, 8 is a getter (70 wt. %Zr-24,6wt%V-5.4wt%F
e).

In this embodiment, both the inner tube 1 and the outer tube 2 are made of stainless steel, but it goes without saying that only one of them may be made of stainless steel. Further, in this embodiment, the getters 8 are installed in a distributed manner on the inner surface of the outer tube 2, but the installation locations and number of getters 8 can be selected as appropriate.

On the other hand, FIG. 2 is a cross-sectional view of FIG. This is a silver mirror film formed in

In this example, the silver mirror film is formed on the entire surface of both the inner and outer tubes, but the silver mirror film may be formed on only one of the surfaces, or on a part of the surface. A silver mirror film may be formed only on the surface.

Next, a method for manufacturing a vacuum insulated pipe will be described. First, the inner tube 1 and the outer tube 2 are formed according to predetermined standards. Next, the outer surface of the inner tube 1 and the inner surface of the outer tube 2 are heat-treated to form an oxide film thereon. The heat treatment is performed by burning the stainless steel tube in an oxidizing atmosphere, and is usually performed at a temperature of 25
5 to 120 minutes at 0 to 550°C, preferably 300 to 4
10 to 60 minutes at 50°C (in this example, 35°C in air)
0℃, 30 minutes). The degree of oxidation on the stainless steel surface is such that the gloss of the stainless steel surface after firing is 10 to 10% higher than the gloss of the polished surface before firing.
A range in which it decreases by 50 is preferable. If the degree of oxidation is small, an oxide film containing a large amount of chromic oxide will be formed, which will inhibit the silver mirror reaction.On the other hand, if the degree of oxidation is excessive, it will have a positive effect on the silver mirror reaction. This is because the ferric oxide that is supposed to be present no longer exists in the oxide film, and only chromium oxide remains.

When the heat treatment is completed, the getter 8 is attached to the inner surface of the outer tube 2, and then the inner tube 1, the outer tube 2, the end plate 3, and the end plate 4 to which the tip tube 5 is welded are assembled, and these are welded together. Assemble.

Incidentally, as the getter 8, a Zr-V-Fe ternary alloy non-evaporable getter is used, and Zr45-75
Component composition consisting of W [%, V20 to 50 wt%, Fe35 wt% (in this example, 7QwL% Zr, 24.5
wt%V, 5.4wt%Fe) is desirable.

When the assembly of each member is completed, an activating solution containing a stannous halogen as a main component (in this example, an aqueous solution containing a stannous halide IQPPM) is injected into the heat insulating space A through the chip tube 5. Activate the oxide film 9. Thereafter, the activation liquid is discharged and the inside of the heat insulating space A is washed with water.

The activation treatment of the oxide film is intended to speed up the precipitation rate of silver by the silver mirror reaction and at the same time cause the silver to be deposited uniformly, and it is also possible to omit the activation treatment.

When the activation process is completed, a silver plating solution is injected from the chip tube 5 and brought into contact with the surfaces of the inner and outer tubes 1.2 to form a silver mirror film 10 by a so-called electroless plating method. Thereafter, the excess silver plating solution is discharged, and the heat insulating space A is washed with water and dried.

As the silver plating solution, conventionally known ones can be used. In this example, the number of people (silver nitrate 200
Dissolve fr in a small amount of water, add 28% ammonia water 10) and water to 96! Then, add 4J of an aqueous solution containing Nylium Hydroxide 2002r to bring the total amount to 1.
ooi) and solution B (400 fr sucrose to 1-1 part water)
Add 5 m4 of concentrated nitric acid to the aqueous solution dissolved in 3 and boil it, add 100 m-e of 37% formaldehyde aqueous solution, and then add water to make the total volume 100 A) in a volume ratio of 1:1. A silver plating solution formed by mixing in proportions is used.

When the formation of the silver mirror film 10 in the heat insulating space A is completed, a vacuum pump is connected to the open end of the chip tube 5, and the space A is evacuated and the getter is activated while heating the assembly (400° C. in this example). . Due to exhaustion, the degree of vacuum in space A is 10-4
~1O-6Torr (10"-' in this example)
Torr), stop the operation of the vacuum pump,
The open end of the chip tube 5 is compressed and vacuum sealed, and then the compressed open end is welded.

According to the results of the heat retention test, the heat retention performance is significantly improved compared to a vacuum insulated pipe in which a silver mirror film is formed on the surfaces of the inner tube 1 and outer tube 2 via an intermediate plating layer. For example, 100
When the inner tube 1 is filled with heated oil at ℃, in the vacuum insulated pipe of the present invention, the oil temperature after 6 hours and 24 hours is 8℃.
While the temperatures were 8°C and 67°C, the temperatures were 82°C and 60°C, respectively, in the vacuum insulated pipe using the intermediate plating layer.

In addition, the inner tube 1 is filled with Dowsome oil at a temperature of about 400°C.
Even when left for 4 hours, the vacuum insulated pipe of the present invention achieved a heat retention effect with a temperature difference of more than 20°C compared to the vacuum insulated pipe using the intermediate plating layer.

Furthermore, the degree of vacuum in the heat insulating space A has hardly changed from the initial value even after 6 months have passed, confirming that the getter 8 is performing a predetermined gas adsorption function.

(Effects of the Invention) As described above, the present invention interposes an oxide film on the surface of the stainless steel part of the heat insulating space and forms a silver mirror film by an electroless method, so an intermediate plating layer is interposed. Compared to the case where this method is used, manufacturing costs can be reduced, and the insulation performance can also be improved.

In addition, since the silver mirror film is formed after installing the space header, the manufacturing process is simplified and
There is no damage to the silver mirror film due to welding, etc., and heat retention performance is further improved.

As mentioned above, the present invention has excellent practical effects.

[Brief explanation of drawings]

FIG. 1 is a partially omitted vertical cross-sectional view of a vacuum insulated pipe according to the present invention. FIG. 2 is an enlarged cross-sectional view of FIG. A Heat insulation space 1 Inner tube 2 Outer tube 3.4 End plate 5 Chip tube 8 Getter 9 Oxide film 10 Silver mirror film

Claims (1)

[Claims] In a vacuum insulated pipe in which at least one of the inner tube (1) and the outer tube (2) is made of stainless steel, and the adiabatic space (A) is evacuated through the tip tube (5), the inner tube ( 1) and the outer pipe (2); both side end plates (3) and (4) forming a heat insulating space; communicate with the heat insulating space (A), and the opening thereof opens after the heat insulating space (A) is evacuated. a sealed chip tube (5); an oxide film (9) formed on the surface of the stainless steel tube forming the heat insulation space (A); and a Zr- A V-Fe ternary alloy non-evaporable getter (8); A silver plating solution is supplied through the chip tube (5) into the heat insulating space (A) in which the getter (8) is arranged, and electroless plating is performed. Silver mirror film formed directly on all or part of the surface of a stainless steel tube (10)
A vacuum insulated pipe made up of