JPH04210193A - Vacuum insulated pipe - Google Patents

Abstract

PURPOSE:To extend the fatigue life of a vacuum insulated pipe due to thermal compression by forming a membrane into a U-shaped cross section having a semicircular portion and a pair of rectilinear portions leading to both ends of the semicircular portion. CONSTITUTION:A membrane 15 has a U-shaped cross section which consists of rectilinear portions 17 of fixed length L leading to both ends of a semicircular portion 16 whose radius R is half the thickness (t) of the radial direction of a vacuum insulated portion 3. The rectilinear portions 17 are welded at their respective ends to the outer periphery of an inner pipe 1 and to the inner periphery of an outer pipe 2, respectively. The length L of each rectilinear portion 17 is set at one eighth to one fourth the radius R of the semicircular portion 16. Because the rectilinear portions 17 are formed in the membrane 15, the membrane 15 has a more flexible structure. The effect of reducing distortion of the welding portion of the membrane 15 for the inner and outer pipes 1,2 and that of the membrane 15 itself is exhibited. When the inner pipe 1 is thermally compressed by reason of the temperature of a fluid inside the tube, the membrane 15 is deformed in such a way as increasing the length L of each of the rectilinear portions 17 of the membrane 15, thereby absorbing this thermal compression and extending the fatigue life of a vacuum insulate pipe to a large extent.

Description

[Detailed description of the invention]

[00011

[Field of Industrial Application] The present invention relates to vacuum insulated pipes for civil and industrial use, which are used for district heating and cooling, transfer of high-temperature and low-temperature fluids, and the like. [0002] [0002] A conventional vacuum insulated pipe of this type is shown in FIG.
As shown in FIG. 4, it has an inner tube 1 and an outer tube 2, a vacuum insulation section 3 is formed between the inner tube 1 and the outer tube 2, and a heat insulation material 4 is filled in the vacuum insulation section 3. However, both ends of the vacuum insulation section 3 are sealed with an annular membrane 5. Normally, both the inner and outer pipes 1.2 are made of steel pipes, the heat insulating material 4 is made of powder such as diatomaceous earth, and the membrane 5 is made of thin stainless steel. The membrane 5 has a semicircular cross-sectional shape with a radius r equal to one half of the radial thickness t of the vacuum insulation section 3, and both ends of the semicircle meet the outer periphery of the inner tube 1 and the outer tube 2. Welded to the inner circumference. And Figure 3
As shown on the right side of the drawing, when the inner tube 1 undergoes thermal expansion and contraction due to the temperature of the inner tube fluid, the membrane 5 is deformed to absorb this thermal expansion and contraction. [0003]

[Problems to be Solved by the Invention] However, in the above-mentioned conventional vacuum insulated pipe, when the inner pipe 1 expands and contracts due to heat, as shown on the right side of FIG. Large strains occur in the weld and in the membrane 5 itself. Therefore, if the inner tube 1 undergoes repeated thermal expansion and contraction, there is a problem that the membrane 5 may suffer fatigue failure. [0004] Therefore, an object of the present invention is to reduce the strain generated in the welded portion between the membrane and the inner and outer tubes and the membrane itself, and to extend the fatigue life due to thermal expansion and contraction. [0005]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a membrane with a U-shaped cross-section having a semicircular portion and a pair of linear portions continuous to both ends of the semicircular portion. It is something. [0006]

[Operation] According to such a structure, by providing the straight portion, the membrane has a more flexible structure, which has the effect of reducing strain occurring in the welded portion and the membrane itself. [0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 and 2 show a vacuum insulated pipe according to an embodiment of the present invention. Here, the membrane 15 is formed by continuously forming linear portions 17 of a constant length L at both ends of a semicircular portion 16 whose radius R is half of the radial thickness t of the vacuum insulation portion 3. It has a letter-shaped cross-sectional shape. The tip of each straight portion 17 is welded to the outer circumference of the inner tube 1 and the inner circumference of the outer tube 2, respectively. The length L of the straight part 17 is equal to the length L of the semicircular part 16.
The radius R is set to 1/8 to 1/4 of the radius R of . [0008] According to such a configuration, the membrane 15
By forming the straight portion 17 in the membrane 15, the membrane 15 has a more flexible structure. Therefore, the effect of reducing the strain generated in the welded portion between the membrane 15 and the inner and outer tubes 1.2 and in the membrane 15 itself is exhibited. Specifically, as shown in the right part of FIG. 1, for example, when the inner tube 1 expands and contracts due to the temperature of the fluid within the tube, the membrane 15 deforms so that the length of the straight portion 17 of the membrane 15 increases or decreases. This absorbs this thermal expansion and contraction. This has the effect of significantly extending fatigue life. [0009] (Specific example) Inner pipe 1: Gas pipe with nominal diameter 125A (SPG38) Outer pipe 2
: Steel pipe (STK41) membrane 15 with nominal diameter 300A
: Stainless steel plate (SUS304) with a thickness of 1 inch+ was processed and then solution annealed Radius R of semicircular part 16: 41 Length L of straight part 17: 10 mm Welding method of straight part 17: TIG welding under the above conditions When a vacuum insulated pipe was prototyped, the fatigue life of the membrane 15 was approximately five times longer than that of a conventional pipe. Note that the reason why the membrane 15 was solution annealed was to remove residual stress caused by processing and to form a complete austenite structure. [00101] [Effects of the Invention] As described above, according to the present invention, the cross-sectional shape of the membrane is U-shaped, which has a semicircular part and a pair of continuous straight parts at both ends of the semicircular part. The presence of this section gives the membrane a more flexible structure, which can reduce strain occurring in the weld and the membrane itself. Therefore, the fatigue life of the membrane can be significantly extended, and fatigue failure of the vacuum insulation section can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a vacuum insulated pipe according to an embodiment of the present invention.

FIG. 2 is a left side view of the vacuum insulated pipe of FIG. 1;

FIG. 3 is a cross-sectional view of a conventional vacuum insulated pipe.

FIG. 4 is a left side view of the vacuum insulated pipe of FIG. 3;

[Explanation of symbols]

1 Contents 2 Outer tube 3 Vacuum insulation section 15 Membrane 16　Semicircular part 17 Straight section

Claims (1)

[Claims] 1. A vacuum insulated pipe comprising an inner tube and an outer tube, a vacuum insulated section is formed between the inner tube and the outer tube, and both ends of the vacuum insulated section are sealed with an annular membrane, comprising: A vacuum insulated pipe characterized in that the cross-sectional shape of the membrane is U-shaped, having a semicircular portion and a pair of linear portions continuous to both ends of the semicircular portion.