JPS5829650A - Manufacture of heat insulating double pipe for low-temperature fluid - 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 The present invention relates to a method for manufacturing an insulated 21F pipe for cryogenic fluids.

4) Insulated double pipes are used for pipes for flowing low-θ1 fluids such as liquefied natural gas and liquefied nitrogen, which have a heat insulating layer formed in the inner pipe, outer pipe, and the gap between the inner and outer pipes. be done. In this case, if the temperature of the low-temperature fluid is relatively high or the pipe length is short, it may be difficult to infiltrate from the outside even if a heat insulating layer is placed on the outside of the pipe. The effects of heat can be prevented. However,
In cases other than the above, use insulated double pipes and insulate both the inner and outer pipes. It is required that j be a vacuum layer or a pearlite-filled iA* empty layer to minimize the amount of heat entering from the outside.

For piping using such a double-walled pipe, ]' JJ
A certain length of evacuated, insulated double pipes (hereinafter referred to as unit pipes) are manufactured at A, and they are joined during on-site construction. When a low-temperature fluid is flowed through the pipe constructed in this way, the inner tube through which the low-temperature fluid flows is cooled to near the temperature of the low-temperature fluid, causing contraction of each unit tube, but the outer tube remains at room temperature and shrinks. doesn't happen.

In a partial tube, both ends of the inner tube are fixed to both ends of the outer tube via a cover plate, and since the inner tube may break due to the above-mentioned contraction, conventionally, beads were attached to both ends of the inner tube. join,
This bead was fixed to both ends of the outer tube via the lid plate at the end.

The use of bellows not only incurs extra costs, but also requires work to join (weld) the inner pipe to the bellows, and requires time and effort to clean and dry the inside. However, the reality is that there is no other means to absorb the shrinkage at low temperatures.

In light of these circumstances, the inventors of the present invention have conducted various studies and found that, without using a bellows, the inner tube is fixed to the outer tube via gap cover plates provided near both ends of the inner and outer tubes. We have found that it is possible to manufacture unit tubes by doing this.

When a 5US304 tube is used as the inner tube, when it is cooled to the temperature of liquefied nitrogen (-196° C.) -1, it shrinks by 0.28% compared to when it is at room temperature. Conversely, in the case of a tube with both ends fixed, if the tube is pulled
This means that the same tensile stress as when stretched by % is applied.

E=- (ε where E: Young's modulus 1,930,000 to 9/cJ (
ε: 028% 0.0028 σ: From the tensile stress generated in the pipe, σ = 1,930,000X0.0028 = 54
00 kg/cll, which is approximately equal to the tensile strength of S LT S 304.
300 kg/* or more. ) Therefore, from this number,
Since the inner tube was quite likely to break, the problem was solved by inserting a bead.

The present inventors focused on the fact that Young's modulus is not constant (and decreases as stress increases), and 5US3
In the case of No. 04, it was calculated that the tensile stress under the above conditions was less than the stiffness (2100 kg/d or more according to JIS G3459 K).

Therefore, it was found that even without using a bellows, the inner tube would not break due to shrinkage at liquefied nitrogen temperature, so a unit tube was manufactured without a bellows, and this was connected by welding. As a result of various tests such as connecting the tubes and flowing liquefied nitrogen through them, it was confirmed that the insulated double tubes made using this method were sufficiently usable for practical use.

One embodiment of the method for manufacturing a unit pipe according to the present invention will be described. The material used is 5US304 for both the inner and outer tubes, and the size of the inner tube is 2 B x t2. The outer tube was 4BXt2. As a heat insulating layer, five layers of polyester film with aluminum deposited on one side were wrapped around the inner tube. S U
Both the inner and outer gaps were closed with a S304 cover plate, and the vicinity of both ends of the inner (5) tube was fixed near both ends of the outer tube via this cover plate by welding.

Thereafter, the gap between both tubes and both lid plates was evacuated. The time required for vacuuming was 100℃, 3
The time was 170 hours, including 6 hours of heating and evacuation, and the degree of vacuum was 1×10-') when 7 yen of liquefied nitrogen was flowed.

The two thus manufactured units were connected by welding and using K611 connecting pipes. After wrapping the connecting portion of the connecting pipe with heat insulating material and evacuating it in the same manner, a cooling test was performed by flowing Yf cleaning liquid nitrogen.

As a result, the heat insulating layer reached the desired degree of vacuum, and no leakage occurred at the weld despite the shrinkage of the inner tube.

This liquefied nitrogen was removed and the temperature of the inner tube was returned to room temperature, and this cooling and heating to room temperature was repeated, but no abnormality occurred.

In addition, as mentioned above, S U S 3 (14 is -196
It shrinks by 0.28% at ℃, but when it is returned to room temperature,
0.17% remains as permanent strain, and the length of the outer tube does not change at room temperature or when cooling in the #1 tube.
Since Bu 1 is longer than the outer tube by a permanent strain of 0.17% at room temperature, it will bend or meander within the outer tube, and some of it will remain as compressive stress.

However, since it contracts again and becomes a straight tube when cooled, there is no problem in practical use.

In this way, the tensile stress caused by the contraction of the inner tube
If the proof stress is less than sFl, there is no possibility of breakage due to shrinkage even without using a bellows as in the conventional case.

In the above embodiment, a polyester film-wound vacuum layer with aluminum vapor deposition on one side is used as the heat insulating layer, but a simple vacuum layer or a vacuum layer filled with other heat insulating material (for example, perlite) may also be used.

According to the method of the present invention, there is no need to use bellows when manufacturing a heat-insulating double pipe for low-temperature fluids, so it is possible to eliminate the various disadvantages mentioned at the beginning. It became.

Patent applicant Tizan Co., Ltd. (7) 293-

Claims (6)

[Claims] (1) In the manufacturing method of an insulated double pipe consisting of an inner pipe, an outer pipe, and a heat insulating layer formed in the gap between the inner and outer pipes, the inner pipe is replaced with a gap cover provided near both ends of the inner and outer pipes. A method of manufacturing a heat-insulating double pipe for low temperature fluid, characterized by fixing it to an outer pipe via a plate. (2) The method for manufacturing a heat-insulating double pipe for low-temperature fluid according to claim 1, wherein the tensile stress applied to the inner pipe due to contraction caused when low-temperature fluid is flowed into the inner pipe is less than the yield strength of the inner pipe material. . (3) The method for manufacturing a heat-insulating double pipe for low temperature fluid according to claim 2, wherein the inner pipe is made of stainless steel pipe. (4) The method of manufacturing a heat-insulating double pipe for low-temperature fluid according to claim 1, wherein the heat-insulating layer is a vacuum layer. (5) The method for manufacturing a heat-insulating double pipe for low-temperature fluid according to claim 1, wherein the front tFi heat-insulating layer is a vacuum layer having a polyester film wound layer. (6) The method of manufacturing a heat-insulating double pipe for low-temperature fluid according to claim 1, wherein the heat-insulating layer is a pearlite-filled layer.