JPS58324A - Manufacture of double pipe - Google Patents

Abstract

PURPOSE:To manufacture a double pipe which has excellent sticking properties, a superior heat quantity flow rate ratio, and superior boundary heat conduction resistance by fitting an internal tube into an external pipe which has a greater coefficient of thermal expansion than the internal pipe and introducing a high- temperature pressurized fluid into the pipe, and thus expanding the both in press contact. CONSTITUTION:An external pipe uses a metal, such as Al, which usefully accelerates heat conduction and is surface-worked easily, and is provided frequently with longitudinal grooves, raised fins, transfer fins, etc., on the external surface for accelerating heat conduction. An internal tube suitably uses a material, such as Ti, which has corrosion resistance and enough hardness to resist mechanical internal pipe surface washing for a countermeasure to contamination, and is reducible in thickness for reduction in cost. As a pressurized fluid, about 250- 400kg/cm<2> pressurized water is used favorably, and working temperature is only about 20-30 deg.C higher than in-use temperature while maximum temperature is determined in accordance with the creep characteristics of the materials with attention paid to work environment and safety.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing double-walled tubes useful, for example, as heat exchanger tubes.

Possible methods for crimping the inner and outer tubes made of different materials include a drawing method and a crimping method using pressure fluid (pressurized water). However, for example, the heat exchanger tube of an ocean temperature difference power generation plant uses a double tube that uses a titanium tube as the inner tube and an aluminum tube with vertical fins as the outer tube. It is difficult to carry out the drawing method due to the fins formed on the inner tube.Therefore, pressurized water is introduced into the inner tube to expand the tube.
The method of crimping the outer tube is not restricted by the surface shape of the outer tube, which increases its applicability.

However, in this case, if the working pressure water is at room temperature, and if the temperature when using the crimped double pipe is much higher than room temperature, the thermal expansion coefficient of the outer aluminum pipe will be lower than that of the inner titanium pipe. Since the outer tube expands more than the inner tube, the crimp loosens. In extreme cases, a gap may be created, increasing the heat transfer resistance at the crimp boundary and reducing the heat exchange effect.

The present invention has been made to improve such drawbacks, and in manufacturing a double tube consisting of an inner tube that forms a fluid passage and an outer tube that promotes heat transfer, the inner tube and the inner tube undergo thermal expansion. After fitting an outer pipe with a high ratio, a pressure fluid having a temperature higher than the temperature when the double pipe is used is fully introduced into the inside, and the two are expanded and crimped. This is a complete summary of the manufacturing method.

The outer tube of the present invention is made of a metal that is useful for promoting heat transfer and whose surface is easy to process; for example, aluminum is suitable. To promote heat transfer, vertical grooves (fluted pipes), cut and raised fins, rolled fins, etc. are provided on the outer surface.

These are processed by extrusion, cutting, rolling, forging, etc. The inner tube is made of a material that is resistant to seawater corrosion and can withstand cleaning of the inner surface of the tube with sponge balls, carporundum balls, slurry brushes, etc. as a countermeasure against biological contamination. Materials that can be made thin to reduce costs are suitable, such as titanium, Stainless steel is used.

Water is suitable as the pressure fluid, but oil may also be used.For example, when used for ocean temperature difference power generation, the operating temperature of double pipes is usually in the range of 0 to 35°C, so in this case, In this case, the temperature of the pressure fluid required for crimping the inner tube and the outer tube is preferably a high temperature of about 60° C., for example. The temperature of this pressure fluid can be increased to 100°C or higher depending on the working environment and safety considerations, but theoretically the maximum temperature should be set taking into account the amount of creep or creep characteristics during processing. It is determined. However, since active shrink fit crimping is not necessarily necessary, it is sufficient to have the effect of reducing the heat transfer resistance at the crimping boundary. Preferably 50℃
or more pressure fluid is used.

Next, examples and test results will be shown.

As an outer tube, the wall thickness is 0.5 to 1. OtIR's aluminum 6063-T6, 6061-T6 is used, and the inner tube is made of titanium JIS type 1 with a wall thickness of 0.2 to 0.3 m.
After fitting both, 250 to 400 as pressure fluid.
Introduce water under pressure of ky/cl G and raise its temperature to 60°C.
The pressure bonding process was performed when the tube temperature reached 60°C. For comparison, pressure bonding was performed with the pressure water at room temperature. Regarding the double tube obtained by each,
Tests were conducted on the heat flow rate ratio and the heat transfer resistance of the crimp boundary.

The results are shown in the table below.

table (Note) Measured at the temperature at which ammonia condenses.

Aluminum pipes are used that have vertical grooves on the entire outer surface in the direction of the pipe axis.

As is clear from the above table, it was found that the double-walled tube obtained when high-temperature pressure water was used had good adhesion and was excellent in both the heat flow rate ratio and the boundary heat transfer resistance.

Unlike the drawing method, the method of the present invention is not limited to the outer tube shape, and therefore has high applicability. For example, it is useful as a processing method for increasing the corrosion resistance of the inner surface of a material that has good workability but lacks corrosion resistance, such as the aforementioned aluminum tube. Therefore, it can be applied to the production of heat exchanger tubes and other human-powered heat exchangers for the ocean temperature difference power generation plant, and heat exchangers that use raw seawater or medium- to low-temperature highly corrosive water for nuclear power plants.

Patent applicant: Sumitomo Light Metal Industries, Ltd. Representative Patent Attorney Hidetake Komatsu

Claims (1)

[Claims] l When manufacturing a double-layered tube consisting of an inner tube that forms a fluid passage and an outer tube that promotes heat transfer, the inner tube is fitted with an outer tube that has a higher coefficient of thermal expansion than the inner tube, and then the inner tube is 1. A method for producing a double pipe, which comprises introducing a pressure fluid having a temperature higher than the temperature during use of the double pipe into the double pipe, and expanding and crimping the two.