JPS5819416B2 - Triple pipe manufacturing method - Google Patents

Description

Detailed Description of the Invention This invention relates to a state in which an inner pipe and an outer pipe are layered relative to a middle pipe when manufacturing triple pipes used for, for example, chemical plant piping, oil country tubular goods, oil conveyance piping, heat exchangers, etc. The present invention relates to a method for manufacturing a triple tube in which pressure is applied to the inside of the inner tube to expand the tube and bond the inner and outer tubes together in the vagina. Before or after expanding the tube, a heating expansion process for the entire length of the outer tube and a cooling contraction process for the inner tube are given as mutually independent processes, and expansion pressure is applied inside the inner tube. After expanding the inner tube and attaching the inner tube to the middle tube or the outer tube via the middle tube, the pressure applied to the vagina is released, and then the outer tube is cooled and contracted and the inner tube is heated and expanded. tube, middle tube,
This invention relates to a method for manufacturing a triple-layered pipe in which the inner pipe is tightly integrated.

Traditionally, double pipes, triple pipes, etc. have been used to improve performance such as not only pressure resistance but also rust prevention and corrosion resistance in chemical plant piping, oil country pipes, oil pipes, heat exchanger installed pipes, etc. Duplex pipes have come to be adopted, and their importance has recently increased as the needs for large-volume fluid transportation have increased.

By the way, in cases where the transportation piping for fluids that are corrosive or contain impurities, etc. is installed in a corrosive environment, the inner and outer tubes may be made of a corrosion-resistant material such as stainless steel pipes to prevent corrosion. A triple-walled pipe can be considered, which has a pressure-resistant function by making the middle pipe a carbon steel pipe, for example.

Therefore, as an important design condition for the triple tube, it is essential that the outer tube, middle tube, and inner tube be tightly integrated with each other through a sufficient interference.

Firstly, the temperature of the transport fluid inside the installed piping and the environmental temperature outside the pipe are often different under operating conditions, so sufficient heat conduction between the tubes in the triple-pipe structure must be achieved. This is because it is necessary to reduce the temperature difference between the tubes as much as possible, and in this case, it is desirable that the tubes be bonded and fixed together with as strong a pressure as possible.

Secondly, as mentioned above, the inner tube, middle tube, and outer tube are usually made of different materials, so they have different coefficients of thermal expansion, and if a temperature change occurs in such a structure, Differences in thermal expansion or contraction of the tubes may cause problems such as misalignment between the tubes, local buckling, stress concentration, and fatigue failure. This is because it is better to allow the three pipes to behave as one as possible by providing a sufficiently large interference based on the design.

Various triple pipe manufacturing techniques have been devised to meet these design conditions, and recently a type of triple pipe that connects three pipes together with a sufficient interference margin has been developed. Generally, the manufacturing methods include shrink fitting method and hydraulic pipe expansion method.

However, the conventional manufacturing method of the triple layer pipe has the following problems, which have been a bottleneck in manufacturing.

In other words, the problem with the former manufacturing method is basically based on the premise that it is unavoidable for manufacturing that each pipe material such as a joint pipe has plate thickness tolerances, flattened parts, etc. This means that shrink-fitting the materials at the base has the disadvantage that it is impossible with the actual processable temperature difference of 400° to 500°C.

To deal with this, it is theoretically conceivable to apply a mirror finish to the joint side surface of each material pipe by mechanical grinding or other means before shrink-fitting, but this would require a large number of man-hours. Particularly in the case of long, thin-walled pipes, it is necessary to achieve high precision and uniformity over the entire length of the pipe, and such processing is not only technically extremely difficult (as a result) It also has the disadvantage of being extremely costly.

Furthermore, it is necessary to provide a predetermined temperature difference between the inner tube, middle tube, and outer tube and to maintain the temperature difference constant along the entire length of the tubes when they are inserted and fitted together. Although this is possible with short tubes, it is extremely difficult to satisfy the conditions with long tubes.

On the other hand, in the latter case, as shown in FIG. 1, the outer tube 1, the middle tube 2, and the inner tube 3 are inserted and stacked one on top of the other with a sufficient gap between them so that they can be stacked relative to each other.

In this case, the (outer diameter, inner diameter) of the outer tube 1, middle tube 2, and inner tube 3 are respectively D', D2. D'2, D3. Let it be D'3.

After layering, a predetermined fluid pressure is applied inside the inner tube 3 to expand the tube, and as shown in FIG. The tube 3 and the middle tube 2 are integrally expanded in diameter and inscribed in the outer tube 1 at point B, and then the pressure is increased and the pressure is released at point 0, so that the outer diameter D3 of the inner tube changes from D3 to D'Q.
In addition, the inner diameter D'2 of the middle tube and the outer diameter D2 are Dl2. Iy2, and the inner diameter D' of the outer tube changes to α1, and the interference between the inner tubes 3 and 2 is -ΔDi, and the interference between the inner and outer tubes 2゜1 is -ΔDo, that is, the interference is a positive amount. .

However, as shown in FIG.
If the stress of
o is positive, that is, the interference is a negative amount, so even if the capacity pipe is expanded by 3°2.1, there will be a gap between the outer pipe 1 and the middle pipe 2, and between the middle pipe 2 and the inner pipe 3. There is a problem in that a positive gap is formed between the two and no fastening force is generated, and as a result, it becomes impossible to manufacture a triple pipe.

In other words, according to the seed hydraulic pipe expansion method, the material mechanical conditions such that the yield point of the outer pipe 1 is higher than that of the middle pipe 2 and the yield point of the inner pipe 3 is higher than that of the middle pipe are met. The disadvantage is that there are restrictions on combinations and selections.

The purpose of the present invention is to solve the problems in the method for manufacturing triple-pipe tubes based on the above-mentioned prior art, and to reduce the pressure in the inner tube, which is being cooled and heat-shrinked, with respect to the middle tube, which is inserted relatively into the heat-expanded outer tube. It is an object of the present invention to provide an excellent method for manufacturing a triple-layered tube, the gist of which is to manufacture the triple-layered tube by thermal contraction of the outer tube of the hindlimb and thermal expansion of the inner tube, which is applied to expand the tube.

Next, an embodiment of the present invention in accordance with the above object will be described below with reference to FIGS. 4-5.

Note that the same parts as in Figures 1, 2 and 3 will be described with the same reference numerals.

In the illustrated embodiment, 2 is a medium pipe made of a normal steel pipe made of carbon steel, has an average plate thickness tolerance, a flat part, and is specially subjected to secondary processing such as mechanical grinding and polishing. The initial outer diameter and inner diameter are D2. This is considered to be D'2.

Further, 1 is an outer tube made of a stainless steel tube, and its outer diameter and inner diameter are initially set to D'.

The inner tube 3 is also made of stainless steel, and its initial outer and inner diameters are D3°D'3.

Therefore, in this embodiment, the outer tube 1, the middle tube 2, and the inner tube 3
The yield points of the diameters are set to be higher in that order, and the diameters are Dl〉D
'1>D2>D'2>D3>D'3.

Therefore, due to the size relationship of the diameters mentioned above, the middle tube 2 is inserted into the outer tube 1, and the inner tube 3 is inserted into the middle tube 2 and set as shown in Fig. 4. When the coil heater 4 is wound and set to a predetermined temperature, the outer tube 1
The inner diameter of p'1 to D'7. The diameter is increased to .

Further, a plug body 7 having a plug body 5 and a liquid supply hole 6 is set at one end of the inner tube 3, and when ice water 8 as a pressure medium and a cooling medium is supplied into the inner tube 3, the outside of the inner tube 3 is Diameter D3 is D33
The diameter is reduced to

Therefore, while the cooling of the inner tube 3 is stopped, the outer tube 1
When heating is also stopped and the supply water 7 is pressurized, the inner pipe 3 is expanded drawing a diameter increasing curve as shown in Fig. When it comes into contact with the inner surface of the middle tube 2 and is further pressurized, it is expanded from the opening to C, and the middle tube 2 is also expanded accordingly, and its outer diameter D2 is increased from the opening to C'.

When the inner tube 2 is expanded and its outer diameter D2 is increased to Pa, it becomes equal to the heating inner diameter D'11 of the outer tube 1, and if pressure is continued to be applied there, the inner tube 3 becomes eight. The diameter of the inner tube 2 is increased from 1 to 2, and the outer tube 1 is increased from 2 to 2.
The pipe was expanded to

In this way, the three pipes 1, 2, and 3 are joined together and integrally increased in diameter to 2, 2', and 2'', and when the joined diameter DS is reached, the expansion pressure is released and the diameter increase is stopped.

Therefore, the inner tube 3 is reduced in diameter from 2 to E, and its outer diameter is D'3.
3, and on the other hand, the inner diameter D' of the outer tube 1 is reduced from D'1 to D'11 to D'11.

Therefore, when water is drained from inside the inner pipe 3 and the temperature is brought to ambient temperature, the temperature is raised, and the outer diameter is expanded from the wood to the inner diameter, which is equal to the original reduced inner diameter D//4 due to the release of pressure in the middle pipe 2. Reverse between,
In other words, an interference of -ΔDi is formed.

On the other hand, due to the natural cooling of the outer tube 1 due to the natural cooling of the outer tube 1, the inner diameter of the outer tube 1 is further reduced from the hole to Dl, which is the original reduction in the outer diameter of the inner tube 2 due to the release of the pressurizing force. Outer diameter D''
2, an opposite interference of -ΔDo is formed.

Therefore, the three pipes are tightly connected and integrated into one body through the interference margins ΔDo and ΔDi.

The embodiments of the present invention are not limited to the above-mentioned embodiments, and a case where the order of yield points of the outer tube, middle tube, and inner tube is reversed from the above embodiment is also considered as an embodiment, and it is clear from FIG. Similarly, -ΔDi, -ΔD due to thermal contraction of the outer tube and thermal expansion of the inner tube after the application of pressure for expansion is released.
o can be obtained.

Further, the heating expansion process for the outer tube and the cooling contraction process for the inner tube are only one event in the embodiment described above, and may be performed prior to relative overlaying, and the selection before and after the two processes can be made in various ways as independent events. There are combinations of

Furthermore, various heating and cooling means can be employed as appropriate, and various means can also be used for the tube expansion pressure.

As described above, according to the present invention, the inner and outer tubes are layered relative to the middle tube, and either before or after the layering process, the heating expansion process for the outer tube and the cooling contraction process for the inner tube are performed independently of each other. By applying this as a process, firstly, there is an effect of increasing the degree of freedom in the relative overlapping fitting of the three inner and outer pipes, and it is possible to freely perform overlapping of the raw pipes without secondary processing such as mechanical grinding. This has the effect that a desired long tube can be fitted in a predetermined manner.

There is also the effect that the tube expansion stress for obtaining the interference can be controlled in advance before the tube expansion pressure is applied.

Thus, by applying expansion pressure to the inner tube to expand the tube, and then thermally shrinking the outer tube and thermally expanding the inner tube, it is possible to reliably create a tightness between each tube. Become,
Also, without secondary processing such as the above-mentioned grinding, the plate thickness tolerance,
General commercially available steel pipes with flat parts can be used, and the economical benefits of using the material pipes are extremely large and excellent.

Furthermore, since it is possible to combine the outer, middle, and inner tubes in any order of their yield points, there are no restrictions on material strength selection, and the tightness can be reliably obtained, a remarkable effect not found in conventional methods. .

Furthermore, since it is possible to adjustably change the heating temperature for the outer tube and the cooling temperature for the inner tube, there is an effect that the tightening force can be freely controlled through free design of the interference.

In addition, heating and cooling can be applied uniformly to the inner and outer tubes over the entire length, so the thermal expansion and contraction of the inner and outer tubes is uniform not only for short tubes but also for long tubes, and uniform for medium tubes. There is also the advantage that tightness is formed, which results in variations in product accuracy and improves yield.

Further, by using the method of the present invention, there is an advantage in application that manufacturing of multiple tubes such as quadruple tubes and quintuple tubes can be developed.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of a pipe layered cross section in a triple pipe manufacturing method based on the prior art, Fig. 2 is an explanatory diagram of the relationship between stress and expansion pressure for the three pipe diameters based on the prior art, and Fig. 3 is a diagram of the prior art. Diameter stress explanatory diagram of triple pipe, which cannot be manufactured with
FIG. 5 is an explanatory view of one embodiment of the present invention, FIG. 4 is a schematic cross-sectional view of the manufacturing process, and FIG. 5 is an explanatory view of the relationship between diameter and stress. 1...outer pipe, 2...middle pipe, 3...
...Inner tube.

Claims (1)

[Claims] 1. A method for manufacturing a triple-layered pipe in which an outer pipe, a middle pipe, and an inner pipe are layered relatively, and the inner pipe is expanded to have a degree of fitting,
An inner tube and an outer tube are layered relative to the middle tube, and a heating expansion process for the outer tube and a cooling contraction process for the inner tube are performed as mutually independent processes either before or after the relative layering process. Then, after applying pressure to the inside of the inner tube to expand the inner tube, the outer tube is thermally shrunk and the inner tube is thermally expanded to tightly fasten the outer tube, middle tube, and inner tube. A method for manufacturing a triple pipe, characterized by: