JPS5916621A - Manufacture of double steel pipe by drawing and pipe expansion - Google Patents

Abstract

PURPOSE:To manufacture a double steel pipe which is excellent in corrosion resistance and hydrogen sulfide resistance, by using a metallic pipe which is excellent in corrosion resistance and hydrogen sulfide resistance, and a high tension steel pipe for the inside pipe and the outside pipe, respectively, and executing the pipe expansion simultaneously with cold drawing by a stepped plug. CONSTITUTION:A high tension steel pipe is used for an outside pipe blank pipe 1, an inside pipe blank pipe 2 having corrosion resistance and hydrogen sulfide resistance is inserted into said pipe, and is made to pass through between a plug having a plug head 9 and a plug drum 10, and a die 8. The blank pipes 1, 2 are reduced as to its diameter by the die 8, are rolled by the plug drum 10, and since tensile residual stress is left in the inside pipe 2, pipe expansion is executed to the inside pipe 2 by the plug head 9 whose diameter is a little larger than the plug drum 10. In this way, the outside pipe 1 is subjected to minute pipe expansion within a range of elastic deformation, and the drawn pipe compresses the inside pipe 2 by elastic compression stress of the outside pipe 1, and on the other hand, the inside pipe 2 is brought to permanent deformation by plastic deformation, and compression residual stress is left in the inside pipe 2.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a double-walled steel pipe having excellent corrosion resistance, hydrogen sulfide resistance, and the like.

Due to rising prices of petroleum products and the effective use of petroleum resources, oil and gas fields are being developed in areas that were previously undeveloped due to profitability considerations. For example, recovery of oil and natural gas, which contain a large amount of hydrogen sulfide, is one example, and in this case, steel materials that are resistant to hydrogen sulfide are required.

Moreover, as the depth of oil wells continues to increase, stronger steel materials are required.

Conventionally, efforts have been made to produce high-tensile, hydrogen sulfide-resistant steel by changing the steel composition and heat treatment conditions. However, as a basic property of steel, as the tensile strength increases, the hydrogen embrittlement resistance in a hydrogen environment decreases, so it has reached the limits of metallurgical technology to manufacture high tensile hydrogen sulfide resistant steel pipes using steel. It is thought that there are.

On the other hand, alloys such as K-Monet and Incollet, or advanced metals (superalloys) have good hydrogen sulfide properties and are sometimes used in special parts that require hydrogen sulfide resistance. However, these alloys are expensive, and it is impossible to manufacture hydrogen sulfide-resistant pipes only from these alloys themselves.

Therefore, by cold bonding these alloys to the inside of a high-strength tube with steel as the main tube (outer tube), high-strength steel tubes are used as strength members, and steel tubes using stainless steel, advanced metal, etc. as corrosion-resistant alloys are created. If it can be easily manufactured, inexpensive corrosion-resistant high-strength steel pipes can be obtained.

Many methods for manufacturing such double pipes have been proposed in the past.

Explosive molding is a method that has been proposed so far.

Another method proposed is to reduce the diameter of the outer tube by pulling it out, roll it, and make it tightly contact with the inner tube.However, even if this method can produce a double tube with high production efficiency, Since compressive residual stress cannot be left in the inner tube as in the case of the method, the hydrogen sulfide resistance is not good.

FIG. 1 shows an example of a conventional explosion molding pipe expansion method, and FIG. 2 shows an example of a hot internal pressure pipe expansion method using hydrostatic pressure. Figure 1 shows a method in which an outer tube 1 is fixed to a die 3, and a mass 4 passed through the center of the inner tube 2 is exploded to bring the inner tube 2 into close contact with the outer tube 1, producing a double-walled tube with high precision. can do.

Further, in FIG. 2, the outer tube 1 is heated by high frequency with a coil 5, and the inner tube 2, which has been cooled with water, is expanded by hydrostatic pressure 6 and brought into close contact with the outer tube 1.

However, none of these can withstand mass production, and is not suitable for producing long items.

Fig. 3 shows an example of the manufacturing method by drawing and expanding the pipe using the plug 7, but it is difficult to process the ends, and the outer pipe 1 and the inner pipe 2 are difficult to process.
Adhesion is also weak.

The method shown in FIG. 4 is a method in which a die 3 is used to draw out the compressed tube, but this method does not leave any compressive residual stress in the inner tube 2.

The present invention has been developed based on consideration of the problems of the prior art as described above.
This paper proposes a completely new method for manufacturing double-walled pipes that overcomes all of these drawbacks. The manufacturing method involves drawing and expanding a double steel tube, which is characterized by using a tube and performing cold drawing with a stepped plug and at the same time slightly expanding the tube. It leaves compressive residual stress in the inner tube, suppresses the diffusion of hydrogen from the inner surface of the pipe, protects the outer tube from hydrogen and other caustic atmospheres, and also makes it possible to mass-produce long tubes. . .

The present invention will be explained in detail below.

FIG. 5 is a schematic diagram showing the method of manufacturing a double steel pipe by drawing and expanding according to the present invention. As shown in FIG. 5, first insert Siragua and expand through the die 8. . At this time, the relationship between the plug diameter and the die hole diameter is the die diameter J.

Plug head diameter Dl Zorag abdominal diameter D2 Pulled outer tube wall thickness t’s Pulled inner tube wall thickness 1゜ Then Do−D2+μ(to+t+), becomes. Here, μ is the rolling ratio.

Further, if the tube expansion rate is η, then D2 = D1 (1-η), and it is sufficient that -0,002≦η≦001.

Therefore, the relationship between die diameter and plug head diameter is 0.99
8) Ox) becomes 0.990. Further, there needs to be a close relationship between the rolling ratio and the tube expansion ratio.

If the tube expansion ratio is within this range, the tube can be expanded easily after rolling.

The above schematic diagram is shown in Fig. 5. In Fig. 5, the raw pipe 1
, 2 are reduced in diameter by a die 8 and rolled by a plug belly 10.

Until this trench, tensile residual stress generally remains in the inner pipe, so
Expand the inner tube using a plug head with a diameter slightly larger than the plug belly. At this time, the outer tube undergoes minute expansion within the range of elastic deformation. Therefore, after the pipe is pulled out, the inner tube is compressed by the elastic compressive stress of the outer tube, while the inner tube undergoes permanent deformation due to plastic deformation, so that compressive residual stress remains in the inner tube.

Figures 1 to 3 are schematic diagrams showing a conventional method for manufacturing a single-dish type double tube, Figure 4 is a schematic diagram showing a conventional method for manufacturing a pull-out type double tube, and Figure 5 is a schematic diagram showing a method for manufacturing a conventional single-dish type double tube. Schematic 1 showing the method for manufacturing a double-walled pipe by cold drawing and expanding pipes: Outer tube, 2...
Inner pipe material tube, 1'...Outer tube after being drawn, 2'...Inner tube after being drawn, 3...Split die, 4...Explosive powder, 5...High frequency coil, 6... ...Water pressure, 7...Plug, 8...Dice, 9...Plug head, 10...Plug belly.

Agent Patent Attorney Masaaki Akizawa 2 others

Claims (1)

[Claims] (1) Drawing expansion of a double steel pipe characterized by using a high-strength steel pipe for the outer pipe and a metal pipe with excellent corrosion resistance and hydrogen sulfide resistance for the inner pipe, and performing pipe expansion at the same time as cold drawing using a stepped plug. manufacturing method.