JPH0245524B2 - KANNAGATEHOKONINIKUATSUSAOMOTSUTAKINZOKUKANNOSEIZOHOHO - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of manufacturing a metal pipe having a wall thickness difference in the longitudinal direction of the pipe, suitable for example as a tension leg or an oil country tubular goods.

Traditionally, fixed production platforms, in which structures are fixed to the seabed, have been used to produce oil (including gas) from offshore oil fields. However, as water depth increased, flexible production platforms were proposed. Tension leg platforms are one example.

A tension leg platform is a production platform floating on the ocean that is moored to an anchor on the seabed using so-called tension legs, which are made by screwing together a large number of steel tubular members. This tubular member, that is, the tension leg, is manufactured in unit lengths (usually about 12 m), and has a male thread (pin part) and a female thread (box part) at both ends. The wall thickness of the tube is thicker at both ends (connector portion). The tension acting on this tension leg constantly fluctuates due to wind power, wave force, tidal current force, and tidal force, and sufficient fatigue strength is required.

(Prior art) As a method to solve this problem, for example, in manufacturing tension leg materials, the connector part between the pin part and the box part is made of a forged product, and the straight pipe part in between is formed by press bending a steel plate and then welded. A suitable method is to manufacture the tension leg as a single piece, and then circumferentially weld the connector part and the straight pipe part to form an integrated tension leg. However, with the current welding technology, it is difficult to make the fatigue strength in seawater the same as that of the base metal for circumferential welds that receive axial force in the right angle direction.

Therefore, in anticipation of the quality deterioration of the welded part, we created a straight pipe part with a wall thickness difference in the longitudinal direction of the pipe by increasing the wall thickness at both ends of the straight pipe part by a certain length. The method of circumferential welding is suitable.

(Object of the Invention) The present invention was made in order to provide a straight pipe having a wall thickness difference in the longitudinal direction as described above (hereinafter referred to as a "differential thickness pipe"). Gansho 57
-184688 (Japanese Patent Application Laid-Open No. 59-76617). However, there are still problems that need to be corrected in the technique proposed by the above inventors. In other words, in the method proposed above, a differential thickness plate (hereinafter referred to as a single-sided differential thick plate) that has a plate thickness corresponding to the thin wall portion and thick wall portion of the pipe, and in which the difference in wall thickness of the thick wall portion extends toward the outer diameter side. This is a method for manufacturing tubes with different thicknesses. By the way, the following method is generally used to manufacture this single-sided thick plate.

Using a planar plate material having the same thickness as the thick portion of the differential thickness plate, the thin-walled portion is cut to a thinner plate thickness to produce a single-sided differential thickness plate.

In the process of rolling plate material, first the plate is rolled to a thickness corresponding to the thick part of the differential thickness plate, then the part corresponding to the thin part is rolled while rolling down the part corresponding to the thin part to the thickness corresponding to the thin part. A differential thick plate (hereinafter referred to as a double-sided differential thick plate) having a step in which the flesh portion extends symmetrically or almost parallel to the center plane in the thickness direction is manufactured. After that, one side of the overhanging portion of the thick portion of this double-sided differential thick plate is cut to produce a single-sided differential thick plate.

In this way, manufacturing a single-sided thick plate requires a cutting process to reduce the thickness of the thinner part.

In the present invention, when bending the double-sided thick plate produced in the above rolling process into a differential-thickness tube using a press bender, a die with a target level difference and a punch without a level difference are used to bend the double-sided thick plate produced in the above rolling process into a double-sided thick plate using a press bender. The present invention provides an inexpensive manufacturing method in which a thick portion of a thick plate is extruded to the outer surface of a tube and simultaneously bent and formed.

(Structure and Effect of the Invention) In the method of the present invention, a rectangular metal plate material having a relatively thick portion corresponding to the thick-walled portion of the pipe and a length equal to the length of the pipe is prepared. The plate material is approximately symmetrical with respect to the center plane in the thickness direction. While feeding this plate material stepwise in the width direction, a punch with a radius of curvature approximately equal to the inner radius of the tube and a punch with a step having two radii of curvature approximately equal to the outer radii of the thick-walled portion of the tube and the outer radius of the thin-walled portion of the tube are used. The thick part is extruded in the radial direction of the pipe using a die and simultaneously bent and formed. Next, the joints of this tubular body are welded to complete the tube.

Hereinafter, this invention will be explained in detail based on the drawings.

The pipe 1 to be manufactured is t ₁ as shown in Figures 1 and 2.
It consists of a thin wall portion 2 having a thickness of _t2 and a thick wall portion 3 that protrudes toward the outer diameter side and becomes thicker. First, the third
As shown in the figure, the plate thickness t ₁ ′, which is symmetrical with respect to the center plane C in the thickness direction of the plate material 4 and corresponds to the thin wall portion 2 of the pipe, is also symmetrical or protrudes toward the outer diameter side and the inner diameter side at a ratio that is almost the same. A double-sided thick plate 4 having a plate thickness t ₂ ' corresponding to the thick pipe portion 3 having a step is prepared.
In this case, the plate widths B ₁ and B ₂ of the double-sided thick plate 4 are respectively,
In order to obtain the desired outer diameter when the molding is completed and the final product is obtained, we have empirically determined the method of trimming the end surface of the plate in advance or the method of trimming the end surface of the plate after forming into a tubular body. Decide.

The thus prepared double-sided thick plate 4 is bent into a tubular shape using a press bender. FIG. 4 shows the punch 7 and die 9 of the press bender. The pressing portion 8 of the punch 7 has no step and its radius of curvature is equal to or slightly smaller than the inner radius _R1 of the manufactured differential thickness tube 1. The radius of curvature of the portion 10 of the die 9 corresponding to the thin tube portion 2 is the outer radius R ₂ of the thin tube portion 2.
The radius of curvature of the portion 11 corresponding to the thick-walled pipe portion 3 is made equal to or slightly smaller than the outer radius _R3 of the thick-walled pipe portion 3. A transition part 12 is formed between the thin pipe-corresponding part 10 and the pipe thick-wall part 11 of the die 9, in which the shape of the hole changes gradually in order to avoid a sudden change in the pipe wall thickness.

When the double-sided differential thick plate 4 is inserted between the punch 7 and the die 9, the pressing part 8 of the punch 7 contacts only the upper surface of the thick wall portion 6 of the double-sided differential thick plate 4, and presses against the upper surface of the thin wall portion 5. do not touch. The plate material 4 is bent as the punch 7 is pressed down by the forming pressure.
As shown in FIG. At the same time, it is bent to the target radius of curvature. In this way, the plate material 4 is fed little by little in the circumferential direction, and the tubular body that is bent in stages is formed into a tube 1 of different thickness with no steps on the inner surface of the tube and with steps on both the outer surfaces of the tube.

In addition to the manufacturing method of the differential thickness tube 1 in which the thick wall portion 6 of the double-sided thick plate 4 is extruded toward the outer surface of the tube, there is also a method of manufacturing the thick-walled double-sided thick plate 4 by providing a step in the punch and eliminating the step in the die. It is also possible to produce a tube with a different thickness by extruding the portion 6 toward the inner surface of the tube and having a step on the inner surface of the tube.

(Example) To give an example of a differential thickness tube manufactured using a small-scale experimental facility using the above method, the dimensions of the differential thickness plate are 4 mm in thickness at the thin wall section, 780 mm in length, and 780 mm in thickness at the thick wall section on both sides. Plate thickness 7.2mm, length 100mm, distance between thin and thick parts 10mm, effective plate width 255mm, total length 1000mm, material yield point 40Kg/mm ²
Class steel plate was used. The produced differential thickness tube had an outer diameter of 80 mm at the thin wall portion and an outer diameter of 83.2 mm at the thick wall portion, making it possible to manufacture a differential thickness tube in which the differential thickness section protruded in the outer diameter direction.

(Effects of the Invention) In this way, a double-sided thick plate, which is relatively easy to roll, is used to produce a differential thickness tube with a step in the outer surface direction at a low cost, and is used for the tension leg or oil country tubular goods.

[Brief explanation of the drawing]

Fig. 1 is a perspective view of a differential thickness tube manufactured by the method of the present invention, Fig. 2 is a sectional view of the thin wall portion and thick wall portion in the circumferential direction of the differential thickness tube, and Fig. 3 is a cross-sectional view of both sides before bending. FIG. 4 is a perspective view showing an example of the punch and die of a press bender used in the bending process of the present invention, and FIGS. 5a and 5b show the step extrusion process using the press bender. Cross-sectional view. 1...Differential thickness pipe, 2...Pipe thin wall part, 3...Pipe thick wall part, 4...Differential thickness plate material, 5...Plate thin wall part, 6...Plate thick wall part, 7...Punch, 9 ……dice.

Claims (1)

[Claims] 1 Prepare a rectangular metal plate material whose portion corresponding to the thick wall part of the pipe is relatively thick and whose length is equal to the pipe length, and bend this plate material in the width direction to form a tubular body. In the method of manufacturing a metal tube having a thin wall part and a thick wall part by welding a joint part, the plate material is substantially symmetrical with respect to a center plane in the thickness direction,
While feeding the plate material in steps in the width direction of the plate, a punch with a radius of curvature approximately equal to the inner radius of the tube and a die with steps each having two radii of curvature approximately equal to the outer radii of the thick wall section and the thin wall section of the tube are used. A method for manufacturing a metal tube having a wall thickness difference in the longitudinal direction of the tube, characterized by extruding the thick wall portion in the tube radial direction and simultaneously bending the tube.