JPS5976617A - Manufacture of metallic tube having difference of thickness in longitudinal direction - Google Patents

Abstract

PURPOSE:To obtain inexpensively a tension leg material of a production platform without forging by bending a square metallic plate in which a part corresponding to thick part of the tube is thick into a tubular body and welding the joint. CONSTITUTION:A tube 1 to be manufactured consists of a thin part 2 and a thick part 3 bulged to outer diameter side. A plate 11 from which the tube 1 is manufactured is made by cutting the central part of a thick plate by machining. Or, it can be obtained easily by forming a thin part 16 in a plate 15 in which a thick part 17 is bulged vertically from the thin part 16 by increasing rolling reduction during rolling of the plate, and a plate 11 is made by scraping one side of the thick part 17. The length and width of the plate 11 are made as specified and thickness t3 of the thick part 13 is made slightly thicker than the thick part 3 of the tube. Then, the plate 11 is bent by a press bender etc. to make the radius of curvature of neutral face of thick part 3 of the tube nearly coincide with the radius of curvature of the thin part 2 of the tube. The joint 9 of the tubular body 8 is welded to obtain a tube 1.

Description

[Detailed description of the invention] Regarding the method.

In recent years, the development of offshore oil fields (including gas fields) has become increasingly deep-sea, and the development of offshore oil fields exceeding 500 meters in depth is also being considered.

Conventionally, open-bottom 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 increases, a problem has arisen in which the natural period of the structure approaches the period of waves.

In order to avoid this problem of resonance with the wave cycle, a flexible production platform was devised. One example is the tension leg platform.

A tension leg platform is a production platform floating in the ocean that is moored to a portion of an anchor on the ocean floor using so-called tension legs, which are screw-connected numerous steel tubular members.

Offshore production graft forms are forcibly submerged to some extent, so that excess buoyancy always acts on them.

Therefore, the tubular abduction is always under tension, i.e., towards the ocean, which is why it is called a tension leg platform.

The tubular part is manufactured with a unit length of usually about 12n,
Both MMs are provided with male threads (bottle part and female box part), but the wall thickness of the tube is thicker at both ends (connector part) to protect the strength of the threaded parts. The tubular members are screwed together one by one and lowered from the production platform to the seabed, with the lower end fixed to a portion of the anchor on the seabed and the upper end fixed to the production platform. The production platform is used until the oil or waste to be extracted is exhausted, and its service life spans more than 20 years.

The production platform changes from time to time during the period of use1-
Therefore, the buoyant force acting on the production platform changes as well. Therefore, the tension acting on the tension leg is constantly changing,
The tubular members constituting this are required to have sufficient fatigue strength in seawater.

To solve this problem, for example, in the manufacture of tension leg materials, part of the connector between the pin part and the box part is manufactured by forging, and the straight W T415 in between is manufactured by forming and welding a steel plate by press bending etc. However, it is conceivable that a part of the connector and the straight pipe part are then circumferentially welded to make a tension leg of good quality.

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 first fabricated a straight pipe part with a wall thickness difference in the longitudinal direction of the pipe by thickening the wall thickness at both ends by a certain length, and then the connector. A possible method is to weld the area and the circumference.

The present invention has been made to solve the above-mentioned problems, and aims to provide a method for inexpensively manufacturing a metal electrode tube having wall thickness differences in the longitudinal direction of the tube.

In this invention, a rectangular metal plate material having a partial thickness and thickness corresponding to the inside thickness of a square tube is prepared. This plate material is bent into a tubular body by rolling or press bending so that the radius of curvature of the neutral plane inside the tube thickness almost matches the radius of curvature of the neutral plane of the thin wall portion of the tube. Then, the joints of the tubular bodies are welded.

As described above, according to the present invention, a tube having a different wall thickness is manufactured by processing and welding, and the tube is manufactured at a low cost because it does not require forging.

Since the material board has a rectangular shape as a whole, it can be prepared at low cost.

In addition, in this invention, the plate material is bent so that the radius of curvature of the neutral plane inside the thick tube almost matches the radius of curvature of the neutral plane of the thin wall part of the tube, so the edge of the joint of the tubular body is bent in the longitudinal direction of the tube. It becomes a straight line along , and the gap between the opposing edges is also constant. Furthermore, welding! No bends or torsions occur in the tubes produced by l1.

The present invention will be described below in detail based on examples.The pipe to be manufactured (stepped pipe) 1 consists of a thin walled portion 3 and a thick walled portion 3 extending from the outer diameter side, as shown in Fig. 1. ing.

FIG. 2 shows a plate material J1 from which the stepped tube 1 is manufactured. The length L of the plate material 11 is equal to the length of the stepped tube to be manufactured, and the plate width B is B-2□r1+2b. Here, ``, as shown in FIG.
is the radius of curvature of the neutral plane N1, and is the length of the bH edge cut portion 6. The bend in the edge cut portion 6 is a part that cannot be processed, and is straight and has a length t)ld dog body (0
, 5~2)・t28 degrees. If the tube is bent while leaving the edge cut portion 6, peaking will occur in the finished tube, which is undesirable from the viewpoint of strength and appearance. Therefore, the edge cut portion 6 is cut and removed before the bending process is completed.

A portion 12 of the plate material 11 corresponding to the thin tube portion 2 has a thickness equal to the wall thickness t1 of the thin tube portion 2. Further, the plate thickness t3H of the portion 13 corresponding to the thick inner part 3 of the pipe is slightly thicker than the wall thickness t2 of the thick wall portion 2 of the pipe for reasons described later.

The plate material 11 having the above-mentioned shape can be prepared by cutting off the central portion of a thick plate by machining. As shown in Fig. 3, the thick part 17 of the plate 15 juts out above and below the thin part +6vc. The plate 4q'11 shown in FIG.

Generally, the length of the thick inner part 3 of the pipe is much shorter than the length of the thin part 2 of the pipe, so using the plate a'15 requires less machining and is therefore economical.

The plate material 11 prepared as described above is bent into a tubular shape using a hobless bender. FIG. 4 shows the punch 21 and die O of the breath bender.

The radius of curvature of the pressing portion 22 of the punch 21 is set to be equal to or slightly smaller than the inner radius 1t1 of the stepped tube 1.

The radius of curvature of the portion 24 of the die 23 corresponding to the thin-walled tube portion is equal to or slightly smaller than the outer radius 1t2VC of the thin-walled tube portion 2;
The radius of curvature of the portion δ corresponding to the inside of the tube thickness is set to be equal to or slightly smaller than the outer radius R3 of the inside 3 of the tube thickness. In order to avoid a sudden change in the tube wall thickness, there is a transition section 26 between the tube thin-wall phase roaring section 24 and the inner tube thickness equivalent section 5 of the die B, in which the hole-shaped shape changes gradually.

The plate material 11 is fed little by little in the width direction, that is, in the circumferential direction, between the bunch 21 and the die B, and is bent in stages to be formed into an O-shape. , 0.
It is about 5 to 3 times. As mentioned above, since the plate thickness t3H of the thick part 13 of the plate material 11 is slightly thicker than the wall thickness t2 of the thick part 3 of the finished pipe 1, the plate material 1 is inserted between the punch 21 and the brace n.
The thick wall portion 13 of No. 1 receives a larger pressing load than the thin wall portion 12. Therefore, the thick inside 3 of the tube is subjected to a tensile force in the circumferential direction, and as shown in the strain distribution S shown in FIG. 1, the neutral plane N2 of the thick inside 3 of the tube is shifted toward the inner diameter side. Thick wall part of plate material] The above direction is 2 to the neutral plane of the inside of the pipe thickness 3 by processing to the plate thickness t3 of 3.
is selected so that it coincides with the neutral plane N1 of the thin tube portion 2.

As a result, as shown in FIG. Note that, as long as the non-uniformity of the gap between the joints 9 does not interfere with welding, the neutral planes N, , N2 do not need to be perfectly aligned.

FIG. 1 also shows a part of the tubular body 5 before the bending process is completed. Since the vicinity of edge 6 cannot be bent, this part 7
The gas is turned off [! Ji and others! ll lino is removed and the joint edge 7 is beveled. Then, by pressing again,
It is fitted into a 0-shaped tubular body 8 shown in FIG.

The joint 9 of the tubular body 8 formed in this way is welded to complete the stepped tube 5.
To give an example of the dimensions of the stepped pipe we manufactured, the total length is 2000m.
m, inner diameter 413+mn.

Thin wall outer diameter 454 mm, wall thickness 20.5 mm, thick inner outer diameter 473 m, wall thickness 30++a, length 400 ns,
It was 150 barrels. In addition, the material has a yield point of 50 Kll/
, J class steel plate.

In the above embodiment, the plate material was formed by press bending, but it is also possible to form it by roll feed bending. 6th
The figure shows 3 used to form the tubular body 8 shown in FIG.
The roll arrangement and roll shape of a roll bender of the 0-1 roll type are shown. The rolls 31, 32, and 33 are arranged in a pyramid shape, and the roll 31 is a reduction roll, roll 32.31J is a fixed roll. The plate material 11 is passed between the reduction roll 31 and the fixed base coals 32 and 33,
At this time, it undergoes bending. .

A groove 34 is provided in each of the fixed rolls 32, 31; I in a portion corresponding to the inside 3 of the tube thickness. The operations other than bending are exactly the same as those for press bending.

FIG. 7 shows an example of a punch 41 and a die 44 of a breath bender used for forming a stepped tube in which the inside of the tube is on the inner diameter side. Punch 41 and two pressing parts 42.4
It's 3-V. The suppressing part 42 has a curved surface J5 with a radius of curvature R4 that is equal to or slightly smaller than the inner radius of the thin walled part of the pipe,
The pressing portion 43 also has a radius of curvature 1, which is the same as or slightly smaller than the inner radius inside the tube thickness, and is also made of a curved side surface. The receiver of die 44 is face 4
The radius of curvature R6 of No. 5 is equal to or slightly smaller than the outer radius of the stepped tube.

A stepped tube in which the inside of the tube is protruded toward the inner diameter side is manufactured using the above-mentioned breath bender in the same manner as the stepped tube, which is extruded to an outer diameter of 111[f].

In the two sets of embodiments, in order to match the neutral plane of the inside of the thick pipe with the neutral plane of the thin walled part of the pipe, the reduction of the inside of the thick pipe is reduced by the reduction of the thin part of the pipe,
The garlic was also bigger. The force is 1, and the plate material 1 shown in Fig. 3 is
5, weld the joint of the tubular body, and then remove either the inner or outer overhang by machining, so there is no need to change the reduction and bend as described above.

That is, the thick portion 17 of the plate material 15 is equally thicker than the thin portion 16. Therefore, when the opening is applied with force, the radius of curvature of the neutral plane inside the thick pipe always matches the radius of curvature of the neutral plane of the thin wall part of the pipe. There is no need to change the exact size between parts. In this case i
A press bender is used by combining the die 2; 3 shown in FIG. 4 and the punch 41 shown in FIG. 7.

In this invention, the bending process is performed cold or hot. Further, even if the thick wall portion is provided not only at both ends of the stepped tube but also in the middle, it can be manufactured by the method described in "-".

The stepped pipe manufactured in this manner is used for the tension leg, oil country tubular goods, etc.

[Brief explanation of drawings]

Fig. 1 is a partial front view of a stepped tube manufactured by the method of the present invention and a tubular body in the process of being formed, Fig. 2 is a perspective view of a plate material before bending, and Fig. 3 shows a thick wall portion vertically. FIG. 4 is a perspective view showing an example of the punch and die of the press bender used in the bending process of the present invention, and FIG. 5 is a perspective view of the overhanging plate material. FIG. 6 is a perspective view showing an example of a roll of a roll bender used in the present invention, and FIG. 7 is a perspective view showing another example of a punch and die of a press bender. DESCRIPTION OF SYMBOLS 1... Stepped pipe, 2... Pipe thin wall part, 3... Pipe thickness inside, 4.8... Tubular body, II, 15... Plate material, 21
．． 41...ノ(nchi, 23, old...dice, 3],
32.33...The song is roll. Patent Applicant Representative Patent Attorney Yoshiyuki Yafuki (and 1 other person)

Claims (1)

[Claims] A rectangular metal plate with a thicker part corresponding to the inner part of the pipe is prepared, and the plate is rolled and bent or pressed so that the radius of curvature of the neutral plane of the inner part of the pipe almost matches the radius of curvature of the thinner part of the pipe. A method of manufacturing a metal tube having wall thickness differences in the longitudinal direction of the tube, which comprises forming the tube into a tube by bending and welding the joints of the tube.