Pipe expander, pipe expanding method of steel pipe, and manufacturing method of steel pipe

Abstract

To provide a pipe expander, a pipe expanding method of a steel pipe, and a manufacturing method of a steel pipe, capable of improving roundness of the steel pipe.SOLUTION: A pipe expander includes: a pull rod that is provided inside a boom and is movable independently of the boom; a cone that is provided at a distal end of the pull rod and is gradually reduced in diameter from a distal end side toward a proximal end side of the boom; and a pipe expanding head in which a plurality of pipe expanding dies are arranged in a circumferential direction on an outer circumference of the cone. The pipe expander is configured so that when the cone is pulled by the pull rod in an axial direction from the distal end side toward the proximal end side of the boom, the pipe expanding head expands in a radial direction so as to expand a steel pipe installed on an outer periphery of the pipe expanding head. A radius of curvature of an outer peripheral surface of the pipe expanding die arranged at a specific position in the peripheral direction among the plurality of pipe expanding dies is larger than the radius of curvature of the outer peripheral surface of any of other pipe expanding dies.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a pipe expansion machine, a method for expanding a steel pipe, and a method for manufacturing a steel pipe. [Background technology]

[0002] Circularity, which is one of the parameters indicating the dimensions and shape of a steel pipe, is defined as the difference between the maximum and minimum outer diameters of the steel pipe, or as the ratio of the difference between the maximum and minimum outer diameters of the steel pipe to the nominal outer diameter. In either case, the smaller the value, the higher the circularity, and the larger the value, the lower the circularity. If the circularity is low, the ends of the UOE steel pipes cannot be butted together during circumferential welding at the field. In addition, when the UOE steel pipe is laid in a high-pressure atmosphere such as deep sea, if the circularity of the steel pipe is low, the steel pipe may be deformed unevenly due to the pressure, leading to buckling. In recent years, the API (American Petroleum Institute) standard has been increasingly requiring strict tolerances for circularity due to the above-mentioned background, and shape improvements that meet these requirements are desired. As a method for improving circularity, Patent Document 1 discloses a technology for pre-correcting the shape of the pipe end before expanding to improve the circularity of the UOE steel pipe after expanding. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2010-167440 A Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, the demand for line pipes for transporting oil and natural gas has been increasing, particularly for deep-sea pipelines that require high collapse resistance, and pipes with a thicker wall thickness than onshore pipelines are used, and higher roundness is also required. It is known that thick-walled steel pipes and high-strength steel pipes are more likely to become elongated when the weld is placed on the upper side after O-forming in the UOE process, compared to thin-walled steel pipes and low-strength steel pipes. In this way, it has been difficult to ensure good roundness for steel pipes that have become elongated after O-forming, even after expansion. In particular, in recent years, there has been a strong demand for improvement in the roundness of steel pipes from the viewpoints of workability of circumferential welding at the line pipe installation site and collapse resistance for deep-sea applications, but at present, no means of solving this problem have been established, and improvement technology has been required.

[0005] The present invention has been made in consideration of the above problems, and an object of the present invention is to provide a pipe expansion machine, a steel pipe expansion method, and a steel pipe manufacturing method that can improve the roundness of a steel pipe. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems and achieve the object, the tube expansion machine of the present invention has a pull rod that is provided inside a boom and can move independently of the boom, a cone that is provided at the tip of the pull rod and reduces in diameter from the tip side to the base end of the boom, and an expansion head in which multiple expansion dies are arranged in the circumferential direction on the outer periphery of the cone, and the cone is pulled in the axial direction from the tip side to the base end of the boom by the pull rod, causing the expansion head to expand radially, thereby expanding a steel tube installed on the outer periphery of the expansion head, and is characterized in that the radius of curvature of the outer periphery of the expansion die that is arranged at a specific circumferential position among the multiple expansion dies is larger than the radius of curvature of the outer periphery of the other expansion dies.

[0007] Furthermore, the pipe expansion machine of the present invention is characterized in that, in the above invention, the steel pipe is a straight seam welded steel pipe, and the specific position is at least one of a position opposite to a seam weld of the straight seam welded steel pipe and a position opposite to a position 180 degrees circumferentially from the seam weld in a cross section perpendicular to the axial direction of the straight seam welded steel pipe.

[0008] In addition, the tube expansion machine of the present invention is characterized in that, in the above invention, the radius of curvature of the outer peripheral surface of the tube expansion die arranged at the specific position is 1.1 to 1.2 times the radius of curvature of the outer peripheral surface of the other tube expansion dies.

[0009] A method for expanding a steel pipe according to the present invention is characterized in that the steel pipe is expanded using the expander of the above-mentioned invention.

[0010] A method for producing a steel pipe according to the present invention is characterized by comprising a step of expanding a steel pipe using the steel pipe expanding method of the present invention. Effect of the Invention

[0011] The pipe expanding machine, the steel pipe expanding method, and the steel pipe manufacturing method according to the present invention have the effect of improving the roundness of the steel pipe. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of a pipe expander used in a method for expanding a welded steel pipe according to an embodiment. [Diagram 2] FIG. 2 is a schematic diagram showing a cross section of a welded steel pipe in a direction perpendicular to the axial direction. [Diagram 3] Fig. 3(a) is a diagram showing an example of the tube expansion die at a position other than the specific position, and Fig. 3(b) is a diagram showing an example of the tube expansion die at the specific position. [Figure 4]Fig. 4(a) shows an example of a cross-sectional shape profile at one end in the axial direction of a conventional welded steel pipe, and Fig. 4(b) shows an example of a cross-sectional shape profile at the other end in the axial direction of a conventional welded steel pipe. [Diagram 5] Fig. 5(a) is an example of a cross-sectional shape profile at one end in the axial direction of a welded steel pipe in an example of the present invention, and Fig. 5(b) is an example of a cross-sectional shape profile at the other end in the axial direction of a welded steel pipe in an example of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment of the pipe expanding machine, the pipe expanding method for a steel pipe, and the steel pipe manufacturing method according to the present invention will be described. Note that the present invention is not limited to the embodiment.

[0014] Fig. 1 is a schematic diagram showing the configuration of a pipe expansion machine 1 used in a method for expanding a welded steel pipe 10 according to an embodiment. Fig. 2 is a schematic diagram showing a cross section of a welded steel pipe 10 in a direction perpendicular to its axial direction. In Fig. 2, the schematic diagram of the cross section is likened to a clock face, with the position of the seam weld 11 of the welded steel pipe 10 being the 12 o'clock position, and the position 180 degrees circumferentially from the seam weld 11 in the cross section perpendicular to the axial direction of the welded steel pipe 10 being the 6 o'clock position.

[0015] As shown in FIG. 1, the expander 1 used in the method for expanding a welded steel pipe according to the first embodiment is, for example, an expander for straight seam welded steel pipe. The expander 1 according to the embodiment includes a cylindrical boom 2 whose tip is inserted from one end of a welded steel pipe 10, and an expansion head 4 that is provided at the tip of the boom 2 and expands the welded steel pipe 10 when expanding the diameter in the direction perpendicular to the axis. The expansion head 4 includes a cone 5, an expansion die 6, and a jaw 7. The welded steel pipe 10 is manufactured, for example, by forming a steel plate, which is a material, into a tubular shape and seam-welding both widthwise ends of the steel plate that are butted together by forming in the longitudinal direction (axial direction).

[0016] The cone 5 is provided at the tip of the pull rod 3 that is provided inside the boom 2 and can move independently of the boom 2, and the diameter of the cone 5 is reduced from the tip side to the base end side of the boom 2. The tube expansion die 6 is provided on the outside of the cone 5 via the jaw 7. The jaw 7 has a tapered inner peripheral surface 7a that is in sliding contact with the tapered outer peripheral surface 5a of the cone 5 and is reduced in diameter from the tip side to the base end side of the boom 2, and a jaw outer peripheral surface 7b that abuts against the tube expansion die 6. The tube expansion die 6 has a die inner peripheral surface 6a that abuts against the jaw outer peripheral surface 7b, and a die outer peripheral surface 6b that faces the inner peripheral surface of the welded steel pipe 10. As shown in FIG. 2, the tube expansion die 6 and the jaw 7 are arranged in a plurality of positions on the outer periphery of the cone 5 along the circumferential direction of the cone 5 (tapered outer peripheral surface 5a).

[0017] Next, a method for expanding a welded steel pipe 10 using the expander 1 will be described. In the method for expanding a welded steel pipe 10 according to the embodiment, the welded steel pipe 10 is expanded using an expansion head 4 having a plurality of expansion dies 6 arranged in the circumferential direction. That is, when expanding a welded steel pipe 10 using the expander 1 according to the embodiment, the expansion dies 6 of the expander 1 are aligned with the expansion start position, and the pull rod 3 of the expander 1 is pulled from the tip side to the base end side to move backward from the expansion start position. As a result, each of the expansion dies 6 in sliding contact with the tapered outer peripheral surface 5a is displaced in the radial direction, that is, in the direction away from the central axis of the welded steel pipe 10 by the wedge action, and the expansion head 4 expands in the radial direction, and the plurality of expansion dies 6 come into contact with the inner peripheral surface of the welded steel pipe 10 to expand the welded steel pipe 10.

[0018] Next, the pull rod 3 is advanced to the expansion start position, and the expansion die 6 is returned to the central axial direction of the welded steel pipe 10 by a release mechanism (not shown), and the welded steel pipe 10 is advanced by an amount corresponding to the pitch (effective axial length) of the expansion die 6. Then, the expansion die 6 is aligned to a new expansion position, and the above operation is repeated. In this way, expansion can be performed over the entire length of the welded steel pipe 10, one step at a time equal to the pitch of the expansion die 6.

[0019] Fig. 3(a) is a diagram showing an example of a tube expansion die other than the specific position, that is, another tube expansion die 6. Fig. 3(b) is a diagram showing an example of a tube expansion die 6 in the specific position.

[0020] In the pipe expanding machine 1 according to the embodiment, the radius of curvature r2 of the die outer peripheral surface 6b of the expansion die 6 at a specific circumferential position shown in FIG. 3(b) among the multiple expansion dies 6 is made larger than the radius of curvature r1 of the die outer peripheral surface 6b of the expansion die 6 at the other than the specific position shown in FIG. 3(a) (hereinafter, simply referred to as other expansion dies 6). The specific position is, for example, at least one of a position facing the seam welded portion 11 of the welded steel pipe 10 (the 12 o'clock position in FIG. 2) and a position 180 degrees circumferentially from the seam welded portion 11 in a cross section perpendicular to the axial direction of the welded steel pipe 10 (the 6 o'clock position in FIG. 2). The specific position may be appropriately changed according to the shape of the welded steel pipe 10 before expansion. By making the radius of curvature r2 of the outer peripheral surface 6b of the expansion die 6 at the specific position larger than the radius of curvature r1 of the other expansion dies 6, the cross-sectional shape of the expansion die 6 at the specific position becomes horizontally elongated, thereby correcting the vertically elongated shape of the welded steel pipe 10.

[0021] In addition, it is preferable that the radius of curvature r2 of the outer peripheral surface 6b of the tube expanding die 6 at the specific position (the position facing the seam welded portion 11) is 1.1 to 1.2 times the radius of curvature r1 of the outer peripheral surface 6b of the other tube expanding die 6. The reason for this is explained below. As shown in FIG. 3(a), the height from the inner peripheral surface 6a of the tube expanding die 6 to the top of the die is h1, and as shown in FIG. 3(b), the height from the inner peripheral surface 6a of the tube expanding die 6 at the specific position to the top of the die is h2. The inventors of the present application have found that it is preferable that the height h2 to the top of the die of the tube expanding die 6 at the specific position is 1.5 to 2.0 mm lower than the height h1 to the top of the die of the other tube expanding die 6. If the change in height to the top of the die is converted into a change in the radius of curvature, the radius of curvature r2 of the outer peripheral surface 6b of the expansion die 6 at a specific position is 1.1 to 1.2 times the radius of curvature r1 of the outer peripheral surface 6b of the other expansion die dies 6.

[0022] If the radius of curvature r2 of the outer peripheral surface 6b of the expansion die 6 at the specific position is less than 1.1 times the radius of curvature r1 of the outer peripheral surface 6b of the other expansion die dies 6, the elongated shape of the welded steel pipe 10 before expansion may not be sufficiently corrected. Therefore, it is preferable that the radius of curvature r2 is 1.1 times or more the radius of curvature r1. Also, if the radius of curvature r2 of the outer peripheral surface 6b of the expansion die 6 at the specific position exceeds 1.2 times the radius of curvature r1 of the outer peripheral surface 6b of the other expansion die dies 6, the outer peripheral surface 6b of the expansion die 6 at the specific position may not be in sufficient contact with the inner peripheral surface of the welded steel pipe 10. Furthermore, when the curvature radius r2 exceeds 1.2 times the curvature radius r1, the distance t2 from the die inner peripheral surface 6a to the circumferential end of the die outer peripheral surface 6b in the specific position of the expanding die 6 becomes excessively larger than the distance t1 from the die inner peripheral surface 6a to the circumferential end of the die outer peripheral surface 6b in the other expanding die dies 6. Therefore, there is a concern that the circumferential end of the die outer peripheral surface 6b in the specific position of the expanding die 6 will abut excessively strongly against the inner peripheral surface of the welded steel pipe 10, causing defects on the inner peripheral surface of the welded steel pipe 10. From this point of view, it is preferable that the curvature radius r2 is 1.2 times or less than the curvature radius r1.

[0023] The tube expanding machine 1 according to the embodiment expands the welded steel tube 10 using the tube expanding head 4 in which the radius of curvature r2 of the die outer peripheral surface 6b of the tube expanding die 6 at the specific position is set to 1.1 to 1.2 times the radius of curvature r1 of the die outer peripheral surface 6b of the other tube expanding dies 6. As a result, the tube expanding machine 1 according to the embodiment can correct the vertically elongated shape of the welded steel tube 10, whose cross-sectional shape in a direction perpendicular to the axial direction before expansion is a vertically elongated ellipse, thereby reducing the degree of vertical elongation, and improve the roundness of the welded steel tube 10. Also, the tube expanding machine 1 according to the embodiment can correct the horizontally elongated shape of the welded steel tube 10, whose cross-sectional shape in a direction perpendicular to the axial direction before expansion is a horizontally elongated ellipse, thereby reducing the degree of horizontal elongation, and improve the roundness of the welded steel tube 10.

[0024] In addition, the tube expansion machine 1 of the embodiment can improve the roundness of the welded steel pipe 10 without fracturing the expansion die 6 by making the radius of curvature r2 of the die outer peripheral surface 6b of the expansion die 6 at the specific position 1.1 to 1.2 times the radius of curvature r1 of the die outer peripheral surface 6b of the other expansion dies 6. EXAMPLES

[0025] In this example, a welded steel pipe 10 was manufactured that conforms to API standard 5L X80M PSL2, has an outer diameter of φ559.0 [mm], a pipe thickness of 25.4 [mm], and a pipe length of 12192 [mm]. The tolerance of the roundness of the welded steel pipe 10 was 5.0 [mm] (0.9 [%]).

[0026] As a conventional example, an example of a cross-sectional shape profile of a welded steel pipe 10 when expanding is performed using only a normal expanding die is shown in Figs. 4(a) and 4(b). Fig. 4(a) is an example of a cross-sectional shape profile of one end side in the pipe axis direction of a welded steel pipe 10 in a conventional example. Fig. 4(b) is an example of a cross-sectional shape profile of the other end side in the pipe axis direction of a welded steel pipe 10 in a conventional example. As an example of the present invention, an example of a cross-sectional shape profile of a welded steel pipe 10 when expanding is performed with the radius of curvature r2 of the die outer peripheral surface 6b of the expanding die 6 facing the seam welded portion 11 set to 1.2 times the radius of curvature r1 of the die outer peripheral surface 6b of the other expanding die 6 is shown in Figs. 5(a) and 5(b). Fig. 5(a) is an example of a cross-sectional shape profile of one end side in the pipe axis direction of a welded steel pipe 10 in an example of the present invention. Fig. 5(b) is an example of a cross-sectional shape profile of the other end side in the pipe axis direction of a welded steel pipe 10 in an example of the present invention. Note that the cross-sectional shape profiles in Figures 4(a), 4(b), 5(a), and 5(b) are enlarged at a common magnification to show the deviation of the radius of each point in the circumferential direction of the welded steel pipe 10 from the radius of the welded steel pipe 10.

[0027] In the conventional example, the cross-sectional shape of the welded steel pipe 10 after expansion tended to be vertically elongated, as shown in FIG. 4. The pass rate of the roundness judgment of the manufactured welded steel pipe 10 was 18% on average between one end side and the other end side in the axial direction of the welded steel pipe 10. For this reason, additional processing such as re-expansion was often required. On the other hand, in the example of the present invention, the cross-sectional shape of the welded steel pipe 10 after expansion tended to be closer to a perfect circle than in the conventional example, as shown in FIG. 5. The pass rate of the roundness judgment of the manufactured welded steel pipe 10 was 86% on average between one end side and the other end side in the axial direction of the welded steel pipe 10. For this reason, the frequency of additional processing such as re-expansion could be reduced.

[0028] The welded steel pipe 10 to be expanded using the present invention is not limited to the grades and sizes described above, but can also be expanded to welded steel pipes 10 of different grades and sizes, and the same effects as those of the above-mentioned examples of the present invention can be obtained.

[0029] In the above description, the tube expansion die 6 has been illustrated as being provided on the outside of the cone 5 via the jaws 7. The present invention is not limited to the tube expansion die of this illustrated form. That is, for example, the tube expansion die 6 may be an integral member having a tapered inner peripheral surface that slides against the tapered outer peripheral surface 5a of the cone 5 and that is tapered from the tip side to the base side of the boom 2, and a die outer peripheral surface 6b that faces the inner peripheral surface of the welded steel pipe 10. [Explanation of symbols]

[0030] 1 Pipe expander 2. Boom 3 Pull Rod 4. Tube expansion head 5. Cone 5a Tapered outer surface 6. Tube expansion die 6a Die inner surface 6b Die outer surface 7. Joe 7a Tapered inner surface 7b Jaw outer surface 10. Welded Steel Pipe

Claims

1. A pull rod provided inside the boom and movable independently of the boom; a cone provided at a tip of the pull rod and tapering from a tip side of the boom toward a base end side; a tube expansion head having a plurality of tube expansion dies arranged in a circumferential direction on an outer periphery of the cone; having The cone is pulled in an axial direction from the tip end side to the base end side of the boom by the pull rod, whereby the expansion head expands in a radial direction to expand a steel pipe installed on an outer periphery of the expansion head, A tube expansion machine characterized in that, among the plurality of expansion dies, the radius of curvature of the outer peripheral surface of the expansion die arranged at a specific circumferential position is larger than the radius of curvature of the outer peripheral surface of the other expansion dies.

2. The steel pipe is a straight seam welded steel pipe, The specific position is The pipe expansion machine according to claim 1, characterized in that the expansion is performed at least one of a position facing the seam welded portion of the straight seam welded steel pipe and a position facing a position 180 degrees circumferentially from the seam welded portion in a cross section perpendicular to the axial direction of the straight seam welded steel pipe.

3. The tube expansion machine according to claim 2, characterized in that the radius of curvature of the outer peripheral surface of the expansion die arranged at the specific position is 1.1 to 1.2 times the radius of curvature of the outer peripheral surface of the other expansion dies.

4. A method for expanding a steel pipe, comprising expanding the steel pipe by using the expander according to any one of claims 1 to 3.

5. A method for manufacturing a steel pipe, comprising a step of expanding a steel pipe by using the method for expanding a steel pipe according to claim 4.

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