JP2018192521A - Method for manufacturing weld steel pipe - Google Patents

Abstract

To provide a method for manufacturing a weld steel pipe by which a weld steel pipe having a high roundness can be obtained.SOLUTION: A method for manufacturing a weld steel pipe comprises: a preparation process in which a weld original pipe is prepared; a first pipe expansion process in which plural dies, which are so located in the weld original pipe as to be arranged in a circumferential direction of the weld original pipe, are brought into contact with an inner peripheral surface of the weld original pipe, thereby expanding the weld original pipe; and a second pipe expansion process in which the plural dies, which are so located in the weld original pipe as to be arranged in the circumferential direction of the weld original pipe after the first pipe expansion process, are brought into contact with the inner peripheral surface of the weld original pipe, thereby expanding the weld original pipe. In the second pipe expansion process, each die is brought into contact with a portion of the inner peripheral surface of the weld original pipe, which is positioned between adjacent dies in the circumferential direction in the first pipe expansion process. A pipe expansion rate in the second pipe expansion process is lower than a pipe expansion rate in the first pipe expansion process.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a method for manufacturing a welded steel pipe.

  Conventionally, welded steel pipes such as UOE steel pipes have been used as line pipes for transporting oil and natural gas. Generally, when manufacturing a UOE steel pipe, first, a steel pipe is manufactured by welding a steel plate formed into a substantially cylindrical shape by a C press, a U press and an O press. Thereafter, the roundness of the steel pipe is corrected by expanding the steel pipe using a pipe expanding device.

  For example, in the steel pipe manufacturing method disclosed in Patent Document 1, the first pipe expansion is performed by a plurality of dies arranged in a substantially cylindrical shape. Thereafter, the second pipe expansion is performed in a state where the steel pipe is rotated relative to the plurality of dies. Patent Document 1 describes that a pipe with particularly good roundness can be manufactured by performing pipe expansion in two steps in this way.

Japanese Patent Laid-Open No. 9-24433

  By the way, in recent years, from the viewpoints of deepening the seabed pipeline and improving the efficiency of welding work, the user's requirement for the roundness of the welded steel pipe has become strict. For this reason, development of the method which can manufacture a steel pipe with still higher roundness is desired.

  Then, this invention aims at providing the manufacturing method of a welded steel pipe which can obtain a welded steel pipe with high roundness.

  This invention makes the summary the manufacturing method of the following welded steel pipe.

(1) a preparation process for preparing a welded pipe made of steel;
A first expanding step of expanding the welded elementary tube by bringing a plurality of dies arranged in the welded elementary tube so as to be aligned in the circumferential direction of the welded elementary tube into contact with the inner peripheral surface of the welded elementary tube;
After the first pipe expansion step, the plurality of dies arranged in the weld base pipe so as to be aligned in the circumferential direction of the weld base pipe are brought into contact with the inner peripheral surface of the weld base pipe to expand the weld base pipe. A second pipe expansion step,
In the second pipe expansion step, the die is brought into contact with a portion of the inner peripheral surface of the welded pipe located between the dies adjacent in the circumferential direction in the first pipe expansion step, and the welding is performed. Expand the tube,
The method for manufacturing a welded steel pipe, wherein the tube expansion rate in the second tube expansion step is lower than the tube expansion rate in the first tube expansion step.

(2) The method for producing a welded steel pipe according to (1), wherein a tube expansion rate in the second tube expansion step is 0.05 to 0.25 times the tube expansion rate in the first tube expansion step.

(3) The method for manufacturing a welded steel pipe according to (1) or (2), wherein a pipe expansion rate in the second pipe expansion process is 0.05 to 0.20%.

(4) Each of the plurality of dies used in the second pipe expanding step has a pressing surface that forms an arc in a cross section orthogonal to the axial direction of the welded element pipe,
The method for manufacturing a welded steel pipe according to any one of (1) to (3), wherein a center angle Ac of the arc formed by the pressing surface satisfies a relationship of the following formula (i).
(360 ° / N) × 0.90 ≦ Ac ≦ (360 ° / N) × 0.95 (i)
However, in said formula (i), N shows the number of dice | dies.

  According to the present invention, a welded steel pipe having a high roundness can be obtained.

FIG. 1 is a cross-sectional view showing a schematic configuration of a pipe expanding machine used in the first pipe expanding step. 2 is a cross-sectional view taken along line AA in FIG. FIG. 3 is a view for explaining the shape of the pressing surface of the die. FIG. 4 is a diagram for explaining the first tube expansion step. FIG. 5 is a diagram for explaining the second tube expansion process. FIG. 6 is a diagram showing an analysis result (relationship between roundness and tube expansion rate). FIG. 7 is a diagram illustrating an analysis result (a relationship between the roundness and the tube expansion rate in the second tube expansion step).

  Hereinafter, the manufacturing method of the welded steel pipe concerning one embodiment of the present invention is explained using a drawing. In addition, each figure demonstrated below is the schematic for demonstrating the manufacturing method of the welded steel pipe which concerns on this embodiment, The dimension of the structural member in a figure is the dimension of an actual structural member, and each structural member. It is not a faithful representation of dimensional ratios.

(Outline of manufacturing method of welded steel pipe)
The method for manufacturing a welded steel pipe according to the present embodiment includes a preparation process for preparing a welded base pipe made of steel, a first pipe expanding process for expanding the welded base pipe, and a first pipe expanding the welded base pipe after the first pipe expanding process. 2 tube expansion process. Note that welded steel pipes manufactured by the manufacturing method according to the present embodiment include UOE steel pipes and JCOE steel pipes.

(Preparation process)
When manufacturing a UOE steel pipe as a welded steel pipe, first, in the preparation process, a C press, a U press, and an O press are performed in this order on a long steel plate cut to a predetermined size. Thereby, a steel plate is shape | molded by the substantially cylindrical shape so that the both ends in the transversal direction (width direction) of a steel plate may mutually oppose. Next, the said both ends of a steel plate are welded. Specifically, the both ends of the steel plate are tack-welded to each other, and then inner surface welding and outer surface welding are performed. Thereby, a welding pipe is obtained. In addition, what is necessary is just to obtain the steel pipe (steel pipe before pipe expansion) manufactured using the manufacturing method of various well-known UOE steel pipes as a welding element pipe in a preparatory process. Moreover, when manufacturing a JCOE steel pipe as a welded steel pipe, in a preparation process, if the steel pipe (steel pipe before pipe expansion) manufactured using the manufacturing method of various well-known JCOE steel pipes is obtained as a welding element pipe, Good.

(First pipe expansion process)
FIG. 1 is a cross-sectional view showing a schematic configuration of a pipe expander used in the first pipe expansion step, and FIG. 2 is a cross-sectional view taken along line AA of FIG. In addition, since a well-known various pipe expander can be used in a 1st pipe expansion process and the 2nd pipe expansion process mentioned later, the structure of a pipe expander is demonstrated easily.

  In FIG. 1 and FIG. 2, a welding element pipe 1 obtained in the preparation process is shown. In the preparation step, a welded portion 1a (see FIG. 2) and a HAZ (not shown) are formed on the welded tube 1 so as to extend in the axial direction of the welded tube 1.

  Referring to FIGS. 1 and 2, a pipe expander 10 includes a cylindrical boom 12 extending in the axial direction of a welding pipe 1, a pull rod 14 inserted through the boom 12 so as to be movable in the axial direction of the boom 12, and a pull rod 14. And a plurality of dies 18 arranged around the cone 16. In the example shown in FIG. 2, twelve dice 18 are provided, but the number of dice 18 is not limited to the example shown in FIG. For example, the number of dies 18 included in the pipe expander may be ten or eight.

  The distal end portion of the boom 12, the distal end portion of the pull rod 14, the cone 16, and the plurality of dies 18 are disposed in the welding element tube 1. In the cross section (the cross section shown in FIG. 1) extending in the axial direction of the welded element tube 1, the die 18 includes a pressing surface 18 a facing the inner peripheral surface of the welded element tube 1 and a sliding surface facing the outer peripheral surface of the cone 16. 18b. In the cross section, the pressing surface 18 a extends in parallel to the axial direction of the welding element tube 1, and the sliding surface 18 b is inclined with respect to the axial direction of the welding element tube 1.

  FIG. 3 is a view for explaining the shape of the pressing surface 18 a of the die 18. In FIG. 3, the welded element pipe 1 and one die 18 are shown in the section AA in FIG. 1. With reference to FIG. 3, the pressing surface 18 a forms an arc in a cross section orthogonal to the axial direction of the welded pipe 1. In the cross section, the radius of curvature of the arc formed by the pressing surface 18a is, for example, substantially the same as the radius of the inner peripheral surface of the welded tube 1 (hereinafter referred to as the inner radius) or from the inner radius of the welded tube 1. Is also set small. FIG. 3 shows the center of curvature C and the center angle Ac of the arc formed by the pressing surface 18a in the cross section. The central angle Ac is appropriately set according to the number of dies 18 and the dimensions of the welding element tube 1. In the following, the central angle Ac of the arc formed by the pressing surface 18a is simply referred to as the central angle Ac of the pressing surface 18a.

  With reference to FIG. 1, when the welded pipe 1 is expanded in the first tube expansion step, the pull rod 14 moves in the direction indicated by the arrow X (hereinafter referred to as the X direction), and the cone 16 is boom 12. Move to the side. Since movement of the plurality of dies 18 in the X direction is regulated by the boom 12, the sliding surface 18 b of each die 18 slides on the outer peripheral surface of the cone 16 when the cone 16 moves in the X direction. However, it moves toward the outside in the radial direction of the welded tube 1. Accordingly, the plurality of dies 18 move so as to expand radially in the welding pipe 1. As a result, as shown in FIG. 4, the pressing surface 18 a of each die 18 comes into contact with the inner peripheral surface of the welded raw tube 1, and the inner peripheral surface of the welded raw tube 1 is directed radially outward by the die 18. Pressed. Thereby, the welding base pipe 1 is expanded.

  In FIG. 4, a portion of the inner peripheral surface of the welded element tube 1 located between the dies 18 adjacent to each other in the circumferential direction of the welded element tube 1 is indicated by a dashed circle 1 b. Below, the part shown with the circle 1b of a broken line is described as the clearance gap part 1b in a 1st pipe expansion process.

In the present embodiment, the tube expansion rate in the first tube expansion step is set to 0.80 to 0.95%, for example. In the present embodiment, for example, the tube expansion rate of each process is set so that the total tube expansion rate of the first tube expansion step and the tube expansion rate of the second tube expansion step described later is 1.0%. . The tube expansion rate is defined by the following formula.
Expansion ratio = (peripheral length of the tube after expansion-outer periphery length of the tube before expansion) / perimeter length of the tube before expansion

(Second pipe expansion process)
In the second pipe expansion process, for example, the welded pipe 1 after the first pipe expansion process is expanded using the above-described pipe expander 10 by the same method as the first pipe expansion process. However, in the second pipe expanding step, as shown in FIG. 5, pipe expansion is performed by bringing the dies 18 into contact with the gap portions 1 b in the first pipe expanding step on the inner peripheral surface of the welding element pipe 1. In addition, although detailed description is abbreviate | omitted, you may use a separate pipe expander in a 1st pipe expansion process and a 2nd pipe expansion process, respectively.

  In the present embodiment, the second pipe expansion step is performed such that the gap portion 1b is pressed by the pressing surface 18a of each die 18 in the cross section orthogonal to the axial direction of the welded element tube 1. Although a detailed description is omitted, the relative positional relationship between the welding base tube 1 and the plurality of dies 18 may be adjusted by rotating the welding base tube 1 in the circumferential direction. The plurality of dies 18) may be adjusted by rotating them in the circumferential direction.

  In this embodiment, the some dice | dies 18 may be replaced | exchanged by a 1st pipe expansion process and a 2nd pipe expansion process. For example, the central angle Ac (see FIG. 3) of the pressing surface 18a of the die 18 used in the second tube expansion step may be set larger than the central angle Ac of the pressing surface 18a used in the first tube expansion step. .

In addition, it is preferable that center angle Ac (degree) of the press surface 18a of the die | dye 18 used in a 2nd pipe expansion process satisfy | fills the relationship of following formula (i), for example.
(360 ° / N) × 0.90 ≦ Ac ≦ (360 ° / N) × 0.95 (i)
However, in said formula (i), N shows the number of dice | dies.

  In addition, when pipe expansion is performed using ten dice | dies 18 in a 2nd pipe expansion process, it is preferable that the center angle Ac of the press surface 18a of the dice | dies 18 is 33 degrees or more, for example. Further, in the first and second tube expanding steps, when tube expansion is performed with ten dies 18, the central angle Ac of the pressing surface 18a of the die 18 used in the first tube expanding step is, for example, 28 °. Set to ~ 32 °.

  The number of dies 18 used in the first tube expansion step and the number of dies 18 used in the second tube expansion step may be the same or different.

  The tube expansion rate in the second tube expansion step is lower than the tube expansion rate in the first tube expansion step. In the present embodiment, the tube expansion rate in the second tube expansion step is set to 0.05 to 0.25 times the tube expansion rate in the first tube expansion step, for example. Moreover, in this embodiment, the pipe expansion rate in a 2nd pipe expansion process is set to 0.05 to 0.20%, for example.

(Function and effect)
In the method for manufacturing a welded steel pipe according to this embodiment, two pipe expansion processes are performed. Specifically, the gap portion 1b generated in the welded pipe 1 in the first pipe expansion process (first pipe expansion process) is pressed by the plurality of dies 18 in the second pipe expansion process (second pipe expansion process). . Thereby, the roundness of the welding pipe 1 (welded steel pipe) can be sufficiently improved.

  Further, the tube expansion rate in the second tube expansion step is lower than the tube expansion rate in the first tube expansion step. That is, in the present embodiment, the roundness of the welded raw material pipe 1 is improved to some extent by expanding the welded raw material pipe 1 at a relatively high expansion rate in the first tube expanding step, and in the second tube expanding step, The roundness of the welded tube 1 is corrected by expanding the welded tube 1 at a low tube expansion rate. Thus, the roundness of the welding base pipe 1 (welded steel pipe) can be appropriately improved by adjusting the pipe expansion ratios of the first pipe expansion process and the second pipe expansion process.

  If the roundness of the welded tube 1 is low, a die 18 having a large size cannot be disposed in the welded tube 1. However, in the present embodiment, as described above, the roundness of the welded tube 1 is improved to some extent in the first pipe expanding step, so that the second pipe expanding step is more than the die 18 used in the first pipe expanding step. It is possible to use a die 18 having a large size. Specifically, the central angle Ac of the pressing surface 18a of the die 18 used in the second pipe expanding step can be set larger than the central angle Ac of the pressing surface 18a used in the first pipe expanding step. Thereby, when performing pipe expansion in the second pipe expansion process, a gap generated between the dies 18 can be reduced, and the roundness of the welded raw pipe 1 (welded steel pipe) can be efficiently improved.

  In general, the radius of curvature of the pressing surface 18a of the die 18 is preferably set so as to correspond to the inner diameter of the welded steel pipe as a product. However, since the inner diameter varies depending on the product, it is difficult to prepare a corresponding die for each product. In this regard, in this embodiment, since the roundness of the welded tube 1 can be appropriately improved by performing the pipe expanding step twice as described above, a die corresponding to each product is prepared. Even if not, the roundness of the welded tube 1 can be sufficiently improved. In other words, one type of die 18 can be shared for a plurality of products having different dimensions. Thereby, the manufacturing cost of a welded steel pipe can be reduced. In addition, when manufacturing different products, it is not necessary to replace the dice 18, so that the working time can be shortened.

  Further, since the roundness of the welded pipe 1 can be sufficiently improved by the first pipe expanding process and the second pipe expanding process, the roundness required in the O press process before the pipe expanding process can be reduced. . This makes it possible to expand the common range of the O-press die.

(simulation)
In order to confirm the effect of the present invention, an analysis model (two-dimensional plane strain model) of the welded pipe 1 and the die 18 was created and FEM analysis was performed. Specifically, the analysis was performed on the assumption that the welding base pipe 1 is expanded with ten dies 18. As the material properties (SS curve) of the welded element tube 1 and the die 18, material properties (SS curve) corresponding to the X65 grade standardized by API (American Petroleum Institute) were used. Note that SS curves obtained by multiplying the stress of the SS curve by 1.1 times and 0.85 times were used as material properties of the welded portion 1a and HAZ, respectively. The coefficient of friction between the welded pipe 1 and the die 18 was set to 0.15. The welding element tube 1 was elliptical. Two types of analysis models were created. Table 1 below shows the conditions of the analysis model.

  Using the two types of analysis models A and B described above, the rounding degree of the welded pipe 1 was examined by changing the pipe expansion rate and performing the first pipe expansion process and the second pipe expansion process. Table 2 below shows the tube expansion rate and the analysis result (roundness) of the first tube expansion step and the second tube expansion step set in the FEM analysis. In this simulation, the difference between the maximum value and the minimum value of the outer diameter of the welded pipe 1 after the second pipe expansion process is defined as roundness. In addition, the analysis No. In 9, the second tube expansion process is not performed.

  As shown in Table 2, analysis no. The roundness of 1 and 3 to 8 and the analysis No. which does not satisfy the requirements of the present invention. From the comparison with the roundness of 2 and 9, it can be seen that according to the present invention, the roundness of the welded tube 1 is sufficiently improved.

  In addition, analysis No. From the comparison between the roundness of 1 and the roundness of analysis No. 7, even if the radius of curvature of the pressing surface 18a of the die 18 is smaller than the inner diameter of the product (nominal diameter in Table 1), the welded tube 1 It can be seen that the roundness of can be sufficiently improved. From this result, according to this invention, even if it does not prepare the die | dye corresponding to every product, it turns out that the roundness of the welding pipe 1 fully improves.

  In FIG. The relationship between roundness in 2-8 and a pipe expansion rate is shown. In FIG. 6, the horizontal axis indicates a value obtained by dividing the tube expansion rate in the second tube expansion step by the tube expansion rate in the first tube expansion step. From the results shown in FIG. 6, by setting the tube expansion rate in the second tube expansion step to 0.05 to 0.25 times the tube expansion rate in the first tube expansion step, the roundness becomes 2.5 mm or less, It can be seen that the roundness is sufficiently improved.

  Further, in FIG. The relationship between the roundness in 2-8 and the pipe expansion rate in a 2nd pipe expansion process is shown. From the result shown in FIG. 7, the roundness becomes 2.5 mm or less and the roundness is sufficiently improved by setting the tube expansion rate in the second tube expansion step to 0.05 to 0.20%. I understand that.

  According to the present invention, a welded steel pipe having a high roundness can be obtained.

1 Welding Element Pipe 10 Expander 18 Die 18a Pressing Surface Ac Center Angle of Arc Formed by Pressing Surface

Claims (4)

A preparation step of preparing a welded pipe made of steel;
A first expanding step of expanding the welded elementary tube by bringing a plurality of dies arranged in the welded elementary tube so as to be aligned in the circumferential direction of the welded elementary tube into contact with the inner peripheral surface of the welded elementary tube;
After the first pipe expansion step, the plurality of dies arranged in the weld base pipe so as to be aligned in the circumferential direction of the weld base pipe are brought into contact with the inner peripheral surface of the weld base pipe to expand the weld base pipe. A second pipe expansion step,
In the second pipe expansion step, the die is brought into contact with a portion of the inner peripheral surface of the welded pipe located between the dies adjacent in the circumferential direction in the first pipe expansion step, and the welding is performed. Expand the tube,
The method for manufacturing a welded steel pipe, wherein the tube expansion rate in the second tube expansion step is lower than the tube expansion rate in the first tube expansion step.   The method for manufacturing a welded steel pipe according to claim 1, wherein a tube expansion rate in the second tube expansion step is 0.05 to 0.25 times the tube expansion rate in the first tube expansion step.   The method for manufacturing a welded steel pipe according to claim 1 or 2, wherein a pipe expansion rate in the second pipe expansion step is 0.05 to 0.20%. Each of the plurality of dies used in the second pipe expanding step has a pressing surface that forms an arc in a cross section orthogonal to the axial direction of the welded element pipe,
The method for manufacturing a welded steel pipe according to any one of claims 1 to 3, wherein a central angle Ac of the arc formed by the pressing surface satisfies a relationship of the following formula (i).
(360 ° / N) × 0.90 ≦ Ac ≦ (360 ° / N) × 0.95 (i)
However, in said formula (i), N shows the number of dice | dies.

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