JP2001252722A - U press tool and manufacturing method of uoe steel tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that the opening of a U tube is breadthwise widened in use of using a conventional U tube tool to manufacture a high strength UOE steel tube of an X-80 grade or higher of an API-5L standard, so that the U tube can not be sent into an O press tool. SOLUTION: The U press tool 21 has a fist bend 22 to form a first bent 40b adjacent to an apex part 40a of an U tube 40 and a second bending part 23 to form a second bent 40c having a radius of curvature smaller than a radius of curvature of the first bending forming part 22.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a U press tool and a UOE steel pipe. More specifically, the present invention relates to a U-press tool suitably used for producing, for example, a high-strength UOE steel pipe of X80 grade or more of API-5L standard, and a method for producing a UOE steel pipe using this U-press tool. And about.

[0002]

2. Description of the Related Art Conventionally, the strength required for UOE steel pipes for line pipes has been the mainstream of API-5L standard X65 grade (yield strength of 65000 psi = 448 MPa or more, tensile strength of 77000 psi = 530 MPa or more). FIGS. 9A to 9C are explanatory diagrams schematically showing an example of a U-press process of a UOE steel pipe for a line pipe using a U-type press machine 1 of the Verson type. FIG.
FIG. 2 is an explanatory diagram extracting and showing a U punch 8 mounted on the U press machine 1.

As shown in FIG. 9 (a), UOE steel pipe U
The press supports a steel plate 2 that has been bent at both ends in the width direction by a crimping press with two rockers 4 rotatably supported by a fulcrum 3 and then a punch spacer 5 and a radius of curvature of R _2. Two Courtlands 6
The U-punch 8 which is constructed by exchanging the nose punches 7 each having a radius of curvature R ₁ in a replaceable manner is pressed down, and a vertical load is applied to the steel plate 2 to perform three-point bending. Thereafter, as shown in FIG. 8B, the rocker 4 starts rotating from the time of contact between the steel plate 2 and the lower shoe 4a of the rocker 4. That is, a part of the vertical load given by the U punch 8 acts as a bending moment for rotating the rocker 4 about the fulcrum 3 as a rotation center. Further, as shown in FIG. 8 (c), the U punch 8 is pushed down until the left and right sides of the steel plate 2 are displaced to a position where they are substantially vertical. After the U-press, the opening amount at the upper part of the U-tube 2 'increases due to springback. Therefore, by actually applying an overbend at the U-press, the left and right sides of the U-tube 2' are arranged substantially vertically after unloading. U-press is performed as follows.

Then, as shown in FIG. 11, the shape of the U-tube 2 'after the U-press is completed is transferred to the O-press machine by the U-tube 2'.
In order to stably transport and produce, the width W of the U pipe 2 '
_u and the outer diameter of the product after pipe production (that is, the O-press tool 9
The ratio (W _U / D) to D) is set to 0.95 or less.

[0005] On the other hand, demand for oil and natural gas transportation line pipes has become very active in recent years, reflecting the energy situation in recent years. For example, X80
Grade (Yield strength 800000 psi = 551MPa)
Above, tensile strength of 90000 psi = 620 MPa or more)
Demands for the above high strength UOE steel pipes are increasing.

[0006] Such a high strength UOE for line pipes
A problem in manufacturing a steel pipe is that the width of the U pipe after the U press is increased by springback.
FIG. 12 shows the width W _U by springback after U-press.
FIG. 4 is an explanatory view showing an example of a U-tube 2 ′ in which the width has spread.

[0007] As described above, the width W _U of the U pipe 2 ′ is increased, and the width O U of the U pipe is almost the same as the outer diameter of the UOE steel pipe as the final product.
If it becomes larger than the inner diameter of the press tool 9, the U pipe 2 '
It becomes physically impossible to convey into the press tool 9. FIG. 13 is an explanatory diagram showing that the U pipe 2 ′ cannot be transported into the O-press tool 9 because the width W _U of the opening has widened.

At present, the transfer of the U pipe 2 'into the O-press tool 9 is performed by an O-shaft supported on the distal end of a large number of continuous arms 11 provided in a transfer facility 10 within the O-press tool shown in FIG. Since the press container lance roll 12 is used, the width of the opening of the U pipe 2 'can be somewhat reduced. However, in order to convey the U-tube 2 ′ of the high-strength UOE steel pipe of, for example, X80 grade with the widened width W _{U of the} opening into the O-press tool 9, the tightening ability by the O-press container lance roll 12 alone is not sufficient. For example, it is necessary to perform a large-scale equipment modification such as adding a U-tube width tightening device to the O-press tool transfer equipment 10, which is not practical.

By the way, until now, U press after U press
Various inventions for optimizing the shape of the tube have been proposed. For example, Japanese Unexamined Patent Publication (Kokai) No. 59-209425 discloses that the range of 100 to 150 degrees at the bottom is such that the radius of the U-tube that springs back after the U-press becomes a radius of curvature substantially equivalent to the inner diameter of the subsequent O-press tool. Optimizing the shape of the U pipe by performing a U-press using a U-press tool having a side curvature radius at both sides continuous to the bottom at least 30% smaller than the bottom curvature radius, An invention has been proposed that improves the workability of subsequent O-pressing, tacking, and the like to improve both quality and productivity.

Japanese Unexamined Patent Publication (Kokai) No. 56-50722 discloses that the gap between two brake rolls supporting a steel plate as a material of a U pipe and the height of a press saddle supporting a bottom of the U pipe are disclosed. By appropriately changing at least one, the pressing contact point of the brake roller against the steel plate in the preceding press is sequentially changed outwardly in the steel sheet width direction from the pressing contact point in the subsequent press, so that the U pipe An invention for reducing the width of the opening has been proposed.

[0011]

However, Japanese Unexamined Patent Publication No.
The invention disclosed in Japanese Patent Publication No. 209425 is "...
The yield stress of UOE steel pipe is 30-70kgmm ² ...
As is clear from the description of ".", Since a steel sheet of at most X75 grade is applied, a higher strength UOE steel pipe such as X80 grade cannot be applied. Further, in the present invention, since the U press tool is integrally formed, in order to change the size of the U pipe for performing the U press, various different U press tools corresponding to the size must be manufactured. U
Both the man-hours and manufacturing costs of the press tool increase.

The invention disclosed in Japanese Patent Application Laid-Open No. 56-50722 discloses a so-called U-press machine in which two brake rolls and a press saddle operate in conjunction with the progress of a press via a link mechanism. Kaiser type U
It can be applied only to a press machine, and cannot be applied to, for example, a so-called burson-type U press machine which performs bending on a steel plate by rotating a rocker beam corresponding to a brake roll and positioned according to a steel pipe dimension. Further, in the present invention, since the press is performed a plurality of times, the cycle time of the U press increases, and the productivity decreases.

Here, an object of the present invention is to surely transport the steel pipe into the O-press tool when manufacturing a high-strength UOE steel pipe of X80 grade or more of the API-5L standard without large-scale equipment remodeling. An object of the present invention is to provide a U-press tool capable of suppressing the widening of the opening of the U-tube as much as possible, and a method of manufacturing a UOE steel pipe using the U-press tool.

[0014]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems by changing the shape of a U-press tool to a shape capable of forming at least two small-diameter bent deformation portions on a steel plate as a raw material. It is based on new and important knowledge that it can be solved reliably.

[0015] The present invention provides at least a first bent deformation portion forming a first bent deformation portion adjacent to a top of a U tube, which is a material of a UOE steel tube; And a second bending deformation forming portion forming a different second bending deformation portion.

In the U press tool according to the present invention,
(1) the radius of curvature of the second bent deformation forming portion is smaller than the radius of curvature of the first bent deformation forming portion; (2) the second bent deformation forming portion has a pressing direction at the time of U-press. Being provided behind the first bending deformation forming portion,
(3) The second bending deformation forming portion is provided apart from the first bending deformation portion with respect to the pressing direction at the time of the U-press, and (4) the first bending deformation forming portion and the second bending deformation forming portion. The curvature radius of each of the bending deformation forming portions is the first.
It is preferable that at least one of the smaller than the radius of curvature of the general portion excluding the bent deformation forming portion and the second bent deformation forming portion is satisfied.

From another viewpoint, the present invention relates to a method of manufacturing a UOE steel pipe by performing a U-press to produce a U-tube and then performing an O-press on the U-tube. A method of manufacturing a UOE steel pipe, comprising forming a second bent deformation section different from the first bent deformation section in a U pipe after forming one bent deformation section.

In the method of manufacturing a UOE steel pipe according to the present invention, the width of the opening of the U pipe after the U press is 0.95 or less of the outer diameter of the product after the pipe is formed.
It is desirable to smoothly perform the O press performed subsequent to the U press.

In the present invention, the term "bent deformed portion" means an arc-shaped deformed portion having such a small diameter that the direction of extension of the side wall portion of the U pipe at the time of completion of the U press can be changed. And the “first bending deformation portion” is U
The “second bent portion” is formed adjacent to the top of the tube, and is formed at a position near the opening of the U tube in the side wall portion of the U tube.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a method for manufacturing a U-press tool and a UOE steel pipe according to the present invention will be described in detail with reference to the accompanying drawings. In the following description of the embodiments, the same components as those in FIGS. 9 to 14 described above are denoted by the same reference numerals, and redundant description will be omitted as appropriate.

FIG. 1 is a simplified perspective view showing a U press machine 20 to which a U press tool 21 of the present embodiment is applied. FIG. 2 is a view taken in the direction of arrow A in FIG.
The press tool 21 and the U pipe 40 are extracted and shown. In addition,
In the present embodiment, a case where a so-called Burson-type U press machine 20 is used will be described as an example.

As shown in FIGS. 1 and 2, the U-press tool 21 of the present embodiment includes a first bending deformation forming portion 22,
Both the second bending deformation forming part 23 and the general part 24 are provided. Hereinafter, these components of the U press tool 21 will be sequentially described.

[First Bending Deformation Forming Section 22] The U-press tool 21 of the present embodiment has a punch spacer 25 and two coat lands 26, like the conventional U-punch 8 described above with reference to FIG. And a nose punch 27, both of which are interchangeably mounted.

On the upper part of the punch spacer 25, a support member 29 is fixed by appropriate means. Support member 29
Is supported by a lifting mechanism (not shown) so as to be movable in the vertical direction (the direction of the double arrow in FIGS. 1 and 2).

At the tip of the nose punch 27, an arc portion 30 having a radius of curvature R1 is formed. The arc portion 30 comes into contact with the inner peripheral surface of the top portion 40a of the U pipe 40 at the time of U press. Since the circular arc portion 30 is formed in the same manner as the conventional U punch 8, further description is omitted.

Further, first bent deformation portions 22 are formed on each of the two coat lands 26. Each of the first bent deformation forming portions 22 is formed adjacent to and continuous with the circular arc portion 30 formed at the tip of the nose punch 27. For this reason, the first bent deformation forming parts 22, 22 are in contact with the inner peripheral surface of the U pipe 40, so that the first bent deformation forming parts 22, 22 are adjacent to the top 40 a of the U pipe 40.
Are formed respectively.

The first bent portions 40b, 40b
Each of the U-shaped punches 8 is a small-diameter arc-shaped deformed portion having a curvature radius R2 (R2> R1) similar to that of the nose punch 7 of the conventional U-punch 8, and the side wall of the U pipe 40 at the time when the U-press is completed. The extension direction is changed to a direction in which the upper opening of the U pipe 40 is narrowed. In the present embodiment, the first bending deformation portions 40b, 40b are different from the conventional U punch 8,
The lower part of each of the two coat lands 26 is formed in a range of about a quadrant.

In this embodiment, the first bending deformation forming section 2
2, 22 are formed as described above. [Second bending deformation forming section 23] In the present embodiment, the second bending deformation forming section 2 is provided on each of the two coat lands 26.
3 and 23 are formed.

Each of the second bending deformation forming portions 23, 23 has a pressing direction (a direction parallel to the double-headed arrow in FIGS. 1 and 2 and a direction from the upper side to the lower side) during the U-press. The first bent deformation forming part 22 is provided at a position rearward of the first bent deformation forming part 22. Further, the second bending deformation forming part 23,
23 is formed in the upper part of each of the two coat lands 26 in a range of about a quadrant.

The radius of curvature R3 of the second bent deformation forming portions 23 is set smaller than the radius of curvature R2 of the first bent deformation forming portions 22. Further, each of the radii of curvature R2 and R3 of the first bending deformation forming portion 22 and the second bending deformation forming portion 23 excludes the first bending deformation forming portion 22 and the second bending deformation forming portion 23. General part 2
4 (described later) is set smaller than the radius of curvature.

For this reason, the second bending deformation forming portions 23, 2
3 comes into contact with the inner peripheral surface of the U pipe 40,
The second bent deformation portions 40c, 40c are formed at positions near the opening of the U-tube 40 in the right and left side wall portions of the zero.

The second bent portions 40c, 40c
Each of them is a small-diameter arc-shaped deformed portion that can change the extending direction of the side wall portion of the U pipe 40 at the time when the U press is completed.
Change the direction to narrow the upper opening of the U-tube 40.

In this embodiment, the second bending deformation forming section 2
3, 23 are formed as described above. [General part 24] As shown in FIGS. 1 and 2, the second bending deformation forming part 23
The general portion 24 is provided separately from the first bending deformation forming portion 22, and is provided between the first bending deformation forming portion 22 and the first bending deformation forming portion 22.

The general portion 24 is formed in a substantially linear shape in order to secure a processing amount of the U-tube 40 in the pressing direction at the time of the U-press. Does not occur.

In the present embodiment, the general portion 24 is formed as described above. U press tool 21 of the present embodiment
As described above, the first bent deformation forming portions 22 and 22 and the general portion 2
4 and the second bending deformation forming portions 23, 23 are formed in this order in the pressing direction at the time of U-press.

The selection of the U press tool 21 depends on the U pipe 4
The size of each part of the U-press tool 21 may be appropriately determined according to the size of the U-tube 40 to be manufactured, because it is limited by equipment conditions such as interference with zero and a press stroke.

Next, the U-press tool 21 is assembled into a so-called Verson-type U-press machine 20, which is commonly used.
The situation in which the press is performed will be described. As shown in FIG. 1, two rockers 4 and 4 rotatably supported by a fulcrum 3 are arranged in this U-press machine 20, and bending is performed on both ends in the width direction by a crimping press. After the stripped steel plate 40 is supported by the two rockers 4, 4, the U-punch 28, which is formed by exchanging the punch spacer 25, the two coat lands 26, and the nose punches 27, is pressed down. A three-point bending process is performed by applying a vertical load.

Thereafter, the outer surface of the steel plate 40 and the rockers 4, 4
The rockers 4 and 4 start to rotate about the fulcrum 3 as the rotation center from the time of contact with the respective lower shoes 4a and 4a. Further, when the U punch 28 is pressed down, the steel plate 40 is displaced to a position where the left and right sides thereof are substantially vertical.

At this time, in the present embodiment, since two coat lands 26, 26 are provided with not only the first bent deformation forming portions 22, 22, but also the second bent deformation forming portions 23, 23, After the first bent portions 40b and 40b are formed adjacent to the top 40a of the tube 40, the second bent portion 40b is located at a position close to the opening of the U tube 40 on the left and right side walls of the U tube 40.
Are formed.

Here, the first bent portions 40b, 40b
And the second bending deformation portions 40c, 40c,
This has the effect of changing the extending direction of the side wall of the U pipe 40 to a direction in which the upper opening of the U pipe 40 is narrowed. Therefore, U pipe 4
Even if 0 is made of a high-strength steel plate corresponding to, for example, the X80 grade of the API-5L standard, it is possible to reliably and easily prevent the width of the U pipe 40 after the U press from being widened by springback.

In the present embodiment, the second bending deformation portions 23, 23 having a smaller diameter than the first bending deformation forming portions 22, 22.
It is considered that the reason why the width of the U pipe 40 is prevented from being increased after the U press by providing the above is technically as follows.

That is, in order to calculate the bending radius of the U pipe 40 after the U press and to calculate the optimum U press tool shape,
Calculate the springback during simple bending. FIG.
Is a graph showing an example of a stress σ-strain ε diagram of the steel sheet 40 subjected to the U press forming. Here, the Young's modulus of the steel sheet 40 is E, the plasticity coefficient is D, and the yield stress is σ _y .

As shown in FIG. 4, assuming that the radius after springback when simple bending is performed on the steel plate 40 with a tool having a radius R is R ′, reference is made to FIG. Thus, the following equation (1) is obtained.

[0044]

(Equation 1)

Here, in the state of spring back, M
Since = 0, the following equation (2) is obtained.

[0046]

(Equation 2)

Therefore, the radius R ′ after the simple bending of the springback is given by the following equation (3).

[0048]

(Equation 3)

FIG. 6 is a graph summarizing the results of calculating the radius R 'after springback using the equation (3). As shown in the graph of FIG. 6, the smaller the thickness of the workpiece and the larger the tool radius R, the larger the radius R 'after springback.

Therefore, in order to reduce the width of the U-tube of the high-strength steel plate, it is effective to reduce the tool radius R for the same thickness and strength. In the present embodiment, since the second bending deformation forming portions 23, 23 having a curvature smaller than the radius of curvature of the first bending deformation forming portions 22, 22, are provided in the U press tool 21, the second bending deformation forming portions 23, 23 after the U press are formed. The widening of the U-tube 40 is prevented.

[0051]

EXAMPLES The present invention will be described more specifically with reference to examples. (Embodiment 1) U-press tools BD according to the present invention shown in FIGS. 1 and 2 and a conventional U-press tool A shown in FIG.
And an outer diameter of 36 ″ (914.4 mm) and a wall thickness of 1
0,12,14,16mm and tensile strength 950MP
a, U-press was performed using four types of steel plates having a YR (yield strength / tensile strength ratio) of 95% or more.

Table 1 summarizes the dimensions of each of the U-press tool 21 and U-press tool 8.

[0053]

[Table 1]

As shown in Table 1, the conventional U-press tool A has a substantially semicircular shape in which only the first bent deformation forming portion is formed on the coat lands 6 and 6 and is combined with the nose punch 7. Thus, it was a so-called double R shape in which two R surfaces were formed. As shown in Table 1, this U-press tool A has a radius of curvature R of an arc portion formed on the outer surface of the coat lands 6,6.
However, each was 144 mm and uniform.

On the other hand, the U press tools B to
D has a first bent deformation forming portion 22 and a second bent deformation forming portion 23 formed on the coat lands 26, 26 in a substantially quadrant shape in the up and down direction. It was a so-called triple R shape formed on the surface. In this embodiment, in order to secure the tool height necessary for the U-press forming, a linear general portion 24 is provided between the first bent deformation forming portion 22 and the second bent deformation forming portion 23. Provided. In the U-press tools B to D, the radius of curvature R3 of the arc-shaped portion formed in the second bending deformation forming portion 23 was set to be gradually smaller.

The results are summarized in the graph of FIG. FIG.
As shown in the graph, when the thickness of the steel plate is as thin as 10 mm, in the conventional U press tool A, the ratio of the U pipe width / outer diameter exceeds 0.95 which is a manufacturable line, and the O press Could not do.

On the other hand, the U press tools B to
In D, the width of the opening at the upper part of the U pipe 40 can be reduced. In particular, if the U press tool D is used, even if the thickness of the steel sheet is the thinnest, the U pipe width / outside can be reduced to below the production line. It has become possible to reduce the diameter ratio.

This is a result substantially similar to the result suggested by the above-described calculation formula for giving a bending radius after springback in simple bending of a steel plate. Next, outer diameter 36 ''
A similar test was conducted for other sizes (26 ″, 50 ″). Table 2 summarizes the dimensions of each of the U-press tool 21 and U-press tool 8 used.

[0059]

[Table 2]

FIG. 8 is a graph collectively showing the test results when the thickness of the steel sheet is 10 mm. As is clear from the graph shown in FIG. 8, the curvature of the second bending deformation forming portion 23 is the same for both the outer diameters of 26 ″ and 50 ″ as in the case of the outer diameter of 36 ″. By setting the radius smaller than the radius of curvature of the first bending deformation forming part 22,
The width of the upper opening of the U pipe 40 can be reduced, and the U pipe width / outer diameter ratio can be suppressed to 0.95 or less, which is a line that can be manufactured.

(Modification) In the description of the embodiment and the examples, the case where a so-called Verson-type U-press machine is used is taken as an example. However, the present invention is not limited to this form. The present invention is equally applicable to other U-press machines such as U-press machines.

In the description of the embodiments and examples,
Although the case where the first bending deformation forming portion and the second bending deformation forming portion are formed on the coat land constituting the U press tool is taken as an example, the present invention is not limited to this form, and Along with the first and second bending deformation forming portions, another bending deformation forming portion capable of forming the bending deformation portion in the U-tube in the same manner as the second bending deformation forming portion is 1 or 2
The above may be provided. In this case, the radius of curvature of each of the second bending deformation forming portion and the other bending deformation forming portion may be set to be larger than the radius of curvature of the second bending deformation forming portion in the embodiment and the example.
It is desirable to reduce the width of the upper opening of the U pipe while performing the U press smoothly.

Further, in the description of the embodiment and the example, the case where the general portion is formed in a substantially linear shape is taken as an example.
However, the present invention is not limited to this form, and may have another shape such as an arc shape.

[0064]

As described above in detail, according to the present invention, for example, API-
When manufacturing a high strength UOE steel pipe of X80 grade or more of 5L standard, a U-press tool capable of suppressing the widening of the opening of the U-tube so as to be surely conveyed into the O-press tool; A method of manufacturing a UOE steel pipe using a tool can be provided together.

The significance of the present invention having such effects is extremely remarkable.

[Brief description of the drawings]

FIG. 1 is a simplified perspective view showing a U press machine to which a U press tool according to an embodiment is applied.

FIG. 2 is a view taken in the direction of arrow A in FIG. 1, and shows a U press tool and a U pipe extracted therefrom.

FIG. 3 shows stress σ-strain ε of a steel sheet subjected to U-press forming
It is a graph which shows an example of a diagram.

FIG. 4 is an explanatory diagram showing a radius after springback R ′ when a simple bending is performed on a steel plate with a tool having a radius R.

FIG. 5 is an explanatory diagram showing symbols of respective parts of a steel plate.

FIG. 6 is a graph collectively showing a result of calculating a radius R ′ after springback using Expression (3).

FIG. 7 is a graph collectively showing the results of Examples.

FIG. 8 is a graph collectively showing the results of Examples.

FIGS. 9A to 9C are explanatory views schematically showing an example of a U-pressing process of a UOE steel pipe for a line pipe using a U-type burson press.

FIG. 10 is an explanatory diagram extracting and showing a conventional U punch mounted on a U press machine.

FIG. 11 is an explanatory view showing a shape of a U pipe after a U press is completed.

[FIG. 12] Width W _U by springback after U-press
It is explanatory drawing which shows an example of the U pipe which spread.

FIG. 13 is an explanatory view showing that the U-tube cannot be transported into the O-press tool because the width W _{U of the} opening is widened.

FIG. 14 is an explanatory view showing the transfer equipment in the O-press tool.

[Explanation of symbols]

 21 U press tool 22 First bending deformation forming part 23 Second bending deformation forming part 40 U pipe 40a Top part 40b First bending deformation part 40c Second bending deformation part

Claims (7)

[Claims] 1. At least U which is a material of UOE steel pipe
A first bending deformation forming portion forming a first bending deformation portion adjacent to a top portion of a pipe; and a second bending deformation portion forming a second bending deformation portion different from the first bending deformation portion in the U-tube. A U-press tool comprising a bending deformation forming portion. 2. The U-press tool according to claim 1, wherein a radius of curvature of the second bending deformation forming portion is smaller than a radius of curvature of the first bending deformation forming portion. 3. The U-press according to claim 1, wherein the second bending deformation forming portion is provided behind the first bending deformation forming portion with respect to a pressing direction at the time of the U-press. tool. 4. The device according to claim 1, wherein the second bending deformation forming portion is provided apart from the first bending deformation portion with respect to a pressing direction at the time of U-press.
U-press tool described in the paragraph. 5. A curvature radius of each of the first bending deformation forming portion and the second bending deformation forming portion,
The U-press tool according to any one of claims 1 to 4, wherein the radius of curvature is smaller than the radius of curvature of the general portion excluding the first bending deformation forming portion and the second bending deformation forming portion. 6. A method of manufacturing a UOE steel pipe by performing a U-press to manufacture a U-tube and then performing an O-press on the U-tube, wherein a first bent deformation portion is formed adjacent to the top of the U-tube. And forming a second bent portion different from the first bent portion on the U-tube.
Manufacturing method of E steel pipe. 7. The production of a UOE steel pipe according to claim 6, wherein the width of the opening of the U pipe after the U press is performed is 0.95 or less of the outer diameter of the product after pipe production. Law.