JPH10277640A - Manufacture of steel tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steel tube manufacture whose yield is improved while various suitable aspects by hot forming are maintained. SOLUTION: During the transportation of a heated tube stock 2 or at the time of hot forming in multiple steps for the tube stock 2, a preventive member 3 against deformation is densely situated inside the end of the tube stock 2, which enables this end part to have a thick state. As a result, a sagging deformation of the end part can be prevented by the receiving of the preventive member 3 and also, forming defects can be avoided at the end part, so that a steel tube product can be perfectly or nearly perfectly formed from one end to the other by hot forming.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for manufacturing a large-diameter rectangular steel pipe having a rectangular shape or a rectangular parallelepiped shape, or a large-diameter round steel pipe, which is used, for example, as a pillar for building. The present invention relates to a method for manufacturing a steel pipe to be employed.

[0002]

2. Description of the Related Art Conventionally, a large-diameter rectangular steel pipe used for, for example, a column material for a building has been obtained by the following manufacturing method. That is, a predetermined diameter corresponding to a large-diameter rectangular steel pipe,
A round steel pipe having a thickness and length is used as a raw pipe, the raw pipe is heated in a heating furnace, and then the heated raw pipe is hot-formed in a round steel pipe forming mill to obtain a purified raw pipe, and It is provided to manufacture a square steel pipe (product steel pipe) by hot forming a raw pipe in a square steel pipe forming mill.

[0003]

The square steel pipe manufactured by the above-mentioned hot forming is transported between the heating furnace and the end of the forming process during the transfer of the heated raw tube or in a plurality of stages by each forming mill. At the time of drawing forming, for example, the end of the raw tube is sagged and deformed, or the end is poorly formed. As a result, both ends are cut and removed in a later step, and the yield is poor (low).

Accordingly, an object of the present invention is to provide a method of manufacturing a steel pipe which can maintain various preferable surfaces by hot forming and can increase the yield. It is.

[0005]

In order to achieve the above-mentioned object, a method for manufacturing a steel pipe according to the first aspect of the present invention is characterized in that a raw pipe is heated, then hot-formed, and then cooled. To obtain the product steel pipe, insert a deformation prevention member to prevent deformation of the end at both ends of the original pipe before heating,
After heating the original tube together with the deformation preventing member, the original tube is hot-formed, and after extracting the deformation preventing member, it is cooled to obtain a product steel tube.

Therefore, according to the first aspect of the present invention, the deformation preventing member is provided inside the end of the original tube during the transportation of the heated original tube or during the forming of the original tube in a plurality of stages of heat. By being densely located, this end can be made thick. Thereby, the sagging deformation of the end portion can be prevented by the receiving of the deformation preventing member, and further, the forming failure of the end portion can be avoided, so that the product steel pipe can be moved from one end to the other end by hot forming. The part can be completely or almost completely formed.

According to a second aspect of the present invention, there is provided a method of manufacturing a steel pipe according to the first aspect, wherein the deformation preventing member is a short tube. Therefore, according to the second aspect of the present invention, the extracted short tube can be used by inserting it again into the original tube.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIGS. 1 to 5 as a state adopted when a square rectangular steel pipe is hot formed.

In FIGS. 1 and 2, for example, in manufacturing a large-diameter rectangular steel pipe, a square hollow polygonal steel pipe (original pipe) 2 having seam welds 1 at most two places is used. At that time, polygonal hollow steel pipe 2 is molded in a wide dimension from the inner surface the width of the flat portion of the opposite internal surface width W ₁ is the final product steel plate portion 2A (described later.) The corner portion the radius of curvature R ₁ of the 2B are formed larger than the radius of curvature of the corner portion of the product steel pipe.

The polygonal hollow steel pipe 2 thus formed is
It is carried on the carrying-in floor device 5. Here, the loading floor device 5 is of a conveyor type, supports a plurality of hollow hollow steel pipes 2 in parallel, and transports the hollow steel pipes 2 in a horizontal direction perpendicular to the length direction. In addition, a short tube (an example of a deformation preventing member) for preventing deformation of the ends of the polygonal hollow steel pipe 2 supported laterally by the loading floor device 5 is provided in the portion of the loading floor device 5. 3) A deformation preventing member supply device 20 for inserting 3 is provided.

As shown in FIGS. 2 to 4, the short tube 3 has a regular square shape similar to the polygonal hollow steel tube 2, and at this time, a flat plate portion 3A having an outer dimension L of the short tube 3 is used. Is equal to the inner width of the product steel pipe, that is,
Are formed in L <W ₁ is narrower dimension than the inner surface the width W ₁ of the polygonal hollow steel tube 2.

As shown in FIGS. 1 and 3, the deformation preventing member supply device 20 is provided on both sides of the loading floor device 5. These deformation preventing member supply devices 20 have the same configuration, and include an arm rod 21 which can be inserted into and removed from the polygonal hollow steel pipe 2 and which can move up and down, and the short pipe provided at a free end of the arm rod 21. The body 3 is constituted by a clamp device 22 capable of clamping the body 3 from the inside.

In order to insert the short tube 3 into both ends of the polygonal hollow steel tube 2, first, as shown by a solid line in FIGS. 1 and 3, the deformation preventing member supply device 20 is pulled out (retracted). At this position, the short tube 3 is clamped (supported) by the clamping device 22. Then, the short tube 3 supported on the deformation prevention member supply device 20 side is opposed to the end of the polygonal hollow steel tube 2 conveyed by the loading floor device 5.

In this state, the arm 21 is pushed into the polygonal hollow steel pipe 2 and the short pipe 3 is inserted into the end of the polygonal hollow steel pipe 2 as shown by the phantom line in FIG. At that time, the outer dimension L of the short pipe body 3 is narrower than the inner face width W ₁ before heating the polygonal hollow steel pipe 2, the flat plate portion on the outer surface 3a and a polygonal hollow steel pipe 2 of the flat portion 3A of the short pipe body 3 2A inner surface 2a
The short tube 3 can be inserted without being caught or clogged since the gap S is generated between the short tube 3 and the gap. The insertion movement of the arm rod 21 is position-controlled by a control device (not shown) so that the short tubular body 3 is located at a predetermined position in the end of the polygonal hollow steel pipe 2.

After the supply (insertion) of the short tubular body 3 is completed, the lower flat plate 2A of the polygonal hollow steel pipe 2 is firstly moved by the downward movement of the arm 21 as shown in FIG.
The lower flat plate portion 3A of the short tube 3 on the inner surface 2a of
The outer surface 3a is brought into contact (landing). Next, after the clamp of the short tube 3 by the clamp device 22 is released,
Move 21 out. In this manner, the short tube 3 can be inserted into the polygonal hollow steel tube 2.

As described above, the inner surface 2a of the polygonal hollow steel pipe 2
When the short tubular body 3 is brought into contact with (landed on), between the inner surface 2a of the upper flat plate portion 2A of the polygonal hollow steel tube 2 and the outer surface 3a of the upper flat plate portion 3A of the short tubular body 3, A gap 2S almost twice as large is formed.

As shown in FIGS. 1 and 2, the polygonal hollow steel pipe 2 having the short pipes 3 inserted at both ends is conveyed to the terminal end of the loading / unloading apparatus 5, and then the roller conveyor 6 is moved.
, And is conveyed in the heating furnace 7 in the longitudinal direction, and is heated at a high temperature A together with the short tube 3 during the conveyance.

Polygonal hollow steel pipe 2 heated to a predetermined temperature
Is carried out of the heating furnace 7 and is carried into the former square steel tube forming mill 8. The former-stage square steel tube forming mill 8 performs hot forming (forming temperature, A ₃ transformation point or more) through a plurality of conical rolls 9 and the like, and draws the front-stage drawing process of the polygonal hollow steel tube 2. Is performed. Next, the polygonal hollow steel pipe 2 is carried into a post-stage square steel pipe forming mill 10. The subsequent RHS molding mill 10, hot forming, such as over a plurality of flat roll 11 (the molding temperature, A ₃ transformation point or above) and performs, stop the subsequent (last stage) to the polygonal hollow steel tube 2 The forming process is performed, and thus, a large-sized square-shaped product square steel pipe (product steel pipe) 4 having a predetermined dimension is hot-formed.

As described above, the polygonal hollow steel pipe 2 is subjected to a plurality of stages of drawing (or a single-stage drawing) by the front-stage square steel tube forming mill 8 and the rear-stage square steel tube forming mill 10. A product square steel pipe (product steel pipe) 4 can be manufactured. At that time, by the draw forming process described above,
Inner surface width W of the phase opposed flat portion 4A in the product RHS 4, narrower than the inner face width W ₁ of the polygonal hollow steel pipe 2, i.e. is molded such that W <W _1, also corner 4B the radius of curvature R of, smaller than the angular portion 2B radius of curvature R ₁ of the polygonal hollow steel pipe 2, i.e. is molded so that R <R _1, the four corners of the corner R are aligned.

Here, the inner surface width dimension W of the product square steel pipe 4 is the dimension of the final product after hot forming and cooling, and immediately after hot forming, as shown in FIG. In addition, due to its thermal expansion, the inner surface width dimension W of the final product
Inner width W + α, ie, W <W + α
<It has become W _1. Accordingly, the outer length L + of the short tubular body 3 equivalent to the inner width W of the product square steel pipe 4 at the time of thermal expansion is obtained.
The internal surface width dimension W + α at the time of thermal expansion is wider than α, that is, W = L + α <W + α.

As described above, the corner 2 of the polygonal hollow steel pipe 2
By the radius of curvature R ₁ of B is molded to a larger size than the radius of curvature R of the corner portion 4B of the product square tube 4, it allows reasonable molding (press molding) easily. The polygonal hollow steel pipe 2 whose material (molecular arrangement) has been returned to the original state by the high-temperature heating A is hot drawn and formed so that the inner surface width dimension W is small and the radius of curvature R of the corner 4B is small. By doing so, the residual stress is also removed, and a final product having a high section modulus, that is, a product square steel pipe 4 can be obtained without changing the material in the entire cross section.

Furthermore, between the heating furnace 7 and the cooling floor device 15, the polygonal hollow steel pipe 2 being heated is being conveyed, and a plurality of stages of drawing forming by the front-stage square steel tube forming mill 8 and the rear-stage square steel tube forming mill 10 are performed. At times, the short tube 3 is densely located within the end of the polygonal hollow steel tube 2, and this end has a plate thickness.

Accordingly, the sagging deformation of the end portion can be prevented by receiving the short tubular body 3, and the end portion can be prevented from being formed poorly. It will be completely or almost completely formed from one end to the other. As a result, cutting and removing of both ends in the post-process becomes unnecessary, or
The cutting and removal is performed in a short dimension, so that a product square steel pipe 4 having a high yield is obtained.

Further, in the product square steel pipe 4 immediately after hot forming, each flat plate portion 4A has a straight surface, and the radius R of the corner portion 4B is sharp and the section modulus is high. In addition, since the polygonal hollow steel pipe 2 has a square shape, the conveyance by the roller conveyor 6 can always be performed in a fixed direction using one flat plate portion 2A. Is
The position of the seam weld 1 can always be aligned in a certain direction.

As shown in FIG. 1, necessary portions (in front of the former square steel tube forming mill 8, between the two square steel tube forming mills 8, 10 and in the subsequent square steel tube forming mills) around the square steel tube forming mills 8 and 10 are shown. One or more places, such as after mill 10)
The required number of descaler devices 12 are provided.
The descaler device 12 injects water with water pressure applied to the product square steel pipe 4 and the like. This water injection removes mill scale and the like and can improve the surface skin.

As described above, the product square steel pipe 4 formed by hot working is received by the cooling floor device 15. The cooling floor device 15 supports a plurality of product square steel pipes 4 in parallel and conveys them in a horizontal direction perpendicular to the length direction. The product square steel pipe 4
Is cooled by an air cooling system, that is, gradually cooled.

The cooling floor device 15 is, for example, an eight-row (multiple-row) chain conveyor device 16 that can be driven intermittently in synchronization.
Are arranged side by side. A post-stage cooling floor device 17 is provided continuously to the end of the cooling floor device 15. The rear cooling floor device 17 has the same configuration as the cooling floor device 15 and is configured by arranging a plurality of chain conveyor devices 18 in parallel. A take-out conveyor device 19 that receives the product square steel pipe 4 from the rear cooling floor device 17 is provided outside the terminal end of the rear cooling floor device 17.

As shown in FIG. 1, on both sides of the cooling floor device 15, a short tubular body 3 located inside the end of the product square steel pipe 4 supported laterally by the cooling floor device 15. Are provided respectively. The deformation preventing member extracting device 25 has the same configuration as the deformation preventing member supply device 20 described above, and has an arm rod 26 that can be inserted into and removed from the product square steel pipe 4 and that can move up and down.
And a clamp device 27 provided at the free end of the arm rod 26 and capable of clamping the short tube 3 from inside.

In order to extract the short pipe 3 from the inside of the product square steel pipe 4, first, the arm rod 26 of the deformation prevention member extracting device 25 is moved into the product square steel pipe 4 and moved to a predetermined position in the short pipe 3. The clamp device 27 is inserted up to. Then clamp device 27
Clamps (supports) the short tubular body 3 (see the phantom line in FIG. 3). And, the arm rod 26 of the deformation preventing member extracting device 25
Is withdrawn (retracted), as shown by the solid line in FIG.
The short tube 3 clamped by the clamp device 27
From the end of the product square steel pipe 4.

At this time, as described above, the width W + α of the inner surface of the short tubular body 3 at the time of thermal expansion is wider than the outer dimension L + α of the short tubular body 3 at the time of thermal expansion, that is, L + α <W + α. Outer surface 3a of body 3 and inner surface 4a of product square steel pipe 4
Since the gap T (approximately 5 mm) or 2T is generated between the short pipe 3 and the short pipe 3, the short pipe 3 can be pulled out without being caught or clogged. Then, the extracted short tube 3 is carried to the deformation preventing member supply device 20 and reused.

The product square steel pipes 4 are successively supplied to the starting end of the chain conveyor device 16 as described above, and the short tube 3 is passed through the deformation preventing member extracting device 25.
Are sequentially extracted.

Thereafter, the product square steel pipe 4 in the cooling floor device 15
By performing intermittent conveyance of the group in a state where the adjacent product square steel pipes 4 are separated from each other, the product square steel pipes 4 are gradually cooled at the same ambient temperature. Then, on the cooling floor device 15, the product square steel pipe 4 is shrunk as it is cooled, and is thereby shrunk to the inner surface width dimension W corresponding to the final product.

The pre-cooled product square steel pipe 4 is transferred from the end of the cooling floor unit 15 to the start end of the post-stage cooling floor unit 17 in FIG.
While being conveyed by the same operation as described above, the subsequent slow cooling is performed. Then, the product square steel pipe 4 which has been cooled in the subsequent stage and has reached the terminal end of the latter cooling floor device 17 is transferred to a take-out conveyor device 19, and thereafter, is conveyed to a cleaning device, a rust prevention device, etc., which are not shown, respectively. And then stored as a product.

Next, a second embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. That is, for example, in manufacturing a large-diameter rectangular steel pipe, a round steel pipe 30 having a predetermined diameter, plate thickness, and length corresponding to a product rectangular steel pipe is prepared on the carry-in floor device 5 as a raw pipe. The loading floor device 5 supports a plurality of round steel pipes 30 in parallel and transports the steel pipes 30 in a horizontal direction perpendicular to the length direction.

Then, a short and round tube (an example of a deformation preventing member) for preventing deformation of the ends of the round steel pipe 30 supported laterally by the carry-in floor device 5 is used to prevent deformation of the ends.
33 is inserted by the deformation preventing member supply device 20. At this time, the short tubular body 33 is supported by the inner peripheral surface 30a of the round steel pipe 30 via the lower circular arc portion (see FIG. 7). In this way, the round steel pipe 30 having the short pipes 33 inserted at both ends is carried into the heating furnace 35 from the end of the carrying-in floor device 5, and in the heating furnace 35, in the longitudinal direction thereof. While being conveyed in a horizontal direction at right angles, it is heated at a high temperature A above the A ₃ transformation point.

That is, the heating furnace 35 is formed in a box shape, in which an intermittent progressive feeding device 36 is disposed, and a carrying-in port 37 is provided in the front furnace wall, and a carrying-out port 38 is provided in the rear furnace wall.
Opening doors 39 and 40 are provided at the carry-in port 37 and the carry-out port 38, respectively. In addition, at a predetermined location,
A predetermined number of heating burners 41 are provided, and a smoke outlet 42 is formed at a predetermined location.

Therefore, after the round steel pipe 30 conveyed to the end of the loading floor apparatus 5 is opened and closed, the round steel pipe 30 is conveyed in a horizontal direction perpendicular to the length direction thereof, and
It is carried into the heating furnace 35 through 37, is supported by the intermittent sequential feeder 36, and after being carried in, the opening / closing door 39 is closed.
Next, the round steel pipe 30 is intermittently conveyed to the rear end side in a transverse direction perpendicular to its length direction by an intermittent sequential feeder 36, and during the conveyance, the A ₃ transformation is caused by the flame from the heating burner 41. High-temperature heating A is performed above the point. The round steel pipe 30 thus heated and transported to the vicinity of the discharge port 38 is discharged through the discharge port 38 that is opened for a short time, and is thus
From 35, it is taken out onto the roller conveyor 6. After the carry-out, the door 40 is closed.

As described above, the round steel pipe 30 heated to a predetermined temperature and carried out in the heating furnace 35 is transferred to the welding seam position adjusting device 43 and is supported by the support roll 44 and the presser roll 45.
By rotating the pipe around the pipe axis through such as to align the position of the seam weld in a certain direction. The round steel pipe 30 from the welding seam position adjusting device 43 is carried into a round steel pipe forming mill 46, is hot-formed in a drawing shape through a plurality of sizing rolls 47 and the like, and is formed into a square product as a final product. The steel pipe is refined to a predetermined diameter so as to be finished in a predetermined dimension, and thus a purified round steel pipe 31 is obtained.

The refined round steel pipe 31 thus purified by the group 46 of round steel pipe forming mills is a pre-stage square steel pipe forming mill.
It is carried into 48. Here, hot forming (forming temperature A ₃ transformation point or higher) is performed via a plurality of conical rolls 49 and the like, and at this time, each flat plate portion of the purified round steel pipe 31 immediately after hot forming is formed. It is formed into an outwardly arcuate surface along the plane.

Next, the refined round steel pipe 31 is formed into a post-stage square steel pipe.
It is carried into the mill 50. This post-stage square tube forming mill 50
Is formed by hot forming (forming temperature
Degree, A _Three Above the transformation point) to the purified round steel pipe 31
On the other hand, the drawing process of the latter stage (final stage) is performed.
Large-diameter product square steel pipe 4 that is the final product with fixed dimensions is hot
Formed. At that time, a short tube that was a perfect circle
33 corresponds to the shape of the product square steel pipe 4 as shown in FIG.
Molded.

The product square steel pipe 4 thus formed by hot working is received on the cooling floor device 15 side. Then,
As described in the first embodiment, the deformation preventing material extracting device
25, the short tube 33 is extracted.

FIGS. 9 and 10 show a third embodiment. As shown in FIG. 9, for example, a square tube 3 having a square shape as shown in the first embodiment is used. It is inserted into the end of a round steel pipe 30 as shown in the second embodiment, and is hot formed as shown in FIG.

FIG. 11 and FIG. 12 show a fourth embodiment. As shown in FIG. 11, for example, a perfect circular short tubular body 33 as shown in the second embodiment is rounded. As shown in FIG. 12, a purified round steel pipe 31 hot-formed and inserted into the end of the steel pipe 30 is used as a product steel pipe.

In each of the above-described embodiments, the polygonal hollow steel pipe 2 is mainly a large-diameter steel pipe, and its size is
For example, the thickness t is 16 to 60 mm, and the material is SN400 B to SN49.
0B and SM520B, and the outer diameter is 450 to 850 mm. In this case, the gap T is formed to 5 to 6 mm. As the polygonal hollow steel pipe 2, for example, a one-seam square steel pipe formed by hot roll forming, a two-seam square steel pipe formed by butt-welding a pair of grooves formed by hot press forming, and a pair of rolled grooves are welded. Become two-seam square steel pipe,
Off-the-shelf large-diameter steel pipes such as a two-seam square steel pipe, a four-sided box, and a seamless steel pipe in which a pair of rolled angle members are welded face to face are used.

In the above-described first embodiment and the like, the product square steel pipe 4 having a square cross section is manufactured, but the product square steel pipe having a rectangular cross section can also be manufactured. By changing the roller arrangement of the double-sided steel pipe forming mills 8 and 10, hot forming of a polygonal product steel pipe such as a pentagonal product square steel pipe or a hexagonal product square steel pipe can be performed.

In each of the above-described embodiments, a square tube 3 or a square tube 33 is used as a deformation preventing member.
Although this is shown, it may be another shape such as a long tube or a cross.

In each of the above embodiments, the short tube 3 and the like are inserted by the deformation preventing member supply device 20, but this may be manually inserted.

[0048]

According to the first aspect of the present invention, during the transportation of a heated raw tube, or during the forming of the raw tube at a plurality of stages of heat, the end of the raw tube is formed. By arranging the deformation preventing member densely, the end portion can be made thick. Thereby, the sagging deformation of the end can be prevented by receiving the deformation preventing member, and furthermore, the forming failure of the end can be avoided, and the product steel pipe can be moved from one end to the other end by hot drawing. Can be completely or almost completely formed. As a result, while being able to maintain various suitable surfaces by hot forming, it is possible to eliminate the need for cutting and removing the both ends in the post-process, or the cutting and removing can be performed in a short dimension, so that the product steel pipe with high yield Can be manufactured.

According to the second aspect of the present invention,
The extracted short tube can be inserted into the original tube again and used, so that the short tube can be used economically.

[Brief description of the drawings]

FIG. 1 shows a first embodiment of the present invention and is a process perspective view of a hot forming facility in a method of manufacturing a steel pipe.

FIG. 2 is a process explanatory view of a hot forming facility in the method of manufacturing the steel pipe.

FIG. 3 is a vertical side view of a deformation preventing member insertion portion in the method of manufacturing the steel pipe.

FIG. 4 is a front view of the steel pipe when a deformation preventing member is inserted in the method for manufacturing the same.

FIG. 5 is a front view of the pipe during hot forming in the method of manufacturing the same steel pipe.

FIG. 6 shows a second embodiment of the present invention and is a process perspective view of a hot forming facility in a method of manufacturing a steel pipe.

FIG. 7 is a front view of the steel pipe when the deformation preventing member is inserted in the method of manufacturing the same.

FIG. 8 is a front view of the steel pipe during hot forming in the method of manufacturing the same.

FIG. 9 shows the third embodiment of the present invention, and is a front view of the pipe when the deformation preventing member is inserted in the method of manufacturing a steel pipe.

FIG. 10 is a front view of the steel pipe at the time of hot forming in the method of manufacturing the same.

FIG. 11 shows a fourth embodiment of the present invention, and is a front view of a pipe when a deformation preventing member is inserted in a method of manufacturing a steel pipe.

FIG. 12 is a front view of the steel pipe during hot forming in the method of manufacturing the same steel pipe.

[Explanation of symbols]

2 Polygonal hollow steel pipe (original pipe) 3 Square-shaped short pipe (deformation prevention member) 4 Product square steel pipe (product steel pipe) 5 Loading floor unit 6 Roller conveyor 7 Heating furnace 8 Front square steel pipe forming mill 10 Rear square steel pipe forming Mill 15 Cooling floor device 17 Rear cooling floor device 19 Removal conveyor device 20 Deformation prevention member supply device 22 Clamp device 25 Deformation prevention member removal device 27 Clamp device 30 Round steel pipe (raw pipe) 31 Refined round steel pipe (product steel pipe) 33 Short tube with perfect circular shape (deformation prevention member) 35 Heating furnace 36 Intermittent progressive feeder 46 Round steel tube forming mill 48 Front stage square tube forming mill 50 Rear stage square tube forming mill A High temperature heating B Heat radiation L Outside of short tube 3 Dimension S Gap T Gap W Inner width of product square steel pipe 4 W ₁ Inner width of polygonal hollow steel pipe 2 W + α Inner width of product square steel pipe 4 when heated and expanded

Claims (2)

[Claims] Claims 1. An original tube is heated and then formed by heating.
And in order to obtain a product steel pipe by cooling, insert a deformation prevention member for preventing deformation of the end portion at both ends of the original tube before heating, and after heating the original tube together with the deformation prevention member,
A method for producing a steel pipe, which comprises forming a raw steel pipe by hot working a raw pipe, extracting a deformation preventing member, and then cooling it. 2. The method according to claim 1, wherein the deformation preventing member is a short tube.