RU2601844C2 - Method of producing steel pipe - Google Patents

Abstract

FIELD: metallurgy; technological processes.

SUBSTANCE: invention relates to metal forming and can be used for production of flexible steel pipe. Cylindrical shape is imparted to a flexible three-point sheet on width. Edges of non-expanded pipe are connected means of a welded seam. Expander pipe with segments for expansion of said pipe is introduced. Expander segments are pressed to all regions, without deformation as a result of three-point bending. Number of three-point bends is set depending on number of expander segments.

EFFECT: providing a regular round pipe shape of pipe.

1 cl, 2 tbl, 7 dwg

Description

Technical field

The invention relates to a method for manufacturing a thick-walled large-diameter steel pipe used in pipelines and the like.

State of the art

UOE steel pipes are widely used as thick-walled large-diameter steel pipes for pipelines. Such steel pipes are manufactured by bending a steel sheet having a predetermined width, length and thickness, first to a U-shape and then to an O-shape, followed by welding a seam to produce a steel pipe and expanding the pipe to increase its diameter and improve roundness . The above method of manufacturing a steel pipe requires the application of a significant pressure force at the stages of processing the pressure of the steel sheet to U-shaped and O-shaped, which is associated with the need to use large-sized press equipment.

A method has been developed for the manufacture of thick-walled steel pipes of large diameter with a reduced pressure force. For example, there is a method of bending an end portion across the width of a steel sheet (bending the edges) and repeatedly performing three-point bending to profile the steel sheet to a substantially cylindrical shape, welding a seam to form a steel pipe, and introducing a pipe expander inside the steel pipe to perform expansion. The pipe expander is equipped with many segments made in the form of separate arc segments with a curved surface, which affect the steel pipe to improve the accuracy of the round shape by pressing the curved surface to the inner side of the steel pipe, increasing the size of the pipe (pipe expansion).

In the manufacture of a steel pipe by the above method, with an increase in the number of three-point bends, the cylindricality of the finished steel pipe increases, but at the same time, it takes a long time to manufacture such a pipe, which reduces productivity. Conversely, if the number of three-point bends decreases, productivity increases, but the accuracy of matching a steel pipe with a regular round shape is degraded. In fact, for the manufacture of a steel pipe, it is required to determine the number of three-point bends depending on the size of the steel pipe.

For example, it was experimentally established that 50-60 three-point bends are required for the manufacture of a steel pipe with a diameter of 1200 mm.

On the other hand, the possibility of reducing the number of bends of a steel pipe and obtaining its regular round shape is investigated. For example, JP 2005324255 A discloses a method in which a steel pipe is subjected to 4 bending in a die, after which welds are made to form a steel pipe, and then the heated steel pipe is hot rolled to obtain the desired shape.

However, in the known method, heating of the steel pipe is required, therefore, it is necessary to use a heating device, which increases production costs. In addition, as a result of heating a steel pipe, its strength, toughness, weldability, etc., acquired by the steel pipe blank due to accelerated cooling, etc., are deteriorated.

Disclosure of invention

The invention was developed taking into account the above problems and is aimed at creating a method for manufacturing a large diameter steel pipe by means of multiple three-point bending, which does not require heating during the manufacture of the pipe and while ensuring the correct round shape even with a reduced number of three-point bends.

In the manufacture of a steel pipe, the number of three-point bends or the center-to-center distance between the stamp elements (pitch of the steel sheet) is usually set so as not to create a gap in the deformable region that is formed during bending to improve the accuracy of the round shape of the steel pipe. In this regard, when reducing the number of three-point bends to reduce the time of manufacturing a steel pipe, the center-to-center distance between the stamp elements increases, and therefore, the deformable region curved by three-point bending will be arched, while the undeformed region will be flat, so the accuracy is round finished steel pipe will be low.

In this regard, attention was drawn to the magnitude of the deformation of the steel pipe during its expansion and additional studies of the method were carried out to improve the accuracy of the round shape of the steel pipe made by multiple three-point flexible. As a result, it was found that during pipe expansion there is a tendency for the strain value (expansion value) to become large at the points of contact between the segments of the inserted pipe expander and the inner surface of the steel pipe, while the value of deformation at places of the pipe that do not contact the expander segments turns out to be small.

Based on the foregoing, it was hypothesized that when expanding a welded steel pipe after three-point bending, an undeformed region remaining in a flat state acquires an arcuate shape due to compression of the expander segment to this undeformed region during pipe expansion and forms a continuous circular arc together with a previously deformed one through a three-point are flexible by the area, providing the correct round shape of the steel pipe, which ultimately leads to ostizheniyu purposes of the invention. The steel pipe after welding and before expansion is hereinafter referred to as the “unexpanded pipe”.

Thus, the invention relates to a method for manufacturing a steel pipe, according to which a steel sheet subjected to bending of its edges is cylindrical by multiple three-point bending along the width of the sheet, the edges of the sheet are welded to form an unexpanded pipe, and a pipe expander with a plurality is inserted into the unexpanded pipe segments to expand this pipe. According to the invention, when expanding a pipe, the expander segments are pressed against all areas that are not deformed during three-point bending.

The number of three-point bends is equal to aN-1, where a is an integer of 1, 2, etc., and N is the number of expander segments.

When manufacturing a thick-walled large-diameter pipe in this way, the number of three-point bends can be reduced without the need for heating the steel pipe, which makes it possible to produce steel pipes of the correct round shape with high productivity without compromising the properties of the steel sheet, such as strength, impact strength, weldability, etc.

Brief Description of the Drawings

In FIG. 1 shows a process for manufacturing an unexpanded pipe in accordance with the invention;

in FIG. 2 schematically illustrates a three-point bending method;

in FIG. 3 - steel pipe A (an example according to the invention) formed by expanding an unexpanded pipe having 12 undeformed regions formed by 11 three-point bends by means of 12 expander segments;

in FIG. 4 - steel pipe B (an example according to the invention) formed by expanding an unexpanded pipe having 20 undeformed regions formed by 19 three-point bends by means of 10 expander segments;

in FIG. 5 - steel pipe D (comparative example) of expansion of an unexpanded pipe having 12 undeformed regions formed by 11 three-point bends by means of 12 expander segments;

in FIG. 6 - steel pipe G (comparative example) expanding unexpanded pipe through 10 segments of the expander, after receiving it through 11 three-point bending;

in FIG. 7 - difference m.

The implementation of the invention

After bending both end sections (dimension L) in the width direction of the steel sheet 3 having a width W, as shown in FIG. 1 (a), to form curved sections (hereinafter referred to as “bending the edges”) one half of the sheet, which is divided in half by the center line CL, as shown in FIG. 1 (b) is repeatedly subjected to three-point bending 4 from one end of the steel sheet 3 in the direction along the width of the sheet to the center (provided that the portion at the center line CL in the width direction remains unpressed), as a result of which one half of the steel sheet 3 acquires, essentially a semicircular shape. When performing three-point bending, the steel sheet 3 is placed on the two lower parts 5a, 5b of the stamp located at a given distance, and the curved curved surface of the upper forming tool 6 is pressed against the steel sheet 3 to perform bending. The distance between the pressure applying positions of the upper forming tool during the three-point bending 4 (which may hereinafter be referred to as the “feed pitch P”) is equal to the distance. However, three-point bending cannot be used when bending the edges, since the end portion of the steel sheet 3 does not touch one of the lower die elements. To this end, edge bending is usually accomplished using a pair of stamp elements, upper and lower.

As shown in FIG. 1 (c), the remaining half of the steel sheet in the width direction from the center line CL is repeatedly subjected to three-point bending 4 at equal distances (provided that the section at the center line CL in the width direction remains unpressed), as a result, the other half of the steel sheet 3 acquires essentially semicircular shape. And finally, as shown in FIG. 1 (d), both end sections along the width of the steel sheet 3 are joined by performing three-point bending 4 at the location of the center line CL along the sheet width, and then a weld is made to form an unexpanded pipe 1, as shown in FIG. 1 (e).

In the unexpanded pipe 1 made in this way, there are arched deformed regions 8 (sections shown in Fig. 3 by a solid line) and flat undeformed regions 9 (sections shown by a dotted line in Fig. 3). The deformed region 8 is a place subject to deformation as a result of a series of three-point bending operations, as shown in FIG. 1 (or a place that underwent deformation as a result of applying pressure using an arcuate curved surface of the upper forming tool 6), and the undeformed region 9 is a place that did not undergo deformation during three-point bending.

A pipe expander containing a series of segments formed as a series of separate arcs with a curved surface is inserted inside an unexpanded pipe and increases in size in the radial direction to expand the unexpanded pipe to give it the desired shape. As indicated above, the unexpanded pipe has arched deformed regions and flat undeformed regions, therefore, it is required to deform the flat undeformed regions to an arched shape to improve the accuracy of the round shape of the steel pipe. However, since there are gaps between the expander segments, an unexpanded pipe cannot expand uniformly in the circumferential direction.

In accordance with the invention, when expanding a pipe by inserting a pipe expander with multiple segments inside an unexpanded pipe, the curved curved surfaces of the expander segments exert pressure on all undeformed areas of the unexpanded pipe. Thus, the deformation of undeformed regions occurs and the deformation of deformed regions that do not contact the expander segments is prevented, as a result of which the undeformed regions can form a continuous arc together with the deformed regions previously deformed to an arcuate shape, which improves the quality of the round shape of the steel pipe.

In order to deform undeformed regions into an arcuate shape to ensure a regular round shape, as described above, it is preferable that the number of undeformed regions in an unexpanded pipe be the same as the number of expander segments in a pipe expander inserted inside an unexpanded pipe. In other words, when the number of expander segments is N, it is preferable to perform three-point bending so that undeformed regions are formed in the unexpanded pipe in N places. In this case, in the gaps between the N segments of the expander, one weld and N-1 deformed areas will be located. The number of operations of three-point bending can also be N-1.

For example, as shown in FIG. 3, the number of undeformed regions 9 coincides with the number of expander segments 2, i.e. An example of expansion of an unexpanded pipe 1 by twelve segments 2 of an expander is presented, while the sheet was subjected to three-point bending 11 times. As shown in FIG. 3, the number of three-point bends 4 made on the sheet stock to produce twelve undeformed regions 9 can correspond to 5 three-point bends 4 of one half of the sheet, separated by a center line CL along the width of the sheet, as shown in FIG. 1 (b), 5 three-point bends 4 of the other half of the sheet, separated by a center line CL along the width of the sheet, as shown in FIG. 1 (c), and 1 three-point bending 4 at the location of the center line CL along the width of the sheet, as shown in FIG. 1 (d) (a total of 11 three-point bends). This is due to the fact that undeformed regions are located in 12 places between the regions deformed by three-point bending (10 places) and between the curved edge region and the deformed three-point flexible region (2 places). Thus, the expansion of the pipe can be performed by pressing the twelve segments of the expander to all 12 corresponding undeformed areas.

The number of undeformed areas in an unexpanded pipe may be a multiple of the number of expander segments inserted inside the unexpanded pipe, for example, 2-fold, 3-fold, etc. In FIG. Figure 4 shows the case where pipe expansion is performed by inserting a ten-segment pipe expander 2 into an unexpanded pipe 1 having twenty undeformed regions formed by 19 three-point bends, i.e. when the number of undeformed regions 9 is 2 times the number of segments 2 of the expander. In this case, each segment of the expander can be pressed to all undeformed areas so that one segment of the expander will be pressed to two adjacent undeformed areas. As shown in FIG. 4, the number of three-point bends required to form 2N places of undeformed areas, corresponding to a 2-fold number of expander segments, can be 2N-1.

As indicated above, when the number of expander segments is N, the number of three-point bends is aN-1, where a is an arbitrary integer, for example, 1, 2, etc. In FIG. 3 shows an example where a = 1, and in FIG. 4 shows an example where a = 2. Even if a is 3 or more, each segment of the expander is pressed to the places of undeformed areas, and all undeformed areas can be pressed to the segments of the expander.

The step of feeding the steel sheet during three-point bending is constant so that the width of the undeformed region corresponds to the pitch of feeding during bending. The feed step P _p is expressed by the following equality (1), where the initial position of the three-point bending from the center of the plate width is W ₀ , and the number of bendings is equal to M:

In addition, W ₀ is equal to (W / 2- (L + P _p / 2)) when the sheet width of the blank sheet is wound W and the width of the edge bending is L. Thus, equality (1) is converted to P _p = (W -2L) / M. In addition, when the number of expander segments (the number of circle divisions) is N, the number of places that do not contact the expander segment is N, and the interval of the undeformed region P _a is expressed by the following equality (2):

Thus, to compress all expander segments to all undeformed regions, it is sufficient to set the number of bends equal to M and the width of the edge bending equal to L, so that the value of P _p is the same as P _d , or the value obtained by dividing P _d by an integer. When determining P _p , taking into account the width of the undeformed region during three-point bending, the expander segments can be pressed in the entire range of undeformed regions, which allows to improve the quality of the round shape of the pipe.

As a result of using the method of the present invention, when the number of expander segments is N, the number of three-point bends required to produce thick-walled large-diameter pipes can be reduced to aN-1, where a is an integer 1, 2, etc., therefore There is a possibility to significantly increase the productivity of steel pipe production. Thus, all the steps from bending the edges of the steel sheet and three-point bending to expanding the pipe can be performed using cold working so that the steel pipes can be manufactured without compromising the performance of the sheet billet. In particular, a significant effect is achieved in the production of thick-walled steel pipes with a thickness of 25.4-50.8 mm.

Examples

There are seven sheet blanks with a sheet width W of 3713 mm (thickness 25.4 mm, tensile strength 745-757 MPa). Both end sections along the width of the steel sheet (width L = 215 mm) are subjected to edge bending using stamp elements with a radius of curvature of 380 mm to obtain a bending angle (Fig. 1 (b)) of 16.9 °. Next, a steel sheet with bent edges is processed to a cylindrical shape by three-point bending with an upper forming tool having a radius of curvature of 380 mm, followed by a weld for the manufacture of an unexpanded pipe. After that, a pipe expander with many segments, each of which is designed to press against the inner surface of an unexpanded pipe, has a radius of curvature of 580 mm on the surface, is inserted into the unexpanded pipe, and the pipe is expanded with a relative expansion of 1% (100 × ( diameter after pipe expansion - diameter before pipe expansion) / (diameter before pipe expansion) Three-point bending conditions differing from the above conditions and pipe expansion conditions vary They are shown as shown in tables 1 and 2.

As for the steel pipe A (an example in accordance with the invention), the sheet blank is formed essentially to a cylindrical shape by 5 three-point bends, starting from a position of 1492 mm from the center line in width to one side with a feed pitch P _p = 298 mm in direction of the center line in width and then through 5 three-point bends, starting from a position of 1492 mm from the center line in width to the other side with a feed pitch P _p = 298 mm in the direction of the center line in width, and finally, through 1 three-point bending in place R memory location center line of width of the sheet (flexible three-point of 11), after which the ends of the steel sheet width are welded to each other, forming neekspandirovannuyu tube 12 having undeformed regions. The bending angle after removing the load applied during the three-point bending (Fig. 2 (b)) is 29.6 °.

After that, the pipe expander, equipped with 12 circumferential segments, is inserted inside the unexpanded pipe, and the expander segment is pressed to the corresponding undeformed region, and the welded section is located in the gap between the expander segments. In this case, the pipe is expanded, as shown in FIG. 1, and its manufacture. In particular, the surface of the expander segment in contact with the inner surface of the unexpanded pipe is an arc of 27.7 ° (as in all cases with the number of expander segments equal to 12) with a radius of curvature of 580 mm.

The steel pipe B (an example in accordance with the invention) is made by producing an unexpanded pipe with 10 undeformed regions under the conditions presented in Table 1, by introducing into the said pipe a pipe expander equipped with 10 circumferential segments and pressing the expander segments against the corresponding undeformed regions , as well as the displacement of the welded portion of the unexpanded pipe into the gap between the segments of the expander to perform the expansion of the pipe, as well as steel pipe A. B in particular, the opening angle (the angle of the circular arc) of the arc of the expander segment in contact with the inner surface of the unexpanded pipe and having a radius of curvature of 580 mm is 33.4 ° (as in all cases with the number of expander segments equal to 10).

The steel pipe C (an example in accordance with the invention) is made by performing 19 three-point bends for manufacturing an unexpanded pipe having 20 undeformed regions, as shown in Table 1, introducing a pipe expander having 10 circumferential segments and pressing one of the expander segments to two undeformed areas, as shown in table 2.

Steel pipe D (comparative example) is made by inserting a pipe expander with 12 segments, as in the case of steel pipe A, into an unexpanded pipe manufactured under the same conditions as steel pipe A, and having 12 undeformed regions, and pressing each of the segments expander to the deformed region, so as to place the undeformed region in the gap between the expander segments, as shown in FIG. 5.

Steel pipe E (comparative example) is made by inserting the same pipe expander with 10 segments, as in the case of steel pipe B, into the unexpanded pipe under the same conditions as in the case of steel pipe B, and having 10 undeformed regions, and pressing each of the expander segments to the deformed region to accommodate the undeformed region in the gap between the expander segments, as shown in FIG. 5.

The steel pipe F (comparative example) and the steel pipe G (comparative example) are made by producing an unexpanded pipe with 8 or 10 undeformed areas, under the conditions shown in table 1, introducing a pipe expander with the number of expander segments different from the number of undeformed areas inside the unexpanded pipes, as shown in table 2, and performing pipe expansion without contacting the expander segment with part of the undeformed areas. For reference, FIG. 6 shows the case of steel pipe G.

Regarding the obtained steel pipes A-G, the roundness of the pipe and the productivity were measured, and the results are shown in Table 2. In addition, the correctness of the round shape was estimated by measuring the difference m between the outer surface of the steel pipe 11 and the imaginary regular circle 10, as shown in FIG. . 7 using a dial indicator at a distance of 150 mm in the circumferential direction to determine the ratio of the maximum value m _{max of the} difference m in each steel pipe, and to calculate the ratio m _{max of} each steel pipe to m _{max of the} steel pipe D (hereinafter referred to as the “difference index” ( relative)). The difference index of the steel pipe D is 1.00, and when the difference m becomes close to zero, the shape of the steel pipe becomes close to a regular circle. In other words, the lower the difference index, the better the quality of the round shape of the steel pipe. In addition, productivity was estimated by the time interval from the beginning of the first three-point bending to the end of the last three-point bending.

As can be seen from table 2, the difference index in steel pipes AC according to the invention is 0.62-0.66, while the difference index in steel pipes according to examples D-G is 0.93-1.14, i.e. the quality of the round shape of the steel pipes according to the invention exceeds the quality of the round shape of the steel pipes according to comparative examples.

In addition, the quality of the round shape of steel pipes A and B, which were subjected to a small number of three-point bends, is slightly worse than the quality of the round shape of steel pipes C, which was subjected to a large number of three-point bends, but the bending time is reduced by at least 30%, as shown in the table 1, from which it can be seen that steel pipes having a proper regular round shape in accordance with the invention can be manufactured with high productivity.

The method of manufacturing steel pipes according to the invention is not limited to the manufacture of thick-walled steel pipes of large diameter and can be applied to all methods of manufacturing steel pipes with a three-point flexible.

Reference Numbers

one Unexpanded pipe 2 Expander Segment 3 Steel sheet four Three point bending 5a, 5b Lower stamp element 6 Upper forming tool 7 Welded section 8 Deformed zone 9 Undeformed zone 10 Imaginary Regular Circle eleven Steel pipe.

Claims (1)

A method of manufacturing a steel pipe, which includes stages in which a steel sheet subjected to bending of its edges is cylindrical by multiple three-point bending along the sheet width, the edges of the sheet are welded to form an unexpanded pipe, and a pipe expander with multiple segments is inserted into the unexpanded pipe for expanding this pipe, characterized in that when expanding the pipe, the expander segments are pressed to all areas undeformed in the three-point process bending, the number of three-point bendings is equal to aN-1, where a is an integer and N is the number of expander segments.

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