RU2414315C2 - Method of tube production by resistance welding - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to tube fabrication by resistance welding and may be sued in producing downhole tubes. To produce tubes with higher-quality welded seam, edges on both sides of strip top and bottom sides in roll gauging with edge guiding element are formed with inclination prior to resistance welding. Forming is performed to allow resistance welding with butt angle between edges carrying from -1° to +1°.

EFFECT: higher efficiency.

28 cl, 12 dwg, 4 tbl

Description

FIELD OF THE INVENTION

The present invention relates to a method for manufacturing a pipe that requires a toughness of a weld, such as an oil well pipe, or a pipe that requires a weld strength, such as an oil well casing.

State of the art

Typically, pipes are subdivided into welded pipes and seamless pipes. A pipe obtained by resistance resistance welding, being a pipe related to welded pipes, is made by folding a sheet by roll forming or a similar method, and then joining each edge and welding. In welded pipes, the toughness and strength of the weld are usually low compared to these characteristics of the original strip. In any case, the use of the pipe, the problem is to provide the toughness and strength of the weld for each application.

For example, since pipes for pipelines for transporting crude oil or natural gas are often laid in cold latitudes, impact strength at low temperature is of primary interest. In addition, in the case of a casing to protect the production pipe in an oil well, strength is essential for the production of crude oil.

As a rule, for a hot-rolled sheet (strip), which will be the initial strip of the pipe obtained by resistance resistance welding, composition development or heat treatment is carried out taking into account the properties acquired by the initial strip after forming the pipe from it, in order to ensure such properties of the initial strip, like toughness and strength.

However, since the characteristics of the welds are more dependent on the method of resistance resistance welding compared to the development of the composition or heat treatment of the original strip, it is important to improve the welding technology.

As the cause of defective contact welding, oxides are referred to as inclusions, which are formed on the edge of the welded sheet material. In many cases, these inclusions are not removed from the edge together with the molten steel during resistance welding and remain on it, and the remaining inclusions cause a decrease in toughness, leading to insufficient strength.

Thus, in order to remove the inclusion from the weld, to date, a serious study has been carried out regarding the technology of active removal of molten steel from the edge of the strip in the weld. For example, Patent Document 1 or Patent Document 2 describes an example study regarding the shape of each side edge of a strip. In this example, it is understood that the lateral edge of the strip, which is usually made approximately rectangular in shape by cutting or scraping the edge, gets its shape before performing resistance resistance welding so that the machined shape of the lateral edge improves the removal of molten steel during welding. In summary, this is as follows.

Namely: the basic production line for the pipe obtained by resistance resistance welding is the line shown in FIG. 1. The production line for pipes produced by resistance resistance welding has a configuration in which a strip (10) is wound from an unwinder (1); then this strip is straightened, turning into a flat, by means of a straightening machine (2); then the strip (10) is gradually folded by a machine (4) for roll forming; then two side edges, right and left, of the rolled strip (10) are welded by resistance welding using a resistance welding machine, which includes an induction heating section (5) and a compression roller (resistance welding section) (6), so so that the strip is molded into a pipe (30); then the section of the welded burr of the pipe (30) is cut off with a tool (7) to cut the burr; then the pipe (30) after cutting is adjusted in the outer diameter by a calibration mill (8); and then the pipe is cut into segments of a given length by a pipe cutting machine (9). The roll forming machine (4) at the last stage has a predetermined number of stands (3) for forming in caliber with an edge guiding element, which give the edge of the strip that was rolled in the last stage an approximately round shape, the stand (3) including the first stand (3a) and a second stand (3b).

In the technology described in Patent Document 1, as shown in Fig. 5A, showing a schematic sectional view, and Fig. 5B, showing a local detailed schematic view of this section, in a first stand (3A) for forming in caliber with an edge guide part the lateral edge of the strip (10), which is shaped like a pipe, comes into contact with the edge guide element of the grooved roll of caliber with the edge guide element so as to form a slope on the side edge, which will be an edge on the inner side pipe surfaces, as shown in FIG. 5C and as shown in FIG. 5D, showing a schematic sectional view, and FIG. 5E, showing a local detailed schematic view of this section, in a second stand (3b) for forming in caliber with an edge guide element another portion of the lateral edge of the strip (10) contacts the edge guide so as to form a slope on the lateral edge, which will be an edge on the side of the outer surface of the pipe, as shown in FIG. 5F, and thus an X-shaped groove is formed. The angle of the edge guide element of each stand from the first stand (3A) for forming in caliber with the edge guide element and the second stand (3b) for molding in caliber with the edge guide element is usually one angle.

In the technology described in Patent Document 2, as shown in FIG. 6A, showing a schematic cross-sectional view, an edger roll (11) is located on the front side of the molding stand in caliber with an edge guide element, and this edger roll (11) is used in order to reduce the lateral edge of the strip (10), which is shaped like a pipe, so as to form a slope on the lateral edge of the strip (10) as a whole, as shown in Fig.6B, and as shown in Fig.6C, showing a schematic view in sectional view, and FIG. 5D showing a local detail a schematic view of this section, in a stand (3) for molding in caliber with an edge guiding element, part of the side edge of the strip (10) comes into contact with the edge guiding element of a roll having a shape with a recess, gauge with an edge guiding element, thereby a side edge that will be an edge on the side of the outer surface of the pipe, is formed to be a vertical surface, as shown in FIG. Patent documents 3 through 5 describe examples of studies of the shape of the strip edge. That is, it is understood that at the edge of the strip, which is usually formed approximately rectangular in shape by cutting or scraping the edge, there is such a slope before roll forming that the shape of the machined edge improves the removal of molten steel during welding.

Patent Document 1: JP - A - 57 - 031485

Patent Document 2: JP - A - 63 - 317212

Patent Document 3: JP - A - 2001 - 170779

Patent Document 4: JP - A - 2001 - 259733

Patent Document 5: JP - A - 2003 - 164909

Disclosure of invention

However, the inventors investigated the method described in Patent Document 1, as a result they found that even if the amount of draft during molding in caliber with the edge guide element was greatly changed, it was very difficult to contact only part of the side edge of the strip (10) with the edge guide element a groove-shaped roll of caliber with an edge guide element. This is because, since the lateral edge of the strip (10) received a slight hardening during the previous molding process, the entire lateral edge of the strip is easily deformed along the edge of the guide element in such a way that it completely fills the portion of the edge guide element, therefore, the shape of the edge guide element is printed on side edge of the strip. As a result, the lateral edge of the strip (10) does not have the desired shape immediately before resistance welding, and in the extreme case, the lateral edge has a flat shape, having an inclination on only one side.

In addition, the inventors investigated the method described in patent document 2, as a result they confirmed the following. Namely: in order to form a slope on the entire lateral edge of the strip (10) using an edger roll (11) during roll forming (on the upstream side of the stand for forming in caliber with edge guide element), because, as described in the patent document 2, for forming it is necessary to use an edger roll, in which the diameter gradually increases from the side of the outer surface of the pipe to the side of the inner surface of the pipe, the side edge, which will be the edge on the side of the inner surface of the pipe, is scraped Jern roll that can, causing the problem, create the following, called "whiskers". In addition, since there is a large reaction force in the direction of the cross section of the strip (10) that will be subjected to roll forming, which opens the pipe-shaped strip (10) to the outside, the pressure between the edger roll (11) and the side edge of the strip (10) is inevitable declining. As a result, as in Patent Document 1, the strip obtains significant hardening by reducing the lateral edge with an edger roll, and even if the amount of precipitation decreases during subsequent molding in caliber with an edge guide element, the strip essentially fills the portion of the edge guide element, so it is difficult to ensure that the lateral the edge of the strip (10) was formed as described in patent document 2, therefore, the slope is completely eliminated, and the edge becomes flat.

The invention was made in the light of the aforementioned circumstances, and the object of the invention is to provide a method for manufacturing a pipe obtained by resistance welding, in which the shape of the side edge can be converted to the corresponding shape immediately before resistance welding, thereby making molten steel sufficiently at least it is diverted during resistance welding by resistance, so that the inclusions are reliably removed, therefore, a pipe can be obtained resistance welding, which has excellent weld characteristics.

As described above, in the prior art described in Patent Document 1 or 2, a portion of the side edge of the strip is pressed against the edge guide element of a groove-shaped roll of caliber with the edge guide element so as to form a slope on the side edge of the strip. However, according to the study, the inventors realized that, even if the roll having a shape with a recess, the caliber with the edge guide was not completely filled with a strip in the circumferential direction, when the strip entered the roll having a shape with a recess, caliber with an edge guiding element, the side edge was under high pressure from the side of the edge guide element, so that the portion of the edge guide element was completely filled with the side edge. That is, they realized that when the strip entered a roll having a shape with a recess, a gauge with an edge guide, a portion of the side edge of the strip in contact with the edge guide, and a laterally central portion of the strip (bottom portion of the shape of the strip pipe) located approximately 180 degrees opposite the side edge portion, were in a deflection state, so that the reaction force of the strip that acted by bending the cross section of the pipe-shaped strip into an arcuate shape led therefore, even if the strip did not fill a groove-shaped roll of caliber with an edge guide element, a large compression force acted on the lateral edge of the strip in the direction along the circumference, as a result of which high pressure exerted on the lateral edge of the strip, and therefore, the shape of the edge guide element is directly imprinted on the side edge of the strip.

Thus, the inventors drew attention to the phenomenon that the lateral edge of the strip was subjected to high pressure from the edge guide element when forming in caliber with the edge guide element, and they came up with a way to form a given slope on the side edge of the strip, actively using this phenomenon. That is, they found that when forming an edge guide element with two or more steps of slope, even if the amount of draft during molding in caliber with an edge guide element was small, the side edge of the strip could be formed with the required slope, so the side edge of the strip could be formed with an appropriate slope immediately before resistance welding.

In addition, patent document 5 discloses various forms of bevels that contribute to the regulation of joint pressure. However, he does not provide any description on the inclusion of inclusions along with the removal of molten steel, and on the improvement of the characteristics of welded joints (especially toughness at low temperature) through such an inclusions. Therefore, it is completely unclear which particular shape among the various bevel shapes disclosed in this patent can improve the characteristics of welds (especially toughness at low temperature).

The invention is based on the above considerations and has the following features.

1. A method of manufacturing a pipe obtained by resistance welding, having excellent characteristics of the weld, characterized in that during the process in which the strip is molded and its edges are joined, and resistance-welded by resistance welding to form a pipe, an edge on either side from the upper and lower sides of the strip or edges on both sides of the upper and lower sides of the strip before resistance welding is formed with a slope.

2. A method of manufacturing a pipe obtained by resistance resistance welding having excellent weld characteristics, characterized in that during the forming process in caliber with an edge guide during the roll forming process, an edge guide shape having two or more angles is used in order to print this shape at the edges of the strip so as to form a slope at these edges.

3. A method of manufacturing a pipe obtained by resistance resistance welding, having excellent weld characteristics, according to the preceding paragraphs 1 or 2, characterized in that the edges on one side in the direction of the strip thickness have a circular shape.

4. A method of manufacturing a pipe obtained by resistance welding, having excellent weld characteristics, according to the preceding paragraphs 1 to 3, characterized in that the edges on the side of the inner diameter of the strip are formed with a slope at an earlier stage of molding in caliber with an edge guide element, and the edges on the side of the outer diameter of the strip are formed with a slope at a later stage of molding in caliber with an edge guide element.

5. A method of manufacturing a pipe obtained by resistance resistance welding, having excellent weld characteristics, according to the preceding paragraphs 1 to 4, characterized in that the edges are formed with a slope in the forming group of the caliber with an edge guide element, including at least the last Caliber cage with edge guide.

6. A method of manufacturing a pipe obtained by resistance resistance welding, having excellent weld characteristics, according to the preceding paragraphs 1 to 5, characterized in that in the slope on the strip after molding in caliber with the edge guide element, the angle from the surface of the strip edge to the vertical direction is range from 25 degrees to 50 degrees, and the length of the perpendicular from the beginning of the formed slope to the place of its end on one side is from 20% to 45% of the thickness.

7. A method of manufacturing a pipe obtained by resistance resistance welding, having excellent weld characteristics, according to the preceding paragraphs 1 to 6, characterized in that resistance resistance welding is performed by blowing inactive gas or deoxidizing gas.

8. A method of manufacturing a pipe obtained by resistance welding, having excellent weld characteristics, according to the preceding paragraphs 1 to 7, characterized in that resistance welding is performed with a joining angle between the edges of the sheet, comprising from -1 degree to +1 degree.

9. A method of manufacturing a pipe obtained by resistance welding, having excellent weld characteristics, according to the preceding paragraphs 1 to 8, characterized in that resistance welding is performed with a V-shaped angle formed by the edge of the strip, comprising from 2 degrees to 8 degrees .

Brief Description of the Drawings

Figure 1 is an explanatory diagram of a line for manufacturing a pipe obtained by resistance resistance welding;

Figures 2A, 2B and 2C are diagrams for illustrating a first embodiment of the invention;

Figures 3A, 3B and 3C are diagrams for illustrating a second embodiment of the invention;

Figures 4A through 4F are schematic drawings for illustrating a third embodiment of the invention;

Figures 5A through 5F are diagrams for illustrating the prior art (prior art described in Patent Document 1);

Figures 6A through 6E are diagrams for illustrating another prior art (prior art described in Patent Document 2);

7 is a schematic drawing showing an example of an embodiment of the invention, where a non-oxidizing gas according to the invention is blown onto the edges of a strip subjected to resistance welding by resistance;

Fig. 8 is a schematic drawing showing an example of an embodiment of the invention, where the periphery of the edges of the strip subjected to resistance welding is stored in a non-oxidizing gas atmosphere according to the invention;

Fig. 9 is a schematic drawing showing a strip that has been formed with a slope in a docking state immediately before performing resistance welding;

10 is a diagram showing a prior art strip having rectangular edges in a docking state just before resistance welding is performed;

11 is a diagram showing a V-shaped angle of a strip formed with a slope just before resistance welding is performed; and

12 is a diagram showing a V-shaped corner of a prior art strip having rectangular edges immediately before resistance welding is performed.

The implementation of the invention

Figure 1 shows the production line for the pipe obtained by resistance welding, used in the invention. Namely, the production line for the pipe obtained by resistance resistance welding has a configuration in which the strip (10) is unwound from the unwinder (1); then this strip is straightened, turning into a flat, by means of a straightening machine (2); then the strip (10) is gradually folded by a machine (4) for roll forming; then two side edges, left and right, of the rolled strip (10) are welded by resistance welding using a resistance welding machine, which includes an induction heating section (5) and a compression roller (resistance welding section) (6), so that the strip is molded into a pipe (30); then the section of the welded burr of the pipe (30) is cut off with a tool (7) to cut the burr; then the pipe (30) after cutting is adjusted in the outer diameter by a calibration mill (8); and then the pipe is cut into segments of a given length by a pipe cutting machine (9). The roll forming machine (4) has a predetermined number of caliber molding stands with an edge guiding element (3) that hold the edge of the sheet that has been folded in the last step so that it has an approximately circular shape, with the stand (3) here includes the first stand (3 a) and the second stand (3 b).

In a first embodiment of the invention, while the edge guide element of the first stand (3 a) for forming in caliber with the edge guide element has a typical one-step slope, as shown in FIG. 2A, showing a schematic cross-sectional view, and FIG. 2B, showing local detailed schematic view for this section, the edge guide element of the stand (3 b), which is the second stand, has a two-stage slope (the slope angle of the second stage is α, and the vertical slope of the second stage is β), and such a shape is imprinted on two lateral edges, right and left, of the strip (10), thereby, as shown in FIG. 2C, two lateral edges, right and left, on the side that will be the side of the outer surface of the pipe, are formed with a given slope (the angle of inclination from the lateral edge to the surface that will be the outer surface of the pipe is α, and the distance in the thickness direction between the origin of the slope at the lateral edge and the surface that will be the outer surface of the pipe is β).

The slope formed on two lateral edges, left and right, of the strip (10) is performed so that the angle (α) of inclination from the lateral edge of the strip (10) to the surface that will be the outer surface of the pipe is 25 ° to 50 °, and the distance (β) in the direction of the strip thickness between the beginning of the slope at the lateral edge and the surface that will be the outer surface of the pipe was 20% to 40% of the strip thickness.

This is because when the angle of inclination (α) is less than 25 °, the molten steel is not sufficiently removed from the central portion of the strip thickness, and inclusions, causing defects, remain, which results in a decrease in impact strength or strength after resistance welding resistance, and when the inclination angle (α) is greater than 50 °, the slope, causing problems, remains in the form of a defect on the pipe-product even after resistance welding is completed. In addition, when the distance (β) of the beginning of the slope is less than 20% of the thickness, the molten steel is not sufficiently removed from the central portion of the thickness, so that inclusions tend to remain, and when the distance (β) of the beginning of the slope is more than 40% of the thickness, the slope, causing problems, it remains in the form of a defect in the pipe - product even after resistance welding is completed.

As described above, in this embodiment, the shape of the edge guide element of the end stand (3 b) for forming in caliber with the edge guide element is configured such that it is a shape having two angles, and this shape of the edge guide element is imprinted on two side edges, right and left strip (10), therefore, the shape of each side edge of the strip (10) can be formed with a proper slope immediately before performing resistance welding. As a result of this, the molten steel during resistance resistance welding is sufficiently removed and the inclusions are reliably removed, and therefore, resistance resistance welding pipe having excellent weld characteristics can be obtained.

In the above description, by changing the shape of the two-stage slope, it is also possible to form two lateral edges, right and left, with a given slope, on the side that will be the side of the inner peripheral surface of the pipe.

In another embodiment, while the edge guide member of the first stand (3 a) for forming in caliber with the edge guide member has a typical one-step slope, as shown in FIG. 3A, showing a schematic cross-sectional view, and FIG. 3B, showing local detailed schematic view for this section, the edge guide element of the second stand (3 b) has a three-step slope (the vertical slope of the first step is δ, the slope of the third step is α; and the vertical length with the bosom of the third stage is β), and this shape is imprinted on the two side edges, the right and left, of the strip (10), thereby, as shown in FIG. 3C, the two side edges, right and left, on the side that will be the outer side pipe surfaces are formed with a given slope (the angle of inclination from the lateral edge to the surface that will be the outer surface of the pipe is α, and the distance in the thickness direction between the starting point on the lateral edge and the surface that will be external is β), and two side edges, right and left, n the side that will be the side of the pipe’s inner surface is formed with a predetermined slope (the angle of inclination from the lateral edge to the surface that will be the pipe’s inner surface is γ, and the distance in the thickness direction between the starting point on the lateral edge and the surface that will be the pipe’s inner surface , is ϕ). However, when one of the corners of the three-stage edge guide element is larger than the angle of the caliber roll with the edge guide element in the vertical direction, the side edge of the strip is scraped by the edge guide element, which can lead to marks called a “mustache” leading to the formation of a defect during molding in caliber with edge guiding element, or generating a spark during resistance welding. Therefore, it is preferable that the angle on the edge guide element does not exceed the angle of the caliber roll with the edge guide element in the vertical direction.

The slope formed on the two lateral edges of the right and left strip (10) is made so that the angle (α) of inclination from the lateral edge of the strip (10) to the surface that will be the outer surface of the pipe and the angle (γ) of lateral edge to the surface, which will be the inner surface of the pipe, is from 25 ° to 50 °, respectively, and the distance β in the direction of the thickness of the strip between the beginning of the slope on the lateral edge and the surface that will be the outer surface of the pipe, and the distance ϕ in the vertical direction strip between m By the beginning of the slope and the surface, which will be the inner surface of the pipe, is, respectively, from 20% to 40% of the strip thickness.

This is because when the angle of inclination (α) or (γ) is less than 25 °, the molten steel is not sufficiently removed from the central portion of the strip thickness, and inclusions, causing defects, remain, resulting in a decrease in toughness or strength after resistance welding, and when the angle (α) or (γ) of the inclination is greater than 50 °, the incline, causing problems, still remains as a defect on the pipe-product even after resistance welding is completed. In addition, when the distance (β) or (ϕ) of the beginning of the slope is less than 20% of the thickness, the molten steel is not sufficiently removed from the central portion of the thickness, so that inclusions tend to remain, and when the distance (β) or (ϕ) of the beginning of the slope more than 40% of the thickness, the slope, causing problems, still remains in the form of a flaw on the pipe-product after the end of resistance welding.

As described above, in this embodiment, the shape of the edge guide element of the end stand (3 b) for forming in caliber with the edge guide element is configured such that it is a shape having three angles, and this shape of the edge guide element is printed on two side edges, right and left strip (10), therefore, the shape of each side edge of the strip (10) can be formed with a proper slope immediately before performing resistance welding. As a result of this, the molten steel during resistance resistance welding is sufficiently removed and the inclusions are reliably removed, and therefore, resistance resistance welding pipe having excellent weld characteristics can be obtained.

In yet another embodiment, as shown in FIG. 4A, showing a schematic cross-sectional view, and FIG. 4B, showing a local detailed schematic view for this cross-section, an edge guide element of the first stand (3 a) for forming in caliber with the edge guiding element, which is at an earlier stage, has a two-stage slope (with the vertical length (δ) of the slope of the first step and the angle (γ) of the slope of the second step), and this form is imprinted on two side edges, right and left, of the strip (10), by themselves m, as shown in FIG. 4C, two side edges, right and left, on the side that will be the side of the inner surface of the pipe are formed with a given slope (the angle of inclination from the side edge to the surface that will be the inner surface of the pipe is γ, and the distance in the thickness direction between the starting point on the lateral edge and the surface that will be the inner surface of the pipe is ϕ). In addition, as shown in FIG. 4D showing a schematic cross-sectional view, and FIG. 4E showing a local detailed schematic view for this section, an edge guide element of the second stand (3 b) for forming in caliber with an edge guide element located at a later stage, has a two-stage slope (the slope angle of the second stage is α, the vertical slope of the second stage is β), and this form is printed on two lateral edges, right and left, of the strip (10), thereby, as shown in Ф Ig.4F, two side edges, right and left, on the side that will be the side of the outer surface of the pipe are formed with a given slope (the angle of inclination from the side edge to the surface that will be the outer surface of the pipe is α, and the distance in the thickness direction between the origin at the lateral edge and the surface that will be the outer surface of the pipe is β).

When each side edge, which will be the inner surface of the pipe, is formed with a slope by the first stand (3 a) for molding in caliber with an edge guiding element, the formed section receives significant hardening due to high pressure, therefore, even if the side edge is further formed with a slope by the second cages (3 b) for molding in caliber with an edge guiding element, the slope formed by the first cage (3 a), do not wrinkle relatively. Therefore, after molding in caliber with an edge guiding element is completed, the lateral edges of the strip can be formed with a given slope on both sides - the inner and outer surfaces of the pipe.

The slope formed on the two lateral edges of the right and left strip (10) is made so that the angle (α) of inclination from the lateral edge of the strip (10) to the surface that will be the outer surface of the pipe and the angle (γ) of lateral edge to the surface, which will be the inner surface of the pipe, is from 25 ° to 50 °, respectively, and the distance β in the direction of the thickness of the strip between the beginning of the slope on the lateral edge and the surface that will be the outer surface of the pipe, and the distance ϕ in the thickness direction strip between place the beginning of the slope and the surface, which will be the inner surface of the pipe, are, respectively, from 20% to 40% of the strip thickness.

This is because when the angle of inclination (α) or (γ) is less than 25 °, the molten steel is not sufficiently removed from the central portion of the strip thickness, and inclusions, causing defects, remain, resulting in a decrease in toughness or strength after resistance welding, and when the angle (α) or (γ) of the inclination is greater than 50 °, the incline, causing problems, still remains as a defect on the pipe-product even after resistance welding is completed. In addition, when the distance (β) or (ϕ) of the beginning of the slope is less than 20% of the thickness, the molten steel is not sufficiently removed from the central portion of the thickness, and inclusions tend to remain, and when the distance (β) or (ϕ) is greater than 40 % of the thickness, the slope, causing problems, still remains in the form of a flaw on the pipe-product after the end of resistance welding.

As described above, in this embodiment, the caliber with the edge guide element is configured so that the shape of the edge guide element of the first stand (3 a), which is at an earlier stage, and the shape of the edge guide element of the second stand (3 a), which is at a later stage the stages are made in such a way that they are a shape having respectively two angles, and each of the shapes of the edge guiding elements is imprinted on two side edges, right and left, of the strip (10), therefore, the shape of each side the edge of the strip (10) can be formed with a proper slope just before resistance welding is performed. As a result of this, the molten steel during resistance resistance welding is sufficiently removed and the inclusions are reliably removed, and therefore, resistance resistance welding pipe having excellent weld characteristics can be obtained.

In the first to third embodiments, the reason why the lateral edges on the side of the outer surface of the pipe and / or on the side of the strip belonging to the strip - the outer surface of the pipe are formed with a slope by the end stand (here, the second stand (3 b)) for molding in caliber with edge guiding element, is that since resistance resistance welding is performed immediately thereafter, resistance resistance welding can be performed while maintaining an excellent slope. However, it is also acceptable that the lateral edges of the strip are formed with a slope by means of an initial stand for molding in caliber with an edge guide element or the middle stand for molding in caliber with an edge guide element, but not formed with a slope by means of an end stand for molding in caliber with an edge guide element. When forming with a slope of the lateral edges of the strip, the lateral edges get significant hardening due to the high pressure, therefore, even if the lateral edges are then molded in caliber with an edge guiding element, the slope is relatively difficult to wrinkle, and therefore there is a condition in which the lateral edges formed with a slope can be saved even after molding in caliber with an edge guide element.

In addition, since the invention uses only molding in caliber with an edge guiding element as a means of forming a slope, equipment such as an edger roll or scraping roll is not necessary, therefore, it is not necessary to replace the roll or scraping stone and, therefore, the pipe obtained by contact welding resistance, having excellent weld quality, can be manufactured efficiently.

Moreover, in this method of forming a slope based on molding in caliber with an edge guide element, it is sometimes difficult to increase the toughness or strength of the weld after resistance welding.

In a detailed study of the reason for this, it turned out that at the stage when the strip edge is heated before pressure welding (draft) during resistance welding, oxides can form on the strip edge, which should cause inclusions as a defect in the welded joint. Oxides float on the surface of molten steel, which melts at the stage of melting at each edge of the strip, and is partially removed along with molten steel at the stage of pressure welding. At this time, if the edge of the strip is formed with a slope, then the molten steel is easily removed, in addition to which inclusions can be effectively removed.

However, since oxides at the edge of the strip, which are the source of inclusions, are formed during heating by resistance welding in an increasing amount, under certain welding conditions the following case takes place: impact strength or strength after welding cannot be sufficiently increased only by the formation of a slope at the edge of the strip.

Thus, the inventors again examined in detail the phenomenon of resistance resistance welding, as a result they noticed that the cause of the inclusions is the formation of oxides. That is, they studied not only the removal of inclusions due to the formation of a slope on the edge of the strip, but also a way to prevent the formation of oxides that cause inclusions.

As a result, the inventors realized that it is possible to suppress the formation of oxides by blowing non-oxidizing gas to each edge of the strip heated by resistance welding (i.e., heated to melt the edges to be pressure welded before pressure welding). In this case, non-oxidizing gas means an inactive gas (gas - nitrogen, gas - helium, gas - argon, gas - neon, gas - xenon and the like, or a gas mixture formed by mixing at least two of them), deoxidizing gas (gas - hydrogen, gas — carbon monoxide, gas — methane, gas — propane and the like, or a gas mixture formed by mixing at least two of them), or a gas mixture formed by mixing inactive gas and deoxidizing gas.

That is, according to the invention, each edge of the strip is pre-formed with a slope before resistance welding is performed, due to which the inclusions are accelerated, in addition, non-oxidizing gas is blown onto the edge of the strip heated during resistance welding, due to which the formation of oxides is suppressed, as the reasons for inclusions. This can reliably improve the toughness or strength of the weld compared with the prior art. However, when the non-oxidizing gas is simply blown in, the effect of suppressing the formation of oxides at the edge of the strip is more or less reduced as the surrounding air is sucked in. Thus, it is preferable to prevent the suction of ambient air. To this end, it is preferable that the edge of the strip heated by resistance welding be fenced so that the inside of such a fencing is retained in an atmosphere of non-oxidizing gas.

Among these types of non-oxidizing gas, it is more preferable to use a gas containing a deoxidizing gas, since the effect of suppressing the formation of oxides as the cause of inclusions is further enhanced, and therefore, the toughness or strength of the weld can be increased to a greater extent.

From the point of view of affordability and cost reduction, it is preferable to use the following gas as non-oxidizing gas as:

- in the case of using a separately taken inactive gas: (A) any gas from the gas — nitrogen, gas — helium, and gas — argon, or a gas mixture of at least two of these gases.

- if a separate deoxidizing gas is used: (B) one gas from a gas — hydrogen and a gas — carbon monoxide, or a gas mixture of these two gases.

- in the case of using a gas mixture of inactive gas and deoxidizing gas: a gas mixture of the above (A) and (B). Obviously, in particular, when using a gas containing a gas - hydrogen and / or gas - carbon monoxide, precautions must be taken.

In addition, to solve the problem, the inventors again investigated in detail the phenomenon of resistance resistance welding, as a result they drew attention to the angle of joining between two edges in the direction of the strip width (the angle between the vertical surfaces of two edges in the direction of the strip width) in resistance welding. Thus, they found that the mating angle between vertical surfaces not formed with a slope is also of great importance for the effective removal of inclusions along with molten steel, in addition to forming a slope at each edge of the strip.

In resistance resistance welding, when the joining angle between the vertical surfaces of the strip edges (vertical strip edges) changes, the mode of removal of molten steel also changes. That is, when the mating angle is set so as to be open towards the outer surface of the pipe, each edge of the strip formed with a slope behaves in such a way that the side of the inner surface of the pipe is first heated, so that molten steel is first formed in this in place, and the molten steel is gradually pushed toward the outer surface of the pipe as each edge of the strip is increasingly joined by resistance welding. When the mating angle is set so as to be open toward the inner surface of the pipe, each edge of the strip formed with a slope behaves in such a way that the side of the outer surface of the pipe is heated first so that molten steel first forms at this point, and molten steel is gradually pushed towards the inner surface of the pipe as each edge of the strip is increasingly joined in resistance welding.

In this case, for example, in the case where it is assumed that the mating angle, which will be open towards the outer surface of the pipe, is positive, and the mating angle, which will be open towards the inner surface of the pipe, is negative if the mating angle is large than + 1 ° or less than -1 °, then since the edge of the strip on one side melts in the first place, and thus, the amount of molten steel that will flow to the edge of the strip on the opposite side increases significantly, lavlennaya steel can not be sufficiently reserved within a period of welding time until completion of splicing, therefore, the contact resistance welding ends, while still molten steel is contained within the strip. As a result, inclusions that collect in molten steel or on its surface remain within the strip, which results in a significant decrease in the toughness or resistance of the resistance weld. Based on the foregoing, the angle of joining of vertical surfaces between the edges of the strip in resistance welding should be within ± 1 ° (from -1 ° to + 1 °).

In this case, in the case where each edge of the strip is preformed with a slope, the amount of molten metal of one edge, which is molten first, is reduced by the amount corresponding to such a reduced volume, and the edge is melted along the slope, so that the molten steel is further reduced, therefore, inclusions can be sufficiently removed from the resistance welding seam due to both effects: the joining angle and the slope, which leads to a significant increase in impact strength and ochnosti.

An embodiment of the invention described above is described below.

FIG. 1 is a diagram showing a production line for a pipe obtained by resistance resistance welding used in an embodiment of the invention. This production line for pipes obtained by resistance resistance welding has a basic configuration in which a sheet (strip) (10) is wound from an unwinder (1); then this strip is straightened, turning into a flat, by means of a straightening machine (2); then the strip (10) is gradually folded by a machine (4) for roll forming; then two side edges, left and right, strips (20), which was rolled in the form of a pipe, are welded by resistance welding using a resistance welding machine, which includes an induction heating section (5) and a compression roll (resistance welding section resistance) (6), so that the strip is formed into a pipe (30); then the section of the welded burr of the pipe (30) is cut off with a tool (7) to cut the burr; then the pipe (30) after cutting is adjusted in the outer diameter by a calibration mill (8);

and then the pipe (30) is cut into segments of a given length by a pipe cutting machine (9).

In this embodiment, the roll forming machine (4) at the last stage has a stand (3) for forming in caliber with an edge guiding element including a plurality of stands (for example, three stands), and, as described above, an edge guiding element of each the stand is made of a corresponding shape, so that the upper side of each edge of the strip (side of the inner surface of the pipe) and / or the lower side of each edge of the strip (side of the outer surface of the pipe) can be formed with a given slope.

For example, as shown in FIG. 2A, showing a schematic cross-sectional view, and FIG. 2B, showing a local detailed schematic view for this section, the additional stand of the stand (3) for forming in caliber with an edge guiding element has the shape of an edge guiding element with a predetermined two-stage slope (the slope angle of the second stage is α, and the vertical slope of the second stage is β). This shape of the edge guide element is imprinted on the lateral edges of the strip (10), thereby two lateral edges, right and left, are formed on the lower side of the strip (10) (side of the outer surface of the pipe) with a slope having a slope angle of α and a slope height constituting β.

According to the aforementioned method, a strip (20) having a pipe shape that is formed on the side of the outer surface with a slope having a slope angle of α and a slope height of β, and on the side of the inner surface is formed with a slope having a slope angle of γ , and a slope height of δ is set so that the joint angle (θ) between the vertical surfaces of the strip edges is from −1 ° to + 1 ° for resistance resistance welding, as shown in FIG. 9.

In this way, the inclusions can be sufficiently removed from the resistance weld seam, therefore, a resistance weld pipe having extremely excellent toughness and strength can be obtained.

In addition, in order to solve the problem, the inventors again examined in detail the phenomenon of resistance resistance welding, as a result they drew attention to the angle of the solution in the form of the letter “V ″ (V-shaped angle), formed in the longitudinal direction by two edges in the direction of the strip width immediately before resistance welding. Thus, they found that the V-angle is also of great importance for the efficient removal of inclusions along with molten steel, in addition to forming a slope at each edge of the strip.

In resistance welding, when the V-shaped angle formed by each edge of the strip changes, the mode of formation / removal of molten steel also changes. That is, when the V-shaped angle is smaller, the edge of the strip begins to heat heated at a point remote from the weld, and as the heating point approaches the weld, the temperature of the strip edge gradually increases, and the heat gradually spreads from the upper and lower parts of thickness to the central portion of the thickness of the strip edge. While molten steel gradually forms during these phenomena, solidification begins before the molten steel formed in the upper part of the thickness (on the side of the outer surface of the pipe) and the lower part of the thickness (on the side of the inner surface of the pipe) of the strip edge arrives at the welded place the weld, therefore, the molten steel in the central portion of the thickness is hardly removed outside. As a result, inclusions formed with molten steel also tend to remain inside the strip, which leads to a significant reduction in the toughness or strength of the electric resistance weld.

Thus, the inventors thoroughly examined the V-shaped angle, as a result of which they realized that if the V-shaped angle is 2 ° or more, the molten steel is excellently retracted, which leads to an increase in toughness or weld strength.

However, if the V-shaped angle is excessively enlarged, the weld is not heated sufficiently, and because of this, the temperature of the strip edge hardly increases, therefore, there is a condition in which each edge is completely covered with oxide films called weld oxides, and not formation molten steel, which leads to a significant decrease in toughness or weld strength. Solving this problem, the inventors realized that if the V-shaped angle was 8 ° or less, then the appearance of weld oxides could be prevented.

In this case, in the case where each edge of the strip is preformed with a slope, the amount of molten metal of one edge, which is molten first, decreases by the amount corresponding to such a reduced volume, and melting continues along the slope, so that the molten steel is further reduced, therefore, inclusions can be sufficiently removed from the resistance welding seam due to both effects: V-shaped angle and slope, which leads to a significant increase in impact strength and strength.

An embodiment of the invention described above is described below.

FIG. 1 is a diagram showing a production line for a pipe obtained by resistance resistance welding used in an embodiment of the invention. This production line for pipes obtained by resistance resistance welding has a basic configuration in which a sheet (strip) (10) is wound from an unwinder (1); then this strip is straightened, turning into a flat, by means of a straightening machine (2); then the strip (10) is gradually folded by a machine (4) for roll forming; then the two side edges, left and right, of the strip (20), rolled in the form of a pipe, are welded by resistance welding using a resistance welding machine, including an induction heating section (5) and a compression roll (resistance welding section) (6) so that the strip is molded into a pipe (30); then the section of the welded burr of the pipe (30) is cut off with a tool (7) to cut the burr; then the pipe (30) after cutting is adjusted in the outer diameter by a calibration mill (8); and then the pipe (30) is cut into segments of a given length by a pipe cutting machine (9).

In this embodiment, the roll forming machine (4) at the last stage has a stand (3) for forming in caliber with an edge guiding element including a plurality of stands (for example, three stands), and, as described above, an edge guiding element of each the stand is made of a corresponding shape, so that the upper side of each edge of the strip (side of the inner surface of the pipe) and / or the lower side of each edge of the strip (side of the outer surface of the pipe) can be formed with a given slope.

For example, as shown in FIG. 2A, showing a schematic cross-sectional view, and FIG. 2B, showing a local detailed schematic view for this section, the additional stand of the stand (3) for forming in caliber with an edge guiding element has the shape of an edge guiding element with a predetermined two-stage slope (the slope angle of the second stage is α, and the vertical slope of the second stage is β. This shape of the edge guide element is printed on the lateral edges of the strip (10), thereby two lateral edges, etc. the left and the left, on the lower side of the strip (10) (the side of the outer surface of the pipe) are formed with a slope having a slope angle of α and a slope height of β.

According to the aforementioned method, a strip (20) having a pipe shape that is formed on the side of the outer surface with a slope having a slope angle of α and a slope height of β, and on the side of the inner surface is formed with a slope having a slope angle of γ , and the slope height, component δ, is set so that the V-shaped angle ϕ for resistance resistance welding is from 2 ° to 8 °, as shown in Fig. 11.

In this way, the inclusions can be sufficiently removed from the resistance weld seam, therefore, a resistance weld pipe having extremely excellent toughness and strength can be obtained.

Examples

Example 1

The following describes example 1.

At the same time, the strip (steel strip), having 1920 mm in width and 19.1 mm in thickness, was used for the manufacture of pipes obtained by resistance resistance welding, having 600 mm in diameter. Test pieces were cut from the weld of the fabricated pipe obtained by resistance resistance welding, and they were subjected to a Charpy test to evaluate pipe performance. Charpy test specimens were taken one at a time for each of ten different points in the pipe length direction such that the longitudinal direction of the test specimen was parallel to the direction along the pipe circumference and the longitudinal center of the notch corresponded to the central position in the thickness of the weld. Test specimens were made in the form of impact test specimens having a 2 mm V-shaped notch conforming to JIS5 (Japanese Industrial Standard 5), and were subjected to an impact test at a temperature of 46 ° C, and impact values were measured using Charpy and brittle fracture surface relationships. A Charpy impact strength of 125 Joules or more, and a brittle fracture surface ratio of 35% or less, respectively, were determined to be an acceptable performance range.

(Example 1 of the invention)

As an example 1 of the invention, resistance resistance welding pipe was manufactured according to the first embodiment of the invention. That is, the lateral edges of the strip on the side that will be the side of the outer surface of the pipe were formed with a slope of the end stand for molding in caliber with an edge guide element, in which the edge guide element has two angles (the first angle of the guide element is 85 ° relative to the perpendicular to the roll axis) . The inclination angle (α) was made equal to 30 ° relative to the vertical edge of the strip.

(Example 2 of the invention)

As an example 2 of the invention, resistance resistance welding pipe was manufactured according to a second embodiment of the invention. That is, in double-gauge molding in caliber with an edge guide element, the side edges of the strip on the side that will be the side of the outer surface of the pipe, and the side edges of the strip on the side that will be the side of the inner surface of the pipe, were formed with a slope of the first stand, in which the edge guide element has three angles (the second angle of the edge guide element is 40 ° relative to the perpendicular to the axis of the roll), respectively. Any angle from the number of the angle (α) of the inclination on the side that will be the side of the outer surface of the pipe and the angle (γ) of the inclination on the side that will be the side of the inner surface of the pipe was made equal to 25 °.

(Example 3 of the invention)

As an example 3 of the invention, resistance resistance welding pipe was manufactured according to a third embodiment of the invention. That is, when three-cage molding in caliber with an edge guide element, the lateral edges of the strip on the side that will be the side of the pipe’s inner surface were formed with a slope of the first stand, in which the edge guide element has two angles (the first angle of the edge guide element is 60 ° relative to the perpendicular to the axis roll), and the lateral edges of the strip on the side that will be the side of the outer surface of the pipe were formed with a slope of the third stand, in which the edge guide element has two angles ( he first angle kromkonapravlyayuschego element is 85 ° relative to the perpendicular to the roll axis). The inclination angle (α) on the side that will be the side of the outer surface of the pipe was made equal to 30 °, and the inclination angle (α) on the side that would be the side of the inner surface of the pipe was made equal to 40 °.

(Example 1 prior art)

As an example 1 of the prior art, resistance resistance welding pipe was manufactured according to the method described in Patent Document 1. That is, an attempt was made that in the first stand for molding in caliber with an edge guide element, in which the edge guide element has one the angle, the amount of draft of the caliber with the edge guide element was adjusted so that the side edges of the strip are in contact with the edge guide element along the edge section corresponding to about half the thickness, so that the side edges on the side that will be the side of the inner surface of the pipe were formed with a slope, and sought that in the second stand for molding in caliber with an edge guide element, in which the edge guide element has one angle, the side edges of the strip contacted, as implied, with the edge guide element over the remaining portion of the edge corresponding to approximately half the thickness, so that the side edges are on the side that will be the side outside therein the pipe were formed with a bias. The slope for this slope was set to 20 °.

(Example 2 prior art)

As an example 2 of the prior art, resistance-resistance welding pipe was manufactured according to the method described in Patent Document 2. That is, an attempt was made to use an edger roll on the front side of the molding from the caliber with the edge guide element, and this edger roll was used to reduce the lateral edges of the strip, due to which the lateral edges of the strip were completely formed with a slope, and in the stand for molding in caliber from the edge guide with the edge-guiding element having one corner, they strive so that the side edges of the strip are in contact, as implied, with the edge-guiding element along a portion of the edge corresponding to approximately half the thickness, so that the side edges on the side that will be the side of the outer surface of the pipe are formed in vertical surfaces. The tilt angle for the slope was set to 20 °.

(Example 3 prior art)

As an example 3 of the prior art, in the production line shown in FIG. 1, the lateral edges of the strip were previously ground to a rectangular shape, and a cage for forming in caliber with an edge guide element was used to produce the pipe obtained by resistance resistance welding which the edge guide element has one angle.

Charpy impact strength values and brittle fracture surface relationship of pipe weld obtained by resistance welding, made in accordance with the above, were measured, and the measurement results are shown in Table 1. In addition, just before resistance welding was performed, the side welds were cut and selected the edges of the strips, and the shapes of the side edges were investigated, and the results of such a study are also described.

Table 1 The set value of the slope during molding in caliber with edge guide element The measured value of the slope immediately before resistance resistance welding Charpy Impact Value Brittle Fracture Surface Ratio Example 1 of the invention 30 ° on the side of the outer surface of the pipe 30 ° on the side of the outer surface of the pipe 150 joules 25% Example 2 of the invention 25 ° on the side of the outer surface of the pipe 25 ° on the side of the inner surface of the pipe 25 ° on the side of the outer surface of the pipe
25 ° on the side of the inner surface of the pipe 180 joule fifteen% Example 3 of the invention 30 ° on the side of the outer surface of the pipe 40 ° on the side of the inner surface of the pipe 30 ° on the side of the outer surface of the pipe
40 ° on the side of the inner surface of the pipe 200 joules 10% Prior Art Example 1 25 ° on the side of the outer surface of the pipe
25 ° on the side of the inner surface of the pipe No bias (smooth) 25 joules 51% Example 2 Prior Art 20 ° on the side of the inner surface of the pipe No bias (smooth) 25 joules fifty% Example 3 Prior Art Not installed Not installed 20 joules 58%

As can be seen from Table 1, in examples 1-3 according to the invention, the weld has high impact strength and low brittle fracture surface ratio, that is, the toughness is excellent and the reliability of the products is high. On the contrary, in examples 1-3 of the prior art, the weld has low impact strength and a large surface brittle fracture ratio, that is, the toughness is reduced and the reliability of the products is low. In addition, when comparing the shapes of the side edges of the strips with each other immediately before resistance welding after molding in caliber with the edge guiding element, it is seen that, while in Examples 1-3 of the invention, the required slope is maintained as on the side edges on the side that will be side of the inner surface of the pipe, and on the side edges on the side that will be the side of the outer surface of the pipe, in both examples 1 and 2 of the prior art, the side edges were smoothed during molding and in caliber with an edge guide, and the slope was not maintained.

Therefore, it was confirmed that, according to the invention, a pipe obtained by resistance resistance welding having excellent weld characteristics can be manufactured.

Example 2

Example 2 is described below. In Example 2, a strip formed by a steel strip having 1920 mm wide and 19.1 mm thick was passed through a pipe welding unit, such as that shown in FIG. 1, that is, including an uncoiler ( 1), a straightening machine (2), a machine (4) for roll forming (including forming in caliber with an edge guiding element, which has many stands (stand of rolls of caliber with an edge guiding element) (3)), a resistance welding machine (including contact tip (50) and pressure roll (6)), means (7) for cutting the burr, a calibration mill (8), and a pipe cutting machine (9), so that a steel pipe with an outer diameter of 60 mm was made. In the manufacture of this pipe, production conditions varied according to the following four conditions.

(Example 21 of the invention)

The side of the outer diameter of the pipe of each edge of the strip was formed with approximately a straight slope (the angle (α) of the slope and the depth (β) of the slope were set as the values shown in Table 2) by the third stand of the forming group (3) of the caliber with an edge guiding element having a total of three stands, and in the embodiment shown in Fig. 7, argon gas was blown from the gas supply nozzles (60) to the edges of the strip (10) subjected to resistance welding by resistance welding (resistance heating from contact tips (50) ) 7, reference numeral 40 shows the direction of advancement of the strip (10) (after welding molded into a pipe (30)), and a compression roll is not shown.

(Example 22 of the invention)

The side of the inner diameter of the pipe of each edge of the strip was formed with approximately a straight slope (the slope angle (α) and the slope depth (β) were set by the values shown in Table 2) by the first stand of the forming group (3) of the caliber with an edge guiding element having in common of complexity are two stands, and the side of the outer diameter of the pipe of this edge was formed with an approximately straight slope, respectively, by the second stand of the forming group (3) of caliber with an edge guiding element, and in the embodiment shown in FIG. , the edges of the strip (10), which are heated by resistance welding (resistance heating by contact tips (50)). When passing in direction (40), the advancements were enclosed by a casing (13) with a gas atmosphere, and the inner part of the casing was stored in an atmosphere of 1% carbon dioxide gas and nitrogen gas as the rest. In Fig. 8, reference numeral 40 shows the direction of advancement of the strip (10) (after welding molded into a pipe (30)), and a compression roll is not shown.

(Comparative example 21)

Each edge of the strip was formed with approximately a straight slope (the slope angle (α) and the slope depth (β) were set as the values shown in Table 2) on the sides of both the inner and outer diameters of the pipe by the first stand of the forming group (3) caliber with an edge guiding element having a total of three stands, and each edge of the strip subjected to resistance welding by resistance welding was left open in air.

(Example 21 prior art)

The shape of each edge of the strip was supported by an approximate rectangular shape (the shape of the longitudinal edge had the appearance of a rectangle), and each edge of the strip exposed to resistance welding was left open in air.

Test specimens were cut from a weld of steel pipes made under the four conditions described above, and they were subjected to a Charpy test to evaluate pipe performance. As Charpy test specimens, impact test specimens having a 2 mm V-notch conforming to JIS5 (Japanese Industrial Standard 5) were used, which were selected one for each of ten different points in the pipe length direction such so that the longitudinal direction of the test specimen was taken parallel to the direction along the circumference of the pipe, and the longitudinal center of the notch was taken in a central position along the thickness of the weld, and the impact test was performed at a temperature of 46 ° C, and Charpy impact strength and brittle fracture surface ratio were measured. A Charpy impact strength of 125 Joules or more, and a brittle fracture surface ratio of 35% or less, respectively, were determined to be an acceptable performance range. The measurement results are shown in Table 2.

As can be seen from Table 2, in examples 21 and 22 according to the invention, the weld has a very high impact strength (Charpy impact strength) and a small brittle fracture surface ratio, that is, the toughness is excellent and the reliability of the products is high. In contrast, in comparative example 21 and example 21 of the prior art, the weld has low impact strength (Charpy impact strength) and a large brittle fracture surface ratio, i.e., impact strength is reduced and product reliability is low.

table 2 Resistance Welding Atmosphere The method of forming a slope Edge slope just before welding Charpy Impact Value Brittle Fracture Surface Ratio Example 21 of the invention Argon gas is blown The third stand of a three-stand forming group (3) of caliber with an edge guide element α = 25 °
β = 4 mm (21% of thickness) 250 joules 12% Example 22 of the invention 1% carbon dioxide gas and nitrogen gas as the rest The first stand and the second stand of the forming group of the caliber with an edge guide element having a total of two stands α = 45 °
β = 7 mm (37% thickness) 310 joules 7% Reference Example 21 air The first stand of a three-stand forming group (3) of caliber with an edge guide element α = 20 °
β = 4 mm (16% of thickness) 130 joules 33% Reference Example 21 air Not formed No bias 25 joules 55%

Example 3

The following describes example 3.

In this case, a strip (steel strip), having 1920 mm in width and 19.1 mm in thickness, was used for the manufacture of pipes obtained by resistance resistance welding, having 600 mm in diameter.

Test pieces were cut from the weld of the pipes produced by resistance resistance welding, and they were subjected to a Charpy test to evaluate the performance of the pipes. Charpy test specimens were taken one at a time for each of ten different points in the pipe length direction such that the longitudinal direction of the test specimen was parallel to the direction along the pipe circumference and the longitudinal center of the notch corresponded to the central position in the thickness of the weld. Test specimens were made as impact test specimens having a 2 mm V-notch conforming to JIS5 (Japanese Industrial Standard 5), and were subjected to an impact test at a temperature of -46 ° C., and impact strength values were measured by Charpy and brittle fracture surface relationships. A Charpy impact strength of 125 Joules or more, and a brittle fracture surface ratio of 35% or less, respectively, were determined to be an acceptable performance range.

(Example 31 of the invention)

By way of example 31 of the invention, resistance resistance welding pipe was manufactured according to an embodiment of the invention. In this case, resistance resistance welding was performed in such a way that the upper side of the strip (10) (the side of the inner surface of the pipe (20)) was formed with approximately a straight slope having a slope angle (γ) of 25 ° and a slope height (δ) , which is 4 mm (21% of the thickness), by the third stand of the stand for molding in caliber with an edge guiding element that includes three stands, and the roll forming was configured so that immediately before the resistance welding, the angle of joining θ between the vert The ical edges of the strip were opened at 0.3 ° to the side of the outer surface of the pipe.

(Example 32 of the invention)

As an example 32 of the invention, resistance welding was performed so that the upper side of the strip (10) (the side of the inner surface of the pipe (20)) was formed with approximately a straight slope having a slope angle (γ) of 45 ° and a height (δ) a slope of 7 mm (37% of the thickness) by the first stand of the stand for forming in caliber with an edge guiding element including two stands, and the lower side of the strip (10) (side of the outer surface of the pipe (20)) was formed with approximately straight slope having an angle (α) a slope of 45 ° and a height (β) of a slope of 7 mm (37% of thickness), the second stand of the stand for forming in caliber with an edge guiding element, and the roll forming was adjusted so that immediately before the resistance welding resistance, the joining angle 9 between the vertical edges of the strip was opened at 0.2 ° to the side of the inner surface of the pipe.

(Comparative example 31)

As comparative example 31, resistance welding was performed so that the lower side of the strip (10) (the side of the outer surface of the pipe (20)) was formed with approximately a straight slope having a slope angle (α) of 20 ° and a height (β) a slope of 3 mm (16% of the thickness) by the first stand of the forming gauge group with an edge guiding element including three stands, and the upper side of the strip (10) (side of the inner surface of the pipe (20)) was formed with approximately straight slope having an angle (γ) a slope of 20 ° and a height (δ) of a slope of 3 mm (16% of the thickness) of the first stand, and the roll forming was configured so that immediately before resistance welding, the angle of joining between the vertical edges of the strip was open 1.1 ° to the side of the outer surface of the pipe.

(Example 31 of the prior art)

As an example 31 of the prior art, the resistance welding was performed so that each edge of the strip was approximately rectangular in shape, and immediately before the resistance welding, the contact angle θ between the vertical edges of the strip was opened 1.1 ° to the side of the outer surface of the pipe as shown in FIG. 10.

Charpy impact strength values and brittle fracture surface relations of pipe weld obtained by resistance resistance welding made in accordance with the above were measured, and the measurement results are shown in Table 3.

Table 3 The method of forming a slope Slope immediately before resistance resistance welding Docking angle between the vertical edges of the strip Charpy Impact Value Brittle Fracture Surface Ratio Example 31 of the invention The third stand of a three-stand forming gauge group with an edge guide element Grade: 25 ° Grade: 4 mm (21% of thickness) 0.3 ° to the side of the outer surface of the pipe 250 joules 12% Example 32 of the invention The first stand and the second stand of a two-stand forming gauge group with an edge guide element Grade: 45 ° Grade: 7 mm
(37% thickness) 0.2 ° to the side of the inner surface of the pipe 310 joules 8% Reference Example 31 The first stand of a three-stand forming group of caliber with an edge guide element Grade: 20 ° Grade: 3 mm
(16% of thickness) 1.1 ° to the side of the outer surface of the pipe 130 joules 33% Example 31 of the prior art Not formed No bias 1.1 ° to the side of the outer surface of the pipe 25 joules 55%

As can be seen from Table 3, in pipes obtained by resistance resistance welding, according to examples 31 and 32 according to the invention, the weld has high impact strength and low brittle fracture surface ratio, that is, the toughness is excellent and the reliability of the products is high. On the contrary, in pipes obtained by resistance resistance welding, according to comparative example 31 and example 31 of the prior art, the weld has low impact strength and a high brittle fracture surface ratio, i.e., toughness is reduced and product reliability is low.

Thus, it was confirmed that, according to the invention, a resistance-welded pipe having excellent weld characteristics can be manufactured.

Example 4

The following is a description according to an example.

In this case, a strip (steel strip), having 1920 mm in width and 19.1 mm in thickness, was used for the manufacture of pipes obtained by resistance resistance welding, having 600 mm in diameter.

Test pieces were cut from the weld of the pipes produced by resistance resistance welding, and they were subjected to a Charpy test to evaluate pipe performance. Charpy test specimens were taken one at a time for each of ten different points in the pipe length direction such that the longitudinal direction of the test specimen was parallel to the direction along the pipe circumference and the longitudinal center of the notch corresponded to the central position in the thickness of the weld. Test specimens were made as impact test specimens having a 2 mm V-notch conforming to JIS5 (Japanese Industrial Standard 5), and were subjected to an impact test at a temperature of -46 ° C., and impact strength values were measured by Charpy and brittle fracture surface relationships. A Charpy impact strength of 125 Joules or more, and a brittle fracture surface ratio of 35% or less, respectively, were determined to be an acceptable performance range.

(Example 41 of the invention)

By way of example 41 of the invention, resistance resistance welding pipe was manufactured according to an embodiment of the invention. In this case, resistance resistance welding was performed in such a way that the lower side of the strip (10) (the side of the outer surface of the pipe (20)) was formed with approximately a straight slope having a slope angle (α) of 25 ° and a slope height (β) , which is 4 mm (21% of the thickness), by the third stand of the stand for forming in caliber with an edge guiding element that includes three stands, and the roll forming was configured so that immediately before the resistance welding, the V-angle ϕ was 2, 5 °.

(Example 42 of the invention)

As an example 42 of the invention, resistance welding was performed so that the upper side of the strip (10) (the side of the inner surface of the pipe (20)) was formed with approximately a straight slope having a slope angle (γ) of 45 ° and a height (δ) a slope of 7 mm (37% of the thickness) by the first stand of the stand for forming in caliber with an edge guiding element including two stands, and the lower side of the strip (10) (side of the outer surface of the pipe (20)) was formed with approximately straight slope having an angle (α) a slope of 45 ° and a height (β) of a slope of 7 mm (37% of thickness), the second stand of the stand for forming in caliber with an edge guiding element, and the roll forming was adjusted so that immediately before the resistance welding resistance V-shaped angle ϕ was 7.5 °.

(Comparative example 41)

As comparative example 41, resistance welding was performed so that the lower side of the strip (10) (the side of the outer surface of the pipe (20)) was formed with approximately a straight slope having a slope angle (α) of 20 ° and a height (β) a slope of 3 mm (16% of the thickness) by the first stand of the forming gauge group with an edge guiding element including three stands, and the upper side of the strip (10) (side of the inner surface of the pipe (20)) was formed with approximately straight slope having an angle (γ) a slope of 20 ° and a slope height (δ) of 3 mm (16% of the thickness) of the first stand, and the roll forming was adjusted so that immediately before the resistance welding, the V-angle ϕ formed by the edges strip, was 1.5 °.

(Example 41 of the prior art)

As an example 41 of the prior art, the resistance welding was performed so that each edge of the strip was approximately rectangular in shape, and immediately before the resistance welding, the V-shaped angle ϕ formed by the edges of the strip was 1.8 °, as shown on Fig.

Charpy impact strength values and brittle fracture surface relationship of pipe weld obtained by resistance resistance welding made in accordance with the above were measured, and the measurement results are shown in Table 4.

Table 4 The method of forming a slope Slope immediately before resistance resistance welding V-shaped corner Charpy Impact Value Brittle Fracture Surface Ratio Example 41 of the invention The third stand of a three-stand forming gauge group with an edge guide element Grade Angle:
25 ° Slope Height:
4 mm
(21% of thickness) 2.5 ° 250 joules 12% Example 42 of the invention The first stand and the second stand of a two-stand forming gauge group with an edge guide element Grade: 45 ° Grade:
7 mm
(37% thickness) 7.5 ° 310 joules 8% Reference Example 41 The first stand of a three-stand forming group of caliber with an edge guide element Grade: 20 ° Grade: 3 mm
(16% of thickness) 1.5 ° 130 joules 33% Example 41 Prior Art Not formed No bias 1.8 ° 25 joules 55%

As can be seen from Table 4, in pipes obtained by resistance resistance welding, according to examples 41 and 42 according to the invention, the weld has high impact strength and low brittle fracture surface ratio, that is, the toughness is excellent and the reliability of the products is high. On the contrary, in pipes obtained by resistance resistance welding, according to comparative example 41 and example 41 of the prior art, the weld has low impact strength and a high brittle fracture surface ratio, i.e., toughness is reduced and product reliability is low.

Thus, it was confirmed that, according to the invention, a resistance-welded pipe having excellent weld characteristics can be manufactured.

Claims (28)

1. A method of manufacturing pipes obtained by resistance resistance welding, having improved characteristics of the weld, characterized in that the strip is molded, then its edges are joined and then resistance-welded by resistance to form a pipe, the edges on both sides of the upper and of the lower sides of the strip during molding in caliber with an edge guiding element in the process of roller forming before resistance welding is formed with a slope, while Ku is performed so as to provide a resistance welding with corner connections between the edges of from -1 to + 1 °. 2. The method of manufacturing pipes according to claim 1, characterized in that the edges on one side in the direction of the thickness of the strip are rounded. 3. The method of manufacturing pipes according to claim 1, characterized in that the edges on the side of the inner diameter of the strip are formed with a slope at an earlier stage of molding in caliber with an edge guide element, and the edges on the side of the outer diameter of the strip are formed with a slope at a later stage of molding in caliber with edge guide element. 4. The method of manufacturing pipes according to claim 2, characterized in that the edges on the side of the inner diameter of the strip are formed with a slope at an earlier stage of molding in caliber with an edge guide element, and the edges on the side of the outer diameter of the strip are formed with a slope at a later stage of molding in caliber with edge guide element. 5. A method of manufacturing pipes according to any one of claims 1 to 4, characterized in that the edges are formed with a slope in the forming group of the caliber with an edge guide element, which includes at least the last stand of caliber with an edge guide element. 6. A method of manufacturing pipes according to any one of claims 1 to 4, characterized in that in the slope on the strip after molding in caliber with the edge guide element, the angle from the surface of the edge of the strip to the vertical direction is in the range from 25 to 50 °, and the perpendicular length is the place of the beginning of the formed slope to the place of its end on one side is from 20 to 45% of the thickness. 7. A method of manufacturing pipes according to claim 5, characterized in that in the slope on the strip after molding in caliber with a guiding element, the angle from the surface of the strip edge to the vertical direction is in the range from 25 to 50 °, and the perpendicular length from the start point of the formed slope to the point of its end on one side is from 20 to 45% of the thickness. 8. A method of manufacturing pipes according to any one of claims 1 to 4, 7, characterized in that resistance resistance welding is performed by blowing inactive gas or deoxidizing gas. 9. A method of manufacturing pipes according to claim 5, characterized in that the resistance resistance welding is performed by blowing inactive gas or deoxidizing gas. 10. The method of manufacturing pipes according to claim 6, characterized in that the resistance resistance welding is performed by blowing inactive gas or deoxidizing gas. 11. A method of manufacturing pipes according to any one of claims 1 to 4, 7, 9 and 10, characterized in that the resistance resistance welding is performed with a V-shaped angle formed by the edge of the strip, comprising from 2 to 8 °. 12. The method of manufacturing pipes according to claim 5, characterized in that the resistance resistance welding is performed with a V-shaped angle formed by the edge of the strip, comprising from 2 to 8 °. 13. The method of manufacturing pipes according to claim 6, characterized in that the resistance resistance welding is performed with a V-shaped angle formed by the edge of the strip, comprising from 2 to 8 °. 14. The method of manufacturing pipes of claim 8, characterized in that the resistance resistance welding is performed with a V-shaped angle formed by the edge of the strip, comprising from 2 to 8 °. 15. A method of manufacturing pipes obtained by resistance resistance welding, having improved characteristics of the weld, characterized in that the molding is carried out in caliber with an edge guide during the roll forming process, using the shape of the edge guide element having two or more angles, in order to copy this shape at the edges of the strip so as to form a slope on the upper and lower surfaces of the edges of the strip, while forming is carried out in such a way as to provide contact with Arch resistance with the angle between the joining edges of from -1 to + 1 °. 16. The method of manufacturing pipes according to clause 15, characterized in that the edges on one side in the direction of the thickness of the strip are rounded. 17. The method of manufacturing pipes according to claim 20, characterized in that the edges on the side of the inner diameter of the strip are formed with a slope at an earlier stage of molding in caliber with an edge guide element, and the edges on the side of the outer diameter of the strip are formed with a slope at a later stage of molding in caliber with edge guide element. 18. The method of manufacturing pipes according to clause 16, characterized in that the edges on the side of the inner diameter of the strip are formed with a slope at an earlier stage of molding in caliber with the edge guide element, and the edges on the side of the outer diameter of the strip are formed with a slope at a later stage of molding in caliber with edge guide element. 19. A method of manufacturing pipes according to any one of paragraphs.15-18, characterized in that the edges are formed with a slope in the forming group of the caliber with the edge guide element, which includes at least the last stand of the caliber with the edge guide element. 20. A method of manufacturing pipes according to any one of paragraphs.15-18, characterized in that in the slope on the strip after molding in caliber with an edge guide element, the angle from the surface of the strip edge to the vertical direction is in the range from 25 to 50 °, and the perpendicular length is from the place of the beginning of the formed slope to the place of its end on one side is from 20 to 45% of the thickness. 21. The method of manufacturing pipes according to claim 19, characterized in that in the slope on the strip after molding in caliber with a guiding element, the angle from the surface of the strip edge to the vertical direction is in the range from 25 to 50 °, and the perpendicular length from the start point of the formed slope to the point of its end on one side is from 20 to 45% of the thickness. 22. A method of manufacturing pipes according to any one of paragraphs.15-18 and 21, characterized in that resistance resistance welding is performed by blowing inactive gas or deoxidizing gas. 23. The method of manufacturing pipes according to claim 19, characterized in that the resistance resistance welding is performed by blowing inactive gas or deoxidizing gas. 24. A method of manufacturing pipes according to claim 20, characterized in that the resistance resistance welding is performed by blowing inactive gas or deoxidizing gas. 25. A method of manufacturing pipes according to any one of paragraphs.15-18, 21, 23 and 24, characterized in that the resistance resistance welding is performed with a V-shaped angle formed by the edge of the strip, comprising from 2 to 8 °. 26. A method of manufacturing pipes according to claim 19, characterized in that the resistance resistance welding is performed with a V-shaped angle formed by the edge of the strip, comprising from 2 to 8 °. 27. The method of manufacturing pipes according to claim 20, characterized in that the resistance resistance welding is performed with a V-shaped angle formed by the edge of the strip, comprising from 2 to 8 °. 28. The method of manufacturing pipes according to item 22, wherein the resistance resistance welding is performed with a V-shaped angle formed by the edge of the strip, comprising from 2 to 8 °.

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