JP2012187590A - Method for producing laser-welded steel pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for obtaining a weld zone of high quality without deteriorating welding efficiency, and further, stably producing a laser-welded steel pipe at a high yield.SOLUTION: In the method for producing the laser-welded steel pipe in which a steel sheet is formed into a cylindrical open pipe by forming rolls, laser beams are emitted from the outer face side of the open pipe while pressurizing the edge parts of the open pipe by squeeze rolls, and the edge parts are laser-welded, the laser welding is performed in such a manner that two laser beams with a diameter of <0.4 mm in a spot size in a just focus are emitted to the right side and the left side of the edge parts, respectively, an interval between the central points on the surface of the steel sheet of the right laser beam emitted to the right side and the left laser beam emitted to the left side is controlled to ≥0.4 mm, and also, the right laser beam and the left laser beam are arranged not to be superimposed on each other in the back face of the steel sheet.

Description

  The present invention relates to a method of manufacturing a steel pipe (hereinafter referred to as a laser welded steel pipe) in which an edge portion of an open pipe is welded using a laser beam, and in particular, extraction and transportation of oil and natural gas such as an oil well pipe or a line pipe. The present invention relates to a method for manufacturing a laser welded steel pipe suitable for the above.

Steel pipes used as oil well pipes or line pipes are roughly classified into welded steel pipes (for example, ERW steel pipes, UOE steel pipes, etc.) and seamless steel pipes. Among these steel pipes, ERW steel pipes are economically advantageous because they can be manufactured at low cost by using hot-rolled strip-shaped steel plates (so-called hot coils) as raw materials.
However, in general, ERW steel pipes are formed by forming steel plates into a cylindrical shape using forming rolls, and open pipes (here, open pipes are pipe-shaped steel strips that are formed by multi-stage forming rolls and not joined at the ends. Hereinafter, it is referred to as an open pipe), and electric resistance welding (also referred to as high-frequency resistance welding) is performed while pressing the edges of the open pipe (that is, both ends of the steel strip formed into a cylindrical shape) with a squeeze roll. Therefore, there is a problem that a seam by welding (so-called seam) inevitably exists, and the low temperature toughness of the seam deteriorates. Therefore, oil well pipes and line pipes of electric resistance steel pipes have problems in use in cold regions. The reason why the low temperature toughness of the seam deteriorates is that when the edge portion is welded, the high temperature molten metal reacts with oxygen in the atmosphere to generate an oxide, and the oxide tends to remain in the seam.

In addition, the ERW steel pipe has a problem that the corrosion resistance of the seam tends to deteriorate because the alloy elements are easily segregated in the molten metal when the edge portion is welded. For this reason, oil-well pipes and line pipes of ERW steel pipes have problems in use in severe corrosive environments (for example, sour environments).
On the other hand, laser beam welding (hereinafter referred to as laser welding) has been attracting attention as a welding method that does not deteriorate the low temperature toughness and corrosion resistance of the seam. Laser welding makes it possible to reduce the size of the heat source and concentrate the heat energy at a high density, thereby preventing the formation of oxides and segregation of alloy elements in the molten metal. Therefore, when laser welding is applied to the production of a welded steel pipe, it is possible to prevent the low temperature toughness and corrosion resistance of the seam from being deteriorated.

Therefore, in the process of manufacturing a welded steel pipe, a technique for manufacturing a steel pipe (that is, a laser welded steel pipe) by irradiating the edge portion of the open pipe with a laser beam for welding has been put into practical use.
However, in laser welding, welding is performed by condensing a laser beam, which is a high-density energy beam, with an optical component and irradiating the welded portion, and this involves rapid melting of the metal during welding. For this reason, the weld metal scatters as spatter from the formed molten pool. The scattered spatter adheres to the laser-welded steel pipe and degrades the quality of the steel pipe, and also adheres to the welding apparatus, optical components, and the pipe making machine, and the welding operation becomes unstable. Further, since laser welding is performed by concentrating heat energy at a high density, a large amount of spatter is generated, and welding defects such as undercut and underfill (that is, dents) are generated. When undercut or underfill occurs, the strength of the welded portion decreases.

  Therefore, various techniques for preventing the adhesion of spatter by laser welding and for preventing the occurrence of spatter have been studied. For example, a technique for preventing the occurrence of sputtering by reducing the laser output, or a technique for preventing the occurrence of sputtering by largely shifting the focal position (so-called defocusing) has been put into practical use. However, the reduction in laser output and defocus not only cause a reduction in welding speed (that is, a reduction in welding efficiency), but also have a problem that poor penetration tends to occur.

Patent Document 1 discloses a technique for preventing underfill using a filler wire when laser welding is performed. However, in this technique, the composition of the weld metal changes depending on the filler wire components. Therefore, a filler wire must be selected according to the component of the open pipe, and the load of filler wire inventory management and laser welding work management increases.
Patent Document 2 discloses a technique for preventing welding defects by using a combination of laser welding and arc welding. However, with this technique, the structure of the welding apparatus becomes complicated and the load of maintenance increases, and the load of work management for welding also increases.

  Patent Document 3 discloses a method of performing butt welding by arranging two circular beam spots in the weld line direction. However, in this technique, welding defects are not suppressed in laser welding under the condition that stress is applied to the welded portion like open pipe welding, and in particular, the amount of spatter generated from the back surface of the steel sheet increases.

JP 2004-330299 A Japanese Patent No. 4120408 JP 2009-178768

  In manufacturing a laser welded steel pipe, the present invention properly arranges two laser beams while appropriately maintaining the spot diameter and the center point interval, and controls the laser welding conditions to thereby undercut the welded portion. Another object of the present invention is to provide a method for stably producing a laser-welded steel pipe with a high yield while obtaining a weld of good quality without suppressing underfill and without reducing the welding efficiency.

The inventors investigated and studied a laser welding technique for forming a laser welded portion having no welding defects when laser welding was performed on an edge portion of an open pipe to manufacture a laser welded steel pipe.
FIG. 2 is a perspective view schematically showing an example in which a welding point of the edge portion 2 of the open pipe 1 is laser-welded using one laser beam when manufacturing a laser-welded steel pipe. An arrow A in FIG. 2 indicates the traveling direction of the open pipe. A deep cavity (hereinafter referred to as a keyhole) 4 generated by irradiation with the laser beam 3 and a molten metal 5 formed around the cavity are shown as perspective views.

  When the laser beam 3 is irradiated, as shown in FIG. 2, the edge portion 2 is melted by heat energy concentrated at a high density, and the molten metal 5 is evaporated by the evaporation pressure and evaporation reaction force generated by the evaporation of the molten metal 5. A keyhole 4 is generated at 5. It is considered that the laser beam 3 enters the inside of the keyhole 4 and high temperature plasma generated by ionizing the metal vapor by the energy of the laser beam 3 is filled.

  The keyhole 4 indicates a position where the heat energy of the laser beam 3 is most converged, and the laser welded steel pipe can be stably manufactured by disposing the joining point of the edge portion in the keyhole 4. However, in order to make the joint point of the edge part 2 and the keyhole 4 correspond, a highly accurate groove processing technique is required. If the processing state and the butting state of the edge portion 2 are unstable, the molten metal 5 becomes unstable. As a result, spatter frequently occurs and welding defects such as undercut and underfill tend to occur.

Further, even if the laser welding conditions and the setting conditions for manufacturing the steel pipe are changed in order to suppress spatter, spatter from the back surface of the steel sheet cannot be suppressed at the same time, and the amount of spatter generated may be increased.
Furthermore, in a situation where the molten metal is stressed by the upset applied to the weld, it is necessary to further increase the energy of the laser beam to be irradiated in order to maintain the keyhole. As a result, spatter increases, the groove does not melt sufficiently, and welding defects such as undercut and underfill occur.

  Therefore, the inventors paid attention to a technique for irradiating the welded portion of the edge portion 2 with two laser beams. As a result, it was found that the occurrence of spatter can be suppressed by properly arranging the laser beam irradiation positions and controlling the respective spot diameters and laser beam irradiation angles. And it became clear that a laser welded steel pipe can be manufactured stably with good yield while obtaining a weld part of good quality, without suppressing undercut and underfill of a weld part, and reducing welding efficiency.

The present invention has been made based on these findings.
That is, the present invention is a laser in which a steel plate is formed into a cylindrical open pipe with a forming roll, and a laser beam is irradiated from the outer surface side of the open pipe while pressurizing the edge portion of the open pipe with a squeeze roll. In the welded steel pipe manufacturing method, two laser beams with a spot diameter of less than 0.4 mm at the just focus are irradiated on the right and left sides of the edge, respectively, the right laser beam irradiated on the right side, and the left irradiated on the left side. This is a method of manufacturing a laser welded steel pipe in which laser welding is performed by setting the distance between the center points of the laser beam on the surface of the steel plate to 0.4 mm or more and arranging the right laser beam and the left laser beam on the back surface of the steel plate so as not to overlap.

In the method for manufacturing a laser welded steel pipe according to the present invention, the irradiation angle of the right laser beam and the left laser beam is set to an advance angle of 5 to 50 °, respectively, and the spot diameter at the just focus (perpendicular to the weld line) is set. The total is preferably 0.5 mm or more. Further, it is preferable that the energy density of the right laser beam and the left laser beam on the surface of the steel plate is 130 kW / mm ² or less, respectively. Moreover, it is preferable to add 0.2-1.0 mm upset to an edge part using a squeeze roll. Further, it is preferable that the total laser output of the right laser beam and the left laser beam is over 16 kW, and the welding speed is over 7 m / min. Further, it is preferable to preheat the steel plate prior to laser welding and to process the weld bead by cutting or grinding after laser welding.

  ADVANTAGE OF THE INVENTION According to this invention, when manufacturing a laser-welded steel pipe, a weld part of favorable quality can be obtained, without suppressing the undercut and underfill of a weld part, and reducing a welding efficiency. As a result, the laser welded steel pipe can be manufactured stably with a high yield. The obtained laser welded steel pipe has excellent seam low-temperature toughness and corrosion resistance, and is suitable for oil well pipes and line pipes used in cold regions and corrosive environments.

It is a perspective view which shows typically the example which welds an open pipe with two laser beams by applying this invention. It is a perspective view which shows typically the conventional example which welds an open pipe with one laser beam. The keyhole and the molten metal formed around it are shown as perspective views.

  FIG. 1 is a perspective view schematically showing an example in which an open pipe is welded with two laser beams by applying the present invention. In the present invention, as shown in FIG. 1, two laser beams are irradiated from the outer surface side of the open pipe 1. In the present invention, two laser beams are transmitted using different fibers, and irradiated to the steel sheet as a right laser beam and a left laser beam that melt the left and right steel sheets sandwiching the weld line from the outside of the open pipe. When two laser beams are transmitted by a single fiber, a spot diameter, a laser beam irradiation position, a laser beam irradiation angle, etc. described later cannot be individually set. Therefore, it is necessary to transmit two laser beams using different fibers.

One or two laser oscillators may be used. When one laser oscillator is used to transmit two laser beams, the oscillated laser light may be divided by optical system components and supplied to each fiber.
The spot diameters of the two laser beams at the just focus must both be less than 0.4 mm. Here, the spot diameter at the just focus refers to the beam diameter of the focal parallel portion of the laser beam by optically condensing the laser beam. That is, at the just focus position, since the laser beam is optically focused, the energy density of the laser beam is the highest.

  When the spot diameter of the laser beam at the just focus is 0.4 mm or more, it is difficult to stably maintain the keyhole during welding. If the laser output is increased to stabilize the keyhole, the weld metal may be burned out. To do. Therefore, the spot diameter at the just focus of the laser beam is less than 0.4 mm. On the other hand, if the spot diameter is less than 0.1 mm, the weld bead width at the time of welding becomes narrow, and the unmelted groove is generated. Therefore, the spot diameter at the just focus of the laser beam is preferably 0.1 mm or more.

The spot shape at the just focus of the laser beam is preferably circular, but may be elliptical. When the spot shape is elliptical, the major axis is less than 0.4 mm. For the same reason as in the case of the circular shape, the major axis is preferably 0.1 mm or more.
If the depth from the outer surface of the open pipe to the focus is t (mm), the steel plate thickness of the open pipe is T (mm), and the depth t from the outer surface of the open pipe to the focus is less than 1/2 × T, the focus Since the position of is too shallow, it is difficult to keep the keyhole stable. On the other hand, if it exceeds 3 × T, since the focus position is too deep, sputtering is likely to occur from the back surface side of the steel plate (that is, the inner surface of the open pipe). Therefore, the depth t from the outer surface of the open pipe to the focus is preferably set in the range of 1/2 × T to 3 × T. In addition, also when giving the irradiation angle mentioned later to a laser beam, the depth t from the outer surface of an open pipe to a focus is within the said range.

  The two laser beams are applied to the left and right sides of the weld line, respectively, so that the line connecting the center points of the spots on the surface of the steel sheet is perpendicular to the weld line and the center point interval is 0.4 mm or more. Are arranged so that the right laser beam and the left laser beam do not overlap on the back surface of the steel plate. As a result, there is no overlap of laser beams in the just focus where the energy density of the laser beam is the highest, and laser welding with less spatter generation becomes possible. In addition, by melting the left and right steel plates sandwiching the welding line with individual laser beams, it is possible to effectively use the energy of the laser beam for welding even when the state of the steel plate butt portion (gap spacing, etc.) changes. Become.

It is preferable to provide an irradiation angle for each of the two laser beams. In addition, let the irradiation angle which the laser beam irradiated ahead of the advancing direction of welding and the perpendicular | vertical line of a steel plate surface make be a forward angle.
The irradiation angles of the right laser beam and the left laser beam are preferably 5 to 50 °, respectively. By giving each laser beam a forward angle of 5 ° or more, the amount of spatter generated from the steel sheet surface is reduced. However, if the advance angle exceeds 50 °, the effect cannot be obtained.

  The two laser beams are arranged so as to travel in a plane parallel to the weld line regardless of the presence or absence of the advance angle. The planes on which the laser beam travels (hereinafter referred to as beam traveling planes) are located on both sides of the weld line. This is preferable because it does not overlap on the back surface of the steel plate. Further, when the beam traveling surfaces are not parallel to each other, even if the interval between the beam traveling surfaces is narrowed on the back surface side of the steel plate, it is acceptable as long as the two laser beams do not overlap on the back surface of the steel plate. That is, the two laser beams are arranged apart from each other in the vertical direction with respect to the welding line so as not to overlap on the back surface of the steel plate. The reason is that when two laser beams overlap on the back surface of the steel plate, sputtering easily occurs from the back surface of the steel plate (that is, the inner surface of the open pipe).

When the distance between the beam traveling surfaces is narrowed on the back side of the steel plate, different advance angles are set for the two laser beams, and they are separated in the welding line direction (welding progress direction) on the back surface of the steel plate to avoid overlap. It is also possible to arrange so as to.
Moreover, it is preferable that the sum of the spot diameters in the just focus of the two laser beams (in the direction perpendicular to the weld line) be 0.5 mm or more. By setting the total spot diameter in the direction perpendicular to the weld line to be 0.5 mm or more, the joining point of the edge portion can be arranged relatively easily in the molten metal. If the total spot diameter of the laser beam exceeds 1 mm, it is difficult to maintain the keyhole. Therefore, the total spot diameter of the laser beam is preferably 1 mm or less.

In the present invention, it is preferable to perform laser welding by setting the energy density of the two laser beams on the steel sheet surface (the laser output divided by the laser irradiation area) to 130 kW / mm ² or less. When the energy density of the laser beam on the steel plate surface exceeds 130 kW / mm ² , spatter from the molten metal increases and a large amount of welding defects such as undercut and underfill occur. Therefore, the energy density of each laser beam is set to 130 kW / mm ² or less.

The energy density of the laser beam can be adjusted by controlling the laser output and controlling the spot diameter by optical system components.
When performing laser welding, it is preferable to add an upset of 0.2 to 1.0 mm to the weld. If the amount of upset is less than 0.2 mm, the blowhole caused by laser welding cannot be eliminated. On the other hand, if it exceeds 1.0 mm, laser welding becomes unstable and the amount of spatter generated increases.

  In general, the amount of spatter generated during laser welding decreases as the laser output decreases and as the welding speed decreases. However, reducing the laser output and the welding speed in order to suppress the amount of spatter generated means that the productivity of the laser welded steel pipe is lowered. Therefore, in the present invention, it is preferable to perform laser welding at a welding speed in which the laser outputs of the two laser beams exceed 16 kW in total and exceed 7 m / min. When the laser output is 16 kW or less in total, the welding speed is 7 m / min or less, which leads to a decrease in productivity of the laser welded steel pipe.

In the present invention, the joining point of the edge portion 2 of the open pipe 1 may be anywhere where the gap G of the edge portion 2 is narrowed by a squeeze roll and the average value of the gap G in the thickness direction is 0.5 mm or less. .
In the present invention, even an open pipe made of a thick material (for example, 4 mm or more) can be laser-welded without preheating the edge portion. However, if the edge portion is preheated by high-frequency heating or the like prior to laser welding, effects such as improved productivity of the laser welded steel pipe can be obtained. If preheating is performed by high-frequency heating, a surplus is formed in the welded portion. However, if the surplus is removed by cutting or grinding after laser welding, the surface properties of the welded portion are further improved.

As the auxiliary heat source for preheating the edge portion, means using burner heating, plasma heating, TIG heating, electron beam heating, or the like in addition to high-frequency heating is suitable.
If the distance between the auxiliary heat source and the laser beam oscillator is increased, not only a large amount of heat is required to obtain the effect of preheating by the auxiliary heat source, but also it is difficult to suppress welding defects (for example, undercut and underfill). become. For this reason, the auxiliary heat source and the laser oscillator are arranged close to each other.

Since the auxiliary heat source preheats the edge portion, it is arranged ahead of the laser beam oscillator. By performing preheating, in addition to the effect of increasing the temperature of the edge portion before laser welding, the effect of removing moisture and oil from the edge portion is also obtained.
Oscillator of the laser beam used in the present invention, an oscillator of various forms can be used, a gas (e.g. CO _2, helium - neon, argon, nitrogen, iodine) gas laser is used as a medium, solid (e.g., a rare earth element A solid-state laser using YAG doped with YAG, etc.) as a medium, and a fiber laser using a fiber instead of a bulk as a laser medium are suitable. Alternatively, a semiconductor laser may be used.

  As described above, according to the present invention, in manufacturing a laser welding tube, the spot diameter and the irradiation angle of the laser beam are appropriately maintained, the two laser beams are properly arranged, and the laser welding conditions are set. By controlling, undercut and underfill of the welded part can be suppressed, and a welded part of good quality can be obtained without lowering the welding efficiency, and the laser welded steel pipe can be manufactured stably with a high yield. The obtained laser welded steel pipe is excellent in low temperature toughness and corrosion resistance of the seam by taking advantage of laser welding, and is suitable for oil well pipes and line pipes used in cold regions and corrosive environments.

  A strip-shaped steel plate was formed into a cylindrical open pipe with a forming roll, and a laser welded steel pipe was manufactured by irradiating two laser beams from the outer surface side while pressing an edge portion of the open pipe with a squeeze roll. The components of the steel sheet are as shown in Table 1.

In laser welding, two 10kW fiber laser oscillators were used, and two laser beams were transmitted through different fibers. The laser welding conditions are as shown in Table 2.
Invention examples (welded steel pipe Nos. 1 to 4 and 6) shown in Table 2 are examples in which laser welding steel pipes were manufactured by adjusting the manufacturing conditions of laser welding steel pipes to the condition range of the present invention. In the welded steel pipe No. 5 of the comparative example, two laser beams overlap on the back surface of the steel plate and the laser energy density on the steel plate surface is outside the range of the present invention. An example in which the back surface of the steel plate overlaps and the center point interval at the just focus is out of the scope of the present invention, the welded steel pipe No. 8 uses one laser beam and the spot diameter at the just focus is within the scope of the present invention. This is an example.

  The obtained laser welded steel pipe was subjected to an ultrasonic flaw detection test and a magnetic particle flaw detection test, and a seam was detected over 20 m in accordance with JIS standard G0582 and JIS standard G0565. Table 3 shows the flaw detection results. In Table 3, the ultrasonic flaw detection test has a peak indication height of 10% or less (◎), more than 10% and 25% or less of the standard N5 inner / outer notch artificial defect. Good (○), 25% to 50% or less was evaluated as acceptable (△), and 50% was evaluated as unacceptable (×). Magnetic particle inspection is performed by inspecting welding defects on the inner surface of a laser-welded steel pipe. Excellent (◎) indicates that no welding defects are observed, acceptable (△) indicates that spot-like welding defects are observed, and linear detection. Those in which welding defects were recognized were evaluated as impossible (x).

  As is apparent from Table 2, in the inventive examples (welded steel pipe Nos. 1 to 4 and 6), the ultrasonic flaw detection and magnetic particle flaw detection were excellent (優) or good (良). Also, no welding defects such as undercut and underfill due to spatter were observed. On the other hand, in the comparative examples (welded steel pipe Nos. 5, 7, and 8), ultrasonic flaw detection was possible (Δ) or not (x), and magnetic particle flaw detection was not possible (x). Welding defects such as undercut and underfill due to spattering were also observed.

  When manufacturing a laser welded steel pipe, the laser welded steel pipe can be manufactured stably with a high yield, so that it has a remarkable industrial effect.

1 Open Pipe 2 Edge 3 Laser Beam 4 Keyhole (Cavity)
5 Molten metal 6 Seam

Claims (6)

  A laser welded steel pipe that forms a steel plate into a cylindrical open pipe with a forming roll, and laser welds the edge by irradiating a laser beam from the outer surface side of the open pipe while pressing the edge of the open pipe with a squeeze roll In the manufacturing method, two laser beams having a spot diameter of less than 0.4 mm at the just focus are irradiated to the right side and the left side of the edge part, respectively, and the right laser beam and the left side are irradiated to the right side. The center point interval on the surface of the steel plate of the left laser beam is 0.4 mm or more, and laser welding is performed by arranging the right laser beam and the left laser beam so as not to overlap on the back surface of the steel plate. Manufacturing method of laser welded steel pipe.   The irradiation angle of the right laser beam and the left laser beam is advancing angle of 5 to 50 °, respectively, and the total in the vertical direction with respect to the weld line of the spot diameter at the just focus is 0.5 mm or more, The method for producing a laser welded steel pipe according to claim 1. 3. The method of manufacturing a laser welded steel pipe according to claim 1, wherein the energy density of the right laser beam and the left laser beam on the surface of the steel sheet is 130 kW / mm ² or less, respectively.   The method for manufacturing a laser welded steel pipe according to any one of claims 1 to 3, wherein an upset of 0.2 to 1.0 mm is added to the edge portion using the squeeze roll.   The laser welded steel pipe according to any one of claims 1 to 4, wherein a total laser output of the right laser beam and the left laser beam exceeds 16 kW, and a welding speed exceeds 7 m / min. Manufacturing method. The laser according to any one of claims 1 to 5, wherein the steel plate is preheated prior to the laser welding, and the welding bead is processed by cutting or grinding after the laser welding. Manufacturing method of welded steel pipe.

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