JP2014018816A - Welded steel pipe and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a welded steel pipe having superior economic efficiency, by improving quality of a seam of the thick-walled welded steel pipe, particularly a temporarily welded part, and also by improving efficiency of tack welding, and to provide a method of manufacturing the same.SOLUTION: A method of manufacturing a welded steel pipe 7 is configured to mold a steel plate with both ends subjected to edge preparation into an open pipe, and to weld an edge preparation part of the open pipe while pressing thereof. An amount of upsetting by pressurization is set to 0.2-1.0 mm. After a butt surface 2 of a central part in the plate thickness direction of the edge preparation part and having a length of 10 mm or less in the plate thickness direction is joined by laser welding, both sides of a surface layer part in the plate thickness direction of the edge preparation part are joined by arc-welding.

Description

  The present invention relates to a steel pipe (hereinafter referred to as a welded steel pipe) obtained by welding an open pipe in the longitudinal direction using both laser welding and arc welding, and a manufacturing method thereof.

  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, UOE steel pipes generally use steel sheets with a thickness of 6 mm or more as raw materials, and after processing to form X-grooves at both ends of the steel sheets, U-type press forming and O-type press forming As the open pipe, the grooved portion is manufactured by welding the grooved portion while matching the grooved portion by the cage method. The electric resistance welded steel pipe is manufactured by forming a steel plate into a cylindrical shape using a forming roll to form an open pipe and welding the grooved portion while applying pressure with a squeeze roll. The welded part is the seam of the welded steel pipe.

  For thick welded steel pipes, such as UOE steel pipes, when welding the groove processed part, the butt surface located at the center of the plate thickness of the X groove formed in the open pipe is tack welded, and then the inner surface is opened. The tip portion is welded, and then the outer surface side groove portion is welded. The welding of the butt face of the X groove (hereinafter referred to as tack welding) is performed continuously over the entire length of the UOE steel pipe, and MIG welding or MAG welding is employed.

Multi-electrode submerged arc welding is widely used for welding of groove portions on the inner surface side and outer surface side after the tack welding (hereinafter referred to as finish welding).
As shown in FIG. 2, such a thick welded steel pipe seam structure has a portion 8 (hereinafter referred to as a tack welded portion) where molten metal solidified by tack welding is formed at the center in the plate thickness direction. And the site | parts 9 and 10 which the molten metal solidified by finish welding are each formed in the inner surface side and the outer surface side of the tack welding part 8 (refer patent document 1, 2). Here, the part 9 that has undergone finish welding on the inner surface side is referred to as an inner surface side finish welding part, and the part 10 that has undergone finish welding on the outer surface side is referred to as an outer surface side finish welding part.

  That is, the inner surface side finish welded portion 9 is formed so that a part of the tack welded portion 8 overlaps, and then the outer surface side finish welded portion 10 is formed so that the entire welded portion of the tack welded portion 8 overlaps. To do. Since tack welding is performed in order to improve the welding efficiency of the groove processing portion, welding defects are likely to occur in the tack welding portion 8. Therefore, since it is necessary to melt the tack welded portion 8 again by finish welding and eliminate the welding defect, the penetration of the inner surface side finish weld portion 9 and the penetration of the outer surface side finish weld portion 10 overlap, Finish welding is performed so as to include the butt face 2 of the groove.

On the other hand, in recent years, from the viewpoint of improving the productivity of welded steel pipes and improving seam characteristics, high speed and high quality of tack welding are required.
By increasing the speed of tack welding and increasing the productivity of the welded steel pipe, the manufacturing cost of the welded steel pipe can be reduced. However, due to the high speed of the tack welding, welding defects are likely to occur in the tack welded portion 2. If a weld defect occurs in the tack welded portion 8, the weld defect remains even after finish welding, greatly affecting the seam characteristics. In addition, if the repair defect is repaired to the welding defect of the tack welded portion 8, the productivity of the welded steel pipe is reduced or the manufacturing cost is increased. That is, it is necessary to achieve both high-speed and high-quality tack welding.

  When tack welding is performed by arc welding (for example, submerged arc welding, gas shielded arc welding, MIG welding, MAG welding, etc.), if the welding speed is increased, the arc becomes unstable. Becomes remarkably high, and the characteristics of the tack welded portion 8 are greatly deteriorated. Therefore, in tack welding, it is necessary to increase the welding speed while maintaining the stability of the arc, and various techniques have been studied conventionally. For example, those that have studied welding power sources such as pulse arcs, those that have examined the welding wire feed system and shape, and those that have studied the components of shielding gas are known. However, sufficient effects are not obtained.

As a welding technique for performing tack welding instead of arc welding, laser beam welding (hereinafter referred to as laser welding) has attracted attention. Laser welding can reduce the size of the heat source and concentrate the heat energy at a high density. Therefore, when applied to tack welding of a welded steel pipe, laser welding enables high-speed tack welding with low heat input.
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, so that rapid melting of the metal is involved during welding. Therefore, molten 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. In laser welding, heat energy is concentrated and welding is performed, so that a large amount of spatter is generated, resulting in a decrease in molten metal, resulting in welding defects such as undercuts and underfills (ie, depressions). Will occur. When undercut or underfill occurs, the strength of the tack 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 the problem that penetration defects are likely to occur.

  Patent Document 3 discloses a technique for preventing the occurrence of sputtering by splitting a laser beam to generate a plurality of spots. However, the technique of performing laser welding by dispersing it in a plurality of spots is equivalent to the technique of performing laser welding by reducing the laser output, not only causing a decrease in welding efficiency, but also causing poor penetration. There is a problem of becoming. In addition, since optical components (such as prisms) that split the laser beam are expensive, it is inevitable that the construction cost for tack welding increases.

  Patent Document 4 discloses a technique for preventing underfill by using a filler wire when performing laser welding. 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 5 discloses a technique for preventing welding defects by using a combination of laser welding and arc welding. However, this technique complicates the structure of the welding apparatus and increases the load of maintenance, and also increases the load of work management for tack welding.
Patent Document 6 discloses a method using two circular beam spots. However, with this technique, welding defects are not suppressed in laser welding under conditions in which stress is applied to the welded portion, and in particular, the amount of spatter generated on the back surface of the steel sheet increases.

  On the other hand, in recent years, in line pipes that carry crude oil and natural gas over long distances, the transportation pressure has been increased to improve transportation efficiency. Therefore, it is necessary to increase the strength of the welded steel pipe (for example, UOE steel pipe) to prevent breakage or damage of the line pipe due to high-pressure transportation. Further, by increasing the strength of the welded steel pipe, it becomes possible to reduce the thickness (that is, reduce the weight), and the effect of improving the construction efficiency of the laying work on site can be obtained. Therefore, research on welded steel pipes for ultra-high-strength line pipes such as X100 and X120 grades is underway.

In order to put such a welded steel pipe for ultra-high-strength line pipe into practical use, while ensuring the toughness of the weld metal of the seam and the heat-affected zone (so-called HAZ), low-temperature cracking of the weld metal (for example, transverse crack) It is a problem to suppress, and it is required to increase the speed of tack welding in the manufacturing process of the welded steel pipe and to prevent the quality deterioration of the tack welded part accompanying it.
In order to solve such a problem, Patent Document 1 proposes a seam portion for expressing high strength and stable low temperature toughness, particularly a composition and a structure of a weld metal. Patent Document 2 proposes preventing lateral cracking by performing welding on the outer surface side so as to keep the maximum temperature of the weld metal surface on the inner surface side within a predetermined range. However, with these technologies, it is difficult to achieve both high speed and high quality of tack welding.

JP 2005-272900 A JP 2005-262253 A Japanese Patent No. 2902550 JP 2004-330299 A Japanese Patent No. 4120408 JP 2009-178768

  The present invention aims to improve the quality of seams of thick welded steel pipes, particularly tack welded parts, improve the efficiency of tack welding, and provide a welded steel pipe excellent in economic efficiency and a method for producing the same. Objective. In addition, by adjusting the setting condition of the tack welding of the butted surface of the X groove formed in the open pipe, by obtaining a healthy tack welded portion without reducing the welding speed of the tack welding, An object of the present invention is to provide a method for stably producing a welded steel pipe with a high yield.

  The inventors have increased the welding speed at the time of tack welding the butted surface of the X groove formed on the open pipe and obtained a high-quality tack weld with a low heat input and high speed. We focused on laser welding, which can be welded. And as a result of investigating and examining the laser welding technology that can prevent the occurrence of welding defects and stably obtain a sound tack weld, the following findings were obtained.

  FIG. 3 schematically shows an example of laser welding (ie, tack welding) of the butted surface 2 of the X groove formed on the open pipe 1 by vertically irradiating one laser beam during tack welding. It is a perspective view shown in FIG. An arrow A in FIG. 3 indicates the welding progress direction. A deep cavity 4 (hereinafter referred to as a keyhole) 4 generated by irradiation with the laser beam 3 and a molten metal 5 formed in the periphery thereof are shown as perspective views.

  When the laser beam 3 is irradiated, as shown in FIG. 3, the edge portion 2 is melted by the heat energy concentrated at high density, and the molten metal 5 is evaporated by the evaporation pressure and the 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 metal vapor by the energy of the laser beam 3 is filled.

The keyhole 4 indicates a position where the thermal energy of the laser beam 3 is most converged. Temporary welding can be stably performed by arranging the joining point of the butting surface 2 in the keyhole 4.
However, as shown in FIG. 3, when the number of laser beams is one, in order to make the junction point of the butt | matching surface 2 and the keyhole 4 correspond, a highly accurate groove processing technique is required. When the processing state and the butt state of the butt surface 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, in a situation where stress is exerted on the molten pool by the upset applied to the tack 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 have further studied a technique for irradiating two junctions of the butt surface 2 with two laser beams. As a result, as shown in FIG. 4, the irradiation positions of the laser beams are properly arranged, and the two laser beams are crossed inside the open pipe steel plate by controlling the incident angle and spot diameter of each laser beam. It was found that the occurrence of spatter can be suppressed by irradiating the light so as not to occur. And the undercut and underfill of the tack welded portion were suppressed, and a good quality tack welded portion could be obtained without reducing the welding efficiency.

  The details of the mechanism by which the generation of spatter is suppressed are unknown, but the energy is distributed to the two laser beams that are irradiated at an inclination angle, and the laser beam preceding the welding direction suppresses the spatter while the sputter is suppressed. After preheating, it is presumed that spatter scattering is suppressed by the subsequent laser beam melting the butted surface. Note that the incident angle of the laser beam refers to an angle formed by a direction perpendicular to the upper surface of the open pipe and a direction in which the laser beam is irradiated.

The present invention has been made based on these findings.
That is, the present invention is a method for manufacturing a welded steel pipe in which a steel plate having a groove processed at both ends is formed into an open pipe and welded while pressurizing the groove processed portion of the open pipe. After joining the butted surfaces with a length of 10 mm or less at the center in the thickness direction of the groove processed part by laser welding, arc welding is performed on both sides of the surface layer part in the thickness direction of the groove processed part. It is a manufacturing method of the welded steel pipe joined by.

  In the method for manufacturing a welded steel pipe according to the present invention, two laser beams having a just-focus spot diameter of 0.3 mm or more transmitted by using different optical fibers in laser welding are applied to the open pipe along the abutting surface. Irradiate from the upper surface side, and incline the preceding laser beam preceding and following the laser beam in the welding progress direction on the upper surface side of the open pipe from the direction perpendicular to the upper surface of the open pipe and tilting it in the welding progress direction. The incident angle of the preceding laser beam is made larger than the incident angle of the following laser beam, and the distance between the center point of the preceding laser beam and the center point of the following laser beam on the back surface of the open pipe is 1 mm or more. It is preferable that Furthermore, the incident angle of the preceding laser beam is greater than 5 ° and less than or equal to 50 °, and the incident angle of the subsequent laser beam is not less than 5 ° and less than 50 °, or one of the preceding laser beam and the subsequent laser beam or Divide the two types by optical parts and irradiate the left and right sides of the abutting surface. The laser output of the preceding laser beam and the following laser beam is 20 kW or less in total, and laser welding is performed at a welding speed of less than 5 m / min. It is preferable to do so.

  ADVANTAGE OF THE INVENTION According to this invention, in the manufacturing process of a thick-walled welded steel pipe, while improving the quality of a tack welding part and improving the efficiency of tack welding, the economically welded steel pipe can be obtained. Therefore, there is a remarkable effect in the industry.

It is sectional drawing which shows typically the example of the seam obtained by applying this invention. It is sectional drawing which shows the example of the conventional seam typically. It is a perspective view which shows typically the example which joins the butt | matching surface of X groove | channel by laser welding. It is a perspective view which shows typically the other example which joins the butt | matching surface of X groove | channel by laser welding. FIG. 5 is a side view schematically illustrating an example of arrangement of the preceding laser beam, the subsequent laser beam, and the line perpendicular to the upper surface of the open pipe in FIG. 4. It is a top view which shows typically the example of arrangement | positioning of the irradiation area | region of a preceding laser beam, the irradiation area | region of a subsequent laser beam, and an edge part in the upper surface of an open pipe.

FIG. 1 is a cross-sectional view schematically showing an example of a seam obtained by applying the present invention. In manufacturing the welded steel pipe 7 by applying the present invention, first, groove processing is performed on both ends of a steel plate as a raw material, and when an open pipe is formed, as shown in FIG. The surfaces 2 are configured to face each other.
If the length in the thickness direction of the butt face 2 of the X groove exceeds 10 mm, the groove will remain unmelted, making it difficult to tack weld. Therefore, the length in the thickness direction of the butt face 2 should be 10 mm or less. preferable.

Next, tack welding of the butt surface 2 is performed to form a tack welding portion 8 as shown in FIG. Below, tack welding is demonstrated.
As shown in FIGS. 3 and 4, laser welding is used for the tack welding. Although tack welding can be performed by electron beam welding or plasma welding, there is a problem that electron beam welding cannot be used in the atmosphere, and plasma welding has a problem that welding speed is inferior. In order to manufacture a large number of welded steel pipes, it is necessary to perform tack welding efficiently in the atmosphere. Therefore, in the present invention, the butt surface 2 is joined by laser welding (that is, tack welding).

FIG. 3 is a perspective view schematically showing an example in which tack welding is performed with one laser beam 3. The keyhole 4 generated by the irradiation of the laser beam 3 and the molten metal 5 formed around the keyhole 4 are shown as perspective views. In this case, the laser beam 3 is irradiated vertically from the upper surface side of the open pipe 1. In addition, the arrow A in FIG. 3 shows the advancing direction of tack welding.
When the spot diameter at the just focus of the laser beam 3 is 0.3 mm or less, the width of the weld bead at the time of tack welding becomes narrow, and the unmelted groove is generated. For this reason, the spot diameter at the just focus is set to exceed 0.3 mm. On the other hand, if the spot diameter exceeds 1 mm, the keyhole becomes difficult to stabilize. Therefore, the spot diameter at the just focus of the laser beam 3 is preferably 1 mm or less.

  The distance from the upper surface of the open pipe 1 to the focus is t (mm), the steel plate thickness of the open pipe 1 is T (mm), and the distance t from the upper surface of the open pipe 1 to the focus is −3 × T (that is, from the upper surface). If it exceeds 3T) upward, the focus position is too high, and it is difficult to stably maintain the keyhole. On the other hand, if it exceeds 3 × T (that is, 3T downward from the upper surface), the focus position is too deep, so that sputtering is likely to occur from the rear surface side of the steel plate (that is, the inner surface of the open pipe). Therefore, the distance t from the upper surface of the open pipe 1 to the focus is preferably set in the range of −3 × T to 3 × T.

The spot shape of the laser beam 3 is preferably circular, but may be elliptical. When the spot shape is an ellipse, the minor axis at the just focus needs to exceed 0.3 mm. For the same reason as in the case of the circular shape, the minor axis is preferably 1 mm or less.
In general, spatter generated during laser welding decreases as the laser output decreases and the welding speed decreases. However, reducing the laser output and the welding speed in order to suppress the occurrence of spatter means reducing the productivity of the welded steel pipe. Therefore, in the present invention, it is preferable to perform tack welding at a welding speed in which the laser output of the laser beam 3 exceeds 16 kW in total and exceeds 7 m / min. If the laser output is 16 kW or less in total, the welding speed will be 7 m / min or less, leading to a decrease in the productivity of the welded steel pipe.

  However, as shown in FIG. 3, when the number of the laser beams 3 is one, in order to make the junction point of the butt | matching surface 2 and the keyhole 4 correspond, a highly accurate groove processing technique is required. When the processing state and the butt state of the butt surface 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, in a situation where stress is exerted on the molten pool by the upset applied to the tack 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, the number of spatters increases, the groove does not melt sufficiently, and welding defects such as undercut and underfill tend to occur.
Therefore, it is preferable to perform tack welding by irradiating the butted surfaces with two laser beams.

FIG. 4 is a perspective view schematically showing an example in which tack welding is performed with two laser beams 3a and 3b. An arrow A in FIG. 4 indicates the traveling direction of tack welding. The keyhole 4 generated by the irradiation of the laser beams 3a and 3b and the molten metal 5 formed around the keyhole 4 are shown as perspective views.
Two laser beams 3 a and 3 b are irradiated from the upper surface side of the open pipe 1 along the butting surface 2 of the open pipe 1. At that time, if a laser beam transmitted by a single optical fiber is irradiated while being divided into two by an optical component (for example, a prism), an incident angle and a spot diameter described later cannot be individually set. Therefore, it is necessary to transmit the two laser beams 3a and 3b using different optical fibers.

One or two laser oscillators may be used. When two laser beams are transmitted with a single laser oscillator, the oscillated laser light may be divided within the laser oscillator and then transmitted by different optical fibers.
As shown in FIG. 4, the laser beams 3 a and 3 b are arranged forward and backward along the abutting surface 2. A laser beam preceding the welding progress direction on the upper surface side of the open pipe 1 is referred to as a preceding laser beam 3a, and a subsequent laser beam is referred to as a subsequent laser beam 3b.

  When the spot diameter at the just focus of the preceding laser beam 3a and the following laser beam 3b is 0.3 mm or less, the width of the weld bead at the time of welding becomes narrow, and the unmelted groove is generated. For this reason, the spot diameter at the just focus is set to exceed 0.3 mm. On the other hand, if the spot diameter exceeds 1 mm, the keyhole becomes difficult to stabilize. Therefore, it is preferable that the spot diameter in the just focus of the preceding laser beam 3a and the succeeding laser beam 3b is 1 mm or less.

  The distance from the upper surface of the open pipe 1 to the focus is t (mm), the steel plate thickness of the open pipe 1 is T (mm), and the distance t from the upper surface of the open pipe 1 to the focus is −3 × T (that is, from the upper surface). If it exceeds 3T) upward, the focus position is too high, and it is difficult to stably maintain the keyhole. On the other hand, if it exceeds 3 × T (that is, 3T downward from the upper surface), the focus position is too deep, so that sputtering is likely to occur from the rear surface side of the steel plate (that is, the inner surface of the open pipe). Therefore, the distance t from the upper surface of the open pipe 1 to the focus is preferably set in the range of −3 × T to 3 × T.

The spot shapes of the preceding laser beam 3a and the following laser beam 3b are preferably circular, but may be elliptical. When the spot shape is an ellipse, the minor axis at the just focus needs to exceed 0.3 mm. For the same reason as in the case of the circular shape, the minor axis is preferably 1 mm or less.
FIG. 5 is a side view schematically showing an example of the arrangement of the preceding laser beam 3a, the trailing laser beam 3b, and the line perpendicular to the upper surface of the open pipe 1 in FIG. As shown in FIG. 5, both the preceding laser beam 3a and the following laser beam 3b are irradiated to the upper surface of the open pipe 1 while being inclined in the welding progress direction indicated by the arrow A. The angle θa formed between the preceding laser beam 3a and a line perpendicular to the upper surface of the open pipe 1 is defined as the incident angle of the preceding laser beam 3a, and the angle θb formed between the succeeding laser beam 3b and the line perpendicular to the surface of the open pipe 1 is defined later. The incident angles of the row laser beam 3b are set so that each incident angle satisfies θa> θb.

Further, the preceding laser beam 3a and the succeeding laser beam 3b are arranged so as not to intersect each other inside the steel plate of the open pipe 1. The reason is that when the preceding laser beam 3a and the succeeding laser beam 3b intersect inside the steel plate, the keyholes 4 of the preceding laser beam 3a and the succeeding laser beam 3b are combined to form a huge keyhole, which causes sputtering. This is because it occurs in large quantities.
If the incident angle θa of the preceding laser beam 3a and the incident angle θb of the subsequent laser beam 3b are set as θa <θb, the distance from the upper surface to the back surface of the open pipe 1 through which the subsequent laser beam 3b passes increases. Therefore, the energy of the subsequent laser beam 3b is attenuated and the heating efficiency is lowered. Therefore, the preheating effect of the edge portion 2 by the preceding laser beam 3a can be obtained, but the melting of the butt surface 2 by the subsequent laser beam 3b becomes unstable.

Further, when θa = θb is set, the keyholes 4 of the preceding laser beam 3a and the succeeding laser beam 3b are likely to be combined, and a huge keyhole is generated, which may cause a large amount of sputtering.
Therefore, it is necessary to set the incident angles of the preceding laser beam 3a and the succeeding laser beam 3b as θa> θb. That is, the preceding laser beam 3a increases the inclination angle θa in order to suppress spattering when preheating the butted surface 2. The trailing laser beam 3b reduces the inclination angle θb in order to increase the heating efficiency when melting the butting surface 2.

  In this way, the preceding laser beam 3a preheats the abutting surface 2. In addition, since the preceding laser beam 3a is irradiated with an inclination in the welding progress direction, generation of spatter can be suppressed. Subsequently, the trailing laser beam 3b melts the butting surface 2. At this time, since the butt surface 2 is preheated, no spatter is generated. As a result, spatter can be reduced, and undercut and underfill can be prevented.

  If the incident angle θa of the preceding laser beam 3a is less than 5 °, the incident angle θa is too small. Therefore, the behavior similar to that in the case of irradiating the preceding laser beam 3a vertically is exhibited, and the effect of suppressing the generation of sputtering cannot be obtained. . On the other hand, if the incident angle θa exceeds 50 °, the distance from the upper surface to the back surface of the open pipe 1 through which the preceding laser beam 3a passes becomes longer, so that the energy of the preceding laser beam 3a is attenuated and a sufficient preheating effect is obtained. It becomes impossible. Therefore, the incident angle θa of the preceding laser beam 3a is preferably in the range of 5 to 50 °.

  Similarly, when the incident angle θb of the subsequent laser beam 3b is less than 5 °, the incident angle θb is too small, so that the behavior similar to that in the case of irradiating the subsequent laser beam 3b vertically is exhibited and the effect of suppressing the generation of spatters is exhibited. Cannot be obtained. On the other hand, when the incident angle θb exceeds 50 °, the distance from the upper surface to the back surface of the open pipe 1 through which the subsequent laser beam 3b passes becomes longer, so that the energy of the subsequent laser beam 3b is attenuated and sufficient penetration occurs. Depth cannot be obtained. Therefore, the incident angle θb of the subsequent laser beam 3b is preferably in the range of 5 to 50 °.

  The distance L between the center points of the preceding laser beam 3a and the succeeding laser beam 3b on the back side of the open pipe 1 is set to 1 mm or more. If the distance L is 1 mm or more, the molten pool extends in the welding progress direction on the back surface side, the amount of spatter generated from the back surface side decreases, and a weld bead without undercut or underfill is obtained. However, if the distance L exceeds 10 mm, the molten pool on the back surface side is separated, so that sputtering is likely to occur. Therefore, the distance L between the center points of the preceding laser beam 3a and the succeeding laser beam 3b is preferably in the range of 1 to 10 mm.

  Of the preceding laser beam 3a and the succeeding laser beam 3b transmitted from the laser oscillator through different optical fibers, the preceding laser beam 3a or the succeeding laser beam 3b is divided into two by an optical component (for example, a prism or the like). Both sides may be irradiated. FIG. 6B shows an example in which the subsequent laser beam 3b is irradiated on both sides of the edge portion 2 while being divided into two (irradiation regions 3-2 and 3-3), and FIG. 6C shows the preceding laser beam 3a. This is an example in which both sides of the butted surface 2 are irradiated while being divided into two (irradiation regions 3-1 and 3-2). Alternatively, as shown in FIG. 6D, the preceding laser beam 3a is divided into two (irradiation regions 3-1 and 3-2) and the subsequent laser beam 3b is divided into two (irradiation regions 3-3 and 3-4). However, you may irradiate both sides of the butting surface 2. By irradiating the preceding laser beam 3a and the succeeding laser beam 3b in this manner, it is possible to easily maintain a state in which the butted surface 2 passes through the irradiation region.

  In general, spatter generated during laser welding decreases as the laser output decreases and the welding speed decreases. However, reducing the laser output and the welding speed in order to suppress the occurrence of spatter means reducing the productivity of the welded steel pipe. Therefore, in the present invention, it is preferable to perform tack welding at a welding speed at which the laser output of the preceding laser beam 3a and the following laser beam 3b exceeds 16 kW in total and exceeds 7 m / min. If the laser output is 16 kW or less in total, the welding speed will be 7 m / min or less, leading to a decrease in the productivity of the welded steel pipe.

  The preceding laser beam 3a and the succeeding laser beam 3b are arranged so that the centers of the irradiation areas 3-1 and 3-2 on the upper surface of the open pipe 1 coincide with the butting surface 2 as shown in FIG. Is preferred. However, it is difficult to perform welding while maintaining such an arrangement, and the centers of the irradiation regions 3-1 and 3-2 on the upper surface of the open pipe 1 do not necessarily coincide with the butt surface 2 during welding. If the distance between the centers of the irradiation areas 3-1 and 3-2 and the butt face 2 increases, the preceding laser beam 3a and the subsequent laser beam 3b will deviate from the butt groove, and the remaining melt of the groove, etc. Welding defects are likely to occur.

Even if the center of the irradiation areas 3-1 and 3-2 does not coincide with the abutting surface 2, welding will occur if welding is performed with the abutting surface 2 passing through the irradiation areas 3-1 and 3-2. do not do. Therefore, it is preferable that the distance between the centers of the irradiation regions 3-1 and 3-2 and the butting surface 2 is within the radius of the irradiation regions 3-1 and 3-2.
When performing tack welding by laser welding as described above, an upset of 0.2 to 1.0 mm is added to the tack welded portion. 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.

  If the length in the plate thickness direction of the butt surface 2 exceeds 10 mm, the groove melts away and it becomes difficult to increase the welding speed of the tack welding, so the length of the butt surface 2 in the plate thickness direction is 10 mm or less is preferable. On the other hand, if it is less than 2 mm, the tack welded portion does not remain after finish welding described later, and a seam is formed only by the finish welded portion. That is, since all the high quality tack welds are melted by finish welding, the effect of improving the quality of the tack welding cannot be obtained. Therefore, the length of the butting surface 2 in the thickness direction is more preferably in the range of 2 to 10 mm.

The joining point of the butted surface 2 of the open pipe 1 may be anywhere as long as the average gap G in the thickness direction of the butted surface 2 is narrowed by a squeeze roll and becomes 0.5 mm or less.
In this way, even an open pipe made of a thick material (for example, 4 mm or more in thickness) can be tack welded without preheating the groove processed portion by high-frequency heating or the like. However, if the groove processed part is preheated by high frequency heating or the like, effects such as improved productivity of the welded steel pipe can be obtained. If preheating is performed by high-frequency heating, a surplus is formed in the tack welded portion, but there is no problem because it is melted by finish welding described later.

Oscillator of the laser beam may be used an oscillator in various forms, gas (e.g. CO _2, helium - neon, argon, nitrogen, iodine) gas laser is used as a medium, solid (e.g., YAG or the like doped with a rare earth element) As a medium, a solid-state laser, a fiber laser using a fiber instead of a bulk, a disk laser, or the like is preferable. Alternatively, a semiconductor laser may be used.

You may heat with an auxiliary heat source from the outer surface side of an open pipe. The configuration of the auxiliary heat source is not particularly limited as long as it can heat and melt the outer surface of the open pipe. For example, a means using a burner melting method, a plasma melting method, a TIG melting method, an electron beam melting method, a laser melting method or the like is suitable.
The auxiliary heat source is preferably disposed integrally with the laser beam oscillator. The reason is that if the auxiliary heat source and the laser are not integrated, a large amount of heat is required to obtain the effect of the auxiliary heat source, and it is very difficult to suppress welding defects (such as undercut and underfill). Because it becomes. Further, it is more preferable that the auxiliary heat source is disposed ahead of the laser beam oscillator. The reason is that the moisture and oil content of the edge portion can be removed.

  Furthermore, the use of an arc is preferred as a preferred auxiliary heat source. As the arc generation source, one that can add electromagnetic force (that is, electromagnetic force generated from the magnetic field of the welding current) in a direction to suppress the molten metal from falling off is used. For example, conventionally known techniques such as TIG welding and plasma arc welding can be used. Note that the arc generation source is preferably arranged integrally with the laser beam. The reason is that, as described above, the influence of the magnetic field generated around the welding current that generates the arc is effectively given to the molten metal generated by the laser beam. Further, it is more preferable that the arc generation source is arranged ahead of the laser beam. The reason is that moisture and oil on the butted surfaces can be removed.

  After performing tack welding in this way, next, finish welding is performed, and as shown in FIG. 1, an inner surface side finish weld portion 9 and an outer surface side finish weld portion 10 are formed. As described above, since the quality of the tack welding is improved, the seam of the welded steel pipe 7 can be maintained even if the inner surface side finish weld portion 9 and the outer surface side finish weld portion 10 are made smaller and the tack weld portion 8 remains. No deterioration of the characteristics occurs. Below, finish welding is demonstrated.

As the finish welding, arc welding (for example, submerged arc welding, gas shielded arc welding, MIG welding, MAG welding, etc.) is employed. In the present invention, multi-electrode submerged arc welding is preferable from the viewpoint of improving the efficiency of finish welding.
Then, after the tack welding, finish welding of the groove portion on the inner surface side is performed, and the inner surface side finish welding portion 9 is formed. At this time, as shown in FIG. 1, finish welding on the inner surface side is performed so that a part of the tack welding portion 8 overlaps with the inner surface side finish welding portion 9.

Next, finish welding of the groove portion on the outer surface side is performed, and the outer surface side finish welding portion 10 is formed. At this time, as shown in FIG. 1, finish welding on the outer surface side is performed so that a part of the tack welding portion 8 overlaps with the outer surface side finish welding portion 10. That is, the outer surface side finish weld portion 10 does not overlap the inner surface side finish weld portion 9.
By performing finish welding in this way, it is possible to extend the length of the tack welded portion 8 in the plate thickness direction and to reduce the inner surface side finished welded portion 9 and the outer surface side finished welded portion 10. Even if the multi-electrode submerged arc welding is adopted, no problem occurs in the soundness of the seam of the welded steel pipe 7. In MIG welding and MAG welding, the welding speed can be increased.

  As described above, according to the present invention, it is possible to obtain a seam of good quality when manufacturing a welded steel pipe, and to manufacture the welded steel pipe stably with a high yield. The obtained 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.

  An X groove was formed in an open pipe of an API standard X80 grade UOE steel pipe, and the butted surfaces were joined by laser welding (ie, tack welding). In the tack welding, as shown in FIG. 4, two laser beams were irradiated. The setting conditions for tack welding are as shown in Table 1.

In all of the inventive examples (tacking numbers 1, 2, 4, 5, 12, 13, 14), no welding defects were observed, and a good tack welded part could be obtained.
In comparative examples, tack numbers 7, 8, 9, 10, and 11 had blow holes because the amount of upset was not sufficient. In the tacking numbers 3, 6, and 9, the tack welded part was too long, so that the groove was left unmelted.

1 Open pipe 2 Butting surface 3 Laser beam
3a Leading laser beam
3b Trailing laser beam 4 Keyhole (cavity)
5 Molten metal 6 Seam 7 Welded steel pipe 8 Tack weld zone 9 Finish weld zone on the inner surface side
10 External finish weld

Claims (5)

  In a manufacturing method of a welded steel pipe, a steel plate with groove processing at both ends is formed into an open pipe and welded while pressing the groove processing portion of the open pipe. After joining the butted surfaces having a length of 10 mm or less in the thickness direction central portion of the groove processed portion by laser welding, both sides of the surface layer portion in the plate thickness direction of the groove processed portion are arc-welded. The manufacturing method of the welded steel pipe characterized by joining.   In the laser welding, two laser beams having a just focus spot diameter exceeding 0.3 mm transmitted using different optical fibers are irradiated from the upper surface side of the open pipe along the mating surface, A preceding laser beam preceding and following a laser beam preceding the welding progress direction on the upper surface side of the open pipe is irradiated with an incident angle from a direction perpendicular to the upper surface of the open pipe and tilted in the welding progress direction. The incident angle of the preceding laser beam is made larger than the incident angle of the succeeding laser beam, and the distance between the center point of the preceding laser beam and the center point of the succeeding laser beam on the back surface of the open pipe is 1 mm. It is set as the above, The manufacturing method of the welded steel pipe of Claim 1 characterized by the above-mentioned.   3. The method for manufacturing a welded steel pipe according to claim 2, wherein an incident angle of the preceding laser beam is 5 ° to 50 ° and an incident angle of the subsequent laser beam is 5 ° to less than 50 °. .   4. The welded steel pipe according to claim 2, wherein one or two of the preceding laser beam and the following laser beam are divided into two by an optical component and irradiated to both left and right sides of the butted surface. Manufacturing method.   The laser welding of the preceding laser beam and the subsequent laser beam is 20 kW or less in total and the laser welding is performed at a welding speed of less than 5 m / min. The manufacturing method of the welded steel pipe of description.

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