JP2010029938A - Method for manufacturing laser-welded steel pipe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a laser-welded steel pipe stably in a high yield by highly and precisely determining a laser welding situation and by changing a welding condition on the basis of the determined result. <P>SOLUTION: The irradiating region of a laser beam irradiated from an outer face side at an edge portion is monitored from the inner face side of an open pipe. When a key hole penetrating to the inner face side of the open pipe is observed, the welding condition of the laser beam is continuously kept. When the keyhole penetrating to the inner face side of the open pipe is not observed, the welding condition of the laser beam is changed. Thus, the welding operation is performed while the keyhole penetrating through the open pipe from the outer face side to the inner face side is formed in the irradiating region of the laser beam. <P>COPYRIGHT: (C)2010,JPO&INPIT

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 in the longitudinal direction is welded using a laser beam, and particularly to oil and natural gas extraction and transportation such as oil well pipes or line pipes. The present invention relates to a method for producing a suitable laser welded steel pipe.

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, molten metal is formed in a very narrow region. Therefore, when a gap occurs between the position where the edge of the open pipe pressed by the squeeze roll joins (hereinafter referred to as the joining point) and the circumferential position where the laser beam is irradiated, the seam of the laser welded steel pipe opens. It becomes a state, and it is necessary to remove the portion as defective welding, which leads to a decrease in the yield of the laser welded steel pipe. In addition, although a junction point is also called a squeeze point, it describes as a junction point here.

Therefore, various techniques for monitoring the irradiation state of a laser beam when manufacturing a laser welded steel pipe have been studied.
For example, Patent Document 1 discloses a technique for determining the state of laser welding by irradiating a laser beam from one surface of a steel plate and monitoring plasma light generated on the other surface. However, since plasma light is widely scattered, this technique not only makes it difficult to accurately grasp the status of laser welding, but also cannot accurately recognize the position where the laser beam is irradiated from the edge portion.

Patent Document 2 discloses a technique for determining the formation state of a back bead by measuring the emission intensity by laser welding. However, since the emission intensity varies significantly due to various factors, it is difficult to accurately grasp the formation state of the back bead with this technique.
Patent Document 3 discloses a technique for controlling a welding condition by photographing a molten metal generated by arc welding and analyzing the shape of a back bead based on the image. If this arc welding technique is applied to laser welding as it is, a clear image of the molten metal cannot be obtained. The reason is that in laser welding, heat energy is concentrated at a high density, so that an excessive amount of light is generated. Therefore, it is difficult to accurately grasp the shape of the back bead in laser welding.

  Patent Document 3 discloses a technique for irradiating a molten metal with a laser beam through an interference filter. However, this laser beam is used for photographing a molten metal and does not contribute to welding.

Japanese Patent Laid-Open No. 10-76383 JP-A-8-267241 Japanese Patent Laid-Open No. 2001-25867

  The present invention provides a method for stably producing a laser welded steel pipe with a high yield by accurately judging the status of laser welding in manufacturing a laser welded steel pipe and changing the welding conditions based on the judgment result. For the purpose.

The inventors investigated and examined a technique for monitoring the state of laser welding in manufacturing a laser welded steel pipe by performing laser welding on an edge portion of an open pipe.
Fig.1 (a) is a perspective view which shows typically the example which welds the junction of the edge part 2 of the open pipe 1 by applying this invention, when manufacturing a laser-welded steel pipe. An arrow A in FIG. 1 (a) indicates the traveling direction of the open pipe. 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. 1A, the edge 2 is melted by the heat energy concentrated at high density, and the evaporation pressure and the reaction force generated by the evaporation of the molten metal 4 are generated. As a result, the keyhole 4 is generated in the molten metal 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.

Moreover, FIG.1 (b) and FIG.1 (c) are sectional drawings of the circumferential direction (perpendicular | vertical direction with respect to a welding line) of a pipe in FIG. 1 (a).
The keyhole 4 indicates a position where the thermal energy of the laser beam 3 is most converged. Therefore, the keyhole 4 is monitored, and laser welding is performed so that the joint C of the edge portion is disposed in the keyhole 4 as shown in FIG. it can. However, in order to make the junction point C of the edge portion 2 coincide with the keyhole 4, a highly accurate position control technique is required. Therefore, laser welding may be performed so that the joining point C of the edge portion 2 is disposed in the molten metal 5 formed around the keyhole 4. The length L _m of the circumferential direction of the open pipe in a molten metal 5 (direction perpendicular to the weld line) is larger than the size (diameter) L _k keyhole 4, the welding head, and in that the welding head By controlling the positions of the condensing lens and the condensing mirror housed in the laser beam, the irradiation position of the laser beam 3 can be easily controlled in the circumferential direction with a relatively simple technique. Therefore, according to the present invention, a laser welded steel pipe can be manufactured stably.

Moreover, when sound laser welding is in progress, the keyhole 4 penetrates from the outer surface side to the inner surface side of the molten metal 5, and the positional relationship between the keyhole 4 and the junction point C can be accurately monitored. It is.
The joining point C of the edge portion 2 in the traveling direction A of the open pipe 1 is anywhere where the average interval G in the thickness direction of the edge portion 2 is narrowed by a squeeze roll and becomes 0.5 mm or less. good.

The present invention has been made based on these findings.
That is, the present invention is a laser welding in which a steel plate is formed into a cylindrical open pipe with a forming roll, and the edge portion of the open pipe is irradiated with a laser beam from the outer surface side of the open pipe while being pressed with a squeeze roll. In the steel pipe manufacturing method, the irradiation part of the laser beam irradiated to the edge part is monitored from the inner surface side of the open pipe, and if a keyhole penetrating to the inner surface side of the open pipe is observed, the welding condition by the laser beam is continued. On the other hand, if a keyhole penetrating to the inner surface side of the open pipe is not recognized, the keyhole penetrating from the outer surface side of the open pipe to the inner surface side is changed by changing the laser beam welding conditions. It is a manufacturing method of the laser welded steel pipe which welds while providing.

  In the laser welded steel pipe manufacturing method of the present invention, it is preferable that the size of the keyhole is 0.2 mm or more on the inner surface side of the open pipe. Moreover, it is preferable to arrange | position the junction of the edge part pressurized with a squeeze roll in the inner surface molten metal produced by laser beam irradiation. Or it is preferable to arrange | position the junction of the edge part pressurized with a squeeze roll in a keyhole.

  According to the present invention, in manufacturing a laser-welded steel pipe, the state of laser welding is accurately determined, and the welding conditions are changed based on the determination result, whereby a keyhole or molten metal generated by laser beam irradiation is included. It becomes possible to always arrange the junctions of the edge portions. 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 figure which shows typically the example which welds the junction of the edge part of an open pipe by applying this invention, (a) is a perspective view, (b) and (c) are perpendicular | vertical with respect to a welding line. It is sectional drawing. It is a perspective view which shows the example of a keyhole monitoring apparatus typically.

  An open pipe 1 shown in FIG. 1 (a) is a strip-shaped steel plate formed into a cylindrical shape by a forming roll. While pressing the edge portion 2 of the open pipe 1 with a squeeze roll (not shown), the laser beam 3 is irradiated from the outer surface side. On the other hand, the irradiation part of the laser beam 3 is monitored from the inner surface side of the open pipe 1 to identify the keyhole 4. If the keyhole 4 penetrates from the outer surface side to the inner surface side of the open pipe 1, it can be easily identified by a normal image processing technique. If the keyhole 4 can be identified on the inner surface side, this indicates that sound laser welding is in progress, and the welding conditions are maintained as they are. In FIG. 1A, the keyhole 4 monitoring device is not shown, but FIG. 2 shows an example of the keyhole monitoring device used in the present invention. The keyhole monitoring device inserted into the open pipe 1 is not visible from the outside of the open pipe 1, but is shown in FIG. 2 as a perspective view.

  When the keyhole 4 cannot be identified, it indicates that the keyhole 4 is closed. Therefore, it is necessary to adjust the welding conditions to change so that sound laser welding proceeds. When the welding conditions are changed and the keyhole 4 can be identified, laser welding is performed while maintaining the welding conditions as they are. The keyhole 4 is most often closed when the junction C of the edge portion 2 is out of the molten metal 5 formed in the keyhole 4 or around the keyhole 4. This is because when the laser beam 3 is irradiated to the junction point C, the laser beam 3 easily propagates efficiently through the gap between the junction points C in the plate thickness direction, so that the keyhole 4 is easily formed. . However, when the laser beam 3 is irradiated to a place other than the junction point C, the molten metal 5 evaporates from the surface of the open pipe 1, so that a deep cavity (that is, a keyhole) is formed in the molten metal 5 by the evaporation pressure and the evaporation reaction force. Since a higher output laser power is required to form 4, the keyhole 4 tends to close.

  A specific welding condition to be adjusted when the keyhole 4 is closed is that the irradiation position of the laser beam 3 is moved in the circumferential direction of the open pipe 1, and the joining point C of the edge portion 2 is irradiated with the irradiation position of the laser beam 3 ( That is, it is most preferable to adjust so as to be disposed in the keyhole 4) or the molten metal 5. For example, the keyhole monitoring device recognizes the joint point C of the edge portion 2 and the positions of the keyhole 4 and the molten metal 5 by image processing, calculates the movement distance in the circumferential direction of the open pipe 1, and The laser beam 3 is controlled by controlling the position of the welding head and the condensing lens and the condensing mirror accommodated in the welding head so that the junction C enters the inside of the keyhole 4 or the molten metal 5. It is preferable to move the irradiation position.

As other welding conditions, for example, it is also preferable to adjust or control the focal position of the laser beam 3, the beam irradiation position in the longitudinal direction of the open pipe 1, the increase / decrease of the laser power, the welding speed, and the like.
Adjustment of the positional relationship between the joint C of the edge portion 2 and the keyhole 4 or the molten metal 5 can be easily performed by monitoring the inner surface of the open pipe 1 and identifying the keyhole 4. It is.

  If the size of the keyhole 4 is less than 0.2 mm in diameter on the inner surface side, the keyhole 4 may be blocked. Therefore, the keyhole 4 preferably has an inner diameter of 0.2 mm or more. However, if the diameter on the inner surface side exceeds 1.0 mm, not only welding defects such as fusing will occur, but the width of the seam (ie, seam 6) where the molten metal has solidified will be significantly enlarged, and the appearance of the laser welded steel pipe will be Damaged. Therefore, the diameter of the keyhole 4 on the inner surface side of the open pipe 1 is more preferably in the range of 0.2 to 1.0 mm.

When the shape of the keyhole 4 is an ellipse, the minor axis is preferably 0.2 mm or more.
The size of the keyhole 4 was monitored from the inside of the open pipe 1 by a monitoring camera 8 fixed to a mandrel bar 7 suspended from between the stands as shown in FIG. The photographing condition is that the illumination device 9 irradiates light having a wavelength component different from that of the laser beam and plasma light from the inner surface of the open pipe 1, and irradiates ultraviolet light having a wavelength of 337 nm (nanometer), for example, and transmits only light of that wavelength. By taking a picture using the filter, the disturbance from the keyhole 4 and the molten metal 5 due to infrared rays, plasma light, and the like was eliminated. Here, the wavelength to be transmitted may be selected in accordance with the spectrum of plasma emission, in a wavelength band that avoids the spectrum, and in consideration of available light sources and filters. The shooting speed was 30 frames / second, and the average value of still images obtained by randomly sampling 5 images was obtained. Note that the shape of the keyhole on the inner surface side is substantially circular or elliptical. When the shape of the keyhole 4 is an ellipse, the minor axis was measured. Further, in order to determine whether the keyhole 4 is blocked or to control the irradiation position of the laser beam 3, the joint C, the keyhole 4, and the molten metal 5 of the edge portion 2 are image-processed from the video taken by the monitoring camera 8. An image processing device 11, a determination processing device 12, and a laser beam position control device 10 that digitize those dimensions and positions were used. The monitoring device for the keyhole 4 is not limited to the above-described configuration, and an arbitrary configuration can be used.

In the present invention, even with an open pipe 1 made of a thick material (for example, 4 mm or more thick), laser welding can be performed without preheating the edge portion 2 by high-frequency heating or the like. However, if the edge part 2 is preheated, effects such as improvement in productivity of the laser welded steel pipe can be obtained.
Oscillator of the laser beam 3 to be used in the present invention, an oscillator of various forms can be used, a gas (e.g. CO _2, helium - neon, argon, nitrogen, Iodine (I), etc.) gas laser is used as a medium, solid ( For example, a solid laser using a rare earth element-doped YAG or the like as a medium, or a fiber laser using a fiber as a medium instead of a bulk is preferable. It is also possible to use a semiconductor laser.

  As described above, according to the present invention, in manufacturing a laser welded steel pipe, the state of laser welding is accurately determined, and the welding condition is changed based on the determination result. It becomes possible to always arrange the junction of the edge portion in the hole or the molten metal. As a result, 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 the edge of the open pipe with a squeeze roll and irradiating a laser beam from the outer surface side. The components of the steel sheet are as shown in Table 1.

In laser welding, a 25 kW CO ₂ laser oscillator is used, and its output and welding speed are as shown in Table 2.
The monitoring device for the keyhole 4 was inserted into the open pipe 1 by attaching the monitoring camera 8 to the mandrel bar 7 of the inner surface bead cutting device using the device shown in FIG. As the monitoring camera 8, a camera capable of visualizing only a specific wavelength (that is, 337 nm) was used in order to suppress disturbance such as plasma light generated by irradiation of the laser beam 3.

  The invention examples shown in Table 2 (welded steel pipe Nos. 1 to 4) monitor the keyhole 4 from the inner surface side of the open pipe 1, adjust the size of the keyhole 4 as shown in Table 2, and the edge This is an example in which the positional relationship between the junction point of the portion and the keyhole 4 or the molten metal 5 is adjusted as shown in Table 2. When the diameter of the keyhole 4 is less than 0.2 mm, the irradiation position of the laser beam 3 is moved in the circumferential direction of the open pipe 1, and the junction point C of the edge portion 2 becomes the irradiation position of the laser beam 3 (that is, Adjustment was made so that it was placed in the keyhole 4) or the molten metal 5.

The welded steel pipe Nos. 5 and 6 of the comparative example are examples in which the keyhole 4 is not monitored. Further, the welded steel pipes Nos. 7 and 8 of the comparative examples are examples in which only the keyhole 4 is monitored and the size and positional relationship of the keyhole 4 are not adjusted.
The obtained laser welded steel pipe was subjected to an ultrasonic flaw detection test, and a seam was flawed over 20 m in accordance with JIS standard G0582. The flaw detection results are shown in Table 2. In Table 2, with respect to the artificial defect of the N5 inner and outer notch used as a reference, the peak indication height is 10% or less excellent (◎), 10% to 25% or less is good (○) , 25% and 50% or less were evaluated as acceptable (△), and those exceeding 50% were evaluated as unacceptable (×).

In addition, laser welded steel pipes of steel type A (ie low alloy steel) are quenched (quenching temperature 880 ° C.) and tempered (tempering temperature 650 ° C.), and laser welded steel pipes of steel type B (ie stainless steel) are heat treated 2 After application (heating temperature: 780 ° C. for the first time and 650 ° C. for the second time), a Charpy impact test was performed in accordance with JIS standard Z2242. The test piece was V-notched and sub-sized in accordance with JIS standard Z2202, and was collected from the seam portion. The test temperature was −60 ° C. and the absorbed energy _−V E _-60 (J) was measured. The results are shown in Table 2.

As is apparent from Table 2, in the invention examples (welded steel pipe Nos. 1 to 4), the ultrasonic flaw detection is excellent (◎) or good (○), and the absorbed energy of the Charpy impact test (−60 ° C.) is 82 It was -112J. On the other hand, in the comparative example (welded steel pipe Nos. 5 to 8), ultrasonic flaw detection was possible (Δ) or not (x), and the absorbed energy in the Charpy impact test (−60 ° C.) was 8.7 to 38 J.
As described above, when the present invention is applied, sound laser welding can be performed even with an open pipe made of a thick material (thickness of 4 mm or more).

  The resulting seam of the laser welded steel pipe has excellent corrosion resistance because generation of welding defects and precipitates is suppressed as shown by the results of ultrasonic flaw detection. And as the result of a Charpy impact test shows, it has the outstanding low temperature toughness.

Laser welded steel pipes can be manufactured stably with good yield, and the obtained laser welded steel pipes have excellent seam low temperature toughness and corrosion resistance, and are suitable for oil well pipes and line pipes used in cold regions and corrosive environments. There are remarkable effects in the industry.

DESCRIPTION OF SYMBOLS 1 Open pipe 2 Edge part 3 Laser beam 4 Keyhole 5 Molten metal 6 Seam 7 Mandrel bar 8 Surveillance camera 9 Illumination device
10 Position control device
11 Image processing device
12 Judgment processing device

Claims (4)

  A steel welded steel pipe is formed by forming a steel plate into a cylindrical open pipe with a forming roll, and welding the edge portion by irradiating a laser beam from the outer surface side of the open pipe while pressing the edge portion of the open pipe with a squeeze roll. In the manufacturing method, the irradiation portion of the laser beam irradiated to the edge portion is monitored from the inner surface side of the open pipe, and when a keyhole penetrating to the inner surface side of the open pipe is recognized, the welding condition by the laser beam is set. On the other hand, if a keyhole penetrating to the inner surface side of the open pipe is not recognized, the keyhole penetrating from the outer surface side of the open pipe to the inner surface side is changed by changing the welding condition by the laser beam. Welding is performed while providing at the laser beam irradiation site. Method of manufacturing a laser welded steel pipe that.   The method for manufacturing a laser welded steel pipe according to claim 1, wherein the size of the keyhole is 0.2 mm or more on the inner surface side of the open pipe.   The method of manufacturing a laser welded steel pipe according to claim 1 or 2, wherein a joint point of an edge portion pressed by the squeeze roll is disposed in an inner surface molten metal generated by irradiation with the laser beam. The method of manufacturing a laser welded steel pipe according to claim 1 or 2, wherein a joint point of an edge portion pressed by the squeeze roll is disposed in the inner surface side keyhole.

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