JP2010240734A - Method for manufacturing laser-welded steel pipe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for stably manufacturing a laser-welded steel pipe in a high yield by determining a laser welding situation highly precisely and by changing a welding condition on the basis of the determination result in manufacturing the laser-welded steel pipe. <P>SOLUTION: An irradiation part of a laser beam emitted to an edge part is watched from the inner face side of an open pipe and, if a key hole penetrating to the inner face side of the open pipe is recognized, a welding condition by the laser beam is continuously maintained. If the key hole penetrating to the inner face side of the open pipe is not recognized, the welding condition by the laser beam is changed. Thus, welding is performed while the key hole penetrating from the outer face side to the inner face side of the open pipe is provided in the irradiation part of the laser beam. <P>COPYRIGHT: (C)2011,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 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 using hot-rolled strip steel plates (so-called hot coils), but in general, ERW steel pipes have a forming roll. A steel plate is formed into a cylindrical shape using an open pipe (here, an open pipe refers to a pipe-shaped steel strip in which ends formed by a multi-stage forming roll are not joined. Hereinafter, it is referred to as an open pipe. ) And the edge of the open pipe (that is, both ends of the steel strip formed into a cylindrical shape) is manufactured by electrical resistance welding (also called high-frequency resistance welding) while applying pressure with a squeeze roll. There is a problem that so-called seams) inevitably exist and the low temperature toughness of the seams 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, if there is a deviation between the position where the edge of the open pipe pressed by the squeeze roll joins (hereinafter referred to as the joining point or the squeeze point) and the circumferential position where the laser beam is irradiated, laser welding is performed. The seam of the steel pipe is in an open state, and that part needs to be removed as a poor weld, leading to a decrease in the yield of the laser welded steel pipe.

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 present invention is as follows.
1. In a method for manufacturing a laser welded steel pipe, a steel plate is formed into a cylindrical open pipe with a forming roll, and the edge portion of the open pipe is pressed with a squeeze roll and irradiated with a laser beam from the outer surface side of the open pipe to weld the edge portion. If the keyhole that penetrates to the inner surface side of the open pipe is observed, the laser beam irradiation part irradiating the edge part is monitored from the inner surface side of the open pipe. If a keyhole penetrating to the inner surface side of the pipe is not recognized, welding is performed while providing a keyhole penetrating from the outer surface side of the open pipe to the inner surface side by changing the laser beam welding conditions. This is a method of manufacturing a laser welded steel pipe.

In the above 1, it is preferable to arrange the joint point of the edge portion pressed by the squeeze roll in the molten metal generated by the laser beam irradiation. Or it is preferable to arrange | position the junction of the edge part pressurized with a squeeze roll in a keyhole.
2. In 1 above, it is a method for manufacturing a laser welded steel pipe, wherein the edge portion is heated and melted by using an auxiliary heat source that is heated from the outer surface side of the open pipe, and the laser beam is irradiated.
3. In 2 above, the auxiliary heat source is a method for manufacturing a laser welded steel pipe which is an arc.

  4). In the above 1-3, the irradiation part of the laser beam irradiated to the edge portion is monitored from the inner surface side of the open pipe, and the reflected light and plasma light generated from the irradiation part by the irradiation of the laser beam are detected by a sensor. And measuring the welding state based on the respective measurement values obtained from the sensor, and the keyhole penetrating to the inner surface side of the open pipe is recognized, and the reflected light and the plasma obtained from the sensor When the variation of the relative value of the light measurement value is small, the welding condition by the laser beam is continuously maintained, while the keyhole penetrating to the inner surface side of the open pipe is unstable and repeatedly clogged, and from the sensor When the relative value of the measured values of the reflected light and the plasma light obtained is large A method for manufacturing a laser-welded steel pipe, wherein welding is performed while changing a welding condition by a laser beam so as to provide a keyhole penetrating from an outer surface side to an inner surface side of the open pipe at an irradiation site of the laser beam It is. Here, the reflected light is also referred to as return light.

5). In the above 1 to 4, it is a method for manufacturing a laser welded steel pipe in which the keyhole is 0.2 mm or more in diameter on the inner surface side of the open pipe.
6). In the above 1 to 5, there is provided a method for producing a laser welded steel pipe, wherein a joint point of an edge portion pressed by the squeeze roll is disposed in a molten metal generated by the laser beam irradiation.

7). In the above 1 to 5, it is a manufacturing method of a laser welded steel pipe in which a joint point of an edge portion pressed by the squeeze roll is disposed in the inner surface side keyhole.
8). 8. The method for producing a laser welded steel pipe according to 2 to 7, wherein the laser beam oscillator and the auxiliary heat source are integrally arranged.
9. 2 to 7, wherein the laser beam oscillator and the auxiliary heat source are integrally disposed, and the auxiliary heat source heats the edge portion in advance of the laser beam.

Ten. 3 to 9, wherein the laser beam oscillator is a fiber laser oscillator, the laser output exceeds 15 kW, and the focal length of the laser is 200 mm or more.
11． 3 to 10, wherein the distance between the irradiation position of the laser beam on the outer surface of the open pipe and the electrode of the arc is 7 mm or less.

12． 4 to 10 above, a method for manufacturing a laser welded steel pipe, wherein the reflected light is measured from an outer surface side of the open pipe, and the plasma light is measured from an inner surface side of the open pipe.
13. Production of a laser welded steel pipe as described in 1 above, wherein a plurality of laser beams are irradiated and welding is performed while providing keyholes penetrating from the outer surface side to the inner surface side of the open pipe at the irradiated portions of the plurality of laser beams, respectively. Is the method.

  14. In the above 13, the irradiation part of the plurality of laser beams irradiated to the edge portion is monitored from the inner surface side, and the reflected light and plasma light generated from the irradiation part by the irradiation of the laser beam are measured using a sensor. The welding status is monitored based on the respective measurement values obtained from the sensor, and a plurality of keyholes penetrating from the outer surface side to the inner surface side of the open pipe are recognized, and the reflected light obtained from the sensor and When the relative value of the measured value of the plasma light is small, the welding condition by the laser beam is continuously maintained, while the keyhole penetrating to the inner surface side of the open pipe is unstable and repeats blocking, and from the sensor When the relative values of the measured values of the reflected light and the plasma light obtained are large, the laser beam Manufacturing a laser welded steel pipe, wherein welding is performed while providing keyholes penetrating from the outer surface side to the inner surface side of the open pipe at the irradiated portions of the plurality of laser beams, respectively, by changing the welding conditions by Is the method.

15． 13. In the above item 13 or 14, the junction of the edge portion between two keyholes provided on both sides of the edge portion and having the longest vertical distance to the edge portion among the plurality of keyholes Is a method for manufacturing a laser welded steel pipe.
16． In the above 13 to 15, a method for manufacturing a laser welded steel pipe in which the size of the plurality of keyholes is set to a diameter of 0.1 mm or more on the inner surface side of the open pipe.

17． In the above 13 to 16, it is a method for manufacturing a laser welded steel pipe in which the joining point of the edge portion is disposed in a molten metal generated by irradiation with the plurality of laser beams.
18． In the above 13 to 17, a method for manufacturing a laser welded steel pipe using two laser beams as the plurality of laser beams.
19. In the above 13 to 18, it is a method for manufacturing a laser welded steel pipe in which the edge portion is supplementarily heated and melted using an auxiliary heat source that heats from the outer surface side of the open pipe.

  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 an explanatory view schematically showing an example of welding the joint of the edge portion of the open pipe by applying the present invention, (a) is a perspective view showing a keyhole and molten metal formed around it, ( b) and (c) are cross-sectional views in the circumferential direction of the pipe (perpendicular to the weld line). Note that (b) indicates that the junction point C is in the keyhole 4, and (c) indicates that the junction point C is in the molten metal 5. It is a top view which shows the example of the irradiation position in the case of using a some laser beam. It is a perspective view which shows typically the example of the measuring apparatus of a keyhole diameter, and the measuring apparatus of plasma light. It is a perspective view which shows typically the example which welds the junction of the edge part of an open pipe by arrangement | positioning of the laser beam of Fig.2 (a). It is a perspective view which shows typically the example of the measuring device of reflected light. It is sectional drawing explaining the method to suppress the molten metal from falling by an arc.

  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. 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. When the laser beam 3 is irradiated, as shown in FIG. 1 (a), the edge portion 2 is melted by the heat energy concentrated at high density, and the molten metal evaporates to cause evaporation pressure and reaction force. Focusing on the formation of deep cavities 4 (hereinafter referred to as keyholes 4) in the molten metal 5. It is considered that the laser beam 3 enters the keyhole 4 and high-temperature plasma generated by ionizing metal vapor by the energy of the laser beam 3 is filled. 1 (b) and 1 (c) show a keyhole 4 and a molten metal 5 formed in the periphery of the pipe in the circumferential direction (perpendicular to the weld line) cross section in FIG. 1 (a). Is shown as a perspective view.

  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 joint point C of the edge part 2 and the keyhole 4 correspond, 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. Since the molten metal 5 has a length Lm in the circumferential direction of the pipe (perpendicular to the weld line) as compared with the size Lk of the keyhole 4, the welding lens 14 and the condensing lens accommodated in the welding head 14 are used. By controlling the position of the focusing mirror and the position of the condenser mirror, the position of the laser beam irradiation can be easily controlled in the circumferential direction of the pipe by a relatively simple technique, and the laser welded steel pipe can be manufactured stably. The joining point C of the edge portion 2 in the traveling direction A of the open pipe 1 may be anywhere as long as 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.

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 can be monitored with high accuracy.
The present invention has been made based on these findings.
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 of the open pipe 1. 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 can penetrate 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 monitoring device for the keyhole 4 is not shown, but FIG. 3 shows the keyhole monitoring device used in the present invention.

  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 easily propagates in the gap between the junction points C efficiently in the plate thickness direction, so that a keyhole is easily formed. When the laser beam 3 is irradiated to a place other than the above, a deep cavity 4 must be formed in the molten metal 5 by evaporating pressure and evaporation reaction force by evaporating the molten metal from the surface of the steel plate, resulting in higher output. Since laser power is required, 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 is moved in the circumferential direction of the open pipe 1, and the joining point C of the edge portion 2 is changed to the irradiation position of the laser beam 3 (key It is most preferable to adjust so as to be arranged in the hole 4) or the molten metal 5. For example, the joint of the edge portion 2 and the positions of the keyhole 4 and the molten metal 5 are image-processed and recognized by the keyhole monitoring device, and the circumferential direction and moving distance of the open pipe are calculated. The irradiation position of the laser beam 3 by controlling the position of the condensing lens and the condensing mirror housed in the welding head 14 and the welding head 14 so that C enters the inside of the keyhole 4 or the molten metal 5. Is preferably moved.

As other welding conditions, it is also preferable to employ, for example, control of the focal position of the laser beam, movement of the beam irradiation position in the longitudinal direction of the open pipe, increase control of laser power, deceleration control of welding speed, and the like.
Such adjustment of the positional relationship between the joining point of the edge portion 2 and the keyhole 4 or the molten metal 5 can be easily performed by identifying the keyhole 4 by monitoring from the inner surface side of the open pipe 1. is there.

  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 keyhole has an elliptical shape, 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 light having a wavelength component different from that of the laser beam and plasma light is irradiated from the inner surface of the open pipe 1 from the illuminating device 9, for example, ultraviolet light having a wavelength of 337 nm (nanometer) is irradiated, and only the light having the above wavelength is irradiated Shooting using a transmitting filter eliminated disturbances from the keyhole 4 and molten metal 5 due to infrared rays, plasma light, and the like. 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. The shape of the keyhole on the inner surface side was almost circular or elliptical, and when the keyhole shape was elliptical, 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, the joint point C, the keyhole 4 and the molten metal 5 of the edge portion 2 are image-processed from the video photographed by the monitoring camera 8 and these are processed. An image processing device 11, a determination device 12 and a laser beam position control device 13 for digitizing the dimensions and positions of the laser beam were used. The monitoring device for the keyhole 4 is not limited to the above-described configuration, and an arbitrary configuration can be used.

  When two or more laser beams 3 are used, a plurality of laser beam irradiation arrangements as shown in FIGS. 2A to 2E can be considered. FIGS. 2A to 2E are plan views showing irradiation positions when using a plurality of laser beams of an open pipe. An arrow A in FIG. 2 indicates the traveling direction of the open pipe. FIG. 2A shows the arrangement of irradiation with two laser beams, and is an example in which the laser beams 3-1 and 3-2 are arranged on both sides of the edge portion. FIG. 4 is a perspective view schematically showing an example of welding the joints of the edge portions of the open pipe with the arrangement of the laser beams of FIG. An arrow A in FIG. 4 indicates the traveling direction of the open pipe. The keyhole 4 generated by the irradiation of the two laser beams 3 and the molten metal 5 formed around the keyhole 4 are shown as perspective views. FIG. 2 (b) shows the arrangement of irradiation of three laser beams. The edge portion is preheated with the laser beam 3-1, and the laser beams 3-2 and 3-3 are placed on both sides of the edge portion. This is an example of arrangement. FIG. 2 (c) shows the arrangement of irradiation with four laser beams. Four laser beams 3-1, 3-2, 3-3 and 3-4 are arranged on both sides of the edge portion. This is an example in which two of each are arranged. FIG. 2 (d) shows an arrangement of irradiation of two laser beams, and is an example in which laser beams 3-1 and 3-2 having different laser powers are arranged on both sides of the edge portion. Since the power of the laser beam 3-1 is smaller than that of the laser beam 3-2, this is an example of an arrangement in which the laser beam 3-1 is closer to the edge portion. FIG. 2 (e) shows the arrangement of irradiation with two laser beams. An example in which two laser beams 3-1 and 3-2 are arranged vertically (tandem) along an edge portion. It is. In this case, not a plurality of laser beams but a single laser beam is handled. The keyhole can be monitored only by monitoring the keyhole of the laser beam 3-2 closest to the molten metal. Similarly, when three or more laser beams are arranged vertically (tandem) along the edge portion, a single laser beam is handled. Only the keyhole closest to the molten metal needs to be monitored.

The arrangement of the laser beam irradiation positions when using a plurality of laser beams is not limited to the example shown in FIGS. 2A to 2E, and can be freely arranged according to the purpose. The number of laser beams used in the present invention is preferably 1 to 4. Five or more laser beams are not preferable because the equipment cost, manufacturing cost, and laser beam position control are complicated.
In the present invention, all the plurality of keyholes 4 are monitored, and are provided on both sides of the edge portion 2 and perpendicular to the edge portion 2 as shown in FIGS. 2 (a) to 2 (e). Laser welding is performed by placing the joint of the edge portion 2 between the two keyholes having the largest distance (L1 and L2). However, in order to arrange the joint point of the edge portion 2 at the predetermined position, a highly accurate control technique is required. Therefore, laser welding may be performed while controlling so as to arrange the joining point of the edge portion 2 in the molten metal 5 formed between the two keyholes 4 described above. Since the length Lm of the molten metal 5 in the circumferential direction of the pipe (perpendicular to the weld line) is larger than the size Lk of the keyhole 4, it can be controlled by a relatively easy technique.

  The adjustment of the positional relationship between the joint point of the edge portion 2 and the two keyholes 4 or the molten metal 5 formed between the two keyholes 4 is monitored from the inner surface side of the open pipe 1. This can be easily done by identifying the keyhole 4. When welding is performed while irradiating a plurality of laser beams and providing a penetrating keyhole, there is often a single molten pool. Thus, when there is one molten pool during welding, if the size of all the keyholes 4 is less than 0.1 mm in diameter on the inner surface side, the keyholes 4 may be blocked. Therefore, the keyhole 4 preferably has an inner diameter of 0.1 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 0.1 to 1.0 mm. In addition, when the shape of the keyhole is an ellipse, the minor axis is preferably 0.1 mm or more.

As shown in FIG. 2 (e), in the example in which the two laser beams 3-1 and 3-2 are arranged vertically (tandem) along the edge portion, a plurality of laser beams are not handled. Since one laser beam is handled, it is only necessary to monitor the keyhole of the laser beam 3-2 closest to the molten metal 5, so that the keyhole 4 preferably has an inner diameter of 0.2 mm or more.
Further, the blockage of the keyhole 4 adversely affects the production of the laser welded steel pipe even for a short time. For example, when laser welding is performed at a welding speed exceeding 5 m / min, if a clogging of 0.01 seconds or more occurs, welding defects such as insufficient penetration and undercut occur due to a large amount of spatter. Yield decreases. Such a short-time keyhole blockage is difficult to detect only by monitoring the keyhole described above. Therefore, in addition to monitoring the keyhole, the reflected light and plasma light generated from the irradiated part of the laser beam are measured by a sensor to measure the state of the keyhole, and the relative values of the obtained reflected light and plasma light measurements are measured. To monitor the welding status.

The reflected light generated from the laser beam irradiation site is preferably measured from the outer surface side of the open pipe 1. The reason is that the intensity of the reflected light can be measured with high accuracy even when the keyhole is blocked for a short time.
Further, it is preferable that the plasma light generated from the laser beam irradiation site is measured from the inner surface side of the open pipe 1. The reason is that, on the outer surface side of the open pipe 1, the shielding gas and fume are disturbed by the plasma light excited by the laser, and the measurement accuracy is lowered. On the other hand, if the plasma light is measured from the inner surface side, This is because, when the clogging for a short time occurs, the plasma on the inner surface side is not generated, so that the presence / absence of the clogging of the keyhole 4 can be measured with high accuracy.

When a plurality of laser beams are used, the reflected light generated from all the laser beam irradiation sites is monitored, but since the irradiation positions are close to each other, it is possible to capture the entire plurality of irradiation positions 1 Monitoring may be performed with two monitoring devices.
When the relative value of the measured value (for example, intensity) of reflected light or plasma light due to laser beam irradiation is small, the keyhole 4 penetrates from the outer surface side to the inner surface side, so the welding conditions are continued as they are. And maintain. When the variation of the relative value is large, the keyhole 4 does not penetrate from the outer surface side to the inner surface side, so the welding conditions are changed and adjustment is performed so that sound laser welding proceeds.

  In addition, the measurement of the reflected light by laser beam irradiation was monitored from the outside of the open pipe 1 by the reflected light sensor 15 and the monitor device 16 suspended from the welding head 14, as shown in FIG. Data collection conditions were measured by using a filter that transmits only the same wavelength as the laser in the reflected light sensor 15, thereby eliminating disturbance due to infrared rays from the keyhole 4 and the molten metal 5. The change in the intensity of the reflected light was determined by the monitor device 16. For example, a photodiode or the like can be used as the reflected light sensor. Note that the reflected light coaxial with the laser light may be measured by sending it to the reflected light sensor with a mirror incorporated in the welding head.

  The plasma light was measured by attaching a plasma light sensor 10 together with a keyhole monitoring device as shown in FIG. Data collection conditions were measured by using a filter that transmits only the wavelength of the plasma light generated by the laser in the plasma light sensor 10, thereby eliminating disturbance due to infrared rays from the keyhole 4 and the molten metal 5. The change in the intensity of the plasma light was determined by the monitor device 17. Examples of the plasma light sensor include those using Si elements in the range of 300 to 900 nm.

  The data collection speed is measured at a frequency of 1kHz, and when the fluctuation of reflected light and / or plasma light intensity exceeds 15% of the relative value, an alarm is issued and the welding conditions are changed. And adjust so that sound laser welding proceeds. Note that a monitoring device for reflected light or plasma light by laser beam irradiation can be used in any configuration, and thus is not limited to the above-described configuration.

  Specifically, the welding conditions to be adjusted when the intensity fluctuation of the reflected light and / or plasma light exceeds 15% relative to the relative value are the welding conditions to be adjusted when the keyhole 4 is closed. The same. Therefore, when the fluctuation of the intensity of the reflected light and / or plasma light exceeds 15% relative to the relative value, the irradiation position of the laser beam is moved in the circumferential direction of the open pipe 1 to It is most preferable to adjust so that the junction point is arranged in the irradiation position of the laser beam 3 (key hole 4) or in the molten metal 5. For example, the joint of the edge portion 2 and the positions of the keyhole 4 and the molten metal 5 are image-processed and recognized by the keyhole monitoring device, and the circumferential direction and moving distance of the open pipe are calculated. However, the laser beam irradiation position is moved by controlling the position of the condensing lens and the condensing mirror housed in the welding head 14 and the welding head 14 so as to enter the inside of the keyhole 4 or the molten metal 5. It is preferable to make it.

Note that the apparatus for measuring reflected light or plasma light by laser beam irradiation is not limited to the above-described configuration, and an arbitrary configuration can be used.
As other welding conditions, it is also preferable to employ, for example, control of the focal position of the laser beam, movement of the beam irradiation position in the longitudinal direction of the open pipe, increase control of laser power, deceleration control of welding speed, and the like.

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.

  However, in the present invention, it is most preferable that a fiber laser oscillator is used, the laser output exceeds 15 kW (total of one or more), and the focal length of the laser is 200 mm or more. When the total laser output of one or a plurality of lasers is 15 kW or less, there is a problem that the welding speed is less than 5 m / min and blow holes are likely to occur. If the focal length of the laser is less than 200 mm, there is a problem that welding becomes unstable due to fluctuations in the Z-axis direction (the optical axis direction of the laser beam) of the edge portion of the open pipe formed from the steel plate.

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 for this is that unless the auxiliary heat source and the laser are arranged integrally, a large amount of heat is required to obtain the effect of the auxiliary heat source, and it becomes very difficult to suppress welding defects (for example, undercut). is there. Further, it is more preferable that the auxiliary heat source is disposed ahead of the laser beam oscillator. The reason is that moisture and oil can be removed from the edge portion.

  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. Specifically, as shown in FIG. 6, the molten metal 5 is collected around the arc 19 by Fleming's left-hand rule by making the electrode 18 a negative pole and the edge 2 of the open pipe 1 a positive pole. Since the Lorentz force 21 that is going to be used can be used, the molten metal 5 can be prevented from falling off. 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 20 that generates the arc 19 is effectively given to the molten metal 5 generated by the laser beam. Furthermore, it is more preferable that the arc generation source is arranged ahead of the laser beam 3. The reason is that the moisture and oil content of the edge portion 2 can be removed.

The distance between the irradiation position of the laser beam 3 on the outer surface of the open pipe 1 and the arc electrode 18 is preferably 7 mm or less. The reason is that when the distance between the irradiation position of the laser beam 3 and the arc electrode 18 exceeds 7 mm, the amount of the molten metal 5 melted by the arc 19 decreases, and the influence of the magnetic field generated around the welding current 20 is small. Because it becomes.
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 portion 2 is preheated by high frequency heating or the like, effects such as improvement in productivity of the laser welded steel pipe can be obtained.

  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.

<Example 1>
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 kWCO 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. Note that the plasma light sensor 10 and its monitor device 17 shown in FIG. 3 are not used. 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 (steel pipe numbers 1-1 to 1-4) monitor the keyhole 4 from the inner surface side of the open pipe 1 and adjust the size of the keyhole 4 as shown in Table 2, In addition, the positional relationship between the edge joint and the keyhole 4 or molten metal 5 is adjusted as shown in Table 2. When the keyhole diameter is less than 0.2 mm, the irradiation position of the laser beam is moved in the circumferential direction of the open pipe 1, and the joining point C of the edge portion 2 becomes the irradiation position of the laser beam 3 (keyhole 4). Or it adjusted so that it might arrange | position in the molten metal 5. FIG.

Steel pipe numbers 1-5 and 1-6 in the comparative example are examples in which the keyhole 4 is not monitored. Steel pipe numbers 1-7 and 1-8 in the comparative example 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 clear from Table 2, in the inventive examples (steel pipe numbers 1-1 to 1-4), the ultrasonic flaw detection is excellent (◎) or good (○), and the absorbed energy of the Charpy impact test (−60 ° C.) Was 82-112J. On the other hand, in the comparative examples (steel pipe numbers 1-5 to 1-8), the ultrasonic flaw detection is possible (△) or not (×), and the absorbed energy in the Charpy impact test (−60 ° C.) is 8.7 to 38 J. It was.
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.
<Example 2>
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 laser beam 3 from the outer surface side while pressing the edge 2 of the open pipe 1 with a squeeze roll. Note that a plasma jet and a TIG arc were used as the auxiliary heat source, and the auxiliary heat source was arranged to heat and melt the edge portion 2 prior to the laser beam 3. The components of the steel sheet are as shown in Table 3.

  In laser welding, a 20 kW fiber laser oscillator is used, and its output and welding speed are as shown in Table 4.

  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. Note that the plasma light sensor 10 and its monitor device 17 shown in FIG. 3 are not used. 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 laser beam irradiation.

  The invention examples shown in Table 4 (steel pipe numbers 2-1 to 2-4) were heated and melted by a plasma jet and a TIG arc from the outer surface side, and then continued to irradiate a laser beam, with a keyhole from the inner surface side of the open pipe. In this example, the size of the keyhole is monitored and adjusted as shown in Table 4, and the positional relationship between the junction of the edge portion and the keyhole or molten metal is adjusted as shown in Table 4. Steel pipe numbers 2-5 and 2-6 of the invention examples are examples in which no auxiliary heat source is used.

When the keyhole diameter is less than 0.2 mm, the irradiation position of the laser beam is moved in the circumferential direction of the open pipe 1, and the joining point C of the edge portion 2 becomes the irradiation position of the laser beam 3 (keyhole 4). Or it adjusted so that it might arrange | position in the molten metal 5. FIG.
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. Table 4 shows the results of the flaw detection. In Table 4, 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, the appearance of the inner bead of the steel pipe was inspected.

As apparent from Table 4, in the invention examples (steel pipe numbers 2-1 to 2-4), the ultrasonic flaw detection was excellent (（) or good (◯). The appearance of the inner bead of the steel pipe was also good. On the other hand, in the invention examples (steel pipe numbers 2-5 and 2-6) in which no auxiliary heat source was used, the ultrasonic flaw detection was good (◯), but it was melted into the inner bead of the steel pipe or an undercut was found.
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).

<Example 3>
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. A TIG arc was used as an auxiliary heating means, and the arc was arranged to heat and melt the edge portion ahead of the laser beam. The components of the steel sheet are as shown in Table 5.

  In laser welding, a 10 kW fiber laser oscillator is used, and its output and welding speed are as shown in Table 6.

  The keyhole monitoring device was inserted into the open pipe 1 by attaching the monitoring camera 5 to the mandrel bar 7 of the inner surface bead cutting device using the device shown in FIG. Note that the plasma light sensor 10 and its monitor device 17 shown in FIG. 3 are not used. As the monitoring camera 5, 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 laser beam irradiation.

  Inventive examples shown in Table 6 (steel pipe numbers 3-1 to 3-4) are heated and melted by a TIG arc from the outer surface side and continuously irradiated with a laser beam while monitoring the keyhole from the inner surface side of the open pipe. In this example, the size of the keyhole is adjusted as shown in Table 6, and the positional relationship between the junction of the edge portion and the keyhole or molten metal is adjusted as shown in Table 6. Steel pipe numbers 3-5 to 3-8 of the invention examples are examples in which no TIG arc is used.

When the keyhole diameter is less than 0.2 mm, the irradiation position of the laser beam is moved in the circumferential direction of the open pipe 1, and the joining point C of the edge portion 2 becomes the irradiation position of the laser beam 3 (keyhole 4). Or it adjusted so that it might arrange | position in the molten metal 5. FIG.
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. Table 6 shows the flaw detection results. In Table 6, with respect to the artificial defect of the N5 inner and outer notch used as a reference, the peak indication height is excellent (◎) when the peak indication height is 10% or less, and good (○) when it exceeds 10% and 25% or less. , 25% and 50% or less were evaluated as acceptable (△), and those exceeding 50% were evaluated as unacceptable (×). In addition, the appearance of the inner bead of the steel pipe was inspected.

As is clear from Table 6, in the invention examples (steel pipe numbers 3-1 to 3-4), the ultrasonic flaw detection was excellent (）) or good (）). The appearance of the inner bead of the steel pipe was also good. On the other hand, in the invention examples (steel pipe numbers 3-5 to 3-8) that do not use the TIG arc, ultrasonic flaw detection was good (◯), but melted down and undercut were found on the inner bead of the steel pipe.
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).

<Example 4>
A strip-shaped steel plate is formed into a cylindrical open pipe with a forming roll, and a laser beam (two or one) is irradiated from the outer surface side while pressing the edge of the open pipe with a squeeze roll to form a laser welded steel pipe. Manufactured. The components of the steel sheet are as shown in Table 7.

  In laser welding, fiber laser oscillators of 5 kW and 10 kW are used, and the welding conditions are as shown in Table 8.

  The keyhole monitoring device was inserted into the open pipe by attaching the monitoring camera 8 to the mandrel bar 7 of the inner surface bead cutting device using the device shown in FIG. Note that the plasma light sensor 10 and its monitor device 17 shown in FIG. 3 are not used. 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 laser beam irradiation.

  The invention examples shown in Table 8 (steel pipe numbers 4-1 to 4-4) are formed from the inner surface of the open pipe while irradiating two laser beams from the outer surface of the open pipe to form two keyholes. This is an example in which the keyhole is monitored, the size of the keyhole is adjusted as shown in Table 8, and the positional relationship between the junction of the edge portion and the keyhole or molten metal is adjusted as shown in Table 8. . Steel pipe numbers 4-5 to 4-8 of the invention examples are examples in which one laser beam is irradiated to form one keyhole.

When the diameter of at least one keyhole is less than 0.1 mm, the laser beam irradiation position and the focal position are moved in the circumferential direction of the open pipe 1 so that the junction point C of the edge portion 2 has two keyholes. It adjusted so that it might arrange | position in the irradiation position (keyhole 4) or the molten metal 5 of the laser beam 3 between.
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. Table 8 shows the flaw detection results. In Table 8, with respect to the reference artificial defect of N5 inner and outer notches, the peak indication height is 10% or less excellent (◎), 10% to 25% or less good (○) , 25% and 50% or less were evaluated as acceptable (△), and those exceeding 50% were evaluated as unacceptable (×). In addition, the appearance of the inner bead of the steel pipe was inspected.

As is apparent from Table 8, in the invention examples (steel pipe numbers 4-1 to 4-4), the ultrasonic flaw detection was excellent (◎) or good (○). The appearance of the inner bead of the steel pipe was also good. On the other hand, in the invention example (steel pipe numbers 4-5 to 4-8) in which one keyhole is formed by irradiating one laser beam, the ultrasonic flaw detection was good (◯), but the inner surface of the steel pipe The bead was undercut.
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).

<Example 5>
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. A TIG arc was used as an auxiliary heating means, and the arc was arranged to heat and melt the edge portion ahead of the laser beam. The components of the steel sheet are as shown in Table 9.

  In laser welding, a 20 kW fiber laser oscillator is used, and its output and welding speed are as shown in Table 10.

The keyhole monitoring device 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 reflected light sensor 15 generated from the irradiated portion of the laser beam 3 is attached to the welding head 14 using the apparatus shown in FIG. 5, and the plasma light sensor 10 is attached to the mandrel bar 7 using the apparatus shown in FIG. .

  Among the invention examples shown in Table 10, steel pipe numbers 5-1 and 5-2 are used to monitor the keyhole from the inner surface side of the open pipe using the apparatus shown in FIG. The intensity of the reflected light was measured from the outer surface side using the apparatus shown in FIG. Table 10 shows the positional relationship between the edge joint and the keyhole or molten metal based on the size of the keyhole, the fluctuation in the relative value of the measured value of the reflected light, and the fluctuation in the relative value of the measured value of the plasma light. It is an example adjusted as shown in FIG. When the keyhole diameter is less than 0.2 mm, the irradiation position of the laser beam is moved in the circumferential direction of the open pipe 1, and the joining point C of the edge portion 2 becomes the irradiation position of the laser beam 3 (keyhole 4). Or it adjusted so that it might arrange | position in the molten metal 5. FIG.

Further, when the fluctuation of the intensity of the plasma light exceeds 15% relative to the relative value, the irradiation position of the laser beam is moved in the circumferential direction of the open pipe 1 so that the junction C of the edge portion 2 is a laser. Adjustment was made so that the irradiation position of the beam 3 (keyhole 4) or the molten metal 5 was arranged.
Steel pipe numbers 5-3 and 5-4 were heated and melted by TIG arc from the outer surface side, and continuously irradiated with a laser beam while monitoring the keyhole from the inner surface side of the open pipe and measuring the intensity of the plasma light. And the intensity | strength of the reflected light was measured from the outer surface side. Table 10 shows the positional relationship between the edge joint and the keyhole or molten metal based on the size of the keyhole, the fluctuation in the relative value of the measured value of the reflected light, and the fluctuation in the relative value of the measured value of the plasma light. It is an example adjusted as shown in FIG.

When the fluctuation of the intensity of the plasma light or the intensity of the reflected light exceeds 15% relative to the relative value, the irradiation position of the laser beam is moved in the circumferential direction of the open pipe 1 to join the edge portion 2 Adjustment was made so that the point C was placed in the irradiation position of the laser beam 3 (keyhole 4) or in the molten metal 5.
Inventive examples (steel pipe numbers 5-5 to 5-8) did not measure reflected light and plasma light, and the fluctuation of the intensity of the plasma light or the intensity of the reflected light exceeded 15% relative to the relative value. Even in this case, it is an example that is not reflected in the adjustment of the positional relationship between the junction of the edge portion and the keyhole or molten metal.

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. Table 10 shows the flaw detection results. In Table 10, with respect to the artificial defect of the N5 inner and outer notch used as a reference, the peak indication height is excellent (◎) when the peak indication height is 10% or less, and good (○) when it exceeds 10% and 25% or less. , 25% and 50% or less were evaluated as acceptable (△), and those exceeding 50% were evaluated as unacceptable (×). In addition, the appearance of the inner bead of the steel pipe was inspected.

  As is clear from Table 10, in the inventive examples (steel pipe numbers 5-1 to 5-4), the ultrasonic flaw detection was excellent (）) or good (◯). The appearance of the inner bead of the steel pipe was also good. On the other hand, even if the reflected light and plasma light are not measured and the fluctuation of the intensity of the plasma light or the intensity of the reflected light exceeds 15% relative to the relative value, the junction between the edge and the keyhole or melting In the invention examples (steel pipe numbers 5-5 to 5-8) that were not reflected in the adjustment of the positional relationship with the metal, ultrasonic flaw detection was good, but it seems that keyholes are frequently closed for a short time. As a result, spatter was generated near the inner surface bead of the steel pipe. Further, in the inventive examples (steel pipe numbers No. 5-5 and 5-6), melting or undercutting was found in the inner bead of the steel pipe. In addition, the presence or absence of blockage of the keyhole was set in place of the surveillance camera (30 frames / second) shown in FIG. 3 used in Examples 1 to 4, and a high-speed camera was set, and the keyhole was photographed at 1000 frames / second. ,confirmed. A keyhole blockage for a short time of 0.01 seconds or longer was considered to be blocked. It was found that the fluctuation of the intensity of the plasma light or the intensity of the reflected light and the clogging of the keyhole for a short time of 0.01 seconds or more occurred almost synchronously.

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).
<Example 6>
A strip-shaped steel plate is formed into a cylindrical open pipe 1 with a forming roll, and an edge 2 of the open pipe 1 is pressed with a squeeze roll and irradiated with a laser beam 3 (two or one) from the outer surface side. Laser welded steel pipe (outer diameter 273.0mm, thickness 6.4mm) was manufactured. A TIG arc was used as an auxiliary heating means, and the arc 19 was arranged so as to heat and melt the edge portion 2 prior to the laser beam 3. The components of the steel sheet are as shown in Table 11.

  In laser welding, 10 kW and 20 kW fiber laser oscillators are used, and the welding conditions are as shown in Table 12.

The monitoring device for the keyhole 4 was inserted into the open pipe 1 by attaching the monitoring camera 5 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.
Further, as shown in FIG. 5, the reflected light sensor 15 generated from the laser beam irradiation site is attached to the welding head 14, and the plasma light sensor 10 is attached to the mandrel bar 7 as shown in FIG.

  Among the invention examples shown in Table 12, steel pipe numbers 6-1 and 6-2 monitor the keyhole 4 from the inner surface side of the open pipe using the apparatus shown in FIG. 3 while irradiating two laser beams. At the same time, the intensity of the plasma light was measured, and the intensity of the reflected light was measured from the outer surface side using the apparatus shown in FIG. Then, based on the size of the keyhole 4, the fluctuation of the relative value of the measured value of the reflected light, and the fluctuation of the relative value of the measured value of the plasma light, the positional relationship between the junction of the edge portion and the keyhole or the molten metal is represented. This is an example adjusted as shown in FIG. When the diameter of at least one keyhole is less than 0.1 mm, the laser beam irradiation position and the focal position are moved in the circumferential direction of the open pipe 1 so that the junction point C of the edge portion 2 has two keyholes. It adjusted so that it might arrange | position in the irradiation position (keyhole 4) or the molten metal 5 of the laser beam 3 between.

Further, when the fluctuation of the intensity of the plasma light or the intensity of the reflected light exceeds 15% with respect to the relative value, the irradiation position and the focal position of the laser beam are moved in the circumferential direction of the open pipe 1, Adjustment was made so that the junction point C of the edge portion 2 was disposed between the two keyholes in the irradiation position of the laser beam 3 (keyhole 4) or in the molten metal 5.
Steel pipe numbers 6-3 and 6-4 are heated and melted by TIG arc from the outer surface side, and then irradiated from the inner surface side of the open pipe 1 while irradiating the laser beam 3 in two parts with the optical system. The keyhole 4 was monitored, the intensity of the plasma light was measured, and the intensity of the reflected light was measured from the outer surface side. Based on the size of the keyhole 4, the fluctuation of the relative value of the measured value of the reflected light, and the fluctuation of the relative value of the measured value of the plasma light, the junction C of the edge 2 and the keyhole 4 or the molten metal 5 This is an example in which the positional relationship is adjusted as shown in Table 12. When the diameter of at least one keyhole is less than 0.1 mm, the laser beam irradiation position and the focal position are moved in the circumferential direction of the open pipe 1 so that the junction point C of the edge portion 2 has two keyholes. It adjusted so that it might arrange | position in the irradiation position (keyhole 4) or the molten metal 5 of the laser beam 3 between.

Further, when the fluctuation of the intensity of the plasma light or the intensity of the reflected light exceeds 15% with respect to the relative value, the irradiation position and the focal position of the laser beam are moved in the circumferential direction of the open pipe 1, Adjustment was made so that the junction point C of the edge portion 2 was disposed between the two keyholes in the irradiation position of the laser beam 3 (keyhole 4) or in the molten metal 5.
Inventive examples (steel pipe numbers 6-5 to 6-8) did not measure the reflected light and plasma light, and the fluctuation of the intensity of the plasma light or the intensity of the reflected light exceeded 15% relative to the relative value. Even in this case, it is an example that is not reflected in the adjustment of the positional relationship between the junction point C of the edge portion 2 and the keyhole 4 or the molten metal 5.

  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. Table 12 shows the flaw detection results. In Table 12, 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, the appearance of the inner bead of the steel pipe was inspected.

  As is apparent from Table 12, in the inventive examples (steel pipe numbers 6-1 to 6-4), the ultrasonic flaw detection was excellent (）) or good (◯). The appearance of the inner bead of the steel pipe was also good. On the other hand, even if the reflected light and the plasma light are not measured and the fluctuation of the intensity of the plasma light or the intensity of the reflected light exceeds 15% with respect to the relative value, the junction C of the edge portion 2 and the keyhole In the invention examples (steel pipe numbers 6-5 to 6-8) that were not reflected in the adjustment of the positional relationship with 4 or molten metal 5, the ultrasonic flaw detection was good, but the keyholes were frequently closed for a short time. And spatter was generated near the inner surface bead of the steel pipe. Further, in the inventive examples (steel pipe numbers 6-5 and 6-6), melting and undercut were found in the inner bead of the steel pipe. In addition, the presence or absence of blockage of the keyhole was set by replacing the surveillance camera (30 frames / second) shown in FIG. 3 used in Examples 1 to 4 with a high-speed camera and photographing the keyhole at 1000 frames / second. ,confirmed. A keyhole blockage for a short time of 0.01 seconds or longer was considered to be blocked. It was found that the fluctuation of the intensity of the plasma light or the intensity of the reflected light and the clogging of the keyhole for a short time of 0.01 seconds or more occurred almost synchronously.

  As described above, when the present invention is applied, sound laser welding can be performed even with an open pipe 1 made of a thick material (thickness 4 mm or more).

  When manufacturing laser welded steel pipes, it is possible to accurately determine the status of laser welding by monitoring keyholes or measuring reflected light and plasma light, and in keyholes or molten metal generated by laser beam irradiation. The joining points of the edge portions can always be arranged, and 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 7 Mandrel bar 8 Surveillance camera 9 Lighting device
10 Plasma light sensor
11 Image processing device
12 Judgment device
13 Position control device
14 Welding head
15 Reflected light sensor
16 Monitor device
17 Monitor device
18 electrodes
19 arc
20 Welding current
21 Lorentz force A Travel direction of open pipe C Joint point Lk Keyhole size Lm Keyhole length in pipe circumference

Claims (19)

  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 steel that performs welding while providing at the laser beam irradiation site Method of production.   2. The method for manufacturing a laser welded steel pipe according to claim 1, wherein the edge portion is heated and melted auxiliary using an auxiliary heat source that heats from the outer surface side of the open pipe, and the laser beam is irradiated. 3. .   The method of manufacturing a laser welded steel pipe according to claim 2, wherein the auxiliary heat source is an arc.   While monitoring the irradiation part of the laser beam irradiated to the edge portion from the inner surface side of the open pipe, the reflected light and plasma light generated from the irradiation part by irradiation of the laser beam is measured using a sensor, A welding situation is monitored based on each measurement value obtained from the sensor, a keyhole penetrating to the inner surface side of the open pipe is recognized, and a relative value of the measurement value of the reflected light and the plasma light obtained from the sensor When the variation of the value is small, the welding condition by the laser beam is continuously maintained, while the keyhole penetrating to the inner surface side of the open pipe is unstable and repeatedly clogged, and the reflected light obtained from the sensor and When the relative value of the measured value of the plasma light varies greatly, the laser beam The welding is performed while changing a welding condition to provide a keyhole penetrating from an outer surface side to an inner surface side of the open pipe at an irradiation site of the laser beam. The manufacturing method of the laser-welded steel pipe as described in 2.   The method for producing a laser welded steel pipe according to any one of claims 1 to 4, wherein the keyhole is 0.2 mm or more in diameter on the inner surface side of the open pipe.   6. The laser welded steel pipe according to claim 1, wherein a joining point of an edge portion pressed by the squeeze roll is disposed in a molten metal generated by irradiation of the laser beam. Production method.   The method for producing a laser welded steel pipe according to any one of claims 1 to 5, wherein a joint point of an edge portion pressed by the squeeze roll is disposed in the inner surface side keyhole.   The method for manufacturing a laser welded steel pipe according to any one of claims 2 to 7, wherein the laser beam oscillator and the auxiliary heat source are integrally arranged.   8. The laser beam oscillator and the auxiliary heat source are integrally disposed, and the auxiliary heat source heats the edge portion ahead of the laser beam. The manufacturing method of the laser welding steel pipe of description.   10. The laser welded steel pipe according to claim 3, wherein the laser beam oscillator is a fiber laser oscillator, the laser output exceeds 15 kW, and the focal length of the laser is 200 mm or more. Production method.   11. The method for producing a laser welded steel pipe according to claim 3, wherein a distance between the irradiation position of the laser beam on the outer surface of the open pipe and the electrode of the arc is 7 mm or less.   11. The laser welded steel pipe according to claim 4, wherein the reflected light is measured from an outer surface side of the open pipe, and the plasma light is measured from an inner surface side of the open pipe. Method.   The welding is performed while irradiating a plurality of laser beams and providing keyholes penetrating from the outer surface side to the inner surface side of the open pipe at the irradiated portions of the plurality of laser beams, respectively. The manufacturing method of the laser welding steel pipe of description.   The irradiation part of the plurality of laser beams irradiating the edge part is monitored from the inner surface side, and the reflected light and plasma light generated from the irradiation part by the irradiation of the laser beam are measured using a sensor, from the sensor A welding situation is monitored based on each obtained measurement value, and a plurality of keyholes penetrating from the outer surface side to the inner surface side of the open pipe are recognized, and the reflected light and the plasma light obtained from the sensor are detected. When the relative value of the measured value is small, the welding condition by the laser beam is continuously maintained, while the keyhole penetrating to the inner surface side of the open pipe is unstable and repeatedly clogged, and the reflection obtained from the sensor If the relative value of the measured values of the light and the plasma light is large, the welding conditions by the laser beam 14. The laser welded steel pipe according to claim 13, wherein welding is performed while providing key holes penetrating from an outer surface side to an inner surface side of the open pipe at each of the irradiated portions of the plurality of laser beams. Manufacturing method.   Of the plurality of keyholes, a junction point of the edge portion is disposed between two keyholes provided on both sides of the edge portion and having the largest distance in the vertical direction with respect to the edge portion. The method for producing a laser welded steel pipe according to claim 13 or 14.   The method for producing a laser welded steel pipe according to any one of claims 13 to 15, wherein each of the plurality of keyholes has a diameter of 0.1 mm or more on the inner surface side of the open pipe. .   The method for manufacturing a laser welded steel pipe according to any one of claims 13 to 16, wherein a joint point of the edge portion is disposed in a molten metal generated by irradiation with the plurality of laser beams.   The method for manufacturing a laser welded steel pipe according to any one of claims 13 to 17, wherein two laser beams are used as the plurality of laser beams. The method for manufacturing a laser welded steel pipe according to any one of claims 13 to 18, wherein the edge portion is supplementarily heated and melted by using an auxiliary heat source that is heated from an outer surface side of the open pipe.

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