JP4786402B2 - UOE steel pipe manufacturing method - Google Patents

Description

  The present invention relates to a UOE steel pipe manufacturing method in which both weld toughness and productivity are dramatically improved.

To ensure good toughness at welds UOE steel pipe is very important in terms of quality control.

In the welded portion, it is difficult to ensure good toughness in the welded heat-affected zone of the base metal (hereinafter sometimes referred to as “HAZ”). In the granulated HAZ, a region that is reheated to a temperature range of not less than Ac ₁ point and not more than Ac ₃ point by heating in the next pass is a region where embrittlement is a concern.

  That is, in the HAZ subjected to such a double heat cycle, an embrittled structure called island martensite (hereinafter sometimes referred to as “MAC”) is generated. In order to improve the HAZ toughness, it is essential to control the generation of this MAC.

  Therefore, many methods for increasing the HAZ toughness have been proposed so far (see, for example, Patent Documents 1 to 5), but all reduce the reheating region by dispersing the heat input in each pass, and toughness. The basic technical idea is to improve.

  Although the above heat input dispersion method is effective in terms of improving toughness, the number of welding passes inevitably increases, so that there is a problem that a reduction in productivity cannot be avoided. Further, when tack welding is necessary, the productivity further decreases.

  On the other hand, in order to reduce the number of welding passes, it is essential to perform welding with high heat input, but it cannot be avoided that the HAZ undergoes double thermal cycles, and it is difficult to ensure the HAZ toughness.

  After all, in the current UOE steel pipe manufacturing technology, it is impossible to reduce the number of welding passes and simultaneously improve productivity and HAZ toughness.

Japanese Patent No. 2650601 JP-A-6-328255 JP 58-32583 A JP-A-6-1555076 JP 2001-113374 A Japanese Patent Laid-Open No. 10-216972 JP-A-10-244369 JP 2002-172477 A Japanese Patent Application No. 2006-113387

  In order to solve the above-mentioned problems in the manufacture of UOE steel pipes, the present invention establishes a welding method with a small heat input and a small number of welding passes, and achieves both improvement in productivity and securing of HAZ toughness. An object of the present invention is to provide a method for manufacturing a simple UOE steel pipe.

  The present inventors diligently studied a method for overcoming the conflicting technical problems of reducing the number of welding passes and improving the toughness of the welded part in the welding of the X groove, and obtained the following knowledge.

(I) the use of composite heat source and supplies the multi-electrode gas shield arc and laser, plasma induces stably top arc to groove bottom.

  (Ii) As a result, a weld with excellent mechanical properties can be formed in one pass.

  Note that the use of a composite heat source for welding is already known in butt welding or tack welding of thick plates (see Patent Documents 6 to 8), but has higher strength than butt welding of ordinary thick plates. In order to ensure the toughness of the weld due to the use of a steel plate, the upper and lower heat input regulation conditions are strictly set. Regarding the upper limit of heat input, since the cross-sectional area of the weld is smaller than that of butt welding, X-groove welding that enables heat input reduction is adopted.

  On the other hand, when manufacturing various welded products such as UOE steel pipes and structures, tack welding is often performed in advance on the groove, but since there is a heat input limit of the lower limit, welding heat input is small. The tack welding construction itself causes problems.

  In response to these problems, the present inventor is the first to use a composite heat source on the premise that tack welding is eliminated using X groove and welding on the outer surface side is completed in one pass. is there.

  The present inventor has already applied for the invention based on the above knowledge as Patent Document 9, but as a result of further research, the following knowledge has been obtained.

(Iii) There is an optimal relationship between the flow rate of the shielding gas and the area of the gas nozzle port.
(Iv) There is also an optimum relationship between the position of the heat source and the position of the gas nozzle.

  This invention was made | formed based on the said knowledge, and the summary is as follows.

(1) In the manufacturing method of UOE steel pipe,
(A1) The gas shield arc first electrode is arranged at the foremost position along the welding direction, and the laser target position is within 10 mm behind the target position of the arc of the first electrode on the weld line. Place the laser torch so that it comes in, arrange the gas shield arc second electrode behind it,
(A 2 ) The groove angle on the outer surface side of the X groove is 20 ° or more and 40 ° or less,
(A 3 ) The outer surface side of the X groove is welded in one pass using a combined heat source of a gas shield arc and a laser having an output of 1 kW to 20 kW, and then
(B) When the inner surface side of the X groove is welded in one pass using submerged arc welding, and the welding is completed in a total of two passes,
(D) A method of manufacturing a UOE steel pipe, characterized in that a shield gas having a flow rate (B) satisfying the following formula (1) is supplied from the gas nozzle ports on the left and right sides of the weld line.
3 ≦ B / A ≦ 30 (1)
A: Area of gas nozzle opening (cm ² )
B: Flow rate of shielding gas (liters / minute)
(2) In the UOE steel pipe manufacturing method according to the above (1), the gas shield arc third electrode is disposed further rearward of the second electrode, or the gas shield third electrode and the gas further rearward thereof. A method for producing a UOE steel pipe, wherein a shield arc fourth electrode is arranged and the outer surface side of the X groove is welded.

( 3 ) The welding line is the X axis (unit: mm), the welding progress direction is the + direction, and the opposite direction is the − direction, and the positions of the last heat source and the first heat source on the X axis are X1 and X2, respectively. When the rear end position and the leading position on the X axis of the gas nozzle are X3 and X4, respectively, X1, X2, X3, and X4 satisfy the following expressions (2) and (3) at the same time The manufacturing method of the UOE steel pipe as described in said (1) or (2) characterized by performing.
5 (mm) <X1-X3 <200 (mm) (2)
5 (mm) <X4-X2 <100 (mm) (3)

( 4 ) The method for manufacturing a UOE steel pipe according to any one of (1) to (3) above, wherein an installation angle of the gas nozzle is 10 ° or more and 80 ° or less with respect to a root face surface.

( 5 ) The method for manufacturing a UOE steel pipe according to any one of (1) to ( 4 ), wherein the gas shield arc is a consumable multi-electrode gas shield arc.

( 6 ) The method for manufacturing a UOE steel pipe according to any one of (1) to ( 5 ), wherein the laser is a laser having a focal length of 100 mm or more.

  According to the present invention, in manufacture of a UOE steel pipe, the X groove can be welded in a total of two passes, and a welded portion excellent in mechanical properties can be formed.

  A UOE steel pipe is usually obtained by cutting a flat steel plate into a predetermined dimension, and using this flat steel plate, adjusting the plate width, groove processing of both width end portions, bending processing of both width end portions, and U shape After the press molding into a tubular shape by O-shaped molding, the butt portion is subjected to tack welding by gas shield arc welding or the like, and then inner seam welding and outer seam welding by submerged arc welding or the like, Then, in order to raise the roundness of a steel pipe, it manufactures in the process of performing pipe expansion molding with an expander etc.

  1 and 2 show the configuration of the present invention, and FIG. 3 schematically shows the groove shape of the welded portion. In the groove shape shown in FIG. 3, the root face length df is sandwiched between the welded portion of the plate thickness t, the groove surface has a groove depth do and a groove angle φo, and the inner surface side. A groove having a groove depth di and a groove angle φi is formed.

  The welding torch 3 of the gas shielded arc first electrode is arranged at the forefront along the welding direction 8 above the groove 2 on the outer surface side of the steel pipe 1, and aimed at a distance M1 behind the target position. The laser torch 4 is arranged so that the position comes, and further, the welding torch 5 of the gas shielded arc second electrode is arranged so that the target position is separated by a distance M2 behind the laser torch 4, and further behind that, The welding torch 6 of the gas shield arc third electrode is disposed so that the target position is separated by the distance M3, and the shielding nozzle 7 for spraying the shielding gas from the left and right sides of the molten pool to the welded portion is disposed, Welding is performed (see FIGS. 1 and 2).

  In addition, a gas shield arc welding torch can be arranged behind the welding torch 6 of the gas shield arc third electrode while further leaving a predetermined distance.

In the present invention, the groove angle (φo in FIG. 3) on the outer surface side of the X groove is 20 ° or more and 40 ° or less, welding on the outer surface side of the X groove is performed with a gas shield arc, and the output is 1 kW or more and 20 kW. Using a combined heat source with the following laser, it is completed in one pass, and welding on the inner surface side is completed in one pass using submerged arc welding, that is, when X groove welding is completed in two passes in total. The shield gas having a flow rate (B) satisfying the following formula (1) is supplied from the gas nozzle ports on both the left and right sides of the weld line.
3 ≦ B / A ≦ 30 (1)
A: Area of gas nozzle opening (cm ² )
B: Flow rate of shielding gas (liters / minute)

  The prior art requires tack welding, inner surface side welding, outer surface side welding, and a welding process for forming at least three layers, but the present invention completes X groove welding in a total of two passes. Compared with welding, it has a significant advantage in productivity.

  Further, in the present invention, in order to improve the HAZ toughness, the "conflicting technical problem" of suppressing the welding heat input and finishing the outer surface side welding in one pass in order to improve the productivity is overcome. For this purpose, outer surface side welding is performed in one pass using a combined heat source of a gas shield arc and a laser.

  First, securing of HAZ toughness will be described.

  Normally, in order to reduce the amount of heat input at the welded portion, the groove is a narrow groove and the required amount of deposited metal is reduced as much as possible. However, in narrow groove welding, the arc does not reach the groove bottom, and FIG. The problem was that the poor fusion 12 as shown.

  In the present invention, since the groove on the outer surface side is a narrow groove having a groove angle of 20 ° or more and 40 ° or less, it is necessary to take measures against the above problem, but in the present invention, a gas shield arc and a laser are combined. The above problems are solved by using a combined heat source.

  That is, since the arc is stably induced to the groove bottom by the plasma generated by the laser, the occurrence of poor fusion at the groove bottom is suppressed.

  In order to sufficiently secure the plasma arc induction function, the leading electrode and the laser torch are arranged so that the leading arc and the laser in the welding direction are combined. Specifically, the distance between the leading arc and the laser target position is set to be within 10 mm, preferably within 5 mm on the weld line.

  As described above, the groove angle on the outer surface side of the present invention is set to 20 ° to 40 °. When the groove angle is less than 20 °, the groove angle is too narrow, and even if the arc is induced by plasma, the arc does not reach the bottom of the groove, resulting in poor fusion. On the other hand, when the groove angle exceeds 40 °, the required amount of deposited metal increases, and it becomes difficult to suppress welding heat input.

  In the present invention, welding is performed by placing a welding torch of the first electrode of the leading gas shield arc and one or more welding shield torches of the gas shield arc behind the laser torch 4. This is because, in order to improve the welding efficiency, when the welding speed is increased, the groove 2 on the outer surface side is filled even in a narrow groove, and further, a predetermined surplus is secured in the weld bead 10. This is because it is necessary to secure the amount of weld metal necessary for the process.

  As a method for increasing the amount of deposited metal, it is common to increase the welding current value. However, if the welding current value of the first electrode of the leading gas shield arc is excessively increased, the weld pool 9 becomes unstable. Undercut defects occur on both sides of the weld bead 10 or irregularities occur on the bead surface, resulting in a poor appearance.

  Therefore, in the present invention, one or two or more gas shield arc welding torches are arranged behind the laser torch 4. With this arrangement, the molten pool 9 can be stabilized and a sufficient amount of deposited metal can be obtained, and the outer surface side groove 2 can be finished in one pass.

  In the present invention, the number of electrodes is increased to ensure the amount of deposited metal necessary to complete the outer surface side welding in one pass. In this case, the problem is the shielding method of the multi-electrode arc. .

  As a method for shielding a multi-electrode arc, for example, a method is known in which a shielding gas is supplied from before and after the welding direction (see Japanese Patent Laid-Open No. 7-204854). In the method, nitrogen in the weld metal is increased to about 150 ppm.

  This is considered to be due to the fact that when the shielding gas is supplied from before and after in the welding direction, it is difficult to completely shield the entire molten pool elongated in the welding direction.

  When low temperature toughness is not required for the weld metal, there is no problem even if the amount of nitrogen in the weld metal increases somewhat. However, in UOE steel pipes, an increase in the amount of nitrogen in the weld metal due to poor shielding is caused by This is a serious problem in securing toughness.

  Therefore, in the present invention, as a countermeasure for complete shielding of the molten pool, as shown in FIGS. 1 and 2, a double-sided supply system that supplies shield gas from both sides of the weld line is adopted. Thereby, it is possible to completely shield the entire molten pool extended in the welding direction.

  In order to effectively perform the shield, it is necessary to maintain the gas nozzle port area and flow rate of the shield gas in an appropriate relationship.

  Except that the inventor sets the groove angle φo on the outer surface side to 30 °, the groove conditions shown in Table 5 are used, and the welding method and welding conditions are the invention methods and welding conditions shown in Table 7, and Table 6 FIG. 5 shows the result of analyzing the amount of nitrogen (N amount) in the weld metal by performing welding while changing the area and flow rate of the gas nozzle opening of the shielding gas under the gas shielding conditions shown in FIG.

When the area of the gas nozzle port is A (cm ² ) and the flow rate of the shield gas is B (liters / minute), when B / A is less than 3, the gas flow rate is too small and extends along the weld line. When the molten pool cannot be shielded completely, on the other hand, if B / A is more than 30, the gas flow rate is too high and turbulence occurs in the shielding gas, which causes the phenomenon of entraining the atmosphere. In any case, the amount of nitrogen (N) in the weld metal increases, and the toughness of the welded portion decreases.

Therefore, it is necessary to set the area and flow rate so as to satisfy the following formula (1) in order to obtain a good shield.
3 ≦ B / A ≦ 30 (1)
However, A: The area (cm ² ) of the outlet of the gas nozzle port, and B: the flow rate of the shielding gas (liter / minute).

Moreover, since it is necessary to supply the shielding gas so as to cover the entire molten pool, the position of the gas nozzle is also an important requirement, and the position of the heat source that forms the molten pool and the shielding gas that covers the molten pool are supplied. It is desirable to maintain the position of the gas nozzle so that the following equations (2) and (3) are satisfied simultaneously.
5 (mm) <X1-X3 <200 (mm) (2)
5 (mm) <X4−X2 <100 (mm) (3)
Where X1: Position of the tail heat source (mm) when the welding line is the X-axis (welding direction is +, the opposite direction is-)
X2: Position of head heat source (mm)
X3: Rear end position of the gas nozzle (mm)
X4: Tip position of the gas nozzle (mm)
It is.

  When (X1-X3) and / or (X4-X2) is 5 mm or less, the shield gas is not sufficiently supplied to the front end and / or rear end of the molten pool, and a good shield cannot be secured. As a result, nitrogen (N) enters the molten pool from the air, the amount of nitrogen (N) in the deposited metal increases, and the low temperature toughness of the welded portion deteriorates.

  On the other hand, when (X1−X3) is 200 mm or more and / or (X4−X2) is 100 mm or more, the amount of shield gas to be supplied increases, causing turbulent flow involving air. This is not appropriate because it results in poor shielding, and defects such as blow holes occur and mechanical properties deteriorate. Furthermore, an increase in the amount of shielding gas to be supplied is not appropriate from the viewpoint of gas cost.

  Further, the installation angle θ of the gas nozzle is preferably 10 ° or more and 80 ° or less with reference to the root face surface as shown in FIG. When the installation angle is less than 10 ° or more than 80 °, the shielding gas cannot be supplied to the groove bottom, resulting in shielding failure.

The shielding gas is preferably a mixed gas in which one or two kinds of He and Ar are added to one or two kinds of 2 to 50 vol% of CO ₂ and O ₂ . CO ₂ and O ₂ act as an oxygen source when forming fine oxides such as Ti in the weld metal. This fine oxide serves as a site for forming fine acicular ferrite in the crystal grains of the weld metal, and contributes to improvement of the toughness of the weld metal by refining the crystal grains.

  Further, as the gas shield arc of the composite heat source, non-consumable electrode type TIG welding arc and plasma welding arc, consumable electrode type MIG welding arc and MAG welding arc can be considered. However, in the non-consumable electrode type, even with the same welding heat input as the consumable electrode type, the amount of welding wire melted per unit time is small, and the amount of weld metal for filling the groove shape is insufficient.

  Therefore, in order to make the amount of deposited metal obtained by the non-consumable electrode type the same as the amount of deposited metal obtained by the consumable electrode type, it is necessary to increase the welding current. Then, the welding heat input increases and the HAZ toughness decreases.

  In the non-consumable electrode type, since the welding torch has a positive polarity, heat generation on the welding torch side is larger than in the consumable electrode type, and it is necessary to increase the cooling capacity. Therefore, the welding torch itself becomes large and complicated, and as a result, it becomes expensive. For these reasons, the gas shield arc in the present invention is preferably a consumable multi-electrode gas shield arc.

  The output of the laser that generates plasma is 1 kW or more in order to perform good welding. If it is less than 1 kW, there is insufficient power, and sufficient plasma is not generated to induce the arc to the groove bottom, resulting in poor fusion.

  The laser output is preferably large in terms of plasma generation, but if it exceeds 20 kW, the power is excessive and the molten pool is pushed into the slight gap by evaporation reaction force. As a result, the amount of deposited metal in the groove Is insufficient to melt, and welding cannot be completed in one pass. Therefore, the laser output is set to 1 kW or more and 20 kW or less.

  The focal length of the laser needs to be 100 mm or more. When the focal length is less than 100 mm, it is extremely difficult to protect the condensing optical system from spatter and fumes generated from the electrodes, which is not practical.

  The upper limit value of the focal length is not particularly limited. However, if the focal length is too long, the focal spot diameter becomes large, and the energy density may be reduced, so that sufficient plasma may not be generated. .

  Next, examples of the present invention will be described. The conditions of the examples are one example of conditions adopted for confirming the feasibility and effects of the present invention, and the present invention is limited to this one example of conditions. Is not to be done. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

(Example)
Hereinafter, the effectiveness of the present invention will be described based on examples. Table 1 shows the component composition of the test steel. The test steel material is a steel material produced by melting in a converter, continuous casting, and rolling.

  In the comparison method, the steel material is cut to a predetermined size, and the flat steel plate is used to adjust the width of the plate, groove processing of both width end portions, bending processing of both width end portions, and further U-shaped Forming, press-molding into a tubular shape by O-shaped molding, then tack-welding the butt portion with a gas shielded arc, etc., then performing inner seam welding and outer surface seam welding with submerged arc welding, etc. In order to increase the roundness, tube expansion is performed with an expander or the like.

  Further, the invention method is a tack welding process in which a tack heat welding and an outer seam welding are simultaneously performed using a combined heat source of a laser and a gas shield arc, and then an inner seam welding is performed, and then pipe expansion molding is performed. Is.

  Tables 2 to 4 show the welding conditions in the comparison method when the conventional technique is used, and Tables 5 to 8 show the welding conditions of the invention examples when the method of the present invention is used.

  In Tables 6 and 7, L1, M1, M2, M3, Wn, θ, Hn, and Ln indicate the dimensions of the same symbols in FIGS. 3 and 4, and M4 in FIG. The distance between the target position of the third electrode torch and the target position of the fourth electrode torch in the case where the fourth electrode torch is arranged further rearward of the gas shield arc torch positioned rearmost in the welding direction Indicates.

  In order to evaluate the occurrence of poor fusion and the weld zone toughness at low temperatures when welding was performed using the comparison method and the invention method shown in Table 7 in Tables 9 to 13, as shown in FIG. 2mmV notch Charpy test specimens were taken in the direction perpendicular to the thickness of the base metal, with the 0.5mm and 1.0mm positions as the notch position on the base metal side, with reference to the weld meeting part of the inner part and the inner surface weld part. The result of having performed each Charpy test at -30 degreeC by making each test piece into HAZ0.5mm and HAZ1.0mm is shown.

  Further, as welding conditions when using the inventive method, the groove angle on the outer surface side shown in Tables 9 to 13, the laser output, the focal length, the area (A) of the shield gas outlet, and the flow rate of the shield gas (B ) (B / A), (X1-X3) and (X4-X2) were each changed and welded.

  Moreover, the presence or absence of generation | occurrence | production of welding defects, such as the fusion | melting failure of a welding part and a melt-down at this time, the chemical analysis of the amount of nitrogen (N) in a weld metal, and the said Charpy test evaluated. In the table, based on these evaluations, the overall evaluation was made. Good was indicated by ◯ and defective was indicated by ×.

  Note that spattering during welding has a small effect on the quality of the welded part, but damages welding equipment such as laser optics, resulting in increased running costs. In addition, the evaluation of the presence or absence of spatter was also described.

  Regarding the nitrogen content in the weld metal, ◯ indicates the case where the nitrogen content is 150 ppm or less, and x indicates the case where the nitrogen content exceeds 150 ppm. It has been confirmed by experiments conducted in advance that the toughness of the weld zone exhibits a good value when the nitrogen content is 150 ppm or less.

  Moreover, the toughness evaluation of a welded part made the low temperature toughness of HAZ pass when the Charpy test result was 80 J or more. Regarding the presence or absence of defects in the welded portion, LP indicates that a fusion failure that is a welding defect has occurred at the groove bottom, and Bt indicates that the weld metal has melted down to the groove back, resulting in a welding defect. Evaluation was based on these.

  From these results, the groove angle on the outer surface side defined by the present invention is 20 ° or more and 40 ° or less, the laser output is 1.0 kW or more and 20 kW or less, and the above formulas (1) to (3) In Invention Examples 1 to 32 satisfying the conditions of (B / A), (X1-X3) and (X4-X2) defined in (1), the amount of nitrogen in the weld metal is low, and the low temperature toughness of HAZ is high. And it turns out that the favorable welding without a fusion defect is made | formed.

On the other hand, Comparative Example 1 using Comparative Method , Comparative Method 1 or Comparative Example 2 using the method of the present invention but welded under conditions deviating from the groove angle on the outer surface defined in the present invention. In No. 11, it can be seen that any of the high amount of nitrogen in the weld metal, the low temperature toughness of HAZ, the occurrence of poor fusion, etc. occurred, and good welding was not performed.

  As described above, according to the present invention, in manufacture of a UOE steel pipe, the X groove can be welded in a total of two passes to form a welded portion having excellent mechanical characteristics. Therefore, the present invention is an innovative one that achieves both improvement in productivity and securing of HAZ toughness, and is highly applicable in the UOE steel pipe manufacturing industry.

It is a figure which shows the aspect which welds the outer surface side of a steel pipe using the composite heat source of a gas shield arc and a laser. It is a figure which shows the aspect which supplies a shielding gas from the both sides of a welding line, and shields a molten pool. (A) shows a side aspect, (b) shows a plane aspect. It is a figure which shows the aspect of the groove shape of a steel pipe. It is a figure which shows the aspect of the poor fusion which generate | occur | produces in a narrow groove. The relationship between the B / A value and the analysis result of the amount of nitrogen (N) in the weld metal when welding is performed while changing the area A and the flow rate B of the gas nozzle opening of the shield gas is shown. It is a figure which shows the aspect which supplies a shielding gas from the both sides of a welding line, and shields a molten pool. It is a figure which shows the aspect at the time of extract | collecting a Charpy test piece from a welding part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steel pipe 2 Groove 3, 5, 6 Gas shield arc torch 4 Laser torch 7 Shield gas 8 Welding direction 9 Weld pool 10 Weld bead 11 Weld metal 12 Fusion failure t Steel pipe plate thickness doo Depth of groove on outer surface side df Route face length di Groove depth on the inner surface side φo Groove angle on the outer surface side φi Groove angle on the inner surface side

Claims (6)

In the manufacturing method of UOE steel pipe,
(A1) The first gas shield arc first electrode is arranged along the welding direction, and the laser target position is within 10 mm behind the target position of the arc of the first electrode on the weld line. Place the laser torch so that it comes in, arrange the gas shield arc second electrode behind it,
(A 2 ) The groove angle on the outer surface side of the X groove is 20 ° or more and 40 ° or less,
(A 3 ) The outer surface side of the X groove is welded in one pass using a combined heat source of a gas shield arc and a laser having an output of 1 kW to 20 kW, and then
(B) When the inner surface side of the X groove is welded in one pass using submerged arc welding, and the welding is completed in a total of two passes,
(D) A method of manufacturing a UOE steel pipe, characterized in that a shield gas having a flow rate (B) satisfying the following formula (1) is supplied from the gas nozzle ports on the left and right sides of the weld line.
3 ≦ B / A ≦ 30 (1)
A: Area of gas nozzle opening (cm ² )
B: Flow rate of shielding gas (liters / minute) 2. The UOE steel pipe manufacturing method according to claim 1, wherein a gas shield arc third electrode is disposed further rearward of the second electrode, or a gas shield arc fourth is disposed further rearward of the gas shield third electrode. by arranging the electrode, method of manufacturing the U OE steel you characterized by welding the outer surface side of the X GMA. The welding line is the X axis (unit: mm), the welding progress direction is the + direction, the opposite direction is the-direction, and the positions of the last heat source and the first heat source on the X axis are X1 and X2, respectively. When the rear end position and the head position on the X axis of the gas nozzle are X3 and X4, respectively, X1, X2, X3, and X4 satisfy the following expressions (2) and (3) at the same time: The manufacturing method of the UOE steel pipe according to claim 1 or 2 characterized by things.
5 (mm) <X1-X3 <200 (mm) (2)
5 (mm) <X4-X2 <100 (mm) (3) The UOE steel pipe manufacturing method according to any one of claims 1 to 3, wherein an installation angle of the gas nozzle is 10 ° or more and 80 ° or less with respect to a root face surface. The method for manufacturing a UOE steel pipe according to any one of claims 1 to 4 , wherein the gas shield arc is a consumable multi-electrode gas shield arc. The method of manufacturing a UOE steel pipe according to any one of claims 1 to 5 , wherein the laser is a laser having a focal length of 100 mm or more.

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