JP2006281313A - Method for producing welded steel tube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a welded steel tube easily applicable to the production of a spiral steel tube without performing large-scale equipment modification, and capable of remarkably improving the efficiency thereof. <P>SOLUTION: In the method for producing a welded steel tube, the butting parts in the width direction of hot rolled steel strips bent to a spiral shape are first subjected to submerged arc welding (SAW) at the inner face side in an inner face welding position P1 by an inner face welding machine, thereafter, the steel tube is conducted to a high frequency heating coil 30 located in the downstream side going one-half round along a welding line, so as to perform the preheating of the butting parts in the steel strips before outer face welding, thereafter, the outer face side is subjected to SAW at an outer face welding position P2 by an outer face welding machine. In this case, the surface temperature of the butting parts in the edge faces in the width direction of the steel sheets before the SAW is preferably controlled to ≥400°C. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a welded steel pipe capable of obtaining a high-speed and sound weld, and particularly to a method suitable for manufacturing a spiral steel pipe.

  Welded steel pipes are roughly classified into ERW steel pipes, forged steel pipes, and submerged arc welded steel pipes. The submerged arc welded steel pipe is usually a large diameter steel pipe, and the spiral steel pipe is a representative of the submerged arc welded steel pipe together with the UOE steel pipe.

  For example, as shown in FIG. 8, the spiral steel pipe is manufactured by forming a steel strip (steel plate) 2 in a spiral shape, and connecting the side edge butt portion of the steel strip (steel plate) with an inner surface welding machine 4 and an outer surface welding machine 6. And by submerged arc welding (hereinafter also referred to as SAW welding as appropriate) from the outer surface side. In the figure, 8 is an uncoiler, 10 is a coil end leveler, 12 is a cross welder, 14 is a leveler, 16 is a trimmer chopper, 18 is an edge shaver, 20 is a main pinch roll, 22 is an edge bender, 24 is a molding machine, 26 is an ultrasonic flaw detector and 28 is a traveling cutting machine.

  The production speed of submerged arc welded steel pipes is slower than that of other welded steel pipes. In the production of spiral steel pipes, multiple electrodes are used on the inner and outer surfaces, and welding is performed in one pass inside and outside to improve efficiency. I am trying.

  However, as the plate thickness increases, the welding speed decreases rapidly, and in the production of thick spiral steel pipes used for steel pipe piles, the line speed must be reduced and the line capacity cannot be fully used. Currently. This is because, as the plate thickness increases, the welding heat input increases, the pool increases, and it takes time to solidify the pool. It is because it flows and causes deterioration of a welded part shape.

  In order to solve this problem, a spiral steel pipe manufacturing method using welding other than submerged arc welding has been considered. When welding other than submerged arc welding is used in combination, the burden of submerged arc welding is reduced, and even if the plate thickness is increased, the welding heat input in submerged arc welding is kept small, and the pool does not increase. Therefore, the welding speed can be increased.

As a means for realizing such an idea, Patent Document 1 discloses a method of manufacturing a spiral steel pipe using electric resistance welding together.
Further, in Patent Document 2, a steel strip (steel plate) is formed into a spiral shape, and the first submerged arc welding is performed on the butt portion from the inner surface side, and the welded portion has a temperature of 150 ° C. or higher. In this state, a carbon dioxide arc welding is performed from the outer surface side, and then a second submerged arc welding is further performed. According to this method, the burden of the first and second submerged arc welding is reduced by carbon dioxide arc welding, and high-speed welding is possible.

JP 60-21180 A Japanese Patent Laid-Open No. 6-23553

  However, as disclosed in Patent Document 1, in the method of manufacturing spiral steel pipes that use electric seam welding together, there are technical problems related to equipment for performing electric seam welding on spiral pipe production lines, and the line speed and There is also a problem in welding quality due to a mismatch with the appropriate welding speed. In other words, the current spiral pipe production line is limited to a maximum line speed of 5 to 6 m / min due to various restrictions, while the appropriate welding speed of electric resistance welding is much faster than this, and the current spiral pipe production is In order to perform electric resistance welding on a line, the speed must be reduced to the line speed, and this causes a reduction in weldability. Therefore, at present, in addition to the problem of equipment technology, this problem of welding quality must be solved, which is very difficult to implement.

  On the other hand, in the welding method of Patent Document 2, it is difficult to synchronize the speed of carbon dioxide arc welding and the speed of submerged arc welding, and in addition to the conventional outer surface side and inner surface side submerged arc welding equipment, There is a problem that welding equipment is required.

  The present invention has been made in view of the above circumstances, and provides a method for manufacturing a welded steel pipe that can be easily applied to the manufacture of spiral steel pipes without significant modifications to the equipment and can greatly improve the efficiency thereof. The purpose is to do.

The inventors of the present invention pre-heated the butt portion of the steel strip (steel plate) at the time of submerged arc welding of the spiral steel pipe so as to have an appropriate temperature condition, so that the width and penetration depth of the weld bead portion, In addition, the present inventors have found that the amount of molten metal increases and completed the present invention. That is, the present inventors preheated the butt portion of steel strips (steel plates) of various thicknesses under various temperature conditions before submerged arc welding of the spiral steel pipe, and then various welding conditions (welding heat input, The shape of the bead part after welding was observed at (welding speed), and the following findings (1) to (5) were found.
In addition, about the butt | matching part (width direction both ends) of the steel strip (steel plate) 2, both the inner surface and the outer surface are processed into a predetermined groove shape in advance by the edge shaver 18 or the like shown in FIG. As shown in FIG. 1, after SAW welding on the inner surface side is performed at the inner surface welding position P1, the steel pipe is energized to the high-frequency heating coil 30 positioned about one and a half times along the welding line before the outer surface welding. The steel strip (steel plate) butt portion was preheated, and thereafter, the outer surface side SAW welding was performed by the outer surface welding machine 6 at the inner surface welding position P2.
Further, the frequency of the current applied to the high-frequency heating coil was 50 kHz, and the maximum output was 75 kW.
Furthermore, for SAW welding of the inner and outer surfaces, two electrodes were used, and the leading electrode was energized with a maximum of 2000 A, and the trailing electrode was energized with a maximum of 1500 A.

(1) The surface temperature of the butt portion of the steel strip (steel plate) before the outer surface SAW welding was raised to 400 ° C. or more by the high-frequency heating coil 30. In the case of no high-frequency heating, the surface temperature of the steel strip (steel plate) butt portion before the outer surface SAW welding was 200 ° C. to 250 ° C.

(2) The rate of increase in the amount of molten metal (ΔS / S ₀ (%)) due to preheating when the welding conditions were made constant was 11.4% on average in various plate thicknesses as shown in FIG. The amount of molten metal S ₀ here represents the amount of penetration of the welding material into the base material 40 as shown in FIG. 3, and the amount of increase in molten metal ΔS is the value before and after preheating as shown in FIG. This represents the amount of change in the amount of molten metal (S ₁ -S ₀ ).

(3) As shown schematically in FIG. 3, by preheating the base material 40 during SAW welding, the surface bead 42 has a higher height as shown in FIG. The amount of molten metal increases in the width direction W in a state where the depth (risk) H and the penetration depth D of the molten material into the base material 40 do not change so much, and as a result, the amount of increase (increase rate) of the molten metal is remarkably improved. To do. 4 is a diagram showing bead width variation (without preheating) in the conventional welding method, and FIG. 5 is a diagram showing bead width variation (with preheating) in the welding method of the present invention. As shown in the figure, it was found that by performing preheating at the time of SAW welding, the bead width variation is also suppressed as compared with the case where preheating is not performed. Here, the bead width fluctuations shown in FIGS. 4 and 5 are values measured at a bead length of 10 mm, and the numbers on the horizontal axis are the numbers. The plus or minus of the width variation is obtained by comparing the measured value with an average value of 0.

(4) On the other hand, when the amount of heat input during SAW welding is increased, as shown in FIG. 3A, the height (swell) H of the surface bead 42 increases, and the bead 42 In addition to the width d changing in a narrowing direction, the penetration depth D of the molten material into the base material 40 changes in the increasing direction. As a result, even if the amount of heat input is increased, the increase in the amount of molten metal is not as significant as when preheating is performed, but on the other hand, wrinkles called overlap occur at the boundary between the raised portion of the bead 42 and the base material 40. In addition to this, there is a risk that hot cracks (longitudinal cracks) may occur inside the beads 42.

(5) As a result of investigating the change in the increase rate of the amount of molten metal (ΔS / S ₀ (%)) when the welding speed was gradually increased with preheating, FIG. 6 (steel pipe after pipe making) As shown in FIG. 7 (dimension: 600Φ × 16t) and FIG. 7 (steel pipe dimensions after pipe making: 800Φ × 10t), it is assumed that the doubling rate of the molten metal is maintained at a level without preheating. It has been found that can be increased from 2.6 m / min to 3.0 m / min and from 3.9 m / min to 4.2 m / min.

The present invention made based on the above knowledge is as follows.
That is, in the method for manufacturing a welded steel pipe according to claim 1, a steel strip (steel plate) is formed into a tubular shape, and at least one width direction end face butt portion of the inner surface and the outer surface of the steel strip (steel plate) formed into the tubular shape is provided. After the heating, the submerged arc welding of the butt portion is performed.

  In the first aspect of the invention, after heating (preheating) at least one width direction end face butt portion of the inner surface and outer surface of the steel strip (steel plate) formed into a tubular shape, submerged arc welding of the butt portion is performed. As can be seen from the experimental data (see Table 1) described later, the weld bead shape can be improved, the product quality can be improved, and the welding speed can be increased. The efficiency can be improved. That is, the present invention can be easily applied to the manufacture of spiral steel pipes without major modification of equipment, and the efficiency can be greatly improved.

  Moreover, the manufacturing method of the welded steel pipe of Claim 2 is set to the invention of Claim 1, so that the surface temperature of the width direction end surface butt | matching part of the steel strip (steel plate) before submerged arc welding may be 400 degreeC or more. It is characterized by heating.

  In the invention according to the second aspect, even if the steel strip (steel plate) is not heated more than necessary, the advantageous effects described in the first aspect can be obtained. The “surface temperature at the end face butt portion of the steel strip in the width direction” here means the surface temperature on and near the butt face in the case of butt joining between steel strips (steel plates) not subjected to groove processing. In the case of a steel strip (steel plate) butt subjected to groove processing, it means the surface temperature on the butt surface and the surface temperature of the groove surface.

  According to a third aspect of the present invention, there is provided a method for manufacturing a welded steel pipe according to the first or second aspect of the invention, wherein the butt portion is heated by high frequency induction heating or burner heating.

  In the invention according to the third aspect, the butt portion can be heated with existing equipment and with a simple configuration, which is beneficial.

  According to the method for manufacturing a welded steel pipe of the present invention, the weld bead shape can be improved and the product quality can be improved. Moreover, since an increase in welding speed can be realized, the pipe making efficiency can be improved.

Next, examples of the present invention will be described.
FIG. 1 is a schematic explanatory view of a method for producing a welded steel pipe according to the present invention. As described above, in FIG. 1, for example, a width direction butt portion of a hot-rolled steel strip (steel plate) bent in a spiral shape using a forming machine 24 as shown in FIG. After SAW welding is performed on the inner surface side at the inner surface welding position P1, the steel pipe (steel plate) butt before outer surface welding is energized through the high-frequency heating coil 30 positioned on the downstream side of the steel pipe along the weld line for about one and a half turns. Then, SAW welding on the outer surface side was performed at the outer surface welding position P <b> 2 by the outer surface welding machine 6.

  Table 1 shows experimental results in which the surface temperature of the steel strip (steel plate) butt portion was preheated in the range of 400 ° C. to 500 ° C. by the high frequency heating coil 30. In addition, the steel strip (steel plate) used as the material of the spiral steel pipe is a commercially available hot rolled steel plate, and the steel material standard is SS400. The frequency of the current applied to the high frequency heating coil is 50 kHz, and the SAW heat input in the table represents the total heat input by two electrodes (leading electrode and trailing electrode).

  As can be seen from Table 1, according to the method for producing a welded steel pipe of the present invention, the surface properties of the steel pipe of various dimensions, high-frequency heating conditions, and welding conditions were excellent in comparison with the comparative example in which high-frequency heating (preheating) was not performed. A bead can be secured and the welding speed can be improved.

  In addition, although the above-mentioned Example has illustrated about the method of installing the high frequency heating coil 30 just before an outer surface side (upstream side), and heating a steel strip (steel plate) butting (preheating before welding), Similarly, preheating by the high-frequency heating coil 30 may be performed before welding. However, when preheating the steel strip (steel plate) before inner surface welding, the steel band (steel plate) butt is heated from room temperature, so compared to preheating before outer surface welding that can use the residual heat of internal welding. Large-capacity high-frequency heating equipment is required. Moreover, you may perform the heating by a burner other than the method by high frequency heating. Furthermore, the frequency of the high-frequency current and the electric energy (voltage × current) applied to the high-frequency heating coil when performing high-frequency heating are such that the surface temperature of the butt portion of the steel strip (steel plate) before SAW welding is a predetermined temperature, as will be described later Any setting may be used as long as it becomes.

  Moreover, in FIG. 1, although the groove processing is made about the width direction both ends butt | matching part of the steel strip (steel plate) before inner and outer surface SAW welding, no matter what the groove shape is, the present invention Even if there is no groove processing, there is no problem in the implementation of the present invention. Regarding SAW welding, the method of two electrodes is adopted in the examples of Table 1, but a multi-electrode exceeding two electrodes may be adopted. Furthermore, regarding the thickness and type of steel strip (steel plate), any steel strip (steel plate) used for spiral steel pipes is not particularly limited in the implementation of the present invention.

  Further, the surface temperature of the butt portion of the steel strip (steel plate) before SAW welding needs to be kept at 400 ° C. or higher, but even if heated to a higher temperature than necessary, there is no difference in the effect of the present invention. It may be in the range of ˜550 ° C. Note that the surface temperature of the steel strip (steel plate) butt here refers to the surface temperature on and near the butt surface in the case of butt welding between steel strips (steel plates) not subjected to groove processing. In the case of a steel strip (steel plate) butt subjected to pre-processing, the surface temperature on the butt surface and the surface temperature of the groove surface are indicated.

  The present invention can be applied to welding of various steel pipes including spiral steel pipes.

It is the schematic of the manufacturing process of the welded steel pipe of this invention. It is a figure which shows the influence which it has on the molten metal amount increase rate of the preheating in the manufacturing method of the welded steel pipe of this invention. It is explanatory drawing of the mechanism of the molten metal amount increase by preheating. It is a figure which shows the bead width fluctuation | variation (without preheating) in the conventional welding method. It is a figure which shows the bead width fluctuation | variation (with preheating) in the welding method of this invention. It is a figure which shows the relationship between the welding speed in the manufacturing method of the welded steel pipe of this invention, and the amount of molten metal increase (steel pipe dimension after pipe making: 600 (PHI) x16t). It is a figure which shows the relationship between the welding speed in the manufacturing method of the welded steel pipe of this invention, and the amount of molten metal increase (steel pipe dimension after pipe making: 800 (PHI) x10t). It is a perspective view which shows an example of the manufacturing process of a spiral steel pipe.

Explanation of symbols

2 Steel strip (steel plate; steel pipe)
4 inner surface welding machine 6 outer surface welding machine 30 high frequency heating coil

Claims (3)

  A steel strip is formed into a tubular shape, and after heating at least one width direction end face butt portion of the inner surface and outer surface of the steel strip formed into the tubular shape, submerged arc welding of the butt portion is performed. Production method.   The method for manufacturing a welded steel pipe according to claim 1, wherein the steel strip is heated so that the surface temperature at the end face butt portion in the width direction of the steel strip before submerged arc welding is 400 ° C. or higher.   The method of manufacturing a welded steel pipe according to claim 1 or 2, wherein the butting portion is heated by high frequency induction heating or burner heating.

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