JP5055843B2 - Manufacturing method of electric resistance welded tube with good weld characteristics - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a method for manufacturing an electric resistance welded tube having good welded portion characteristics, and in particular, a tube that requires toughness of a welded portion such as for oil well line pipes or a tube that requires welded portion strength such as an oil well casing pipe. The present invention relates to a method for manufacturing an electric resistance welded tube that can be preferably used for manufacturing a welded part and has good welded portion characteristics.

  Usually, pipes are roughly classified into welded pipes and seamless pipes. Welded pipes are manufactured by rolling plates (meaning strips; the same shall apply hereinafter) and welding the ends together, as in the case of ERW steel pipes. It is manufactured by rolling with a mandrel mill or the like. In the case of a welded pipe, it is generally said that the properties of the welded part are inferior to that of the base metal, and in the application of the pipe, guarantees of toughness and strength of the welded part have always been discussed for each application.

For example, in line pipes that transport crude oil, natural gas, etc., low temperature toughness is important because pipes are often laid in cold regions, and casing pipes are required to protect mining pipes in oil wells for crude oil mining. The strength of the tube is regarded as important.
In general, a hot-rolled sheet serving as a base material of a pipe is subjected to component design, heat treatment, and the like in consideration of the base material characteristics after the manufacture of the pipe, and characteristics such as toughness and strength of the base material are ensured.

However, since the characteristics of the welded part are greatly influenced by the electric resistance welding method more than the component design and heat treatment of the base metal, the development of the welding technique has been important.
The reason for the failure of ERW welding is that the oxide generated on the end face of the welded plate material called penetrator remains without being discharged from the end face together with the molten steel during ERW welding, and the toughness decreases due to this residual penetrator. There were many examples of insufficient strength.

Therefore, as a conventional technique, in order to remove the penetrator, which is the main cause of ERW welding failure, from the welded portion, a technique for actively discharging molten steel from the plate end surface of the welded portion has been intensively studied. For example, Patent Documents 1 to 4 describe examples of examining the shape of the plate end surface.
Further, in Patent Document 5, the width end of the plate is chamfered into various shapes for the purpose of facilitating the adjustment of the butt pressure of both side edges of the strip material during welding of the ERW pipe and enhancing the welding reliability. It is stated to do.
Japanese Unexamined Patent Publication No. 57-31485 JP 63-317212 A JP 2001-170779 JP 2003-164909 JP 2001-259733 A

Patent Documents 1 to 4 all intend to give a taper to the plate end surface and discharge the penetrator together with the molten steel. The reason for imparting the taper is considered to be because the shape is easily given to the end face of the plate. However, when a linear or flat taper is provided, there is a problem that it may not be sufficient for the discharge of defects such as oxides accompanying the discharge of molten steel.
Patent Document 5 discloses various chamfering shapes that facilitate adjustment of the butt pressure, but also discharges the penetrator together with the molten steel, and thereby improves the weld properties (particularly low temperature toughness). Is not described at all, it is completely unknown which of the various chamfered shapes disclosed therein can improve the welded portion characteristics (particularly low temperature toughness).

  An object of the present invention is to solve the above-mentioned problems and to provide a method for manufacturing an electric resistance welded tube with good welded portion characteristics, which can sufficiently promote the discharge of defects such as oxides accompanying discharge of molten steel.

  The present inventors diligently studied to solve the above problems, and as a result, obtained the following knowledge. In other words, the molten steel generated at the start of welding at the taped end face of the plate is small because the contact area is small, and the area of the welded part increases due to the upset (pressure welding) of ERW welding. Will increase. However, with the conventional taper shape, the discharge angle (discharge amount) of the molten steel is constant, so even if the molten steel discharge at the initial stage of welding is sufficient, the discharge at the latter stage of welding may be insufficient. It was found that it overflowed and solidified on the surface of the plate to become a lid, which could interfere with the molten steel that would later come out of the weld surface.

  Therefore, the present inventors diligently studied a method in which molten steel is always discharged satisfactorily with the lapse of time of welding. As a result, since there was little molten steel in the early stage of welding and molten steel increased in the latter stage of welding, it was grasped that the end face shape which always discharges about a constant molten steel was needed. As a result of examining various shapes, it has been found that the discharge of molten steel can always be improved by subjecting the plate end surface to R processing.

The present invention has been made based on this finding, and the gist thereof is as follows.
1. In the process of forming the strip, but joining both ends in the width direction to make a pipe by electro-welding and welding, on the lower surface side of the both ends in the width direction of the strip by cutting or grinding in the middle of forming the strip characterized in that to improve the weld low temperature toughness by welding after performing R processing which imparts the strip inside the R shape protruding convexly outwards, at -46 ° C. weld thickness center position Manufacturing method for ERW pipes for line pipes or casing pipes with good weld properties, with an absorbed energy of 125J or more and a brittle fracture surface ratio of 35% or less.

  When the R process is performed, the contact area increases rapidly with the passage of time in the initial stage of welding, so the discharge amount of molten steel increases, and the contact area gradually increases with the passage of time in the later stage of welding. The amount of molten steel is reduced. By these actions, the molten steel can be discharged stably, and the molten steel that has come out from the welded surface solidifies and becomes a lid that does not interfere with the molten steel that comes out later. .

As a result, the molten steel is sufficiently discharged from the end portion of the plate, and the penetrator can be sufficiently removed. As a result, the properties such as the toughness and strength of the welded portion can be satisfactorily maintained.
Therefore, according to the present invention, it is possible to sufficiently promote the discharge of defects such as oxides accompanying discharge of molten steel at the time of ERW welding, and to obtain extremely good weld toughness and weld strength.

  FIG. 1 is a schematic diagram of a pipe making facility showing an example of an embodiment of the present invention. In this pipe making equipment, a strip material (plate) 100 made of a steel strip is discharged by an uncoiler 1 and flattened by a leveler 2, and then the stand of the fin pass forming roll 6 is moved from the initial forming stage including the first stand 3 of breakdown. In the roll forming machine 5 to the final forming stage including, the forming is performed by gradually rounding the width of the band material and butting both ends of the width.

Next, the strip having the rounded width is pressed with a squeeze roll 8 while induction heating both ends of the rounded width with an induction heating means (for example, an induction heating coil) 7, Eggplant. The bead generated in the pressure contact portion (welded portion) of the tube is removed by cutting with the bead portion cutting means 9, and then fixed-diameter rolled with a sizer 10 and cut into a predetermined length with a tube cutting machine 11.
In this example, as a means for performing R processing, a grindstone polishing machine 4 is disposed immediately after the first breakdown stand 3 and is used to grind the grindstone in the embodiment as shown in FIG. so that performing R processing in the thickness direction lower end side of both ends. A cutting tool (not shown) may be used instead of the grindstone polishing machine 4.

In addition, although the R process of a board edge part may be the one side edge part of a board thickness direction, if it gives to both sides, an effect will be large.
When the R processing is performed with a hole-type roll such as an edger roll, it is difficult to obtain a desired shape because the plate end receives halfway plastic processing, but the desired shape can be obtained by cutting or grinding with a grindstone. Can be obtained as is.

  In addition, the R processing by cutting or grinding by the grinding wheel may be performed before the band material is formed (on the entry side of the roll forming machine 5 (on the exit side of the leveler 2)), but the initial forming stage in the roll forming machine 5 ( In particular, there is a possibility that the shape of the plate end portion changes in the first stand 3). Therefore, from the viewpoint of obtaining a desired shape as it is, it is preferable that the R processing by cutting or grindstone polishing is performed on the downstream side of the initial forming stage (particularly the first stand 3 of the rake down) in the roll forming machine 5.

  Further, instead of performing R processing by cutting or grinding with a grindstone, R processing may be performed by fin pass forming using a fin pass forming roll (fin for short) 6. In fin pass molding, for example, as shown in FIG. 3, the plate 100 is rounded to have a circular cross section, so that the plate end is strongly pressed by the fins 6. Therefore, by giving the desired R shape to the fins 6 in advance, the plate end shape can be made sufficiently close to the desired R shape.

Hereinafter, a description will be given based on examples.
As an example, a steel strip having a plate width of 1920 mm and a plate thickness of 19.1 mm is used as a strip, and an uncoiler 1, leveler 2, roll forming machine 5, electric welding machine (induction heating means 7 + squeeze roll 8), bead part cutting means 9 A steel pipe having an outer diameter of 600 mm was manufactured by a pipe making machine in which the sizer 10 was arranged as shown in FIG.

  A test piece was cut out from the welded portion of the manufactured steel pipe and a Charpy test was performed to evaluate the performance. Each Charpy test piece is taken from 10 points with different pipe longitudinal directions, the specimen length direction is taken in the pipe circumferential direction, the notch length center is taken as the weld thickness center position, and the JIS5 2mmV notch impact is taken. A test piece was obtained. An impact test was conducted at a specimen temperature of -46 ° C., and the absorbed energy and the brittle fracture surface ratio were measured.

In addition, the allowable energy performance was 125 J or more and the brittle fracture surface ratio was 35% or less.
(No. 1) As an example of the present invention, during the pipe making, immediately after the breakdown first stand 3 in the roll forming machine 5, grinding is performed on the lower surface side (to the pipe outer surface side) at both ends in the plate width direction. R; see FIG. 2) was given an R process with a radius of 9 mm. After that, through roll forming, electric resistance welding was performed, and the steel pipe was manufactured through the sizer 10. A test piece was cut out from the welded portion of the manufactured steel pipe and a Charpy test was performed.

(No. 2) As a reference example, in the above-mentioned pipe making, in the fin pass forming in roll forming, the shape of the fin 6 was devised, and R processing with a radius of 5 mm was given to the upper and lower both sides of both ends in the plate width direction. Thereafter, electric welding was performed, and a steel pipe was manufactured by passing through sizer 10. A test piece was cut out from the welded portion of the manufactured steel pipe and a Charpy test was performed.
(No. 3) As a comparative example, after the leveler processing before roll forming during the pipe making, from the vertical end surface (end surface in the plate width direction) on the upper surface side of both ends in the plate width direction, using a perforated roll A substantially linear taper was applied with an angle of 30 degrees and a vertical distance from the taper starting point to the plate surface of 3 mm. Thereafter, the steel sheet was roll-formed, electro-welded, and passed through the sizer 10 to produce a steel pipe. A test piece was cut out from the welded portion of the manufactured steel pipe and a Charpy test was performed.

(No. 4) As a conventional example, a steel pipe was manufactured by making the plate end face of a steel strip into a substantially rectangular shape (without R processing) and pipe-making in the above process. A test piece was cut out from the welded portion of the manufactured steel pipe and a Charpy test was performed.
Table 1 shows the results of measuring the Charpy impact value and the brittle fracture surface ratio by the Charpy test in each of the above examples.

  From Table 1, in the present invention example (R processing), the impact strength of the welded portion is high, the brittle fracture surface ratio is small, the toughness is good, and the reliability of the product is high. On the other hand, in the comparative example (linear taper processing), although it was within the allowable range of performance, the impact strength of the welded portion was low and the brittle fracture surface ratio was sometimes large. Further, in the conventional example (rectangular end face; neither R nor taper), the toughness is lowered and the reliability of the product is poor.

It is a schematic diagram of the pipe making equipment which shows an example of embodiment of this invention. It is a schematic diagram which shows one example of embodiment of R process by grindstone grinding | polishing. It is a schematic diagram which shows an example of embodiment of R process by fin pass shaping | molding.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Uncoiler 2 Leveler 3 Breakdown 1st stand 4 Grinding wheel polisher 5 Roll forming machine 6 Fin pass forming roll (fin)
7 Induction heating means 8 Squeeze roll 9 Bead section cutting means
10 Sizer
11 Pipe cutting machine
100 strip (plate)

Claims (1)

In the process of forming the strip, but joining both ends in the width direction to make a pipe by electro-welding and welding, on the lower surface side of the both ends in the width direction of the strip by cutting or grinding in the middle of forming the strip characterized in that to improve the weld low temperature toughness by welding after performing R processing which imparts the strip inside the R shape protruding convexly outwards, at -46 ° C. weld thickness center position Manufacturing method for ERW pipes for line pipes or casing pipes with good weld properties, with an absorbed energy of 125J or more and a brittle fracture surface ratio of 35% or less.

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