JP2008105062A - Manufacturing method of electric welded tube having excellent characteristic of weld zone - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of an electric welded tube having excellent characteristic of a weld zone capable of achieving the toughness of the weld zone requested for the electric welded tube intended for a line pipe of an oil well, and the strength of the weld zone requested for the electric welded tube intended for a casing pipe of the oil well. <P>SOLUTION: In the middle of a process in which a strip 11 is formed, its ends are butted to each other and subjected to the electric welding to form a tube, a taper shape in which an inclined surface 13 is continuous to an end face 12 substantially orthogonal to the width direction of the strip is given to the ends by the rolling of a grooved roll 4, and then, the electric welding is performed while the upset amount in a squeeze roll during the electric welding is set to be 0.5-2.0% of the outer circumferential length of the tube. The angle of inclination from the end face 12 of the inclined surface 13 is preferably 25-50°, and the length of the inclined surface in the thickness direction of the strip is preferably 20-40% of the thickness of the strip. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electric resistance welded tube manufacturing method having excellent welded portion characteristics. Here, the welded portion characteristics include welded portion toughness required for an electric-welded pipe for an oil well line pipe and weld strength required for an electric-welded pipe for an oil well casing pipe.

  Usually, pipes are roughly classified into welded pipes and seamless pipes. Welded pipes are manufactured by rounding strips (plates) and welding by joining the ends, as in the case of ERW steel pipes. Seamless pipes are made by drilling a lump of material at high temperatures, such as mandrel mills, etc. Rolled to produce. In the case of a welded pipe, it is generally said that the toughness of the welded part is inferior to that of the base material, and in the application of the pipe, guarantee of the toughness and strength of the welded part has 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.
Usually, a hot-rolled sheet as a base material of a welded pipe is subjected to component design, heat treatment, and the like in consideration of the base material characteristics after manufacturing the welded 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 cause of the failure of ERW welding is that an oxide called penetrator generated on the end face of the plate to be welded (end face in the plate width direction) remains without being discharged from the end face together with the molten steel during ERW welding. There were many cases where the toughness was lowered due to the cause and the strength was insufficient.

Therefore, conventionally, in order to remove the penetrator, which is the main cause of poor ERW welding, from the welded portion, techniques for actively discharging molten steel from the plate end surface have been intensively studied. For example, Patent Documents 1 to 5 describe examples in which the shape of the plate end surface is examined. In other words, the plate end surface usually has a substantially flat surface due to slitting or end surface grinding, but this is tapered before roll forming to improve the discharge of molten steel during welding by the processed end shape. It is aimed.
JP 57-31485 A Japanese Patent Laid-Open No. Sho 63-317212 JP 2001-17079A JP 2001-259733 A JP 2003-164909 A

However, in the above prior art, the taper processing means was used alone to give a tapered shape to the end portion, or the taper processing means were simply listed and introduced. The effect may not be sufficient to apply to the process, and further detailed examination is necessary.
The present invention solves the above-mentioned problems, and achieves welded portion toughness required for an electric seam pipe for oil well line pipes and weld strength required for an electric seam pipe for oil well casing pipes. An object of the present invention is to provide a method for producing an electric resistance welded tube having excellent characteristics.

The present invention made to achieve the above object is as follows.
1. In the course of the process of forming the strip material, butting the ends and electrowelding to form a pipe, the end portion has a tapered shape in which an inclined surface is connected to an end surface substantially perpendicular to the width direction of the strip material. After being applied by die roll rolling, the amount of upset in the squeeze roll during ERW welding is set to 0.5 to 2.0% of the pipe outer peripheral length, and ERW welding is characterized in that it has excellent weld characteristics. Sewing tube manufacturing method.

  2. The inclined surface has an angle of inclination of 25 to 50 degrees from the end surface, and the length of the inclined surface in the thickness direction of the band is 20 to 40% of the thickness of the band. The method for producing an electric resistance welded tube having excellent welded portion characteristics described in 1.

  According to the present invention, it is possible to manufacture an electric resistance welded tube that sufficiently satisfies the welded portion toughness required for an electric well pipe for an oil well line pipe and the weld strength required for an electric pipe for an oil well casing pipe. Can do.

Conventionally, in order to improve the toughness or strength of the ERW weld, a taper was given to the end of the strip before roll forming, but since it was not specified more specifically, these methods are sufficient. There were many cases where it was difficult to obtain the effect.
Therefore, the inventors first studied a method of imparting a taper by rolling using a hole roll (that is, hole roll rolling). When the hole-type roll is used, the shape of the end portion of the strip is easily obtained with high accuracy according to the hole type. In particular, it is necessary to constrain the strip during operation in order to provide a taper with high accuracy, while the end of the strip has a large flutter before roll forming or before roll forming, and it is possible to apply taper. was difficult. However, by using a hole-type roll, it is possible to efficiently give a taper while restraining the end portion of the band material. Further, since the equipment may be relatively small, it is easy to install before roll forming or in the middle of roll forming before ERW welding.

  For example, as shown in FIG. 2, the tapered shape is a shape in which an inclined surface 13 is connected to an end surface 12 that is substantially perpendicular to the width direction of the strip 11 (which forms an angle within 90 ° ± 0.4 ° with the width direction). It is. Here, α is an angle of the inclined surface 13 with respect to the average surface of the end surface 12 (referred to as a taper angle), and β is a length in the thickness direction of the inclined surface 13 (referred to as a taper depth). 2 (a) is the upper surface side of the strip end (tube inner diameter side), FIG. 2 (b) is the lower surface side of the strip end (tube outer diameter side), and FIG. 2 (c) is the top and bottom of the strip end. The case where a taper shape was given to both surface sides (both inner and outer diameter sides) was shown.

  FIG. 1 is a schematic view showing an example of a pipe making machine used for carrying out the present invention. This pipe making machine includes an uncoiler 1, a leveler 2, a roll forming machine 5, an electric seam welding machine (including a contact tip 6 and a squeeze roll 7), a bead portion cutting machine 8, a sizer 9, and a pipe cutting machine 10. The ERW steel pipe is manufactured through the strip (plate; pipe after end welding) 11. Reference numeral 3 denotes a first breakdown stand. In this example, the perforated roll 4 is installed immediately after the first breakdown stand 3 and is used to give a taper shape to the end of the band material. For example, it may be immediately after the leveler 2 (immediately before the roll forming machine 5).

However, it may be difficult to sufficiently improve the toughness or strength of the welded portion after ERW welding only by providing the tapered shape by the hole roll rolling.
When this cause is investigated in detail, an oxide that causes a penetrator, which is a welding defect, is formed on the end face of the strip at the stage where the end of the strip is heated before pressure welding (upset) during ERW welding. . This oxide floats on the surface of the molten steel at the stage where the end of the strip is melted, and part of the oxide is discharged together with the molten steel at the stage of pressure welding. At this time, if the end face of the strip is tapered, the molten steel is easily discharged, and at the same time, the penetrator can be effectively discharged.

However, the oxide on the end face of the strip that is the source of the penetrator is sequentially generated with the heating of ERW welding, so depending on the welding conditions, only the taper shape at the end of the strip will increase the toughness or strength after welding. In some cases, it could not be improved sufficiently.
Therefore, the present inventors have re-observed the ERW welding phenomenon in detail, and as a result, focused on the upset amount in the squeeze roll during ERW welding. That is, in order to effectively discharge the penetrator together with the molten steel, not only the taper shape at the end of the strip material but also the amount of upset during ERW welding is greatly affected.

In ERW welding, upsetting is performed with the squeeze rolls in contact with the end faces of the strips, but when the amount of upset changes, the discharge state of the molten steel varies greatly. That is, if the amount of upset by the squeeze roll is small, the discharge of the molten steel becomes slight, the discharge of the penetrator is insufficient together with the molten steel, and it tends to remain in the welded part even after the ERW welding.
Then, as a result of earnestly examining the amount of upset in the squeeze roll at the time of ERW welding, it was found that the value should be 0.5 to 2.0% of the pipe outer peripheral length. That is, with an upset amount of less than 0.5%, the molten steel is not sufficiently discharged and the penetrator tends to remain, and if a taper shape is applied to the end of the strip, the taper cannot be sufficiently crushed by the upset and the groove and There is a problem that remains. Further, when the upset amount exceeds 2.0%, there is a problem that the bead after the electric resistance welding, that is, the swelled portion of the discharged molten steel becomes too large to be sufficiently cut off after the electric resistance welding.

In addition, as a result of optimization of the taper shape, the angle of the inclined surface (taper angle) α and the direction of the thickness (plate thickness) of the inclined surface with respect to the average surface of the end surface substantially perpendicular to the width direction of the band material An appropriate range exists for the length (taper depth) β (see FIG. 2), that is, the taper angle should be in the range of 25 to 50 degrees, and the taper depth should be in the range of 20 to 40% of the plate thickness. I figured out.
If the taper angle is less than 25 degrees, the molten steel discharge from the central part of the plate thickness is insufficient and the penetrator remains, and the toughness and strength after ERW welding tend to decrease, while the taper angle exceeds 50 degrees. Then, the taper shape tends to remain as a flaw of the product pipe after the electric resistance welding. Also, if the taper depth is less than 20% of the plate thickness, the molten steel discharge at the center of the plate thickness becomes insufficient and the penetrator tends to remain. On the other hand, if the taper depth exceeds 40% of the plate thickness, The taper shape tends to remain as wrinkles of the product pipe after the electric resistance welding.

In Examples, a steel pipe having an outer diameter of 600 mm was manufactured by passing a steel strip having a steel width of 1920 mm × thickness 19.1 mm through a pipe making machine having the configuration shown in FIG. 1 or a modified version thereof. The manufacturing conditions were as follows.
(No. 1: Example of the present invention)
The pipe making machine shown in FIG. 1 was used. The end of the strip 11 was rolled using the hole roll 4 immediately after the first breakdown stand 3, and the taper shape shown in Table 1 was given to the upper and lower surfaces (both inner and outer diameter sides) of the strip. The amount of upset in the squeeze roll during ERW welding was set to the value shown in Table 1.

(No. 2: Example of the present invention)
In FIG. 1, the pipe making machine used was one in which the hole roll 4 was moved from immediately after the breakdown first stand 3 to immediately before the roll molding machine 5 and its hole shape was changed. The end portion of the strip 11 was rolled using this hole-shaped roll, and the taper shape shown in Table 1 was given to the upper and lower surfaces (both inner and outer diameter sides) of the strip end. The amount of upset in the squeeze roll during ERW welding was set to the value shown in Table 1.

(No.3: Comparative example)
As the pipe making machine, the one in which a cutting tool was arranged at the same place in place of the hole-type roll 4 in No. 3 was used. By cutting with the cutting tool, the taper shape shown in Table 1 was given to the upper and lower surfaces (both inner and outer diameter sides) of the end of the strip. The amount of upset in the squeeze roll during ERW welding was set to the value shown in Table 1.

(No.4: Conventional example)
The pipe making machine used was obtained by removing the perforated roll 4 in FIG. The shape of the end portion of the strip material before the ERW welding remains substantially rectangular. The amount of upset in the squeeze roll during ERW welding was set to the value shown in Table 1.
A test piece was cut out from a welded portion of a steel pipe manufactured under the above conditions, and a Charpy test was performed to evaluate the performance. As a Charpy test piece, JIS No. 2 mm V notch, sampled from 10 points with different pipe longitudinal directions, each with the length of the specimen taken in the circumferential direction of the pipe and the center of the notch length as the center of the weld thickness. Using the impact test piece, an impact test was performed at a test piece temperature of −46 ° C., and the absorbed energy and the brittle fracture surface ratio were measured. In addition, the absorbed energy: 125 J or more and the brittle fracture surface ratio: 35% or less were set as the allowable performance range. The results are shown in Table 1.

  From Table 1, in the present invention example, the impact strength (absorbed energy) of the welded portion is remarkably high, the brittle fracture surface ratio is small, the toughness is good, and the reliability of the product is high. In the conventional example, the impact strength (absorbed energy) of the welded portion is low, the brittle fracture surface ratio is large, the toughness is lowered, and the reliability of the product is poor. In the comparative example (No. 3), a groove remained in the welded portion after ERW welding, and the tube was rejected as a product.

It is a schematic diagram which shows an example of the pipe making machine used for implementation of this invention. It is a definition explanatory drawing of a taper angle and taper depth.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Uncoiler 2 Leveler 3 Breakdown 1st stand 4 Hole type roll 5 Roll forming machine 6 Contact tip 7 Squeeze roll 8 Bead part cutting machine 9 Sizer
10 pipe cutting machine
11 Strip (plate; pipe after end welding)
12 End face almost perpendicular to strip width direction
13 Inclined surface

Claims (2)

  In the course of the process of forming the strip material, butting the ends and electrowelding to form a pipe, the end portion has a tapered shape in which an inclined surface is connected to an end surface substantially perpendicular to the width direction of the strip material. After being applied by die roll rolling, the amount of upset in the squeeze roll during ERW welding is set to 0.5 to 2.0% of the pipe outer peripheral length, and ERW welding is characterized in that it has excellent weld characteristics. Sewing tube manufacturing method.   The inclined surface has an angle of inclination of 25 to 50 degrees from the end surface, and the length of the inclined surface in the thickness direction of the band is 20 to 40% of the thickness of the band. The method for producing an electric resistance welded tube having excellent welded portion characteristics described in 1.

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