JP4682779B2 - ERW pipe manufacturing method with good weld characteristics - Google Patents

Description

  The present invention relates to a method for manufacturing an electric resistance welded tube having good welded portion characteristics, and particularly, the strength of a welded portion such as a pipe that requires toughness of a welded portion, such as an oil well line pipe, or a casing pipe of an oil well. This is related to a manufacturing method for pipes that are required.

  Usually, the pipe is roughly classified into a welded pipe and a seamless pipe. The welded pipe is manufactured by rounding the width of the strip material and welding by welding both ends of the rounded width, as in the case of an ERW steel pipe, and the seamless pipe drills a lump of material at a high temperature, It is manufactured by rolling with a mandrel mill. 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 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 pipe laying sites often hit cold regions, and casings for protecting mining tubes in oil wells for crude oil mining Pipes are needed and the strength of the pipes is important.
Usually, a hot-rolled sheet that is 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 pipe is manufactured, 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, it is important to develop a welding technique.
As a cause of poor ERW welding, the oxide generated on the welded end face, called a penetrator, remains without being discharged from the end face together with the molten steel during ERW welding. There were many examples of insufficient strength.

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 welded end face have been intensively studied. For example, Patent Documents 1 to 5 describe examples of examining the shape of the welded end face. In other words, the welded end face is generally rectangular due to slits and end face grinding, but this is tapered before roll forming, and the processed end shape improves the discharge of molten steel during welding. It is aimed.
Japanese Unexamined Patent Publication No. 57-31485 JP 63-317212 A JP 2001-170779 JP 2001-259733 A JP 2003-164909

  On the other hand, in the manufacturing process of the electric resistance welded tube, the band material is roll-formed and then subjected to electric resistance welding. In this roll forming, in order to make the strip into a tube, in the vicinity of both ends of the width of the strip, bending in the circumferential direction, or to maintain good butting accuracy of the welded end in ERW welding In roll forming called fin pass rolling, a step of constraining both end portions of the strip rounded width to make the cross section of the strip close to a circle is necessary.

In these roll forming processes, for example, if bending is applied in the middle of roll forming, the taper shape processed before roll forming is distorted, resulting in an irregular end shape and sufficient molten steel cannot be discharged during ERW welding. It cannot be removed.
Further, in the above-described fin pass rolling, in order to make the cross section of the strip whose width is rounded into a circular shape, it is necessary to sufficiently fill both ends of the strip whose width is rounded in the hole mold of the roll for fin pass rolling. For this reason, the end portion is strongly pressed by the fin. As a result, the taper processed before roll forming is crushed and a sufficient amount of taper cannot be secured, and the taper shape depends on the fin pass rolling conditions, making it difficult to predict the shape. As a result, the molten steel could not be discharged sufficiently during the ERW welding, the penetrator could not be removed sufficiently, and it was extremely difficult to maintain good welding quality.

  Accordingly, the present invention provides an electric sewing machine with good welded portion characteristics that can reliably form the desired taper shape at both ends of the rounded width of the strip immediately before electric welding and can maintain good welding quality. An object is to provide a method for manufacturing a pipe.

  As described above, all of the conventional techniques taper both end faces of the width of the strip before roll forming. This is because the end of the width of the strip is in a flat state, which is considered because it is easy to process the end, but on the other hand, because bending and fin pass rolling are added in the middle of roll forming, Immediately before welding, it was extremely disadvantageous to ensure that both ends of the rounded width of the strip were in the desired shape.

Therefore, the inventors have studied to perform taper processing of the welded end portion of the band material by a process that does not cause the above-mentioned problem, and have made the present invention.
That is, the present invention forms a band material having a width of 1920 mm × thickness of 19.1 mm , and in the course of fin pass roll rolling , in the middle of the process of forming a pipe by abutting the end portions and performing electric resistance welding , electric resistance welded to the upper and lower sides 6mm grooved roll which imparted a linear taper of 40 degrees in a range of after arranged in a zigzag pattern, imparted with tapered rolling by the grooved rolls is subjected to an end portion of the strip material This is a method for producing an electric resistance welded pipe for a line pipe or a casing pipe with good weld characteristics, characterized by welding.

  According to the present invention, the shape of the both ends of the rounded width of the strip just before the ERW welding is surely formed into a desired taper shape, and the welding quality can be kept good, so that the remarkably good weld toughness and An electric resistance welded tube having welding strength can be obtained.

In the present invention, the forming of the strip is to round the width of the strip in a stepwise manner so that the cross section of the strip is circular, and the forming process is performed near both ends of the width of the strip. A roll forming initial stage in which the bending process is performed, and a fin pass rolling stage in which the strip is finally finished into a circular cross section.
First, bending in the vicinity of the end of the width of the strip is performed at the initial stage of roll forming. Therefore, after the end portion is bent, if the end portion is tapered, the taper shape is hardly distorted by the bending, and a good taper shape can be maintained. However, the end portion after the bending process is gently bent, and it is difficult to process the taper shape as desired by the end removing means such as grinding. It is desirable to grind while directly observing the shape online, but it is difficult due to the adverse effects of the lubricant and cooling water supplied, and as a result, there is only a means to predict the shape, so it is processed to the desired taper shape That's difficult. In addition, since the cross section of the strip gradually approaches a circular shape, both ends of the width of the strip are brought close to each other, so that it is difficult to attach a grinding device to the narrow gap.

  Therefore, as a result of intensive studies, the inventors installed a hole roll in the middle of the molding process, and matched the hole mold shape to the appropriate shape, that is, the target shape of the welded end of the strip, As a result, it was found that even if both ends of the width of the strip are gently bent, it is sufficiently possible to impart a desired tapered shape to both ends. That is, if it is a perforated roll, by pre-determining and processing the roll perforated shape, both ends of the width of the band material will offset the influence of bending to fill the perforated form of the perforated roll, It is possible to give a desired tapered shape to both ends.

Next, in fin pass rolling, when both ends of the strip being rolled are subjected to strong pressure, it is preferable to taper both ends of the strip that has been subjected to fin pass rolling. In addition, after fin pass rolling, the cross section of the strip has a substantially circular shape, and both ends of the rounded width of the strip are extremely close to each other. Was extremely difficult. Therefore, as described above, the inventors installed a perforated roll after fin pass rolling (that is, after the forming process and before the ERW process) and set the perforated shape to an appropriate one, that is, It was grasped that it was sufficiently possible to give the desired tapered shape to both ends of the rounded width of the band material by matching with the target shape of the welded end of the band material. In other words, a perforated roll can be miniaturized, and even if the gap between both ends of the rolled material is extremely small, the perforated rolls are arranged in a staggered manner in the direction of travel of the strip. Then, by pre-determining and processing the roll hole shape suitable for this arrangement, both ends of the strip material having a rounded width fill the hole mold of the hole roll, and the end is tapered as desired. The shape can be given.

  By these, it becomes possible to make the shape of the both ends of the rounded width of the strip just before welding into a desired tapered shape, and the molten steel is sufficiently discharged from the end, and the penetrator can be sufficiently removed. This makes it possible to favorably maintain characteristics such as toughness and strength of the welded portion.

Hereinafter, a description will be given based on examples.
Here, a steel strip (band material) 20 having a width of 1920 mm and a thickness of 19.1 mm is made into an uncoiler 1, a leveler 2, a roll forming machine 5, an electric resistance welding machine (induction heating section 6) as shown in FIG. 1 or 2. And a steel pipe (tube) 30 having an outer diameter of 600 mm. 1 and 2, 8 is a bead cutting machine, and 10 is a pipe cutting machine.

  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 positions in the longitudinal direction of the pipe, the length direction of the test piece is parallel to the circumferential direction of the pipe, the center of the notch length is taken as the center position of the weld thickness, and JIS 5 As a 2 mm V notch impact test piece of No. 1, an impact test at −46 ° C. was performed, and the absorbed energy and the brittle fracture surface ratio were measured. The acceptable performance range was an absorbed energy of 125 J or more and a brittle fracture surface ratio of 35% or less.

( Reference Example ) In the reference example , in the perforated roll 4 having the shape shown in FIG. 3, in the taper regions 13 and 14 in the range from the corner of the vertical end face 15 to the position of 5 mm in the vertical direction of the vertical end face 15. In addition, a perforated roll 4 for a reference example , which is provided with a substantially linear taper with an angle from the vertical end surface 15 (that is, a perforated taper angle of 11 and 12) of 30 degrees, is prepared, as shown in FIG. 1, in the middle of the process of roll forming, it is disposed on the outlet side of the breakdown first stand 3 for bending near both ends of the width of the ribbon 20, during the pipe-making, reference By rolling both end portions of the width of the band member 20 with the hole roll 4 for an example , a desired taper shape was given to the upper and lower portions of the end portion. Thereafter, the steel pipe 30 was manufactured through roll forming, electro-welding welding, and sizer rolling. A test piece was cut out from the welded portion of the manufactured steel pipe and a Charpy test was performed.

( Example of the present invention ) In the example of the present invention , in the perforated roll 4 shown in FIG. 3, in the taper regions 13 and 14 in the range from the corner of the vertical end surface 15 to the position of 6 mm in the vertical direction of the vertical end surface 15. A hole roll 4 for an example of the present invention , which is provided with a substantially linear taper with an angle from the vertical end surface 15 (that is, hole taper angles 11 and 12) of 40 degrees, is prepared. As shown in FIG. 2, after the roll forming process, after the final stage of the fin pass rolling stand of the roll forming machine 5 and before the induction heating unit 6 which is the front stage of the electric resistance welding machine, By rolling both ends of the rounded width of the strip 20 with the perforated roll 4 for the present invention during pipe making, a desired taper is formed on the upper and lower portions of the end. Added shape. Thereafter, the steel pipe 30 was manufactured by electric welding and sizer rolling. A test piece was cut out from the welded portion of the manufactured steel pipe and a Charpy test was performed.

(Conventional Example 1) As Conventional Example 1, a steel strip 20 (with the same steel type and size as the present invention example) having both ends of the width substantially rectangular before pipe making was removed from the perforated roll 4 in FIG. The steel pipe 30 was manufactured through a pipe making machine. A test piece was cut out from the welded portion of the manufactured steel pipe and a Charpy test was performed.
(Conventional Example 2) As Conventional Example 2, in the perforated roll 4, the vertical end face is within the taper regions 13 and 14 in the range from the corner of the vertical end face 15 to the position of 2 mm in the vertical direction of the vertical end face 15. A perforated roll 4 provided with a substantially linear taper whose angle from 15 is 10 degrees is prepared, and this is applied to the leveler 2 before roll forming in the pipe making machine used in the conventional example 1. Later, it is arranged on the entrance side to the first stand 3 for breakdown, and during pipe making, both ends of the width of the strip 20 are rolled to give a taper shape, roll forming, electro-welding welding, sizer The steel pipe 30 was manufactured by rolling. 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 in the welded portion of the steel pipe manufactured by these.

According to Table 1, the product steel pipe according to the conventional example has a low impact strength at the welded portion and a high brittle fracture surface ratio, and the toughness is reduced. It is clear that the impact strength of the weld zone is high, the brittle fracture surface ratio is small, the toughness is good, and the reliability of the product is high.

In a reference example , it is an ERW pipe manufacturing process figure which shows the example which rolls with a perforated roll in the middle of the process of roll forming. It is an ERW pipe manufacturing process figure which shows the example which performs the rolling by a hole-type roll after the process of roll formation in the embodiment of this invention, and before the process of ERW welding. It is a side view which shows an example of the hole-type roll used for this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Uncoiler 2 Leveler 3 Breakdown 1st stand 4 Hole type roll 5 Roll forming machine 6 Induction heating part 7 Squeeze roll (electro-sewing welding part)
8 Bead cutting machine 9 Sizer 10 Pipe cutting machine 11, 12 Hole type taper angle 13, 14 Taper area of hole type roll 15 Vertical end face 20 Steel strip (band)
30 Steel pipe (pipe)

Claims (1)

In the process of forming a strip with a width of 1920 mm and a thickness of 19.1 mm , butting the ends together to form a pipe by electro- welding, and after fin pass roll rolling, within a range of 6 mm above and below the vertical end face the grooved roll which imparted a linear taper of 40 degrees arranged in a zigzag pattern, and characterized in that electric resistance welding after applying a tapered rolling by the grooved rolls is subjected to an end portion of the strip material This is a method for manufacturing ERW pipes for line pipes or casing pipes with good weld characteristics.

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