JP4682780B2 - 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 and 2 describe examples in which the shape of the end face to be welded is examined. 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.
JP 2001-259733 A Japanese Patent Laid-Open No. 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 end portions of the round width of the strip in the hole mold of the fin pass rolling roll. 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 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, as a cutting means in the middle of the process of forming an end-to-end portion of the strip and performing electro- welding welding. The upper and lower sets of cutting tools are arranged in a staggered manner in which one set of both end portions of the strip material to be abutted and the other set of cutting portions are arranged in a staggered manner. ERW pipe manufacture for line pipes or casing pipes with good weld characteristics, characterized by applying a 40 degree taper shape from the upper and lower surfaces of the strip to 6 mm in the upper and lower thickness direction, followed by ERW welding Is the method.

  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. Therefore, in order to obtain a desired tapered shape, the inventors decided to use a cutting means . In order to give the desired taper shape, there is a means for removing unnecessary portions or a means for changing the shape by plastic deformation. and around the cause protrusion of the excess thickness it is to be obtained shape, but the optimization of the tapered it is also necessary to consider the excess thickness portion thereof, by removing more unnecessary portion cutting, the excess thickness portion There is no need to consider the influence, and the taper shape can be easily optimized. In addition, in order to obtain an accurate taper shape, it is desirable to perform cutting while directly observing the shape online.

  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. The applied taper shape is subjected to ERW welding as it is, so that the molten steel is sufficiently discharged from the welded end portion with the desired taper and the penetrator can be sufficiently removed, resulting in good welding. Properties such as toughness and strength of the welded portion are remarkably improved. In addition, after the fin pass rolling, the cross section of the strip is almost circular, and both ends of the rounded width of the strip are extremely close to each other, so it may be difficult to secure a space for putting the grinding roll, In that case, it is good to give a taper with the cutting tool which can be processed even in a narrow space. Furthermore, by reducing the size of the grinding roll or installing small cutting tools and arranging them in a staggered manner in the direction of travel of the strip, a taper shape can be imparted to the end of the strip even in a narrow space.

  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.
In the embodiment, in common with the present invention example and the conventional example, a steel strip (band material) 20 having a width of 1920 mm × thickness of 19.1 mm is converted into an uncoiler 1, a leveler 2, and a roll as shown in FIG. A steel pipe (pipe) 30 having an outer diameter of 600 mm is passed through a pipe making machine in which a forming machine 5, an electric resistance welding machine (consisting of an induction heating part 6 and a squeeze roll (electric resistance welding part) 7), and a sizer 9 are sequentially arranged. Manufactured. 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 was conducted at -46 ° C., 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 , as shown in FIG. 1, cutting or grinding means 4 is provided on the exit side of the first breakdown stand 3 that performs bending near the end of the steel strip 20 during roll forming. A grinding roll 14 (see FIG. 4) in which the grinding wheel is formed into a roll shape is disposed, and the vertical end face 12 ( The angle from the corner of the vertical end surface 12 is 30 degrees, and the taper 13 is substantially linear from the corner of the vertical end face 12 to a position that is 5 mm inward in the vertical direction (thickness direction of the steel strip 20) to the inside of the steel strip (see FIG. 3). 3). Thereafter, the steel pipe 30 was manufactured through roll forming, electro-welding welding, and sizer rolling.

( Example of the present invention ) In the present invention example , as shown in FIG. 2, a set of upper and lower cutting tools 11 (see FIG. 3) is used as the cutting means 4 before the ERW welding machine after roll forming and fin pass rolling. A pair of cutting both ends of the steel strip 20 to be abutted and a pair of cutting the other end are arranged in a staggered arrangement, and the steel strip 20 is rounded by a cutting tool 11 during pipe forming. The angle from the vertical end surface 12 (refer to FIG. 3) is set to 40 degrees by cutting both ends of the width, and the steel strip is vertically inside and out from the corner of the vertical end surface 12 in the vertical direction (thickness direction of the steel strip 20). A substantially linear taper 13 (see FIG. 3) was applied to a position 6 mm to the side. Thereafter, the steel pipe 30 was manufactured by electric welding and sizer rolling.

(Conventional Example 1) As Conventional Example 1, the steel strip 20 having a substantially rectangular width at both end faces before pipe making is passed through a pipe making machine from which the grinding or cutting means 4 is removed in FIG. did.
(Conventional Example 2) As Conventional Example 2, a grinding wheel is formed in a roll shape on the exit side of the leveler 2 and the entrance side of the breakdown first stand 3 before roll forming in the pipe making machine used in Conventional Example 1. A grinding roll 14 is disposed, and both ends of the width of the steel strip 20 are ground by the grinding roll 14 during pipe making, so that the angle from the vertical end face 12 is 10 degrees, and the vertical end face 12 is perpendicular to the corner. A substantially linear taper 13 was applied up to a position 2 mm inward in the direction toward the inside of the steel strip. Thereafter, the steel pipe 30 was manufactured through roll forming, electro-welding welding, and sizer rolling.

  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.

表１より、従来例１及び従来例２による製品鋼管は、溶接部の衝撃強度が低く脆性破面率が大きくて、靭性が低下しており、製品の信頼性に乏しいのに対し、本発明例による製品鋼管は、溶接部の衝撃強度が高く脆性破面率が小さくて、靭性が良好であり、製品の信頼性が高いことが明らかである。

From Table 1, the product steel pipes according to Conventional Example 1 and Conventional Example 2 have low impact strength at the welded portion, high brittle fracture surface ratio, reduced toughness, and poor product reliability. It is clear that the product steel pipe according to the example has a high impact strength at the welded portion, a small brittle fracture surface ratio, good toughness, and high product reliability.

It is an ERW pipe manufacturing process figure which shows the example which grinds in the middle of the process of roll forming in a reference example . It is an ERW pipe manufacturing process figure which shows the example which cuts after the process of roll formation in the embodiment of this invention, and before the process of ERW welding. It is a schematic side view which shows a mode during the cutting of the edge part of a strip | belt material. It is a schematic diagram which shows an example of a grinding roll.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Uncoiler 2 Leveler 3 Breakdown 1st stand 4 Cutting or grinding (cutting or grinding means)
5 Roll Forming Machine 6 Induction Heating Section 7 Squeeze Roll (Electronic Welding Section)
8 Bead cutting machine 9 Sizer 10 Pipe cutting machine 11 Cutting tool 12 Vertical end face 13 Taper 14 Grinding roll 20 Steel strip (band)
30 Steel pipe (pipe)

Claims (1)

A band with a width of 1920 mm and a thickness of 19.1 mm is formed , and a pair of cuttings as a cutting means is used as a cutting means after fin pass roll rolling in the course of forming a pipe by abutting the ends and making an electro- welded weld. The cutting tool is arranged in a zigzag pattern in which one of both end portions of the band member to be abutted and the other cutting group are cut, and by the cutting means, the both ends of the band member are thickened from the upper and lower surfaces of the band member. A method for producing an electric-welded pipe for a line pipe or a casing pipe with good welded portion characteristics, characterized by applying a 40-degree taper shape in the vertical direction to a position of 6 mm both in the vertical direction and then performing an electric-resistance welding.

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