JP2007319869A - Highly efficient method of producing electric resistance welded tube having good weld zone characteristic - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly efficient method of producing an electric resistance welded tube having good weld zone characteristics by which discharge of defects such as oxides resulting from discharge of molten steel can be sufficiently promoted, and degradation in the production efficiency can be prevented. <P>SOLUTION: In a process of forming a band material 100, butt-jointing its ends in the width direction and subjecting the material to electric resistance welding to form a tube, a corner part of any one of upper and lower sides (preferably the upper side) of the ends in the width direction is rounded by cutting or grinding by a grinding machine (a grinding means 4), and a corner part on the other side (preferably the lower side) is radiused by a fin-pass forming (a fin pass forming roll 6) while forming the band material. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a high-efficiency manufacturing method for electric resistance welded pipes with good welded part characteristics, and particularly, the strength of welded parts such as pipes that require toughness of welded parts for oil well line pipes or casing pipes of oil wells is required. The present invention relates to a high-efficiency manufacturing method for an electric resistance welded tube having good welded portion characteristics, which can be preferably used for manufacturing a welded tube.

  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, 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 planar taper is provided, there has been a case where it is not sufficient for discharging defects such as oxides accompanying 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 unclear which of the various chamfered shapes disclosed therein improves weld properties (particularly low temperature toughness).

In an actual electric resistance welded tube manufacturing process, various thickness plates are roll-formed into a tube. When a means for giving a taper shape to the plate end is used alone, for example, it is necessary to adjust the position for installing cutting tools or grinding rolls with an accurate interval equivalent to the plate thickness. It was decreasing.
Accordingly, the object of the present invention is to provide a high-efficiency manufacturing method for an ERW pipe that can sufficiently promote the discharge of defects such as oxides accompanying discharge of molten steel, and that does not involve a decrease in manufacturing efficiency, and that has good weld joint characteristics. And

The present invention that has achieved the above object is as follows.
1. In the process of forming a band material, butting both ends in the width direction and electro-welding to form a pipe, the corner on either the upper or lower side of the width direction both ends is cut or grinded by grinding stone A high-efficiency manufacturing method of an electric resistance welded tube with good welded portion characteristics, characterized in that R processing is performed, and a corner portion on the other surface side is subjected to R processing by fin pass forming in the middle of forming a band material.

2. The above-mentioned item is characterized in that the corner on the upper surface side of the strip that becomes the inner diameter side of the tube is R-processed by the above-mentioned cutting or grindstone polishing, and the corner portion on the lower surface side of the strip that becomes the outer diameter side of the tube is R-processed by the above-mentioned fin pass molding. 2. A high-efficiency manufacturing method of an electric resistance welded tube having good weld-part characteristics according to 1.
3. 3. A highly efficient method for producing an electric resistance welded tube having good weld joint characteristics according to item 1 or 2, wherein the radius R of the R shape provided by the R processing is set to 20 to 50% of the thickness of the strip.

  According to the present invention, the shape of the both ends in the width direction of the band material to be abutted at the time of ERW welding is an R shape, and the R shape is separately applied to the upper surface side corner portion and the lower surface side corner portion of the band material. By giving it by the R processing means, it becomes possible to produce an ERW pipe excellent in welded portion characteristics (particularly low temperature toughness) with high efficiency.

Hereinafter, the present invention will be described in detail in comparison with the prior art.
As described above, the cause of the failure of ERW welding is that the oxide generated on the plate end face called penetrator remains without being discharged from the end face together with the molten steel during ERW welding, and the toughness is caused by this remaining penetrator. There were many cases where the strength decreased and the strength was insufficient.
Therefore, all of the conventional techniques intended to taper 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 given, there are cases where it is not sufficient for discharging defects such as oxides accompanying discharge of molten steel.

  In order to clarify this cause, the present inventors have intensively studied and found the following. In other words, the molten steel generated at the start of welding on the plate end face with taper 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, in the conventional taper shape, the discharge angle (discharge amount) of the molten steel is constant, so even if the molten steel discharge near the end of the plate thickness is sufficient, the discharge near the center of the plate thickness may be insufficient. Thus, it was found that the molten steel overflows and solidifies on the plate surface to become a lid, which may interfere with the molten steel that is about to come out from the welding surface later.

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, the amount of molten steel was small at the time of welding near the center of the plate thickness, and the amount of molten steel increased at the time of welding near the plate thickness end.
Based on this result, various shapes were examined, and it was found that the discharge of molten steel can always be improved by subjecting the plate end surface to R processing. That is, when the R processing is performed, the contact area increases rapidly with the passage of time when welding near the center of the plate thickness, so that the discharge amount of molten steel increases, and even when the time passes when welding near the end of the plate thickness. Since the contact area gradually increases, the discharge of molten steel decreases. 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.
Further, the R processing of the plate end portion is effective when applied to both sides in the plate thickness direction (corner portions on both the upper and lower surfaces).
In addition, when the R processing is performed with a perforated roll, it is difficult to obtain the desired shape because the plate end receives halfway plastic processing, but the desired shape is obtained as it is by cutting or grinding with a grindstone. It is possible. In fin pass molding, the plate is rounded to have a circular cross section, and the plate end is strongly pressed by the fin. Therefore, by giving the desired R shape to the fins in advance, the plate end shape can be made sufficiently close to the desired R shape.

  Therefore, since the plate is substantially flat on the roll forming entry side, it is preferable to give an R shape by cutting or grinding with a grindstone. These R-shaped imparting means require an installation space because the apparatus is relatively large, and are difficult to install because the interval between the plate end portions becomes narrow during or after roll forming. In addition, since it is difficult for a cutting or grinding apparatus to restrain the plate up and down by itself, accuracy of the apparatus installation position is required together with an apparatus that maintains the positional accuracy through which the plate passes.

  Therefore, it is necessary to increase the rigidity of the gantry of the apparatus, and a larger installation space is required. Here, when both the upper and lower ends of the plate (the corners on the upper and lower surfaces) are cut or grinded, in the fin pass rolling in the middle of roll forming (meaning of fin pass forming, the same applies hereinafter), in order to fill the fin pass rolling roll with the plate, There is a case where the desired shape is not obtained because the R shape applied in advance is crushed due to the plate edge being strongly pressed. Therefore, it is better to give a large R shape in advance in consideration of the crushing of the end of the plate in fin pass rolling, but the R shape is given to both the upper and lower end portions (upper and lower side corners) of the plate. Since it is difficult to obtain a large R shape due to the limitation of the plate thickness, it is preferable to cut or grind only one side (upper or lower corner).

Next, with respect to the other end portion (corner portion on the other surface side) not imparted with the R shape, the R shape was imparted by utilizing fin pass rolling. For the above reason, the R shape is given to only one side. Therefore, in order to give the R shape to both ends, the opposite side R shape may be given during or after roll forming.
Therefore, the present inventors have paid attention to the fact that the end portion of the plate is easily crushed by the above-described fin pass rolling, and decided to utilize this. That is, if an R shape is imparted to the fins of the fin pass rolling roll, and the angle and the position where the plate edge hits are optimized according to the drawing amount (upset amount) of the fin pass rolling, the R shape is formed before the roll forming. An R shape can also be imparted on the opposite side of the plate end portion to which the is imparted. Since this is performed by fin pass rolling itself, even if the distance between both end portions in the plate width direction, which is rounded and narrowed by roll forming, is short and close, sufficient processing is possible.

In this way, an R shape can be imparted to the upper and lower ends of the plate (corners on the upper and lower surfaces of the plate) immediately before the electric welding.
In addition, R processing by cutting or grinding may be applied to the corner on the upper surface side of the plate so that the relatively large apparatus does not interfere with the table on the roll forming entrance side. Since it becomes the outer surface side (outer diameter side) of the tube, it is preferable to apply R processing to the corner portion on the lower surface side by changing the fin shape of the fin pass rolling.

  In addition, as a result of optimization of the R shape just before the ERW weld using the above cutting or polishing and fin pass rolling, it is understood that the radius R of R processing should be 20 to 50% of the plate thickness. did. In other words, if the radius R of the R processing immediately before electric seam welding is less than 20% of the plate thickness, the molten steel discharge from the central portion of the plate thickness is somewhat insufficient, and the penetrator remains somewhat. This is because the strength slightly decreases.

  Further, if the radius R is more than 50% of the plate thickness, the distance in the plate width direction of the R processed portion becomes too small or too large. If it is too small, the molten steel discharge from the center portion of the plate thickness becomes insufficient and the penetrator remains. However, the toughness and strength after ERW welding will be reduced. On the other hand, if it is too large, it will be difficult to upset and the pipe thickness will be insufficient near the boundary between the welded part and the base metal part. Phenomenon of less than thickness) is likely to occur.

  Hereinafter, a description will be given based on examples. In the embodiment, the pipe making facility shown in FIG. 1 or a part of it was changed. This pipe making equipment includes an uncoiler 1, leveler 2, roll forming machine 5, induction heating means (induction heating coil) 7, squeeze roll 8, bead part cutting means (bead part cutting bite) 9, sizer 10, pipe Cutting machines 11 are arranged in this order. The roll forming machine 5 is formed by arranging a plurality of roll stands from a rough forming stage including the first breakdown stand 4 to a finish forming stage including the fin pass forming roll 6.

  In this pipe making equipment, the strip material (plate) 100 is discharged by the uncoiler 1 and flattened by the leveler 2, and then the width is measured by a plurality of roll stands from the rough forming stage to the finish forming stage of the roll forming machine 5. Are gradually rounded, and finish forming is performed by the fin pass forming roll 6. In addition, since it is from the breakdown 1st stand 4 that the width | variety of the strip | belt material 100 begins to be substantially rounded, before roll forming, it is the entrance side of the breakdown 1st stand 4 from the leveler 2 exit side. Point to.

Both ends in the width direction (open pipe circumferential direction) of the strip 100 that has become an open tubular shape after finish molding are heated by induction heating means 6 and pressure-welded (electro-sewn welding) by a squeeze roll 8 to form a pipe. After this bead is cut and removed by the bead cutting means 9, the pipe is subjected to constant diameter rolling with a sizer 10 and cut into a predetermined length with a pipe cutting machine 11.
1, as an example of the embodiment of the present invention, a grindstone polishing means 3 for performing R processing on a corner on the upper surface side of the plate by grinding stone polishing (see FIG. 2) is arranged on the roll forming entrance side. At the same time, an R shape is applied to the fin corners of the fin pass forming roll 6 for R processing (see FIG. 3) of the corners on the plate lower surface side (tube outer diameter side) by fin pass forming.

As a strip, a steel strip with a plate width of 1920 mm × plate thickness of 19.1 mm and a steel strip with a plate width of 1920 mm × plate thickness of 15.3 mm are used in this order. ERW pipe) was manufactured.
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.
The manufacturing conditions were as follows (No. 1 to 4).
(No. 1) As an example of the present invention, the pipe was made using the pipe making equipment of FIG. During pipe making, an R shape was imparted to the corner portion on the upper surface side of the plate by grinding the grindstone before roll forming, and then an R shape was imparted to the corner portion on the lower surface side (tube outer diameter side) by fin pass molding. The radius R of the imparted R shape was 7 mm (47% of the 19.1 mm plate thickness, 46% of the 15.3 mm plate thickness).

When the plate thickness was switched from 19.1 mm to 15.3 mm, fine adjustment was performed to move the position of the polishing grindstone downward by 3.8 mm.
(No. 2) As an example of the present invention, a pipe was formed using a pipe making facility in which a cutting roll (not shown) was disposed in place of the grindstone polishing means 3 in FIG. During pipe making, an R shape is applied to the corner on the upper surface side of the plate by roll cutting using the cutting roll before roll forming, and then an R shape is applied to the corner on the lower surface side of the plate (tube outer diameter side) by fin pass molding. Was granted. The radius R of the imparted R shape was 4 mm (21% of the 19.1 mm plate thickness and 26% of the 15.3 mm plate thickness).

In addition, when the plate thickness was switched from 19.1 mm to 15.3 mm, fine adjustment was performed to move the position of the cutting roll downward by 3.8 mm.
(No. 3) As a comparative example, instead of the grindstone polishing means 3 in FIG. 1, a wide end forming hole roll (not shown) is arranged, and the fin corners of the fin pass forming roll 6 are formed to have a substantially right-angle shape. Pipes were made using pipe making equipment. During pipe making, an R shape was imparted to the corners on the upper and lower surfaces of the plate by perforating rolling using the above-mentioned wide end forming perforated roll before roll forming. The radius R of the imparted R shape was 3 mm (16% of the 19.1 mm plate thickness, 19% of the 15.3 mm plate thickness).

When the plate thickness was switched from 19.1 mm to 15.3 mm, the production line was temporarily stopped and the hole-type roll was changed from 19.1 mm to 15.3 mm.
(No. 4) As a conventional example, the pipe was made using the pipe making equipment used in the pipe making equipment used in the comparative example (No. 3), from which the hole roll for forming the width end portion was removed. The corners on both the upper and lower sides of the plate remain substantially rectangular (substantially perpendicular).

Table 1 shows the results of measuring the Charpy impact value (absorbed energy) and the brittle fracture surface ratio in the welded portion of the steel pipe manufactured under these conditions. In the same table, the production time of each example is shown as a relative ratio with respect to 1 for the comparative example (No. 3).
From Table 1, in the present invention example, 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, whereas in the conventional example, the impact strength of the welded portion is high. The brittle fracture surface ratio was low, the toughness was reduced, and the reliability of the product was poor.

  Moreover, in the example of the present invention, the manufacturing time is remarkably shortened as compared with the comparative example, and according to the present invention, it was found that the electric resistance welded tube product excellent in welded portion characteristics can be manufactured with high efficiency. .

It is a schematic diagram of the pipe making equipment which shows one example of embodiment of this invention. It is a schematic diagram which shows one example of embodiment which carries out R process of the corner | angular part at the board upper surface side by grindstone grinding | polishing. It is a schematic diagram which shows one example of embodiment which carries out R process of the corner | angular part of a board lower surface side (pipe outer diameter side) by fin pass shaping | molding.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Uncoiler 2 Leveler 3 Grinding stone grinding means 4 First breakdown stand 5 Roll forming machine 6 Fin pass forming roll 7 Induction heating means (induction heating coil)
8 Squeeze roll 9 Bead cutting means (bead cutting tool)
10 Sizer
11 Pipe cutting machine
100 strip (plate)

Claims (3)

  In the process of forming a band material, butting both ends in the width direction and electro-welding to form a pipe, the corner on either the upper or lower side of the width direction both ends is cut or grinded by grinding stone A high-efficiency manufacturing method of an electric resistance welded tube with good welded portion characteristics, characterized in that R processing is performed, and a corner portion on the other surface side is subjected to R processing by fin pass forming in the middle of forming a band material.   The corner portion on the upper surface side of the strip material that becomes the inner diameter side of the tube is R-processed by the cutting or the grinding wheel polishing, and the corner portion on the lower surface side of the strip material that becomes the outer diameter side of the tube is R-processed by the fin pass molding. Item 2. A high-efficiency manufacturing method of an electric resistance welded tube having good weld joint characteristics according to Item 1.   3. A highly efficient method for producing an electric resistance welded tube with good weld characteristics according to claim 1 or 2, wherein the radius R of the R shape provided by the R processing is 20 to 50% of the thickness of the strip. .

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