JP2008012582A - Method for manufacturing electric resistance welded tube having excellent weld characteristic - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing an electric resistance welded tube having excellent weld characteristics, which method surely and sufficiently improves weld characteristics (particularly, low temperature toughness). <P>SOLUTION: During a step of forming a strip 110, the end parts of a strip are butted each other, and subjected to electric resistance welding to make a tube. A taper shape is given to the end parts before the electric resistance welding by fin pass forming 3, and a non-oxidizing gas is blown on the end parts being heated by the electric resistance welding. The circumference of the end parts are preferably held to a non-oxidizing atmosphere. <P>COPYRIGHT: (C)2008,JPO&INPIT

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 rounding the width of the strip material and welding the ends, as in the case of ERW steel pipes. Seamless pipes are made by drilling a lump of material at a high temperature and rolling it with a mandrel mill, etc. To manufacture. 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 for 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, the development of the welding technique has been important.
The reason for the failure of ERW welding is that an oxide called penetrator formed on the end face of the welded plate 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 end portion of the strip and discharge the penetrator together with the molten steel. The reason for imparting the taper is considered to be because it is easy to give a shape to the end portion of the strip. However, simply giving a linear or flat taper may not be sufficient in improving the welded portion characteristics (particularly, low temperature toughness), and further detailed examination is required.

  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).

  Therefore, an object of the present invention is to provide a method of manufacturing an electric resistance welded tube with good welded part characteristics, which can reliably and sufficiently improve welded part characteristics (particularly low temperature toughness).

The inventors diligently studied to achieve the above-mentioned object and arrived at the present invention having the following gist configuration.
1. In the process of forming the strip material and butting the end parts, and welding the end parts to make a pipe by electro-welding, a taper shape is imparted to the end parts before electro-sewing welding by fin pass molding. A method for producing an electric resistance welded tube having good welded portion characteristics, characterized in that a non-oxidizing gas is blown onto the end portion which is being subjected to heating by sewing welding.

2. In the process of forming the strip material and butting the end parts, and welding the end parts to make a pipe by electro-welding, a taper shape is imparted to the end parts before electro-sewing welding by fin pass molding. A method for producing an electric resistance welded tube having good welded portion characteristics, wherein the periphery of the end portion being subjected to heating during sewing welding is maintained in a non-oxidizing gas atmosphere.
3. 3. The method of manufacturing an electric resistance welded tube with good welded portion characteristics according to item 1 or 2, wherein a gas containing a reducing gas is used as the non-oxidizing gas.

  4). The taper shape is a taper shape in which the angle of the taper surface with respect to the end surface in the width direction of the strip is 25 to 50 degrees, and the length of the taper surface in the thickness direction of the strip is 20 to 40% of the thickness of the strip. 4. A method for producing an electric resistance welded tube having good welded portion characteristics according to any one of items 1 to 3.

  According to the present invention, the welded portion characteristics (especially low temperature toughness) of the ERW pipe can be reliably improved from the conventional level.

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, in order to obtain a desired shape, the inventors examined utilizing fin pass molding.

  As a result, in the fin pass molding, even when the fin pass roll is not filled with the entire circumference in the circumferential direction of the strip, when the strip is inserted into the fin pass roll, the end of the strip is strongly pressed by the fin, It was grasped that the end of the strip material was sufficiently adhered to the fin. That is, when the strip is inserted into the fin pass roll, the end of the strip in contact with the fin and the bottom of the strip located on the opposite electrode (almost opposite to 180 degrees) are in a state of beam bending, The reaction force of the band material that tries to bend it into a circular arc shape acts greatly, and even if the band material does not fill the fin pass roll, a large compressive force acts on the end of the band material in the circumferential direction. It was grasped that the end of the strip was strongly pressed by the fins and the shape of the fin was transferred to the end of the strip as it was.

Accordingly, the inventors have studied means for actively utilizing this phenomenon, paying attention to the fact that the end of the strip is strongly pressed by the fins. That is, if the taper is provided with two or more levels of taper on the fin, the desired taper can be sufficiently applied to the end portion of the strip even if the amount of upset in the fin pass molding is small.
When a taper is applied to either the upper surface side (= tube inner diameter side) or the lower surface side (= tube outer diameter side) of the end portion of the band member, the fin shape may have a two-step inclined surface.

  Moreover, what is necessary is just to make it into the fin shape which has a 3-step inclined surface, when providing a taper to both the upper surface side and lower surface side of a strip | belt material edge part. However, if any one of the three inclined surfaces is separated from the vertical bisector passing through the fin center of the roll axis as the inclined surface inner point is further away from the roll axis of the fin pass roll, The end part is scraped off by the fins, and a surplus material called “beard” may be generated, which may cause wrinkles during fin pass molding and cause sparks in ERW welding. In any case, it is preferable that the inclined plane inner point be closer to the vertical bisector passing through the fin center of the roll axis as the distance from the roll axis of the fin pass roll increases.

  If possible, if taper is applied to one or both of the upper surface side and the lower surface side of the end portion of the strip material at the final stand of the fin pass, since electro-welding welding is performed immediately thereafter, a good taper shape is obtained. ERW welding is possible while holding. In addition, even if taper is applied at the fin-pass start stand or on the way, the end of the strip once provided with a taper is markedly hardened by the strong pressure at the time of applying the taper. Therefore, the taper shape can be maintained almost satisfactorily after the fin pass molding.

  In addition, when fin path molding with two or more stands is possible, a two-step inclined surface is provided on the fin of one stand, and a taper is provided on one of the upper and lower sides of the end portion of the band member, and another stand is provided. It is preferable to provide a taper on the opposite side of the one end of the strip material to a two-step inclined surface having a shape different from that described above. In addition, since the one surface side that has been previously tapered by one stand is hardened and hardened by the strong pressure at that point, even if a taper is applied to the opposite side by another stand, it will be given first. The tapered shape is relatively difficult to collapse. Accordingly, the end portion of the strip after the fin pass molding has a tapered shape sufficiently close to the target on both the inner diameter side and the outer diameter side of the pipe.

Further, in the present invention, only fin pass forming is used as the taper imparting means, so that equipment such as an edger roll and a grinding roll is unnecessary, and it is not necessary to replace those rolls and a grinding wheel, so that efficient and good welding quality is achieved. Tubes can be manufactured.
Here, it is sometimes difficult to sufficiently improve the toughness or strength of the welded portion after the electro-sealing welding with the provision of the tapered shape by the fin pass molding.

  When this cause is investigated in detail, the oxide that causes the 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 electric resistance welding phenomenon in detail, and as a result, have focused on the generation of oxides that cause penetrators. That is, a method for preventing not only the discharge of the penetrator due to the taper shape at the end of the strip but also the generation of oxides causing the penetrator was studied.

  As a result, when non-oxidizing gas is blown toward the end of the strip that is undergoing heating by ERW welding (ie, heating to melt the pressed end before pressing), the formation of oxide is suppressed. I understood what I could do. Here, the non-oxidizing gas is an inert gas (nitrogen gas, helium gas, argon gas, neon gas, xenon gas, or a mixed gas obtained by mixing two or more of these), a reducing gas (hydrogen gas). , Carbon monoxide gas, methane gas, propane gas, etc., or a mixed gas formed by mixing two or more of these), or a mixed gas formed by mixing these.

In other words, in the present invention, by providing a taper shape to the end of the strip material before ERW welding, the discharge of the penetrator is promoted, and at the same time, the plate end being subjected to heating during ERW welding. By spraying the non-oxidizing gas, generation of oxides that cause the penetrator is suppressed. Thereby, the toughness or strength of the welded portion can be reliably improved from the conventional level.
Of course, simply blowing non-oxidizing gas can weaken the effect of suppressing oxide generation at the edge of the plate more or less because the surrounding air is entrained. Therefore, it is preferable to eliminate the entrainment of the surrounding air. For this purpose, it is preferable to surround the end of the plate that is being heated by the electric resistance welding and keep the inside of the enclosure in a non-oxidizing gas atmosphere.

In addition, among non-oxidizing gases, the use of a gas containing a reducing gas has a stronger effect of suppressing the formation of oxides that cause penetrators, and greatly improves the toughness or strength of the weld. Can be made.
From the viewpoint of availability and low cost, it is preferable to use the following gas as the non-oxidizing gas.
-When using inert gas alone: (A) When using nitrogen gas, helium gas, argon gas or a mixture of two or more of these or reducing gas alone: (B) Hydrogen gas, carbon monoxide In the case of using any one of these gases or a mixed gas of these two kinds of mixed gas / inert gas and reducing gas: mixed gas of the above (A) and (B) In particular, hydrogen gas and / or carbon monoxide gas Needless to say, safety measures should be taken when using gas containing gas.

  In addition, as a result of optimization of the taper shape, the angle of the inclined surface (taper angle) with respect to the average surface of the end surface that is almost perpendicular to the width direction of the strip (which forms an angle within 90 ° ± 0.4 ° with the width direction) Α) and the thickness direction length (referred to as taper depth) β of the sloped surface of the slant surface exists, that is, the taper angle α is in the range of 25 to 50 degrees, and the taper depth β is the thickness of the belt material I grasped that it would be good to be in the range of 20-40%. 2 shows a taper angle α and a taper depth of the inclined surface 12 when a taper shape is given to the outer diameter side of the end of the strip 110 by adjusting the shape of the fin 3A of the fin pass molding (fin pass roll stand) 3. β was shown. Illustration of taper angle α and taper depth β in the case of providing a taper shape on the inner diameter side of the tube or both inner and outer diameter sides of the tube is omitted.

  If the taper angle is less than 25 degrees, the molten steel discharge from the central part of the strip thickness becomes 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. If the taper depth is less than 20% of the strip thickness, the molten steel discharge at the center of the strip thickness becomes insufficient and the penetrator tends to remain, while the taper depth exceeds 40% of the strip thickness. Then, the taper shape tends to remain as a wrinkle of the product pipe after the electric resistance welding.

  Hereinafter, a description will be given based on examples. In this embodiment, a strip made of a steel strip having a width of 1920 mm × thickness of 19.1 mm is made into a pipe making machine as shown in FIG. 1, that is, an uncoiler 1, a leveler 2, a roll forming machine 4 (multi-stand fin pass forming (fins Pass roll stand (including 3), electric seam welding machine (including contact tip 5 and squeeze roll 7), bead section cutting means 8, sizer 9, and pipe cutting machine 10 and outer diameter 600 mm In manufacturing the steel pipe, the manufacturing conditions were changed in the following four ways.

  (No.1: Example of the present invention) In the third stand of the fin pass molding 3 having all three stands, a substantially linear taper shape is given to the outer diameter side of the end of the strip (taper angle α, taper depth β). Is set to the values shown in Table 1), and in the embodiment shown in FIG. 3, the argon gas is supplied from the gas supply nozzle 6 to the end of the strip 110 that is undergoing electric welding welding heating (electric heating from the contact tip 5). Sprayed. In FIG. 3, reference numeral 20 denotes a material passing direction of the strip 110 (becomes the pipe 11 after welding), and illustration of a squeeze roll is omitted.

  (No. 2: Example of the present invention) The first stand of the fin pass molding 3 with all 2 stands is on the tube inner diameter side at the end of the strip material, and the second stand is on the outer diameter side of the tube at the same end. A linear taper shape is added (taper angle α and taper depth β are set to the values shown in Table 1), and in the embodiment shown in FIG. The end portion of the strip 110 that is being subjected to electrical heating from 5) was surrounded by a gas atmosphere box 13, and the inside of the box was maintained in an atmosphere of 1% carbon dioxide gas + remaining nitrogen gas. In FIG. 4, 20 is the material passing direction of the strip 110 (becomes the pipe 11 after welding), and the squeeze roll is not shown.

(No.3: Comparative example) In the first stand of the fin pass molding 3 with all three stands, a substantially linear taper shape is provided on both the inner and outer diameter sides of the end of the strip (taper angle α, taper depth). β was set to the value shown in Table 1), and the end of the strip that was being heated by ERW welding was left exposed to the atmosphere.
(No.4: Conventional example) The strip end shape remains almost rectangular (rectangular length end shape), and the strip end that is undergoing electro-welding welding heating remains exposed to the atmosphere. did.

  A test piece was cut out from a welded portion of a steel pipe manufactured under the above four 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 conducted 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.

It is a schematic diagram which shows an example of the pipe making machine used for implementation of this invention. It is a schematic diagram which shows one example of embodiment which provides a taper shape to a strip | belt material edge part by fin pass shaping | molding according to this invention. It is a schematic diagram which shows one example of embodiment which sprays nonoxidizing gas on the strip | belt-material edge part which is receiving the electric-welding welding heating according to this invention. It is a schematic diagram which shows one example of embodiment which keeps the circumference | surroundings of the strip | belt-material edge part which is receiving the electric-welding welding heating according to this invention in non-oxidizing gas atmosphere.

Explanation of symbols

1 Uncoiler 2 Leveler 3 Fin pass molding (Fin pass roll stand)
3A fin 4 roll forming machine 5 contact tip 6 gas supply nozzle 7 squeeze roll 8 bead cutting means 9 sizer
10 pipe cutting machine
11 tubes
12 Inclined surface
13 Gas atmosphere box
20 Feeding direction
110 Band material

Claims (4)

  In the process of forming the strip material and butting the end parts, and welding the end parts to make a pipe by electro-welding, a taper shape is imparted to the end parts before electro-sewing welding by fin pass molding. A method for producing an electric resistance welded tube having good welded portion characteristics, characterized in that a non-oxidizing gas is blown onto the end portion which is being subjected to heating by sewing welding.   In the process of forming the strip material and butting the end parts, and welding the end parts to make a pipe by electro-welding, a taper shape is imparted to the end parts before electro-sewing welding by fin pass molding. A method for producing an electric resistance welded tube having good welded portion characteristics, wherein the periphery of the end portion being subjected to heating during sewing welding is maintained in a non-oxidizing gas atmosphere.   The method for manufacturing an electric resistance welded tube with good welded portion characteristics according to claim 1 or 2, wherein a gas containing a reducing gas is used as the non-oxidizing gas.   The taper shape is a taper shape in which the angle of the taper surface with respect to the end surface in the width direction of the strip is 25 to 50 degrees, and the length of the taper surface in the thickness direction of the strip is 20 to 40% of the thickness of the strip. The method for manufacturing an electric resistance welded tube with good welded portion characteristics according to any one of claims 1 to 3.

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