JP2008087022A - Method for manufacturing seam welded pipe having excellent characteristics of welded portion - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a seam welded pipe having excellent characteristics of a welded portion, which method can surely and sufficiently improve characteristics (especially low temperature toughness) of a welded portion. <P>SOLUTION: During a process for manufacturing a pipe by forming a strip material 110, and by butting both ends thereof, and by carrying out the seam welding of the ends, tapered shapes are formed on the ends before the seam welding by rolling the ends with a caliber roll 14, and non-oxidative gas is blown to the ends being heated by the seam welding. It is preferable that the surroundings of the end portions are kept in the non-oxidative gas 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, butting the end portions, and welding the end portions into a pipe by electro-welding, a taper shape is given to the end portions before electro-resistance welding by hole roll rolling. A method of manufacturing an electric resistance welded tube with good welded portion characteristics, characterized in that a non-oxidizing gas is sprayed on the end portion that is being heated by electric resistance welding.

2. In the process of forming the strip material, butting the end portions, and welding the end portions into a pipe by electro-welding, a taper shape is given to the end portions before electro-resistance welding by hole roll rolling. A method of manufacturing an electric resistance welded tube with good welded portion characteristics, wherein the periphery of the end portion being subjected to heating during electric resistance welding is maintained in a non-oxidizing gas atmosphere.
3. 3. The method for producing an electric resistance welded tube with good welded portion characteristics according to any one of the preceding items 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 tapered shape, the inventors examined a method 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.

However, it may be difficult to sufficiently improve the toughness or strength of the welded portion after the 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 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%. FIG. 2 shows the taper angle α and the taper depth β of the inclined surface 12 when a taper shape is provided on the outer diameter side of the end of the strip 110. 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.

  In the embodiment, a strip made of steel strip having a plate width of 1920 mm × thickness of 19.1 mm is formed into a pipe making machine as shown in FIG. 1, that is, an uncoiler 1, a leveler 2, and a roll forming machine 4 (multi-stand fin pass forming Roll stand) 3), electric welding machine (including contact tip 5 and squeeze roll 7), bead portion cutting means 8, sizer 9, and tube cutting machine 10 to make a punch roll 14 When manufacturing a steel pipe having an outer diameter of 600 mm through the one installed in the immediate vicinity of the first roll 4A exit side, the manufacturing conditions were manufactured in the following four ways.

  (No. 1: Example of the present invention) Rolling with the perforated roll 14 gives substantially straight taper shapes to both the inner and outer diameter sides of the end of the strip (taper angle α and taper depth β are shown in Table 1). 3), in the embodiment shown in FIG. 3, nitrogen gas was blown from the gas supply nozzle 6 to the end of the strip 110 that was undergoing electric welding welding heating (electric heating from the contact tip 5). . 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 inner and outer pipes at the end of the strip material were rolled by rolling with the hole-type roll 14 changed from the first roll 4A exit side closest to the breaker first roll to the leveler 2 exit side (not shown). A substantially linear taper shape is provided on both diameter sides (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 sewing welding heating (electric current heating from the contact tip 5) was surrounded by a gas atmosphere box 13, and the inside of the box was maintained in an atmosphere of 3% hydrogen gas + balance argon 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) Rolling with a perforated roll 14 at the same installation location as No. 2 gives almost straight taper shapes to both the inner and outer diameter sides of the end of the strip (taper angle α, taper The depth β was set to the value shown in Table 1), and the end of the strip that was being heated by the electric resistance 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)
4 roll forming machine
4A Breakdown first stand 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
14 hole roll (for taper)
20 Feeding direction
110 Band material

Claims (4)

  In the process of forming the strip material, butting the end portions, and welding the end portions into a pipe by electro-welding, a taper shape is given to the end portions before electro-resistance welding by hole roll rolling. A method for producing an electric resistance welded tube having good welded portion characteristics, characterized in that a non-oxidizing gas is sprayed on the end portion that is being heated by electric resistance welding.   In the process of forming the strip material, butting the end portions, and welding the end portions into a pipe by electro-welding, a taper shape is given to the end portions before electro-resistance welding by hole roll rolling. A method of manufacturing an electric resistance welded tube with good welded portion characteristics, wherein the periphery of the end portion that is being heated during electric resistance 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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