JP2008105075A - Method for manufacturing electric resistance welded tube having excellent characteristic of weld zone - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing an electric resistance welded tube having excellent characteristic of a weld zone capable of keeping the excellent welding quality by making an end of a plate before the electric resistance welding have an adequate shape when manufacturing the electric resistance welded tube. <P>SOLUTION: The V-shape angle θ immediately before the electric resistance welding of a plate 1 is set to be 3-10°, and the taper angle α of a tapered shape is set to be 25-50°, and the taper height δ is set to be 20-40% of the plate thickness. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a pipe that requires toughness of a welded portion such as for oil well line pipes or a pipe that requires welded portion strength such as a casing pipe of oil well.

  Usually, pipes are roughly classified into welded pipes and seamless pipes. Welded pipes are manufactured by rolling a plate by roll forming or the like and welding by welding the end, as in the case of ERW steel pipes, and seamless pipes are made by drilling a lump of material at high temperature and using a mandrel mill, etc. Rolled and manufactured. 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., pipes are often laid in cold regions, so low temperature toughness is important, and in oil wells for crude oil mining, casing pipes are required to protect the mining pipes. The strength of the tube is regarded as important.

  In general, hot strips (strips), which are the base material of pipes, are subjected to component design and heat treatment in consideration of the base material characteristics after pipe manufacture, ensuring characteristics such as toughness and strength of the base material. The

  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 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 and the strength. There were many cases where there was a shortage.

Therefore, conventionally, in order to remove the penetrator, which is the main cause of poor ERW welding, 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 5 describe examples of examining the shape of the plate end surface. In other words, the end face of the plate is generally rectangular due to slits and end face grinding, but this is tapered before roll forming to improve the discharge of molten steel during welding with the processed end shape. It is aimed.
JP 57-31485 A Japanese Patent Laid-Open No. Sho 63-317212 JP 2001-17079A JP 2001-259733 A JP 2003-1649095 A

  However, in Patent Documents 1 to 5, since the taper processing means is merely listed and introduced, the effect may not be sufficient even if it is applied to the ERW tube manufacturing process. Was necessary.

  The present invention has been made in view of the circumstances as described above. When manufacturing an electric resistance welded tube, the end of the plate (strip material) before the electric resistance welding is formed into an appropriate shape so that the welding quality is improved. It is an object of the present invention to provide a method for manufacturing an electric resistance welded tube with good welded portion characteristics.

  In order to solve the above problems, the present invention has the following features.

  [1] In a method of manufacturing an electric resistance welded tube which forms a plate, abuts the end portions, and is welded by electro-welding to form a tube, after both ends of the plate are tapered, A method of manufacturing an electric resistance welded tube having good weld characteristics, wherein the electric resistance welding is performed with a V shape angle of 3 ° or more.

  [2] The taper shape to be imparted to the end of the plate is characterized in that the angle of the taper with respect to the plate thickness direction is 25 ° to 50 °, and the length of the taper in the plate thickness direction is 20% to 40% of the plate thickness. The method for producing an electric resistance welded tube having good welded portion characteristics according to [1].

  The present invention can obtain an electric resistance welded tube having remarkably good toughness and weld strength.

  An embodiment of the present invention will be described.

  As described above, in Patent Documents 1 to 5, since only taper processing means are introduced, the effect is not sufficient even if it is applied to the ERW pipe manufacturing process. In some cases, it was difficult to sufficiently improve the toughness or strength of the later welded portion.

  Detailed investigation of this cause revealed the following.

  That is, in the process in which the plate end before the electric seam welding is heated, an oxide that causes a penetrator, which is a welding defect, is formed on the end surface of the plate. Thereafter, the oxide on the end face floats on the surface of the molten steel during ERW welding, and a part is discharged together with the molten steel. At this time, if the end face of the plate is tapered, the molten steel is easily discharged, and at the same time, the penetrator can be effectively discharged. However, because the oxide on the plate end surface that becomes the basis of the penetrator is sequentially generated with the heating of ERW welding, depending on the welding conditions, only the taper shape of the plate end portion can provide sufficient toughness or strength after welding. There was a case where it could not be improved sufficiently.

  Therefore, in order to cope with the above-mentioned problem, the present inventors have re-observed the electric seam welding phenomenon in detail, and as a result, a V-shaped shape in which both end faces in the width direction of the plate are formed in the longitudinal direction immediately before the electric seam welding. Attention was paid to the vertex angle (V-shape angle). That is, in order to effectively discharge the penetrator together with the molten steel, it has been found that not only the taper shape of the plate end but also the V shape angle has a great influence.

  In ERW welding, when the V shape angle between the plate end faces changes, the discharge state of the molten steel changes. That is, in the case of a normal rectangular end surface, the portions close to the corners (corner portions) on the upper surface side and the lower surface side of the plate end surface are preferentially heated by induction heating immediately before ERW welding, and the end surfaces of ERW welding are brought into contact Melting starts from a very short distance. As a result, only the corner causes the molten steel to be generated first and covers it, and the molten steel generated by the later melting of the inside of the plate end face is difficult to be extruded. As a result, the penetrator remained difficult to be discharged, and the toughness or strength of the welded portion was reduced.

  Accordingly, the present inventors have studied a method of shortening the heating area of the portion near the corner of the plate end surface as much as possible by shortening the time until the butt welding of ERW welding. That is, when the heating area near the corner is shortened, the portion where the lid is formed by the molten steel of the corner is reduced, the molten steel generated from the inside of the end portion is easily discharged, and the penetrator is less likely to remain. .

  Based on the above idea, the present inventors have decided that the V-shape angle of ERW welding is an appropriate angle. As the V-shape angle increases, the induced current suddenly weakens and becomes harder to heat as it moves farther from the butt portion of ERW welding. Become. As a result, the heating area near the corner is shortened, the molten steel is easily discharged, and the penetrator hardly remains.

  As a result of intensive studies on the optimum size of the V-shape angle, it has been found that if it is 3 ° or more in combination with the taper shape of the plate end, good toughness or strength can be obtained. However, if the V-shape angle becomes too large, the forming of the tube becomes unstable, and the butting accuracy between the plate ends becomes poor.

  In addition, as a result of optimization of the taper shape to be applied to the plate end, the angle from the perpendicular (angle with respect to the thickness direction of the taper) is set to 25 ° to 50 °, and from the taper start position to the end position It was understood that the length of the vertical line (the length of the taper in the thickness direction) should be 20% to 40% of the thickness.

  That is, if the angle from the perpendicular (taper angle) is less than 25 °, the molten steel discharge from the central portion of the plate thickness becomes insufficient, the penetrator remains and becomes defective, and the toughness and strength after ERW welding decrease. When the angle from the perpendicular (taper angle) exceeds 50 °, the taper shape remains as a flaw on the tube of the product even after the electric resistance welding. Furthermore, if the length of the perpendicular (taper height) from the taper start position to the end position is less than 20% of the plate thickness, the molten steel discharge at the center portion of the plate thickness becomes insufficient and the penetrator tends to remain, If it exceeds 40% of the plate thickness, the taper shape remains as a flaw on the tube of the product even after the electric resistance welding.

  As described above, in the embodiment of the present invention, as shown in FIG. 1, the V-shape angle θ immediately before ERW welding of the plate 1 formed into a tubular shape is set to 3 ° to 10 °, and the tapered taper is formed. The angle α is set to 25 ° to 50 °, and the taper height δ is set to 20% to 40% of the plate thickness.

  As a result, the penetrator of the electric resistance welded portion can be sufficiently discharged, and an electric resistance welded tube having remarkably good toughness and welding strength can be obtained.

  Hereinafter, a description will be given based on examples.

  Here, a φ600 ERW pipe is manufactured by using a strip material (steel band) with a plate width of 1920 mm x 19.1 tmm by a pipe making machine equipped with an uncoiler, leveler, roll forming machine, electric welding machine, and sizer. did.

  And the test piece was cut out from the weld part of the manufactured ERW pipe, the Charpy test was done, and the performance was evaluated. Each Charpy test piece is taken from 10 points with different pipe longitudinal directions, the specimen length direction is parallel to the pipe circumferential direction, the notch length center is taken as the weld thickness center position, and 2 mmV of JIS5 An impact test at −46 ° C. was performed as a notch impact test piece, and the absorbed energy and the brittle fracture surface ratio were measured. In addition, the absorbed energy was 125 J or more and the brittle fracture surface ratio was 35% or less as the allowable performance range.

  (Invention Example 1) As Invention Example 1, the above-described electric resistance welded tube was manufactured based on the above-described embodiment of the present invention. At that time, by utilizing fin pass rolling in a roll forming machine, a taper shape with a taper angle α = 25 ° and a taper height δ = 4 mm (21% of the plate thickness) is provided on the upper and lower surfaces of the plate end, The roll forming machine was adjusted so that the V shape angle θ of the end face was 3 °, and electric resistance welding was performed.

  (Invention Example 2) As Invention Example 2, the above-described electric resistance welded tube was manufactured based on the above-described embodiment of the present invention. At that time, by utilizing a perforated roll installed in front of the roll forming machine, a taper shape with a taper angle α = 45 ° and a taper height δ = 7 mm (37% of the plate thickness) was given to the upper and lower surfaces of the plate end. Thereafter, the roll forming machine was adjusted so that the V shape angle θ of the plate end face was 8 °, and electro-welding welding was performed.

  (Comparative Example) As a comparative example, using a cutting tool installed in front of a roll forming machine, a taper shape with a taper angle α = 20 ° and a taper height δ = 3 mm (16% of the plate thickness) on the upper and lower surfaces of the plate end. Then, the roll forming machine was adjusted so that the V shape angle θ of the plate end face was 2.5 °, and electro-welding welding was performed.

  (Conventional example) As a conventional example, as shown in FIG. 2, the end face of the plate was made substantially rectangular, and the roll forming machine was adjusted so that the V shape angle θ = 2.5 °, and electro-welding welding was performed.

  Table 1 shows the results of measuring the Charpy impact value and the brittle fracture surface ratio at the welded portion of the electric resistance welded tube manufactured as described above.

  From Table 1, the ERW pipes according to Examples 1 and 2 of the present invention have high impact strength at the welded portion, small brittle fracture surface ratio, good toughness, and high product reliability. On the other hand, the ERW pipes according to the comparative example and the conventional example have low impact strength at the welded portion, high brittle fracture surface ratio, reduced toughness, and poor product reliability.

  Thereby, it was confirmed that the electric resistance welded tube with a favorable welded part characteristic can be manufactured by the present invention.

It is a figure which shows the state just before ERW welding in the example of this invention. It is a figure which shows the state just before ERW welding in a prior art example.

Explanation of symbols

  1 Tubular shaped plate

Claims (2)

  In a method of manufacturing an electric resistance welded tube which forms a plate, butts the end portions and is electro-welded and welded to form a tube, a V shape angle formed between both end surfaces of the plate in the longitudinal direction after a tapered shape is imparted to the plate end portion A method of manufacturing an electric resistance welded tube having good welded portion characteristics, wherein the electric resistance welding is performed at an angle of 3 ° or more.   The taper shape imparted to the plate end portion is characterized in that the angle of the taper with respect to the plate thickness direction is 25 ° to 50 °, and the length of the taper in the plate thickness direction is 20% to 40% of the plate thickness. Item 2. A method for producing an electric resistance welded tube having good weld joint characteristics according to Item 1.

Images