JP2008110399A - Method of manufacturing electric resistance welded tube excellent in property of weld zone - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing an electric resistance welded tube excellent in the properties of a weld zone by which toughness of the weld zone required for the electric resistance welded tube for line pipes of an oil well and strength of the weld zone required for the electric resistance welded tube for casing pipes of the oil well are achieved. <P>SOLUTION: On the way of a process in which a strip material 11 is formed into a tube by forming the strip materia 11, butting end parts thereof and applying electric resistance welding to the end parts, the electric resistance welding is performed by giving each of the end parts a tapered shape formed of a slope 13 continuous with an end face 12 approximately perpendicular to the width direction of the strip material by rolling with grooved rolls 4 or fin pass forming 51, then increasing the amount of heat input when performing electric resistance welding by 5 to 20% as compared with that when the tapered shape is not given. It is preferable that the slope 13 is 25 to 50° in the inclined angle to the end face 12 and the length of the slope in the thickness direction of the strip material is 20 to 45% of the thickness of the strip material. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for manufacturing an electric resistance welded tube having good welded portion characteristics. Here, the welded portion characteristics include welded portion toughness required for an electric-welded pipe for an oil well line pipe and weld strength required for an electric-welded pipe for an oil well casing pipe.

  Usually, pipes are roughly classified into welded pipes and seamless pipes. Welded pipes are manufactured by rounding strips (plates) and welding by joining the ends, as in the case of ERW steel pipes. Seamless pipes are made by drilling a lump of material at high temperatures, such as mandrel mills, etc. Rolled to produce. In the case of a welded pipe, it is generally said that the toughness of the welded part is 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 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.
Usually, a hot-rolled sheet as a base material of a welded pipe is subjected to component design, heat treatment, and the like in consideration of the base material characteristics after manufacturing the welded 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, the development of the welding technique has been important.
The cause of the failure of ERW welding is that an oxide called penetrator generated on the end face of the plate to be welded (end face in the plate width direction) remains without being discharged from the end face together with the molten steel during ERW welding. There were many cases where the toughness was lowered due to the cause and the strength was insufficient.

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 plate end surface have been intensively studied. For example, Patent Documents 1 to 5 describe examples in which the shape of the plate end surface is examined. In other words, the plate end surface usually has a substantially flat surface due to slitting or end surface grinding, but this is tapered before roll forming to improve the discharge of molten steel during welding by 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 2003-164909 A

However, in the above prior art, the taper processing means was used alone to give a tapered shape to the end portion, or the taper processing means were simply listed and introduced. The effect may not be sufficient to apply to the process, and further detailed examination is necessary.
The present invention solves the above-mentioned problems, and achieves welded portion toughness required for an electric seam pipe for oil well line pipes and weld strength required for an electric seam pipe for oil well casing pipes. An object of the present invention is to provide a method for producing an electric resistance welded tube having good characteristics.

The present invention made to achieve the above object is as follows.
1. In the course of the process of forming the strip material, butting the ends and electrowelding to form a pipe, the end portion has a tapered shape in which an inclined surface is connected to an end surface substantially perpendicular to the width direction of the strip material. After application by die roll rolling, the heat input at the time of ERW welding is increased by 5 to 20% compared to that when the taper shape is not applied, and electroweld welding is characterized by good welding characteristics ERW pipe manufacturing method.
2. During the process of forming the strip material, butting the ends and electro-welding to form a pipe, the end portion has a tapered shape with an inclined surface connected to an end surface substantially perpendicular to the width direction of the strip material. After applying by forming, the amount of heat input at the time of ERW welding is increased by 5 to 20% compared to that when the tapered shape is not applied. Tube manufacturing method.
3. 3. When providing the taper shape by the fin pass molding, both the tube outer diameter side and the tube inner diameter side of the end portion are tapered at the same stand. ERW pipe manufacturing method.
4). The inclined surface has an inclination angle of 25 to 50 degrees from the end surface, and the length of the inclined surface in the thickness direction of the band is 20 to 45% of the thickness of the band. 4. The method for producing an electric resistance welded tube having good welded portion characteristics according to any one of items 3 to 3.
5. 5. The method of manufacturing an electric resistance welded tube with good welded portion characteristics according to the item 4, wherein a length in the thickness direction of the inclined surface is 20 to 40% of the thickness of the belt material.

  According to the present invention, it is possible to manufacture an electric resistance welded tube that sufficiently satisfies the welded portion toughness required for an electric well pipe for an oil well line pipe and the weld strength required for an electric pipe for an oil well casing pipe. Can do.

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, the inventors first studied a method of imparting a taper 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.

  FIG. 2 is a schematic diagram showing an example of a pipe making machine used for carrying out the present invention. This pipe making machine includes an uncoiler 1, a leveler 2, a roll forming machine 5, an electric seam welding machine (including a contact tip 6 and a squeeze roll 7), a bead portion cutting machine 8, a sizer 9, and a pipe cutting machine 10. The ERW steel pipe is manufactured through the strip material (pipe after end welding) 11. In addition, 3 is a breakdown 1st stand, 51 is a fin pass roll (fin pass shaping | molding).

FIG. 1 is a schematic diagram showing an example of an embodiment of the present invention. In this example, when producing an ERW steel pipe using the pipe making machine of FIG. 1, a perforated roll 4 is arranged immediately after the first breakdown stand 3, and a band material is obtained by perforating roll rolling using this. 11 Taper shape is added to the end.
In addition, the inventors examined using 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. In this case, it is possible to taper both the upper and lower sides at the same stand at the same time, so that the taper can be easily applied and the taper shape is not easily disturbed when fin path molding is performed on a stand other than the same stand. preferable.
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.

  3, 4, and 5 are schematic diagrams illustrating an example of a taper shape imparting method by fin pass molding. In these examples, the shape of any one of the fins 51A of the fin path molding 51 of FIG. 1 is devised, so that either the lower surface side (tube outer diameter side) or the upper surface side (tube inner diameter side) of the end of the strip 11 is selected. One or both of them is provided with a taper shape in which an inclined surface 13 is connected to an end surface 12 substantially perpendicular to the strip width direction (which forms an angle within 90 ° ± 0.4 ° with the width direction). Here, α and γ are angles of the inclined surface 13 on the tube outer diameter side and the tube inner diameter side with respect to the average surface of the end surface 12 (referred to as a taper angle), and β and δ are inclined surfaces on the tube outer diameter side and the tube inner diameter side. 13 strip material length direction length (referred to as taper depth).

However, it may be difficult to sufficiently improve the toughness or strength of the welded portion after ERW welding only by providing the taper shape by hole roll rolling or fin pass molding.
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, paid attention to heat input during electric resistance welding. That is, in order to effectively discharge the penetrator together with the molten steel, not only the taper shape at the end of the strip material but also the amount of heat input is greatly affected during the electric resistance welding.

  In ERW welding, when the heat input changes, the state of molten steel generation / discharge changes. That is, if the heat input is small, the melting of the end portion is insufficient and the generation of molten steel becomes small, and the penetration of the penetrator is insufficient together with the molten steel, and it tends to remain in the welded portion after ERW welding. On the other hand, if the heat input becomes too small, welding with iron oxide is called cold welding, and the toughness and strength of the welded portion are significantly deteriorated. Furthermore, when a taper shape is imparted to the end portion of the strip material, the induced current acting between the end faces immediately before the ERW welding decreases, so that the generation of molten steel tends to be insufficient, and cold welding may occur. .

  Therefore, as a result of earnestly examining the amount of heat input at the time of ERW welding, when a taper shape is given, a taper shape is not given to the band material end (that is, the band material width direction end cross-sectional shape is a rectangular end part and It has been found that the heat input amount may be 5 to 20% higher than the appropriate heat input amount (referred to as heat input when no taper). In other words, when the amount of heat input is less than 5% with respect to the amount of heat input when no taper is applied, the taper shape is applied to the end of the strip material to reduce the induced current, so that the molten steel is not sufficiently generated and the penetrator tends to remain. . On the other hand, when the amount of heat input is more than 20% with respect to the amount of heat input without taper, spattering during ERW welding occurs frequently and enters the gap of the welded part or adheres to the surface of the ERW steel pipe It is a problem. In addition, the amount of heat input when there is no taper is determined from a welding experiment or a conventional operation record.

In addition, it is preferable to employ | adopt the primary side heat input as an amount of heat input at the time of electric resistance welding. Here, the primary heat input means the amount of heat input to high-frequency or medium-frequency induction heating.
In addition, as a result of optimization of the taper shape, the angle of the inclined surface (taper angle) α and γ with respect to the average surface of the end surface substantially perpendicular to the width direction of the band material, and the length of the inclined surface in the thickness direction ( Taper depth) β, δ (see Fig. 3, Fig. 4, Fig. 5) has an appropriate range, that is, the taper angle is in the range of 25 to 50 degrees, and the taper depth is 20 to 45% of the strip thickness. It was grasped that it is good to set it as the range of 20-40%, more preferably 20-40%.

  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. Also, 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 45% of the strip thickness. Then, the taper shape tends to remain as a wrinkle of the product pipe after the electric resistance welding.

In this example, a steel strip having a plate width of 1920 mm and a plate thickness of 19.1 mm is passed through the pipe making machine shown in FIG. 1 or 2 (or a slightly modified version thereof) to produce a steel pipe having an outer diameter of 600 mm. did. The manufacturing conditions were as follows.
(No. 1: Example of the present invention)
The pipe making machine shown in FIG. 1 was used. The end of the strip 11 was rolled using the hole roll 4 immediately after the first breakdown stand 3, and the taper shape shown in Table 1 was given to the upper and lower surfaces (both inner and outer diameter sides) of the strip. The heat input amount (primary side heat input amount) during ERW welding was set to the ratio shown in Table 1 with respect to the heat input amount without taper.
(No. 2: Example of the present invention)
In FIG. 1, the pipe making machine used was one in which the hole roll 4 was moved from immediately after the breakdown first stand 3 to immediately before the roll molding machine 5 and its hole shape was changed. The end of the strip 11 was rolled using this hole roll, and the taper shape shown in Table 1 was given to the upper and lower surfaces (both inner and outer diameter sides) of the strip. The heat input amount (primary side heat input amount) during ERW welding was set to the ratio shown in Table 1 with respect to the heat input amount without taper.
(No. 3: Example of the present invention)
In FIG. 2, the pipe making machine used was obtained by changing the fin shape of the third stand of the fin path molding 51 of all three stands from a single inclined surface shape to a two-step inclined surface shape. The taper shape shown in Table 1 was given to the lower surface side (tube outer diameter side) of the band material by fin pass molding at the third stand. The heat input amount (primary side heat input amount) during ERW welding was set to the ratio shown in Table 1 with respect to the heat input amount without taper.
(No. 4: Example of the present invention)
In FIG. 2, the pipe-forming machine is changed from a total of 3 stands to 2 stands, and the fin shape of each stand is changed from a single inclined surface shape to a two-step inclined surface shape (different for each stand). It was. The taper shape shown in Table 1 was given to the upper surface side (tube inner diameter side) of the band material at the first stand and the lower surface side (tube outer diameter side) of the band material at the second stand. The heat input amount (primary side heat input amount) during ERW welding was set to the ratio shown in Table 1 with respect to the heat input amount without taper.
(No. 5: Comparative example)
As the pipe making machine, a machine in which a cutting bit was arranged immediately before the roll forming machine 5 in FIG. 2 was used. The taper shape shown in Table 1 was given to the upper and lower surfaces (both inner and outer diameter sides) of the strip by cutting with the cutting tool. The heat input amount (primary side heat input amount) during ERW welding was set to the ratio shown in Table 1 with respect to the heat input amount without taper.
(No. 6: Comparative example)
In FIG. 2, the pipe making machine used was obtained by changing the fin shape of the first stand of the fin path molding 51 of all three stands from a single inclined surface shape to a three-step inclined surface shape. The taper shape shown in Table 1 was given to the upper and lower surfaces (both inner and outer diameter sides) of the band material by fin pass molding at the first stand. The heat input amount (primary side heat input amount) during ERW welding was set to the ratio shown in Table 1 with respect to the heat input amount without taper.
(No.7: Conventional example)
The pipe making machine shown in FIG. 2 was used. The fin shape of all three stand fin path moldings 51 is a single inclined surface shape, and the shape of the end portion of the strip material before the ERW welding remains the substantially rectangular end shape. The amount of heat input during ERW welding (primary side heat input) was the same as the heat input during non-tapering.
(No. 8: Example of the present invention)
In FIG. 2, the pipe making machine used was obtained by changing the fin shape of the third stand of the fin path molding 51 of all three stands from a single inclined surface shape to a three-step inclined surface shape. The taper shape shown in Table 1 was given to the upper and lower surfaces (both inner and outer diameter sides) of the band material by fin pass molding at the third stand. The heat input amount (primary side heat input amount) during ERW welding was set to the ratio shown in Table 1 with respect to the heat input amount without taper.
(No. 9: Example of the present invention)
In FIG. 2, the pipe making machine used was one in which the fin path forming 51 was changed from all three stands to all two stands, and the fin shape of the first stand was changed from a single inclined surface shape to a three-step inclined surface shape. The taper shape shown in Table 1 was given to the upper and lower surfaces (both inner and outer diameter sides) of the band material by fin pass molding at the first stand. The heat input amount (primary side heat input amount) during ERW welding was set to the ratio shown in Table 1 with respect to the heat input amount without taper.

  A test piece was cut out from a welded portion of a steel pipe manufactured under the above 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 one example of embodiment of this invention. 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 (giving to the pipe outer diameter side) of the taper shape provision method by fin pass shaping | molding. It is a schematic diagram showing one example (applied to the inner diameter side of the tube) of a taper shape applying method by fin pass molding. It is a schematic diagram showing one example (applied to both the inner and outer diameter sides of the tube) of a taper shape applying method by fin pass molding.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Uncoiler 2 Leveler 3 Breakdown 1st stand 4 Hole roll 5 Roll forming machine 6 Contact tip 7 Squeeze roll 8 Bead part cutting machine 9 Sizer
10 pipe cutting machine
11 Strip (plate, pipe after end welding)
12 End face almost perpendicular to strip width direction
13 Inclined surface
51 Fin pass roll (fin pass forming)
51A Fin

Claims (5)

  A taper shape in which an inclined surface is connected to an end surface substantially perpendicular to the width direction of the strip in the middle of the process of forming the strip and abutting the end portions to form a pipe by electro-sewing welding, After application by die roll rolling, the heat input at the time of ERW welding is increased by 5 to 20% compared to that when the taper shape is not applied, and electroweld welding is characterized by good welding characteristics ERW pipe manufacturing method.   During the process of forming the strip material, butting the ends and electro-welding to form a pipe, the end portion has a tapered shape with an inclined surface connected to an end surface substantially perpendicular to the width direction of the strip material. After applying by forming, the amount of heat input at the time of electric resistance welding is increased by 5 to 20% compared to that when the taper shape is not applied. Tube manufacturing method.   3. The welded portion having good weld characteristics according to claim 2, wherein, when the tapered shape is provided by the fin pass molding, the tapered shape is provided on both the outer diameter side and the inner diameter side of the end portion at the same stand. ERW pipe manufacturing method.   The inclined surface has an inclination angle of 25 to 50 degrees from the end surface, and the length of the inclined surface in the strip thickness direction is 20 to 45% of the thickness of the strip. The method for producing an electric resistance welded tube having good welded portion characteristics according to any one of?   The method of manufacturing an electric resistance welded tube with good welded portion characteristics according to claim 4, wherein the length of the inclined surface in the thickness direction of the strip is 20 to 40% of the thickness of the strip.

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