Electro-resistance-welded metal pipe and method of manufacturing electro-resistance-welded metal pipe

Abstract

To provide an electro-resistance-welded metal pipe and a method of manufacturing the electro-resistance-welded metal pipe such that discharged metal from an inner surface of an electro-resistance welded metal pipe can be suppressed from peeling and then the need to remove the discharged metal is reducible.SOLUTION: An electro-resistance-welded metal pipe comprises a metal pipe body 10 which has a butt joint part 11, and excess metal 113 and discharged metal 114 formed at the but joint part 11, wherein the excess metal 113 is provided with a bottom surface 115 which extends from the root 114a of the discharged metal 114 in a circumferential direction of the metal pipe body 10 and a side wall surface 116 which protrudes from the bottom surface 115 into the metal pipe body 10 in a cross section perpendicular to the length of the metal pipe body 10, and the discharged metal 114 comes into contact with the bottom surface 115 and the side wall surface 116, but is not welded.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an electric-resistance welded metal pipe in which side ends of a metal strip are joined to each other, and a method for manufacturing an electric-resistance welded metal pipe. [Background technology]

[0002] An example of this type of electric resistance welded metal pipe that has been used in the past is the structure shown in Patent Document 1 below. Patent Document 1 describes an electric resistance welded metal pipe that includes a metal pipe body having a butt welded portion, and a welded portion and a discharged metal. The welded portion has an inclined surface that extends between a corner of the welded portion that protrudes toward the inside of the metal pipe body and the base of the discharged metal in a cross section perpendicular to the longitudinal direction of the metal pipe body. Furthermore, because the discharged metal is not welded to the welded portion, even if a crack occurs in the discharged metal due to severe processing, the crack can be prevented from propagating to the base material. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6552723 Summary of the Invention [Problem to be solved by the invention]

[0004] Although the conventional electric-resistance welded metal pipe described above makes it possible to prevent cracks in the expelled metal from propagating to the base material, the present inventors have discovered a new problem as follows. Specifically, the expelled metal is formed when the molten metal is forced out of the welded joint and solidifies when the side ends of the metal strips are pressed against each other. In conventional electric-resistance welded metal pipes, the expelled metal is not welded to the welded joint, and is only connected to the welded joint at its base. For this reason, the expelled metal is easily peeled off from the inner surface of the electric-resistance welded metal pipe due to external forces, such as when the electric-resistance welded metal pipe is cut, making it necessary to remove the expelled metal.

[0005] The present invention has been made to solve the above-mentioned problems, and one of its objects is to provide an electric-welded metal pipe and a method for manufacturing an electric-welded metal pipe that can suppress peeling of exhaust metal from the inner surface of the electric-welded metal pipe and reduce the need for the operation of removing the exhaust metal. [Means for solving the problem]

[0006] In one embodiment, an electric-welded metal pipe according to the present invention comprises a metal pipe main body having a butt joint, and an excess filler and expendable metal formed at the butt joint, and in a cross section perpendicular to the longitudinal direction of the metal pipe main body, the excess filler has a bottom surface extending from a base of the expendable metal in the circumferential direction of the metal pipe main body, and a side wall surface protruding from the bottom surface towards the inside of the metal pipe main body, and the expendable metal is in contact with the bottom surface and the side wall surface but is not welded to them.

[0007] In one embodiment, a manufacturing method of electric-welded metal pipe according to the present invention is a manufacturing method of electric-welded metal pipe in which side ends of metal bands are butted together and then the side ends are welded by high-frequency heating to manufacture an electric-welded metal pipe, the metal band having an inner surface corresponding to the inner circumferential surface of the electric-welded metal pipe, end faces of the side ends, and an inner surface side corner provided at a position where the inner surface and the end face butt together, and the manufacturing method includes a straightening step of straightening the shape of the inner surface side corner before butting the side ends of the metal band, and in the straightening step, a first inclined surface and a second inclined surface are formed on the inner surface side corner, the first inclined surface is connected to the inner surface and extends at an incline with respect to the inner surface, and the second inclined surface is provided between the first inclined surface and the end face of the side end and extends at an incline with respect to the first inclined surface, and the inner surface side corner is straightened so that when the metal band is bent and the side ends of the metal band are butted together, a connection point between the first inclined surface and the inner surface is located inside in the width direction of the metal band with respect to an extension line of the end face of the side end. Effect of the Invention

[0008] According to the electric welded metal pipe of the present invention, the discharged metal is in contact with the bottom surface and the side wall surface but is not welded thereto, so peeling of the discharged metal from the inner surface of the electric welded metal pipe can be suppressed and the need for removal of the discharged metal can be reduced.

[0009] Furthermore, according to one embodiment of the electric-welded metal pipe and the manufacturing method of the electric-welded metal pipe of the present invention, the inner corner is corrected so that when the metal strip is bent and the side ends of the metal strip are butted together, the connection point between the first inclined surface and the inner surface is located inside in the width direction of the metal strip from the extension line of the end face of the side end, which reduces the risk of the discharged metal bonding to the excess metal and more reliably forms a state in which the discharged metal is in contact with the bottom surface and the side wall surface but is not bonded thereto. This makes it possible to suppress peeling of the discharged metal from the inner surface of the electric-welded metal pipe and reduces the need for the operation of removing the discharged metal. [Brief description of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view of an electric-resistance welded metal pipe according to an embodiment of the present invention. [Diagram 2] FIG. 2 is an explanatory diagram illustrating the excess metal and the expelled metal of FIG. 1. [Diagram 3] 4 is a cross-sectional view of a metal strip whose side end shape has been corrected in a correction step of a manufacturing method for an electric-resistance welded metal pipe according to an embodiment of the present invention. FIG. [Figure 4] 4 is an explanatory diagram showing a state in which the side ends of the metal strips in FIG. 3 are butted together. FIG. [Diagram 5] 5 is an explanatory diagram showing an enlarged view of region V in FIG. 4. [Figure 6] 1 is an explanatory diagram showing an electric-resistance welded metal pipe production apparatus for carrying out a method of producing an electric-resistance welded metal pipe according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, the embodiments for carrying out the present invention will be described with reference to the drawings. The present invention is not limited to each embodiment, and the components can be modified and embodied without departing from the gist of the present invention. In addition, various inventions can be formed by appropriately combining multiple components disclosed in each embodiment. For example, some components may be deleted from all the components shown in the embodiments. Furthermore, components of different embodiments may be appropriately combined.

[0012] Fig. 1 is a cross-sectional view of an electric-resistance welded metal pipe 1 according to an embodiment of the present invention. As shown in Fig. 1, the electric-resistance welded metal pipe 1 comprises a metal pipe body 10 having a butt joint 11, and a reinforcement 113 and an expendable metal 114 formed at the butt joint 11.

[0013] The metal pipe body 10 is a longitudinal pipe body, and has a butt joint 11 in a circumferential portion thereof. Fig. 1 shows a cross section of the electric resistance welded metal pipe 1 at the butt joint 11, which is perpendicular to the longitudinal direction of the metal pipe body 10.

[0014] As will be described later with reference to FIG. 6, the electric-resistance welded metal pipe 1 is formed by joining side ends 20 of a metal band 2 together. The metal band 2 can be gradually curved to form an open pipe 3. The open pipe 3 is a tube with a C-shaped cross section in which both side ends 20 of the metal band 2 along the width direction 2b are butted against each other, and an opening is provided at the portion where the side ends 20 are butted. By restraining the outer periphery of the open pipe 3 and heating the side ends 20 of the metal band 2 while pressing them against each other, the side ends 20 are welded to each other to form the butt joint 11 shown in FIG. 1.

[0015] The butt joint 11 includes a joint 110 and a heat-affected zone 111. The joint 110 is a portion where the side ends 20 of the molten metal strip 2 are joined to each other. The heat-affected zone 111 is a portion affected by heating when the side ends 20 are melted, and is formed on both sides of the joint 110. Non-heat-affected zones 112 are provided on both sides of the heat-affected zone 111. The non-heat-affected zone 112 constitutes a part of the metal pipe body 10. The joint 110 and the heat-affected zone 111 have structures that are changed from the non-heat-affected zone 112 due to the influence of heat.

[0016] A weld 113 is formed in the heat-affected zone 111. The weld 113 is a portion in which metal softened in the heat-affected zone 111 is raised by the pressure when the side ends 20 of the metal strip 2 are pressed against each other. The weld 113 protrudes inward of the metal pipe body 10 beyond a virtual inner circumferential surface 112a connecting the inner circumferential surfaces of the non-heat-affected zones 112 on both sides of the weld 113. The virtual inner circumferential surface 112a may be a straight line. The weld 113 is provided on both sides of the joint 110 in the circumferential direction of the metal pipe body 10.

[0017] A discharge metal 114 is formed at the joint 110. The discharge metal 114 protrudes from the joint 110 toward the inside of the metal pipe body 10. The discharge metal 114 is located inside the metal pipe body 10 from the imaginary inner circumferential surface 112a. The discharge metal 114 is formed by the molten metal being extruded from the joint 110 and solidified when the side ends 20 of the metal strip 2 are pressed against each other. The discharge metal 114 has a role of discharging oxides (penetrators) contained in the molten metal from the joint 110. A root 114a of the discharge metal 114 is integral with the joint 110. The maximum width of the discharge metal 114 in the circumferential direction of the metal pipe body 10 is wider than the width of the joint 110 in the same direction.

[0018] In the cross section (cross section shown in FIG. 1) perpendicular to the longitudinal direction of the metal pipe body 10, the excess weld 113 has a bottom surface 115 extending from the base 114a of the discharge metal 114 in the circumferential direction of the metal pipe body 10, and a side wall surface 116 protruding from the bottom surface 115 toward the inside of the metal pipe body 10. The excess weld 113 may further have a top portion 117 located at the tip of the side wall surface 116, and an outer surface 118 extending in the circumferential direction of the metal pipe body 10 from the top portion 117 toward the non-heat-affected zone 112. The discharge metal 114 is in contact with the bottom surface 115 and the side wall surface 116, but is not welded to them. In other words, a concave groove is formed in the excess weld 113, and the discharge metal 114 is located inside the concave groove so as to be in contact with the inner wall of the concave groove. The discharge metal 114 is exposed toward the inside of the metal pipe body 10 between the top portions 117. The innermost end of the exhaust metal 114 may be located inside the metal tube body 10 from the top 117 .

[0019] Here, the toughness of the discharged metal 114 is reduced due to the influence of heat, and cracks are likely to occur in the discharged metal 114 when subjected to severe processing. Since the discharged metal 114 is not welded to the bottom surface 115 and the side wall surface 116, it is possible to prevent the cracks in the discharged metal 114 from propagating to the base material (recess 113). Meanwhile, since the discharged metal 114 is in contact with the bottom surface 115 and the side wall surface 116, it is possible to suppress peeling of the discharged metal 114 from the inner surface of the electric-resistance welded metal pipe 1. It is believed that the suppression of peeling of the discharged metal 114 is achieved by an anchor effect caused by a part of the discharged metal 114 entering fine gaps on the surfaces of the bottom surface 115 and the side wall surface 116 in the process of the discharged metal 114 being pushed out of the joint 110, and / or friction between the outer surface of the discharged metal 114 and the bottom surface 115 and the side wall surface 116.

[0020] 2 is an explanatory diagram that shows a schematic diagram of the excess filler 113 and the expulsion metal 114 in FIG. 2. As shown in FIG. 2, in a cross section perpendicular to the longitudinal direction of the metal pipe body 10, the bottom surface 115 and the side wall surface 116 are connected at a connection point 119. The connection point 119 may be the apex of a recessed corner formed by the bottom surface 115 and the side wall surface 116. The connection point 119 may form a line that extends along the longitudinal direction of the metal pipe body 10.

[0021] The angle θ0 formed by a first straight line L1 extending along the bottom surface 115 and a second straight line L2 extending along the side wall surface 116 outside the reinforcement 113 may be equal to or greater than 80° and less than 180°. The first straight line L1 may be a straight line passing through a base 114a of the discharge metal 114 and a connection point 119 between the bottom surface 115 and the side wall surface 116. The second straight line L2 may be a straight line passing through the connection point 119 and an apex 117 at the tip of the side wall surface 116. The apex 117 can be said to be the point of the reinforcement 113 that is located furthest inward of the electric-resistance welded metal pipe 1.

[0022] In addition, in a cross section perpendicular to the longitudinal direction of the metal pipe body 10, the angle θ1 between the first straight line L1 extending along the bottom surface 115 and the weld joint surface S0 inside the excess metal 113 is preferably 80° or more and 120° or less, and more preferably 90° or more and 120° or less. When the angle θ1 is less than 80°, the bottom surface 115 extends excessively in a direction approaching the imaginary inner circumferential surface 112a, and there is a risk that the contact area between the discharged metal 114 and the bottom surface 115 and the side wall surface 116 is reduced. That is, when the angle θ1 is 80° or more, the risk of the contact area between the discharged metal 114 and the bottom surface 115 and the side wall surface 116 being reduced can be reduced. When the angle θ1 is 90° or more, the risk of the contact area being reduced can be more reliably reduced. When the angle θ1 is more than 120°, the discharged metal 114 may be bitten in and / or insufficiently discharged, which may cause concerns about the strength of the welded portion. That is, by setting the angle θ1 to 120° or less, the possibility of concerns about the strength of the welded portion can be reduced. The weld joint surface S0 can be a surface that passes through the center position of the joint 110 in the circumferential direction of the metal pipe body 10. The weld joint surface S0 may pass through the center position of the metal pipe body 10 in the radial direction.

[0023] As described below, before the side ends 20 on both sides along the width direction 2b of the metal strip 2 are butted against each other, the shape of the inner side corner 23 of the metal strip 2 can be corrected as shown in Fig. 3. The angle θ1 can be adjusted by correcting the shape of the inner side corner 23. In addition, when the side ends 20 of the metal strip 2 are welded to each other by heating the side ends 20 of the metal strip 2 while pressing them against each other, the angle θ1 can be adjusted by adjusting the amount of upset (the amount of pressing of the side ends 20). The smaller the amount of upset, the larger the angle θ1.

[0024] In addition, in a cross section perpendicular to the longitudinal direction of the metal pipe body 10, the angle θ2 formed by the second straight line L2 extending along the side wall surface 116 and the third straight line L3 perpendicular to the welded joint surface S0 and passing through the connection point 119 between the bottom surface 115 and the side wall surface 116 outside the excess metal 113 is preferably 135° or less, more preferably 130° or less. When the angle θ2 exceeds 135°, there is a risk that the contact area between the side wall surface 116 and the discharged metal 114 will decrease. That is, by making the angle θ2 135° or less, the risk of the contact area between the side wall surface 116 and the discharged metal 114 decreasing can be reduced. Furthermore, by making the angle θ2 130° or less, the risk of the contact area decreasing can be more reliably reduced. Note that the lower limit of the angle θ2 is not particularly limited, but for example, a lower limit of about 80° is considered as the lower limit at which the side wall surface 116 can remain without melting.

[0025] As described below, before the side ends 20 on both sides along the width direction 2b of the metal strip 2 are butted against each other, the shape of the inner side corner 23 of the metal strip 2 can be corrected as shown in Fig. 3. The angle θ2 can be adjusted by correcting the shape of the inner side corner 23. In addition, when the side ends 20 of the metal strip 2 are welded to each other by heating the side ends 20 of the metal strip 2 while pressing them against each other, the angle θ2 can be adjusted by adjusting the amount of upset (the amount of pressing of the side ends 20). The greater the amount of upset, the greater the angle θ2.

[0026] In addition, in a cross section perpendicular to the longitudinal direction of the metal pipe body 10, the height H of the side wall surface 116 is preferably 0.2 mm or more. When the height H is 0.2 mm or more, the side wall surface 116 envelops the exhaust metal 114, and the contact area between the side wall surface 116 and the exhaust metal 114 can be secured, and peeling of the exhaust metal 114 can be more reliably suppressed. The height H may be the shortest distance between the top 117 and the third straight line L3. Note that, although there is no particular limit to the upper limit of the height H, even if the height H exceeds the height of the exhaust metal 114, it does not contribute to securing the contact area between the exhaust metal 114 and the side wall surface 116, so the height of the exhaust metal 114 is considered to be the upper limit of the height H. In general, the height of the exhaust metal 114 may be about 30% of the wall thickness of the metal pipe body 10.

[0027] As described below, before the side ends 20 on both sides along the width direction 2b of the metal strip 2 are butted against each other, the shape of the inner side corners 23 of the metal strip 2 can be corrected as shown in Fig. 3. The height H can be adjusted by correcting the shape of the inner side corners 23. In addition, when the side ends 20 of the metal strip 2 are welded to each other by heating the side ends 20 of the metal strip 2 while pressing them against each other, the height H can be adjusted by adjusting the amount of upset (the amount of pressing of the side ends 20). The greater the amount of upset, the smaller the height H.

[0028] Next, a method for producing an electric-resistance welded metal pipe 1 according to an embodiment of the present invention will be described with reference to Fig. 3 to Fig. 5. Fig. 3 is a cross-sectional view of a metal strip 2 whose side ends 20 have been straightened in a straightening step in the method for producing an electric-resistance welded metal pipe 1 according to an embodiment of the present invention, Fig. 4 is an explanatory diagram showing a state in which the side ends 20 of the metal strip 2 in Fig. 3 are butted together, and Fig. 5 is an explanatory diagram showing an enlarged view of region V in Fig. 4.

[0029] The manufacturing method of the electric-resistance welded metal pipe 1 involves butting side ends 20 of metal bands 2 together and then welding the side ends 20 by high-frequency heating to manufacture the electric-resistance welded metal pipe 1. As shown in Fig. 3, the metal band 2 has an inner surface 21 that corresponds to the inner circumferential surface of the electric-resistance welded metal pipe 1, an end face 22 of the side end 20, and an inner surface side corner portion 23 provided at a position where the inner surface 21 and the end face 22 butt against each other.

[0030] The manufacturing method of the electric-resistance welded metal pipe 1 includes a straightening step of straightening the shape of the inner surface corner 23 as shown in FIG. 3 before butting the side ends 20 of the metal strip 2. The straightening step may be performed before bending the metal strip 2. In the straightening step, a first inclined surface 231 and a second inclined surface 232 are formed on the inner surface corner 23. The first inclined surface 231 is connected to the inner surface 21 and extends at an incline with respect to the inner surface 21. The second inclined surface 232 is provided between the first inclined surface 231 and the end face 22 of the side end 20 and extends at an incline with respect to the first inclined surface 231. Note that the inner surface corner 23 before straightening may form a right angle defined by an extension line of the inner surface 21 and an extension line of the end face 22 in FIG. 3.

[0031] As shown in Fig. 4, the inner surface corner 23 is corrected so that when the metal strip 2 is bent and the side ends 20 of the metal strip 2 are butted together, the connection point 231a between the first inclined surface 231 and the inner surface 21 is located inside the extension line EL (see Fig. 5) of the end face 22 of the side end 20 in the width direction W of the metal strip 2. If the connection point 231a protrudes outside the extension line EL of the end face 22 in the width direction W of the metal strip 2, the discharged metal 114 tends to be welded to the excess metal 113 after the side ends 20 of the metal strip 2 are pressed against each other and joined (welded). That is, by correcting the inner surface corner 23 as described above, the risk of the discharged metal 114 being welded to the excess metal 113 can be reduced, and a state in which the discharged metal 114 is in contact with the bottom surface 115 and the side wall surface 116 but not welded can be more reliably formed. The time when the metal strip 2 is curved and the side ends 20 of the metal strip 2 are butted together may be the time immediately after the metal strip 2 leaves the final roll of the forming roll group 5 in Fig. 6 and before the metal strip 2 is introduced into the squeeze roll 61 in Fig. 6. The final roll of the forming roll group 5 may be a fin pass roll.

[0032] As shown in Figures 4 and 5, in a state where the metal strip 2 is curved and the side ends 20 of the metal strip 2 are butted against each other, in a cross section perpendicular to the longitudinal direction of the metal strip 2, the length of the second inclined surface 232 is B (mm), the length of the first inclined surface 231 is C (mm), the angle formed by an extension line EL of the end surface 22 and a fourth straight line L4 extending along the second inclined surface 232 at the outside of the inner surface side corner 23 is φ1 (°), and the angle formed by a fifth straight line L5 extending along the first inclined surface 231 and the fourth straight line L4 at the outside of the inner surface side corner 23 is φ2 (°), B≧0.76 mm; φ2<180°, Bsin(φ1)-Ccos(φ1+φ2-90°)>0.3 By satisfying these conditions, it is possible to more reliably form a state in which the exhaust metal 114 is in contact with the bottom surface 115 and the side wall surface 116 while being not welded thereto.

[0033] It is more preferable to correct the inner side corner 23 so as to further satisfy B≧0.80 mm, and to set the upset amount when joining the side end 20 to 0.5 mm or more and 0.8 mm or less. This makes it possible to more reliably form a state in which the discharge metal 114 contacts the bottom surface 115 and the side wall surface 116 while being not welded thereto.

[0034] The upset amount corresponds to the amount by which the side ends 20 are pressed when they are joined, and is the difference between the circumferential length of the open pipe 3 immediately before welding and the circumferential length of the electric-resistance welded metal pipe 1 immediately after welding. More specifically, the upset amount can be expressed as the difference between the circumferential length of the open pipe 3 at a position immediately before it is introduced into a squeeze roll 61 (described below) minus the distance between the end faces of the open pipe 3 at the same position, and the circumferential length of the electric-resistance welded metal pipe 1 after electric-resistance welding. The position immediately before it is introduced into the squeeze roll 61 can be set to a position 1 m before the squeeze roll 61.

[0035] The fourth straight line L4 may be a straight line passing through a connection point 232a between the end face 22 and the second inclined surface 232 and a connection point 232b between the second inclined surface 232 and the first inclined surface 231. The fifth straight line L5 may be a straight line passing through a connection point 232b between the second inclined surface 232 and the first inclined surface 231 and a connection point 231a between the first inclined surface 231 and the inner surface 21. "Bsin(φ1)-Ccos(φ1+φ2-90°)" represents the shortest distance between the connection point 231a between the first inclined surface 231 and the inner surface 21 and the extension line EL of the end face 22.

[0036] In addition, the upper limit of the length B of the second inclined surface 232, the lower limit of the angle φ2, and the upper limit of "Bsin(φ1)-Ccos(φ1+φ2-90°)" can be appropriately determined according to the implementation conditions. By keeping the length B of the second inclined surface 232 at an appropriate length, it is possible to avoid the risk of the contact area between the first inclined surface 231 and the discharge metal 114 becoming small. By ensuring an appropriate angle φ2, it is possible to avoid the welding of the discharge metal 114 to the excess metal 113. By keeping "Bsin(φ1)-Ccos(φ1+φ2-90°)" at an appropriate value, it is possible to avoid the risk of the contact area between the first inclined surface 231 and the discharge metal 114 becoming small.

[0037] The metal band 2 also has an outer surface 24 that corresponds to the outer peripheral surface of the electric-resistance welded metal pipe 1, and an outer surface side corner 25 provided at a position where the outer surface 24 and the end face 22 butt against each other. The manufacturing method of the electric-resistance welded metal pipe 1 may further include a second straightening step of straightening the shape of the outer surface side corner 25 as shown in FIG. 4 before butting the side ends 20 of the metal band 2 together. In straightening the outer surface side corner 25, a third inclined surface 251 is formed at the outer surface side corner 25. The third inclined surface 251 is connected to the outer surface 24 and extends at an angle relative to the outer surface 24.

[0038] Next, Fig. 6 is an explanatory diagram showing an electric-welded metal pipe production apparatus for carrying out a method for producing an electric-welded metal pipe 1 according to an embodiment of the present invention. The electric-welded metal pipe production apparatus in Fig. 6 is an apparatus for producing an electric-welded metal pipe 1 from a flat metal strip 2 via an open pipe 3. The electric-welded metal pipe production apparatus is provided with crushing equipment 4, a group of forming rolls 5, and welding equipment 6.

[0039] The crushing equipment 4 is equipment for correcting the shape of the inner corners 23 (see FIG. 3, etc.) of the metal strip 2 before the side ends 20 of the metal strip 2 are butted together. The crushing equipment 4 is provided with a pair of crushing rolls 40 arranged at a distance from each other along the width direction 2b of the metal strip 2. The metal strip 2 is passed between the pair of crushing rolls 40, and the inner corners 23 are pressed against the crushing rolls 40, thereby correcting the shape of the inner corners 23.

[0040] The forming roll group 5 is composed of a plurality of forming rolls, and is disposed downstream of the crushing equipment 4 along the conveying direction 2a of the metal strip 2. The metal strip 2, the shape of which has been corrected at the crushing equipment 4, is gradually curved by the forming roll group 5 into an open pipe 3. The open pipe 3 is formed by butting both side ends 20 of the metal strip 2 along the width direction 2b against each other, and is a tubular body with a C-shaped cross section having an opening at the portion where the side ends 20 are butted against each other.

[0041] Although not shown in detail, the final roll of the forming roll group 5 may be a fin pass roll. The fin pass roll can correct the shape of the outer surface side corner portion 25 as shown in FIG.

[0042] The welding equipment 6 is an equipment arranged downstream of the forming roll group 5 along the conveying direction 2a of the metal strip 2, and has a heating coil 60 and a squeeze roll 61. The heating coil 60 is a coil through which a high-frequency current is passed. When the open pipe 3 is passed inside the heating coil 60, the side end 20 of the metal strip 2 constituting the open pipe 3 is heated (high-frequency heating) and melted. The squeeze roll 61 is composed of a pair of side rolls that restrain the outer periphery of the open pipe 3, and the side ends 20 of the metal strip 2 in the open pipe 3 that have been melted by heating in the heating coil 60 are pressed against each other to join (weld).

[0043] That is, in the electric-welded metal pipe manufacturing apparatus of the present embodiment, side ends 20 of metal strips 2 are butted together and then the side ends 20 are welded by high-frequency heating to produce an electric-welded metal pipe 1. Although not shown, straightening equipment may be provided downstream of the welding equipment 6 to straighten the size and shape of the metal pipe after electric-welding (the metal pipe immediately after the welding equipment 6). When straightening equipment is provided, the metal pipe after straightening in the straightening equipment corresponds to the electric-welded metal pipe 1. On the other hand, when straightening equipment is not provided, the metal pipe after electric-welding corresponds to the electric-welded metal pipe 1.

[0044] In the above explanation, the shape of the inner corner 23 is corrected by pressing the crushing roll 40 against the inner corner 23, but the shape of the inner corner 23 can also be corrected by forming with a fin pass roll of a forming roll, cutting with a cutting tool, grinding with a grinder, or a combination of these methods.

[0045] Although the preferred embodiment of the present invention has been described in detail above with reference to the accompanying drawings, the present invention is not limited to such an example. It is clear that a person having ordinary knowledge in the technical field to which the present invention pertains can conceive of various modified or altered examples within the scope of the technical ideas described in the claims, and it is understood that these also naturally belong to the technical scope of the present invention. EXAMPLES

[0046] The inventors produced a number of prototype electric-welded metal pipes 1 while changing the correction conditions for the inner corners 23 as shown in Table 1 below. An electric-welded metal pipe manufacturing apparatus shown in Fig. 6 was used to produce the electric-welded metal pipes 1, and the shape of the crushing roll 40 was changed to change the correction conditions for the inner corners 23. All of the prototype electric-welded metal pipes 1 had an outer diameter of 25.4 mm and a wall thickness of 4.5 mm.

[0047] [Table 1]

[0048] The column "Edge Shape 1" in Table 1 shows the shape of the inner corner portion 23 immediately after it has exited the crushing roll 40. The shape immediately after it has exited the crushing roll 40 corresponds to the shape in FIG.

[0049] The column "Edge Shape 2" in Table 1 shows the shape of the inner corner portion 23 immediately after it has exited the group of forming rolls 5. The shape immediately after it has exited the group of forming rolls 5 corresponds to the shapes in Figs. 4 and 5, and its dimensions are also affected by the curvature of the metal strip 2.

[0050] The "Upset Amount" column in Table 1 indicates the upset amount of the open pipe 3 in the welding equipment 6. As described above, the upset amount corresponds to the amount by which the side ends 20 are pressed when they are joined, and is the difference between the circumferential length of the open pipe 3 immediately before welding and the circumferential length of the electric-resistance welded metal pipe 1 immediately after welding.

[0051] The "Bead Shape" column in Table 1 shows the shape of the butt joint 11 after it has exited the welding equipment 6. The shape after it has exited the welding equipment 6 corresponds to the shapes in Figs. 1 and 2.

[0052] The "peeling" column in Table 1 indicates the frequency of peeling of the discharge metal 114. A double circle (◎) indicates that the frequency of peeling of the discharge metal 114 was extremely low, a circle (◯) indicates that the frequency of peeling of the discharge metal 114 was low, and a cross (×) indicates that the frequency of peeling of the discharge metal 114 was high.

[0053] The "Overall" column in Table 1 shows an overall evaluation taking into consideration the welding condition of the electric-resistance welded metal pipe 1 and the frequency of peeling of the discharged metal 114. A double circle (◎) indicates that the welding condition was good and the frequency of peeling of the discharged metal 114 was extremely low, a circle (◯) indicates that the welding condition was good and the frequency of peeling of the discharged metal 114 was low, a triangle (△) indicates that the frequency of peeling of the discharged metal 114 was low but the welding condition was not good, and a cross (×) indicates that the welding condition was poor.

[0054] Examples 1 to 6 are examples in which the inner surface side corner 23 is corrected so that when the metal strip 2 is bent and the side ends 20 of the metal strip 2 are butted together, the connection point 231a between the first inclined surface 231 and the inner surface 21 is located more inward in the width direction W of the metal strip 2 than the extension line EL of the end face 22 of the side end 20. When "Bsin(φ1)-Ccos(φ1+φ2-90°)" in the table is positive, it indicates that the connection point 231a is located more inward in the width direction W of the metal strip 2 than the extension line EL.

[0055] In contrast, comparative example 1 is an example in which the inner side corner 23 is corrected so that when the metal strip 2 is bent and the side ends 20 of the metal strip 2 are butted together, the connection point 231a between the first inclined surface 231 and the inner surface 21 protrudes outward in the width direction W of the metal strip 2 beyond the extension line EL of the end face 22 of the side ends 20.

[0056] In Comparative Example 1, the expulsion metal 114 was welded to the excess metal 113. In contrast to this, in Examples 1 to 5, the expulsion metal 114 was not welded to the excess metal 113, and the expulsion metal 114 was in contact with the bottom surface 115 and the side wall surface 116 while remaining unwelded.

[0057] From these results, it was confirmed that, when the metal strip 2 is bent and the side ends 20 of the metal strip 2 are butted together, by correcting the inner side corner 23 so that the connection point 231a between the first inclined surface 231 and the inner surface 21 is positioned inside the extension line EL of the end face 22 of the side end 20 in the width direction W of the metal strip 2, the risk of the discharge metal 114 welding to the excess metal 113 can be reduced, and a state in which the discharge metal 114 is in contact with the bottom surface 115 and the side wall surface 116 while being non-welded can be more reliably formed.

[0058] As described above, Examples 1 to 6 are examples in which the exhaust metal 114 was in contact with the bottom surface 115 and the side wall surface 116 while remaining in a non-welded state. When peeling of the exhaust metal 114 was investigated in these examples, the occurrence frequency of peeling of the exhaust metal 114 was low in all cases.

[0059] In contrast, the frequency of peeling of the discharged metal 114 was high in Comparative Examples 2 and 3. These Comparative Examples 2 and 3 are examples in which the discharged metal 114 was not welded to the excess metal 113, but either the bottom surface 115 or the side wall surface 116 was missing. It is believed that because either the bottom surface 115 or the side wall surface 116 was missing, the discharged metal 114 was prone to peeling from the inner surface of the electric-resistance welded metal pipe 1.

[0060] From these results, it was confirmed that by forming a state in which the discharge metal 114 is in contact with the bottom surface 115 and the side wall surface 116 while being non-welded, peeling of the discharge metal 114 from the inner surface of the electric-welded metal tube 1 can be suppressed, and the need for removal work of the discharge metal 114 can be reduced.

[0061] In particular, Examples 1 to 3 are examples in which, in a cross section perpendicular to the longitudinal direction of the metal pipe body 10, the angle θ1 that a first straight line L1 extending along the bottom surface 115 makes with the weld joint surface S0 inside the excess metal 113 is equal to or greater than 90° and equal to or less than 120°, and, in a cross section perpendicular to the longitudinal direction of the metal pipe body 10, the angle θ2 that a second straight line L2 extending along the side wall surface 116 makes with a third straight line L3 that is perpendicular to the weld joint surface S0 and passes through a connection point 119 between the bottom surface 115 and the side wall surface 116 outside the excess metal 113 is equal to or less than 130°, and, in a cross section perpendicular to the longitudinal direction of the metal pipe body 10, the height H of the side wall surface 116 is 0.2 mm or more.

[0062] On the other hand, Example 4 is an example in which the angle θ1 is less than 90°, Example 5 is an example in which the angle θ2 exceeds 130°, and Example 6 is an example in which the height H of the side wall surface 116 is less than 0.2 mm. In Examples 1 to 3, the frequency of peeling of the discharged metal 114 was lower than in Examples 4 to 6. In Comparative Example 5, the angle θ1 exceeds 120°, and the welding state in Comparative Example 5 was poor. From this, it was confirmed that peeling of the discharged metal 114 from the inner surface of the electric-seam welded metal pipe 1 can be more reliably suppressed by setting the angle θ1 to 90° or more and 120° or less, the angle θ2 to 130° or less, and the height H of the side wall surface 116 to 0.2 mm or more, as in Examples 1 to 3.

[0063] Here, as shown in the column "Edge shape 2", when B≧0.76 mm, φ2<180°, and Bsin(φ1)-Ccos(φ1+φ2-90°)>0.3, Examples 1 to 6 with an overall evaluation of double circle (◎) or circle (◯) could be manufactured. From this, it can be understood that by correcting the inner surface side corner 23 so as to satisfy B≧0.76 mm, φ2<180°, and Bsin(φ1)-Ccos(φ1+φ2-90°)>0.3, it is possible to more reliably suppress peeling of the discharged metal 114 from the inner surface of the electric-resistance welded metal pipe 1. In addition, by correcting the inner surface side corner 23 so as to further satisfy B≧0.80 mm and setting the upset amount when joining the side end 20 to 0.5 mm or more and 0.8 mm or less, Examples 1 to 3 with an overall evaluation of double circle (◎) could be manufactured. From this, it can be seen that by correcting the inner surface side corner 23 so as to further satisfy B≧0.80 mm, and setting the upset amount when joining the side end 20 to 0.5 mm or more and 0.8 mm or less, it is possible to even more reliably suppress peeling of the discharged metal 114 from the inner surface of the electric welded metal pipe 1. [Explanation of symbols]

[0064] 1: ERW metal pipe 2: Metal strip 10:Metal tube body 11: Butt joint 110: Joint 113:Yamori 114: Discharge metal 114a :root 115: Bottom 116: Side wall surface 119: Connection point 20: Side edge 21 :Inner surface 22: End face 23: Inner side corner 231: 1st slope 232:Second slope 40: Crushing roll

Claims

1. A metal pipe body having a butt joint; The excess metal and the discharged metal formed on the butt joint portion; Equipped with the excess weld has, in a cross section perpendicular to the longitudinal direction of the metal pipe body, a bottom surface extending from a base of the discharged metal in a circumferential direction of the metal pipe body and a side wall surface protruding from the bottom surface toward an inside of the metal pipe body, The exhaust metal is in contact with the bottom surface and the side wall surface while being non-welded. ERW metal tube.

2. In a cross section perpendicular to the longitudinal direction of the metal pipe main body, an angle (θ1) formed between a first straight line extending along the bottom surface and a weld joint surface within the reinforcement is 90° or more and 120° or less, in a cross section perpendicular to the longitudinal direction of the metal pipe main body, an angle (θ2) formed by a second straight line extending along the side wall surface and a third straight line perpendicular to the weld joint surface and passing through a connection point between the bottom surface and the side wall surface outside the reinforcement is 130° or less, In a cross section perpendicular to the longitudinal direction of the metal pipe body, the height (H) of the side wall surface is 0.2 mm or more. The electric-resistance welded metal tube according to claim 1 .

3. In a cross section perpendicular to the longitudinal direction of the metal pipe body, an angle (θ1) formed between a first straight line extending along the bottom surface and a weld joint surface within the reinforcement is 90° or more and 120° or less. The electric-resistance welded metal tube according to claim 1 .

4. In a cross section perpendicular to the longitudinal direction of the metal pipe body, an angle (θ2) formed by a second straight line extending along the side wall surface and a third straight line perpendicular to the weld joint surface and passing through a connection point between the bottom surface and the side wall surface outside the reinforcement is 130° or less. The electric-resistance welded metal tube according to claim 1 .

5. In a cross section perpendicular to the longitudinal direction of the metal pipe body, the height (H) of the side wall surface is 0.2 mm or more. The electric-resistance welded metal tube according to claim 1 .

6. A method for manufacturing an electric-resistance welded metal pipe, comprising the steps of: butting side ends of metal strips together and then welding the side ends by high-frequency heating to manufacture an electric-resistance welded metal pipe, wherein the metal strip has an inner surface corresponding to an inner circumferential surface of the electric-resistance welded metal pipe, end faces of the side ends, and an inner surface side corner portion provided at a position where the inner surface and the end face butt against each other, A correction process is included in which the shape of the inner side corner portion is corrected before the side ends of the metal strips are butted together, In the straightening step, a first inclined surface and a second inclined surface are formed on the inner surface side corner portion, the first inclined surface is connected to the inner surface and extends at an incline with respect to the inner surface, and the second inclined surface is provided between the first inclined surface and an end surface of the side end and extends at an incline with respect to the first inclined surface, the inner surface side corner is corrected so that, when the metal strip is bent and the side ends of the metal strip are butted together, a connection point between the first inclined surface and the inner surface is positioned inside in the width direction of the metal strip with respect to an extension line of the end face of the side end. A method for manufacturing electric resistance welded metal pipe.

7. When the metal strip is bent and the side ends of the metal strip are butted together, in a cross section perpendicular to the longitudinal direction of the metal strip, the length of the second inclined surface is B (mm), the length of the first inclined surface is C (mm), the angle between an extension line of the end surface and a fourth straight line extending along the second inclined surface at the outside of the inner surface side corner is φ1 (°), and the angle between a fifth straight line extending along the first inclined surface and the fourth straight line at the outside of the inner surface side corner is φ2 (°), B≧0.76 mm, φ2<180°, and Bsin(φ1)-Ccos(φ1+φ2-90°)>0.3 The inner surface side corner is corrected so as to satisfy the above. The method for producing an electric-resistance welded metal pipe according to claim 6.

8. The inner corner is corrected so as to further satisfy B≧0.80 mm, The upset amount when joining the side ends is set to 0.5 mm or more and 0.8 mm or less. The method for producing an electric-resistance welded metal pipe according to claim 7.

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