Steel pipe connection structure and steel pipe pile

Abstract

To achieve both low cost and structural performance.SOLUTION: A steel pipe connection structure for axially connecting a first steel pipe and a second steel pipe includes an inner fitting member joined to an axial end of the first steel pipe and an outer fitting member joined to an axial end of the second steel pipe. The inner fitting member includes an inner fitting portion that fits inside the outer fitting member, and the outer fitting member includes an outer fitting portion that fits outside the inner fitting member. The inner fitting portion and the outer fitting portion are provided with a retaining portion in the axial direction. At least one of the inner fitting member and the outer fitting member is formed from a ring-forged material. At least one of the yield point and 0.2% proof stress of the ring-forged material is 215 MPa or more and 550 MPa or less, and the tensile strength is 400 MPa or more and 720 MPa or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a steel pipe connection structure and a steel pipe pile. [Background technology]

[0002] Welding is a common method for connecting steel pipes. However, as pipe diameters increase, welding time increases, and welding quality varies depending on the welder's skill and weather conditions. Furthermore, in construction sites with headroom restrictions, it is necessary to increase the number of joints and reduce work time. In such cases, a steel pipe joining method using mechanical joints, which allows for rapid construction without on-site welding, is effective. However, because joints are made by fitting together, materials must be strengthened to compensate for the loss of structural performance due to cross-sectional defects. Furthermore, mechanical joints generally require machining to ensure dimensional accuracy during fitting, resulting in significant costs. Furthermore, increasing joint strength necessitates welding using high-strength materials that require preheating and postheating when attached to the steel pipe. While reducing the weight of the material itself is an effective way to reduce the manufacturing and installation costs of mechanical joints, thinning joints can lead to unintended deformations that can degrade the fit and potentially compromise the design strength.

[0003] For example, Patent Documents 1 and 2 disclose a method for manufacturing steel pipes at low cost by rolling steel plates that meet certain chemical composition requirements into a cylindrical shape and welding the ends of the steel plates together. Patent Document 3 discloses a steel pipe pile in which the joints of a straight-seam steel pipe manufactured by rolling are positioned in a position with higher rigidity in the circumferential direction than other parts. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-105550 [Patent Document 2] Patent No. 7207245 [Patent Document 3] Patent No. 6579945 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the technologies described in Patent Documents 1 and 2 not only increase costs and reduce weldability due to the use of alloys such as Cr and Mo, but also necessitate skill and inspection to ensure high-quality welding, as the presence of welds at the joints can become weak points when transmitting loads. Furthermore, because high-strength materials are assumed, the joints are expected to be relatively thin compared to the thickness of the steel pipe to which they are attached in their final use. This results in insufficient rigidity, which can lead to unexpected deformation and failure to achieve the designed yield strength. Furthermore, the technology described in Patent Document 3 has the risk of unexpected fracture due to the presence of seams in highly rigid areas where loads are easily transmitted.

[0006] Therefore, an object of the present invention is to provide a steel pipe connection structure and a steel pipe pile that can achieve both low cost and structural performance. [Means for solving the problem]

[0007] [1] A steel pipe connection structure that axially connects first and second steel pipes, comprising an inner fitting member joined to the axial end of the first steel pipe and an outer fitting member joined to the axial end of the second steel pipe, wherein the inner fitting member includes an inner fitting portion that fits inside the outer fitting member, and the outer fitting member includes an outer fitting portion that fits outside the inner fitting member, and the inner fitting portion and the outer fitting portion are provided with anti-slip portions in the axial direction, and at least one of the inner fitting member and the outer fitting member is formed from a ring forged material, and at least one of the ring forged material has a yield point or 0.2% proof stress of 215 MPa or more and 550 MPa or less, and a tensile strength of 400 MPa or more and 720 MPa or less. [2] A steel pipe connection structure for axially connecting first and second steel pipes, comprising an inner fitting member joined to the axial end of the first steel pipe and an outer fitting member joined to the axial end of the second steel pipe, wherein the inner fitting member includes an inner fitting portion that fits inside the outer fitting member, and the outer fitting member includes an outer fitting portion that fits outside the inner fitting member, and the inner fitting portion and the outer fitting portion are provided with anti-slip portions in the axial direction, and at least one of the inner fitting member and the outer fitting member is formed from a ring forged material, and the carbon equivalent Ceq of the ring forged material, defined by formula (i) in which the content of each element is expressed in mass%, is 0.2 or more and Ceq is 0.51 or less. TIFF2025154079000002.tif15170[3] A steel pipe connection structure as described in [1] or [2], wherein the thickness of the joint portion of the inner fitting member joined to the first steel pipe is thicker than the thickness of the first steel pipe, and the thickness of the joint portion of the outer fitting member joined to the second steel pipe is thicker than the thickness of the second steel pipe, or the thickness of the joint portion of the inner fitting member joined to the first steel pipe is thicker than the thickness of the first steel pipe, or the thickness of the joint portion of the outer fitting member joined to the second steel pipe is thicker than the thickness of the second steel pipe. [4] The steel pipe connection structure according to [1] or [2], wherein the ring forging has a non-circular cross section. [5] The steel pipe connection structure described in [1] or [2], wherein the retaining portion includes a first protrusion formed on the outside of the inner fitting portion, sandwiching a first gap portion in the circumferential direction, and a second protrusion formed on the inside of the outer fitting portion, sandwiching a second gap portion in the circumferential direction, and the first and second protrusions are configured to engage with each other when the inner fitting member is fitted inside the outer fitting member and rotated to a predetermined position. [6] The steel pipe connection structure described in [5], wherein the inner fitting portion includes one or more first protrusions arranged in the axial direction with a first groove portion therebetween, and the outer fitting portion includes one or more second protrusions arranged in the axial direction with a second groove portion therebetween, and when the first and second protrusions are engaged with each other, the first protrusions are located in the second groove portion and the second protrusions are located in the first groove portion. [7] The steel pipe connection structure described in [6], wherein the thickness of the first groove portion of the inner fitting member is formed thinner as it approaches the tip of the inner fitting portion in the axial direction, and the thickness of the second groove portion of the outer fitting member is formed thinner as it approaches the tip of the outer fitting portion in the axial direction. [8] A steel pipe connection structure as described in [6], wherein the thickness of the first groove portion of the inner fitting member is uniform regardless of the axial position, and the thickness of the second groove portion of the outer fitting member is uniform regardless of the axial position. [9] A steel pipe pile comprising multiple steel pipes connected by a steel pipe connection structure described in either [1] or [2]. [Effects of the Invention]

[0008] According to the above configuration, by forming the joint components having a retaining portion in the axial direction of the steel pipe from low-strength ring forging material, it is possible to provide joints with relatively thick walls and consistent material quality. This reduces the risk of unexpected deformation due to insufficient rigidity of the joint components and unexpected fractures originating from seams, for example, and enables stable joint performance to be achieved inexpensively without requiring special skills. By using low-strength forging material that does not use expensive alloy materials for the joint components, it is possible to provide joints that avoid the presence of singular points such as seams while keeping material costs and heat treatment costs low. This reduces the risk of unexpected fractures originating from singular points and enables stable joint performance to be achieved. [Brief explanation of the drawings]

[0009] [Figure 1]1 is a perspective view showing a steel pipe connection structure according to an embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view of the connection structure shown in FIG. [Figure 3] 3A to 3C are diagrams illustrating examples of cross-sectional shapes of joint members according to an embodiment of the present invention. [Figure 4] 3A to 3C are diagrams illustrating examples of cross-sectional shapes of joint members according to an embodiment of the present invention. [Figure 5] 3A to 3C are diagrams illustrating examples of cross-sectional shapes of joint members according to an embodiment of the present invention. [Figure 6] 1A to 1C are diagrams showing examples of cross-sectional shapes of a ring forging and a joint member according to an embodiment of the present invention. [Figure 7] 1A to 1C are diagrams showing examples of cross-sectional shapes of a ring forging and a joint member according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this specification and drawings, components having substantially the same functional configurations are designated by the same reference numerals, and redundant description will be omitted.

[0011] FIG. 1 is a perspective view showing a steel pipe connection structure according to one embodiment of the present invention, and FIG. 2 is a cross-sectional view of the connection structure shown in FIG. 1. The steel pipe connection structure 1 according to this embodiment connects steel pipes 21 and 22 in the axial direction. The manufacturing process for the steel pipes 21 and 22 is not particularly limited; for example, they may be spiral steel pipes with spirally formed welds, or electric resistance welded pipes or UO steel pipes with linearly formed welds. The connection structure 1 includes an inner fitting member 3 and an outer fitting member 4. In the following description, the axial direction refers to the axial direction of the steel pipes 21 and 22 and is illustrated as the z-direction. The circumferential direction is the direction of rotation around the axial direction and is illustrated as the y-direction. The radial direction is the direction perpendicular to the axial direction and is illustrated as the x-direction. The steel pipes 21 and 22, the inner fitting member 3, and the outer fitting member 4 are arranged coaxially after connection, so the axial, circumferential, and radial directions are common to these members.

[0012] The inner fitting member 3 and the outer fitting member 4, which are coupling members, are joined to the axial ends of the steel pipes 21 and 22 at welds 23 and 24, respectively, so that they face each other. The steel pipes 21 and 22 joined to the inner fitting member 3 and the outer fitting member 4 are connected by rotating the inner fitting member 3 axially to a predetermined position while fitted inside the outer fitting member 4 and fixing it with a rotation prevention key (not shown). The inner fitting member 3 includes a joint portion 31 joined to the steel pipe 21 and a fitting portion 32 (inner fitting portion) formed adjacent to the joint portion 31 and fitted inside the outer fitting member 4. One or more protrusions 321 (first protrusions) are formed on the outside of the fitting portion 32, sandwiching a gap portion 323 (first gap portion) in the circumferential direction. The length of the protrusions 321 in the circumferential direction is shorter than the length of the gap portion 323. One or more protrusions 321 are arranged in the axial direction, sandwiching a groove 322 therebetween. The outer fitting member 4 includes a joint portion 41 that is joined to the steel pipe 22, and a fitting portion 42 (outer fitting portion) that is formed subsequent to the joint portion 41 and fits onto the outside of the inner fitting member 3. Inside the fitting portion 42, one or more protrusions 421 (second protrusions) are formed, sandwiching a gap portion 423 therebetween in the circumferential direction. The length of the protrusion 421 is shorter than the length of the gap portion 423 in the circumferential direction. One or more protrusions 421 are arranged in the axial direction, sandwiching the groove portion 422 therebetween.

[0013] The lengths and spacing (circumferential dimensions), thickness (axial dimensions), and protrusion height (radial dimensions) of the protrusions 321, 421 correspond to each other so that the protrusions 321, 421 engage with each other when the inner fitting member 3 is rotated axially to a predetermined position while fitted inside the outer fitting member 4. With this configuration, the protrusions 321, 421 form a retaining structure in the axial direction. When the protrusions 321, 421 engage with each other, the protrusions 321 of the inner fitting member 3 are positioned in the grooves 422 of the outer fitting member 4, and the protrusions 421 of the outer fitting member 4 are positioned in the grooves 322 of the inner fitting member 3. By engaging the multiple protrusions provided on the inner and outer fitting members with each other, the risk of separation between the inner and outer fitting members is further reduced, allowing the joint structure to exhibit stable performance. In other embodiments, the anti-slip structure does not necessarily have to be formed by a protrusion, and may be formed, for example, by a screw, shear key, or shear plate that transmits load between the inner fitting member 3 and the outer fitting member 4.

[0014] 3 to 5 are diagrams showing examples of cross-sectional shapes of coupling members according to embodiments of the present invention. While each figure illustrates an inner fitting member, a similar configuration is also possible for the outer fitting member. In the example shown in FIGS. 3 and 4, the fitting portion 32 (inner fitting portion) of the inner fitting member includes three axially arranged protrusions 321A, 321B, and 321C, and grooves 322A, 322B, and 322C (first grooves) formed between the protrusion 321A and the joint portion 31 and between the protrusions 321A, 321B, and 321C, respectively. In the example shown in FIG. 5, the fitting portion 32 includes two protrusions 321A and 321B and grooves 322A and 322B. As shown in these examples, the number of steps in the inner fitting member and the outer fitting member, i.e., the number of protrusions and grooves, is not particularly limited and can be any number of one or more, preferably two or more. There is no particular upper limit, but it is preferably 4 stages or less.

[0015] In the example shown in FIG. 3 , the thickness of grooves 322A, 322B, and 322C of the inner fitting member is largest at groove 322A, followed by groove 322B, and smallest at groove 322C. In other words, the thickness of grooves 322A, 322B, and 322C of the inner fitting member in the illustrated example is thinner toward the axial tip of fitting portion 32 (positive side of the z-axis). In this case, fitting portion 42 (outer fitting portion) of the outer fitting member is formed similarly, and the thickness of the grooves of the outer fitting member is thinner toward the axial tip of fitting portion 42 (negative side of the z-axis). Similarly, gaps 323 and 423 in the circumferential direction are thinner toward the tip of fitting portion 32 and the tip of fitting portion 42, thereby serving as a guide during fitting and improving workability. In the example shown in FIG. 3 , gaps 323 and 423 are tapered. On the other hand, in the example shown in FIG. 4, the thickness of the grooves 322A, 322B, and 322C of the inner fitting member is uniform regardless of the axial position. In the example shown in FIG. 5, the thickness of the grooves 322A and 322B of the inner fitting member is also uniform regardless of the axial position. In these cases, the fitting portion 42 (outer fitting portion) of the outer fitting member is formed in the same way, and the thickness of the grooves of the outer fitting member is uniform regardless of the axial position. Here, the term "uniform thickness" is a concept based on design or drawing. For example, a uniform thickness is also considered when thickness differences occur within the range of manufacturing tolerances (within ±5%, strictly within ±3%, more strictly within ±1%), or when the radially cut surfaces of the protrusions and grooves are on approximately the same radius. By making the groove thickness uniform, the distribution of groove stress generated in response to the load received from the mutual engagement between the inner and outer fitting members is leveled, preventing localized concentration, especially at the tip end. This more effectively reduces the risk of separation between the inner and outer fitting members, resulting in stable performance of the joint structure. Furthermore, by increasing the thickness of grooves 322C and 422C, the joint's overall rigidity is increased, improving resistance to out-of-plane deformation. This allows for more uniform load distribution across each protrusion and groove. Furthermore, eliminating thickness differences in the grooves also reduces the thickness required for the ring forging 30, leading to cost savings.

[0016] 6 and 7 are diagrams showing examples of the cross-sectional shapes of ring forgings and joint members according to an embodiment of the present invention. In this embodiment, at least one of the joint members, the inner fitting member 3 and the outer fitting member 4, is manufactured by cutting a ring forging. In the example shown in FIG. 6, the inner fitting member 3, which has a different shape from that shown in FIG. 2, is manufactured by cutting a ring forging 30. Specifically, the outer peripheral surface of the ring forging 30 is machined to form the protrusions and grooves of the inner fitting member 3. In the illustrated example, the entire cross-sectional shape of the ring forging 30 is machined. However, the inner peripheral surface where no protrusions or grooves are formed and the portion of the outer peripheral surface corresponding to the joint 31 may be left unmachined and unfinished. On the other hand, in the example shown in FIG. 7, the outer fitting member 4 is manufactured by cutting a ring forging 40. Specifically, the inner peripheral surface of the ring forging 40 is machined to form the protrusions and grooves of the outer fitting member 4. In the illustrated example, the entire circumference of the cross-sectional shape of the ring forging 40 is machined, but the outer surface where no protrusions or grooves are formed and the portion corresponding to the joint 41 on the inner surface may be left as black skin without being machined.

[0017] In the example shown in FIG. 6 , the ring forged material 30 is a deformed forged material forged to a cross-sectional shape that matches the inner fitting member 3. Here, the deformed forged material is a forged material whose cross-sectional shape is not a simple shape such as a rectangle or a circle. The cross-sectional shape of the deformed forged material may be tapered on the outer and / or inner surfaces, as shown in the example shown in FIG. 6 , or may be thicker at the center than at the axial ends. Although the cost of the forging process is higher in the case of deformed forged material, the amount of cutting required to produce a joint member from the ring forged material is reduced, thereby reducing the cost of the cutting process. In this case, the deformed forged material has a cross-sectional shape that is thicker than the inner and outer surfaces of the inner fitting member 3 by, for example, about 5 mm or more. Deformed forged material can be used not only for the inner fitting member 3 but also for the outer fitting member 4. By manufacturing the joint components from ring forgings with irregular cross sections, the joint can be machined from ring forgings that are closer to the shape of the joint product, which minimizes the volume of the ring forgings and makes it easier to stabilize the quality of the ring forgings. This further reduces the risk of singularities in the joint components and enables more stable joint performance.

[0018] On the other hand, in the example shown in Figure 7 above, the ring forging 40 has a rectangular cross section and is not a deformed forging. The rectangular cross section referred to here does not necessarily have to be a strict rectangle, and includes shapes with rounded corners or beveled edges. For example, when the cross section of the outer fitting member 4 is close to a rectangle, as in the example shown in Figure 7 , the ring forging 40 can be made rectangular, reducing the cost of the forging process and the cost of the cutting process by reducing the amount of cutting. Ring forgings with rectangular cross sections can also be used for the inner fitting member 3, not just the outer fitting member 4. While the cross-sectional shape of the joint member according to the present invention is not particularly limited, a cross-sectional shape in which the thickness of the groove portion is uniform regardless of the axial position, as shown in Figures 4 and 5, is advantageous in that it facilitates reducing the amount of cutting when the ring forging is made into a shape with a rectangular cross section, which reduces the cost of the forging process.

[0019] In the present embodiment, the steel material used for the ring forging material for forming at least one of the fitting member 3 and the outer fitting member 4, which are joint members, is not one whose strength is enhanced by using alloy materials such as Cr and Mo or by heat treatment, but is a steel material having the same strength as, for example, the steel pipes 21 and 22. Specifically, for example, the ring forging material is formed of a steel material satisfying the conditions of 0.1 < C ≦ 0.25, Si ≦ 0.55, 0.6 ≦ Mn ≦ 2.0, P ≦ 0.035, and S ≦ 0.035 in terms of mass%. The carbon equivalent Ceq of this steel material is obtained from the following formula (1), and Ceq ≦ 0.51%, preferably Ceq ≦ 0.44%, more preferably Ceq ≦ 0.40%, and still more preferably Ceq ≦ 0.38%. The element symbols in formula (1) represent the content of each element in mass%. In the following description, % means mass% unless otherwise specified. The lower limit value of Ceq is, for example, 0.2 or more.

[0020]

Number

[0021] In particular, the upper limit of C in ordinary steel is 0.25% or less, but may be preferably 0.20% or less, more preferably 0.18% or less, and even more preferably 0.15% or less. The lower limit of C is preferably 0.05% or more, but more preferably 0.1% or more. The upper limit of Mn is preferably 2.0% or less, but more preferably 1.7% or less, and even more preferably 1.65% or less. The upper limit of P is preferably 0.035% or less, but more preferably 0.02% or less. The upper limit of S is preferably 0.035% or less, but more preferably 0.006% or less. The upper limit of Si is preferably 0.55% or less, but more preferably 0.35% or less. The upper limit of Ni is preferably 0.8% or less, but more preferably 0.4% or less. The upper limit of V is preferably 0.1% or less. By using forged materials with reduced carbon equivalents for the joint components, preheating and postheating are not required when attaching to the steel pipe, and expensive welding materials tailored to the strength of the joint are also not required, thereby reducing the cost of fitting. Furthermore, by eliminating the need for preheating and postheating, thermal deformation of the joint or steel pipe that accompanies these heating processes can be suppressed, making it easy to ensure the dimensional accuracy of the joint. This allows the joint engagement state to be closer to the design assumption, enabling stable joint performance.

[0022] As described above, the steel material constituting the ring forging material is not strengthened by using alloy materials such as Cr and Mo, so the Cr content is less than 0.4%, preferably 0.2% or less, and the Mo content is less than 0.15%, preferably 0.08% or less. Such steels have at least one of a yield point or 0.2% proof stress of 215 MPa to 550 MPa and a tensile strength of 400 MPa to 720 MPa, and include, for example, rolled steels for general structures such as SS400 specified in JIS G3101 and equivalent steels, rolled steels for welded structures such as SM400A, SM400B, SM400C, SM490A, SM490B, SM490C, SM490YA, SM490YB, SM520B, SM520C, and SM570 specified in JIS G3106 and equivalent steels, and high-performance steels for bridges such as SBHS400 and SBHS500 specified in JIS G3140 and equivalent steels. Note that the chemical compositions and standards of the steels described above are merely examples, and the steels are not necessarily limited to the chemical compositions and standards described above as long as they can be formed into ring forged material. Furthermore, the above steel material constitutes a ring forging material for forming the inner fitting member 3 and the outer fitting member 4, which are joint members, and may be different from the steel material for forming the steel pipes 21 and 22.

[0023] Here, we will explain how to measure the mechanical properties of the above-mentioned steel materials, including the yield point and 0.2% proof stress. For steel materials formed into steel pipes, the axial mechanical properties are investigated based on the tensile test method specified in JIS Z2241. Test specimens used for the tensile test are taken axially at a position 1 / 4 or 3 / 4 of the radial thickness, and one of the following JIS Z2241 No. 11, No. 12 (No. 12A, No. 12B, and No. 12C), No. 4 or No. 5, and No. 14 (No. 14A, No. 14B, and No. 14C) test specimens is used. However, No. 4 test specimens must have a diameter of 14 mm (gauge length of 50 mm). Furthermore, when No. 5 test specimens are taken from steel pipes, they are flattened and then processed into test specimens. In the tensile test, the 0.2% proof stress, upper yield point, and lower yield point are measured, and the mechanical properties are evaluated by averaging the data from three test specimens.

[0024] In an embodiment of the present invention, the thickness of the inner fitting member manufactured from the ring forged material may be thicker than the thickness of the steel pipe 21. For example, it may be 30 mm or more, which is the upper limit for the thickness typically used for spiral steel pipes. The thickness of the inner fitting member may be 70 mm or less to prevent excessive radial inward or outward protrusions as a steel pipe pile, thereby hindering workability. The thickness of the outer fitting member is preferably equal to or less than the thickness of the inner fitting member described above. The outer fitting member may be thicker than the inner fitting member, but in this case, the thickness of the inner fitting member is preferably 30 mm or more and 70 mm or less, as described above. The thicker joint member increases its rigidity, thereby suppressing thermal deformation of the joint member when welding the joint member to the steel pipe. As a result, additional processes such as thermal straightening are unnecessary, inspection efficiency is improved, and joint installation costs can be reduced. Furthermore, increasing the rigidity reduces the risk of separation between the inner and outer fittings due to poor engagement caused by unexpected deformation, avoiding situations where the design strength is not met, and ensuring stable performance as a joint structure. As described above, lowering the joint material strength allows the joint to be relatively thicker than joints made with conventional high-strength materials, increasing the joint's rigidity. This suppresses localized deformation at the mating portion and enables sufficient load transmission. As a result, joint separation (jump-out) due to localized deformation of the fitting components that was not anticipated in the design can be prevented, ensuring appropriate structural performance. On the other hand, excessively thick fitting components can result in excessively high stiffness relative to the stiffness of the steel pipes 21 and 22, potentially resulting in a sudden increase in load acting near the joint. This sudden increase in load acts distributedly near the joint, and therefore increases the load not only on the high-rigidity fitting components but also on the steel pipes 21 and 22 connected to the fitting components, resulting in localized damage to the steel pipes 21 and 22 near the joint, increasing the risk of instability in the behavior of the entire steel pipe. Considering this risk, it is preferable to limit the thickness of the joint member to approximately twice the thickness of the steel pipes 21 and 22 or less.Note that cutting does not necessarily have to be performed on both the inner and outer circumferential surfaces. Processing costs can be reduced by reducing the amount of cutting except for areas where dimensional accuracy is required to ensure structural performance, specifically, areas excluding the contact area between the inner and outer fitting members. Furthermore, in joint members formed from ring-forged material, the thickness of the side that joins the steel pipes 21 and 22 need only be equal to or greater than that of the steel pipes 21 and 22. Furthermore, the thickened joint mating portion ensures the necessary rigidity while effectively reducing the risk of separation between the inner and outer fitting members. While the inner fitting member 3 and the outer fitting member 4 are described as being made from ring-forged material, they may also be made from sheet-wrapped material made by bending flat plates.

[0025] As described above, in this embodiment, material costs are kept low by using low-strength materials, rather than expensive alloy materials, for the joint members. Therefore, there is no need to thin the joint members to reduce material costs. By not thinning the joint members, it is possible to avoid situations where, for example, unanticipated deformation in the design could cause poor engagement and result in the design yield strength being compromised. To strengthen the engagement of the joint, relatively lowering the strength of the joint member material allows for thicker walls while keeping material costs low. Furthermore, because thicker joint members increase their rigidity, deformation of the joint members when welding them to the steel pipes (steel pipes 21, 22) can be suppressed. Suppressing deformation during welding eliminates the need for additional processes such as thermal straightening, improving the efficiency of inspections to determine whether the product meets the required dimensional accuracy and reducing inspection costs. Even if deformation requires thermal straightening, the steel material constituting the joint members has a low content of alloy materials such as Cr and Mo, or is not directly used for the purpose of improving strength, so it is highly resistant to cracking due to heat input. Furthermore, because the joint components are not made of high-strength materials containing large amounts of Cr, etc., preheating and post-heating are not required when attaching to the steel pipe, and expensive welding materials required to match the strength of the joint are also not required, which helps to reduce the costs associated with manufacturing and attaching mechanical joints.

[0026] In this way, in this embodiment, for example, by forming the inner fitting member 3 and the outer fitting member 4, which are joint members, from a material with the same strength as the steel pipes 21 and 22, it is possible to achieve cost reduction while ensuring structural performance. Multiple steel pipes connected by such a connecting structure can be used, for example, as steel pipe piles, wall structures, column structures, and temporary structures for construction and civil engineering. Furthermore, multiple steel pipes connected by such a connecting structure can also be used as steel pipe sheet piles by connecting joints that have been previously joined to the steel pipes.

[0027] Although the above description has been given of an example in which the protrusions 321, 421 and the grooves 322, 422 are formed on the fitting portions 32, 42 of the inner fitting member 3 and the outer fitting member 4 included in the connecting structure 1, the configuration of the inner fitting member and the outer fitting member is not limited to this example. For example, the inner fitting member and the outer fitting member may each have circumferential grooves, which face each other when the inner fitting member is fitted into the outer fitting member, and axial force may be transmitted by inserting a key member (a retaining member) spanning these grooves. In this case, the inner fitting member and the outer fitting member themselves do not have retaining members. Alternatively, the pile bodies may be connected to each other by threading a male thread formed on the outer periphery of the inner fitting member into a female thread formed on the inner periphery of the outer fitting member while the inner fitting member is fitted into the outer fitting member. In this case, the inner fitting member and the outer fitting member have spirally continuous protrusions and grooves, and the inner fitting member and the outer fitting member are connected by engaging these protrusions with each other. In these cases, the inner and outer fitting members can also be formed from ring forged material using the above-mentioned steel material. [Explanation of symbols]

[0028] 1...connecting structure, 3...inner fitting member, 4...outer fitting member, 21...steel pipe, 22...steel pipe, 23...weld portion, 24...weld portion, 30...ring forging, 31...joint portion, 32...fitting portion, 40...ring forging, 41...joint portion, 42...fitting portion, 321...protrusion, 321A...protrusion, 321B...protrusion, 321C...protrusion, 322...groove, 322A...groove, 322B...groove, 322C...groove, 323...gap portion, 421...protrusion, 422...groove, 423...gap portion.

Claims

1. A steel pipe connection structure that axially connects first and second steel pipes, an inner fitting member joined to the end of the first steel pipe in the axial direction; and an outer fitting member joined to the end of the second steel pipe in the axial direction; the inner fitting member includes an inner fitting portion that fits into the inner side of the outer fitting member, and the outer fitting member includes an outer fitting portion that fits into the outer side of the inner fitting member, and the inner fitting portion and the outer fitting portion are provided with anti-slip portions in the axial direction, At least one of the inner fitting member and the outer fitting member is formed from a ring-forged material, and at least one of the yield point and 0.2% proof stress of the ring-forged material is 215 MPa or more and 550 MPa or less, and the tensile strength is 400 MPa or more and 720 MPa or less.

2. A steel pipe connection structure that axially connects first and second steel pipes, an inner fitting member joined to the end of the first steel pipe in the axial direction; and an outer fitting member joined to the end of the second steel pipe in the axial direction; the inner fitting member includes an inner fitting portion that fits into the inner side of the outer fitting member, and the outer fitting member includes an outer fitting portion that fits into the outer side of the inner fitting member, and the inner fitting portion and the outer fitting portion are provided with anti-slip portions in the axial direction, At least one of the inner fitting member and the outer fitting member is formed from a ring forged material, and the carbon equivalent Ceq of the ring forged material, defined by formula (i) in which the content of each element is expressed in mass%, is 0.2 or more and Ceq is 0.51 or less.

3. The thickness of the joint portion of the inner fitting member that is joined to the first steel pipe is thicker than the thickness of the first steel pipe, and the thickness of the joint portion of the outer fitting member that is joined to the second steel pipe is thicker than the thickness of the second steel pipe, or The thickness of the joint portion of the inner fitting member that is joined to the first steel pipe is thicker than the thickness of the first steel pipe, or 3. The steel pipe connection structure according to claim 1, wherein the thickness of the joint portion of the outer fitting member that is joined to the second steel pipe is greater than the thickness of the second steel pipe.

4. 3. The steel pipe connection structure according to claim 1, wherein the ring forged material has a modified cross section.

5. the retaining portion includes a plurality of first protrusions formed on the outer side of the inner fitting portion and sandwiching a first gap portion in the circumferential direction, and a plurality of second protrusions formed on the inner side of the outer fitting portion and sandwiching a second gap portion in the circumferential direction, 3. The steel pipe connection structure according to claim 1 or claim 2, wherein the first and second protrusions are configured to engage with each other when the inner fitting member is rotated to a predetermined position while fitted inside the outer fitting member.

6. the inner fitting portion includes one or more first protrusions arranged in the axial direction with a first groove portion therebetween, the outer fitting portion includes one or more second protrusions arranged in the axial direction with second grooves interposed therebetween, 6. The steel pipe connection structure according to claim 5, wherein when the first and second protrusions are engaged with each other, the first protrusion is located in the second groove, and the second protrusion is located in the first groove.

7. a plate thickness of the first groove portion of the inner fitting member is formed to be thinner as it approaches a tip of the inner fitting portion in the axial direction, The steel pipe connection structure according to claim 6 , wherein the thickness of the second groove portion of the outer fitting member is formed to be thinner as it approaches the tip of the outer fitting portion in the axial direction.

8. The plate thickness of the first groove portion of the inner fitting member is formed uniformly regardless of the position in the axial direction, The steel pipe connection structure according to claim 6 , wherein the plate thickness of the second groove portion of the outer fitting member is formed uniformly regardless of the position in the axial direction.

9. A steel pipe pile comprising a plurality of steel pipes connected by the steel pipe connection structure according to claim 1 or 2.

Images