Connection structure of steel pipe and steel pipe pile

Abstract

To provide a connection structure of steel pipes capable of effectively suppressing out-of-plane deformation of a connection tip part for a mechanical connection of a steel pipe.SOLUTION: A connection structure of steel pipes connecting first and second steel pipes in an axial direction is provided with an inner fitting member connected to an end part of the first steel pipe in the axial direction, and an outer fitting member connected to an end part of the second steel pipe in the axial direction, wherein the inner fitting member includes an inside fitting part fitted inside of the outer fitting member, the outer fitting member includes an outside fitting part fitted outside of the inner member, the inside fitting part and the outside fitting part contact to each other at contact surfaces thereof perpendicular to the axial direction, and in a radial direction of the first steel pipe and the inner fitting member, a distance X from a thickness center of the first steel pipe to a center of the contact surface, a thickness t of the first steel pipe, and the number of rows n in a pipe axial direction of the outside fitting part and the inside fitting part satisfy 0<X / t≤3n / 4.SELECTED DRAWING: Figure 4

Description

[Technical Field]

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

[0002] While welding is a common method for connecting steel pipes, a steel pipe joining method using mechanical joints that can be installed in a short time without on-site welding has also been proposed. For example, Patent Document 1 describes a connecting method using an inner fitting member and an outer fitting member that are joined to the axial ends of steel pipe piles. In this method, when the inner fitting member is rotated while fitted inside the outer fitting member, multiple protrusions formed on the outside of the inner fitting member and the inside of the outer fitting member, each sandwiching a gap in the circumferential direction, engage with each other, thereby connecting the steel pipe piles. This type of connecting structure has the advantages of being easier to install than the conventional welding of steel pipe piles, and of ensuring sufficient bending rigidity. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6202102 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the above-mentioned mechanical joint, when an external force equivalent to or greater than the yield stress of the steel pipe is applied, out-of-plane deformation becomes significant at the joint tip, which has a thinner plate thickness than other parts, and there is a possibility that the required performance cannot be satisfied. Increasing the plate thickness at the joint tip can sometimes suppress deformation, but in other cases, this alone does not improve the out-of-plane deformation.

[0005] Therefore, an object of the present invention is to provide a steel pipe connection structure and a steel pipe pile that can effectively suppress out-of-plane deformation at the tip of a mechanical joint of steel pipes. [Means for Solving the Problem]

[0006] [1] A connecting structure for steel pipes that axially connects a first steel pipe and a second steel pipe, 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. 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 contact each other with contact surfaces perpendicular to the axial direction. For the first steel pipe and the inner fitting member in the radial direction, when the distance from the center of the plate thickness of the first steel pipe to the center of the contact surface is X, the plate thickness of the first steel pipe is t, and the number of arrangements of the outer fitting portion and the inner fitting portion in the pipe axis direction is n, 0 < X / t ≤ 3n / 4. A connecting structure for steel pipes. [2] A connecting structure for steel pipes that axially connects a first steel pipe and a second steel pipe, 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. 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. A first circumferential groove portion is formed on the outer peripheral surface of the inner fitting portion, and a second circumferential groove portion is formed on the inner peripheral surface of the outer fitting portion. When the inner fitting member is fitted into the outer fitting member, the first and second circumferential groove portions face each other, and a retaining member spanning the first and second circumferential groove portions is inserted. The inner fitting portion or the outer fitting portion, the retaining member, and the contact surfaces perpendicular to the axial direction contact each other. For the first steel pipe and the inner fitting member in the radial direction, when the distance from the center of the plate thickness of the first steel pipe to the center of the contact surface is X, the plate thickness of the first steel pipe is t, and the number of arrangements of the outer fitting portion and the inner fitting portion in the pipe axis direction is n, 0 < X / t ≤ 3n / 4. A connecting structure for steel pipes. [[ID=IO]] [3] The connecting structure for steel pipes according to [1] or [2], where 0.50 ≤ X / t. [4] A steel pipe connection structure according to [1] or [2], wherein at least one of the yield point or 0.2% proof stress of the steel material forming the inner fitting member and the outer fitting member is 215 MPa or more and 550 MPa or less, and the tensile strength is 400 MPa or more and 720 MPa or less. [5] The carbon equivalent Ceq of at least one of the inner fitting member or the outer fitting member, 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. [6] A steel pipe connection structure according to [1] or [2]. TIFF2025153987000002.tif22166 [6] A steel pipe connection structure according to [1] or [2], wherein a plurality of first protrusions are formed on the outside of the inner fitting portion, sandwiching a first gap portion in the circumferential direction, and a plurality of second protrusions are 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. [7] A steel pipe connection structure as described in [6], wherein the first protrusions are formed at 16 to 32 locations on the outside of the inner fitting portion, sandwiching the first gap portion in the circumferential direction, and the same number of second protrusions as the first protrusions are formed on the inside of the outer fitting portion, sandwiching the second gap portion in the circumferential direction. [8] The steel pipe connection structure described in [7], wherein the inner fitting portion includes three or four of the first protrusions arranged in the axial direction, and the outer fitting portion includes the same number of second protrusions as the first protrusions arranged in the axial direction. [9] A steel pipe connection structure as described in [8], wherein the thickness of the first groove formed between the first protrusions arranged in the axial direction in the inner fitting member is uniform regardless of the axial position, and the thickness of the second groove formed between the second protrusions arranged in the axial direction in the outer fitting member is uniform regardless of the axial position.

[10] The side of the tip of the outer fitting portion in the direction toward the second steel pipe and the side of the tip of the inner fitting portion in the direction toward the first steel pipe are not provided with a protrusion extending in the pipe axis direction or a groove recessed in the pipe axis direction. The steel pipe connection structure according to [9].

[11] A steel pipe connection structure according to [1] or [2], wherein at least one of the inner fitting member and the outer fitting member is formed of a bent roll pipe having a weld extending in the axial direction.

[12] A steel pipe connection structure according to [1] or [2], wherein at least one of the inner fitting member and the outer fitting member is formed from a ring forged material.

[13] A rotation prevention structure that prevents relative rotation of the connecting structure of these steel pipes when the outer fitting portion and the inner fitting portion are engaged, comprising: a key groove portion that is formed continuously on a side surface of a tip end of the outer fitting portion in a direction toward the second steel pipe and a side surface of a tip end of the inner fitting portion in a direction toward the first steel pipe when the outer fitting portion and the inner fitting portion are engaged; and a key member that is fitted into the key groove portion across a side surface of the tip end of the outer fitting portion in a direction toward the second steel pipe and a side surface of the tip end of the inner fitting portion in a direction toward the first steel pipe, a first groove formed by cutting out an end surface facing the inner fitting portion on a side surface of the tip of the inner fitting portion in a direction toward the first steel pipe, and a second groove formed by cutting out an end surface facing the outer fitting portion on a side surface of the tip of the inner fitting portion in a direction toward the first steel pipe, and either or both of the first groove and the second groove have a contact point portion that rotates the key member while contacting a side edge of the key member by a predetermined relative rotation between the outer fitting portion and the inner fitting portion, and a contact edge portion that is provided horizontally or inclined with respect to the longitudinal direction of the axial core of the steel pipe and that contacts a side edge of the key member in a circumferential direction by a predetermined relative rotation between the outer fitting portion and the inner fitting portion. The steel pipe connection structure according to [6], characterized in that:

[14] The inner fitting portion of the inner fitting member and the portion other than the joint with the first steel pipe The outer fitting member is provided at a portion other than the outer fitting portion and the joint portion with the second steel pipe. The steel sheet may have black scale remaining due to high-temperature oxidation. [1] or [2]. The steel pipe connection structure.

[15] A steel pipe pile comprising multiple steel pipes connected by a steel pipe connection structure described in [1] or [2]. [Effects of the Invention]

[0007] According to the above configuration, the distance X from the center of thickness of the steel pipe to the center of the contact surface of the inner fitting member between the inner fitting member and the second steel pipe is determined within an appropriate range. This ensures rigidity against out-of-plane deformation of the outer fitting member and the inner fitting member due to external forces acting from the steel pipe, and satisfies the required performance of the joint. In addition, the eccentric bending moment generated by the misalignment of the lines of action between the force applied from the outer fitting member to the inner fitting member at the contact surface of the fitting portion and the force applied from the steel pipe at the base side is reduced, effectively suppressing out-of-plane deformation of the joint tip and deformation of the steel pipe due to rotational displacement of the inner fitting member relative to the steel pipe. [Brief explanation of the drawings]

[0008] [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] 10A and 10B are diagrams for explaining out-of-plane deformation that may occur in a connection structure. [Figure 4] 10A and 10B are diagrams for explaining conditions for effectively suppressing out-of-plane deformation due to eccentric bending. [Figure 5] FIG. 10 is a diagram showing an analytical model (example 1) for verifying differences due to plate thickness of a groove portion of a joint member. [Figure 6] FIG. 10 is a diagram showing an analytical model (example 2) for verifying differences due to plate thickness of a groove portion of a joint member. [Figure 7] 10 is a graph showing a load-displacement relationship calculated by analysis. [Figure 8] 10 is a graph showing the distribution of stress generated in the axial direction calculated by analysis. [Figure 9] FIG. 10 illustrates another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] 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.

[0010] 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.

[0011] 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.

[0012] The number of protrusions 321, 421 arranged in the axial direction is not particularly limited, but for example, the fitting portion 32 may include three or four protrusions 321 arranged in the axial direction, and the fitting portion 42 may include the same number of protrusions 421 as the protrusions 321 arranged in the axial direction. When the number of protrusions 321 arranged in the axial direction is three, it is also referred to as three stages, and when the number is four, it is also referred to as four stages. In addition, the number of protrusions 321, 421 arranged in the circumferential direction is also not particularly limited, but for example, the protrusions 321 may be formed in 16 to 32 locations on the outer side of the fitting portion 32, with gaps 323 sandwiched between them in the circumferential direction, and the same number of protrusions 421 as the protrusions 321 may be formed on the inner side of the fitting portion 42, with gaps 423 sandwiched between them in the circumferential direction.

[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 protrusion 321 of the inner fitting member 3 is positioned in the groove 422 of the outer fitting member 4, and the protrusion 421 of the outer fitting member 4 is positioned in the groove 322 of the inner fitting member 3. Note that in other embodiments, the retaining structure does not necessarily have to be formed by the protrusions, and may be formed by, for example, a screw, shear key, or shear plate that transmits load between the inner fitting member 3 and the outer fitting member 4. A plurality of steel pipes connected by such a connecting structure can be used, for example, as steel pipe piles for architectural and civil engineering foundations, wall structures, column structures, and temporary structures. Furthermore, a plurality of steel pipes connected by the above-mentioned connecting structure can also be used as a steel pipe sheet pile by connecting joints that have been previously joined to the steel pipes.

[0014] The inner fitting member 3 and the outer fitting member 4 may be manufactured by, for example, cutting a bent roll pipe or a ring-forged material having an axially extending weld. The steel material forming the inner fitting member 3 and the outer fitting member 4 does not need to be strengthened by using alloy materials such as Cr or Mo. For example, the Cr content may be less than 0.4%, preferably 0.2% or less, and the Mo content may be less than 0.15%, preferably 0.08% or less, by mass. Such steel has at least one of a yield point and a 0.2% proof stress of 215 MPa to 550 MPa, a tensile strength of 400 MPa to 720 MPa, and a carbon equivalent Ceq calculated by the following formula (1) that satisfies Ceq≦0.51%, preferably Ceq≦0.44%, more preferably Ceq≦0.40%, and even more preferably Ceq≦0.38%. The element symbols in formula (1) represent the content of each element in mass. The lower limit of Ceq is, for example, 0.2% or more. Examples of steel materials with these material properties include rolled steel materials for welded structures, such as SM400A, SM400B, SM400C, SM490A, SM490B, SM490C, SM490YA, SM490YB, SM520B, SM520C, and SM570, as specified in JIS G3106, and high-performance steel materials for bridges, such as SBHS400 and SBHS500, as specified in JIS G3140. The above-mentioned composition and specifications of the steel materials are merely examples, and the steel materials are not necessarily limited to the above-mentioned composition and specifications as long as they can be formed into, for example, bent roll pipes or ring forged materials. Furthermore, the above-mentioned steel materials constitute the inner fitting member 3 and outer fitting member 4, which are joint components, and may be different from the steel materials constituting the steel pipes 21 and 22.

[0015]

number

[0016] Here, we will explain how to measure the mechanical properties of the above-mentioned steel, including the yield point and 0.2% proof stress. For steel 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 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.

[0017] FIG. 3 is a diagram illustrating out-of-plane deformation that may occur in a connection structure. In a mechanical joint, for example, when a large external force, specifically, an external force equivalent to or greater than the yield stress of a steel pipe, acts in the axial direction, significant out-of-plane deformation may occur at the joint tip. In the illustrated example, the end portion on the tip side (positive side of the z-axis) of the inner fitting member 3 and the end portion on the tip side (negative side of the z-axis) of the outer fitting member 4 are out-of-plane deformed. For example, if the inner fitting member has a tapered shape in which the outer diameter gradually decreases toward the tip, significant out-of-plane deformation may occur at the joint tip where the plate thickness is thinner than in other parts. On the other hand, such out-of-plane deformation of the inner fitting member 3 may be eccentric bending caused by a mismatch between the line of action of the axial force transmitted from the steel pipe at the base portion (near the welded portion 23) of the steel pipe and the line of action of the axial force transmitted from the protrusion 421 of the outer fitting member, with which the protrusion 321 of the inner fitting member engages. In this case, even if the inner fitting is not tapered and the thickness of the groove is uniform regardless of axial position, as in the example shown in Figure 3, out-of-plane deformation may not be improved. Here, uniform thickness is a design or drawing concept. For example, it is also considered uniform when thickness variations occur within the manufacturing tolerance range (within ±5%, more specifically, ±3%) or when the radial cutting surfaces of the protrusions and grooves are on approximately the same radius. Furthermore, increasing the thickness of grooves 322C and 422C increases the overall rigidity of the joint, improving resistance to out-of-plane deformation and thereby enabling more uniform load distribution across each protrusion and groove. Furthermore, eliminating thickness variations in the grooves reduces the thickness required for ring forging 30, leading to labor savings in joint manufacturing.

[0018] Fig. 4 is a diagram for explaining the conditions for effectively suppressing out-of-plane deformation due to eccentric bending. Assuming that the axial force acting on the steel pipe contributes to eccentric bending at the joint root portion (near the joint portion 31) of the inner fitting member 3, the condition under which eccentric bending does not occur even when a full plastic bending moment occurs at the base portion of the steel pipe can be defined as shown in the following formula (2). Note that n is the number of stages of the protrusion (in the illustrated example, n = 3, so F1 = F2 = F3 = F / 3), F is the magnitude of the axial force acting on the steel pipe, X is the distance from the center of thickness C1 of the steel pipe to the center C2 of the contact surface in the radial direction, and σ yp is the yield stress of the steel pipe, Z p is the plastic section modulus of the base portion of the steel pipe, and β is a correction coefficient that takes into account the spread of stress. For simplicity, the circumferential curvature is not taken into account, and the depth is modeled as a unit length. In the illustrated example, the axial force is transmitted between the inner and outer fitting members at a contact surface that is perpendicular to the pipe axis direction. Note that "perpendicular" here means that the angle it forms with respect to the pipe axis direction is 90 degrees ± 10 degrees or less, preferably 90 degrees ± 5 degrees or less. The contact surface may be threaded, and in that case, the angle it forms with respect to the pipe axis direction should be within the above range.

[0019]

number

[0020] Here, the center C2 of the contact surface refers to the center of the surface where the protrusion 321 of the inner fitting member 3 and the protrusion 421 of the outer fitting member 4 actually contact, as viewed in the longitudinal cross section (x-z cross section) of the joint member. Even without deformation such as eccentric bending, there are design clearances between the inner fitting member 3 and the outer fitting member 4, namely, an axial gap g1 and a radial gap g2. The size of gap g1 is, for example, approximately 1.0 mm to 1.5 mm, and the size of gap g2 is, for example, approximately 1.5 mm. Therefore, the center C2 of the contact surface is not the height center of the protrusion formed on the inner fitting member 3, but the center of the height range of the protrusion, excluding the gap g2 where the protrusions of the inner fitting member 3 and the outer fitting member 4 are not in contact with each other. On the other hand, the correction coefficient β represents the reduction of the axial force contributing to eccentric bending by dispersing the applied axial force to the grooves before and after the protrusion. Based on previous studies by the inventors, β is set to 2.

[0021] When the axial force F is the axial force when the steel pipe is fully plastic, the cross-sectional area A of the steel pipe base p Using F=σ yp A p As mentioned above, the depth is a unit length in equation (2), so the cross-sectional area A p is equal to the thickness t of the steel pipe. In this model, the cross section of the steel pipe (xy cross section) is a rectangle with a width of unit length and a height of the steel pipe thickness t, so the plastic section modulus Z p is t 2 / 4. Therefore, equation (2) can be expressed as equation (3) below, which can be rearranged to give equation (4).

[0022]

number

[0023] The above formula (4) means that by making the ratio of the distance X from the center C1 of the pipe wall thickness of the steel pipe to the center C2 of the contact surface to the pipe wall thickness t of the steel pipe not exceed the value on the right side, even when a fully plastic bending moment occurs at the root part of the steel pipe, eccentric bending can be prevented. Considering the work hardening of the steel pipe and multiplying the value on the right side by the material coefficient γ = 1.5, we get X / t ≦ 3n / 4. When the number of steps n = 3, 0 < X / t ≦ 2.25. When the number of steps n = 4, 0 < X / t ≦ 3.00. Since the number of steps n is generally 3 or more, for the joint member, regardless of the number of steps n, X / t ≦ 2.25 may be adopted. Here, the number of steps n is the number of arrangements in the pipe axis direction of the outer fitting part and the inner fitting part. n is the number of arrangements in the state where both joint members are engaged, and is synonymous with the number of protrusions. Also, in both joints, this number of arrangements n must always be equal. When the contact surface is formed in a spiral shape, the number of arrangements varies depending on the circumferential position. In that case, the maximum number of arrangements in the circumferential direction is taken as n. The lower limit of n is 1. The upper limit of n is 10 from the perspective of a reasonable limit value considering the manufacturable range and manufacturing cost. When the contact surface is formed in a spiral shape, the number of steps n may be, for example, 3 or 4.

[0024] On the other hand, if X / t is extremely reduced to suppress out-of-plane deformation due to eccentric bending as described above, the protrusion heights of the inner fitting member and the outer fitting member will be extremely low. As a result, even if a small eccentric bending acts, the engagement between the two is likely to be disengaged, and the joint structure cannot exhibit stable performance. Therefore, it is necessary to set a lower limit value of X / t to reduce the above risk. For example, it is desirable to make the distance X from the center C1 of the pipe wall thickness of the steel pipe to the center C2 of the contact surface not less than 0.50 times the pipe wall thickness t of the steel pipe. In this case, 0.50 ≦ X / t.

[0025] The results of an analysis verifying the effects of the present invention and the differences depending on the thickness of the groove of the coupling member are described below. For a coupling applied to an SKK490 steel pipe specified in JIS A5525, with a pipe diameter of 800 mm and a thickness of 19 mm, the load deformation and axial stress distribution were calculated for two types of coupling members as shown in Figures 5 and 6. In Example 1 shown in Figure 5, the thickness of the groove of the inner fitting member is made thinner toward the tip of the fitting portion (positive side of the z-axis), and the thickness of the groove of the outer fitting member is also made thinner toward the tip of the fitting portion (negative side of the z-axis). Specifically, if the thicknesses of the groove of the inner fitting member are t1, t2, and t3, respectively, from the base side (negative side of the z-axis), t1 > t2 > t3. In the analysis, t1 = 24.3 mm, t2 = 20.2 mm, and t3 = 16.1 mm. On the other hand, in Example 2 shown in Figure 6, the thicknesses of the grooves of the inner and outer fitting members are uniform regardless of the axial position. Specifically, if the thicknesses of the grooves of the inner fitting member are t1, t2, and t3, in order from the joint side, then t1 = t2 = t3. In the analysis, t1 = t2 = t3 = 18.6 mm. Furthermore, in Example 1 of Figure 5, the value of X / t mentioned above is 1.2, and in Example 2 of Figure 6, the value of X / t mentioned above is 0.8.

[0026] Figure 7 is a graph showing the load-displacement relationship calculated by analysis. As shown in the graph, the maximum vertical load reached when each steel pipe was subjected to a forced displacement amount separating it in the axial direction (vertical direction) was greater than the load equivalent to the full plastic yield strength of the steel pipe (required performance) in both Example 1 and Example 2. This result shows that, despite the fact that the plate thickness at the groove portion on the root side of the joint member is smaller in Example 2 than in Example 1, the required joint structural performance can be achieved by keeping the value of X / t within a specified range. Furthermore, when comparing Example 1 and Example 2, the maximum vertical load is slightly greater in Example 2, demonstrating the effect of making the plate thickness of the grooves uniform.

[0027] Figure 8 is a graph showing the axial stress distribution calculated by analysis. As shown in Figure 3, the joint components deform in an out-of-plane direction, generating compressive stress in each groove. In Example 1, the groove thickness decreases toward the end of the mating section. Therefore, as shown in Figure 6, when the grooves are numbered P1, P2, and P3 from the base, the stress generated in groove P3 at the tip end is greater. In Example 1, almost no stress is generated in groove P1 at the base end, and the generated stress is biased toward grooves P2 and P3 at the tip end. In Example 2, stress is generated more evenly in grooves P1, P2, and P3 (see Figure 7) than in Example 1. In Example 2, the thickness t3 of groove P3 at the tip end is greater than in Example 1, and this, combined with the fact that Example 2 is more effective at preventing out-of-plane deformation of the joint components, is also evident.

[0028] A steel pipe joint structure according to an embodiment of the present invention, as described in Japanese Patent No. 6347193, for example, is a rotation prevention structure that prevents relative rotation of the outer fitting portion and the inner fitting portion when they are engaged with each other, and includes a key groove portion that is formed continuously on a side surface of a tip end of the outer fitting portion facing the second steel pipe and a side surface of a tip end of the inner fitting portion facing the first steel pipe when the outer fitting portion and the inner fitting portion are engaged with each other, and a key member that is fitted into the key groove portion across the side surface of the tip end of the outer fitting portion facing the second steel pipe and the side surface of the tip end of the inner fitting portion facing the first steel pipe, and The outer fitting may have a first groove formed by cutting out the end surface facing the inner fitting on the side surface of the tip of the outer fitting in the direction toward the second steel pipe, and a second groove formed by cutting out the end surface facing the outer fitting on the side surface of the tip of the inner fitting in the direction toward the first steel pipe, and either or both of the first groove and the second groove may have a contact point portion that rotates the key member while coming into contact with the side edge of the key member due to a predetermined relative rotation between the outer fitting and the inner fitting, and a contact edge portion that is arranged horizontally or inclined with respect to the longitudinal direction of the axis of the steel pipe and comes into contact with the side edge of the key member in the circumferential direction due to the predetermined relative rotation between the outer fitting and the inner fitting. Such a key member (rotation prevention key) is a structure that prevents unintended relative rotation and attachment / detachment of the inner and outer fitting members after they have been rotated relative to each other and connected, and is a useful structure when using the inner and outer fitting members as steel pipe piles or steel pipe sheet piles after they have been connected.

[0029] In a steel pipe joint structure according to an embodiment of the present invention, black scale resulting from high-temperature oxidation of the steel material may remain on the inner fitting member in a portion other than the joint between the inner fitting portion and the first steel pipe, and on the outer fitting member in a portion other than the joint between the outer fitting portion and the second steel pipe. Black scale is an oxide film on the steel material produced by hot rolling at temperatures above 800°C, for example, and is also called mill scale. Its chemical composition is Fe2O3 or Fe3O4, with most of it being Fe3O4. Black scale is a thin rust layer of several tens of micrometers or less, with small holes (pinholes) and irregularities formed on its surface, resulting in weak adhesion between the steel material and the black scale. Because high dimensional accuracy is required at the fitting surfaces of a joint and force is transmitted through the contact surfaces, it is undesirable for black scale to remain on these fitting surfaces. On the other hand, black scale may remain on areas other than the fitting surfaces, since dimensional accuracy is not required and these areas are not points of force application. Black scale is removed by pickling, polishing, or cutting. To confirm this, black scale is formed by high-temperature oxidation, for example, at temperatures above 800°C, and therefore differs in chemical composition and color (appearance) from stable rust that occurs when a product is exposed to air or underground after manufacture. Therefore, the presence of black scale can be confirmed visually, or more specifically, by chemical analysis. Note that "it's okay if black scale remains" means "it's okay if there are areas that have not been polished or cut," and if there are no cutting or polishing marks, it can be determined that black scale remains.

[0030] In the above, an example has been described in which protrusions 321, 421 and grooves 322, 422 are formed in the fitting portions 32, 42 of the inner fitting member 3 and the outer fitting member 4 included in the connecting structure 1, but the configurations of the inner fitting member and the outer fitting member are not limited to these examples.

[0031] For example, as shown in FIG. 9, it includes an inner fitting member 3A joined to the axial end of the first steel pipe 21 and an outer fitting member 4A joined to the axial end of the second steel pipe 22. The inner fitting member 3A includes an inner fitting portion 32A that fits inside the outer fitting member 4A. The outer fitting member 4A includes an outer fitting portion 42A that fits outside the inner fitting member 3A. A first circumferential groove portion 321A is formed on the outer peripheral surface of the inner fitting portion 32A, and a second circumferential groove portion 421A is formed on the inner peripheral surface of the outer fitting portion 42A. When the inner fitting member 3A is fitted into the outer fitting member 4A, the first and second circumferential groove portions 321A, 421A face each other, and retaining members 5A, 5B spanning the first and second groove portions 321A, 421A are inserted. The inner fitting portion 32A or the outer fitting portion 42A and the retaining members 5A, 5B contact each other on a contact surface perpendicular to the axial direction. Regarding the radial direction of the first steel pipe 21 and the inner fitting member 3A, when the distance from the center of the plate thickness of the first steel pipe 21 to the center of the contact surface is X, the plate thickness of the first steel pipe 21 is t, and the number of arrangements in the pipe axial direction of the outer fitting portion 42A and the inner fitting portion 32A, specifically the number of groove portions 321A, 421A is n, it may be 0 < X / t ≦ 3n / 4. Here, the retaining members in such a joint structure have approximately the same contact extension in the radial direction with respect to the inner fitting member and the outer fitting member. Also, the axial force acting on the inner fitting member from the first steel pipe through the welded portion 23 and the axial force acting on the outer fitting member from the second steel pipe through the welded portion 24 are equal from the perspective of force balance. Therefore, in the example shown in FIG. 9, similar to the above distance X, regarding the radial direction of the second steel pipe 22 and the outer fitting member 4A, when the distance from the center of the plate thickness of the second steel pipe 22 to the center of the contact surface is X', the plate thickness of the second steel pipe 22 is t', and the number of groove portions 321A, 421A is n, it may be 0 < X' / t' ≦ 3n / 4.

[0032] Alternatively, the pile bodies may be connected by screwing 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 fitting the inner fitting member into the outer fitting member. In this case, spiral continuous protrusions and grooves are formed on the inner fitting member and the outer fitting member, and the inner fitting member and the outer fitting member are connected by engaging these protrusions with each other. Also in these cases, the inner fitting member and the outer fitting member can be formed of a ring forging material using the steel material as described above.

[0033] Embodiments of the present invention will be summarized below. A steel pipe connection structure for axially connecting a first steel pipe and a second steel pipe, comprising 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 contact each other with contact surfaces perpendicular to the axial direction. For the first steel pipe and the inner fitting member in the radial direction, when the distance from the center of the plate thickness of the first steel pipe to the center of the contact surface is X, the plate thickness of the first steel pipe is t, and the number of arrangements in the pipe axis direction of the outer fitting portion and the inner fitting portion is n, 0 < X / t ≤ 3n / 4. According to the steel pipe connection structure, by making the ratio of the distance X from the center of the plate thickness of the steel pipe to the center of the contact surface of the inner fitting member to the plate thickness t of the steel pipe 3n / 4 or less, the rigidity required in terms of structural performance can be ensured, and even when a full plastic bending moment occurs at the root portion of the steel pipe, excessive eccentric bending deformation can be prevented from occurring in the fitting portion, the risk of separation between the inner fitting member and the outer fitting member can be suppressed, and stable performance can be exhibited as a joint structure.

[0034] Particularly, according to the steel pipe connection structure where 0.50 ≤ X / t, by making the distance X from the center of the plate thickness of the steel pipe to the center of the contact surface of the inner fitting member 0.50 times or more the plate thickness t of the steel pipe, a lower limit value is provided for the rigidity of the joint and the protrusion height of the inner fitting member and the outer fitting member, and the risk of separation between the inner fitting member and the outer fitting member can be more reliably suppressed, and stable performance can be exhibited as a joint structure.

[0035] In particular, according to a steel pipe connection structure in which at least one of the yield point or 0.2% proof stress of the steel material forming the inner fitting member and the outer fitting member is 215 MPa or more and 550 MPa or less, and the tensile strength is 400 MPa or more and 720 MPa or less, by keeping the material strength of the inner fitting member and the outer fitting member within a specified range, there is no need to excessively thin the plate thickness of the inner fitting member and the outer fitting member to reduce material costs, and rigidity against eccentric bending deformation can be ensured.Furthermore, the rigidity required for the joint can be effectively ensured, the risk of separation of the inner fitting member and the outer fitting member can be reduced, and stable performance can be achieved as a joint structure.

[0036] In particular, according to a steel pipe connection structure characterized by having a chemical composition in which Ceq, defined by the following formula (1), is 0.51 or less, preheating is not required when welding the inner and outer fitting members to the steel pipe, and initial deformation of the inner and outer fitting members due to welding heat can be suppressed, making it possible to minimize residual stress that may occur in the inner and outer fitting members, ensuring the rigidity required for the joint while further reducing the risk of separation and enabling the joint structure to exhibit stable performance. Ceq=C+Mn / 6+Si / 24+Ni / 40+Cr / 5+Mo / 4+V / 14…(1)

[0037] In particular, according to a steel pipe connection structure in which a plurality of first protrusions are formed on the outside of the inner fitting portion, sandwiching a first gap portion in the circumferential direction, and a plurality of second protrusions are formed on the inside of the outer fitting portion, sandwiching a second gap portion in the circumferential direction, and the first and second protrusions engage with each other when the inner fitting member is rotated to a predetermined position while fitted inside the outer fitting member, by forming a plurality of inner fitting portions and outer fitting portions in the circumferential direction of the pipe, the external force acting on the joint is effectively dispersed in the circumferential direction of the pipe, the joint as a whole effectively resists the external force, ensures the rigidity required for the joint, further reduces the risk of separation of the inner fitting member and the outer fitting member due to eccentric bending deformation, and can exhibit stable performance as a joint structure.

[0038] Furthermore, according to a steel pipe connection structure in which the first protrusions are formed at 16 to 32 locations on the outside of the inner fitting portion, sandwiching the first gap portion in the circumferential direction, and the same number of second protrusions as the first protrusions are formed on the inside of the outer fitting portion, sandwiching the second gap portion in the circumferential direction, the inner fitting portion and the outer fitting portion are formed at 16 to 32 locations in the circumferential direction of the pipes, thereby rationally reducing the processing resources for the fitting and enabling the fitting structure to exhibit stable performance.

[0039] In particular, according to a steel pipe connection structure in which the inner fitting portion includes three or four of the first protrusions arranged in the axial direction, and the outer fitting portion includes the same number of second protrusions as the first protrusions arranged in the axial direction, by setting the number of protrusions arranged in the pipe axial direction to three or four, the balance of stress burden in the pipe axial direction is optimized, external forces are more effectively resisted, the rigidity required for the joint is ensured, and the risk of separation of the inner and outer fitting members due to eccentric bending deformation is further reduced, allowing the joint structure to exhibit stable performance.

[0040] In particular, according to a steel pipe connection structure in which the plate thickness of the first groove portion of the inner fitting member is formed uniformly regardless of the axial position, and the plate thickness of the second groove portion of the outer fitting member is formed uniformly regardless of the axial position, by making the groove plate thickness constant, the distribution of groove stress generated in response to the load received from the mutual engagement portions of the inner fitting member and the outer fitting member is leveled out, and in particular, stress is not locally concentrated on the tip end side. This more effectively ensures the rigidity required for the joint, reduces the risk of separation of the inner fitting member and the outer fitting member, and enables the joint structure to exhibit stable performance.

[0041] In particular, a steel pipe joint structure in which the side of the tip of the outer fitting portion facing the second steel pipe and the side of the tip of the inner fitting portion facing the first steel pipe do not have a protrusion extending in the pipe axial direction or a groove recessed in the pipe axial direction, eliminates the need for a countersunk structure to reduce the risk of separation at the fitting portion of the joint. This countersunk structure creates a localized thin-walled portion, which carries the risk of breakage due to external forces and may impair the stability of the joint structure. By eliminating the countersunk structure, this instability is eliminated, allowing the joint structure to exhibit stable performance.

[0042] In particular, when at least one of the inner fitting member and the outer fitting member is formed of a bent roll pipe with a weld extending in the axial direction, fuel, personnel, and other resources required for manufacturing are saved. Furthermore, this is a widely used raw pipe material and is easy to procure. Joints using this raw pipe material can exhibit stable performance as a joint structure.

[0043] In particular, when at least one of the inner fitting member and the outer fitting member is formed from a ring-forged steel pipe connection structure, the material of the present invention can be used as a base pipe material even when the joint becomes too thick to use a bent rolled pipe. Furthermore, this base pipe material has no welded joints, making it possible to more effectively transmit circumferential forces. A joint using this base pipe material can exhibit stable performance as a joint structure. [Explanation of symbols]

[0044] 1...connecting structure, 3...inner fitting member, 4...outer fitting member, 21, 22...steel pipe, 23, 24...weld portion, 31, 41...joint portion, 32, 42...fitting portion, 321, 421...protrusion portion, 322, 422...groove portion, 323, 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, the outer fitting member includes an outer fitting portion that fits into the outer side of the inner fitting member, the inner fitting portion and the outer fitting portion contact each other at a contact surface perpendicular to the axial direction, A steel pipe connection structure in which, in the radial direction of the first steel pipe and the inner fitting member, the distance from the center of the plate thickness of the first steel pipe to the center of the contact surface is X, the plate thickness of the first steel pipe is t, and the number of arrangements of the outer fitting portion and the inner fitting portion in the pipe axial direction is n, satisfies 0 < X / t ≦ 3n / 4.

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, a first circumferential groove portion is formed on an outer peripheral surface of the inner fitting portion, and a second circumferential groove portion is formed on an inner peripheral surface of the outer fitting portion, and when the inner fitting member is fitted into the outer fitting member, the first and second circumferential groove portions face each other, and a retaining member is inserted across the first and second circumferential groove portions; the inner fitting portion or the outer fitting portion and the retaining member contact each other at a contact surface perpendicular to the axial direction, A steel pipe connection structure in which, in the radial direction of the first steel pipe and the inner fitting member, the distance from the center of the plate thickness of the first steel pipe to the center of the contact surface is X, the plate thickness of the first steel pipe is t, and the number of arrangements of the outer fitting portion and the inner fitting portion in the pipe axial direction is n, satisfies 0 < X / t ≦ 3n / 4.

3. 3. The steel pipe connection structure according to claim 1, wherein X / t satisfies 0.50≦X / t.

4. 3. A steel pipe connection structure according to claim 1 or claim 2, wherein at least one of the yield point or 0.2% proof stress of the steel material forming the inner fitting member and the outer fitting member is 215 MPa or more and 550 MPa or less, and the tensile strength is 400 MPa or more and 720 MPa or less.

5. 3. The steel pipe connection structure according to claim 1 or 2, wherein the carbon equivalent Ceq of at least one of the inner fitting member or the outer fitting member, 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.

6. a plurality of first protrusions are formed on the outer side of the inner fitting portion, with a first gap portion sandwiched between them in the circumferential direction; a plurality of second protrusions are formed on the inner side of the outer fitting portion, with a second gap portion sandwiched between them 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.

7. the first protrusions are formed at 16 to 32 locations on the outer side of the inner fitting portion, with the first gap portion sandwiched between them in the circumferential direction; The steel pipe connection structure according to claim 6, wherein the second protrusions are formed on the inside of the outer fitting portion, with the same number as the first protrusions, sandwiching the second gap portion in the circumferential direction.

8. the inner fitting portion includes three or four of the first protrusions arranged in the axial direction, The steel pipe connection structure according to claim 7 , wherein the outer fitting portion includes the second protrusions arranged in the axial direction in the same number as the first protrusions.

9. a plate thickness of a first groove portion formed between the first protrusions arranged in the axial direction in the inner fitting member is formed uniformly regardless of a position in the axial direction, 9. The steel pipe connection structure according to claim 8, wherein the plate thickness of the second groove portion formed between the second protrusions arranged in the axial direction in the outer fitting member is formed uniformly regardless of the axial position.

10. a side surface of a tip end portion of the outer fitting portion in a direction toward the second steel pipe; On the side surface of the tip portion of the inner fitting portion in the direction toward the first steel pipe, No protrusions extending in the tube axis direction or grooves recessed in the tube axis direction are provided. The steel pipe connection structure according to claim 9 .

11. 3. The steel pipe connection structure according to claim 1, wherein at least one of the inner fitting member and the outer fitting member is formed of a bent roll pipe having a welded portion extending in the axial direction.

12. 3. The steel pipe connection structure according to claim 1, wherein at least one of the inner fitting member and the outer fitting member is formed from a ring forged material.

13. A rotation suppression structure that suppresses relative rotation of the connecting structure of these steel pipes when the outer fitting portion and the inner fitting portion are engaged, a key groove portion formed continuously on a side surface of the tip end of the outer fitting portion facing the second steel pipe and a side surface of the tip end of the inner fitting portion facing the first steel pipe when the outer fitting portion and the inner fitting portion are engaged with each other; and a key member fitted into the key groove portion so as to extend from the side surface of the tip end of the outer fitting portion facing the second steel pipe to the side surface of the tip end of the inner fitting portion facing the first steel pipe, the keyway portion has a first groove formed by cutting out an end surface facing the inner fitting portion on a side surface of a tip end portion of the outer fitting portion in a direction toward the second steel pipe, and a second groove formed by cutting out an end surface facing the outer fitting portion on a side surface of a tip end portion of the inner fitting portion in a direction toward the first steel pipe, Either one or both of the first groove and the second groove has a contact point portion that rotates the key member while contacting the side edge of the key member due to a predetermined relative rotation between the outer fitting portion and the inner fitting portion, and a contact edge portion that is provided horizontally or inclined with respect to the longitudinal direction of the axis of the steel pipe and that contacts the side edge of the key member in the circumferential direction due to a predetermined relative rotation between the outer fitting portion and the inner fitting portion. The steel pipe connection structure according to claim 6,

14. a portion of the inner fitting member other than the inner fitting portion and the joint portion with the first steel pipe; The outer fitting member is provided at a portion other than the outer fitting portion and the joint portion with the second steel pipe. The steel sheet may have black scale remaining due to high-temperature oxidation. The steel pipe connection structure according to claim 1 or 2.

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

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