Surface-modified steel pipe and its manufacturing method

Abstract

To provide a surface-modified steel pipe that can achieve high adhesive strength. [Solution] A surface-modified steel pipe 20 has an outer peripheral surface 12 extending in the circumferential direction, protrusions 16 protruding radially outward from the outer peripheral surface 12, and grooves 24 recessed radially inward from the outer peripheral surface 12. The outer diameter of the outer peripheral surface 12 is d1 (mm), the height of the protrusions 16 is h1 (mm), the depth of the grooves 24 is u2 (mm), and the average area occupied by the protrusions 16 and grooves 24 per axial length d1 (mm) is s (mm 2 ) and the index value K, defined as K = α × h1 + β × u2 + γ × s / d1 (where α = 34.7, β = 2.0, and γ = 0.4), is 20 or more.

Description

[Technical field]

[0001] The present invention relates to a surface-modified steel pipe and a method for producing the same. [Background technology]

[0002] Conventionally, steel pipe piles have been embedded and fixed in the ground, concrete, or cement to construct foundations for civil engineering buildings. In order to increase the adhesive strength between the steel pipe pile and the material to which the steel pipe pile is fixed, surface-modified steel pipes have been considered in which recesses are provided on the surface of the steel pipe pile to increase friction (see, for example, Patent Document 1). In recent years, in the construction of large civil engineering buildings, there has been a demand for surface-modified steel pipes that can achieve even higher adhesive strength. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2008-175055 A Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention has been made in consideration of the above problems of the conventional technology, and has an object to provide a surface-modified steel pipe that can achieve high adhesive strength. [Means for solving the problem]

[0005] According to one aspect of the present invention, there is provided a surface-modified steel pipe capable of realizing high adhesive strength. The surface-modified steel pipe has a reference outer peripheral surface extending in the circumferential direction, and at least one of a convex portion protruding radially outward from the reference outer peripheral surface and a concave portion recessed radially inward from the reference outer peripheral surface. The outer diameter of the reference outer peripheral surface is d (mm), the height of the convex portion from the reference outer peripheral surface is h (mm), the depth of the concave portion from the reference outer peripheral surface is u (mm), and the average value of the area occupied by the convex portion and the concave portion per length d (mm) along the axial direction is s (mm 2 ) ass / d≧30.6, The index value K defined as K = α × h + β × u + γ × s / d (where α = 34.7, β = 2.0, γ = 0.4) is 20 or more. [Brief description of the drawings]

[0006] [Figure 1A] FIG. 1A is a front view showing a surface-modified steel pipe in a first embodiment of the present invention. [Figure 1B] FIG. 1B is a cross-sectional view taken along line AA in FIG. 1A. [Figure 2A] FIG. 2A is a front view showing a surface-modified steel pipe according to a second embodiment of the present invention. [Figure 2B] FIG. 2B is a cross-sectional view taken along line BB in FIG. 2A. [Diagram 3] FIG. 3 is a diagram showing a schematic configuration of an electric resistance welded pipe manufacturing apparatus for manufacturing a surface-modified steel pipe according to the present invention. [Figure 4] FIG. 4 is a partial cross-sectional view of a breakdown roll in the electric-resistance-welded pipe manufacturing apparatus shown in FIG. [Diagram 5] FIG. 5 is a graph showing the relationship between the index value K and the adhesive strength for the examples according to the present invention and the comparative examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] Hereinafter, an embodiment of the surface-modified steel pipe according to the present invention will be described in detail with reference to Figs. 1A to 5. In Figs. 1A to 5, identical or corresponding components are denoted with the same reference numerals, and duplicated explanations will be omitted. In addition, in Figs. 1A to 5, the scale and dimensions of each component may be exaggerated, or some components may be omitted. In the following description, unless otherwise specified, terms such as "first" and "second" are used only to distinguish components from each other, and do not indicate a specific order or sequence.

[0008] The surface-modified steel pipe according to the present invention is used by being fixed to a base material such as cement or concrete in the construction of civil engineering buildings. In this specification, the load per unit area required to push the surface-modified steel pipe fixed to such a base material out of the base material is defined as the adhesion strength (peel strength). Here, in this application, the term "surface-modified steel pipe" refers to a steel pipe on whose surface at least one of a convex portion protruding radially outward and a concave portion recessed radially inward is formed.

[0009] In the case where a steel pipe has a convex or concave portion formed on its outer surface, if the base material, such as cement, adheres to or comes into contact with the outer surface of the steel pipe before the base material solidifies, the base material will penetrate into the convex or concave portion of the steel pipe. In this case, if the steel pipe has a smooth surface with few irregularities, the adhesion strength between the base material and the steel pipe after solidification is weak, whereas if the steel pipe has a surface with many irregularities, the adhesion strength between the base material and the steel pipe after solidification is strong. This is because a strong mechanical bonding force is generated between the steel pipe and the base material due to the anchor effect between the steel pipe with convex or concave portions formed on its outer surface. The inventors have conducted extensive research into what type of surface-modified steel pipe has a high anchor effect, and have found that a specific index value K determined by the convex or concave portion formed on the outer surface increases according to the adhesion strength. The inventors have found that if this index value K is 20 or more, the adhesion strength with the base material is extremely high (35 N / mm 2 We found that the above

[0010] The index value K of the surface-modified steel pipe discovered by the present inventors is defined by the following formula. K = α × h + β × u + γ × s / d Here, α = 34.7, β = 2.0, γ = 0.4, d is the outer diameter (mm) of the reference outer peripheral surface of the surface-modified steel pipe, h is the height (mm) of the convex part protruding radially outward from the reference outer peripheral surface, u is the depth (mm) of the concave part recessed radially inward from the reference outer peripheral surface, and s is the average area (mm) occupied by the convex part and the concave part in the axial length d (mm). 2 ).

[0011] Since it is difficult to manufacture a steel pipe having a convex portion with a height exceeding 2 mm, it is preferable that the height h of the convex portion is 2 mm or less. Also, since it is difficult to manufacture a steel pipe having a concave portion with a depth exceeding 5 mm, it is preferable that the depth u of the concave portion is 5 mm or less. However, as long as it is possible to manufacture the steel pipe, the height h of the convex portion may exceed 2 mm, and the depth u of the concave portion may exceed 5 mm.

[0012] In this specification, the reference outer peripheral surface of a surface-modified steel pipe refers to the outer peripheral surface when the outer peripheral surface extending along the circumferential direction exists only at one radius, refers to the outer peripheral surface with the largest total area when there are multiple outer peripheral surfaces extending along the circumferential direction at different radii, and refers to the outer peripheral surface with the smallest radius when there are multiple outer peripheral surfaces with the same total area.

[0013] Examples of the base material used include a material containing 1 to 90% moisture, at least one of 3CaO·SiO2, MgO, Al2O3, 3CaO·Al2O3, 4CaO·Al2O3·Fe2O3, MgCO3, and CaCO3, and having a compressive strength of 30 N / mm 2 Materials having compressive strengths above this level (e.g., cement and concrete) are examples of such materials.

[0014] In addition, when the wall thickness of the surface-modified steel pipe is t, the ratio of the wall thickness t to the outer diameter d of the reference outer peripheral surface of the surface-modified steel pipe (t / d) is preferably 0.01 or more and 0.10 or less. If t / d is 0.01 or more, it is easy to ensure the strength of the surface-modified steel pipe, and if t / d is 0.10 or less, the weight of the surface-modified steel pipe can be reduced.

[0015] FIG. 1A is a front view showing a surface-modified steel pipe 10 according to a first embodiment of the present invention, and FIG. 1B is a cross-sectional view taken along line AA in FIG. 1A. As shown in FIG. 1A and FIG. 1B, the surface-modified steel pipe 10 has an outer peripheral surface 12 extending along the circumferential direction, and a plurality of protrusions 16 (convex portions) protruding radially outward from the outer peripheral surface 12. These protrusions 16 include two types of protrusions 161, 162 oriented perpendicular to each other, and these two types of protrusions 161, 162 are alternately arranged in a regular pattern along the axial direction. In the example shown in FIG. 1A, the protrusions 161 are provided at 90° intervals around the axis, and the four protrusions 161 arranged in the circumferential direction are arranged side by side in the axial direction at a predetermined pitch P1. The protrusions 162 are also provided at 90° intervals around the axis, and the four protrusions 162 arranged in the circumferential direction are arranged side by side in the axial direction at the same pitch P1.

[0016] The top faces of the protrusions 16 also extend in the circumferential direction, but the total area of ​​the top faces is smaller than the total area of ​​the outer peripheral surface 12, so in this embodiment, the outer peripheral surface 12 is the reference outer peripheral surface. Therefore, the outer diameter d1 of the reference outer peripheral surface is defined as the outer diameter of the outer peripheral surface 12. In addition, the height h1 of the protrusions 16 is defined as the distance that the protrusions 16 protrude radially outward from the outer peripheral surface 12.

[0017] The protrusions 16 are formed in the same pattern repeatedly at the above-mentioned pitch P1 along the axial direction. Therefore, by measuring the area S1 occupied by the protrusions 16 per pitch P1, the average area s1 occupied by the protrusions 16 per length d1 along the axial direction can be calculated by s1=S1×(d1 / P1).

[0018] As described above, the index value K of such a surface-modified steel pipe 10 is K=α×h1+γ×s1 / d1=α×h1+γ×S1 / P1 (α=34.7, γ=0.4). The index value K of the surface-modified steel pipe 10 in this embodiment is 20 or more.

[0019] Fig. 2A is a front view showing a surface-modified steel pipe 20 according to a second embodiment of the present invention, and Fig. 2B is a cross-sectional view taken along line BB in Fig. 2A. As shown in Figs. 2A and 2B, this surface-modified steel pipe 20 is obtained by forming a plurality of grooves 24 (recesses) that are recessed radially inward on the outer circumferential surface 12 of the surface-modified steel pipe 10 shown in Figs. 1A and 1B. Each groove 24 extends in the axial direction, and the plurality of grooves 24 are arranged in the axial direction at a predetermined pitch P2 (>P1). In the illustrated example, the grooves 24 are formed at intervals of 90 degrees around the central axis, but are offset in the axial direction at intervals of 90 degrees around the central axis (groove 241 and groove 242).

[0020] The depth u2 of the groove 24 is defined as the distance from the outer circumferential surface 12 to the deepest portion of the groove 24.

[0021] The projections 16 and grooves 24 are repeatedly formed in the same pattern at the above-mentioned pitch P2 along the axial direction. Therefore, by measuring the area S2 occupied by the projections 16 and grooves 24 per pitch P2, the average area s2 occupied by the projections 16 and grooves 24 per length d1 along the direction can be calculated by s2=S2×(d1 / P2).

[0022] The index value of such a surface-modified steel pipe 20 is: K=α×h1+β×u2+γ×s2 / d1=α×h1+β×u2+γ×S2 / P2 (α=34.7, β=2.0, γ=0.4). The index value K of the surface-modified steel pipe 20 in this embodiment is 20 or more.

[0023] The above-mentioned surface-modified steel pipes 10, 20 can be manufactured by, for example, an electric resistance welded pipe manufacturing apparatus 100 as shown in Fig. 3. This electric resistance welded pipe manufacturing apparatus 100 includes an uncoiler 120 that continuously sends out a coil-shaped strip-shaped steel plate material 110 downstream (pipe-making direction), a set of modification rolls 131, 132 that form a convex portion protruding from the surface of the steel plate material 110 and / or a concave portion recessed from the surface, a plurality of sets of forming rolls 140 that form the steel plate material 110 into a cylindrical shape downstream of the modification rolls 131, 132, a coil 150 that forms a surface-modified steel pipe 170 by electric resistance welding the butted portions of the end faces of the cylindrically formed steel plate material 110 by high-frequency induction heating, and a cooling unit 160 that cools the electric resistance welded surface-modified steel pipe. The forming rolls 140 shown in Fig. 3 include an upstream breakdown roll 142 and a downstream fin pass roll 144.

[0024] When forming the above-mentioned protrusions 16, for example, on the surface-modified steel pipe 170, protrusions are provided on the modification roll 132 on the side corresponding to the inner peripheral surface of the steel pipe, and grooves corresponding to the protrusions of the modification roll 132 are provided on the modification roll 131 on the side corresponding to the outer peripheral surface of the steel pipe. The protrusions of the modification roll 132 can be used to push the steel plate material 110 toward the modification roll 131 side, thereby forming protrusions (which will become the protrusions 16 after electric resistance welding) on ​​the steel plate material 110. Furthermore, when forming the above-mentioned grooves 24, for example, on the surface-modified steel pipe 170, protrusions are provided on the modification roll 131 on the side corresponding to the outer peripheral surface of the steel pipe, and grooves corresponding to the protrusions of the modification roll 131 are provided on the modification roll 132 on the side corresponding to the inner peripheral surface of the steel pipe. The protrusions of the modification roll 131 can be used to push the steel plate material 110 toward the modification roll 132 side, thereby forming grooves (which will become the grooves 24 after electric resistance welding) on ​​the steel plate material 110. The shapes and dimensions of the protrusions and grooves of these modifying rolls 131, 132 are set so that the index value K of the surface-modified steel pipe 170 to be manufactured is 20 or more.

[0025] FIG. 4 is a partial cross-sectional view showing one set of breakdown rolls 142. For example, when forming the groove portion 24 in the surface-modified steel pipe 170, the groove portion 111 is formed in the steel plate material 110 by the protrusion of the modification roll 131 and the groove of the modification roll 132 as described above, and accordingly, the steel plate material 110 is formed with a protrusion 112 protruding on the opposite side. In this embodiment, an escape groove 143 is formed on the outer circumferential surface of the breakdown roll 142A facing the protrusion 112 of the steel plate material 110 so that the breakdown roll 142 does not crush the protrusion 112 and the groove portion 111 of the steel plate material 110. When forming the protrusion 16 in the surface-modified steel pipe 170, a similar escape groove is formed in the breakdown roll 142B on the opposite side. In this embodiment, such an escape groove 143 is formed in the breakdown roll 142 of the forming rolls 140, but it is also possible to form such an escape groove in all the forming rolls 140.

[0026] Thus, in the example shown in Figure 3, at least one of convex portions and concave portions corresponding to the above-mentioned protrusions 16 and groove portions 24 is formed in the steel plate material 110 by the modification rolls 131, 132 (modification step), then the steel plate material 110 is formed into a cylindrical shape using a plurality of forming rolls 140 (forming step), the butt joints of the end faces of the cylindrically formed steel plate material 110 are electric welded by a coil 150 to form a surface-modified steel pipe 170 (steel pipe forming step), and the formed surface-modified steel pipe 170 is cooled by a cooling unit 160 to complete the surface-modified steel pipe 170.

[0027] 3, protrusions and / or recesses are formed in the steel plate material 110 using the modification rolls 131, 132, but a modification step may be performed before the steel plate material 110 is wound into a coil. For example, when a carbon steel plate containing 0.01 to 0.4 mass % carbon is heated and rolled (hot rolling process), the steel plate may be passed between rolling rolls having a pattern consisting of protrusions and / or recesses to transfer the pattern to the steel plate, thereby producing a steel plate having protrusions and / or recesses, which may then be wound into a coil and introduced into the electric resistance welded pipe manufacturing apparatus 100. EXAMPLES

[0028] 1A and 1B was prepared as Example 1. The outer diameter d1 of the reference outer peripheral surface (outer peripheral surface 12) of this surface-modified steel pipe 10 was 48.6 mm, and the height h1 of the projections 16 was 0.8 mm. The area S1 occupied by the projections 16 per pitch P1 was measured, and the average value s1 of the area occupied by the projections 16 per length d1 along the axial direction was calculated from the measured value, resulting in s1 = 1487 mm. 2 The index value K of the surface-modified steel pipe 10 of Example 1 was calculated as follows: K=34.7×0.8+0.4×1487 / 48.6=40.0 It was.

[0029] 2A and 2B was prepared as Example 2. The outer diameter d1 of the reference outer peripheral surface (outer peripheral surface 12) of this surface-modified steel pipe 20 was 48.6 mm, the height h1 of the projections 16 was 0.8 mm, and the depth u2 of the grooves 24 was 1.8 mm. The area S2 occupied by the projections 16 and the grooves 24 per pitch P2 was measured, and the average value s2 of the area occupied by the projections 16 and the grooves 24 per length d1 along the axial direction was calculated from the measured value, resulting in s2=1578 mm. 2 The index value K of the surface-modified steel pipe 20 of Example 2 was calculated as follows: K=34.7×0.8+2.0×1.8+0.4×1578 / 48.6=44.3 It was.

[0030] As Example 3, a surface-modified steel pipe was prepared in which numerous small protrusions were distributed in a matte pattern on the outer circumferential surface. The outer diameter d3 of the outer circumferential surface (reference outer circumferential surface) of this surface-modified steel pipe was 48.6 mm, and the height h3 of the matte pattern protrusions was 0.2 mm. The average area s3 of the matte pattern protrusions per axial length d3 was calculated to be 2974 mm. 2 The index value K of the surface-modified steel pipe of Example 3 was calculated as follows: K=34.7×0.2+0.4×2974 / 48.6=31.4 It was.

[0031] As Example 4, a surface-modified steel pipe of Example 3 was prepared with the same grooves formed on the outer circumferential surface as in Example 2. That is, the outer diameter of the outer circumferential surface was d3 = 48.6 mm, the height of the matte-patterned protrusions h3 = 0.2 mm, and the depth of the grooves u4 = 2.2 mm. The average area s4 of the matte-patterned protrusions and grooves per axial length d3 was calculated to be s4 = 3849 mm 2 The index value K of the surface-modified steel pipe of Example 4 was calculated as follows: K=34.7×0.2+2.0×2.2+0.4×3849 / 48.6=43.0 It was.

[0032] As Example 5, a surface-modified steel pipe was prepared which differed from Example 3 only in the height of the pear-skin-patterned protrusions (height h5 = 0.1 mm). The index value K of the surface-modified steel pipe of Example 5 was calculated as follows: K=34.7×0.1+0.4×2974 / 48.6=27.9 It was.

[0033] A round steel pipe with an outer diameter of 48.6 mm and no protrusions or recesses on the outer circumferential surface was prepared as Comparative Example 1. The index value K of this round steel pipe of Comparative Example 1 was calculated as follows: K=0.0 It was.

[0034] As Comparative Example 2, a surface-modified steel pipe was prepared in which a groove similar to the groove 24 shown in Figures 2A and 2B was formed on the outer circumferential surface of the round steel pipe of Comparative Example 1. The depth of the groove of this surface-modified steel pipe was 3.0 mm, and the average area occupied by the groove per 48.6 mm in the axial length was calculated to be 1458 mm 2 The index value K of the grooved round steel pipe of Comparative Example 2 was calculated as follows: K=2.0×3.0+0.4×1458 / 48.6=18.0 It was.

[0035] As Comparative Example 3, a surface-modified steel pipe was prepared in which the number of grooves was half that of Comparative Example 2. The index value K of the grooved round steel pipe of Comparative Example 3 was calculated as follows: K = 2.0 x 3.0 + 0.4 x 729 / 48.6 = 12.0 It was.

[0036] As Comparative Example 4, a surface-modified steel pipe was prepared which differed from that of Example 1 only in the height of the projections (projection height 0.2 mm). The index value K of the surface-modified steel pipe of Comparative Example 4 was calculated as follows: K=34.7×0.2+0.4×1487 / 48.6=19.2 It was.

[0037] Steel pipes (200 mm long) of Examples 1 to 5 and Comparative Examples 1 to 4 were prepared, and each steel pipe was placed in a container with a length of 120 mm and an inner diameter of 165.2 mm. 120 mm of the 200 mm long steel pipe was immersed in cement milk as a base material, and then the cement milk was solidified. The cement milk was made by mixing 1.0 parts of ordinary Portland cement manufactured by Taiheiyo Cement Corporation with 0.5 parts of tap water, and had a compressive strength of 37.6 N / mm 2 The bond strength was measured by the load required to push the steel pipe out of the base material using a hydraulic press 7 days after casting. This experiment was carried out three times, and the average values ​​were compared. The results are as follows: [Table 1]

[0038] Figure 5 shows the above results as a graph showing the relationship between the index value K and adhesive strength. From Figure 5, it can be seen that the adhesive strength increases as the index value K increases. From this graph, it can be seen that the adhesive strength of 35 N / mm 2 It can be seen that in order to achieve the above, the index value K should be 20 or more. The surface-modified steel pipes of Examples 1 to 5, which have an index value K of 20 or more, achieve an adhesive strength that is more than 8 times that of the round steel pipe of Comparative Example 1. In order to further increase the adhesive strength, the index value K of the surface-modified steel pipe is preferably 30 or more, and more preferably 40 or more.

[0039] As described above, the outer diameter of the reference outer peripheral surface is d (mm), the height of the convex portion from the reference outer peripheral surface is h (mm), the depth of the concave portion from the reference outer peripheral surface is u (mm), and the average area occupied by the convex portions and concave portions per length d (mm) along the axial direction is s (mm 2 If the convex and / or concave portions are formed on the outer peripheral surface of the steel pipe so that the index value K, defined as K=α×h+β×u+γ×s / d (where α=34.7, β=2.0, γ=0.4), is 20 or more, preferably 30 or more, and more preferably 40 or more, the adhesive strength with the base material will be extremely high. 2 If such a surface-modified steel pipe is fixed to a base material having a compressive strength of 35N / mm 2 The above adhesion strength can be obtained.

[0040] Although the preferred embodiments of the present invention have been described above, it goes without saying that the present invention is not limited to the above-described embodiments and may be embodied in various different forms within the scope of the technical concept thereof. [Explanation of symbols]

[0041] 10,20 Surface-modified steel pipe 12 Outer circumferential surface (reference outer circumferential surface) 16,161,162 Protrusion (convex part) 24,241,242 Groove (recess) 100 ERW pipe manufacturing equipment 110 Steel plate material 111 Groove 112 Protrusion 120 Uncoiler 131,132 Modified roll 140 Forming roll 142, 142A, 142B Breakdown Roll 143 Undercut 144 Finpass Roll 150 Coil 160 Cooling Unit 170 Surface-modified steel pipes

Claims

1. A reference outer circumferential surface extending in a circumferential direction; At least one of a convex portion protruding radially outward from the reference outer circumferential surface and a concave portion recessed radially inward from the reference outer circumferential surface; having The outer diameter of the reference outer peripheral surface is d (mm), the height of the convex portion from the reference outer peripheral surface is h (mm), the depth of the concave portion from the reference outer peripheral surface is u (mm), and the average value of the area occupied by the convex portion and the concave portion per length d (mm) along the axial direction is s (mm 2 ) as s / d≧30.6, K=α×h+β×u+γ×s / d (However, α=34.7, β=2.0, γ=0.4) The index value K defined by is 20 or more. Surface modified steel pipe.

2. The surface-modified steel pipe according to claim 1 , wherein the index value K is 30 or more.

3. The surface-modified steel pipe according to claim 2 , wherein the index value K is 40 or more.

4. 35N / mm 2 When fixed to a base material with a compressive strength of 35 N / mm 2 The surface-modified steel pipe according to any one of claims 1 to 3.

5. The base material contains 1 to 90% water and is 3CaO.SiO 2 , MgO, Al 2 O 3 , 3CaO.Al 2 O 3 , 4CaO.Al 2 O 3 Fe 2 O 3 , MgCO 3 , and CaCO 3 The surface-modified steel pipe according to claim 4, comprising at least one of the following:

6. A modification step of forming at least one of a protrusion protruding from a surface of the steel plate material and a recess recessed from the surface; a forming step of forming the steel plate material having at least one of the convex portion and the concave portion into a cylindrical shape using a plurality of forming rolls; a steel pipe forming step of electric resistance welding the butt joints between the end faces of the cylindrically shaped steel plate material to form a surface-modified steel pipe; having In the modification step, The outer diameter of the reference outer peripheral surface extending along the circumferential direction of the surface-modified steel pipe formed by the steel pipe forming step is d (mm), the height of the convex portion from the reference outer peripheral surface is h (mm), the depth of the concave portion from the reference outer peripheral surface is u (mm), and the average value of the area occupied by the convex portion and the concave portion per length d (mm) along the axial direction is s (mm 2 ) as K=α×h+β×u+γ×s / d (However, α=34.7, β=2.0, γ=0.4) At least one of the convex portion and the concave portion is formed so that an index value K defined by is 20 or more. In the forming step, a relief groove is formed on at least a part of the outer peripheral surface of the plurality of forming rolls, thereby preventing a protrusion generated when forming the convex portion and the concave portion of the steel plate material from contacting the forming roll. Manufacturing method for surface-modified steel pipes.

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