Surface-modified steel pipe and method for manufacturing the same

Abstract

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

Description

[Technical Field]

[0001] This invention relates to surface-modified steel pipes and methods for manufacturing the same. [Background technology]

[0002] Traditionally, steel pipe piles have been embedded and fixed in the ground, concrete, or cement to construct the foundations of civil engineering structures. To increase the adhesion strength between the steel pipe pile and the material to which it is fixed, surface-modified steel pipes have been developed with recesses on their surface to increase friction (see, for example, Patent Document 1). In recent years, surface-modified steel pipes that can achieve even higher adhesion strength have become necessary in the construction of large-scale civil engineering structures. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2008-175055 [Overview of the project] [Problems that the invention aims to solve]

[0004] This invention has been made in view of the problems of the prior art, and aims to provide a surface-modified steel pipe that can achieve high adhesion strength. [Means for solving the problem]

[0005] According to one aspect of the present invention, a surface-modified steel pipe capable of achieving high adhesion strength is provided. The surface-modified steel pipe has a reference outer surface extending along the circumferential direction, and at least one of a convex portion projecting radially outward from the reference outer surface and a concave portion recessing radially inward from the reference outer surface. The outer diameter of the reference outer surface is d (mm), the height of the convex portion from the reference outer surface is h (mm), the depth of the concave portion from the reference outer surface is u (mm), and the average value of the area occupied by the convex portion and the concave portion per axial length d (mm) is s (mm 2The 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 greater. [Brief explanation of the drawing]

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

[0007] Hereinafter, embodiments of the surface-modified steel pipe according to the present invention will be described in detail with reference to Figures 1A to 5. In Figures 1A to 5, identical or corresponding components are denoted by the same reference numerals, and redundant explanations are omitted. Also, in Figures 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 one another and do not represent a specific rank or order.

[0008] The surface-modified steel pipe according to the present invention is used in construction of civil engineering buildings and other structures, fixed to foundation materials such as cement and concrete. In this specification, the load per unit area required to push out such a surface-modified steel pipe fixed to a foundation material from the foundation material is defined as the adhesion strength (peel strength). Herein, in this application, "surface-modified steel pipe" refers to a steel pipe on which at least one of a convex portion projecting radially outward and a concave portion recessing radially inward is formed on the surface of the steel pipe.

[0009] When protrusions or recesses are formed on the outer surface of a steel pipe, if the base material, such as cement, adheres to or comes into contact with the outer surface of the steel pipe before it hardens, the base material will penetrate into the protrusions and recesses 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 hardening will be weak, while if the steel pipe has a surface with many irregularities, the adhesion strength between the base material and the steel pipe after hardening will be strong. This is because the anchoring effect (anchoring effect) between the steel pipe with protrusions or recesses formed on its outer surface and the base material creates a strong mechanical bonding force between the steel pipe and the base material. The inventors diligently researched what kind of surface-modified steel pipe structure enhances this anchoring effect and discovered that a specific index value K, determined by the protrusions and recesses formed on the outer surface, increases in accordance with the adhesion strength. The inventors then discovered that if this index value K is 20 or higher, the adhesion strength with the base material becomes extremely high (35 N / mm²). 2 The above findings were discovered.

[0010] The index value K for surface-modified steel pipes 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 of the reference outer surface of the surface-modified steel pipe (mm), h is the height of the protrusions projecting radially outward from the reference outer surface (mm), u is the depth of the recesses projecting radially inward from the reference outer surface (mm), and s is the average area (mm²) occupied by the protrusions and recesses along 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, the height h of the convex portion is preferably 2 mm or less. Further, since it is difficult to manufacture a steel pipe having a concave portion with a depth exceeding 5 mm, the depth u of the concave portion is preferably 5 mm or less. Incidentally, if it can be manufactured, the height h of the convex portion may exceed 2 mm, or the depth u of the concave portion may exceed 5 mm.

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

[0013] Examples of the base material used include, for example, materials containing 1 to 90% moisture, containing 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 or more (for example, cement or concrete).

[0014] Further, when the wall thickness of the surface-modified steel pipe is t, the ratio (t / d) of the wall thickness t to the outer diameter d of the reference outer peripheral surface of the surface-modified steel pipe 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 as a surface-modified steel pipe, and if t / d is 0.10 or less, the weight reduction of the surface-modified steel pipe can be achieved.

[0015] Fig. 1A is a front view showing the surface-modified steel pipe 10 in the first embodiment of the present invention, and Fig. 1B is a cross-sectional view taken along line A-A of Fig. 1A. As shown in Figs. 1A and 1B, this 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 and 162 in directions orthogonal to each other, and these two types of protrusions 161 and 162 are alternately and regularly arranged along the axial direction. In the example shown in Fig. 1A, the protrusions 161 are provided every 90 degrees around the axis, and four protrusions 161 arranged in the circumferential direction are arranged side by side in the axial direction at a predetermined pitch P1. Also, the protrusions 162 are provided every 90 degrees around the axis, and 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 surfaces of the protrusions 16 also extend along the circumferential direction, but since the total area thereof is smaller than the total area of the outer peripheral surface 12, in this embodiment, the outer peripheral surface 12 serves as 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. Also, the height h1 of the protrusion 16 is defined as the distance by which the protrusion 16 protrudes radially outward from the outer peripheral surface 12.

[0017] The protrusions 16 are formed in the same pattern repeatedly at every pitch P1 along the axial direction. Therefore, by measuring the area S1 occupied by the protrusions 16 per one pitch P1, the average value s1 of the area 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 (where α = 34.7 and γ = 0.4). The index value K of the surface-modified steel pipe 10 in this embodiment is 20 or more.

[0019] Figure 2A is a front view showing a surface-modified steel pipe 20 in a second embodiment of the present invention, and Figure 2B is a cross-sectional view taken along line BB in Figure 2A. As shown in Figures 2A and 2B, this surface-modified steel pipe 20 has a plurality of grooves 24 (recesses) formed on the outer circumferential surface 12 of the surface-modified steel pipe 10 shown in Figures 1A and 1B, which are further recessed radially inward. 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 90-degree intervals around the central axis, but are offset in the axial direction at 90-degree intervals 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 surface 12 to the deepest part of the groove 24.

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

[0022] The index values ​​for such surface-modified steel pipes 20 are: K=α×h1+β×u2+γ×s2 / d1=α×h1+β×u2+γ×S2 / P2 It is defined as (α=34.7, β=2.0, γ=0.4). In this embodiment, the index value K of the surface-modified steel pipe 20 is 20 or more.

[0023] The surface-modified steel pipes 10 and 20 described above can be manufactured, for example, by an electric resistance welded pipe manufacturing apparatus 100 as shown in Figure 3. This electric resistance welded pipe manufacturing apparatus 100 includes an uncoiler 120 that continuously feeds a coiled strip of steel sheet material 110 downstream (in the pipe-making direction), a pair of modification rolls 131 and 132 that form protrusions and / or recesses protruding from the surface of the steel sheet material 110, a plurality of forming rolls 140 that form the steel sheet material 110 into a cylindrical shape downstream of the modification rolls 131 and 132, a coil 150 that forms a surface-modified steel pipe 170 by electric resistance welding the butt joints of the end faces of the cylindrically formed steel sheet material 110 using 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 Figure 3 include an upstream breakdown roll 142 and a downstream fin pass roll 144.

[0024] For example, when forming the above-described projection 16 on the surface-modified steel pipe 170, the modification roll 132 on the side corresponding to the inner circumferential surface of the steel pipe is provided with a projection, and the modification roll 131 on the side corresponding to the outer circumferential surface of the steel pipe is provided with a groove corresponding to the projection of the modification roll 132. The projection of this modification roll 132 pushes the steel plate material 110 toward the modification roll 131, thereby forming a projection (which becomes projection 16 after electric resistance welding) on ​​the steel plate material 110. Also, for example, when forming the above-described groove 24 on the surface-modified steel pipe 170, the modification roll 131 on the side corresponding to the outer circumferential surface of the steel pipe is provided with a projection, and the modification roll 132 on the side corresponding to the inner circumferential surface of the steel pipe is provided with a groove corresponding to the projection of the modification roll 131. The projection of this modification roll 131 pushes the steel plate material 110 toward the modification roll 132, thereby forming a groove (which becomes groove 24 after electric resistance welding) on ​​the steel plate material 110. The shape and dimensions of the protrusions and grooves of these modification rolls 131 and 132 are set so that the index value K of the surface-modified steel pipe 170 produced is 20 or higher.

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

[0026] As shown in Figure 3, the modification rolls 131 and 132 form at least one of the convex and concave portions corresponding to the projections 16 and grooves 24 described above on the steel plate material 110 (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 welded together by electric resistance welding using a coil 150 to form a surface-modified steel pipe 170 (steel pipe forming step). The formed surface-modified steel pipe 170 is then cooled by a cooling unit 160 to complete the surface-modified steel pipe 170.

[0027] In the example shown in Figure 3, the steel sheet material 110 is formed with convex and / or concave portions using modifying rolls 131 and 132, but the modification step may be performed before winding the steel sheet material 110 into a coil. For example, when heating and rolling a carbon steel sheet containing 0.01 to 0.4 mass% of carbon (hot rolling process), the steel sheet may be passed between rolling rolls having a pattern consisting of convex and / or concave portions to transfer the pattern to the steel sheet, thereby producing a steel sheet with convex and / or concave portions, which may then be wound into a coil and introduced into the electric resistance welded pipe manufacturing apparatus 100. [Examples]

[0028] As Example 1, a surface-modified steel pipe 10, as shown in Figures 1A and 1B, was prepared. The outer diameter d1 of the reference outer surface (outer surface 12) of this surface-modified steel pipe 10 was 48.6 mm, and the height h1 of the protrusions 16 was 0.8 mm. The area S1 occupied by the protrusions 16 per pitch P1 was measured, and the average value s1 of the area occupied by the protrusions 16 per length d1 along the axial direction was calculated from this measurement, resulting in s1 = 1487 mm². 2 The index value K for the surface-modified steel pipe 10 in this Example 1 was calculated as follows: K=34.7×0.8+0.4×1487 / 48.6=40.0 That was the case.

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

[0030] As Example 3, a surface-modified steel pipe was prepared with numerous small protrusions distributed in a textured pattern on its outer surface. The outer diameter d3 of the outer surface (reference outer surface) of this surface-modified steel pipe was 48.6 mm, and the height h3 of the textured protrusions was 0.2 mm. The average value s3 of the area occupied by the textured protrusions per axial length d3 was calculated to be s3 = 2974 mm². 2 The index value K for the surface-modified steel pipe in this Example 3 was calculated as follows: K=34.7×0.2+0.4×2974 / 48.6=31.4 That was the case.

[0031] As Example 4, a surface-modified steel pipe having the same groove portion as in Example 2 formed on the outer peripheral surface of the surface-modified steel pipe of Example 3 was prepared. That is, the outer diameter d3 of the outer peripheral surface was 48.6 mm, the height h3 of the matte-finish-like protrusions was 0.2 mm, and the depth u4 of the groove portion was 2.2 mm. When the average value s4 of the area occupied by the matte-finish-like protrusions and the groove portion per length d3 along the axial direction was calculated, s4 = 3849 mm 2 was obtained. When the index value K of the surface-modified steel pipe of this Example 4 was calculated, K = 34.7×0.2 + 2.0×2.2 + 0.4×3849 / 48.6 = 43.0 was obtained.

[0032] As Example 5, a surface-modified steel pipe having only the height of the matte-finish-like protrusions different from that of the surface-modified steel pipe of Example 3 (height h5 = 0.1 mm) was prepared. When the index value K of the surface-modified steel pipe of this Example 5 was calculated, K = 34.7×0.1 + 0.4×2974 / 48.6 = 27.9 was obtained.

[0033] As Comparative Example 1, a round steel pipe with an outer diameter of 48.6 mm without convex or concave portions on the outer peripheral surface was prepared. When the index value K of the round steel pipe of this Comparative Example 1 was calculated, K = 0.0 was obtained.

[0034] As Comparative Example 2, a surface-modified steel pipe having a groove portion similar to the groove portion 24 shown in FIGS. 2A and 2B formed on the outer peripheral surface of the round steel pipe of Comparative Example 1 was prepared. The depth of the groove portion of this surface-modified steel pipe was 3.0 mm, and when the average value of the area occupied by the groove portion per length of 48.6 mm along the axial direction was calculated, it was 1458 mm 2 was obtained. When the index value K of the grooved round steel pipe of this Comparative Example 2 was calculated, K = 2.0×3.0 + 0.4×1458 / 48.6 = 18.0 was obtained.

[0035] As Comparative Example 3, a surface-modified steel pipe having half the number of grooves of Comparative Example 2 was prepared. When the index value K of the grooved round steel pipe of this Comparative Example 3 was calculated, K = 2.0×3.0 + 0.4×729 / 48.6 = 12.0 That was the case.

[0036] As Comparative Example 4, a surface-modified steel pipe was prepared that differed from the surface-modified steel pipe of Example 1 only in the height of the protrusions (protrusion height 0.2 mm). When the index value K of this surface-modified steel pipe of Comparative Example 4 was calculated, K=34.7×0.2+0.4×1487 / 48.6=19.2 That was the case.

[0037] Steel pipes (200 mm in length) for Examples 1-5 and Comparative Examples 1-4 were prepared. Each steel pipe was placed in a container 120 mm long with an inner diameter of 165.2 mm. 120 mm of the 200 mm steel pipe was immersed in cement grout as a base material, and then the cement grout was allowed to solidify. For the cement grout, 0.5 parts tap water was added to 1.0 parts ordinary Portland cement manufactured by Taiheiyo Cement Corporation, resulting in a compressive strength of 37.6 N / mm². 2 Materials with the following characteristics were used. Seven days after casting, the load required to push the steel pipe out of the foundation material using a hydraulic press was measured as the adhesion strength. Three such experiments were conducted, and the average values ​​were compared. The results are as follows. [Table 1]

[0038] Figure 5 shows the relationship between the index value K and adhesion strength as a graph. From Figure 5, it can be seen that the adhesion strength increases as the index value K increases. From this graph, it can be seen that the adhesion strength of 35 N / mm² is required for steel pipes in recent years. 2 To obtain the above results, it is sufficient that the index value K is 20 or higher. The surface-modified steel pipes in Examples 1 to 5, with an index value K of 20 or higher, achieve more than eight times the adhesion strength of the round steel pipe in Comparative Example 1. To further increase the adhesion strength, it is preferable that the index value K of the surface-modified steel pipe is 30 or higher, and even more preferable that it is 40 or higher.

[0039] As described above, the outer diameter of the reference outer surface is d (mm), the height of the protrusion from the reference outer surface is h (mm), the depth of the recess from the reference outer surface is u (mm), and the average area occupied by the protrusion and recess per unit length d (mm) along the axial direction is s (mm 2 If 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, then the adhesion strength to the base material will be extremely high. 35 N / mm 2 If such surface-modified steel pipes are fixed to a base material having the above compressive strength, the compressive strength will be 35 N / mm². 2 The above adhesion strength can be achieved.

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

[0041] 10,20 Surface-modified steel pipes 12 Outer circumferential surface (reference outer circumferential surface) 16,161,162 Protrusions (convex parts) 24,241,242 Groove (recess) 100 ERW pipe manufacturing equipment 110 Steel plate material 111 Groove 112 Protrusion 120 Ankoira 131,132 Modification Roll 140 forming rolls 142, 142A, 142B Breakdown Roll 143 Escape ditch 144 Fin Pass Roll 150 coils 160 Cooling Units 170 Surface-modified steel pipe

Claims

1. A reference outer surface extending along the circumferential direction, At least one of a convex portion projecting radially outward from the reference outer surface and a concave portion recessing radially inward from the reference outer surface It has, The outer diameter of the reference outer surface is d (mm), the height of the protrusion from the reference outer surface is h (mm), the depth of the recess from the reference outer surface is u (mm), and the average area occupied by the protrusion and recess per unit 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) The index value K, as defined by, is 20 or greater. Surface-modified steel pipe.

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

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

4. 35 N / mm 2 The adhesive strength when fixed to a base material having the above compressive strength is 35 N / mm². 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 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 them.

6. A modification step that forms at least one of a protrusion that extends from the surface of the steel plate material and a recess that is indented from the surface, A forming step of forming the steel sheet material, on which at least one of the convex portion and the concave portion is formed, into a cylindrical shape using a plurality of forming rolls, A steel pipe forming step involves forming a surface-modified steel pipe by electric resistance welding the butt joint portions of the end faces of the cylindrically formed steel plate material. It has, In the above modification step, The outer diameter of the reference outer surface extending circumferentially in the surface-modified steel pipe formed by the steel pipe forming step is d (mm), the height of the protrusion from the reference outer surface is h (mm), the depth of the recess from the reference outer surface is u (mm), and the average value of the area occupied by the protrusion and recess per axial length d (mm) 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 such that the index value K defined by becomes 20 or more. A method for manufacturing surface-modified steel pipes.

7. The method for manufacturing a surface-modified steel pipe according to claim 6, wherein in the forming step, relief grooves formed on the outer circumferential surfaces of at least some of the plurality of forming rolls prevent the protrusions generated when forming the convex and concave portions of the steel sheet material from coming into contact with the forming rolls.

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