JP6909969B2 - Steel pipe and manufacturing method of steel pipe - Google Patents

Description

The present invention relates to steel pipes and methods for manufacturing steel pipes.

Conventionally, in order to improve the corrosion resistance of a steel pipe, a plating layer containing zinc may be provided on the inner surface and the outer surface of the steel pipe. For example, Patent Document 1 discloses a so-called "ditch-pickled plating method" in which a steel pipe is immersed in a hot-dip galvanized bath to form a plating layer.

Japanese Patent No. 5663840

However, since the steel pipe produced by the sewage plating method has irregularities on the surface of the plating layer, it is difficult to pass the electric wire through the steel pipe. That is, the linearity is poor. Further, since the plating layer is conductive, the electrical insulation between the electric wire to be passed and the steel pipe is low.

Therefore, the present invention has been made in view of such a problem, and an object of the present invention is to provide a steel pipe having improved performance and a method for manufacturing the steel pipe.

In order to achieve the above object, the steel pipe according to one aspect of the present invention includes a tubular steel layer joined at a joint along the pipe axis direction, the steel layer and the steel layer from the outside in the radial direction of the steel layer. Electrical insulation that covers the first plating layer that covers the joint, the second plating layer that covers the inner surface of the steel layer, the inner surface of the second plating layer, and the inner surface of the joint, and has electrical insulation. With layers.

Further, in order to achieve the above object, the method for manufacturing a steel pipe according to one aspect of the present invention includes a steel plate preparation step of preparing a strip-shaped steel plate having a plating layer formed on at least one surface, and the strip-shaped steel plate. A tubular body forming step of forming a tubular steel sheet whose inner surface is the surface on which the plating layer is formed by forming a tubular shape and joining the butt portions by welding, and covering the inner surface of the tubular steel sheet. It includes an insulating layer forming step of forming an electrically insulating layer and a plating step of forming a hot-dip zinc plating layer covering the outer surface of the tubular steel sheet.

According to the present invention, it is possible to provide a steel pipe having improved performance and a method for manufacturing the steel pipe.

FIG. 1 is a perspective view showing the appearance of the steel pipe according to the embodiment. FIG. 2 is a cross-sectional view of the steel pipe according to the embodiment in line II-II of FIG. FIG. 3 is a flowchart showing a method for manufacturing a steel pipe according to an embodiment. FIG. 4 is a schematic view schematically showing a method for manufacturing a steel pipe according to an embodiment. FIG. 5 is a cross-sectional view of a steel pipe according to a conventional example corresponding to the line II-II of FIG.

(Knowledge that became the basis of the present invention)
As described above, in order to improve the corrosion resistance of the steel pipe, a plating layer containing zinc may be provided on the inner surface and the outer surface of the steel pipe. In order to ensure the desired corrosion resistance, it is necessary to increase the thickness of the plating layer. For example, the plating layer is formed by a sewage plating method. A steel pipe in which a plating layer is formed by a sewage plating method will be described with reference to FIG.

FIG. 5 is a cross-sectional view of a steel pipe 110 according to a conventional example, which corresponds to line II-II of FIG. 1 (see FIG. 1). The steel pipe 110 according to the comparative example is an electric wire pipe extending in the X-axis direction like the steel pipe 10 according to the present embodiment shown in FIG.

As shown in FIG. 5, the steel pipe 110 includes a steel layer 111, a welded portion 112, and plating layers 114 and 116. Further, the steel pipe 110 is formed with a space 110a for passing wiring and the like.

The steel layer 111 is a long tubular base material made of steel. The welded portion 112 is a joint portion that joins the abutting ends of the tubular steel layer 111 to each other. The plating layer 114 is a metal layer for ensuring the corrosion resistance on the inner surface of the steel pipe 110, and the plating layer 116 is a metal layer for ensuring the corrosion resistance on the outer surface of the steel pipe 110.

The steel pipe 110 is produced by forming a flat plate-shaped steel plate into a tubular shape and plating a tubular body in which the butt portions are joined by welding. The welded portion 112 is a joint portion for joining the butt portions of the tubular steel plate (that is, the steel layer 111). The tubular body thus produced is plated by the sewage plating method. The plating layers 114 and 116 are plating layers formed by a sewage plating method. Since the plating layers 114 and 116 are formed after being joined by welding, the plating layer 114 covers the inner surfaces of the steel layer 111 and the weld 112, and the plating layer 116 is the outer surface of the steel layer 111 and the weld 112. Cover.

As shown in FIG. 5, unevenness is formed on the surface of the plating layer formed by the sewage plating method. Specifically, irregularities are formed on the inner surface of the plating layer 114 and the outer surface of the plating layer 116.

If unevenness is formed on the inner surface of the plating layer 114, it becomes difficult to pass the electric wire when passing the electric wire. That is, the linearity deteriorates. Further, in order for the steel pipe 110 to have the desired corrosion resistance, it is necessary to form the plating layers 114 and 116 thickly. That is, in order to secure the desired corrosion resistance, the weight of the steel pipe 110 is increased. Further, since the plating layer 114 is a metal layer, the electrical insulation between the electric wire to be passed and the steel pipe 110 is low.

As described above, the steel pipe 110 according to the conventional example has problems in linearity, weight, and electrical insulation. Therefore, the inventors diligently investigated whether a steel pipe having improved linearity, weight, and electrical insulation could be produced. Then, the inventors have found that the above-mentioned problems can be solved by forming a pre-plating layer and a resin layer having an electrically insulating property on the inner surface of the steel layer.

Hereinafter, the steel pipe according to the embodiment of the present invention and the method for manufacturing the steel pipe will be described in detail with reference to the drawings. It should be noted that all of the embodiments described below show a specific example of the present invention. Therefore, the numerical values, shapes, materials, components, steps, the order of steps, etc. shown in the following embodiments are examples, and are not intended to limit the present invention. Therefore, among the components in the following embodiments, the components not described in the independent claims indicating the highest level concept of the present invention will be described as arbitrary components.

Further, each figure is a schematic view and is not necessarily exactly illustrated. Therefore, for example, the scales and the like do not always match in each figure.

In addition, coordinate axes may be shown in the drawings used for explanation in the following embodiments. The X-axis is a direction parallel to the extending direction of the steel pipe (in other words, the pipe axis direction). Further, the Y-axis and the Z-axis are directions orthogonal to each other on a plane perpendicular to the X-axis. For example, in the following embodiments, "cross-sectional view" means viewing a steel pipe cut at a surface including a cutting line from the side perpendicular to the cut surface. For example, when the cross section is cut on a plane defined by the Y axis and the Z axis (an example of a surface cut by a cutting line), the cross-sectional view means that the cross section is viewed from the X-axis direction side.

In addition, the description of "abbreviated **" is intended to include what is substantially recognized as **. For example, when "substantially cylindrical" is taken as an example, it is not only a perfect cylindrical shape but also substantially a cylindrical shape. Intended to include what is considered cylindrical. That is, in the present specification, "abbreviation" means to include manufacturing error and dimensional tolerance. The same applies to "about".

(Embodiment)
Hereinafter, the present embodiment will be described with reference to FIGS. 1 to 4.

[1. Steel pipe structure]
First, the steel pipe according to the present embodiment will be described with reference to FIGS. 1 and 2. The steel pipe according to the present embodiment is a steel pipe through which a signal line such as an optical fiber and / or an electric wire for supplying electric power to an electric device is passed through the inside of the pipe.

FIG. 1 is a perspective view showing the appearance of the steel pipe 10 according to the present embodiment. FIG. 2 is a cross-sectional view of the steel pipe 10 according to the present embodiment in line II-II of FIG.

As shown in FIG. 1, the steel pipe 10 is a steel electric wire pipe having a substantially cylindrical shape and having a space 10a in which a signal line and / or an electric line or the like is laid. The steel pipe 10 is, for example, an electric wire pipe extending in the X-axis direction. A plurality of signal lines and / or electric lines are laid.

The size of the steel pipe 10 is not particularly limited, but as an example, the length of the steel pipe 10 in the X-axis direction (in other words, the length in the pipe axis direction) is about 3.6 m, and the outer diameter is about 20 mm or more and 80 mm or less. be. The size of the steel pipe 10 is appropriately determined depending on the conditions of the installation location, the signal line to be laid, and / or the number of electric lines.

As shown in FIG. 2, the steel pipe 10 includes a steel layer 11, a welded portion 12, pre-plated layers 13 and 14, an electrically insulating layer 15, and a plating layer 16. The present embodiment is characterized in that the pre-plating layer 14 and the electrically insulating layer 15 are laminated in this order on the inner surface of the steel layer 11. Although FIG. 2 shows an example in which the cross-sectional view shape of the steel pipe 10 is substantially circular, the cross-sectional view shape is not limited to this.

The steel layer 11 is a long tubular base material made of steel. The steel layer 11 is, for example, a base layer on which the pre-plating layers 13 and 14 are arranged. The steel layer 11 is formed to have a substantially constant thickness. The thickness of the steel layer 11 is, for example, about 1 to 2 mm. The elongated direction of the steel layer 11 is a direction parallel to the X-axis and a direction parallel to the pipe axis direction of the steel pipe 10. The thickness in the present specification may be an average thickness obtained by averaging the thicknesses of the components (for example, the steel layer 11, the pre-plating layer 13, etc.) along the circumferential direction of the steel pipe 10, or the maximum thickness. It may be the minimum thickness, or it may be an intermediate thickness between the maximum thickness and the minimum thickness.

A plating layer is provided on the steel layer 11 from the viewpoint of corrosion resistance. In the present embodiment, an example in which the pre-plating layer 13 is provided on the outer surface of the steel layer 11 and the pre-plating layer 14 is provided on the inner surface of the steel layer 11 is shown. In the following, an example in which the pre-plated layers 13 and 14 are provided on the steel layer 11 will be described. However, it suffices if the pre-plated layer 14 is provided on the inner surface of the steel layer 11, and the steel layer 11 may be provided with the pre-plated layers 14. The pre-plating layer 13 may not be provided on the outer surface.

The steel layer 11 is formed by rolling a steel sheet produced by, for example, rolling a steel piece, and irregularities are formed on the surface of the steel sheet when the steel sheet is produced. The unevenness is formed on both sides of the steel sheet. In other words, irregularities are formed on both the outer surface and the inner surface of the steel layer 11.

The welded portion 12 is arranged along the long direction of the steel layer 11 (that is, the pipe axis direction of the steel pipe 10) and penetrates the steel layer 11 in the thickness direction, and joins the steel layer 11 in a tubular shape. The welded portion 12 joins the abutting ends of the steel layer 11 to each other along the elongated direction of the tubular curved steel layer 11. That is, by welding, the butted portions of the tubular curved steel layer 11 are joined. The welding method is not particularly limited, but for example, resistance welding such as high frequency resistance welding may be used. The welded portion 12 is an example of a joined portion.

The welded portion 12 is formed so that at least a part thereof protrudes from the steel layer 11 in a cross-sectional view. Further, the surface of the welded portion 12 is not a substantially flat surface, and unevenness is formed on at least a part of the surface. For example, the inner surface and the outer surface of the welded portion 12 are formed with irregularities. The unevenness occurs when the steel layers 11 are joined by welding.

The pre-plating layer 13 is a plating layer that is arranged on the outer surface side of the steel layer 11 and is provided to improve the corrosion resistance of the steel pipe 10. The pre-plating layer 13 is formed, for example, by being directly laminated on the outer surface of the steel layer 11 so that the outer surface is not exposed. The outer surface of the pre-plating layer 13 is a substantially flat curved surface. That is, the outer surface of the pre-plating layer 13 is a smooth surface.

The thickness of the pre-plating layer 13 is, for example, 5 μm or more and 100 μm or less. The thickness of the pre-plating layer 13 is not limited to this.

The pre-plating layer 13 is not formed on at least a part of the outer surface of the welded portion 12. The pre-plated layer 13 covers only the outer surface of the steel layer 11 among the outer surfaces of the steel layer 11 and the welded portion 12 in a cross-sectional view, for example. That is, the pre-plated layer 13 is formed by cutting a part of the steel layer 11 in the circumferential direction in a cross-sectional view. For example, in a state where the plating layer 16 is not arranged, the pre-plating layer 13 is formed so as to expose at least a part of the outer surface of the welded portion 12 and not to expose the outer surface of the steel layer 11. The pre-plating layer 13 is an example of the third plating layer. Further, being exposed is intended to be in a state of being in direct contact with air.

The pre-plating layer 14 is a plating layer that is arranged on the inner surface side of the steel layer 11 and is provided to alleviate the uneven shape formed on the inner surface of the steel layer 11. The pre-plated layer 14 is formed to be thicker than the depth of the unevenness on the inner surface of the steel layer 11. The pre-plated layer 14 is formed, for example, by being directly laminated on the inner surface of the steel layer 11 so that the inner surface is not exposed. The inner surface of the pre-plated layer 14 is a substantially flat curved surface. That is, the inner surface of the pre-plating layer 14 is a smooth surface.

The thickness of the pre-plating layer 14 is, for example, 5 μm or more and 100 μm or less. The thickness of the pre-plating layer 14 is not limited to this. Further, although FIG. 2 shows a case where the thicknesses of the pre-plating layers 13 and 14 are substantially the same, the thicknesses of the pre-plating layers 13 and 14 may be different.

The pre-plating layer 14 is not formed on at least a part of the inner surface of the welded portion 12. The pre-plated layer 14 covers only the inner surface of the steel layer 11 among the inner surfaces of the steel layer 11 and the welded portion 12 in a cross-sectional view, for example. That is, the pre-plated layer 14 is formed by cutting a part of the steel layer 11 in the circumferential direction in a cross-sectional view. For example, in a state where the electrical insulating layer 15 is not arranged, the pre-plating layer 14 is formed so as to expose at least a part of the inner surface of the welded portion 12 and not to expose the inner surface of the steel layer 11. The pre-plating layer 14 is an example of the second plating layer.

The pre-plating layers 13 and 14 are plating layers formed by, for example, hot metal plating and containing at least zinc. In the present embodiment, the pre-plating layers 13 and 14 are galvanized layers formed by hot-dip galvanizing. In the galvanized layer, even if the galvanized layer is scratched and the steel layer 11 is exposed, the zinc around the scratches dissolves before the steel layer 11 (iron), and the steel layer 11 is electrochemically formed. Can be protected. That is, since zinc plating has a self-corrosion-preventing action (sacrificial anticorrosion action), it is possible to further suppress the rusting of the steel layer 11.

At least one of the pre-plating layers 13 and 14 may be a zinc-based alloy plating layer containing a metal other than zinc. At least one of the pre-plating layers 13 and 14 may contain, for example, at least one of Al (aluminum), Mg (magnesium), Si (silicon) and Sn (tin). For example, the content of a metal other than zinc is 1 wt% or more and 60 wt% or less with respect to zinc. When a plurality of types of metals other than zinc are contained, the content is calculated based on the total weight of the plurality of types of metals.

Further, an alloy layer (not shown) containing an iron-zinc alloy layer is formed between the pre-plating layer 13 and the steel layer 11 and at least one of the pre-plating layer 14 and the steel layer 11. May be good. The alloy layer is formed by forming the pre-plating layers 13 and 14 and then applying a predetermined heat to alloy the zinc constituting the pre-plating layer 13 and the iron constituting the steel layer 11. The iron-zinc alloy layer has higher corrosion resistance than the steel layer 11.

Further, the steel pipe 10 according to the present embodiment is formed by bending and welding a strip-shaped steel layer 11 (hereinafter, also referred to as a steel plate) in which the pre-plated layers 13 and 14 are arranged. The pre-plated layers 13 and 14 can further reduce the unevenness formed on the surface of the welded portion 12 described above. The unevenness formed in the welded portion 12 of the steel layer 11 on which the pre-plating layer 13 is arranged has a depth of unevenness and the unevenness formed in the welded portion 12 of the steel layer 11 in which the pre-plating layer 13 is not arranged. At least one of the number of irregularities becomes smaller. Further, the unevenness formed in the welded portion 12 of the steel layer 11 on which the pre-plating layer 14 is arranged is deeper than the unevenness formed in the welded portion 12 of the steel layer 11 in which the pre-plating layer 14 is not arranged. At least one of the number of welds and irregularities becomes smaller.

Although the details will be described later, the pre-plating layer 14 reduces the unevenness formed on the inner surface of the welded portion 12, so that, for example, the electrically insulating layer 15 can be easily formed. When the electrical insulating layer 15 cannot cover at least a part of the inner surface of the welded portion 12 due to the unevenness formed on the inner surface of the welded portion 12, rust progresses from the part, but by providing the pre-plated layer 14. It is possible to prevent the inner surface of the welded portion 12 from being exposed. The electrically insulating layer 15 is not directly laminated on the inner surface of the steel layer 11, and the pre-plated layer 14 is arranged between the steel layer 11 and the electrically insulating layer 15.

The electrical insulating layer 15 is arranged on the inner surface side of the pre-plated layer 14 to improve at least one of linearity, insulation and weight. In the present embodiment, the electrically insulating layer 15 is realized by a resin layer having an electrically insulating property. Since the electrical insulating layer 15 is laminated on the substantially flat inner surface of the pre-plating layer 14, the inner surface of the electrical insulating layer 15 is also a substantially flat surface. Since the pre-plating layer 14 is arranged in the electric insulating layer 15, it is less likely to be affected by the unevenness formed on the inner surface of the steel layer 11. The inner surface of the electrically insulating layer 15 is a substantially flat curved surface. That is, the inner surface of the electrically insulating layer 15 is a smooth surface. For example, the surface roughness Ra of the inner surface of the electrically insulating layer 15 is smaller than the surface roughness Ra of the inner surface of the steel layer 11.

When the plating layer is directly formed on the inner surface of the steel layer 11, the plating layer is formed with irregularities that follow the irregularities of the steel layer 11. Therefore, when the plating layer is directly formed on the inner surface of the steel layer 11, the linearity is poor due to the unevenness. On the other hand, the steel pipe 10 is formed by directly laminating the steel layer 11, the pre-plating layer 14, and the electrically insulating layer 15 in this order toward the inside. Since the inner surface of the pre-plating layer 14 is a substantially flat surface, the inner surface of the electrically insulating layer 15 is also a substantially flat surface. As a result, the linearity is improved as compared with the case where the plating layer is directly provided on the inner surface of the steel layer 11. It should be noted that "toward the inside" is intended to be directed toward the center side of the steel pipe 10 which is substantially circular in the cross-sectional view of the steel pipe 10.

As shown in FIG. 2, the electrically insulating layer 15 covers both the inner surface of the welded portion 12 and the pre-plated layer 14 from the inner side of the steel pipe 10 in a cross-sectional view. In other words, the electrically insulating layer 15 is formed so that both the welded portion 12 and the pre-plated layer 14 are not exposed, such as when the inner surfaces of the welded portion 12 and the pre-plated layer 14 are exposed to air in a cross-sectional view. ..

Further, since the electrically insulating layer 15 is less likely to rust than metal, it is possible to prevent the inner surface of the steel layer 11 from rusting. For example, the steel pipe 10 in which the electrically insulating layer 15 is arranged on the inner surface of the pre-plating layer 14 can withstand a salt spray test (for example, a test based on JIS Z 2371 (salt spray test method)). Further, the electrically insulating layer 15 is lighter than the plating layer containing zinc. Therefore, by providing the electrically insulating layer 15 on the inner surface of the steel layer 11, the corrosion resistance of the steel pipe 10 can be improved and the weight can be reduced as compared with the case where the plating layer is provided on the inner surface of the steel layer 11. The thickness of the electrical insulating layer 15 is, for example, 5 μm or more and 100 μm or less, but is not limited thereto.

The electrically insulating layer 15 is formed of a resin material having an electrically insulating property. The electrical insulating layer 15 is formed of, for example, a resin material containing silicone or epoxy. The electrical insulating layer 15 is formed by applying, for example, a resin coating material containing silicone or epoxy. The paint is, for example, a highly corrosion-resistant paint that can withstand the corrosion of a salt spray test. The electrical insulating layer 15 is, for example, a coating film formed by spraying a highly corrosion-resistant paint that can withstand a salt spray test onto the inner surface of the steel layer 11. The salt spray test is not limited to the test based on JIS Z 2371. The salt spray test may be, for example, a test based on another standard, or a test similar to JIS Z 2371 or another standard.

The electrical insulating layer 15 is not arranged on the outer surface side of the steel layer 11.

The plating layer 16 is a plating layer arranged on the outer surface side of the steel layer 11 in order to improve the corrosion resistance of the steel pipe 10. That is, the plating layer 16 covers the steel layer 11 and the welded portion 12 from the outside in the radial direction of the steel layer 11. In the present embodiment, the plating layer 16 covers the outer surface of the pre-plating layer 13 and the outer surface of the welded portion 12. The plating layer 16 is formed, for example, by directly laminating the outer surface of the pre-plating layer 13 and the outer surface of the welded portion 12 so that the outer surface of the pre-plated layer 13 and the outer surface of the welded portion 12 are not exposed.

It should be noted that covering the steel layer 11 and the welded portion 12 from the outside in the radial direction of the steel layer 11 means that the steel layer 11 and the welded portion 12 are formed in contact with the steel layer 11 and the welded portion 12, and that the steel layer 11 and the welded portion 12 are covered. Includes that both are formed without contact. For example, when the pre-plating layer 13 is not formed, the plating layer 16 may be formed in contact with the outer surface of the steel layer 11 and the outer surface of the welded portion 12.

The corrosion resistance of the outer surface of the steel pipe 10 varies depending on, for example, the total thickness of the pre-plating layer 13 and the plating layer 16. The thicker the total thickness, the better the corrosion resistance of the steel pipe 10. When the desired corrosion resistance is provided, the thickness of the plating layer 16 can be reduced as compared with the case where the pre-plating layer 13 is not provided by providing the pre-plating layer 13.

As shown in FIG. 2, the plating layer 16 covers both the outer surface of the welded portion 12 and the pre-plating layer 13 from the outer side of the steel pipe 10 in a cross-sectional view. In other words, the plating layer 16 is formed so that both the welded portion 12 and the pre-plated layer 13 are not exposed, such as when the outer surfaces of the welded portion 12 and the pre-plated layer 13 are exposed to air in a cross-sectional view.

The plating layer 16 is a plating layer containing at least zinc. The plating layer 16 is formed by, for example, hot-dip galvanizing. The plating layer 16 may be a zinc-based alloy plating layer containing a metal other than zinc. The plating layer 16 may contain at least one of Al (aluminum), Mg (magnesium), Si (silicon) and Sn (tin), for example. For example, the content of a metal other than zinc is 1 wt% or more and 60 wt% or less with respect to zinc. When a plurality of types of metals other than zinc are contained, the content is calculated based on the total weight of the plurality of types of metals.

Further, the pre-plating layer 14 and the plating layer 16 may be made of the same metal material or may be made of different metal materials. The plating layer 16 is an example of the first plating layer.

As described above, in the steel pipe 10 according to the present embodiment, the pre-plating layer 13 is arranged between the steel layer 11 and the plating layer 16, and the pre-plating layer 13 is pre-plated between the steel layer 11 and the electrically insulating layer 15. It has a structure in which the layer 14 is arranged. Corrosion resistance is ensured on the outer surface of the steel layer 11 by the pre-plating layer 13 and the plating layer 16. When the pre-plating layer 13 is not provided, the corrosion resistance equivalent to that when the pre-plating layer 13 and the plating layer 16 are provided can be realized by increasing the thickness of the plating layer 16. Further, the inner surface of the steel layer 11 can be improved in corrosion resistance, linearity, and weight by the pre-plating layer 14 and the electrically insulating layer 15.

[2. Steel pipe manufacturing method]
Next, a method of manufacturing the steel pipe 10 will be described with reference to FIGS. 3 and 4. As shown below, the steel pipe 10 according to the present embodiment is an iron pipe produced by bending and welding a steel plate.

FIG. 3 is a flowchart showing a manufacturing method of the steel pipe 10 according to the present embodiment. FIG. 4 is a schematic view schematically showing a manufacturing method of the steel pipe 10 according to the present embodiment.

As shown in FIG. 4, the production line for producing the steel pipe 10 includes a roll forming apparatus M1, a welding apparatus M2, a welding beat processing apparatus M3, a coating apparatus M4, an outer surface plating apparatus M5, a sizing apparatus M6, an inspection apparatus M7, and a cutting apparatus. It is composed of an apparatus M8 and a coating apparatus M9. In addition, as long as the above manufacturing order is maintained, devices other than the above may be included.

As shown in FIG. 3, first, a steel sheet preparation step (S11) for preparing a strip-shaped steel sheet 20 provided with a pre-plating layer containing at least zinc on at least one surface is performed. That is, in the steel plate preparation step, the steel plate 20 provided with the pre-plating layer on at least one surface of the steel layer 11 is prepared. In this embodiment, a steel plate 20 in which pre-plated layers 13 and 14 containing at least zinc are provided on both sides of the steel layer 11 is used. The pre-plating layers 13 and 14 are plating layers that have already been provided in the state of the strip-shaped steel plate 20. Further, as shown in FIG. 4, in the present embodiment, an example in which a strip-shaped steel plate 20 wound in a coil shape is prepared is shown. The pre-plating layer is an example of a plating layer.

The pre-plating layer is formed by a method such as electroplating (for example, electrogalvanization) that can make the plating thickness substantially uniform. That is, the pre-plating layers 13 and 14 are not formed by the sewage plating method.

Subsequently, the strip-shaped steel plate 20 is formed into a tubular shape, and the abutted both ends are joined by welding to form a tubular steel plate 20 having pre-plated layers (for example, pre-plated layers 13 and 14) formed on both sides. The tubular body forming step is performed (S12). For example, the strip-shaped steel plate 20 is rolled and formed into a tubular shape, and both ends of the butted steel plate 20 (in the present embodiment, both ends of the steel plate 20 in the lateral direction, hereinafter also referred to as butt joints) are welded. The tubular steel plate 20 is formed by joining with the above. When the plating layer (for example, the pre-plating layer 14) is formed only on one surface of the steel sheet 20, the tubular steel sheet 20 whose inner surface is the surface on which the pre-plating layer 14 is formed in the tubular body forming step. To form.

As shown in FIG. 4, the tubular body forming step is realized by the roll forming apparatus M1, the welding apparatus M2, and the welding beat processing apparatus M3. The strip-shaped steel plate 20 is continuously supplied to the roll forming apparatus M1 and is continuously formed into a tubular shape by the roll forming apparatus M1. The strip-shaped steel plate 20 is formed into a tubular shape by being cold-formed by the roll forming apparatus M1. The steel plate 20 formed into a tubular shape is supplied to the welding device M2, and the butt portions (for example, seams) of the steel plate 20 are continuously joined. That is, both ends of the steel sheet 20 in the lateral direction are continuously joined by the welding device M2. As a result, the welded portion 12 is formed so as to extend in the pipe axis direction of the steel plate 20. Hereinafter, the steel plate 20 formed into a tubular shape will also be referred to as a tubular body. Tubular bodies are formed continuously.

The welding device M2 joins both ends of the steel sheet 20 by resistance welding such as high frequency resistance welding. That is, the steel pipe 10 according to the present embodiment is an electrosewn steel pipe. The welding method is not limited to this.

The steel plate 20 welded by the welding apparatus M2 is supplied to the welding beat processing apparatus M3, and the welding beat formed by welding is processed. The welding beat processing device M3 is, for example, a cutting device that removes welding beats formed on the outer surface of a tubular body by continuously cutting them. For example, the cutting device has a cutting tool having a shape along the outer surface of the tubular body, and scrapes off the welding beat formed on the outer surface to form a substantially smooth surface. As a result, the weld beat formed on the outer surface can be beat-cut, and a tubular body having a substantially smooth outer surface is formed. As a result, the welded portion 12 shown in FIG. 2 is formed.

The welding beat processing device M3 is not limited to such a cutting device. The welding beat processing device M3 may be a device that processes the molten beat by other methods such as applying pressure to the welding beat and crushing it. At this point, the electrical insulating layer 15 is not formed on the inner surface side of the steel sheet 20.

With reference to FIG. 3 again, an insulating layer forming step of forming the electrical insulating layer 15 on the inner surface side of the tubular body is subsequently performed (S13). In the insulating layer forming step, the electrically insulating layer 15 is formed by, for example, coating after welding in the tubular forming step. Specifically, a resin paint containing a resin such as silicone or epoxy is sprayed onto the inner surface of the pre-plating layer 14 arranged on the steel plate 20 and the inner surface of the welded portion 12 to form an electrically insulating layer. 15 is formed. Since the inner surface of the pre-plating layer 14 is a substantially flat surface, the inner surface of the electrically insulating layer 15 is also formed on a substantially flat surface. Further, since the pre-plating layer 14 is arranged, the unevenness formed on the surface of the welded portion 12 is reduced, so that the electric insulating layer 15 can be applied by coating as compared with the case where the pre-plating layer 14 is not formed. It can be easily formed.

As shown in FIG. 4, the insulating layer forming step is realized by the coating device M4. The tubular body is continuously supplied to the coating device M4, and the resin material is continuously coated by the coating device M4. Then, the resin material is cured by the heat applied in the plating step, so that the inner surface of the pre-plating layer 14 and the electrically insulating layer 15 covering the inner surface of the welded portion 12 are formed. That is, the electrically insulating layer 15 that covers the inner surface of the tubular body is formed. Since the electrically insulating layer 15 is formed after welding, it is possible to form the electrically insulating layer 15 that covers the entire inner surface of the tubular body. The heat applied in the plating step is the heat applied by the outer surface plating apparatus M5.

The resin paint is not limited to being cured by the heat applied in the plating process. For example, the coating device M4 has a heat source for curing the coated resin material, and the coated resin material may be cured by the heat applied by the coating device M4.

With reference to FIG. 3 again, a plating step of forming a hot-dip galvanized layer by hot-dip galvanizing the outer surface side of the tubular body is subsequently performed (S14). That is, in the plating step, a hot-dip galvanized layer covering the outer surface of the tubular body is formed. In the present embodiment, since the pre-plating layer 13 is provided, the hot-dip galvanizing layer is formed on the outer surface of the pre-plating layer 13. That is, in the plating step, a hot-dip galvanized layer covering the outer surface of the pre-plating layer 13 and the outer surface of the welded portion 12 is formed. The hot-dip galvanized layer is an example of the plated layer 16 shown in FIG. That is, the hot-dip galvanized layer is an example of the first plated layer. Further, in the plating step, thermal spraying is not performed in which the molten metal and the solvent are sprayed onto the object (for example, the steel layer 11) to be laminated.

As shown in FIG. 4, the plating step is realized by the outer surface plating apparatus M5 and the sizing apparatus M6. The outer surface plating apparatus M5 is, for example, a hot dip galvanizing apparatus that applies hot dip galvanizing to the outer surface of a tubular body. The outer surface plating apparatus M5 performs a hot-dip plating process by passing a tubular body through, for example, a molten metal (for example, molten zinc). By passing the tubular body through the molten metal, the tubular body is continuously immersed. As a result, a molten metal plating layer is formed on the entire outer surface of the tubular body.

In the present embodiment, since the pre-plating layer 13 is arranged on the outer surface of the tubular body, the thickness of the plating layer formed in the plating step can be reduced. For example, the thickness of the plating layer formed in the plating step can be reduced as compared with the case where the pre-plating layer 13 is not provided.

A plurality of outer surface plating devices M5 may be continuously arranged. Further, the metal material forming the plating layer may be different or the same as the pre-plating layer 13 and the plating layer (for example, the plating layer 16) formed in the plating step. Further, the outer surface plating apparatus M5 may perform a process of making the thickness of the molten metal plating layer uniform.

Then, the sizing device M6 performs processing to make the outer diameter a specified dimension. The sizing device M6 performs sizing processing such as cold roll processing.

As described above, in the present embodiment, the tubular body forming step is followed by the insulating layer forming step and the plating step.

With reference to FIG. 3 again, an inspection step of inspecting the sized tubular body for the presence or absence of scratches or the like is subsequently performed (S15). In the inspection step, for example, an appearance inspection is performed to see if the plating layer 16 and the electrically insulating layer 15 are scratched. In the inspection step, for example, an inspection is performed to see if the steel layer 11 of the steel plate 20 is exposed.

As shown in FIG. 4, the inspection step is realized by the inspection device M7. The inspection device M7 is a flaw detection device that detects scratches in the steel sheet 20 by applying, for example, ultrasonic waves. As a result, the corresponding portion can be repelled so that the scratched portion does not become a product (that is, the steel pipe 10). The inspection device M7 is not limited to the flaw detection device as long as it can inspect for scratches and the like.

With reference to FIG. 3 again, a cutting step of cutting the inspected tubular body to a predetermined length (length in the Y-axis direction) is subsequently performed (S16). In the cutting step, for example, the tubular body is continuously cut to a length of about 3.6 m. In the cutting step, for example, the product is cut so that the portion that has been scratched in the inspection step is not included in the product.

As shown in FIG. 4, the cutting step is realized by the cutting device M8. The cutting device M8 cuts the tubular body to a predetermined length.

With reference to FIG. 3 again, a painting step is subsequently performed in which at least one of the outer and inner surfaces of the cut tubular body is painted (S17). In the painting process, for example, painting for improving corrosion resistance is performed. In the painting step, for example, a protective film made of resin or the like is formed on at least one of the outer surface and the inner surface of the cut tubular body.

As shown in FIG. 4, the coating process is realized by the coating apparatus M9. The coating apparatus M9 performs coating to have a desired function such as improving corrosion resistance on at least one of the outer surface and the inner surface of the tubular body cut to a predetermined length. As a result, the steel pipe 10 according to the present embodiment is produced. In FIG. 2, the coating film formed in the coating process is not shown.

As described above, in the method for manufacturing the steel pipe 10 according to the present embodiment, a series of steps from the tubular body forming step to the painting step are continuously performed. For example, the tubular body forming step, the insulating layer forming step, and the plating step are continuously performed. That is, the steel pipe 10 is manufactured in-line. The steel pipe 10 is integratedly produced from, for example, the steel plate 20. Thereby, it is possible to shorten the period for manufacturing the steel pipe 10.

[3. Effect]
As described above, the steel pipe 10 according to the present embodiment has a tubular steel layer 11 joined by a welded portion 12 along the pipe axis direction, and the steel layer 11 and the welded portion from the outer side in the radial direction of the steel layer 11. A plating layer 16 covering 12; a pre-plating layer 14 covering the inner surface of the steel layer 11, and an electrically insulating layer 15 covering the inner surface of the pre-plating layer 14 and the inner surface of the welded portion 12 and having electrical insulation properties. , Equipped with.

As a result, since the pre-plating layer 14 is formed, the unevenness of the inner surface of the electric insulating layer 15 provided on the inner surface of the pre-plating layer 14 can be reduced, so that a signal line, an electric line, or the like can be used. The wire permeability when passing through the steel pipe 10 is improved. Further, since the electrically insulating layer 15 has an insulating property, the insulating property of the steel pipe 10 can be improved as compared with the case where the inner surface of the steel layer 11 is provided with a plating layer for corrosion resistance. .. Therefore, the performance of the steel pipe 10 can be improved. Specifically, the linearity and insulation of the steel pipe 10 can be improved.

The inner surface of the pre-plating layer 14 is a flat curved surface.

As a result, the inner surface of the electrically insulating layer 15 provided on the inner surface of the pre-plating layer 14 can be made a substantially flat surface. That is, when the signal line or the electric wire is passed through the steel pipe 10, the unevenness of the surface with which the signal line or the electric wire comes into contact can be further reduced. Is further improved. Therefore, the performance of the steel pipe 10 can be further improved.

The electrical insulating layer 15 is a resin layer.

As a result, since the resin is lighter than the metal, the steel pipe 10 can be made lighter than the case where the plating layer is formed by providing the resin layer which is the electrically insulating layer 15 on the inner surface of the steel layer 11. can. Further, since the resin has higher corrosion resistance than the metal, the corrosion resistance of the steel pipe 10 can be improved. Therefore, the performance of the steel pipe 10 can be further improved.

Further, the plating layer 16 and the pre-plating layer 14 contain at least zinc.

As a result, even when the steel layer 11 is exposed due to scratches on the plating layer, it is possible to prevent the steel layer 11 from rusting due to the self-corrosion action of zinc. That is, the corrosion resistance of the steel pipe 10 can be further improved.

Further, at least one of the plating layer 16 and the pre-plating layer 14 further contains at least one of Al (aluminum), Mg (magnesium), Si (silicon), and Sn (tin).

As a result, the corrosion resistance of the plating layer itself can be improved as compared with the case where the plating layer 16 and the pre-plating layer 14 are composed of zinc. That is, the performance of the steel pipe 10 can be further improved. The fact that the plating layer is composed of zinc means that it does not substantially contain a metal other than zinc, or intentionally does not contain a metal other than zinc.

Further, between the steel layer 11 and the plating layer 16, a pre-plating layer 13 that covers only the outer surface of the steel layer 11 among the outer surface of the welded portion 12 and the outer surface of the steel layer 11 and contains at least zinc is provided. Be prepared.

As a result, the thickness of the plating layer 16 can be reduced, so that the time required to form the plating layer 16 by post-plating can be shortened.

Further, the pre-plating layer 13 further contains at least one of Al (aluminum), Mg (magnesium), Si (silicon), and Sn (tin).

As a result, the corrosion resistance of the pre-plating layer 13 itself can be improved as compared with the case where the pre-plating layer 13 is composed of zinc. That is, the performance of the steel pipe 10 can be further improved.

Further, as described above, the method for manufacturing the steel pipe 10 according to the present embodiment is a steel plate preparation step (for example, a steel plate preparation step of preparing a strip-shaped steel plate 20 having a plating layer (for example, a pre-plating layer 14) formed on at least one surface. S11) and a tubular body forming step (S12) in which the strip-shaped steel plate 20 is formed into a tubular shape and the butt portions are joined by welding to form a tubular steel plate 20 whose inner surface is the surface on which the plating layer is formed. , An insulating layer forming step (S13) for forming an electrically insulating layer 15 covering the inner surface of the tubular steel sheet 20, and a molten zinc plating layer (for example, a plating layer) covering the outer surface of the tubular steel sheet 20. A plating step (S14) for forming 16) is included.

As a result, the electrically insulating layer 15 is formed after the tubular steel plate 20 is formed in the tubular body forming step. Since the steel plates 20 are joined by welding or the like in the tubular body forming step, it is possible to prevent the electrically insulating layer 15 from being destroyed by welding or the like. That is, it is possible to prevent a part of the steel layer 11 from being exposed on the inner surface of the steel pipe 10. Therefore, the steel pipe 10 having improved corrosion resistance, insulating property, and weight can be stably manufactured.

(Other embodiments)
Although the steel pipe and the method for manufacturing the steel pipe have been described above based on the embodiment, the present invention is not limited to this embodiment. As long as it does not deviate from the gist of the present invention, a form in which various modifications conceived by those skilled in the art are applied to the present embodiment and a form constructed by combining components in different embodiments are also included in the scope of the present invention.

For example, in the above embodiment, the description is based on the premise that the steel plate 20 is used, but other metal plates may be used. That is, the steel layer 11 shown in FIG. 2 may be a metal layer made of another metal material.

Further, in the above embodiment, an example in which the pre-plating layers 13 and 14 are plating layers containing at least zinc has been described, but the present invention is not limited thereto. At least one of the pre-plating layers 13 and 14 may be a zinc-free plating layer such as a Ni plating layer. That is, the metal used for plating may be a zinc-free metal. For example, when the pre-plating layer 13 is a Ni plating layer, the Ni plating layer is formed thicker than the depth of the unevenness on the inner surface of the steel layer 11. For example, the inner surface of the Ni plating layer is a substantially flat surface.

Further, in the above embodiment, an example in which the pre-plating layer 13, the pre-plating layer 14, and the plating layer 16 are zinc-plated layers has been described, but the present invention is not limited thereto. The pre-plating layer 13, the pre-plating layer 14, and the plating layer 16 may be a zinc-based alloy plating layer containing zinc and a metal other than zinc. The pre-plating layer 13, the pre-plating layer 14, and the plating layer 16 may be, for example, a Zn—Fe plating layer or another zinc-based alloy plating layer. The pre-plating layer 13, the pre-plating layer 14, and the plating layer 16 may be formed of the same metal or different metals.

Further, the electrically insulating layer 15 described in the above embodiment may contain a metal powder. For example, the electrically insulating layer 15 may contain a metal powder such as zinc, which has a higher ionization tendency than iron. Thereby, the corrosion resistance of the steel pipe 10 can be further improved.

Further, in the above embodiment, an example in which the pre-plating layer 13 is directly laminated on the outer surface of the steel layer 11 and the plating layer 16 is directly laminated on the outer surface of the pre-plating layer 13 has been described, but the present invention is not limited thereto. .. A plating layer different from the pre-plating layer 13 and the plating layer 16 is arranged between the steel layer 11 and the pre-plating layer 13 and at least one of the pre-plating layer 13 and the plating layer 16. May be good.

Further, in the above embodiment, an example in which the pre-plating layer 14 is directly laminated on the inner surface of the steel layer 11 and the electrical insulating layer 15 is directly laminated on the inner surface of the pre-plating layer 14 has been described, but the present invention is limited to this. Not done. At least one between the steel layer 11 and the pre-plating layer 14 and between the pre-plating layer 14 and the electrically insulating layer 15 has a plating layer or a resin layer different from the pre-plating layer 14 and the electrically insulating layer 15. It may be arranged. The electric insulating layer 15 may be arranged so as to cover the inner surface of the steel layer 11 and the inner surface of the welded portion 12 and to be in contact with the signal line or the electric line, for example.

Further, in the above embodiment, the round steel pipe which is substantially circular in cross-sectional view has been described, but the cross-sectional shape of the steel pipe 10 is not limited to this. The steel pipe 10 may be, for example, a square steel pipe having a substantially polygonal cross-sectional shape, a deformed steel pipe having a substantially fan shape, or any other shape.

Further, in the above embodiment, an example in which the thicknesses of the pre-plated layers 13 and 14 are substantially the same has been described, but the present invention is not limited to this. The pre-plating layer 13 is preferably formed thick in order to shorten the post-plating time for forming the plating layer 16. The pre-plating layer 13 may be formed thicker than the pre-plating layer 14, for example.

Further, in the above embodiment, the example in which the tubular body forming step to the coating step of the steel pipe 10 are continuously performed in a series of steps has been described, but the present invention is not limited to this. If the insulating layer forming step and the plating step are performed after the tubular forming step, the steel pipe 10 does not have to be continuously manufactured in a series of steps.

Further, in the above embodiment, an example of preparing the steel sheet 20 on which the pre-plating layers 13 and 14 are formed in the steel sheet preparation step has been described, but the present invention is not limited to this. In the steel sheet preparation step, the steel sheet 20 may be produced by forming a pre-plating layer on at least one surface of the steel layer 11. For example, in the steel sheet preparation step, the steel sheet 20 may be prepared by forming the pre-plating layers 13 and 14 on the steel layer 11 to produce the steel sheet 20. In this case, the pre-plating layers 13 and 14 are formed by a method other than sewage plating. The pre-plating layers 13 and 14 may be formed by, for example, electroplating.

Further, in the above embodiment, the example in which the steel sheet 20 prepared in the steel sheet preparation step has a pre-plated layer containing at least zinc has been described, but the pre-plated layer does not have to contain zinc. The pre-plating layer may be, for example, a nickel plating layer containing nickel, or may be another.

Further, in the above embodiment, an example of forming a hot-dip galvanized layer in the plating step has been described, but the present invention is not limited to this. In the plating step, a zinc-free hot-dip plating layer may be formed by performing hot-dip plating on the tubular body. In the plating step, for example, an aluminum plating layer containing aluminum may be formed as the hot-dip plating layer.

Further, the order of the plurality of steps in the steel pipe manufacturing method described in the above embodiment is an example, and the order may be changed as long as the insulating layer forming step and the plating step are performed after the tubular body forming step. However, some steps do not have to be performed.

Further, each step in the steel pipe manufacturing method described in the above embodiment may be carried out in one step or may be carried out in separate steps. It should be noted that the term "implemented in one step" means that each step is carried out using one device, each step is carried out continuously, or each step is carried out in the same place. Is. In addition, separate steps mean that each step is carried out using a different device, each step is carried out at a different time (for example, a different day), or each step is carried out in a different place. It is intended to include.

10 Steel pipe 11 Steel layer 12 Welded part (joint part)
13 Pre-plating layer (third plating layer)
14 Pre-plating layer (second plating layer)
15 Electrical insulation layer 16 Plating layer (1st plating layer)
20 steel plate

Claims (8)

A tubular steel layer joined at a joint along the pipe axis direction,
From the outside in the radial direction of the steel layer, the steel layer and the first plating layer covering the joint portion,
A second plating layer covering the inner surface of the steel layer and
An electrically insulating layer that covers the inner surface of the second plating layer and the inner surface of the joint and has electrical insulation is provided.
The second plating layer is not formed on at least a part of the inner surface of the joint portion provided so as to project inward of the tubular from the inner surface of the steel layer.
At least a part of the pipe is formed along the axial direction of the pipe.
Steel pipe. The inner surface of the second plating layer is a flat curved surface.
The steel pipe according to claim 1. The electrically insulating layer is a resin layer.
The steel pipe according to claim 1 or 2. The first plating layer and the second plating layer contain at least zinc.
The steel pipe according to any one of claims 1 to 3. The first plating layer and at least one of the second plating layers further contain at least one of aluminum, magnesium, silicon, and tin.
The steel pipe according to claim 4. Further, between the steel layer and the first plating layer, a third plating layer that covers the outer surface of the steel layer and contains at least zinc is provided.
The steel pipe according to any one of claims 1 to 5. The third plating layer further contains at least one of aluminum, magnesium, silicon, and tin.
The steel pipe according to claim 6. A steel sheet preparation process for preparing a strip-shaped steel sheet having a plating layer formed on at least one surface,
A tubular steel plate in which the surface on which the plating layer is formed is an inner surface by forming the strip-shaped steel plate into a tubular shape and joining the butt portions by welding. The plating layer is not formed on at least a part of the inner surface of the joint portion which is provided so as to project and the abutting portion is joined by the welding, and at least a part thereof is formed along the pipe axis direction. The tubular body forming step of forming the tubular steel plate to be welded, and
An insulating layer forming step of forming an electrically insulating layer covering the inner surface of a tubular steel sheet,
A plating step of forming a hot-dip galvanized layer covering the outer surface of the tubular steel sheet is included.
Manufacturing method of steel pipe.

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