Weld joint and cylindrical structure

Abstract

To provide a weld joint that is excellent in workability and fatigue resistance, and a cylindrical structure provided with the weld joint.SOLUTION: In a weld joint, an edge 11d of an outside plate surface 11a pointing to outside with an obtuse angle of one thick steel plate 11 and an edge of an outside plate surface pointing to the outside with the obtuse angle of the other thick steel plate are arranged to oppose to each other. An extending surface 11e from the edge 11d of the outside plate surface 11a of the one thick steel plate 11 crosses an extending surface 12e from the edge 12d of the outside plate surface 12a of the other thick steel plate 12. A space between an end face 11c of the one thick steel plate 11 and an end face 12c of the other thick steel plate 12 and both end faces are coated with weld metal M1, at the outside with the obtuse angle. A space between the end face 11c of the one thick steel plate 11 and the inside plate surface 12b pointing to inside with an obtuse angle of the other thick steel plate 12 and the end face 11c and the inside plate surface 12b are coated with weld metal, at inside with an obtuse angle.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a welded joint formed by welding steel plates having different thicknesses, and to a tubular structure utilizing the welded joint. [Background technology]

[0002] Renewable energy has been attracting attention in recent years from the perspective of reducing greenhouse gas emissions. Wind power generation is more efficient than other power generation methods, and in areas where strong winds blow constantly, it can generate electricity day and night. Therefore, it is one of the renewable energy methods that is attracting attention as one whose use is expected to expand in the future. Wind power generation is already seeing a certain degree of popularity, but in the future, there are plans to expand it to include offshore power generation, as there are no noise issues and the risk of it tipping over is reduced.It is expected that power generation facilities will become larger in order to generate power more efficiently, and that this will lead to further popularity.

[0003] On the other hand, as power generation equipment becomes larger, problems arise in equipment manufacturing. Specifically, in wind power generation equipment, cylindrical steel pipes are used for the support columns (towers, columnar floating structures in floating offshore wind power generation facilities) that mount the nacelle on top. Increasing the size of power generation equipment requires increasing the strength and rigidity of the support columns, which necessitates increasing the outer diameter and thickness of the columns. Steel pipes for support columns are manufactured by bending steel plates to create curves and then welding them. However, there is a certain limit to the capacity of bending equipment, and it is not possible to sufficiently bend thick steel plates, which limits the ability to manufacture large-diameter, thick-walled support columns. Furthermore, larger columns can cause problems with transportation from the factory to the installation site, such as the need for special vehicles or ships, or the need to transport them at night. For this reason, it is preferable to manufacture them locally rather than in a factory.

[0004] Because of these problems, it has been considered to manufacture the support pillars by forming a large number of steel plates into a cylindrical shape, rather than by bending thick steel plates. For example, Patent Document 1 describes a support (tower) in which steel plates (metal wall components) with flanges are connected with fixing means (nuts and bolts). Patent Document 2 also describes a support (columnar floating body) in which multiple steel plates (facing members or bent facing members) are connected in the circumferential direction to form a polygonal cross-sectional shape. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2007-520653 [Patent Document 2] Japanese Patent Publication No. 2022-1374 Summary of the Invention [Problem to be solved by the invention]

[0006] As shown in the above Patent Documents 1 and 2, the manufacturing problems associated with increasing the size of the support pillars are considered, but neither of these patent documents mentions anything about the characteristics of the support pillars themselves, i.e., the material characteristics. Therefore, there are many technical issues that need to be resolved before they can be used as support pillars.

[0007] Under the above circumstances, the present inventors have considered the manufacture of a support pillar. In the manufacturing of the support pillars shown in Patent Documents 1 and 2, bending can be omitted, but the joining work of thick steel plates (riveting and welding) inevitably increases. In particular, when the manufacturing of support pillars by welding is assumed, the more welding work there is, the lower the manufacturing efficiency becomes, so from a manufacturing standpoint, it is desirable to have as little welding work as possible. On the other hand, because the columns are subjected to repeated stress during power generation, they must have fatigue resistance. Considering the characteristics, fatigue resistance is particularly required for welded joints, which are the joining points of thick steel plates and are therefore susceptible to fatigue fracture.

[0008] From a manufacturing perspective, or in other words, in terms of the welding work, the number of welding passes can be reduced. To do this, the thickness of the steel plates could be reduced, but if they are made thinner, there is a risk that they will not be strong enough as pillars. For this reason, we considered using steel plates of different thicknesses, ensuring the pillar's overall strength with thick steel plates, while reducing the number of welding passes by making some of the plates thinner. This would make it possible to reduce the weight of the pillar itself and also enjoy cost benefits.

[0009] When manufacturing a column (tubular structure) with a polygonal cross section, if the outer surfaces of the thick steel plates are aligned (if welding is performed using the so-called "outside dimension"), grooves are inevitably formed on both the inside and outside, and both are welded. From a property perspective, if the weld is discontinuous, the fatigue resistance of the welded joint may be reduced. Since fatigue resistance is particularly poor at the welds on the inner surface, eliminating weld residue on the inner surface and ensuring a smooth weld surface can prevent this from happening. Furthermore, if the welds on the inner surface have a smooth weld surface, this can lead to a decline in fatigue resistance at the welds on the outer surface. Therefore, it is necessary to ensure a smooth weld surface on the outer surface as well. Furthermore, by chamfering the edges of thin steel plates and ensuring a root face for welding, highly efficient, high-heat-input welding can be applied. In this case, the number of welding passes can be reduced, further improving welding efficiency.

[0010] The present invention was created based on the above, and aims to provide a welded joint that is excellent in workability and fatigue resistance, and a tubular structure that includes such a welded joint. [Means for solving the problem]

[0011] In order to achieve the above object, the welded joint according to the present invention is a welded joint in which thick steel plates of different thicknesses are welded together at an obtuse angle, An edge of an outer plate surface of one of the thick steel plates facing outward from the obtuse angle and an edge of an outer plate surface of the other of the thick steel plates facing outward from the obtuse angle are arranged opposite to each other, An extension surface from an edge of the outer plate surface of one of the thick steel plates intersects with an edge of the outer plate surface of the other of the thick steel plates or an extension surface from the edge, a portion between an end surface of one of the thick steel plates and an end surface of the other of the thick steel plates, including both end surfaces, covered with weld metal on the outside of the obtuse angle, The present invention is characterized in that the area between the end face of one of the thick steel plates and the inner plate surface of the other of the thick steel plates facing inward of the obtuse angle, including the end face and the inner plate surface, is covered by weld metal on the inside of the obtuse angle.

[0012] The thick steel plate used is rectangular (including trapezoidal) and has a thickness of, for example, 20 to 150 mm. The type of steel plate may be a steel material particularly used for structures, such as rolled steel for welded structures (SM400, SM490, SM520, SM570; JIS G 3106), high-performance steel for building structures (SA385, SA440), rolled steel for building structures SN490 (JIS G 3136; 2012), steel for building structures YP385, 440, and rolled steel for ship hulls (Nippon Kaiji Kyokai hull steel standard) KE36, KE40, etc. These steel plates may be selected appropriately depending on the structure (tubular structure) to be manufactured.

[0013] "Welded at an obtuse angle" means that adjacent steel plates are positioned to form an obtuse angle (an angle greater than 90 degrees and less than 180 degrees) and then the edges of the steel plates are welded together. "The edge of the outer plate surface of one of the thick steel plates facing inward of the obtuse angle and the edge of the outer plate surface of the other thick steel plate facing outward of the obtuse angle are arranged opposite each other" means that in order to ensure the continuity of the weld, the edge of the outer plate surface of one of the thick steel plates and the edge of the outer plate surface of the other thick steel plate are arranged opposite each other at a predetermined distance. "An extension plane from the edge of the outer plate surface of one of the steel plates intersects with the edge or an extension plane from the edge of the outer plate surface of the other steel plate" means that the edge of the outer plate surface of the other steel plate is located on the extension plane from the edge of the outer plate surface of the steel plate.

[0014] There are no particular restrictions on the welding method used for the welded joints. Normally, welding in factories is done in the downward position, and efficient submerged arc welding is commonly used. If the structure is large, welding may be done in the factory and then in an outdoor yard. When welding outdoors (in the case of manufacturing support structures for wind power generation equipment, at locations such as ports and yards where assembly or installation work is carried out), there are certain equipment restrictions, so it is best to choose gas metal arc welding, or efficient single-pass welding such as electroslag welding or electrogas welding.

[0015] There are no particular restrictions on the welding conditions. The welding conditions can be determined according to the thickness and characteristics of the steel plate. From the standpoint of welding efficiency (manufacturability), welding in one pass is preferable, but a weld line can also be formed by multiple passes. The outer surface of a steel plate (the outer surface facing outward of the obtuse angle) naturally forms a groove because the two steel plates form an obtuse angle. A groove also naturally forms between the edge of the inner surface of one steel plate facing inward of the obtuse angle and the inner surface of the other steel plate. Therefore, a welded joint can be easily formed by welding from the outer surface (the outer surface facing outward of the obtuse angle) and the inner surface (the inner surface facing inward of the obtuse angle). As described below, in the present invention, the ends and the space between the ends of the steel plate to be welded must be covered with weld metal. In practice, welding can be performed first on either the surface of the steel plate that forms an obtuse angle (the inner surface facing the obtuse angle) or the opposing surface (the outer surface facing the obtuse angle), depending on the constraints of the factory equipment and process. After welding one surface, the steel plate is flipped over using a flipper, and welding is performed from the opposite surface. Depending on the constraints of the plate thickness and assembly equipment, a root face or gap may be created on the groove surface of the steel plate, and several passes, such as temporary welding and the first layer, may be performed from the inner surface (inner surface). In this case, gas metal arc welding or manual stick welding may be used as the welding method.

[0016] In the present invention, an extension of the edge of the outer plate surface of one steel plate facing outward from the obtuse angle intersects with the edge of the outer plate surface of the other steel plate facing outward from the obtuse angle or with an extension of that edge, the area between the end surfaces of one steel plate and the other steel plate, including both end surfaces, is covered with weld metal on the outside of the obtuse angle, and the area between the end surface of one steel plate and the inner plate surface of the other steel plate facing inward from the obtuse angle, including both end surfaces, is covered with weld metal on the inside of the obtuse angle. Therefore, the outer plate surfaces and the inner plate surfaces of the steel plates forming the obtuse angle are smoothly joined, ensuring continuity and eliminating poor penetration, thereby suppressing a decrease in high fatigue resistance. This results in a welded joint with excellent fatigue resistance.

[0017] Furthermore, the area between the end face of one thick steel plate and the end face of the other thick steel plate, including both end faces, is covered by weld metal on the outside of the obtuse angle, and the area between the end face of one thick steel plate and the inner plate surface of the other thick steel plate facing inward of the obtuse angle, including the end face and inner plate surface, is covered by weld metal on the inside of the obtuse angle.Therefore, the weld metal is sufficiently distributed to the areas facing outward and inward of the obtuse angle at the weld joint between the two thick steel plates, ensuring toughness and tensile strength on the outside and inside of the obtuse angle of the welded joint. Furthermore, since the edge of the outer plate surface of one steel plate facing outward from the obtuse angle and the edge of the outer plate surface of the other steel plate facing outward from the obtuse angle are arranged opposite each other, grooves are naturally formed between the edges of the outer plate surfaces facing outward from the obtuse angle and between the edge of the inner plate surface of one steel plate facing inward from the obtuse angle and the inner plate surface of the other steel plate. Therefore, by welding from the outer plate surface side and the outer plate surface side, welded joints can be easily formed, resulting in excellent workability. In addition, thick steel plates of different thicknesses are welded together at an obtuse angle, allowing one thick steel plate to be thinner than the other, which reduces the number of welding passes and improves workability.

[0018] In the above-described configuration of the present invention, the thinner steel plate of the steel plates to be welded has a root face formed by chamfering an edge portion of an end surface of the steel plate, The length of the root face may be 5.0 mm or more.

[0019] If the root face length is short, i.e., shorter than 5.0 mm, the tip of the groove is likely to melt away when welding. For this reason, when the root face length is short, welding must be performed with a reduced heat input, which increases the number of welding passes and reduces manufacturing efficiency. For this reason, it is preferable to ensure that the root face when chamfering the edge of the thinner steel plate and welding it is 5.0 mm or longer. Note that the presence or absence of a root face is a matter of manufacturing efficiency and does not affect the properties.

[0020] The cylindrical structure according to the present invention is a cylindrical structure formed by welding a plurality of thick steel plates together, the cross-sectional shape of which is polygonal in a direction perpendicular to the axis, The cross-sectional shape is hexagonal or greater and 24-sided or less, The plurality of thick steel plates are a mixture of steel plates with different thicknesses, The steel plates having different thicknesses that are adjacent in the circumferential direction are welded and joined together by the weld joint.

[0021] Examples of cylindrical structures include, but are not limited to, support structures for wind power generation facilities (pillars for onshore wind power generation facilities, pillars for offshore wind power generation facilities (fixed type, floating type), and floating facilities (floating structures) for floating offshore wind power generation facilities).

[0022] The cross-sectional shape of the cylindrical structure is set to be hexagonal or more because if it is less than hexagonal, it will be impossible to obtain a pillar with the same strength as a conventional cylindrical structure with a circular cross-sectional shape (a pillar manufactured by bending and curving thick steel plates and then welding them). Also, the greater the number of sides, the closer the cross-sectional shape will be to a circular cylindrical structure in strength, so it is preferable to make it octagonal or more.

[0023] On the other hand, the reason why the cross-sectional shape of the cylindrical structure is set to 24 or less sides is that if the number of sides exceeds 24, the cross-sectional shape will be close to a circle, but the weld lines will be long, causing manufacturing problems (cost, time). Considering manufacturing problems, it is preferable to set the cross-sectional shape to 16 or less sides. In addition, in consideration of ease of handling during manufacturing, it is preferable that the number of corners is an even number, and the width of the steel plate is also the same. "The plurality of thick steel plates are a mixture of different thicknesses" means that when a plurality of thick steel plates are welded together in the circumferential direction, it is sufficient that at least one thick steel plate is thinner than the other thick steel plates, and it is preferable that one of two circumferentially adjacent thick steel plates is thinner than the other thick steel plate.

[0024] In the present invention, a cylindrical structure having a polygonal cross-sectional shape perpendicular to the axis is formed by welding multiple thick steel plates together in the circumferential direction, and adjacent thick steel plates of different thicknesses in the circumferential direction are welded together by the weld joints, so that a cylindrical structure having excellent fatigue resistance, toughness, and tensile strength can be ensured, and further, excellent workability can be obtained. It also makes it possible to manufacture large-diameter, thick-walled pillars (tubular structures) that could not be manufactured using bending processes.

[0025] In the above-described configuration of the present invention, the thick steel plates having different thicknesses may be arranged alternately in the circumferential direction.

[0026] With this configuration, the strength balance is improved throughout the tubular structure, ensuring a consistent strength for the tubular structure, and all welding conditions can be made the same, making it possible to efficiently manufacture the tubular structure (efficient on-site construction). [Effects of the Invention]

[0027] According to the present invention, it is possible to provide a welded joint that is excellent in workability and fatigue resistance, and a tubular structure that includes the welded joint. [Brief explanation of the drawings]

[0028] [Figure 1] 1 is a cross-sectional plan view showing a thick steel plate before a welded joint is formed according to an embodiment of the present invention. FIG. [Figure 2] 1 is a cross-sectional plan view showing a welded joint according to an embodiment of the present invention. [Figure 3] FIG. 4 is a cross-sectional plan view showing another example of a thick steel plate before a welded joint is formed according to an embodiment of the present invention. [Figure 4] FIG. 10 is a cross-sectional plan view showing yet another example of a thick steel plate before a welded joint is formed according to an embodiment of the present invention. [Figure 5] 1 shows an example of a method for manufacturing a welded joint according to an embodiment of the present invention, in which (a) is a cross-sectional plan view showing two thick steel plates of different thicknesses arranged at an obtuse angle, (b) is a cross-sectional plan view showing the thick steel plates welded from the inner plate side, and (c) is a cross-sectional plan view showing the thick steel plates welded from the outer plate side. [Figure 6] 1 is a perspective view showing a schematic configuration of a cylindrical structure according to an embodiment of the present invention. [Figure 7] 1 is a cross-sectional plan view of a cylindrical structure according to an embodiment of the present invention. [Figure 8] 1 is a cross-sectional plan view showing a thick steel plate before a welded joint is formed according to an embodiment of the present invention. [Figure 9] FIG. 1 is a diagram schematically illustrating an angled joint fatigue testing machine and a test piece according to an embodiment of the present invention. [Figure 10]FIG. 10 is a diagram showing a cantilever model used in finite element analysis in an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0029] Hereinafter, embodiments of a welded joint and a tubular structure according to the present invention will be described with reference to the drawings. Fig. 1 is a plan cross-sectional view showing a thick steel plate before the weld joint of this embodiment is formed, Fig. 2 is a plan cross-sectional view showing the weld joint of this embodiment, Fig. 3 is a plan cross-sectional view showing another example of a thick steel plate before the weld joint of this embodiment is formed, Fig. 4 is a plan cross-sectional view showing yet another example of a thick steel plate before the weld joint of this embodiment is formed, Fig. 5 is a plan cross-sectional view for explaining a method of forming the same weld joint, Fig. 6 is a perspective view showing a tubular structure of this embodiment, and Fig. 7 is a cross-sectional view of the tubular structure of this embodiment in a direction perpendicular to its axis. Hatching is omitted in Figs. 1, 3, and 4.

[0030] 1 and 2, a welded joint 10 of this embodiment is formed by welding two thick steel plates 11, 12 of different thicknesses together at an obtuse angle. The thick steel plates 11, 12 are formed into a substantially rectangular plate shape (including a trapezoidal plate shape), and the thicknesses of the thick steel plates 11, 12 are 20 to 150 mm. In this embodiment, the thick steel plate 12 is thinner than the thick steel plate 11, and the thickness of the thick steel plate 12 is about half the thickness of the thick steel plate 11, but this is not limited to this.

[0031] An edge 11d of the outer plate surface 11a of one thick steel plate 11 facing inward of the obtuse angle and an edge 12d of the outer plate surface 12a of the other thick steel plate 12 facing outward of the obtuse angle are arranged opposite to each other. That is, to ensure the continuity of the weld, the edge 11d of the outer plate surface 11a and the edge 12d of the outer plate surface 12a are arranged opposite to each other at a predetermined distance. The edge 12d is arranged opposite to the edge 11d at a predetermined distance in a direction inclined relative to the outer plate surface 11a. In addition, an extension surface 11e from an edge 11d of the outer plate surface 11a of one thick steel plate 11 facing outward from the obtuse angle intersects with an extension surface 12e from an edge 12d of the outer plate surface 12a of the other thick steel plate 12 facing outward from the obtuse angle at an intersection point P.

[0032] As shown in Figure 3, when the base end (edge ​​11d) of the extended surface 11e from the edge 11d of the outer plate surface 11a facing outward of the obtuse angle of one thick steel plate 11 intersects with the extended surface 12e from the edge 12d of the outer plate surface 12a facing outward of the obtuse angle of the other thick steel plate 12, this is considered to include the case where the extended surface 11e from the edge 11d of the outer plate surface 11a facing outward of the obtuse angle of one thick steel plate 11 intersects with the extended surface 12e from the edge 12d of the outer plate surface 12a facing outward of the obtuse angle of the other thick steel plate 12.

[0033] 1, of the steel plates 11, 12 to be welded together, the thinner steel plate 12 has a root face 12f formed by chamfering the edge of the end surface of the steel plate 12 (the edge of the end surface on the inner plate surface 12b side), and the length L of the root face 12f is 5.0 mm or more. The portion of the end surface 11c of the steel plate 11 that faces the root face 12f becomes the root face of the steel plate 11.

[0034] 2, the area between the end face 11c of one steel plate 11 and the end face 12c of the other steel plate 12, including both end faces 11c, 12c, is covered with weld metal M1 on the outside of the obtuse angle, and the area between the end face 11c of one steel plate 11 and the inner plate face 12b of the other steel plate 12 facing the inside of the obtuse angle, including the end face 11c and the tip end portion (the end portion closer to the steel plate 11) of the inner plate face 12b, is covered with weld metal M2 on the inside of the obtuse angle. These weld metals M1, M2 melt together and intersect at approximately the center of the root face 12f.

[0035] 1, in this embodiment, an extended surface 11e from an edge 11d of the outer plate surface 11a of one steel plate 11 facing outward of the obtuse angle intersects with an extended surface 12e from an edge 12d of the outer plate surface 12a of the other steel plate 12 facing outward of the obtuse angle at an intersection P. Alternatively, as shown in FIG. 4, an extended surface 11e from an edge 11d of the outer plate surface 11a of one steel plate 11 facing outward of the obtuse angle may intersect with an edge 12d of the outer plate surface 12a of the other steel plate 12 facing outward of the obtuse angle. In other words, the edge 12d of the outer plate surface 12a of the other steel plate 12 facing outward of the obtuse angle may be located on the extended surface 11e from the edge 11d of the outer plate surface 11a of one steel plate 11 facing outward of the obtuse angle. Even in such a case, as shown in Figure 2, the area between the end face 11c of one thick steel plate 11 and the end face 12c of the other thick steel plate 12, including both end faces 11c, 12c, is covered by weld metal M1 on the outside of the obtuse angle, and the area between the end face 11c of one thick steel plate 11 and the inner plate surface 12b of the other thick steel plate 12 facing inward of the obtuse angle, including the end face 11c and the tip of the inner plate surface 12b, is covered by weld metal M2 on the inside of the obtuse angle.

[0036] The thick steel plates 11, 12 are formed into rectangular, square, trapezoidal, etc. Furthermore, as will be described later, when a truncated pyramidal cylindrical structure is constructed using the thick steel plates 11, 12, trapezoidal thick steel plates 11, 12 are used.

[0037] Such a welded joint 10 can be formed, for example, as shown in FIG. First, as shown in Figure 5(a), the thick steel plate 11 is arranged so that the edge 11d of the outer plate surface 11a facing inward of the obtuse angle of one thick steel plate 11 and the edge 12d of the outer plate surface 12a facing outward of the obtuse angle of the other thick steel plate 12 face each other, and so that the extended surface 11e from the edge 11d of the outer plate surface 11a facing outward of the obtuse angle of one thick steel plate 11 intersects with the extended surface 12e from the edge 12d of the outer plate surface 12a facing outward of the obtuse angle of the other thick steel plate 12. In addition, the edge of the end surface of the thinner steel plate 12 (the edge of the end surface on the inner plate surface 12b side) is chamfered to form a root face 12f, and the root face 12f is brought into contact with or close to the end surface 11c of the steel plate 11. The length L of this root face 12f is set to 5.0 mm or more.

[0038] The end face 11c of the thick steel plate 11 and the end face 12c of the thick steel plate 12 are spaced apart toward the outer plate faces 11a and 12a facing outward at the obtuse angle, so that a groove is formed by the end faces 11c and 12c on the outer plate faces 11a and 12a. The end faces 11c and 12c become groove faces during welding. The end face 11c of the thick steel plate 11 and the inner plate face 12b of the thick steel plate 12 are spaced apart toward the inner plate face 11b facing inward of the obtuse angle, so that a groove is formed by the end face 11c and the inner plate face 12b on the inner plate face 11b, 12b side. The end face 11c and the inner plate face 12b become groove faces during welding.

[0039] Next, as shown in Fig. 5(b), the steel plates 11 and 12 are welded together from the inside of the obtuse angle, i.e., from the side of the inner plate surfaces 11b and 12b. As a result, the area between the end surface 11c of one steel plate 11 and the inner plate surface 12b of the other steel plate 12 facing the inside of the obtuse angle, including the end surface 11c and the tip of the inner plate surface 12b, is covered with weld metal M2 on the inside of the obtuse angle. In this case, gas metal arc welding or manual stick welding is used as the welding method. Furthermore, from the viewpoint of welding efficiency (manufacturability), welding in one pass is preferable, but in this embodiment, a weld line is formed by multiple passes (multiple passes).

[0040] Next, as shown in Fig. 5(c), the steel plates 11 and 12 are welded together from the outside of the obtuse angle, i.e., from the side of the outer plate surfaces 11a and 12a. As a result, the area between the end surface 11c of one steel plate 11 and the end surface 12c of the other steel plate 12, including both end surfaces 11c and 12c, is covered with weld metal M1 on the outside of the obtuse angle. The weld metal M1 melts and intersects with the weld metal M2 at approximately the center of the root face 12f. In this case, gas metal arc welding or manual stick welding is used as the welding method. Although one-pass welding is preferable from the viewpoint of welding efficiency (manufacturability), in this embodiment, a weld line is formed by multiple passes (plural passes). In this way, one thick steel plate 11 and the other thick steel plate 12 are welded together to form a welded joint 10. In this embodiment, the thick steel plates 11 and 12 are welded together from the inside of the obtuse angle first, but conversely, the welding may be performed from the outside of the obtuse angle first.

[0041] There is no particular restriction on the welding method, but welding in factories is usually done in the downward position, and efficient submerged arc welding is commonly used. If the structure is large, welding may be done in the factory and then in an outdoor yard. When welding outdoors (when manufacturing support structures for wind power generation equipment, in places such as ports and yards where assembly or installation work is carried out), there are certain equipment restrictions, so it is best to choose gas metal arc welding, or efficient single-pass welding such as electroslag welding or electrogas welding.

[0042] Next, the cylindrical structure of this embodiment will be described. As shown in FIG. 6, the tubular structure 20 of this embodiment has a head (upper end in FIG. 6) formed in the shape of a truncated pyramidal cylinder cut by a plane parallel to the direction orthogonal to the axis. Such a tubular structure 20 is used, for example, as a support structure for a wind power generation facility (a pillar for an onshore wind power generation facility, a pillar for an offshore wind power generation facility (fixed type, floating type), a floating facility (floating structure) for a floating type offshore wind power generation facility), etc., but is not limited to this.

[0043] The cylindrical structure 20 is formed by welding multiple thick steel plates 11, 12 circumferentially, so that its cross-sectional shape perpendicular to the axis is octagonal, and by welding multiple thick steel plates 11, 12 axially as well, it is formed into a truncated octagonal pyramidal cylindrical shape. Each of the multiple steel plates 11, 12 is formed in a trapezoidal shape, with the lower ones having larger areas. Furthermore, for adjacent steel plates 11, 11 (12, 12) in the vertical direction (axial direction), the bottom edge of the upper steel plate 11 (12) and the top edge of the lower steel plate 11 (12) are equal in length. Six steel plates 11, 12 are arranged in the axial direction (vertical direction), and the bottom edge of the upper steel plate 11, 12 and the top edge of the lower steel plate 11, 12 are welded and joined by, for example, butt welding.

[0044] As described above, the thick steel plate 12 is formed thinner than the thick steel plate 11, and the thick steel plates 11, 12 adjacent in the circumferential direction and having different thicknesses are welded and joined together by the weld joint 10 described above. That is, as shown in Fig. 7, thick steel plates 11, 12 of different thicknesses are arranged alternately in the circumferential direction, and thick steel plates 11, 12 of different thicknesses that are adjacent in the circumferential direction are welded and joined together by weld joints 10. When adjacent thick steel plates 11, 12 are welded and joined together by weld joints 10, the steps shown in Figs. 5(a) to (c) are performed. By welding together the thick steel plates 11 and 12 in this manner, a ring-shaped divided body 21 having an octagonal cross section is formed.

[0045] 6, the divided bodies 21 are provided in six vertical stages, with the lower divided bodies 21 having larger diameters. Of the divided bodies 21, 21 adjacent to each other, the lower surface of the upper divided body 21 and the upper surface of the lower divided body 21 have the same shape. Six such segments 21 are arranged adjacent to each other vertically, and the thick steel plates 11, 11 of the vertically adjacent segments 21, 21 are axially welded together, and the thick steel plates 12, 12 of the vertically adjacent segments 21, 21 are axially welded together, thereby constructing a cylindrical structure 20 in the shape of a truncated octagonal pyramidal cylinder.

[0046] As described above, according to this embodiment, the extension surface 11e from the edge 11d of the outer plate surface 11a of one of the steel plates 11 facing outward of the obtuse angle intersects with the extension surface 12e from the edge 12d of the outer plate surface 12a of the other steel plate 12 facing outward of the obtuse angle, and the area between the end surface 11c of one of the steel plates 11 and the end surface 12c of the other steel plate 12, including both end surfaces 11c, 12c, is covered by the weld metal M1 on the outside of the obtuse angle, and the end surface 11c of one of the steel plates 11 and the inner plate surface 12b of the other thick steel plate 12 facing the inside of the obtuse angle, including the end face 11c and the tip of the inner plate surface 12b, are covered by the weld metal M2 on the inside of the obtuse angle, so the outer plate surfaces 11a, 12a and the inner plate surfaces 11b, 12b of the thick steel plates 11, 12 that form the obtuse angle are smoothly joined, ensuring continuity and eliminating poor penetration, thereby suppressing a decrease in the high fatigue resistance. This results in a welded joint 10 with excellent fatigue resistance. Furthermore, the area between the end face 11c of one thick steel plate 11 and the end face 12c of the other thick steel plate 12, including both end faces 11c, 12c, is covered by weld metal M1 on the outside of the obtuse angle, and the area between the end face 11c of one thick steel plate 11 and the inner plate face 12b of the other thick steel plate 12 facing inward of the obtuse angle, including the end face 11c and the tip of the inner plate face 12b, is covered by weld metal M2 on the inside of the obtuse angle.Therefore, the weld metals M1, M2 are sufficiently distributed in the areas facing outward and inward of the obtuse angle at the weld joint of the two thick steel plates 11, 12, and toughness and tensile strength can be ensured on the outside and inside of the obtuse angle of the weld joint 10.

[0047] Furthermore, because the edge 11d of the outer plate surface 11a of one steel plate 11 facing outward from the obtuse angle and the edge 12d of the outer plate surface 12a of the other steel plate 12 facing outward from the obtuse angle are arranged opposite each other, grooves naturally form between the edges of the outer plate surfaces 11a, 12a facing outward from the obtuse angle and between the edge of the inner plate surface 11b of one steel plate 11 facing inward from the obtuse angle and the inner plate surface 12b of the other steel plate 12. For this reason, welding can be performed from the outer plate surface side and the inner plate surface side, and the welded joint 10 can be easily formed, resulting in excellent workability. Furthermore, the thick steel plates 11, 12 of different thicknesses are welded together at an obtuse angle, and one thick steel plate 12 can be made thinner than the other thick steel plate 11, which reduces the number of welding passes and improves workability.

[0048] Furthermore, in the cylindrical structure 20 having a polygonal (octagonal) cross section in the direction perpendicular to the axis, a plurality of thick steel plates 11, 12 are welded in the circumferential direction, and adjacent thick steel plates 11, 12 of different thicknesses are welded and joined together by weld joints 10, so that the cylindrical structure 20 has excellent fatigue resistance, as well as toughness and tensile strength, and is easy to work with. It also becomes possible to manufacture large-diameter, thick-walled pillars (cylindrical structures 20) that could not be manufactured by bending processing. Furthermore, the welded joint 10 is made by welding thick steel plates 11, 21 of different thicknesses at an obtuse angle, and since a thin thick steel plate 12 is used, the number of welding passes can be reduced, making it easier to work with. Furthermore, since the welding was performed with the inner surfaces (inner plate surfaces) aligned (so-called internal dimension welding), the fatigue resistance characteristics are also good. Furthermore, since the thick steel plates 11, 12 of different thicknesses are arranged alternately in the circumferential direction, the strength balance of the entire tubular structure 20 is improved, and not only can a constant strength of the tubular structure 20 be ensured, but the welding conditions can all be made the same, making it possible to efficiently manufacture the tubular structure 20 (efficient on-site construction).

[0049] The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, the cylindrical structure may be a straight rectangular tube having a uniform diameter at all positions in the axial direction, in addition to a truncated rectangular tube. In this case, the multiple thick steel plates constituting the rectangular cylindrical structure may be rectangular plates. Furthermore, in this embodiment, two types of thick steel plates 11 and 12 with different thicknesses are used, but three or more types of thick steel plates with different thicknesses may be used.

[0050] Next, an example will be described. Example 1 Thick steel plates (1000 mm long, 500 mm wide, 20-150 mm thick) made from steel materials commonly used in structures (rolled steel for welded structures (SM400, SM490, SM570; JIS G 3106), high-performance steel for architectural structures (SA385, SA440)) were prepared, and welded joints with a longitudinal weld length of 1000 mm (a welded joint with the same shape as welded joint 10 shown in Figure 2) were fabricated. Submerged arc welding was primarily used for welding, with factory manufacturing in mind, but gas metal arc welding and electroslag welding were also used in some areas to allow for on-site manufacturing. In particular, when forming an obtuse angle in the welded joint, the part must be placed at that obtuse angle during welding, so a jig capable of setting the angle was used for welding. Figure 8 shows the relative positions of the steel materials in a welded joint made of thick steel plates of different thicknesses.

[0051] Table 1 shows the welded joints produced and their welding methods. The items in Table 1 correspond to the items in Figure 8. The ideal gap upper limit in Table 1 is a calculated value of the gap, which is the distance between the edge of the outer plate surface facing outward of the obtuse angle of one steel plate (steel material) and the edge of the outer plate surface facing outward of the obtuse angle of the other steel plate (steel material) or the portion where the extended surface from the edge intersects with the edge of the outer plate surface facing outward of the obtuse angle of the other steel plate (steel material), when the root face is set to the value in the table. In the present invention, the gap is defined to be greater than or equal to 0 and less than or equal to the ideal gap upper limit. It should be noted that hatching is omitted in FIG.

[0052] [Table 1]

[0053] The welding conditions for the welding method are shown in Table 2. In Table 2, welding condition SAW2 is the same submerged arc welding as welding condition SAW, but the average heat input is lower than that of welding condition SAW. [Table 2]

[0054] The properties of the welded joints were evaluated by cutting out test pieces from the welded joints and carrying out an appearance test for weld defects, a Charpy impact test, and an angled joint fatigue test. The appearance test was conducted based on JIS Z 3090 and the pass / fail judgment was made. The pass condition was that the undercut depth e was e≦0.5 mm. The Charpy impact test was conducted in accordance with JIS Z 3128. The test specimens were notched at the center of the plate thickness of Steel Material 1. The notches were positioned at the center of the weld metal and the bond, with 2 mm V-notches machined in a direction perpendicular to the base metal surface, and then submitted to the Charpy impact test. The test temperature was 0°C, and the average impact values ​​measured for three specimens each at the center of the weld metal and the bond were deemed to have passed if they both recorded 27 J or more.

[0055] For angled joint fatigue tests, strain gauges were attached at positions 4 mm and 10 mm away from the center of the test piece's width and perpendicular to the weld line from the weld toe, and fatigue tests were conducted while changing the load range. The stress at the weld toe (hot spot stress) was calculated by extrapolation from the strain at the two points. Figure 5 shows the angled joint fatigue testing machine and test piece. The fatigue life was determined to be the point at which the strain on the strain gauge at the 4 mm position had decreased by 10% from the initial load. The fatigue test was terminated after 3.5 million cycles. A hot spot stress range of 90 MPa or more, which corresponds to a fatigue life of 2 million cycles, was considered to have passed.

[0056] This shows that the welded joint of the present invention has good evaluation results in all of the above tests and can be used as a welded joint required for manufacturing support structures for wind power generation facilities. In particular, for welded joints No. 14 to 16, the edges of thin steel plates (steel material) were not chamfered or were chamfered only slightly, so there was concern that the edges of the steel material would melt through if welding was performed under high heat input conditions (SAW in Table 2).In this case, although the number of passes was high, no burn-through occurred.

[0057] On the other hand, in welded joints No. 17 and No. 18, the positional relationship between the two steel materials was changed compared to welded joint No. 4, an example of the present invention, with the gap set to a negative value in welded joint No. 17 and a value exceeding the upper limit of the ideal gap in welded joint No. 18. Although welding was performed in the same way as welded joint No. 4, undercut occurred, and the appearance test and the angled joint fatigue properties were evaluated as failing. Welded joint No. 19 is an example in which the number of welding passes was reduced compared to welded joint No. 4, an example of the present invention. When the number of passes is insufficient, the amount of weld metal is reduced and both end faces of the steel material cannot be covered, and this condition was confirmed in welded joint No. 19. In addition, undercutting occurred, and the appearance test and angled joint fatigue properties were evaluated as failing. Like No. 19, welded joint No. 20 is also an example of a low number of passes. Both ends of the steel were not covered, and undercutting occurred, resulting in a failing evaluation of the appearance test and the angled joint fatigue properties.

[0058] Example 2 Example 1 showed that the welded joint of the present invention has good fatigue resistance, can be manufactured with high efficiency, and is suitable as a welded joint for support structures of wind power generation facilities. Therefore, assuming that a support structure (pillar) of a wind power generation facility is manufactured using the welded joint of the present invention, a numerical simulation (finite element analysis) was performed on the horizontal strength of the pillar. More specifically, with the aim of manufacturing a tubular structure with the same strength as the cylindrical structure shown in Table 3 as a support pillar, a tubular structure consisting of welded joint No. 4 in Table 1 was designed, as well as a tubular structure consisting of welded joints made of steel material of the same thickness (125 mm) made of SM400 steel.Finite element analysis was then performed on tubular structures with multiple cross-sectional shapes based on these two design guidelines. Figure 10 shows the cantilever model used in the finite element analysis.

[0059] [Table 3]

[0060] In the finite element analysis, a horizontal load was applied to the apex of a 50m-long cylindrical structure (upper arrow in Figure 10), and the horizontal strength of the cylindrical structure was evaluated. Here, the horizontal strength is the theoretical value of the horizontal load when the bottom end of the cylindrical structure reaches the yield stress, and can be calculated based on the section modulus and yield stress, which can be calculated according to the polygonal cross section. The analysis was conducted by keeping the perimeter of the tubular structures with each cross-sectional shape constant (31.4 m). It was found that the tubular structure with a cross-sectional shape with fewer strokes (quadrilateral) buckled early under low horizontal loads, while the tubular structure with a decagonal cross-sectional shape achieved horizontal strength equivalent to that of a cylindrical structure.

[0061] Table 4 shows the horizontal strength of a cylindrical structure with a decagonal cross section. In Table 4, column 1 was designed as a tubular structure consisting of welded joint No. 4 in Table 1 (different steel type, different thickness), and column 2 was designed as a tubular structure consisting of welded joints made of steel material of type SM400, all of the same thickness (125 mm) (same steel type, same thickness). Table 4 also shows the mass of the columns.

[0062] [Table 4]

[0063] As shown in Table 4, numerical simulations using finite element analysis have shown that by using the welded joint of the present invention, the mass of the cylindrical structure can be reduced by 14% while maintaining the same horizontal bearing strength as conventional cylindrical structures, and it has been confirmed that the structure can withstand use as a support for offshore wind power generation equipment. [Explanation of symbols]

[0064] 10 Welded joints 11,12 thick steel plate 11a,12a Outer plate surface 11b,12b Inner plate surface 11c,12c end face 11d,12d edge 11e,12e extension surface 20 Cylindrical Structure M1, M2 weld metal

Claims

1. A welded joint in which steel plates of different thicknesses are welded together at an obtuse angle, An edge of an outer plate surface of one of the thick steel plates facing outward from the obtuse angle and an edge of an outer plate surface of the other of the thick steel plates facing outward from the obtuse angle are arranged opposite to each other, An extension surface from an edge of the outer plate surface of one of the thick steel plates intersects with an edge of the outer plate surface of the other of the thick steel plates or an extension surface from the edge, a portion between an end surface of one of the thick steel plates and an end surface of the other of the thick steel plates, including both end surfaces, covered with weld metal on the outside of the obtuse angle, A welded joint characterized in that the area between the end face of one of the thick steel plates and the inner plate surface of the other of the thick steel plates facing inward of the obtuse angle, including the end face and the inner plate surface, is covered by weld metal on the inside of the obtuse angle.

2. Of the steel plates to be welded together, the thinner steel plate has a root face formed by chamfering an end surface edge of the steel plate, The welded joint according to claim 1, wherein the root face has a length of 5.0 mm or more.

3. A cylindrical structure having a polygonal cross section in a direction perpendicular to the axis, formed by welding a plurality of thick steel plates in a circumferential direction, The cross-sectional shape is a hexagon or more and a 24-sided polygon or less, The plurality of thick steel plates are a mixture of steel plates with different thicknesses, 3. A cylindrical structure, characterized in that the thick steel plates having different thicknesses adjacent to each other in the circumferential direction are welded and joined by the weld joint according to claim 1 or 2.

4. 4. The cylindrical structure according to claim 3, wherein the thick steel plates having different thicknesses are arranged alternately in the circumferential direction.

Images