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 10, in which thick steel plates having different thicknesses are weld-bonded to each other at an obtuse angle, an edge 11d of an inside plate surface 11a pointing to inside with obtuse angle of one thick steel plate 11 and an edge 12d of an inside plate surface 12a pointing to the inside with the obtuse angle of the other thick steel plate 12 are arranged to oppose to each other. 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 is coated with weld metal 13, outside with the obtuse angle.SELECTED DRAWING: Figure 1

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 have been investigated, but neither of these 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] On the other hand, when considering the properties, welding thick steel plates of different thicknesses together can result in discontinuity in the welded joint, which can lead to a decrease in fatigue resistance at the welded joint.When manufacturing a support column (tubular structure) with a polygonal cross section, fatigue resistance is lower at the weld on the inner side of the column than at the outer side. Therefore, if the thick steel plates are welded with the inner surfaces aligned (if welding is performed to the so-called "inner dimension"), the continuity of the weld can be ensured and the decrease in fatigue resistance can be suppressed.

[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 inner plate surface of one of the thick steel plates facing the inside of the obtuse angle and an edge of an inner plate surface of the other thick steel plate facing the inside of the obtuse angle are arranged opposite to each other, The present invention is characterized in that the area between the end face of one of the thick steel plates and the end face of the other of the thick steel plates, including both end faces, is covered with weld metal outside 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. "Arranged opposite to each other" means that the edge of the inner plate surface of one thick steel plate facing the inside of the obtuse angle and the edge of the inner plate surface of the other thick steel plate facing the inside of the obtuse angle are arranged in contact with each other, or that there is a predetermined gap between these edges.

[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 the steel plate (the outer surface facing outward of the obtuse angle) naturally forms a groove because the two steel plates form an obtuse angle. Therefore, if welding is performed from the outer surface (the outer surface facing outward of the obtuse angle), a welded joint can be easily formed. As will be described later, in the present invention, the ends and the space between the ends of the steel plates to be welded must be covered with weld metal. Therefore, actual welding is essentially performed primarily from the side of the steel plate (the outer plate surface facing the outside of the obtuse angle) opposite the surface that forms the obtuse angle (the inner plate surface facing the inside of the obtuse angle). However, depending on the plate thickness and assembly equipment constraints, a root face or gap may be provided on the groove surface of the steel plate, and several passes of welding, such as temporary welding or the first layer, may be performed from the inner surface (the inner plate surface). In this case, gas metal arc welding or manual stick welding may be used as the welding method.

[0016] In the present invention, the edge of the inner surface of one steel plate facing the obtuse angle and the edge of the inner surface of the other steel plate facing the obtuse angle are positioned opposite each other and then welded, so the inner surfaces of the steel plates facing the obtuse angle are smoothly joined, ensuring continuity and eliminating poor penetration, resulting in a welded joint with excellent fatigue resistance. Furthermore, since 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, the weld metal is sufficiently distributed to the area facing outward from the obtuse angle at the weld joint between the two thick steel plates, ensuring toughness and tensile strength on the outside of the obtuse angle of the welded joint. Furthermore, since the edge of the inner plate surface of one steel plate facing the obtuse angle and the edge of the inner plate surface of the other steel plate facing the obtuse angle are arranged opposite each other, a groove is formed between the edges of the outer plate surfaces facing the obtuse angle. Therefore, by welding from the outer plate surface side, a welded joint 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.

[0017] 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.

[0018] 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).

[0019] 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.

[0020] 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.

[0021] 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.

[0022] In the above-described configuration of the present invention, the thick steel plates having different thicknesses may be arranged alternately in the circumferential direction.

[0023] 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]

[0024] 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]

[0025] [Figure 1] 1 is a cross-sectional plan view showing a welded joint according to an embodiment of the present invention. [Figure 2] 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 3] 1 is a perspective view showing a schematic configuration of a cylindrical structure according to an embodiment of the present invention. [Figure 4] 1 is a cross-sectional plan view of a cylindrical structure according to an embodiment of the present invention. [Figure 5] 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 6] 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

[0026] 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 cross-sectional plan view showing a welded joint of this embodiment, FIG. 2 is a cross-sectional plan view for explaining a method of forming the same welded joint, FIG. 3 is a perspective view showing a tubular structure of this embodiment, and FIG. 4 is a cross-sectional view of the tubular structure of this embodiment in a direction perpendicular to the axis.

[0027] As shown in Fig. 1, 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. An edge 11d of an inner plate surface 11a of one thick steel plate 11 facing inward of the obtuse angle and an edge 12d of an inner plate surface 12a of the other thick steel plate 12 facing inward of the obtuse angle are arranged opposite to each other. In addition, the thick steel plates 11 and 12 are welded together, and 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 and 12c, is covered by weld metal 13 on the outside of the obtuse angle.

[0028] The thick steel plates 11, 12 are formed into rectangular, square, trapezoidal, etc. When a truncated pyramidal cylindrical structure is constructed using the thick steel plates 11, 12 as will be described later, trapezoidal thick steel plates 11, 12 are used.

[0029] Such a welded joint 10 can be formed, for example, as shown in FIG. First, as shown in FIG. 2(a), one thick steel plate 11 is arranged so that an edge 11d of the inner surface 11a facing the obtuse angle faces the edge 12d of the inner surface 12a of the other thick steel plate 12 facing the obtuse angle faces each other. In this case, the edges 11d and 12d may abut each other, but in this embodiment, a gap (g) of a predetermined width is provided between the edges 11d and 12d. Furthermore, the end faces 11c and 12c of the thick steel plate 11 and 12 become more spaced apart toward the outer surface 11b and 12b facing the obtuse angle, thereby forming a groove between the end faces 11c and 12c on the outer surface 11b and 12b. The end faces 11c and 12c serve as groove faces during welding.

[0030] Next, as shown in Figure 2(b), a gap (gap) g of a predetermined width is provided between the groove faces 11c, 12c due to constraints such as plate thickness and assembly equipment, so several passes of welding, such as temporary welding and the first layer, are performed from the inner plate faces 11a, 12a. In this case, gas metal arc welding or manual stick welding is used as the welding method. The symbol w indicates the welded portion in the temporary welding and the first layer.

[0031] Next, as shown in FIG. 2(c), welding is performed from the outer plate surfaces 11b, 12b side to form a welded joint 10. In this case, from the viewpoint of welding efficiency (manufacturability), it is preferable to perform welding in one pass, but in this embodiment, a weld line is formed by multiple passes (plural passes). As a result, the end face 11c of one thick steel plate 11 and the end face 12c of the other thick steel plate 12 are welded together, forming a welded joint 10 as shown in FIG. 1. In this welded joint 10, 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 is covered by weld metal 13 on the outside of the obtuse angle.

[0032] 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.

[0033] Next, the cylindrical structure of this embodiment will be described. As shown in FIG. 3, the cylindrical structure 20 of this embodiment has a head (upper end in FIG. 3) 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.

[0034] 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.

[0035] 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. 4, 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. 2(a) to 2(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.

[0036] 3, 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.

[0037] As described above, according to this embodiment, the edge 11d of the inner plate surface 11a of one thick steel plate 11 facing the inside of the obtuse angle and the edge 12d of the inner plate surface 12a of the other thick steel plate 12 facing the inside of the obtuse angle are positioned opposite each other and then welded together, so the inner plate surfaces 11a, 12a of the thick steel plates 11, 12 facing the inside of the obtuse angle are smoothly joined, ensuring continuity and eliminating poor penetration. This results in a welded joint 10 with excellent fatigue resistance. Furthermore, since 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 the weld metal 13 on the outside of the obtuse angle, the weld metal 13 is sufficiently distributed to the area facing the outside of the obtuse angle at the weld joint between the two thick steel plates 11, 12, ensuring toughness and tensile strength on the outside of the obtuse angle of the weld joint 10.

[0038] Furthermore, since an edge 11d of the inner plate surface 11a of one steel plate 11 facing the inside of the obtuse angle and an edge 12d of the inner plate surface 12a of the other steel plate 12 facing the inside of the obtuse angle are arranged opposite each other, a groove naturally forms between the edges 11d, 12d. Therefore, by welding from the outer plate surfaces 11b, 12b side, 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.

[0039] 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 formed by welding thick steel plates 11, 21 of different thicknesses together 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 welding is performed according to the so-called inside dimensions, 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).

[0040] 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.

[0041] 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 1) 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.

[0042] Table 1 shows the welded joints produced and the welding methods used. [Table 1]

[0043] Table 2 shows the welding conditions for the welding method. [Table 2]

[0044] 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.

[0045] 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.

[0046] According to this, as shown in Table 1, the welded joints No. 1 to No. 11 of the present invention had good evaluation results in all of the above tests, and it can be seen that they can be used as welded joints necessary for manufacturing support structures for wind power generation facilities. On the other hand, the welded joint No. 12 had a small number of welding passes and was unable to cover the edge of the outer surface (outer plate surface), resulting in undercutting, and was rated as failing the appearance test and the angled joint fatigue properties. Both the welded joint No. 13 and the welded joint No. 14 achieved good evaluation results in all of the above tests.

[0047] However, because the weld joint No. 13 was welded with the outer surface (outside plate surface) aligned (so-called "outside welding"), and the weld joint No. 14 was welded to the center of the plate thickness, it was necessary to weld the inner surface and then flip the steel plate over to weld the outer surface, significantly reducing welding efficiency. In other words, when flipping the steel plate during welding, the entire weld joint must be lifted by a crane, and the work must be carried out with due consideration given to safety, which can take several hours. Furthermore, the need to attach a lifting ring to the weld joint for lifting increases the number of processes. While it would be possible to weld the steel plate without flipping it, in that case the inner surface welding would be performed in an overhead position, reducing the welding heat input and reducing welding efficiency.

[0048] 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 6 shows the cantilever model used in the finite element analysis.

[0049] [Table 3]

[0050] In the finite element analysis, a horizontal load was applied to the apex of a 50m-long cylindrical structure (upper arrow in Figure 6), 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.

[0051] 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.

[0052] [Table 4]

[0053] 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]

[0054] 10 Welded joints 11,12 thick steel plate 11a,12a Inner plate surface 11b,12b Outer plate surface 11c,12c end face 11d,12d edge 13 Weld metal 20 Cylindrical Structure

Claims

1. A welded joint in which steel plates of different thicknesses are welded together at an obtuse angle, An edge of an inner plate surface of one of the thick steel plates facing the inside of the obtuse angle and an edge of an inner plate surface of the other thick steel plate facing the inside of the obtuse angle are arranged opposite to each other, A welded joint characterized in that the area between the end face of one of the thick steel plates and the end face of the other of the thick steel plates, including both end faces, is covered by weld metal outside the obtuse angle.

2. 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, 2. A cylindrical structure, wherein 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.

3. 3. The cylindrical structure according to claim 2, wherein the thick steel plates having different thicknesses are arranged alternately in the circumferential direction.

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