Welded joint and its manufacturing method

Abstract

The present invention provides a welded joint for a floating offshore wind power plant consisting of a tower member, a floating body member, and a bracket, in which the fatigue strength of the welded part is improved by extending the weld bead onto the floating body member, and a method for manufacturing the same. The welded joint of the present invention has a first weld bead, a second weld bead, and a third weld bead, and the first weld bead is formed along one short side of a rectangular abutment surface where the bracket abuts against the floating body member, and the second weld bead and the third weld bead are formed along both long sides of the rectangular abutment surface and are formed by covering a part of either the start end or the end end of the first weld bead and extending onto the floating body member. Furthermore, it is preferable that M / N, which represents the ratio of the distance M between the tip of the second weld bead and the tip of the third weld bead to the length N of the extension part of the second weld bead or the third weld bead, is 2.0 or less.

Description

[Technical field]

[0001] The present invention relates to a welded joint and a manufacturing method thereof, and more particularly to a welded joint having excellent fatigue strength, such as a welded joint portion of a floating offshore wind power generation device, in which floating body members and the like are gas-shielded arc-welded via a bracket, and a manufacturing method thereof. [Background technology]

[0002] In recent years, in the field of offshore wind power generation, floating offshore wind turbines have been considered due to their ease of installation even in waters 50m or deeper. Because floating offshore wind turbines are exposed to external forces such as waves, the issue being considered is how to improve the fatigue life of the weld toes in the welded joints of these devices.

[0003] Therefore, various techniques for improving the fatigue strength of welded joints in large structures such as offshore wind power generation equipment have been studied. For example, Patent Document 1 discloses that in a welded girder structure consisting of ribs and face members, the ends of the ribs are attached to the structural members by fillet welding on both sides, and the fillet weld beads are slightly extended on the structural members to form a pair of extension beads with the structural members. Patent Document 1 also discloses that the face members are attached to the side edges of the ribs by fillet welding on both sides, and the fillet weld beads are slightly extended on both sides of the side edges of the ribs to form a pair of extension beads with the ribs. It is said that these extension beads can suppress the occurrence of fatigue cracks from the weld toes.

[0004] Patent Document 2 discloses a weld bead structure having two weld beads formed by butting an end face of one plate against one side of the other plate and fillet welding both sides, and two extended weld beads formed by extending the weld beads on both sides from the end of the other plate onto one side. Patent Document 2 also describes the presence of an end weld bead formed by additionally welding the ends of one plate and the other plate between the extended weld beads on both sides. This is said to move the weld bead toe away from high stress areas where defects are likely to occur in the weld bead, increasing the durability of the weld.

[0005] Furthermore, Patent Document 3 discloses a boxing welded joint between a gusset and a main plate, which has a first weld bead extending onto the main plate from both sides of the short side of the gusset along the short side of the gusset, and second and third weld beads extending onto the main plate along the long side of the gusset, covering the first weld bead. This is said to provide a boxing welded joint that can inexpensively and stably improve fatigue strength. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 8-155634 [Patent Document 2] Japanese Patent Application Publication No. 9-253843 [Patent Document 3] JP 2018-158380 A Summary of the Invention [Problem to be solved by the invention]

[0007] The methods described in the above-mentioned patent documents are said to be effective in improving the fatigue strength of welded joints. However, in the case of welded joints in large structures such as offshore wind power generation devices, it has not been clarified whether they are effective in improving the fatigue strength of welded joints in towers, floating bodies, brackets, and the like of floating offshore wind power generation devices, where structural stress concentration is superimposed in addition to local stress concentration.

[0008] Therefore, the inventors have sought a method for improving the fatigue strength of welded joints in floating offshore wind turbines, which suffer from both local and structural stress concentrations, and have found that the fatigue strength can be improved by controlling the shape and arrangement of the weld beads.

[0009] The present invention aims to solve the problems of the prior art by extending a weld bead onto a floating body member in a welded joint of a large structure, for example, a welded joint of a floating offshore wind power generation system including a tower member, a floating body member, and a bracket. The present invention aims to provide a welded joint and a manufacturing method thereof that improves fatigue strength. [Means for solving the problem]

[0010] In order to achieve the above-mentioned object, the inventors first fabricated a simulated structure of a welded joint that simulates an actual structure of a floating offshore wind power generation device. As the welded joint of the simulated structure, a welded joint that was normally fillet welded along the member and a welded joint that had an extended weld bead were fabricated, and fatigue tests were performed. By comparing the fatigue test results, it was found that the fatigue strength of the welded joint with the extended weld bead was improved.

[0011] The present invention was completed based on these findings and through further investigation, and the gist of the present invention is as follows. [1] A welded joint comprising a first member, a second member abutted against a surface of the first member, and a support member in contact with the first member and the second member, the weld joint has a first weld bead, a second weld bead, and a third weld bead; The first weld bead is formed along one short side of a first rectangular abutment surface where the support member abuts against the first member, The second weld bead and the third weld bead are formed along respective long sides of the first rectangular abutment surface, and are formed by covering a portion of either a starting end or a terminal end of the first weld bead and extending onto the first member, forming a welded joint. [2] The welded joint described in [1], wherein M / N, which represents the ratio of the distance M between the tip of the second weld bead and the tip of the third weld bead to the length N of the extension of the second weld bead or the extension of the third weld bead, is 2.0 or less. [3] The welded joint according to [1] or [2], wherein a length N of the extension portion of the second weld bead and the extension portion of the third weld bead is in the range of 4.0 mm to 60.0 mm. [4] The welded joint described in [1] or [2], further comprising a fourth weld bead formed along a long side and a short side of a second rectangular abutment surface where the support member abuts against the second member. [5] The welded joint is used as a welded joint for a floating offshore wind turbine, The welded joint according to [1] or [2], wherein the first member is a floating body member, the second member is a tower member, and the support member is a bracket. [6] A method for manufacturing a welded joint including a first member, a second member abutted against a surface of the first member, and a support member in contact with the first member and the second member, the weld joint has a first weld bead, a second weld bead, and a third weld bead; The first weld bead is formed along one short side of a first rectangular abutment surface where the support member abuts against the first member; A method for manufacturing a welded joint, wherein the second weld bead and the third weld bead are formed along respective long sides of the first rectangular abutment surface, and are extended onto the first member while covering a portion of either a starting end or a terminal end of the first weld bead. [7] The method for manufacturing a welded joint according to [6], wherein M / N, which represents a ratio of a distance M between a tip end of the second weld bead and a tip end of the third weld bead and a length N of the extension of the second weld bead or the extension of the third weld bead, is 2.0 or less. [8] The method for manufacturing a welded joint according to [6] or [7], wherein a length N of the extension portion of the second weld bead and the extension portion of the third weld bead is in the range of 4.0 mm to 60.0 mm. [9] The weld joint further has a fourth weld bead, The method for manufacturing a welded joint described in [6] or [7], wherein a fourth weld bead is formed along the long sides and short sides of a second rectangular abutment surface where the support member abuts against the second member.

[10] The welded joint is used as a welded joint for a floating offshore wind turbine, The method for manufacturing a welded joint described in [6] or [7], wherein the first member is a floating body member, the second member is a tower member, and the support member is a bracket. Effect of the Invention

[0012] According to the present invention, it is possible to provide a welded joint and a manufacturing method thereof that improve fatigue strength in a welded joint portion of a large structure, for example, a welded joint of a floating offshore wind power generation plant including a tower member, a float member, and a bracket, by extending a weld bead onto the float member. Also, the present invention has a remarkable industrial effect. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a perspective view that shows a schematic overall view of a welded joint (simulated structure) of a floating offshore wind turbine according to the present invention. [Diagram 2] 2(a) and 2(b) are schematic diagrams showing an overall image of the welded joint (simulated structure) of FIG. 1, where FIG. 2(a) is a plan view and FIG. 2(b) is a front view. [Diagram 3] FIG. 3 is an enlarged plan view showing a schematic view of a part of the welded joint (simulated structure) of FIG. [Figure 4] 4(a) to 4(d) are schematic diagrams showing an example of the procedure of a method for producing the welded joint (simulated structure) of FIG. [Diagram 5] FIG. 5 is a schematic diagram showing a fixed state in a fatigue test of the welded joint (simulated structure) of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The present invention relates to a welded joint including a first member, a second member butted against a face (e.g., a surface) of the first member, and a support member in contact with the first member and the second member, as shown in Fig. 1 etc., and a manufacturing method thereof. The second member is sandwiched between a pair of support members. The welded joint of the present invention is suitable for use as a welded joint of a floating offshore wind power generation device, for example. Hereinafter, the welded joint of a floating offshore wind power generation device will be described as an example. In this example, the first member is a floating body member 3 described later, the second member is a tower member 2 described later, and the support member is a bracket 4 described later.

[0015] The present invention relates to a welded joint for a floating offshore wind turbine generator, in which fatigue strength is improved by extending a weld bead onto a floating body member, and a manufacturing method thereof.

[0016] Hereinafter, embodiments of the present invention will be described.

[0017] [Floating offshore wind turbines] First, an overview of the floating offshore wind turbine will be given. Wind power generation is a form of renewable energy. Offshore wind turbines installed on the sea can be of the fixed-bottom type or the floating type, with floating offshore wind turbines being used in areas with a depth of 50m or more. A floating offshore wind turbine is structured so that a structure carrying a wind turbine is suspended on the sea by connecting it with chains or the like. The structure is composed of a tower section that holds up and holds the wind turbine (wind turbine generator), and a floating section that floats on the sea with the tower section on it. The tower section and the floating section that serves as the base are joined by welding, and improving the fatigue life of the welded joints is an important issue.

[0018] [Mock structure of welded joints in floating offshore wind turbines] In order to study joint structures that improve the fatigue life of the welded joints of the above-mentioned floating offshore wind power generation equipment, welded joints of a simulated structure that simulates the actual structure of a floating offshore wind power generation equipment were fabricated, and simulation tests were conducted on improving the fatigue life. The simulated structure of the welded joint used here is shown in Figure 1. This welded joint (i.e., simulated structure) 1 has a structure in which a rectangular parallelepiped tower member 2 is placed on a floating body member 3, and two brackets 4 sandwich the tower member 2 from both sides. The joints between each member are mainly fillet welded by gas-shielded arc welding, and weld beads 5 are formed at each boundary.

[0019] The tower member 2 is a rectangular parallelepiped. The shape is not particularly limited, but an example of the simulated structure has a bottom long side (plate width) of 100 mm to 200 mm, a bottom short side (plate thickness) of 50 mm to 60 mm, and a height (plate length) of 250 mm to 400 mm. Examples of the material of the tower member 2 include YP460 and YP355.

[0020] The floating body member 3 is a thick plate. The shape is also not particularly limited, but an example of the simulated structure has a plate width (plate width) of 100 mm to 200 mm, a plate thickness (plate thickness) of 25 mm to 40 mm, and a plate length (plate length) of 800 mm to 1000 mm. The floating body member 3 may be made of the same material as the tower member 2.

[0021] The bracket 4 is a triangular prism with a right-angled bottom, and two side surfaces forming right angles of the triangular prism abut against the tower member 2 and the floating body member 3. FIG. 2(a) is a plan view of the simulated structure 1 as viewed from above. FIG. 2(a) shows a rectangular abutment surface 4a (hereinafter, sometimes referred to as a "first rectangular abutment surface") of the bracket 4 that abuts against the floating body member 3. The shape of the bracket 4 is not particularly limited, but as an example of the simulated structure, for example, the rectangular abutment surface 4a of the bracket 4 has a long side length of 200 mm to 400 mm and a short side length of 30 mm to 40 mm. The material of the bracket 4 is preferably the same as that of the tower member 2 and the floating body member 3.

[0022] [Weld bead 5] As one embodiment, weld bead 5 formed mainly by fillet welding is composed of first weld bead 5a, second weld bead 5b, and third weld bead 5c formed according to a welding procedure described below. It is preferable that weld bead 5 further includes fourth weld bead 5d. The structure is shown in the plan view of Fig. 2(a) and the front view of Fig. 2(b). Fig. 2(a) and Fig. 2(b) show weld bead 5 composed of first to fourth weld beads.

[0023] In Fig. 2(a), the bracket is shown as a rectangular contact surface (first rectangular contact surface) 4a that contacts the floating body member 3. The same applies to Fig. 3 and Fig. 4(a) to Fig. 4(d) described later.

[0024] The welding method is preferably gas shielded arc welding.

[0025] [First weld bead 5a] First weld bead 5a is a weld bead formed along one short side of rectangular contact surface 4a of bracket 4 (see FIG. 4(a) and the like).

[0026] The weld toe of the weld bead (i.e., first weld bead 5a) formed on this short side is the part where localized stress concentration occurs most easily and fatigue cracks are likely to occur. Furthermore, in the case of the floating offshore wind power generation equipment that is the subject of the present invention, fatigue cracks occur more frequently due to the superposition of structural stress concentration from wind power generation in addition to localized stress concentration. In order to suppress the occurrence of fatigue cracks, it is important to form second weld bead 5b and third weld bead 5c, which will be described below, and further extend these weld beads onto the floating body member 3.

[0027] [Second weld bead 5b and third weld bead 5c] The second weld bead 5b is a weld bead formed along one long side of the rectangular contact surface 4a of the bracket 4, covering a part of either the starting end or the ending end of the first weld bead 5a, and extending further onto the floating body member 3 (see FIG. 4(b) and the like). The third weld bead 5c is a weld bead formed along the other long side of the rectangular contact surface 4a, covering a part of either the starting end or the ending end of the first weld bead 5a, and extending further onto the floating body member 3 (see FIG. 4(c) and the like).

[0028] For example, when second weld bead 5b is placed over the starting end of first weld bead 5a, third weld bead 5c is formed to cover the ending end of first weld bead 5a.

[0029] In FIG. 2(a), second weld bead 5b and third weld bead 5c are formed symmetrically from top to bottom, with second weld bead 5b on the upper side of rectangular abutment surface 4a and third weld bead 5c on the lower side, but they may be arranged upside down.

[0030] The above phrase "covering a portion of either the end or start end of the first weld bead" includes not only covering a portion of either the end or start end of the first weld bead, but also overlapping and welding onto a portion of the first weld bead after "covering". As shown in Fig. 2(a) etc., second weld bead 5b and third weld bead 5c are not straight but have a short bead interval to reduce stress concentration on the short sides of the beads.

[0031] [Gap between the tip of the second weld bead and the tip of the third weld bead M] As shown in Fig. 3, the distance between the tip of the second weld bead 5b and the tip of the third weld bead 5c is M. Here, the distance M between the tips is the distance between the opposing weld toes at the tip portions of the second weld bead and the third weld bead, respectively. In order to improve the fatigue strength of the welded joint, it is preferable that the ratio M / N of the distance M to the length N of the extension of the second weld bead or the third weld bead described below is 2.0 or less. If the ratio M / N of the distance M to the length N of the extension exceeds 2.0, fatigue cracks may occur and the fatigue strength may not be improved significantly. It is more preferable that the ratio M / N of the distance M to the length N of the extension is 1.8 or less.

[0032] Furthermore, even when the interval M is 0 mm or less, i.e., when both the tips of the second weld bead and the third weld bead are in contact with each other and when both the weld beads overlap, the effect of improving fatigue strength is seen. For this reason, no lower limit is set for the ratio M / N of the interval M to the length N of the extension portion. In other words, the ratio M / N of the interval M to the length N of the extension portion is preferably 0.0 or more, and more preferably 1.0 or more.

[0033] [Length N of the second weld bead extension and the third weld bead extension] As shown in FIG. 3, the length of the extension of the second weld bead 5b and the extension of the third weld bead 5c is N. The length N of the extension is the length from the weld toe of the first weld bead 5a to the weld end of the tip of the second and third weld beads. The length N is preferably 4.0 mm to 60.0 mm for both the second weld bead 5b and the third weld bead 5c. If it is less than 4.0 mm, the effect of improving the fatigue life is not observed. On the other hand, if it exceeds 60.0 mm, excessive weld bead formation occurs, which leads to an increase in the welding construction cost, and is therefore undesirable. The length N is preferably 10.0 mm or more and 50.0 mm or less.

[0034] [4th weld bead 5d] As shown in Figures 2(a) and 2(b), the fourth weld bead 5d is a weld bead formed along the long and short sides of a rectangular abutment surface (hereinafter sometimes referred to as a "second rectangular abutment surface") where the bracket 4 abuts against the tower member 2, and is a weld bead for joining the entire boundary between the bracket 4 and the tower member 2. Note that welding along the long side of the rectangular abutment surface (second rectangular abutment surface) is vertical welding. To improve the overall strength of the welded joint, it is preferable to provide this fourth weld bead 5d.

[0035] From the viewpoint of more effectively obtaining the above-mentioned effects, it is more preferable that d5 / a4, which represents the ratio of the length a4 of the short side of the first rectangular abutment surface 4a of the bracket 4 to the length d5 ​​of the outer flank in the short side direction of the second rectangular abutment surface of the fourth weld bead 5d, be within a range of 1.2 to 1.5. For example, the length of the long side of the second rectangular abutment surface of the bracket 4 is 100 mm to 300 mm, and the length of the short side of the second rectangular abutment surface is 10 mm to 50 mm.

[0036] [Manufacturing method for welded joints] Next, with regard to the welding method which is a method for producing a welded joint according to the present invention, one embodiment of a specific welding procedure will be described with reference to Figures 4(a) to 4(d). Welding is performed in the order from Figure 4(a).

[0037] First, a second member (here, tower member 2) is butted against the surface of a first member (here, floating body member 3), and a support member (here, bracket 4) is positioned so as to contact the first member and the second member.

[0038] Next, the arranged members are gas-shielded arc-welded together. By welding in the order of (a) to (c), a weld bead of the welded joint of the present invention having the above-mentioned characteristics can be obtained. As described above, when a fourth weld bead is also provided to improve the overall strength of the welded joint, welding (c) can be followed by welding (d). (a) A first weld bead 5a is formed along one short side (the side away from the tower member 2) of the rectangular contact surface 4a where the bracket 4 contacts the floating body member 3 (see FIG. 4(a)). (b) A second weld bead 5b is formed along one long side of the rectangular contact surface 4a, covering the first weld bead 5a and extending onto the floating body member 3 (see FIG. 4(b)). (c) Similarly, a third weld bead 5c is formed along the other long side of the rectangular contact surface 4a, covering the first weld bead 5a and extending further onto the floating body member 3 (see FIG. 4(c)). (d) Furthermore, if necessary, a fourth weld bead 5d is formed along the long and short sides of the rectangular abutment surface where the bracket 4 abuts against the tower member 2. That is, it is formed along the two vertical long sides on both sides of the rectangular abutment surface to the tower member and the upper short side (see FIG. 4(d)).

[0039] Although Figures 4(a) to 4(d) show only one side of the simulated welded joint structure 1, it is preferable to similarly form four weld beads around the bracket on the other side (i.e., the opposite side).

[0040] [Gas shielded arc welding conditions] An example of welding conditions for gas shielded arc welding is shown below. Welding current: 200A~400A, welding voltage: 20V~50V, welding speed: 20cm / min~40cm / min Shielding gas: CO2 gas or Ar gas 80% by volume + CO2 gas 20% by volume mixture Welding wire diameter: 1.0mm~2.0mm EXAMPLES

[0041] The present invention will be further described below with reference to examples. However, the following examples are merely intended to illustrate and explain the present invention in more detail, and are not intended to limit the scope of the present invention.

[0042] First, we produced a welded joint (i.e., a simulated structure) that simulates an actual structure related to the welded joint of a floating offshore wind power generation device. The test material for this purpose was YP470 material with a plate width of 100 mm. The test material was used as the floating body member of the floating offshore wind power generation device, and a tower member and a bracket made of the same material were prepared. Here, the dimensions of the floating body member were 100 mm in plate width, 25 mm in plate thickness, and 800 mm in plate length, the dimensions of the tower member were 100 mm in plate width, 50 mm in plate thickness, and 100 mm in plate length, and the dimensions of the bracket were 200 mm in the long side of the first rectangular abutment surface, 25 mm in the short side of the first rectangular abutment surface, and 250 mm in the long side of the second rectangular abutment surface. These members were fillet welded by gas-shielded arc welding at a current of 230 A, a voltage of 30 V, and a speed of 34 cm / min to produce six types of welded joints. The six types of joints were a normal fillet weld (Joint No. 1) and five types with extended weld beads (Joints No. 2 to No. 6). The Young's modulus and Poisson's ratio, which are the characteristics of the welded joints, were measured in accordance with ASTM E8M "Method of tensile testing for metallic materials." All six types of joints had a Young's modulus E of 206,000 MPa and a Poisson's ratio v of 0.3.

[0043] Fatigue tests on welded joints were carried out by fixing the welded joint specimens in a chuck, which is a fixture of a fatigue testing machine (e.g., a fatigue load testing device), and applying fatigue loads (specifically, tension and compression) to the specimens as indicated by the arrows in the figure, as shown in Figure 5. The applied stress range was 150 MPa in both cases. The number of cycles until fracture was recorded as the fatigue life.

[0044] The results of these tests are shown in Table 1.

[0045] [Table 1]

[0046] Joint No. 1 is a comparative example, and is a test result in which normal fillet welding was performed. Joint No. 2 is a test result in which the weld bead of an example of the present invention is stretched, and the ratio M / N of the extended weld bead spacing M to the length N of the stretched portion is 2.1. Joint No. 3 is a test result in which the weld bead of an example of the present invention is stretched, and the ratio M / N of the extended weld bead spacing M to the length N of the stretched portion is 0.3. Joint No. 4 is a test result in which the weld bead of an example of the present invention is stretched, and the ratio M / N of the extended weld bead spacing M to the length N of the stretched portion is 0.0. Joint No. 5 is a test result in which the weld bead of an example of the present invention is stretched, and the ratio M / N of the extended weld bead spacing M to the length N of the stretched portion is 2.0. In joint No. 6, the weld bead of the example of the present invention is elongated, and the ratio M / N of the elongated weld bead interval M to the length N of the elongated portion is 1.0.

[0047] In addition, all joints from No. 2 onwards were configured with the first to fourth weld beads and tested.

[0048] Regarding the number of fractures, when the ratio M / N of the distance M of the extended weld beads to the length N of the extended portion was 2.1 (Joint No. 2), the fatigue strength was slightly improved compared to the case of normal fillet welding (Joint No. 1). On the other hand, when the ratio M / N of the distance M of the extended weld beads to the length N of the extended portion was 2.0 or less (Joints No. 3 to No. 6), the number of fractures was greater than the number of fractures in the case of normal fillet welding (Joint No. 1). Therefore, the effect of improving the fatigue strength of the welded joint was confirmed by extending the weld beads onto the floating body member. Furthermore, an even greater effect of improving the fatigue strength was confirmed by narrowing the distance M of the extended weld beads and setting the ratio M / N of the distance M of the extended weld beads to the length N of the extended portion to 2.0 or less. [Explanation of symbols]

[0049] 1. Welded joint (simulated structure) 2 Tower components 3 Floating body components 4 Bracket 4a Rectangular contact surface of bracket that contacts the floating member 5 Weld Bead 5a First weld bead 5b Second weld bead 5c 3rd weld bead 5d 4th weld bead 6 Chucking (fixture) of fatigue load test equipment M Distance between the tip of the second weld bead and the tip of the third weld bead (mm) N Length of the extension of the second weld bead and the extension of the third weld bead (mm)

Claims

1. A welded joint comprising a first member, a second member abutted against a surface of the first member, and a support member in contact with the first member and the second member, the weld joint has a first weld bead, a second weld bead, and a third weld bead; The first weld bead is formed along one short side of a first rectangular abutment surface where the support member abuts against the first member, the second weld bead and the third weld bead are formed along respective long sides of the first rectangular abutment surface, and are formed by covering a portion of either a starting end or a terminal end of the first weld bead and extending onto the first member, forming a weld joint.

2. 2. The welded joint according to claim 1, wherein M / N, which represents a ratio of a distance M between a tip of the second weld bead and a tip of the third weld bead to a length N of the extension of the second weld bead or the extension of the third weld bead, is 2.0 or less.

3. 3. The welded joint according to claim 1, wherein a length N of the extension portion of the second weld bead and the extension portion of the third weld bead is in the range of 4.0 mm to 60.0 mm.

4. The welded joint according to claim 1 or 2, further comprising a fourth weld bead formed along a long side and a short side of a second rectangular abutment surface where the support member abuts against the second member.

5. The welded joint is used as a welded joint for a floating offshore wind power generation device, 3. The welded joint of claim 1 or 2, wherein the first member is a floating body member, the second member is a tower member, and the support member is a bracket.

6. A method for manufacturing a welded joint including a first member, a second member abutted against a surface of the first member, and a support member in contact with the first member and the second member, the weld joint has a first weld bead, a second weld bead, and a third weld bead; The first weld bead is formed along one short side of a first rectangular abutment surface where the support member abuts against the first member; a weld joint manufacturing method comprising: forming the second weld bead and the third weld bead along respective long sides of the first rectangular abutment surface, covering a portion of either a starting end or a terminal end of the first weld bead, and extending the second weld bead onto the first member.

7. 7. The method for manufacturing a welded joint according to claim 6, wherein M / N, which represents a ratio of a distance M between a tip end of the second weld bead and a tip end of the third weld bead to a length N of the extension portion of the second weld bead or the extension portion of the third weld bead, is 2.0 or less.

8. The method for manufacturing a welded joint according to claim 6 or 7, wherein a length N of the extension portion of the second weld bead and the extension portion of the third weld bead is in a range of 4.0 mm to 60.0 mm.

9. The weld joint further includes a fourth weld bead, The method for manufacturing a welded joint according to claim 6 or 7, further comprising forming a fourth weld bead along a long side and a short side of a second rectangular abutment surface of the support member that abuts against the second member.

10. The welded joint is used as a welded joint for a floating offshore wind power generation device, The method for manufacturing a welded joint according to claim 6 or 7, wherein the first member is a floating body member, the second member is a tower member, and the support member is a bracket.

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