Multi-layer rotation welding method and multi-layer rotation welding joint

Abstract

Provided are a multi-layer boxing welding method and a multi-layer boxing welded joint for large structures such as floating offshore wind power generation facilities. The present invention is a multi-layer boxing welding method in which a bracket 6 that reinforces a standing plate 5 provided on a steel plate 4 is welded to the steel plate 4 and the standing plate 5, in which a first weld bead 1 is formed in multiple layers along the short side of a rectangular abutment surface 6a where the bracket 6 abuts against the steel plate 4, and then a second weld bead 2 and a third weld bead 3 are placed on the end of the first weld bead along the long side of the rectangular abutment surface 6a and further extended onto the steel plate 4 to form multiple layers.

Description

[Technical Field]

[0001] The present invention relates to a multi-layer box welding method and a multi-layer box welded joint. In particular, the present invention relates to a multi-layer box welding method and a multi-layer box welded joint with a bracket that can improve the fatigue strength of the welded portion between the steel plate and the bracket of a steel structure where stress concentration is high by extending the weld bead. [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 50 meters or deeper. Floating offshore wind turbines have brackets to ensure the strength of their steel structures. However, because these steel structures are exposed to external forces such as wind and waves, there is a problem of reduced fatigue strength at the weld toes of welded joints in the brackets. Therefore, various technologies for improving the fatigue strength of weld toes in welded joints of large structures such as floating offshore wind turbines have been investigated.

[0003] For example, Patent Document 1 discloses a boxing welded joint for a gusset, which has a first weld bead extending from both sides of the short side of the gusset onto the main plate, and second and third weld beads extending along the long side of the gusset, covering the first weld bead, onto the main plate. It is claimed that this welded joint can improve fatigue strength by extending the weld beads.

[0004] The method described in Patent Document 1 is effective in improving the fatigue strength of joints welded in one layer. However, when components such as brackets in floating offshore wind power generation facilities become thicker, multi-layer welding becomes necessary, and Patent Document 1 does not clarify whether the method is effective in improving the fatigue strength of welded joints in such cases. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2018-158380 A Summary of the Invention [Problem to be solved by the invention]

[0006] The above-mentioned multi-layer welded joint has a problem in that the fatigue strength of the multi-layer welded joint is lower than that of a one-layer, one-pass welded joint because the stress concentration at the weld toe is higher than that of a one-layer, one-pass welded joint due to the shape of the weld toe.

[0007] The present invention aims to solve the problems of the prior art and to provide a multi-layer boxing welding method and a multi-layer boxing welded joint that can improve the fatigue strength of the welded joint without reducing it, even when the bracket part is welded in multiple layers in a large structure such as a floating offshore wind power generation facility. [Means for solving the problem]

[0008] Here, conventional examples of multi-layer boxing welded joints for bracket portions in steel structures having brackets are shown in FIGS. 7 and 8. FIG. 8 is a top view of the welded joint shown in FIG. 7. In the conventional example, as shown in the external view of the welded joint in FIG. 7, a standing plate 5 on a steel plate 4 is sandwiched between brackets 6 arranged on both sides of the standing plate 5, and the joint has a weld bead 7 formed by multi-layer box welding. As shown in the plan view of one side of the welded joint in FIG. 8, the welding method involves multi-layer box welding from the joint between the steel plate 4 and the standing plate 5, from one long side of the rectangular abutment surface 6a of the bracket 6, through its short side, around to the other long side, and continuing to the joint between the steel plate 4 and the standing plate 5, thereby forming the multi-layer boxing weld bead 7.

[0009] The present inventors conducted various studies. As a result, they discovered that in a multi-layer welded joint having a bracket, fatigue strength can be improved by extending the multi-layer weld bead on the long side of the rectangular abutment surface 6a beyond the weld bead on the short side of the rectangular abutment surface 6a on the steel plate, as shown in Figure 2, described below, rather than simply performing boxing multi-layer welding. Furthermore, based on this discovery, they investigated an optimal multi-layer welding method.

[0010] The study was conducted on steel structures with brackets. Two types of welded joints were fabricated: one in which a multilayer weld bead was simply welded around the bracket, as shown in Figure 7, and another in which a multilayer weld bead was added around the bracket and extended onto the steel plate, with the length of each extension adjusted, as shown in Figure 1 (described later). Fatigue tests were conducted using these welded joints. The fatigue test results were compared to verify the fatigue strength improvement effect of welded joints with extended multilayer weld beads. As a result, it was found that extending the multilayer weld bead on the steel plate in a bracket for a steel structure improves the fatigue strength of the welded joint. Furthermore, it was found that appropriately adjusting the length of the extension of each layer of the multilayer weld bead consistently improves the fatigue strength of the welded joint.

[0011] The present invention was completed based on these findings and further investigations, and the gist of the present invention is as follows. [1] A multi-layer rotation welding method in which a vertical plate is provided on a steel plate and a bracket reinforcing the vertical plate is welded to the steel plate and the vertical plate, a first weld bead is formed in multiple layers along a short side of a rectangular contact surface where the bracket contacts the steel plate, and then a second weld bead and a third weld bead are placed on the end of the first weld bead along a long side of the rectangular contact surface and extended onto the steel plate to form multiple layers; Rotation multi-layer welding method. [2] The length of the extension of the final layer in the extension of the second weld bead and the third weld bead (N F ) is in the range of 5 mm to 50 mm. [3] When each layer in the extension portion of the second weld bead and the third weld bead is represented as the i-th layer, the length of the extension portion of each layer is N i When the previous layer of each layer is represented as the i-1th layer, the length of the extension part of the previous layer of each layer is N i-1 Then, The difference is expressed as ΔN=N i-1 -N i is in the range of 5 mm to 50 mm, and i is a natural number of 2 to 10. [4] The multi-layer boxing welding method according to any one of [1] to [3], wherein the steel plate is a floating body member of a floating offshore wind power generation facility, and the standing plate is a tower member of the floating offshore wind power generation facility. [5] A welded joint in which a bracket is arranged on a steel plate and sandwiches a vertical plate provided on the steel plate, and the bracket is welded to the steel plate and the vertical plate, a first weld bead is formed in multiple layers along a short side of a rectangular contact surface where the bracket contacts the steel plate, A multi-layer boxing welded joint in which the second weld bead and the third weld bead cover the end of the first weld bead 1 along the long sides of the rectangular abutment surface and extend onto the steel plate 4 to form multiple layers. [6] The length (N F ) is in the range of 5 mm to 50 mm. [7] When each layer in the extension portion of the second weld bead and the third weld bead is represented as the i-th layer, the length of the extension portion of each layer is N i When the previous layer of each layer is represented as the i-1th layer, the length of the extension part of the previous layer of each layer is N i-1 Then, The difference is expressed as ΔN=N i-1 -N i The multi-layer boxing welded joint according to [5] or [6], wherein i is in the range of 5 mm to 50 mm, and i is a natural number of 2 to 10. [8] The boxing multi-layer welded joint according to any one of [5] to [7], wherein the steel plate is a floating body member of a floating offshore wind power generation facility, and the standing plate is a tower member of the floating offshore wind power generation facility. [Effects of the Invention]

[0012] According to the present invention, by extending the multi-layer weld beads in the brackets of a steel structure, it is possible to provide a welding method and a welded joint that can improve fatigue strength compared to a boxing multi-layer welded joint that does not have an extension portion, thereby achieving significant industrial benefits. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a perspective view that schematically shows the appearance of an example of a welded joint obtained by a multi-layer boxing welding method according to the present invention. [Figure 2] FIG. 2 is a plan view schematically showing one side of an example of a welded joint obtained by a multi-layer boxing welding method according to the present invention. [Figure 3] FIG. 3 is a schematic diagram showing the cross-sectional shape of a first weld bead in an example of a welded joint obtained by a multi-layer boxing welding method according to the present invention. [Figure 4] FIG. 4 is a schematic diagram showing the cross-sectional shapes of a second weld bead and a third weld bead in an example of a welded joint obtained by a multi-layer boxing welding method according to the present invention. [Figure 5] FIG. 5 is a plan view that schematically shows a method for measuring the length of each layer of a weld bead extension in a weld joint of the present invention. [Figure 6] FIG. 6 is a plan view schematically showing an example of the procedure of the multi-layer box welding method according to the present invention. [Figure 7] FIG. 7 is a perspective view that schematically shows the appearance of an example of a conventional welded joint obtained by a multi-layer boxing welding method without an extension portion. [Figure 8] FIG. 8 is a plan view schematically showing one side of an example of a conventional welded joint obtained by a multi-layer boxing welding method without an extension portion. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention is directed to a welded joint in which the weld bead is formed in multiple layers in a boxing weld of a steel structure having a vertical plate and a bracket on the steel plate. The present invention provides a welding method in which the multi-layer weld bead on the long side of the rectangular abutment surface where the bracket abuts the steel plate in the multi-layer welded joint extends beyond the short side of the rectangular abutment surface, and the length of each layer is set to a specific condition, thereby improving the fatigue strength of the multi-layer welded joint. An embodiment of the method will be described below with reference to the drawings.

[0015] [Boxing welded joints for steel structures with steel plates, vertical plates, and brackets] First, we will explain a welded joint obtained by the multi-layer boxing welding method according to the present invention. An external perspective view of one example of such a welded joint is shown in Fig. 1. This multi-layer boxing welded joint has a rectangular parallelepiped vertical plate 5 placed on steel plate 4, and two brackets 6 sandwiching vertical plate 5 from both sides. These brackets 6 reinforce vertical plate 5. The joints are joined by multi-layer fillet welding using, for example, gas-shielded arc welding, to form first weld bead 1 through third weld bead 3.

[0016] An example of multi-layer box welding is 3 layers and 6 passes, in which the first layer is welded in 1 pass, the second layer in 2 passes, and the third layer in 3 passes (see Figure 1, etc.). Other examples include 6 layers and 21 passes. There are no particular restrictions on the number of layers or passes, but it is preferable to decide them appropriately depending on the shape and dimensions of the structural member to be welded.

[0017] The present invention is directed to a structure made of thick steel plates, and the thickness (t4) of the steel plate 4 is preferably 25 mm to 50 mm (see FIG. 1). Other shape specifications are not particularly limited. Examples of the material for the steel plate 4 include YP460 and YP355.

[0018] The standing plate 5 is a rectangular parallelepiped. Its plate thickness (t5) is preferably 25 mm to 50 mm (see FIG. 1). Other shape specifications are not particularly limited. The material of the standing plate 5 is preferably the same as that of the steel plate 4.

[0019] Bracket 6 is a triangular prism with a right-angled triangular base, and the two side surfaces that form the right angles of the triangular prism abut against steel plate 4 and vertical plate 5 (see FIG. 1). FIG. 2 is a diagram that schematically illustrates the shape of one side of a welded joint, showing rectangular abutment surfaces 6a of the bracket that abut against steel plate 4 and vertical plate 5, as well as first weld bead 1, second weld bead 2, and third weld bead 3, which will be described later. Regarding the shape of bracket 6 in the welded joint, its plate thickness (t6), i.e., the length of the short side of rectangular abutment surface 6a, is preferably 25 mm to 50 mm (see FIGS. 1 and 2). Furthermore, the material of bracket 6 is preferably the same as that of steel plate 4 and vertical plate 5. The specifications of the shape of an actual steel structure (real structure) are selected as appropriate.

[0020] Weld Bead A multi-layer weld bead, primarily formed by fillet welding, is composed of a first weld bead 1, a second weld bead 2, and a third weld bead 3, which are formed in the order of the welding procedure described below. The outline of the shape is shown in FIGS. 1 and 2. FIG. 2 is a plan view of one side of the steel plate in the external appearance of the welded joint in FIG. 1, showing the bracket 6 as a rectangular abutting surface 6a abutting on the steel plate 4. The shape of the weld bead in fillet welding of such a T-joint has a leg length (width of the weld) in the range of, for example, 18 mm to 35 mm. In the example of FIG. 2, the total width of the weld (leg length) of the third layer, which is the final layer, is calculated by multiplying the width (here, a value in the range of 18 mm to 35 mm) by 3 (passes). In this case, an example of the shape of the vertical plate 5 is one in which the long side of the bottom (plate width) is 100 mm to 200 mm and the height (plate length) is 250 mm to 400 mm. As an example of the shape of the bracket 6, the length of the long side of the rectangular contact surface 6a is 200 mm to 400 mm.

[0021] [First weld bead 1] First weld bead 1 is a weld bead formed on one short side of rectangular contact surface 6a (i.e., the short side not in contact with vertical plate 5). First weld bead 1 is formed along the short side. Here, first weld bead 1 is a general term for multiple multi-layer weld beads, and this "multiple multi-layers" preferably means 2 to 10 layers, more preferably 2 to 6 layers. The first layer is preferably welded in one pass. The second and subsequent layers are formed using multiple passes, with the number of passes preferably being 2 to 30, more preferably 2 to 21. 1 and 6(a) to 6(c), first weld bead 1 is formed in a straight line. The length of first weld bead 1 only needs to be at least the same as the length of the short side of rectangular contact surface 6a.

[0022] The weld toe of the first weld bead 1 formed on the short side is the part where localized stress concentration occurs most and fatigue cracks are likely to occur. Furthermore, as will be described later, in the case of a floating offshore wind power generation facility to which the welding method of the present invention can be applied, fatigue cracks are more likely to occur due to the superposition of structural stress concentration of the wind power generation facility in addition to localized stress concentration.

[0023] In order to suppress the occurrence of such fatigue cracks, it is important that second weld bead 2 and third weld bead 3, which will be described below, extend onto steel plate 4.

[0024] [Second weld bead 2 and third weld bead 3] Second weld bead 2 is a weld bead formed along one long side of rectangular abutment surface 6a of bracket 6, covering a portion of the starting end (or terminal end) of first weld bead 1, and extending onto steel plate 4. Third weld bead 3 is a weld bead formed along the other long side of rectangular abutment surface 6a, covering a portion of the terminal end (or starting end) of first weld bead 1, and extending onto steel plate 4. Here, second weld bead 2 and third weld bead 3 are each collectively referred to as multi-layer beads formed from multiple welds. The number of layers and passes of the multiple layers is preferably the same as those of first weld bead 1 described above. As shown in (d) to (i) of FIG. 1 and FIG. 6, second weld bead 2 and third weld bead 3 are formed in a linear stepped shape.

[0025] 2, second weld bead 2 and third weld bead 3 are formed symmetrically in the up-down direction. Although second weld bead 2 is above rectangular contact surface 6a and third weld bead 3 is below rectangular contact surface 6a, they may be arranged upside down.

[0026] In order to improve the fatigue strength of multi-layer welded joints, it is important to appropriately adjust the length of each layer in the extension portion shape of the multi-layer, that is, the extension portion 2a of the second weld bead 2 and the extension portion 3a of the third weld bead 3.

[0027] [Multi-layer shape of weld bead] Next, the multi-layer shape of a weld bead will be described with reference to Figs. 3 and 4, which show the shape of a weld bead formed by three layers and six passes as one embodiment of a multi-layer weld joint.

[0028] Fig. 3 shows the three-layer, six-pass cross-sectional structure of first weld bead 1 in a cross section parallel to the long sides of rectangular abutment surface 6a of bracket 6 and perpendicular to the short sides. Fig. 4 shows the three-layer, six-pass cross-sectional structures of second weld bead 2 and third weld bead 3 in a cross section parallel to the short sides of rectangular abutment surface 6a of bracket 6 and perpendicular to the long sides. That is, Fig. 3 is a cross-sectional view taken along line AA in Fig. 2, and Fig. 4 is a cross-sectional view taken along line BB in Fig. 2.

[0029] 3, the number of passes in the first layer of first weld bead 1 is 1. This first layer (corresponding to 1-1-1 in the figure. Hereinafter, the bead, layer, and pass in the figure will be referred to as "bead-layer-pass") is formed on steel plate 4 along one short side of rectangular contact surface 6a of bracket 6 (i.e., the short side on the side not in contact with upright plate 5).

[0030] Next, the number of passes for the second layer of first weld bead 1 is two. The first pass (1-2-1) of this second layer is formed on steel plate 4 along the first layer (1-1-1) described above, and the second pass (1-2-2) is formed between bracket 6 and the first pass (1-2-1) of the second layer.

[0031] The third layer of first weld bead 1 has three passes. The first pass (1-3-1) of this third layer is formed on steel plate 4 along the first pass (1-2-1) of the second layer, and the next second pass (1-3-2) is formed along the previous first pass (1-3-1) of the third layer. The final third pass (1-3-3) is formed between bracket 6 and the second pass (1-3-2) of the third layer.

[0032] Next, as shown in Fig. 4, the number of passes in the first layer of second weld bead 2 is one. This first layer (corresponding to 2-1-1 in the figure. Hereinafter, the bead, layer, and pass in the figure will be referred to as "bead-layer-pass") of second weld bead 2 is formed on steel plate 4 along the long side of one side of rectangular contact surface 6a of bracket 6 (i.e., the left side of bracket 6 in Fig. 4). Furthermore, the number of passes in the first layer of third weld bead 3 is one. This first layer (3-1-1) of third weld bead 3 is formed on steel plate 4 along the long side of the other side of rectangular contact surface 6a of bracket 6 (i.e., the right side of bracket 6 in Fig. 4).

[0033] Next, the number of passes for the second layers of second weld bead 2 and third weld bead 3 is two each. The first pass (2-2-1) of this second layer of second weld bead 2 is formed on steel plate 4 along the first layer (2-1-1) described above, and the second pass (2-2-2) is formed between bracket 6 and the second layer first pass (2-2-1). Furthermore, the first pass (3-2-1) of the second layer of third weld bead 3 is formed on steel plate 4 along the first layer (3-1-1) described above, and the second pass (3-2-2) is formed between bracket 6 and the second layer first pass (3-2-1).

[0034] Furthermore, the number of passes for the third layers of the second weld bead 2 and the third weld bead 3 is three. The first pass (2-3-1) of the third layer of the second weld bead 2 is formed on the steel plate 4 along the first pass (2-2-1) of the second layer, and the next second pass (2-3-2) is formed along the previous first pass (2-3-1) of the third layer. The final third pass (2-3-3) is formed between the bracket 6 and the second pass (2-3-2) of the third layer. The third layer of the third weld bead 3 is formed on the steel plate 4 along the first pass (3-2-1) of the second layer, and the next second pass (3-3-2) is formed along the previous first pass (3-3-1) of the third layer. The final third pass (3-3-3) is formed between the bracket 6 and the second pass of the third layer (3-3-2).

[0035] [Adjusting the extension length] Here, as the shape of the multi-layer weld bead, it is preferable to adjust the length of the extension portion in each layer (hereinafter also referred to as "extension portion length") as follows.

[0036] The shape of the extension portion that is preferable for improving the fatigue strength of the multi-layer welded joint is determined by first determining the length (N F The final layer's extension length N F If the thickness is less than 5 mm, the fatigue strength cannot be improved. F If the welding distance exceeds 50 mm, the welding cost increases, which is not preferable. F More preferably, N F is 20mm to 30mm. The length of the extension portion of the final layer of the second weld bead 2 and the length of the extension portion of the final layer of the third weld bead 3 can be changed for each weld bead, but it is preferable to make them the same length to prevent the welding process from becoming complicated.

[0037] Next, the extension length of each layer (each layer is represented by the i-th layer) in the extension portion of the second weld bead 2 and the third weld bead 3 is determined as N i The length of the extension part of the previous layer of each layer (the previous layer of each layer is represented as the i-1th layer) is N i-1 Then, the difference is expressed as ΔN=N i-1 -N i is preferably in the range of 5 mm to 50 mm, where i is a natural number from 2 to 10.

[0038] If i exceeds 10, the construction becomes complicated and costs increase, which is undesirable. If this difference ΔN is less than 5 mm, it becomes difficult to distribute the stress flowing into bracket 6 to the extended weld bead, which results in insufficient improvement in fatigue properties, which is undesirable. Furthermore, if the difference ΔN exceeds 50 mm, the welding construction costs increase, which is undesirable. More preferably, the difference ΔN is 10 mm to 40 mm. Even more preferably, the difference ΔN is 20 mm to 30 mm. Note that the difference ΔN between each layer can be changed for each layer, but to prevent the welding construction from becoming complicated, it is preferable that the difference be the same for each layer. Furthermore, the difference ΔN between each layer of second weld bead 2 and the difference ΔN between each layer of third weld bead 3 can be changed for each weld bead, but to prevent the welding construction from becoming complicated, it is preferable that both be the same length. Since the present invention is a technology relating to multi-layer box welding, i is 2 or more.

[0039] Here, the length of the extension part of each layer N i The length N of the extension of the final layer is the distance from the widthwise end of the first weld bead 1 formed on the short side of the rectangular abutment surface 6a of the bracket 6 in the direction of the extension of the second weld bead 2 and the third weld bead 3 to the tip of the extension of each layer. F The difference ΔN between each layer can be determined by measuring the shape (length) of the extension of each layer after the weld bead is formed using a vernier caliper, as shown in the example of weld bead formation by three layers and six passes in Figure 5.

[0040] Next, a specific example of the three-layer welding described above, that is, when i=3, will be described. The extension length N3 of the third layer, which is the final layer, is N F If the difference ΔN between layers is set to 10 mm, the extension length N2 of the second layer should be set to 30 mm, and the extension length N1 of the first layer should be set to 40 mm. F By setting the difference ΔN in the length of the extension part between each layer and ΔN, the length of the extension part from the first layer is automatically determined. As explained above, by forming the extension part in multiple layers, it is possible to improve fatigue strength.

[0041] [Rotation welding method] Next, the multi-layer boxing welding method for a steel structure having a bracket according to the present invention will be described with reference to Fig. 6, which shows one embodiment of the procedure. Welding is carried out in order from (a) in Fig. 6.

[0042] In this example, first, a standing plate (not shown) is placed on the top surface of the steel plate 4, and then the standing plate is sandwiched between two brackets on both sides. The brackets are placed so as to be in contact with the steel plate 4 and the standing plate. Note that Fig. 6 shows only one side of the steel plate, with one bracket shown, and also shows the rectangular contact surface 6a of the bracket for ease of explanation.

[0043] Next, the arranged members are gas-shielded arc-welded. Note that, by welding in the following order (a) to (i), a multi-layer boxing weld bead in the weld joint of the present invention having the above-mentioned properties can be obtained. (a) The first layer of the first weld bead 1 is formed in one pass (1-1-1) along one short side (in this example, the side away from the vertical plate) of the rectangular contact surface 6a where the bracket contacts the steel plate 4 (see (a) in Figure 6). (b) The first layer is covered with the first pass (1-2-1) and the second pass (1-2-2) of the second layer of the first weld bead 1 (see (b) in Figure 6). (c) Furthermore, the first pass (1-3-1), second pass (1-3-2), and third pass (1-3-3) of the third layer of the first weld bead 1 are formed by covering the second layer (see (c) in Figure 6). (d) Next, the first layer of the second weld bead 2 is formed in one pass (2-1-1) along one long side of the rectangular abutment surface 6a of the bracket, covering one end of the first weld bead 1. The extension length N1 of this first layer in one pass (2-1-1) is determined by subtracting the extension length N of the set final layer (the third layer in this example) from the extension length N of the set final layer, as explained above with reference to FIG. F The length is set to the sum of the two differences ΔN (see (d) in FIG. 6). (e) The first pass (2-2-1) and second pass (2-2-2) of the second layer of the second weld bead 2 are formed by covering the first layer of the second weld bead 2. The extension length N2 of this second layer is equal to the extension length N of the final layer. F The difference ΔN is added to the length (see (e) in FIG. 6). (f) Then, the first pass (2-3-1), second pass (2-3-2), and third pass (2-3-3) of the third layer of the second weld bead 2 are formed on the second layer to form the final layer. The extension length N3 here is the same as the initially set N F (See (f) in Figure 6). (g) to (i) Finally, the third weld bead 3 is formed from the first layer, first pass (3-1-1) to the third layer, third pass (3-3-3) along the other long side of the bracket's rectangular abutment surface 6a (see (g) to (i) in Figure 6). The formation methods for these layers and passes are the same as the formation methods (d) to (f) above.

[0044] In this manner, a multi-layer weld bead extending along both long sides of the rectangular contact surface 6a of the bracket can be formed on the steel plate 4.

[0045] Although FIG. 6 mainly shows the area around the bracket on one side of the welded joint, it is preferable to similarly form multi-layer weld beads around the bracket on the other side (opposite side). Furthermore, the joint between the steel plate and the vertical plate can be multi-layer welded. After multi-layer welding of the two steel plate and vertical plate locations, the bracket is multi-layer welded using the procedure described above.

[0046] [Welding conditions] From the viewpoint of welding efficiency, gas-shielded arc welding is preferable for the welding. 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: 100% CO2 gas by volume or a mixture of CO2 and Ar gas (An example of the mixture ratio of the mixed gas is 20% by volume of CO2 gas + 80% by volume of Ar gas.) Welding wire diameter: 1.2mm~2.4mm

[0047] [Welded joints in floating offshore wind turbines] The multi-layer rotary welding method according to the present invention can also be applied to welded joints in floating offshore wind power plants. Here, an overview of floating offshore wind power plants will be described. Wind power generation is a form of renewable energy. Offshore wind power plants installed on the sea are classified into bottom-mounted and floating types, and floating offshore wind power plants are used in waters with a depth of 50 meters or more. A floating offshore wind power plant is structured by floating a structure carrying a wind turbine, connected by chains or the like. The structure is composed of a tower section that holds the wind turbine (wind power generator) aloft and a floating body section that floats on the sea and carries the tower section. The tower section and the floating body section, which serves as the base, are joined by welding, and improving the fatigue life of the welded joint is an important issue.

[0048] Therefore, when the present invention is applied to such a floating offshore wind power generation facility, the above-mentioned steel plate 4 serves as a floating body member of the floating offshore wind power generation facility, and the standing plate 5 serves as a tower member of the floating offshore wind power generation facility, and the boxing multi-layer welding method of the present invention is carried out. In other words, by extending the multi-layer weld beads onto the floating body member and further by appropriately adjusting the length of the extension part of each layer as described above, a multi-layer welded joint with improved fatigue strength can be obtained. [Example]

[0049] 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.

[0050] First, a 100 mm wide YP460 sheet was used as the test material. The test material was multi-layer welded by gas-shielded arc welding using a gas containing 100% CO2 by volume at a welding current of 230 A, a welding voltage of 30 V, and a welding speed of 34 cm / min to produce a welded joint. The welded joints produced were a multi-layer boxing welded joint with no extensions in the weld bead as shown in Figures 7 and 8, and a welded joint with a multi-layer weld bead having an extension according to the present invention as shown in Figures 1 and 2.

[0051] Note that the values ​​in the "Number of welding layers and passes" column in Table 1 are the welding conditions for the weld beads formed on the periphery of rectangular contact surface 6a of bracket 6 shown in Figures 7 and 8 for joints No. 1 and 2. Also, for joints Nos. 3 to 19, these are the welding conditions for all of first weld bead 1 to third weld bead 3 shown in Figures 1 and 2.

[0052] Fatigue tests of welded joints were carried out by fixing the welded joint in a chuck, which is a fixture of the fatigue testing machine, and applying fatigue loads (specifically, tension and compression) to the welded joint. The applied stress range was 100 MPa in all cases. The number of cycles until fracture was counted as the fatigue life.

[0053] The fatigue test results of these welded joints are shown in Table 1.

[0054] [Table 1]

[0055] Joints No. 1 and No. 2 are comparative examples showing the test results of simple multi-layer box welding without any extensions.

[0056] Joints No. 3 and No. 4 are examples of the present invention in which the weld beads are extended by multi-layer box welding, but the extension length of the final layer is N F The test results are for a difference ΔN of 5 mm between the lengths of the extensions of each layer and 4 mm.

[0057] Joints No. 5 and No. 6 are examples of the present invention in which the weld beads are extended by multi-layer box welding, but the extension length of the final layer is N F The test results are for a difference ΔN of 4 mm between the lengths of the extensions of each layer.

[0058] Joints No. 7 to No. 19 are also examples of the present invention in which the weld bead is extended by multi-layer box welding, and the extension length of the final layer is N F The test results show that the difference ΔN in the length of the stretched portion of each layer is also in the preferred range of 5 mm to 50 mm.

[0059] The number of breaks was as follows: Length of the stretched part of the final layer N F In the case of welded joints (i.e., joints No. 7 to No. 19) in which the difference ΔN between the extension lengths of the layers was in the preferred range of 5 mm to 50 mm, the number of fractures was greater than in the case of multi-layer welded joints without extensions (i.e., joints No. 1 and No. 2). On the other hand, when the extension length N of the final layer was F Alternatively, when the difference ΔN in the extension length of each layer was smaller than 5 mm (i.e., joints Nos. 3 to 6), the number of fractures was greater than in the case of multi-layer welding without extensions (i.e., joints Nos. 1 and 2). However, the number of fractures was not as great as when the difference ΔN was in the preferred range of 5 mm or more.

[0060] From the above, the extension length of the final layer N F The fatigue strength of the welded joint was improved by controlling the difference ΔN between the extension lengths of each layer. [Explanation of symbols]

[0061] 1 First weld bead 2 Second weld bead 2a Extension of second weld bead 3 Third weld bead 3a Extension of the third weld bead 4 steel plate 5 standing board 6 Bracket 6a Rectangular contact surface that contacts the steel plate of the bracket (i.e., bracket rectangular contact surface) 7 Multi-layer turn weld bead N F Length of the final layer extension of the second and third weld beads (unit: mm) N i Length of extension of each layer (ith layer) in the extension of the second weld bead and the third weld bead (unit: mm) ΔN The difference in the extension length between each layer (i-th layer) and its previous layer (i-1 layer) (i.e., N i-1 -N i ) Thickness of t4 steel plate (mm) T5 vertical plate thickness (mm) t6 Bracket thickness (i.e., the length of the short side of the bracket's rectangular contact surface) (unit: mm)

Claims

1. A multi-layer boxing welding method in which a vertical plate is provided on a steel plate, and a bracket for reinforcing the vertical plate is welded to the steel plate and the vertical plate, forming a first weld bead in multiple layers along a short side of a rectangular contact surface of the bracket that contacts the steel plate; Then, a second weld bead and a third weld bead are placed on the end of the first weld bead along the long sides of the rectangular abutment surface and extended onto the steel plate to form multiple layers. Rotation multi-layer welding method.

2. The length (N) of the extension of the final layer in the extension of the second weld bead and the third weld bead F 2. The multi-layer welding method according to claim 1, wherein the welding length is in the range of 5 mm to 50 mm.

3. When each layer in the extension portion of the second weld bead and the third weld bead is represented as the i-th layer, the length of the extension portion of each layer is represented as N i When the previous layer of each layer is represented as the (i-1)th layer, the length of the stretched portion of the previous layer of each layer is represented as N i-1 Then, The difference is expressed as ΔN=N i-1 -N i The multi-layer turning welding method according to claim 1 or 2, wherein i is in the range of 5 mm to 50 mm, and i is a natural number from 2 to 10.

4. 3. The multi-layer boxing welding method according to claim 1, wherein the steel plate is a floating body member of a floating offshore wind power generation facility, and the standing plate is a tower member of the floating offshore wind power generation facility.

5. A multi-layer rotary welding method as described in claim 3, wherein the steel plate is a floating member of a floating offshore wind power generation facility and the standing plate is a tower member of the floating offshore wind power generation facility.

6. A welded joint formed by welding a bracket disposed on a steel plate across a vertical plate provided on the steel plate to the steel plate and the vertical plate, a first weld bead is formed in multiple layers along a short side of a rectangular contact surface of the bracket that contacts the steel plate, a second weld bead and a third weld bead are formed in multiple layers along the long sides of the rectangular abutment surface, covering the end of the first weld bead and extending onto the steel plate; Multi-layer welded joint.

7. The length (N) of the extension of the final layer in the extension of the second weld bead and the third weld bead F 7. The boxing multi-layer welded joint according to claim 6, wherein the distance between the welded joint and the outer periphery of the welded joint is in the range of 5 mm to 50 mm.

8. When each layer in the extension portion of the second weld bead and the third weld bead is represented as the i-th layer, the length of the extension portion of each layer is represented as N i When the previous layer of each layer is represented as the (i-1)th layer, the length of the stretched portion of the previous layer of each layer is represented as N i-1 Then, The difference is expressed as ΔN=N i-1 -N i The boxing multi-layer welded joint according to claim 6 or 7, wherein i is in the range of 5 mm to 50 mm, and i is a natural number from 2 to 10.

9. The boxing multi-layer welded joint according to claim 6 or 7, wherein the steel plate is a floating body member of a floating offshore wind power generation facility, and the standing plate is a tower member of the floating offshore wind power generation facility.

10. A multi-layer turn welded joint as described in Claim 8, wherein the steel plate is a floating member of a floating offshore wind power generation facility and the standing plate is a tower member of the floating offshore wind power generation facility.

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