Turning multi-layer welding method and turning multi-layer welded joint

Abstract

Provided are a turning multi-layer welding method and a turning multi-layer welded joint in a large structure such as a floating offshore wind power generation facility. The present invention provides a turning multi-layer welding method in which a bracket 6 for reinforcing a standing plate 5 provided on a steel plate 4 is welded to the steel plate 4 and the standing plate 5, the welding method including forming a first welding bead 1 in multiple layers along the short side of a rectangular abutment surface 6a where the bracket 6 abuts the steel plate 4, subsequently placing a second welding bead 2 and a third welding bead 3 on the end section of the first welding bead 1 along the long side of the rectangular abutment surface 6a, and furthermore stretching the second welding bead 2 and the third welding bead 3 onto the steel plate 4 to form said welding beads in multiple layers.

Description

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

[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.

[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 a joint welded in one layer. However, when components such as brackets in a floating offshore wind power generation facility 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.

[0005] JP 2018-158380 A

[0006] The above-described 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.

[0008] Here, conventional examples of multi-layer boxing welded joints for bracket portions in steel structures having brackets are shown in Figures 7 and 8. Figure 8 is a top view of the welded joint shown in Figure 7. In the conventional example, as shown in the external view of the welded joint in Figure 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 half-side plan view of the welded joint in Figure 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 have conducted various studies. As a result, they have found 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 by simply performing boxing multi-layer welding. Furthermore, based on this finding, they have studied an optimal multi-layer welding method.

[0010] The study was conducted on steel structures having brackets. Two types of welded joints were fabricated: one in which a multilayer weld bead was simply welded around the periphery of a bracket, as shown in the example of 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 the example of Figure 1 (described later). Fatigue tests were then 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 stably improves the fatigue strength of the welded joint.

[0011] The present invention was completed based on these findings and further studies, and the gist of the present invention is as follows: [1] A boxing multi-layer welding method in which a standing plate is provided on a steel plate and a bracket reinforcing the standing plate is welded to the steel plate and the standing plate, the boxing multi-layer welding method including: forming a first weld bead in multiple layers along a short side of a rectangular abutment surface where the bracket abuts against the steel plate; and then covering an end of the first weld bead along a long side of the rectangular abutment surface and extending it onto the steel plate to form multiple layers. [2] A boxing multi-layer welding method in which the length (N of the extension portion of the final layer of the extension portion of the second weld bead and the third weld bead) is determined. F [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-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 ΔN = N i-1 -N iis in the range of 5 mm to 50 mm, and i is a natural number from 2 to 10. [4] The boxing multi-layer 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 boxing multi-layer welded joint formed by welding a standing plate provided on a steel plate to a bracket arranged on either side of the standing plate to the steel plate, wherein a first weld bead is formed in multiple layers along a short side of a rectangular abutment surface where the bracket abuts against the steel plate, and a second weld bead and a third weld bead are formed in multiple layers along a long side of the rectangular abutment surface, covering an end of the first weld bead 1 and extending onto the steel plate 4. [6] A boxing multi-layer welded joint formed by covering an end of the first weld bead 1 along a long side of the rectangular abutment surface to extend onto the steel plate 4. F [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-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 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. [8] The boxing multi-layer welded joint according to any one of [5] to [7], wherein the steel plate is a float 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.

[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.

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

[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 Joint of Steel Structure Having Steel Plate, Vertical Plate, and Bracket] First, a welded joint obtained by the multi-layer boxing welding method according to the present invention will be described. An external perspective view of an 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 a steel plate 4, and two brackets 6 sandwich the vertical plate 5 from both sides. The brackets 6 reinforce the vertical plate 5. The joint is formed by multi-layer fillet welding using, for example, gas-shielded arc welding, to form first weld beads 1 to third weld beads 3.

[0016] An example of multi-layer box welding is three layers and six passes, in which the first layer is welded in one pass, the second layer in two passes, and the third layer in three passes (see Figure 1, etc.). Other examples include six layers and 21 passes. There are no particular restrictions on the number of layers or passes, but it is preferable to determine them appropriately depending on the shape, dimensions, etc. 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 of the steel plate 4 include YP460 and YP355.

[0018] The standing plate 5 is a rectangular parallelepiped. Its 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] The 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 the steel plate 4 and the vertical plate 5 (see FIG. 1). FIG. 2 is a diagram schematically illustrating the shape of one side of the welded joint, showing the rectangular abutment surface 6a of the bracket that abuts against the steel plate 4 and the vertical plate 5, as well as the first weld bead 1, second weld bead 2, and third weld bead 3 described below. Regarding the shape of the bracket 6 in the welded joint, its plate thickness (t6), i.e., the length of the short side of the rectangular abutment surface 6a, is preferably 25 mm to 50 mm (see FIGS. 1 and 2). The material of the bracket 6 is also preferably the same as that of the steel plate 4 and the vertical plate 5. The dimensions of the shape of an actual steel structure (actual structure) are selected as appropriate.

[0020] [Weld Bead] A multi-layer weld bead formed primarily by fillet welding consists of a first weld bead 1, a second weld bead 2, and a third weld bead 3, each of which is formed in the order described below by the welding method. The shape of the weld bead is generally shown in FIGS. 1 and 2. FIG. 2 is a plan view of one steel plate in the external appearance of the welded joint shown 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) ranging from 18 mm to 35 mm, for example. In the example shown in 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 ranging from 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 surface (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] The first weld bead 1 is a weld bead formed on one short side of the rectangular contact surface 6a (i.e., the short side not in contact with the vertical plate 5). The first weld bead 1 is formed along the short side. Here, the term "first weld bead 1" refers collectively to a weld bead having multiple layers. This "multiple layers" preferably refers to a range of 2 to 10 layers, more preferably a range of 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 ranging from 2 to 30, more preferably ranging from 2 to 21. The first weld bead 1 is formed linearly, as shown in FIGS. 1 and 6(a) to 6(c). The length of the first weld bead 1 need only be equal to the length of the short side of the 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 the second weld bead 2 and the third weld bead 3 described below extend onto the steel plate 4 .

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

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

[0026] In order to improve the fatigue strength of a multi-layer welded joint, it is important to appropriately adjust the length of each layer in the extension portion shape of the multi-layer, i.e., 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 a weld bead shape 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 contact 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 contact surface 6a of bracket 6 and perpendicular to the long sides. That is, Fig. 3 is a cross-sectional view taken along line A-A in Fig. 2, and Fig. 4 is a cross-sectional view taken along line B-B 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), 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 number of passes for the third layer of first weld bead 1 is three. 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 for each. The first pass (2-2-1) of the second layer of second weld bead 2 is formed on steel plate 4 along the first layer (2-1-1), and the second pass (2-2-2) is formed between bracket 6 and the first pass (2-2-1) of the second layer. 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), and the second pass (3-2-2) is formed between bracket 6 and the first pass (3-2-1) of the second layer.

[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 first pass (3-3-1) of 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] [Adjustment of Length of Extension Portion] Here, as a shape of a 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 ) in the range of 5 mm to 50 mm (see Figures 2 and 5). F If the thickness is less than 5 mm, the effect of improving fatigue strength cannot be obtained. F If the welding length exceeds 50 mm, the welding cost increases, which is not preferable. F is 10 mm to 40 mm. F The length of the extension portion of the final layer of second weld bead 2 and the length of the extension portion of the final layer of 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 procedure 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 layer before each layer (the layer before each layer is represented as the (i-1)th layer) is N i-1 Then, the difference 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 the bracket 6 to the extended weld bead, resulting 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. While the difference ΔN between each layer can be changed for each layer, it is preferable to set the difference to the same for each layer to prevent the welding construction from becoming complicated. Furthermore, the difference ΔN between each layer of the second weld bead 2 and the difference ΔN between each layer of the third weld bead 3 can be changed for each weld bead, but it is preferable to set both to the same length to prevent the welding construction from becoming complicated. Since the present invention is a technology related to multi-layer box welding, i is 2 or greater.

[0039] Here, the length N of the extension part of each layer i The term "length N" refers to the distance from the widthwise end of first weld bead 1 formed on the short side of rectangular abutment surface 6a of bracket 6 in the direction of extension of second weld bead 2 and 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, i.e., when i=3, will be described. The extension length N3 of the third layer, which is the final layer, is N F When the difference ΔN between layers is set to 10 mm, the extension length N2 of the second layer is set to 30 mm, and the extension length N1 of the first layer is set to 40 mm. F By setting the difference ΔN in the length of the extension portion between each layer and the extension portion length between the first and second layers, the length of the extension portion from the first layer is automatically determined. As explained above, by forming the extension portion in multiple layers, the fatigue strength can be improved.

[0041] [Box Welding Method] Next, a multi-layer box 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 performed in order from (a) in Fig. 6.

[0042] In this example, a vertical plate (not shown) is first placed on the top surface of the steel plate 4, and the vertical 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 vertical 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 the sake of explanation.

[0043] Next, the arranged components are gas-shielded arc-welded. Note that a multi-layer boxed weld bead for the welded joint of the present invention, having the above-described characteristics, can be obtained by welding in the following order (a) to (i). (a) A 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 farther from the vertical plate) of the rectangular contact surface 6a where the bracket contacts the steel plate 4 (see (a) in FIG. 6 ). (b) A first pass (1-2-1) and a second pass (1-2-2) of the second layer of the first weld bead 1 are formed over the first layer (see (b) in FIG. 6 ). (c) A first pass (1-3-1), a second pass (1-3-2), and a third pass (1-3-3) of the third layer of the first weld bead 1 are formed over the second layer (see (c) in FIG. 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 dividing the extension length N1 of the set final layer (the third layer in this example) by the extension length N1 of the set final layer (the third layer in this example) as explained above with reference to FIG. F (e) The first pass (2-2-1) and the second pass (2-2-2) of the second layer of second weld bead 2 are formed by covering the first layer of second weld bead 2. The extension length N2 of this second layer is set to be equal to the extension length N of the final layer. F(f) Then, the first pass (2-3-1), second pass (2-3-2), and third pass (2-3-3) of the third layer of second weld bead 2, which is the final layer, are formed over the second layer. The extension length N3 here is the initially set N F (See (f) in FIG. 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 FIG. 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] While Figure 6 mainly shows the area around the bracket on one side of the welded joint, it is preferable to similarly form a multi-layer weld bead around the bracket on the other side (opposite side). Furthermore, the joint between the steel plate and the vertical plate may be multi-layer welded. After multi-layer welding of the two steel plate / vertical plate locations, the bracket is multi-layer welded using the procedure described above.

[0046] [Welding conditions] From the viewpoint of welding efficiency, it is preferable to use gas-shielded arc welding. An example of welding conditions for gas-shielded arc welding is shown below. Welding current: 200 A to 400 A, welding voltage: 20 V to 50 V, welding speed: 20 cm / min to 40 cm / min Shielding gas: 100% CO2 gas by volume or a mixture of CO2 gas and Ar gas (An example of the mixture ratio of the mixed gas is a mixture of 20% CO2 gas by volume and 80% Ar gas by volume.) Welding wire diameter: 1.2 mm to 2.4 mm

[0047] [Welded Joints in Floating Offshore Wind Power Plants] The rotary multi-layer 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-fixed and floating types, and floating offshore wind power plants are used in waters with a depth of 50 meters or more. Floating offshore wind power plants are structured by floating a structure carrying wind turbines on the sea, connected by chains or the like. The structure is composed of a tower section that holds the wind turbines (wind power generators) 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 joints is an important issue.

[0048] Therefore, when the present invention is applied to such a floating offshore wind power generation facility, the multi-layer boxing welding method of the present invention is carried out with the steel plate 4 as the float member of the floating offshore wind power generation facility and the standing plate 5 as the tower member of the floating offshore wind power generation facility. In other words, by extending the multi-layer weld beads onto the float 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.

[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 steel plate was used as the test material. The test material was multi-layer welded by gas-shielded arc welding using a gas containing 100% CO gas at a welding current of 230 A, a welding voltage of 30 V, and a welding speed of 34 cm / min to produce welded joints. 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, for joints Nos. 1 and 2, 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 abutment surface 6a of bracket 6 shown in Figures 7 and 8. For joints Nos. 3 to 19, the values ​​are the welding conditions for all of first weld bead 1 to third weld bead 3 shown in Figures 1 and 2.

[0052] The fatigue tests of the welded joints were carried out by fixing the welded joints in a chuck, which is a fixture of the fatigue testing machine, and applying fatigue loads (specifically, tension and compression) to the welded joints. 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]

[0055] Joints No. 1 and No. 2 are comparative examples showing test results of simple multi-layer box welding without an extension portion.

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

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

[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 N of the final layer is F The test results showed that the difference ΔN in the length of the stretched portion of each layer was also in the preferred range of 5 mm to 50 mm.

[0059] The number of breaks was as follows: Length of the stretched portion of the final layer N FIn the case of welded joints (i.e., joints No. 7 to 19) in which the difference ΔN between the lengths of the extensions 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 welded joints by multi-layer welding without extensions (i.e., joints No. 1 and 2). On the other hand, when the extension length N of the final layer was F Alternatively, when the difference ΔN in the lengths of the extension portions of the layers 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 extension portions (i.e., joints Nos. 1 and 2). However, the number of fractures was not as great as in the above-mentioned preferable range of 5 mm or more.

[0060] From the above, the length of the extension part of the final layer N F By controlling the difference ΔN between the lengths of the extensions of the layers, the fatigue strength of the welded joint was improved.

[0061] 1 First weld bead 2 Second weld bead 2a Extension of second weld bead 3 Third weld bead 3a Extension of third weld bead 4 Steel plate 5 Standing plate 6 Bracket 6a Rectangular abutment surface of bracket abutting against steel plate (i.e. bracket rectangular abutment surface) 7 Multi-layer box weld bead N F Length of the extension of the final layer in the extension of the second weld bead and the third weld bead (unit: mm) N i The extension length of each layer (i-th layer) in the extension portions 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-th layer) (i.e., N i-1 -N i ) t4 Thickness of steel plate (mm) t5 Thickness of vertical plate (mm) t6 Thickness of bracket (i.e., length of the short side of the bracket rectangular contact surface) (unit: mm)

Claims

1. A multi-layer rotary welding method in which a vertical plate is placed on a steel plate and a bracket reinforcing the vertical plate is welded to the steel plate and the vertical plate, the method comprising: forming a first weld bead in multiple layers along the short side of a rectangular contact surface where the bracket contacts the steel plate; and then covering the end of the first weld bead along the long side of the rectangular contact surface with a second weld bead and a third weld bead, extending onto the steel plate to form multiple layers.

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 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 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. A multi-layer rotary welding method according to any one of claims 1 to 3, wherein the steel plate is a floating body component of a floating offshore wind power generation facility, and the standing plate is a tower component of the floating offshore wind power generation facility.

5. A welded joint formed by welding a bracket placed on a steel plate with a vertical plate sandwiched therebetween to the steel plate and the vertical plate, wherein a first weld bead is formed in multiple layers along the short side of a rectangular contact surface where the bracket contacts the steel plate, and second and third weld beads are formed in multiple layers along the long sides of the rectangular contact surface, covering the ends of the first weld bead and extending onto the steel plate. A boxed multi-layer welded joint.

6. The length of the extension of the final layer in the extension of the second weld bead and the third weld bead (N F 6. The boxing multi-layer welded joint according to claim 5, wherein the distance between the weld joint and the groove 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 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 ΔN = N i-1 -N i The boxing multi-layer welded joint according to claim 5 or 6, wherein i is in the range of 5 mm to 50 mm, and i is a natural number from 2 to 10.

8. A boxing multi-layer welded joint according to any one of claims 5 to 7, wherein the steel plate is a floating body component of a floating offshore wind power generation facility, and the standing plate is a tower component of the floating offshore wind power generation facility.

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