Turning multilayer welded joint and welding method therefor

Abstract

Provided are a turning multilayer welded joint and a welding method therefor. The present invention relates to a turning multilayer welded joint in which a vertical plate 6, having grooves formed on long and short sides thereof, and a steel plate 5 are welded together with a weld bead consisting of multiple passes and layers. The weld bead consists of a first weld bead, a first' weld bead, a second weld bead, and a third weld bead. The first weld bead is formed in a groove provided on one short side of the vertical plate 6, the first' weld bead is formed in a groove provided on the other short side of the vertical plate 6, the second weld bead is formed in a groove provided on one long side of the vertical plate 6, and the third weld bead is formed in a groove provided on the other long side of the vertical plate 6. A first pass of the second weld bead is extended onto the steel plate 5 to form an extended portion 2a, and a first pass of the third weld bead is extended onto the steel plate 5 to form an extended portion 3a.

Description

Rotary multi-layer welded joint and welding method thereof

[0001] The present invention relates to a rotary multi-layer welded joint and a welding method thereof. In particular, it relates to a rotary multi-layer welded joint and a welding method thereof that can improve the fatigue strength of the welded part of a steel structure with high stress concentration by stretching the welding bead.

[0002] Ships and offshore wind power generation facilities are exposed to external forces such as waves, so the fatigue life of the welded end parts of the members decreases. Therefore, various techniques for improving the fatigue strength of the welded end parts have been studied in the welded parts of large structures such as ships and offshore wind power generation facilities.

[0003] For example, Patent Document 1 discloses a method of stretching the welding bead of a welded joint to improve the fatigue strength. However, the welding method described in Patent Document 1 is effective for improving the fatigue strength of single-layer welding, and it is not clear whether it is effective for improving the fatigue strength of welded parts where members are multi-layer welded, such as ships and offshore wind power generation facilities.

[0004] Japanese Patent No. 6,919,640

[0005] As described above, there has been a long-felt need for a welding method that can prevent the fatigue strength of the welded part from decreasing even when vertical plates are multi-layer welded on a steel plate without using a bracket, which is a component for improving strength, for reinforcement.

[0006] The present invention solves the problems of the prior art, and an object thereof is to provide a rotary multi-layer welded joint and a welding method thereof that can improve the fatigue strength of the welded part even in the multi-layer welding of members in a large structure.

[0007] Furthermore, the multi-layer welded joint and welding method according to the present invention can also be applied to the formation of welded joints in floating offshore wind power generation facilities. Wind power generation is one of the renewable energy sources. Offshore wind power generation facilities installed on the sea include fixed-bottom and floating types, and floating offshore wind power generation facilities are used in sea areas with a water depth of 50m or more. The structure of a floating offshore wind power generation facility is one in which a structure with a wind turbine on it is connected to the sea by chains or the like and floats. The structure consists of a tower section that raises and holds the wind turbine (i.e., wind turbine generator) and a floating section that floats on the sea on which the tower section is placed. The tower section and the floating section that serves as the base are joined by welding, and improving the fatigue life of the welded joint is an important issue.

[0008] To solve the aforementioned problems, the inventors first fabricated a welded joint (welded joint) in which the vertical plate and the steel plate were completely fused together. Two types of welded joints were fabricated: one in which the welding was performed by wrapping around the vertical plate as in the conventional method, and another in which the welding bead was extended along the groove of the vertical plate. Fatigue tests were then conducted on both. By comparing the results of these fatigue tests, it was found that the wrapping multilayer welded joint according to the present invention, in which the welding bead was extended, exhibited a superior improvement in fatigue strength.

[0009] In other words, it was found that by extending a portion of the weld beads on both long sides of the vertical plate as a pair, a portion of the stress flowing through the steel plate is redirected to the extended portion, thereby easing the stress concentrated at the weld toe of the weld bead on the short side of the vertical plate and improving the fatigue strength of the weld. The "both long sides of the vertical plate" mentioned above refers to the two long sides of the vertical plate 6 in the example shown in Figure 2. Furthermore, "extending a portion of the weld beads on both long sides as a pair" refers to extending the ends of the two weld beads formed along the two long sides while keeping them facing each other, as shown in Figure 2.

[0010] This invention was completed based on the aforementioned findings and further investigations, and the gist of this invention is as follows. [1] A multilayer welded joint comprising a steel plate and a vertical plate erected on the steel plate with grooves formed on its long and short sides, wherein a weld bead consisting of multiple passes and layers is formed within the groove, the weld bead comprising a first weld bead, a first' weld bead, a second weld bead, and a third weld bead, the first weld bead being formed in a groove provided on one short side of the vertical plate, the first' weld bead being formed in a groove provided on the other short side of the vertical plate, the second weld bead being formed in a groove provided on one long side of the vertical plate, and the third weld bead being formed in a groove provided on the other long side of the vertical plate, the first pass of the second weld bead extending onto the steel plate on the first weld bead side to form an extended portion of the second weld bead. A multi-layer welded joint with a wrap-around construction, wherein the first pass of the third weld bead extends onto the steel plate on the first weld bead side to form an extended portion of the third weld bead. [2] The multi-layer welded joint with a wrap-around construction according to [1], wherein the first pass of the second weld bead further extends onto the steel plate 5 on the first' weld bead side to form an extended portion of the second weld bead, and the first pass of the third weld bead further extends onto the steel plate on the first' weld bead side to form an extended portion of the third weld bead. [3] The multi-layer welded joint with a wrap-around construction according to [2], wherein the second weld bead and the third weld bead have extended portions of the second weld bead and the third weld bead formed on the first weld bead side and / or the first' weld bead side in subsequent passes in addition to the first pass. [4] The multilayer welded joint according to any one of [1] to [3], wherein the distance N between the tip of each extended portion of the[5] In a multilayer welding method for a vertical plate in which grooves are provided on the long and short sides of the vertical plate, the vertical plate is erected on the steel plate 5 using the rectangular contact surface formed by the long and short sides, and a welding bead consisting of multiple passes and layers is formed in the groove, the welding bead consists of a first welding bead, a first' welding bead, a second welding bead, and a third welding bead, first, the first welding bead is formed in a groove provided on one short side of the vertical plate, then, the first' welding bead is formed in a groove provided on the other short side of the vertical plate, then, the second welding bead is formed in a groove provided on one long side of the vertical plate, then, the third welding bead is formed in a groove provided on the other long side of the vertical plate, and the first pass when forming the second welding bead is extended onto the steel plate on the side of the first welding bead to form an extended portion of the second welding bead. A multilayer welding method using a pass-through method, wherein the first pass used to form the third weld bead is extended onto the steel plate on the first weld bead side to form an extended portion of the third weld bead. [6] The multilayer welding method using a pass-through method according to [5], wherein the first pass used to form the second weld bead is further extended onto the steel plate on the first' weld bead side to form an extended portion of the second weld bead, and the first pass used to form the third weld bead is further extended onto the steel plate on the first' weld bead side to form an extended portion of the third weld bead. [7] The multilayer welding method using a pass-through method according to [6], wherein, when forming the second and third weld beads, the extended portions of the second weld bead and the extended portions of the third weld bead are formed on the first weld bead side and / or the first' weld bead side in the second and subsequent passes in addition to the first pass. [8] The multilayer welding method according to any one of [5] to [7], wherein the distance N between the tip of each extended portion of the

[0011] This invention provides a multi-layer welded joint and a welding method thereof that can improve fatigue strength by stretching a portion of the weld bead used to join a vertical plate and a steel plate. This will yield significant industrial benefits.

[0012] Figure 1 is a schematic external perspective view showing a four-layer weld as one embodiment of a steel structural member (i.e., a welded joint) obtained by the multi-layer welding method according to the present invention. Figure 2 is a schematic plan view showing a four-layer weld as one embodiment of a steel structural member (i.e., a welded joint) obtained by the multi-layer welding method according to the present invention. Figures 3(a) and 3(b) are schematic diagrams showing the groove shape and cross-sectional shape of the multi-layer weld as one embodiment of a steel structural member (i.e., a welded joint) obtained by the multi-layer welding method according to the present invention. Figure 3(a) is a side cross-sectional view showing the cross-sectional shapes of the second and third weld beads as seen from the short side of the vertical plate, and Figure 3(b) is a front cross-sectional view showing the cross-sectional shape of the first weld bead as seen from the long side of the vertical plate. Figures 4(a) and 4(b) are schematic diagrams showing the weld bead, layer number, and pass number in a four-layer welded joint as one embodiment of the multilayer welded joint according to the present invention. Figure 4(a) is a schematic diagram showing the multilayer structure of the second and third weld beads as viewed from the short side, which is the side of the vertical plate, and Figure 4(b) is a schematic diagram showing the multilayer structure of the first weld bead as viewed from the long side, which is the front of the vertical plate. Figures 5(a) to 5(i) are schematic partial plan views showing various examples of the weld bead shape patterns of the extended portion obtained by four-layer welding as one embodiment of the multilayer welded joint according to the present invention. Figures 6(a) to 6(n) are partial plan views showing the weld bead formation procedure in four-layer welding as one embodiment of the multilayer welded joint according to the present invention.

[0013] [Rotating Multilayer Welding Method] The rotating multilayer welding method according to the present invention will be described based on Figures 1 and 2.

[0014] The present invention relates to a multi-layer welding method for welding a vertical plate 6 onto a steel plate 5 by multi-layer welding. Specifically, as shown in Figures 1 and 2, it is a multi-layer welding method in which welds are formed in multiple layers within the grooves of the steel plate 5 and the vertical plate 6. The welds consist of a first weld bead 1, a first' weld bead 1', a second weld bead 2, and a third weld bead 3. The fatigue strength is improved by extending a portion of the second weld bead 2 and the third weld bead 3 formed by this multi-layer welding onto the steel plate (i.e., the surface of the steel plate 5).

[0015] The main point of the present invention is to provide an extended portion on the steel plate 5 on at least one short side of the vertical plate 6, and it is not essential to provide extended portions on both short sides of the vertical plate 6. Therefore, in the following description, we will mainly describe the extended portions of the second and third weld beads in the first weld bead on one short side of the vertical plate 6. That is, in the example of Figure 1, we will describe the extended portion 2a of the second weld bead and the extended portion 3a of the third weld bead.

[0016] The key point of the present invention is to extend the first pass, which is part of the second weld bead 2 and the third weld bead 3 on the long sides of the vertical plate 6. The first pass is the pass that first contacts the steel plate among the passes that make up each layer from the first layer (i.e., the initial layer) to the final layer of multilayer welding. Furthermore, it is preferable to extend the first pass between weld beads that are in symmetrical positions with respect to a center line that passes through the center of the plate thickness Q (i.e., the thickness of the short side) of the vertical plate 6 and is parallel to the long side. That is, the weld beads that are in symmetrical positions with respect to a center line that passes through the center of the plate thickness Q of the vertical plate 6 and is parallel to the long side are the second and third weld beads 2 and 3, and a part of these weld beads means the same layer among any of the layers that make up the multilayer welding. The same layer means, for example, if the second weld bead 2 is the first layer, then the third weld bead 3 is also the first layer, and for example, if the second weld bead 2 is the second and third layers, then the third weld bead 3 is also the second and third layers. In other words, the "first pass which is part of the second weld bead 2 and the third weld bead 3" means that if the second weld bead 2 is the first pass of the first layer, then the third weld bead 3 is also the first pass of the first layer, or if the second weld bead 2 is the first pass of both the second and third layers, then the third weld bead 3 is also the first pass of both the second and third layers.

[0017] Furthermore, it is preferable to extend any of the layers constituting the multilayer welding not only in the first pass but also in the second pass and beyond, as this makes it possible to alleviate the stress concentrated at the weld toe even in high stress ranges. The position of the weld bead to be extended is preferably the same as in the first pass, where the weld beads are symmetrically positioned with respect to a center line that passes through the center of the plate thickness Q of the vertical plate 6 and is parallel to the long side.

[0018] As a result, a portion of the stress flowing through the steel plate 5 is redirected to its stretched portion, easing the stress concentrated at the weld toe of the weld bead on the short side of the vertical plate 6, and improving the fatigue strength of the weld. In other words, in the example shown in Figure 1, the stress concentrated at the weld toe of the first weld bead 1 is relieved.

[0019] Here, the steel plate 5 refers to a thick steel plate structure, and its plate thickness t is preferably 50 mm to 200 mm. Other specifications of the shape are not particularly limited. Examples of materials for the steel plate 5 include YP355 material and YP470 material.

[0020] Furthermore, the vertical plate 6 is a rectangular parallelepiped. Its plate thickness Q is preferably 10 mm to 200 mm. More preferably, the plate thickness Q is 25 mm to 100 mm. Other specifications of the shape are not particularly limited. The material of the vertical plate 6 is also preferably the same type of material as the steel plate 5.

[0021] [Multilayer structure of the welded joint] The structure of the wrap-around multilayer welded joint will be explained with reference to Figures 3(a) and 3(b). Figures 3(a) and 3(b) are schematic diagrams showing the groove shape of a four-layer weld and the cross-sectional shape of the multilayer welded joint as one embodiment of a steel structural member (i.e., a welded joint) obtained by the wrap-around multilayer welding method according to the present invention. In this specification, the term "wrap-around multilayer welded joint" may also be simply referred to as "welded joint". Figure 3(a) is a side cross-sectional view showing the cross-sectional shape of the second weld bead 2 and the third weld bead 3 as seen from the short side of the vertical plate 6, and Figure 3(b) is a front cross-sectional view showing the cross-sectional shape of the first weld bead 1 as seen from the long side of the vertical plate 6. As shown in Figure 3(a), grooves are provided on both long sides of the vertical plate 6, and a four-layer welded joint of the second weld bead 2 and the third weld bead 3 is formed within these grooves. Furthermore, in Figure 3(b), a groove is provided on one of the short sides of the vertical plate 6, and four layers of welded material of the first weld bead 1 are formed within the groove. Only the weld bead corresponding to the first pass of any of the layers of the second weld bead 2 is extended, forming the extended portion 2a of the second weld bead.

[0022] Here, the relationship between the weld bead, layer, and pass will be explained using Figures 4(a) and 4(b).

[0023] Figures 4(a) and 4(b) are schematic diagrams showing the weld beads, layer numbers, and pass numbers in a four-layer weld as one embodiment of the multi-layer welded joint according to the present invention. Figure 4(a) is a schematic diagram showing the four-layer structure of the second weld bead 2 and the third weld bead 3 as viewed from the short side, which is the side of the vertical plate 6, and Figure 4(b) is a schematic diagram showing the four-layer structure of the first weld bead 1 as viewed from the long side, which is the front of the vertical plate 6.

[0024] As shown in Figure 4(b), the first pass of the first layer of the first weld bead 1 (see 1-1-1 in the figure) is formed on the steel plate 5 along the groove of the vertical plate 6. In the following description, the weld bead, layer number, and pass number in the figure will be indicated using a hyphen "-" as "weld bead-layer-pass", and will be written in parentheses. Next, the second layer of the first weld bead 1 has its first pass (i.e., 1-2-1 in the figure) formed on the steel plate 5 along the first pass of the first layer (1-1-1), and the next second pass of the second layer (i.e., 1-2-2 in the figure) is formed between the first pass of the second layer (1-2-1) and the vertical plate 5. Then, the third layer of the first weld bead 1 is formed by its first pass (i.e., 1-3-1 in the figure) along the first pass of the second layer (1-2-1) on the steel plate 5, followed by the second pass of the third layer (i.e., 1-3-2 in the figure) along the first pass of the third layer (1-3-1). Subsequently, the third pass of the third layer (i.e., 1-3-3 in the figure) is formed between the second pass of the third layer (1-3-2) and the vertical plate 5. Finally, the fourth layer of the first weld bead 1 is formed by its first pass (i.e., 1-4-1 in the figure) along the first pass of the third layer (1-3-1) on the steel plate 5. Next, the fourth layer second path (i.e., 1-4-2 in the figure) is formed along the fourth layer first path (1-4-1), and then the fourth layer third path (i.e., 1-4-3 in the figure) is formed along the fourth layer second path (1-4-2). After that, the final fourth layer fourth path (i.e., 1-4-4 in the figure) is formed between the fourth layer third path (1-4-3) and the vertical plate 6.

[0025] Similarly, as shown in Figure 4(a), a four-layer weld is formed within the grooves of the second weld bead 2 and the third weld bead 3. The second weld bead 2 has a four-layer structure from the first layer, first pass (i.e., 2-1-1 in the figure) to the fourth layer, fourth pass (i.e., 2-4-4 in the figure), and the third weld bead 3 has a four-layer structure from the first layer, first pass (i.e., 3-1-1 in the figure) to the fourth layer, fourth pass (i.e., 3-4-4 in the figure).

[0026] The above explanation focused on a four-layer, four-pass structure, but depending on the size of the steel structure, it is also possible to apply the same criteria to structures with approximately 10 layers and 20 passes. In other words, it is preferable to limit the number of layers to 10 or less and the number of passes to 20 or less.

[0027] Furthermore, the angle [θ] of the grooves provided on the long and short sides of the vertical plate 6 is preferably 5° to 70°. This is because construction becomes difficult if the groove angle is less than 5° or greater than 70°. The groove angle is more preferably 20° to 60°.

[0028] Furthermore, the width of the area where the bottom surface, which is the rectangular contact surface of the vertical plate 6 with a groove, and the steel plate 5 come into contact (i.e., the contact width, also called the root face) is preferably 5 mm to 10 mm in order to completely fuse the vertical plate 6 and the steel plate 5 together.

[0029] [Length N of the extended portion] As described above, the main point of the present invention is to provide an extended portion in the weld bead on the steel plate 5 on at least one short side of the vertical plate 6. In other words, the key point of the present invention is to extend a portion of the second weld bead 2 and the third weld bead 3 on the long sides on both sides of the vertical plate 6, that is, the weld bead of the first pass in the same layer, onto the steel plate 5.

[0030] As shown in Figure 2, the first pass of welding beads is extended between weld beads located symmetrically on both sides with respect to a center line that passes through the center of the plate thickness Q of the vertical plate 6 and is parallel to the long side. The extended portion of the welding bead is called the "extended portion," and the portion extended by the second welding bead 2 formed on the side of the first welding bead 1 which is one of the short sides of the vertical plate 6 is called the extended portion 2a of the second welding bead, and similarly the portion extended by the third welding bead 3 is called the extended portion 3a of the third welding bead.

[0031] Furthermore, the portion extended by the second weld bead 2 formed on the other short side of the vertical plate 6, which is the first' weld bead 1' side, is called the extended portion 2a' of the second weld bead, and similarly, the portion extended by the third weld bead 3 is called the extended portion 3a' of the third weld bead.

[0032] The length N of these extended portions is the distance between the tip of the extended portion and the corresponding short side, as shown in Figures 1, 2, and 3(b), and is preferably between 20 mm and 500 mm. By adjusting the length N to this range, stress concentration is alleviated and the fatigue strength of the weld can be improved. If the length N of the extended portion is less than 20 mm, the effect of improving fatigue strength cannot be obtained. Also, if the length N of the extended portion exceeds 500 mm, the welding construction cost increases, which is undesirable. The length N of the extended portion is more preferably between 30 mm and 300 mm. The length N of the extended portion is even more preferably 60 mm or less. The "corresponding short side" mentioned above refers to the short side on the side where the second and third weld beads are extended, as described above.

[0033] Furthermore, the above-mentioned effects can be obtained if the length N of the extended portion on the first weld bead side and the first' weld bead side is within the above numerical range. It is desirable that the length N of the extended portion satisfies N ≥ 20 + (Q × z) and 0 ≤ z ≤ 4.8. It is even more desirable that the length N of the extended portion satisfies N ≥ 20 + (Q × z) and 0 ≤ z ≤ 2.8. Here, in the formula, Q is the plate thickness of the vertical plate (unit: mm), and z is the coefficient (dimensionless unit).

[0034] In this invention, the weld bead width W of the stretched portion (see Figure 2) is not specifically defined. As illustrated in each figure of Figure 5, this value W can be set appropriately according to the number of passes. For example, when using a vertical plate 6 with a plate thickness Q within the above numerical range, it is desirable that the weld bead width W be in the range of 12 to 50 mm.

[0035] Furthermore, it is preferable that the length of the extended portion 2a of the second weld bead and the length of the extended portion 3a of the third weld bead be approximately the same. Also, even when multiple extended portions are provided for each weld bead, it is preferable that their lengths be approximately the same (see Figure 5(e), etc.). It is possible to change the length N of the extended portion for each weld bead, but in order to avoid complicating the welding process, it is preferable that they be the same length.

[0036] Similarly, it is preferable that the length of the extended portion 2a' of the second weld bead and the length of the extended portion 3a' of the third weld bead be approximately the same. Furthermore, even when multiple extended portions are provided for each weld bead, it is preferable that their lengths be approximately the same. It is possible to change the length N of the extended portion for each weld bead, but in order to prevent complications in the welding process, it is preferable that they be the same length. The above-mentioned "approximately the same length" also includes having an error of within ±5 mm.

[0037] [Examples of Extended Section Patterns] Figures 5(a) to 5(i) show examples of combination patterns of the extended sections of the second and third weld beads in the multi-layer welded joint according to the present invention. The specific pattern examples illustrated in each figure are as follows.

[0038] Figure 5(a) shows the pattern of extending the first pass (2-1-1) of the first layer of the second weld bead 2 and the first pass (3-1-1) of the first layer of the third weld bead 3. When the first layer of each weld bead is extended, it is also referred to as "one layer to one layer," and the same applies hereafter.

[0039] Figure 5(b) shows the pattern of extending the first pass (2-2-1) of the second layer of the second weld bead 2 and the first pass (3-2-1) of the second layer of the third weld bead 3. The case where the second layer of each weld bead is extended will henceforth be referred to as "two layers together".

[0040] Figure 5(c) shows the pattern of extending the first pass (2-3-1) of the third layer of the second weld bead 2 and the first pass (3-3-1) of the third layer of the third weld bead 3. The case where the third layer of each weld bead is extended will henceforth be referred to as "extending three layers together".

[0041] Figure 5(d) shows a pattern extending the first pass (2-4-1) of the fourth layer of the second weld bead 2 and the first pass (3-4-1) of the fourth layer of the third weld bead 3. The case of extending the third layer of each weld bead is also hereinafter referred to as "between four layers".

[0042] Figure 5(e) shows a pattern extending the first pass (2-1-1) of the first layer and the first pass (2-2-1) of the second layer of the second weld bead 2, and the first pass (3-1-1) of the first layer and the first pass (3-2-1) of the second layer of the third weld bead 3. In this pattern, the first and second layers are extended.

[0043] Figure 5(f) shows a pattern extending the first pass (2-2-1) of the second layer and the first pass (2-3-1) of the third layer of the second weld bead 2, and the first pass (3-2-1) of the second layer and the first pass (3-3-1) of the third layer of the third weld bead 3. In this pattern, the second and third layers are extended.

[0044] Figure 5(g) shows a pattern extending the first pass (2-3-1) of the third layer and the first pass (2-4-1) of the fourth layer of the second weld bead 2, and the first pass (3-3-1) of the third layer and the first pass (3-4-1) of the fourth layer of the third weld bead 3. In this pattern, the third and fourth layers are extended.

[0045] Figure 5(h) shows a pattern extending the first pass (2-1-1) of the first layer, the first pass (2-2-1) of the second layer, and the first pass (2-3-1) of the third layer of the second weld bead 2, and the first pass (3-1-1) of the first layer, the first pass (3-2-1) of the second layer, and the first pass (3-3-1) of the third layer of the third weld bead 3. In this pattern, the first, second, and third layers are extended.

[0046] Figure 5(i) shows a pattern extending the first pass (2-1-1) of the first layer, the first pass (2-2-1) of the second layer, the first pass (2-3-1) of the third layer, and the first pass (2-4-1) of the fourth layer of the second weld bead 2, and the first pass (3-1-1) of the first layer, the first pass (3-2-1) of the second layer, the first pass (3-3-1) of the third layer, and the first pass (3-4-1) of the fourth layer of the third weld bead 3. In this pattern, the first, second, third, and fourth layers are extended.

[0047] As described above, in any combination, it is preferable to extend the first pass of at least one layer among the multiple layers of the second weld bead 2 and the first pass of the third weld bead 3, which is located symmetrically to this first pass. The reason why it is preferable to extend a pair of weld beads in symmetrical positions is that a portion of the stress flowing through the steel plate 5 is evenly distributed to the extended portion, thereby relieving the stress concentrated at the weld toe on the short side of the vertical plate 6. As a result, the fatigue strength of the weld is further improved.

[0048] [Welding Procedure] Next, the procedure for the multilayer welding method according to the present invention will be explained with reference to Figure 6. Figure 6 shows the welding procedure when the first pass (i.e., the two layers together) of the second layer of the second weld bead and the third weld bead in Figure 5(b) is extended, among the pattern examples in Figure 5 mentioned above. The welding shown in (a) in Figure 6 is performed first, and thereafter, welding is performed in the order of (b) to (n).

[0049] First, let's explain the preparation work before welding. As mentioned above, it is preferable that the steel plate 5 and the vertical plate 6 used are made of the same material (composition, etc.). The thickness t of the steel plate 5 is preferably 50 mm to 200 mm. The thickness Q of the vertical plate 6 is preferably 10 mm to 200 mm. More preferably, the thickness Q is 25 mm to 100 mm.

[0050] Next, grooves are made on the long and short sides of the vertical plate 6. The groove angle [θ] is preferably 5° to 70°, as mentioned above. Also, the width of the area where the bottom surface, which is the rectangular contact surface of the vertical plate 6 with the grooves, contacts the steel plate 5 (i.e., the contact width, also called the root face) is preferably 5 mm to 10 mm.

[0051] When the grooved vertical plate 6 is erected on the steel plate 5, it is important to stabilize it by tack welding it in place to prevent it from shaking or moving during welding.

[0052] After the above preparations are complete, the welding procedures (a) to (n) shown in Figure 6 are carried out.

[0053] (a) Formation process of [1-1-1] First, welding as shown in Figure 6(a) is performed. As shown in Figure 6(a), the first pass (1-1-1) of the first layer of the first weld bead is formed on the steel plate 5 in a groove provided on one short side of the vertical plate 6. In this case, the length of the weld bead (i.e., the first weld bead) corresponds to the width of the lowest layer of the weld in the groove (see Figure 4(b)).

[0054] (b) Forming process of [2-1-1] Next, welding as shown in Figure 6(b) is performed. As shown in Figure 6(b), the first pass (2-1-1) of the first layer of the second weld bead is formed on the steel plate 5 in a groove provided on one long side of the vertical plate 6. At this time, the second weld bead is formed so that the weld end of the second weld bead overlaps with the end of the first weld bead formed in (a) above (see Figure 4(a)).

[0055] (c) Following the formation process of [3-1-1], welding as shown in (c) in Figure 6 is performed. As shown in (c) in Figure 6, the first pass (3-1-1) of the first layer of the third weld bead is formed on the steel plate 5 in a groove provided on the other long side of the vertical plate 6. At this time as well, the third weld bead is formed so that the weld end of the third weld bead overlaps with the end of the first weld bead formed in (a) above that is opposite to the end in (b) above (see Figure 4(a)).

[0056] (d) Formation process of [1-2-1, 1-2-2] Next, welding as shown in Figure 6(d) is performed. As shown in Figure 6(d), the first pass (1-2-1) of the second layer of the first weld bead is formed on the steel plate 5 on top of the first pass (1-1-1) of the first layer of the first weld bead formed in (a) above. Subsequently, the second pass (1-2-2) of the second layer is formed on top of the first pass (1-2-1) (see Figure 4(b)).

[0057] (e) Following the formation process of [2-2-1], welding as shown in Figure 6(e) is performed. As shown in Figure 6(e), the first pass (2-2-1) of the second layer of the second weld bead is formed on the steel plate 5 on top of the first pass (2-1-1) of the first layer of the second weld bead formed in (b) above. At this time, only this first pass (2-2-1) of the second layer extends beyond the end of the second layer (1-2-1 and 1-2-2) of the first weld bead in (d) above, and is extended on the steel plate 5 by a length N from the short side of the vertical plate 6 to form an extended portion 2a of the second weld bead (see Figure 4(a)).

[0058] (f) Following the formation process of [2-2-2], welding as shown in Figure 6(f) is performed. As shown in Figure 6(f), the second pass (2-2-2) of the second layer of the second weld bead of (e) is formed from above the first pass (2-2-1) of the second layer of the second weld bead up to the end of the second layer of the first weld bead (see Figure 4(a)).

[0059] (g) Formation process of [3-2-1] Next, welding as shown in (g) in Figure 6 is performed. As shown in (g) in Figure 6, the second layer of the third weld bead is also formed in the same manner as in (e) and (f) above. First, the first pass (3-2-1) of the second layer of the third weld bead is formed on the steel plate 5 on top of the first pass (3-1-1) of the first layer of the third weld bead formed in (c) above. At this time, only the first pass (3-2-1) of this second layer extends beyond the end of the second layer (1-2-1 and 1-2-2) of the first weld bead in (d) above, and is extended on the steel plate 5 by a length N from the short side of the vertical plate 6 to form the extended portion 3a of the third weld bead (see Figure 4(a)).

[0060] (h) Following the formation process of [3-2-2], welding is performed as shown in (h) in Figure 6. As shown in (h) in Figure 6, the second pass (3-2-2) of the second layer of the third weld bead of (g) is formed from above the first pass (3-2-1) of the second layer of the first weld bead up to the end of the second layer of the first weld bead (see Figure 4(a)).

[0061] (i) Formation process of [1-3-1, 1-3-2, 1-3-3] Next, welding as shown in (i) in Figure 6 is performed. As shown in (i) in Figure 6, the first pass (1-3-1) of the third layer of the first weld bead is formed on the steel plate 5 on top of the first pass (1-2-1) of the second layer of the first weld bead formed in (d) above. Subsequently, the second pass (1-3-2) of the third layer is formed on top of the first pass (1-3-1) of the third layer, and then the third pass (1-3-3) of the third layer is formed on top of that (see Figure 4(b)).

[0062] (j) Following the formation process of [2-3-1, 2-3-2, 2-3-3], welding as shown in (j) in Figure 6 is performed. As shown in (j) in Figure 6, the third layer of the second weld bead is formed sequentially on the steel plate 5 in the first pass (2-3-1), second pass (2-3-2), and third pass (2-3-3). These weld ends are formed overlapping the ends of the third layer of the first weld bead described in (i) above (see Figure 4(a)).

[0063] (k) Welding is performed in the same manner as in the formation process of [3-3-1, 3-3-2, 3-3-3], as shown in (k) in Figure 6. As shown in (k) in Figure 6, the third layer of the third weld bead is formed sequentially on the steel plate 5 in the first pass (3-3-1), second pass (3-3-2), and third pass (3-3-3). These weld ends are formed overlapping the ends of the third layer of the first weld bead described in (i) above (see Figure 4(a)).

[0064] (l) Formation process of [1-4-1, 1-4-2, 1-4-3, 1-4-4] Next, welding as shown in (l) in Figure 6 is performed. As shown in (l) in Figure 6, the first pass (1-4-1), second pass (1-4-2), third pass (1-4-3), and fourth (1-4-4) are sequentially formed on the steel plate 5 as the fourth layer of the first weld bead (see Figure 4(b)).

[0065] (m) Formation process of [2-4-1, 2-4-2, 2-4-3, 2-4-4] Next, welding as shown in (m) in Figure 6 is performed. As shown in (m) in Figure 6, the first pass (2-4-1), second pass (2-4-2), third pass (2-4-3), and fourth (2-4-4) are formed sequentially on the steel plate 5 as the fourth layer of the second weld bead. The ends of these welds are formed overlapping the ends of the fourth layer of the first weld bead in (l) (see Figure 4(a)).

[0066] (n) Welding is performed in the same manner as the formation process for [3-4-1, 3-4-2, 3-4-3, 3-4-4] as shown in (n) in Figure 6. As shown in (n) in Figure 6, the first pass (3-4-1), second pass (3-4-2), third pass (3-4-3), and fourth (3-4-4) are sequentially formed on the steel plate 5 as the fourth layer of the third weld bead. The ends of these welds are formed overlapping the ends of the fourth layer of the first weld bead described in (l) above (see Figure 4(a)).

[0067] By following the welding procedure described above, a first weld bead, a second weld bead, and a third weld bead with a multilayer structure of four layers and four passes can be formed. In an intermediate step, the first passes of the second layer in the second and third weld beads can be stretched to form the stretched portions of the second and third weld beads.

[0068] Furthermore, while the welding procedure in Figure 6 above was explained using a 4-layer, 4-pass structure with an example of a pattern where the second layers are stretched, the fatigue strength of the welded joint can be improved by performing the welding procedure for other patterns, such as those shown in Figure 5, in the same manner.

[0069] Although the illustrations showing the welding procedure are omitted, for example, if the first passes of the first layer of the second and third weld beads in Figure 5(a) above are extended, the welding procedure should be as follows. Figure 5(a) only shows one short side of the vertical plate, but the other short side also has a similar extended portion.

[0070] First, as preparation before welding, grooves are made on the long and short sides of the vertical plate 6, and the vertical plate 6 is erected on the steel plate 5 using the rectangular contact surface formed by the long and short sides. Then, using the welding procedure described below, the vertical plate 6 is welded along its perimeter, forming a weld bead consisting of multiple passes and layers within the grooves.

[0071] First, as the first step, a first weld bead 1 is formed in a groove provided on one short side of the vertical plate 6. This step forms the first pass (1-1-1) of the first layer of the first weld bead. Next, as the second step, a first' weld bead 1' is formed in a groove provided on the other short side of the vertical plate 6. This step forms the first pass (1'-1-1) of the first layer of the first' weld bead. Next, as the third step, a second weld bead 2 is formed in a groove provided on one long side of the vertical plate 6. This step forms the first pass (2-1-1) of the first layer of the second weld bead. Next, as the fourth step, a third weld bead 3 is formed in a groove provided on the other long side of the vertical plate 6. This step forms the first pass (3-1-1) of the first layer of the third weld bead. In the pattern shown in Figure 5(a), the first pass (2-1-1) of the first layer when forming the second weld bead 2 is extended onto the steel plate 5 on the side of the first weld bead 1 to form the extended portion 2a of the second weld bead. Similarly, the first pass (3-1-1) of the first layer when forming the third weld bead 3 is extended onto the steel plate 5 on the side of the first weld bead 1 to form the extended portion 3a of the third weld bead. Subsequently, the above steps 1 to 4 are repeated for the second to fourth layers, according to the number of passes for each layer. By performing rotational welding along the perimeter of the vertical plate 6, the weld beads and extended portions shown in Figure 5(a) are formed.

[0072] As described above, the extended portions may be formed on both short sides of the vertical plate 6. In this case, similar to the first weld bead side, the first pass used to form the second and third weld beads can be extended onto the steel plate 5 on the first' weld bead side to form the extended portion 2a' of the second weld bead and the extended portion 3a' of the third weld bead.

[0073] Each extension may be formed in the first pass, or it may be formed in the second pass and subsequent passes in addition to the first pass (see Figures 5(e) and 5(h)).

[0074] When the second and third passes of each layer of the second and third weld beads are to be extended beads, the weld beads should be formed using the same procedure as the first pass of each layer, extending beyond the end of the first weld bead onto the steel plate 5 by a length N from the short side of the vertical plate 6 to form the extended portion 2a of the second weld bead and the extended portion 3a of the third weld bead. Preferably, the positions of the second and third weld beads to be extended are such that they are symmetrical with respect to a center line that passes through the center of the plate thickness Q of the vertical plate 6 and is parallel to the long side.

[0075] When the second and third passes of each layer described above are to be extended weld beads, welding may first be performed according to the procedure shown in (a) to (n) in Figure 6, and then a process may be added to form the extended weld beads of the second and third passes at the positions where the second and third passes of each layer are extended. In this case as well, the extended portion 2a of the second weld bead and the extended portion 3a of the third weld bead may be formed by extending the extension by a length N from the short side of the vertical plate 6 onto the steel plate 5, beyond the end of the first weld bead.

[0076] In addition, the above explanation only describes the welding procedure for the first weld bead 1 formed on one short side of the vertical plate 6 and the second and third weld beads 2 and 3 formed on the long sides of the vertical plate 6.

[0077] As shown in Figures 1 and 2, the welding procedure for the first' weld bead 1' formed on the other short side of the vertical plate 6 and the extended portions 2a' and 3a' of the second and third weld beads extended toward the short side can be carried out using the exact same procedure as for the first weld bead 1, etc., from the first to the fourth layer.

[0078] However, it is preferable to form the layer containing the first weld bead first, then the corresponding layer containing the 1' weld bead, and then sequentially form the corresponding layer containing the second weld bead and the corresponding layer containing the third weld bead.

[0079] Furthermore, the extended portion 2a' of the second weld bead formed on the first' weld bead side may be formed at the same timing as the extended portion 2a of the second weld bead, and the extended portion 3a' of the third weld bead may be formed at the same timing as the extended portion 3a of the third weld bead. As a result, by performing multi-layer welding around all four sides of the vertical plate 6 and forming extended portions on both short sides of the vertical plate, the fatigue strength of the welded joint can be further improved.

[0080] [Welding Conditions] From the viewpoint of welding efficiency, welding should preferably be performed by gas shielded arc welding. Below is an example of welding conditions for gas shielded arc welding: • Welding current: 200A to 400A, Welding voltage: 20V to 50V, Welding speed: 20cm / min to 40cm / min • Shielding gas: CO ２ 100% by volume of gas or CO ２ A mixture of gas and Ar gas. An example of the mixing ratio of the mixed gas is CO ２ Examples include a mixed gas of 20% gas by volume + 80% Ar gas by volume. • Welding wire diameter: 1.2 mm to 2.4 mm

[0081] [Wrap-around multilayer welded joint] The wrap-around multilayer welded joint of the present invention is a welded joint formed by creating a weld bead in the groove of a vertical plate 6 erected on a steel plate 5 using the wrap-around multilayer welding method of the present invention, as described above. The groove is a groove provided on the joining surface of the vertical plate 6, which is the base material, at the groove angle (θ) described above.

[0082] The weld bead consists of a first weld bead 1, a first'weld bead 1', a second weld bead 2, and a third weld bead 3. As shown in Figures 1 and 2, the weld bead is formed in a rectangular shape along the perimeter of the vertical plate 6 on the bottom surface (rectangular contact surface) side of the vertical plate 6 that is in contact with the steel plate 5. The weld beads formed on the two short sides of the vertical plate 6 are the first weld bead 1 and the first'weld bead 1'. The weld beads formed on the two long sides of the vertical plate 6 are the second weld bead 2 and the third weld bead 3.

[0083] The second weld bead 2 and the third weld bead 3 each have an extended portion 2a of the second weld bead and an extended portion 3a of the third weld bead on the side of the first weld bead 1, which are formed by extending them on the steel plate 5. As described above, each extended portion 2a and 3a is formed symmetrically with respect to a center line that passes through the center of the plate thickness Q of the vertical plate 6 and is parallel to the long side of the vertical plate 6. The extended portion may be formed only on one short side of the vertical plate 6 (not shown), or it may be formed on both short sides of the vertical plate 6 (see Figures 1 and 2). When formed on both short sides of the vertical plate 6, in addition to the first weld bead 1 side described above, the first' weld bead 1' side also has an extended portion 2a' of the second weld bead and an extended portion 3a' of the third weld bead, which are formed by extending them on the steel plate 5.

[0084] As described above, each extension may be formed in the first pass, or it may be formed in the second pass and subsequent passes in addition to the first pass. Since the explanations regarding each weld bead and extension, as well as the steel plate and vertical plate, have already been described in detail, they will be omitted here.

[0085] The present invention will be further described below based on examples. However, the following examples are merely illustrative and intended to illustrate the present invention in more detail, and do not limit the scope of the rights of the present invention.

[0086] The test materials were YP355 and YP470 steel plates with a thickness of 100 mm. The angle (θ) of the groove formed on the vertical plates of the test materials was set to 45°. The same test material was used for both the steel plates and the vertical plates. YP355 steel was used for joints No. 1-5, 9-16, and 19-23, while YP470 steel was used for joints No. 6-8 and 17-18.

[0087] The main welding conditions were a welding current of 230A, a welding voltage of 30V, and a welding speed of 34cm / min, CO ２ A multilayer welded joint consisting of four layers and four passes was fabricated using gas-shielded arc welding with 100% volume of shielding gas. The welding wire diameter was 1.2 mm.

[0088] As shown in Table 1, welded joints were prepared using both conventional rotational welding and the welding method of the present invention, which involved stretching the weld bead. The fatigue test results for these welded joints, evaluated using the test method described later, are shown in Table 1.

[0089]

[0090] Joint No. 1 is a comparative example and represents the test results when conventional rotation welding is performed. In other words, Joint No. 1 is a welded joint that does not have an extended portion of the weld bead as in the present invention.

[0091] Joints No. 2 to No. 11 and 21 are examples of the present invention, and represent test results when the first passes of either the second or third weld bead layers are stretched.

[0092] Joints No. 12 to No. 20 are examples of the present invention, and represent test results when, in addition to extending the first passes of either the second and third weld bead layers, one or more of the second, third, and fourth passes are also extended.

[0093] Joints No. 22 to No. 23 are examples of the present invention, and represent test results when, in addition to extending the first passes of either the second or third weld bead layer, one or more of the second to seventh passes are also extended.

[0094] Tests were conducted on joints No. 2 to No. 10 using the nine patterns shown in the previously mentioned examples of extended sections. Illustrations of other pattern examples have been omitted. Table 1 shows the layers on which the extended sections were formed.

[0095] The fatigue strength was evaluated by conducting a fatigue test with an applied stress range of 100 MPa and a stress ratio of 0.1, based on the statistical fatigue testing method of the Japan Society of Mechanical Engineers (JSME) standard: JSME S 002-1994. The number of cycles of fractures using the fatigue testing machine was counted for evaluation.

[0096] From these results, the number of fracture cycles for the examples of the present invention (joints No. 2 to 11) was more than twice as large as that of the comparative example (joint No. 1) manufactured by conventional rotational welding, demonstrating an excellent fatigue strength improvement effect. The number of fracture cycles for joints No. 21 to 23 was higher than that of joint No. 1, but still close.

[0097] Among the examples of the present invention, joints No. 12 to 20 showed an even greater improvement in fatigue strength compared to joints No. 2 to 11, due to the increased stress concentration mitigation effect.

[0098] 1. First weld bead 1' First' weld bead 2. Second weld bead 2a, 2a' Extended portion of the second weld bead 3. Third weld bead 3a, 3a' Extended portion of the third weld bead 5. Steel plate 6. Vertical plate N Length of extended portion (unit: mm) t Thickness of steel plate (unit: mm) Q Thickness of vertical plate (unit: mm)

Claims

1. A multilayer welded joint comprising a steel plate and a vertical plate erected on the steel plate with grooves formed on its long and short sides, wherein a weld bead consisting of multiple passes and layers is formed within the groove, the weld bead comprising a first weld bead, a first' weld bead, a second weld bead, and a third weld bead, the first weld bead being formed in a groove provided on one short side of the vertical plate, the first' weld bead being formed in a groove provided on the other short side of the vertical plate, the second weld bead being formed in a groove provided on one long side of the vertical plate, the third weld bead being formed in a groove provided on the other long side of the vertical plate, and the first pass of the second weld bead extending onto the steel plate on the first weld bead side to form an extended portion of the second weld bead. A multi-layer welded joint in which the first pass of the third weld bead extends onto the steel plate on the first weld bead side, forming an extended portion of the third weld bead.

2. The first pass of the second weld bead is further extended onto the steel plate on the side of the first' weld bead to form an extended portion of the second weld bead, and the first pass of the third weld bead is further extended onto the steel plate on the side of the first' weld bead to form an extended portion of the third weld bead, as described in claim 1.

3. The multilayer welded joint according to claim 1, wherein the second weld bead and the third weld bead are formed on the first weld bead side in the second pass and subsequent passes in addition to the first pass.

4. The second weld bead and the third weld bead are formed in the second pass and subsequent passes in addition to the first pass, with extended portions of the second weld bead and / or the first' weld bead formed on the first weld bead side and / or the first' weld bead side, respectively, in the multilayer welded joint according to claim 2.

5. The multilayer welded joint according to any one of claims 1 to 4, wherein the distance N between the tip of each extended portion of the 6. In a multi-layer welding method for forming a weld bead consisting of multiple passes and layers, the weld bead is formed within the grooves by providing grooves on the long and short sides of a vertical plate, erecting the vertical plate on a steel plate using the rectangular contact surface formed by the long and short sides, and forming a weld bead within the grooves, the weld bead consists of a first weld bead, a first' weld bead, a second weld bead, and a third weld bead, firstly, the first weld bead is formed within a groove provided on one short side of the vertical plate, then, the first' weld bead is formed within a groove provided on the other short side of the vertical plate, then, the second weld bead is formed within a groove provided on one long side of the vertical plate, then, the third weld bead is formed within a groove provided on the other long side of the vertical plate, and the first pass used to form the second weld bead is extended onto the steel plate on the side of the first weld bead to form an extended portion of the second weld bead. A multi-layer welding method for forming the third weld bead, wherein the first pass during the formation of the third weld bead is extended onto the steel plate on the side of the first weld bead to form an extended portion of the third weld bead.

7. The multilayer welding method according to claim 6, wherein the first pass when forming the second weld bead is further extended onto the steel plate on the side of the first' weld bead to form an extended portion of the second weld bead, and the first pass when forming the third weld bead is further extended onto the steel plate 5 on the side of the first' weld bead to form an extended portion of the third weld bead.

8. The multilayer welding method according to claim 6, wherein, when forming the second weld bead and the third weld bead, the extended portion of the second weld bead and the extended portion of the third weld bead are formed on the first weld bead side in the second pass and subsequent passes in addition to the first pass.

9. The multilayer welding method according to claim 7, wherein, when forming the second weld bead and the third weld bead, an extended portion of the second weld bead and an extended portion of the third weld bead are formed on the first weld bead side and / or the 1' weld bead side in the second pass and subsequent passes in addition to the first pass.

10. The multilayer welding method according to any one of claims 6 to 9, wherein the distance N between the tip of each extended portion of the

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