Joint structure and joint method

Abstract

To provide a joint structure which is suitable for joint work such as a monopile and a transition piece in the offshore wind power generation, and to provide a joint method.SOLUTION: A joint structure 10 comprises a slip joint formed by externally fitting a second cylindrical body 20 having an inner peripheral surface 18 whose diameter is reduced in a tapered manner to an outer peripheral surface 14 of a first cylindrical body 16 having the outer peripheral surface 14 whose diameter is reduced in a tapered manner toward a cylinder tip 12. The cylinder tip 12 of the first cylindrical body 16 is welded to the inner peripheral surface 18 with the second cylindrical body 20 being a backing metal.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a joining structure and joining method suitable for joining columnar members such as a pile foundation (monopile) of an offshore wind turbine and a wind turbine tower. [Background technology]

[0002] Conventionally, the pile foundation (monopile) of an offshore wind turbine has been connected to the wind turbine tower by connecting it to the monopile MP via a connecting steel pipe transition piece TP, as shown in Figure 5(1) (see, for example, Patent Document 1). The connection methods between the monopile MP and the transition piece TP can be broadly divided into three types: grout connection, bolt connection, and slip joint, as shown in Figure 5(2).

[0003] Grout joints are a method of joining double steel pipes by filling the gaps formed by them with grout. Bolted joints are a method of tension-joining flanges protruding from steel pipes with high-strength bolts. Slip joints are a friction joint in which steel pipes are fitted together. Grout joints and bolted joints have been widely adopted in Europe. Slip joints are not widely adopted in Europe, but are being actively researched in Japan. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2023-56370 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the conventional grout and bolt joints mentioned above have the problem of unavoidably increasing the amount of material used. With grout joints, harmful cracks in the grout are not permitted during design review, so the grout thickness and grout joint length are designed to be large. This inevitably increases the amount of grout to be filled, leading to higher costs. Bolted joints are also elastically designed joints, but require large-diameter bolts (M64 to M72) to be tightened offshore, increasing construction labor. Furthermore, the amount of steel used increases with the number of bolts, resulting in increased costs.

[0006] Furthermore, although slip joints use less material than grout joints and bolt joints, they require high manufacturing precision because the steel pipes are fitted together to form a friction joint. Considering that there are few examples of this method being used in Europe, it is likely that there are problems with the casting method, in addition to the high costs that come with the high manufacturing precision required.

[0007] On the other hand, welding has not yet been put into practical use to connect pile foundations and wind turbine towers. This is due to the difficulty of installing temporary erection pieces and backing plates, as is the case with column joints in the construction industry, when using large-diameter steel pipes like those used in offshore wind turbines. Furthermore, external welding requires the construction of scaffolding, which creates a dangerous and harsh offshore environment. If welding could be put into practical use, it would potentially reduce costs by reducing the amount of material used, and could streamline design and obtain certification by utilizing existing welding knowledge. The use of welding robots during construction would reduce labor and shorten construction time. For offshore wind turbines in particular, early start-up is a key condition in bidding, so shortening construction time is a major advantage.

[0008] The present invention has been made in view of the above, and aims to provide a joining structure and joining method suitable for joining monopiles and transition pieces, etc. in offshore wind power plants. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems and achieve the object, the joining structure of the present invention is a joining structure consisting of a slip joint formed by externally fitting a second cylindrical body having an inner peripheral surface that tapers in diameter onto the outer peripheral surface of a first cylindrical body having an outer peripheral surface that tapers in diameter toward the tip, and is characterized in that the tip of the first cylindrical body is welded to the inner peripheral surface using the second cylindrical body as a backing metal.

[0010] Further, another joint structure according to the present invention is characterized in that in the above-mentioned invention, the inner peripheral surface is welded by fillet welding or penetration welding.

[0011] Another joining structure according to the present invention is characterized in that, in the above-described invention, the first cylindrical body is the foundation of an offshore wind power generation facility, and the second cylindrical body is a foundation member of a wind turbine tower installed on the foundation.

[0012] In addition, the joining method of the present invention is a joining method in which a second cylindrical body having an inner peripheral surface that tapers in diameter is fitted onto the outer peripheral surface of a first cylindrical body having an outer peripheral surface that tapers in diameter toward the tip to form a slip joint, and is characterized in that the second cylindrical body is used as a backing metal and the tip of the first cylindrical body is welded to the inner peripheral surface.

[0013] Further, another joining method according to the present invention is characterized in that in the above-mentioned invention, welding is performed on the inner peripheral surface by fillet welding or penetration welding.

[0014] Furthermore, another joining method according to the present invention is characterized in that, in the above-described invention, the first cylindrical body is the foundation of an offshore wind power generation facility, and the second cylindrical body is a foundation member of a wind turbine tower to be installed on the foundation. [Effects of the Invention]

[0015] The joining structure of the present invention includes a slip joint formed by fitting a second cylindrical body having a tapered inner peripheral surface onto the outer peripheral surface of a first cylindrical body having an outer peripheral surface tapered toward the tip. The tip of the first cylindrical body is welded to the inner peripheral surface using the second cylindrical body as a backing. This allows the first and second cylindrical bodies to be easily joined using a combination of the slip joint and welding, without using grouting or bolting. This reduces the amount of material used and labor, resulting in cost savings. This effectively provides a joining structure suitable for joining monopiles and transition pieces in offshore wind power plants.

[0016] Furthermore, according to another joining structure of the present invention, the inner peripheral surface is welded by fillet welding or penetration welding, which has the effect of allowing easy joining by using a slip joint in combination with fillet welding or penetration welding.

[0017] Furthermore, according to another joining structure of the present invention, the first cylindrical body is the foundation of an offshore wind power generation facility, and the second cylindrical body is a foundation member of a wind turbine tower that is installed on the foundation, thereby achieving the effect of providing a joining structure between a monopile that is the foundation and a transition piece that is the foundation member.

[0018] Furthermore, according to the joining method of the present invention, a slip joint is formed by fitting a second cylindrical body having a tapered inner peripheral surface onto the outer peripheral surface of a first cylindrical body having an outer peripheral surface tapered toward the tip. The tip of the first cylindrical body is welded to the inner peripheral surface using the second cylindrical body as a backing metal. This allows the first and second cylindrical bodies to be easily joined using a combination of a slip joint and welding, without using grout or bolts. This reduces the amount of material used and labor, resulting in cost savings. Therefore, it is possible to provide a joining method suitable for joining monopiles and transition pieces in offshore wind power plants.

[0019] Furthermore, according to another joining method of the present invention, welding is performed on the inner peripheral surface by fillet welding or penetration welding, which has the effect of enabling easy joining by using a slip joint in combination with fillet welding or penetration welding.

[0020] Furthermore, according to another joining method of the present invention, the first cylindrical body is the foundation of an offshore wind power generation facility, and the second cylindrical body is a foundation member of a wind turbine tower to be installed on the foundation, thereby providing the effect of providing a method of joining a monopile, which is the foundation, and a transition piece, which is the foundation member. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a side cross-sectional view showing an embodiment of a joining structure and joining method according to the present invention. [Figure 2] FIG. 2 is a schematic diagram of a bolted joint. [Figure 3] FIG. 3 is a schematic diagram of Example 1 in which a slip joint and a fillet weld are used in combination. [Figure 4] FIG. 4 is a schematic diagram of Example 2 in which a slip joint and penetration welding are used in combination. [Figure 5] FIG. 5 is an explanatory diagram of a conventional joining method for an offshore wind turbine. DETAILED DESCRIPTION OF THE INVENTION

[0022] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a joining structure and a joining method according to the present invention will be described in detail below with reference to the accompanying drawings. However, the present invention is not limited to these embodiments.

[0023] As shown in Fig. 1(1), a joining structure 10 according to an embodiment of the present invention is a joining structure consisting of a slip joint formed by fitting a second cylindrical body 20 having a tapered inner peripheral surface 18 onto the outer peripheral surface 14 of a first cylindrical body 16 having an outer peripheral surface 14 tapered toward a cylindrical tip 12. Fig. 1(2) is an enlarged view of part A in Fig. 1(1). As shown in this figure, the cylindrical tip 12 of the first cylindrical body 16 is welded to the inner peripheral surface 18 of the second cylindrical body 20 via a weld 22.

[0024] The first cylindrical body 16 is assumed to be a steel monopile used as the foundation of an offshore wind power generation facility. The first cylindrical body 16 extends in the vertical direction and is a tapered, approximately cylindrical body in which the diameter D1 of the cylindrical body gradually decreases (tapering) as it approaches the cylindrical tip 12 at the upper end. The plate thickness of the first cylindrical body 16 is approximately constant.

[0025] The second cylindrical body 20 is intended to be a steel transition piece used as a foundation member of a wind turbine tower. The second cylindrical body 20 extends in the vertical direction and is a tapered, approximately cylindrical cylinder in which the diameter D2 of the cylindrical body gradually decreases (contracts) as it approaches the cylindrical tip 24 at the upper end (not shown). In other words, the second cylindrical body 20 can also be described as tapered in that the diameter D2 of the cylindrical body gradually increases (expands) as it approaches the cylindrical tip 24 at the lower end. The inner diameter of the second cylindrical body 20 is large enough to fit onto the outside of the first cylindrical body 16. The plate thickness of the second cylindrical body 20 is approximately constant.

[0026] The weld 22 can be constructed by fillet welding, penetration welding, or the like, using the second cylindrical body 20 as a backing metal. The size of the weld 22 can be set appropriately based on the required tensile strength, etc. To save labor, the welding is preferably performed by robot welding using a welding robot. Alternatively, submerged arc welding, which is used to weld thick components such as box columns and can use a large current, may be used. By using submerged arc welding, the work can be performed faster while ensuring welding quality.

[0027] Next, a method for constructing the above-described joint structure (a joining method according to an embodiment of the present invention) will be described.

[0028] First, as shown in FIG. 1(3), the first cylindrical body 16 is fixed with the cylindrical tip 12 facing upward and the cylindrical axis C facing in the vertical direction. Next, the second cylindrical body 20 is placed coaxially above the first cylindrical body 16 with the cylindrical tip 24 facing downward. If the first cylindrical body 16 is a monopile in an offshore wind power generation facility and the second cylindrical body 20 is a transition piece, the second cylindrical body 20 may be placed by being suspended from a crane ship or the like.

[0029] Next, the second cylindrical body 20 is lowered along the cylindrical axis C so that the cylindrical tip 24 fits over the cylindrical tip 12 of the first cylindrical body 16, and is then lowered further so that it is fitted onto the outer peripheral surface 14 of the first cylindrical body 16. As a result, the outer peripheral surface 14 of the first cylindrical body 16 and the inner peripheral surface 18 of the second cylindrical body 20 come into contact and join, forming a slip joint.

[0030] Finally, the tip 12 of the first cylindrical body 16 is welded to the inner circumferential surface 18 of the second cylindrical body 20 from the inside of the second cylindrical body 20. This forms a weld 22, and the joining structure 10 shown in FIG. 1(1) is obtained. The second cylindrical body 20 is used as a backing metal for the welding work. Fillet welding, penetration welding, or the like can be used for welding. To save labor, it is preferable to perform the welding by robot welding using a welding robot.

[0031] According to this embodiment, the first cylindrical body 16 and the second cylindrical body 20 can be easily joined by using a combination of slip joints and welding, without using grout joints or bolt joints. Therefore, compared to grout joints or bolt joints, cost reduction effects can be obtained by reducing the amount of material used and by saving labor through robot welding. Furthermore, labor savings can be achieved to shorten the construction period, which can also result in cost reduction effects.

[0032] Furthermore, when the first cylindrical body 16 is used as a monopile for an offshore wind power generation facility and the second cylindrical body 20 as a transition piece, using a slip joint to join them eliminates the need for the erection piece previously required for temporary fastening. When welding the transition piece and the monopile, the transition piece is used as a backing metal, and welding is performed from the inside of the transition piece, eliminating the need for the peripheral scaffolding previously installed, and using a welding robot can shorten the construction period. This shortened construction period makes it possible to start operation of the offshore wind power generation facility earlier.

[0033] Therefore, according to this embodiment, it is possible to provide a joining structure and joining method that are suitable for joining monopiles and transition pieces, etc. in offshore wind power plants.

[0034] In the above embodiment, the present invention has been described with reference to an example in which the present invention is applied to the joining of a monopile and a transition piece in an offshore wind power generation facility, but the present invention is not limited to this and can be applied to structures other than offshore wind power generation facilities. Even in such cases, the same effects as those described above can be achieved.

[0035] (Example) Next, examples of the present invention will be described. In the examples, the sizes of the welded portion 22 required to have the same yield strength as a conventional bolted joint were set as follows for fillet welding and penetration welding.

[0036] (1) Tower shell tensile strength in case of bolted joints First, the tower shell tensile strength in conventional bolted joints is calculated as follows. Figure 2(1) shows a side cross-sectional view of the bolted joint under consideration, and (2) shows a plan cross-sectional view. As shown in this figure, this bolted joint is assumed to be an L-shaped flange cut out from the joint between the monopile and the transition piece (tower shell) for two high-strength bolts. The high-strength bolts are assumed to be F10TM64. The dimensions of the element are as shown in the figure. Each flange 30 is L-shaped in side cross-sectional view, bending radially inward from the upper end of the approximately cylindrical monopile and the lower end of the approximately cylindrical transition piece. The flanges 30 face each other and are in surface contact. Each flange 30 has two bolt holes 32 at corresponding positions. High-strength bolts 34 are inserted into the bolt holes 32. Nuts 36 are threaded onto the tips of the high-strength bolts 34, and washers 40 are inserted between the nuts 36 and the bolt heads 38. Tightening the nuts 36 tightly secures the flanges 30 together.

[0037] From the bolt tensile strength review of the well-known wind guideline (see Reference 1 below), the tower shell tensile strength T sy is calculated using the following formula:

[0038] [Reference 1] "Guidelines and Commentary on the Structural Design of Wind Power Generation Facilities Support Structures [2010 Edition]," Japan Society of Civil Engineers, 2011

[0039]

number

number

number

[0040] However, T y : Bolt yield axial force e: Distance from the bolt core to the flange end g: Distance from the center of the tower shell plate thickness to the bolt center σ y : Bolt yield stress A e: Bolt effective cross-sectional area In the case of the bolted joint in Figure 2, e = 190 mm, g = 145 mm, σ y =900N / mm 2 , A e =2680mm 2 Therefore, the tower shell tensile strength T sy is T sy =2735kN (value for two bolts).

[0041] (2) Example 1: Proof strength of slip joint and welded joint (fillet weld) In Example 1, fillet welding is used in a joining structure 10 using a slip joint and welding. The size of the weld 22 is set as follows based on the proof strength of the fillet weld and the tower shell tensile proof strength of the bolt joint. Figure 3 (1) is a side cross-sectional view of the main part of Example 1, and (2) is a plan cross-sectional view. As shown in this figure, the plate element to be joined is a shell with a plate thickness of 70 mm, the same as the bolt joint described above, and the width of the element to be examined is also the same, 400 mm. Note that the welding is a fillet weld, and in calculating the proof stress, the stress state of the weld 22 is considered to be a front fillet weld. Proof strength P of the front fillet weld (weld 22) y is expressed by the following formula:

[0042]

number

number

[0043] Where, B: Length of fillet weld w y : Yield strength of fillet weld per unit length σ y : Weld metal yield stress s: Size of fillet weld

[0044] P y =T syAssuming this, the size s of the fillet weld can be calculated from equations (4) and (5): B = 400 mm, σ y =325N / mm 2 Therefore, s = 37.18 mm. If s = 40 mm, the diagram will look like Figure 3. The size s of the fillet weld is within the range of the plate thickness, and it can be seen that the size of weld 22 is realistic for the required yield strength.

[0045] (3) Example 2: Proof strength of slip joint and welded joint (penetration welding) In Example 2, penetration welding is used in a joining structure 10 using a slip joint and welding. The size of the weld 22 is set as follows based on the strength of the penetration weld and the tower shell tensile strength of the bolt joint. 4(1) is a side cross-sectional view of the main part of Example 2, and (2) is a plan cross-sectional view. As shown in this figure, in the case of penetration welding, unlike the case of fillet welding described above, a groove 42 is provided on the monopile side (first cylindrical body 16 side). Proof strength P of penetration weld (weld 22) y is expressed by the following formula:

[0046]

number

number

[0047] Where, B: Length of fillet weld w y : Yield strength of penetration weld per unit length σ y : Weld metal yield stress s: size of penetration weld

[0048] P y =T sy Assuming this, the size s of the penetration weld can be calculated from equations (6) and (7): B = 400 mm, σ y =325N / mm2 Therefore, s = 36.44 mm. If we set s = 40 mm as in the case of fillet welding above, the result will be as shown in Figure 4.

[0049] Fillet welding requires inspection to determine whether the size of the weld 22 is the required size, but penetration welding makes it clear that the required size is secured once the weld metal exceeds the thickness of the edge of the monopile (first cylindrical body 16). Also, submerged arc welding, which is used to weld thick components such as box columns and can use a large current, can be used to speed up the work while ensuring welding quality.

[0050] As described above, the joining structure of the present invention is a joining structure comprising a slip joint formed by fitting a second cylindrical body having a tapered inner peripheral surface onto the outer peripheral surface of a first cylindrical body having an outer peripheral surface tapered toward the cylindrical tip. The tip of the first cylindrical body is welded to the inner peripheral surface using the second cylindrical body as a backing metal. This allows the first cylindrical body and the second cylindrical body to be easily joined using a combination of the slip joint and welding, without using grouting or bolting. This reduces the amount of material used and labor, resulting in cost savings. Therefore, a joining structure suitable for joining monopiles and transition pieces in offshore wind power plants can be provided.

[0051] Furthermore, according to another joining structure of the present invention, the inner peripheral surface is welded by fillet welding or penetration welding, so joining can be easily performed by using a slip joint in combination with fillet welding or penetration welding.

[0052] Furthermore, according to another joining structure of the present invention, the first cylindrical body is the foundation of an offshore wind power generation facility, and the second cylindrical body is a foundation member of a wind turbine tower that is installed on the foundation, so it is possible to provide a joining structure between a monopile that is the foundation and a transition piece that is the foundation member.

[0053] Furthermore, according to the joining method of the present invention, a slip joint is formed by fitting a second cylindrical body having a tapered inner peripheral surface onto the outer peripheral surface of a first cylindrical body having an outer peripheral surface tapered toward the tip. The tip of the first cylindrical body is welded to the inner peripheral surface using the second cylindrical body as a backing metal. This allows the first and second cylindrical bodies to be easily joined using a combination of a slip joint and welding, without using grout or bolts. This reduces the amount of material used and labor, resulting in cost savings. This provides a joining method suitable for joining monopiles and transition pieces in offshore wind power plants.

[0054] Furthermore, according to another joining method of the present invention, welding is performed on the inner peripheral surface by fillet welding or penetration welding, so joining can be easily performed by using a slip joint in combination with fillet welding or penetration welding.

[0055] Furthermore, according to another joining method of the present invention, the first cylindrical body is the foundation of an offshore wind power generation facility, and the second cylindrical body is a foundation member of a wind turbine tower that is installed on the foundation, so a method for joining a monopile that is the foundation and a transition piece that is the foundation member can be provided.

[0056] The Sustainable Development Goals (SDGs) are 17 international goals that were adopted at the United Nations Summit in September 2015. The joining structure and joining method according to this embodiment can contribute to achieving one of the 17 SDGs, for example, goal 9, "Build resilient infrastructure, promote inclusive and sustainable industrialization, and foster innovation." [Industrial Applicability]

[0057] As described above, the joining structure and joining method according to the present invention are useful for joining cylindrical bodies together, and are particularly suitable for joining monopiles and transition pieces in offshore wind power generation. [Explanation of symbols]

[0058] 10 Joint structure 12,24 Tube tip 14 Outer surface 16 First cylindrical body 18 Inner surface 20 Second cylindrical body 22 Welded section

Claims

1. A joining structure consisting of a slip joint formed by fitting a second cylindrical body having a tapered inner peripheral surface onto the outer peripheral surface of a first cylindrical body having a tapered outer peripheral surface toward a cylindrical tip, A joining structure characterized in that the tip of the first cylindrical body is welded to the inner peripheral surface using the second cylindrical body as a backing metal.

2. 2. The joining structure according to claim 1, wherein the inner peripheral surface is welded by fillet welding or penetration welding.

3. The joining structure according to claim 1 or 2, characterized in that the first cylindrical body is a foundation for an offshore wind power generation facility, and the second cylindrical body is a foundation member for a wind turbine tower installed on the foundation.

4. A joining method for forming a slip joint by fitting a second cylindrical body having an inner peripheral surface tapered toward the outer peripheral surface of a first cylindrical body having an outer peripheral surface tapered toward the cylindrical tip, A joining method characterized in that the second cylindrical body is used as a backing metal and the tip of the first cylindrical body is welded to the inner peripheral surface.

5. The joining method according to claim 4, wherein welding is performed on the inner peripheral surface by fillet welding or penetration welding.

6. The joining method according to claim 4 or 5, characterized in that the first cylindrical body is a foundation for an offshore wind power generation facility, and the second cylindrical body is a foundation member for a wind turbine tower to be installed on the foundation.

Images