Method for assembling a tubular floating structure and its use

Abstract

A method for assembling a tubular floating structure and its use. First and second tubular members (11, 12) are welded to opposite sides of a stiffening ring (10) to obtain a double segment (12 / 11). Additional segments (13, 14) can be added to form a tubular multi-segment with a stiffening ring (10) between three adjacent tubular members (11, 12, 13). The resulting multi-segment (12 / 11 / 13) is used as a tubular buoyancy module for a floating offshore structure.

Description

[Technical Field]

[0001] The present invention relates to a method for assembling a tubular floating structure for an offshore support, for example a tubular floating structure for an offshore wind turbine. [Background technology]

[0002] For example, offshore wind turbine support platforms disclosed in U.S. Patent Application Publication No. 2020 / 269960, and other types of support platforms in the marine industry for floating fish farms, for example, disclosed in International Patent Application Publication No. WO 2021 / 053361, include buoyancy tanks that are moored to the seabed to maintain the structure in a desired location.

[0003] For large platforms, buoyancy tanks can be correspondingly large and difficult to manufacture. Typically, buoyancy tanks are manually assembled and welded using curved steel plates supported by stiffening rings and stringers in a highly labor-intensive process similar to shipbuilding. In a more industrial process, buoyancy tanks can be manufactured by assembling fully fabricated tubular elements and welding them edge-to-edge in succession to form a tank having the desired tubular length. To maintain the tubular shape underwater, stiffening rings are inserted into the tubular members and welded to the inner surface of the tubular members as a countermeasure against hydrostatic and dynamic pressures when installed under marine conditions.

[0004] Reinforcing rings are heavy, expensive, and time-consuming to install. Therefore, it is desirable to reduce the number of reinforcing rings, facilitate production, and shorten production time. Furthermore, inserting the reinforcing ring requires that the inner circle of the tubular member match the outer circle of the reinforcing ring with a small tolerance. However, due to the large size of the tubular member, there is a risk that its diameter may change or that the shape of the segment may deviate slightly from a circular shape and become oval. This may occur, for example, during handling and transportation of the segments. Such deviations in diameter and from a circular shape can cause difficulties when inserting circular reinforcing rings. This is particularly problematic when the central axis of the segment is oriented horizontally. Therefore, it is appropriate to insert the ring when the axis of the segment is oriented vertically. However, in this case, when welding is performed along both edges of the ring, a single weld must be performed from below the ring, which increases the difficulty of the welding process. Each method has its disadvantages.

[0005] It would therefore be desirable to find an improved assembly method that overcomes these disadvantages.

[0006] In other technical fields, the assembly of tubular elements into elongated tanks is standard practice, for example, when assembling silos in agriculture. In some silo structures, segments are provided with internal rings that are used for assembly using bolts. Another example can be found in French patent application FR 2 395 903, in which segments are provided with rings at their opposite ends, and then adjacent rings are stacked one on top of the other and welded to each other by welding from the side. However, side welding of such rings is difficult, especially if the welds are to be watertight. Therefore, methods known from silo manufacturing do not appear to be successfully applied to the production of large buoyancy tanks for floating offshore structures.

[0007] As a result, other improved assembly principles are needed. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] U.S. Patent Application Publication No. 2020 / 269960 [Patent Document 2] International Publication No. 2021 / 053361 [Patent Document 3] French Patent Application Publication No. 2395903 Summary of the Invention

[0009] It is therefore an object of the present invention to provide an improvement in the art, in particular to provide an assembly method for buoyancy tanks of offshore structures, in particular for offshore wind turbines. This object and further advantages are achieved by the assembly method and its uses as described and claimed below.

[0010] In essence, two tubular members are welded to opposite sides of a stiffening ring to obtain a double segment. Additional segments can be added to form a tubular multi-segment with the stiffening ring being a structural stabilizing ring between adjacent tubular members. The resulting multi-segment is used as a tubular buoyancy module for a floating offshore structure.

[0011] In the following, the term "tank" will be used together with the term "tubular buoyancy module" to follow the terminology of the art. Similarly, the segments for tubular buoyancy modules will also be referred to as tank segments, or simply as segments.

[0012] The assembly method includes two main steps:

[0013] 1. Tank segment manufacturing 2. Assembling the tank segments to form a complete tank

[0014] The tank segment includes a cylindrical tubular member and a reinforcing ring. The tubular member forms the wall of the segment and the final complete tank. Both sections are made of steel. The tubular member has a first edge and an opposing second edge at opposite ends of the tubular member. The reinforcing ring has a first surface and an opposing second surface at opposite ends of the reinforcing ring. The reinforcing ring also has an outer periphery that is larger than the outer periphery of the first edge of the tubular member and an inner periphery that is smaller than the inner periphery of the first edge of the tubular member. In this way, a certain degree of tolerance is ensured when positioning the tubular member on the reinforcing ring.

[0015] In the manufacture of tank segments, a reinforcing ring is placed horizontally and flat with its vertically oriented central axis facing upward, with its first surface facing upward and resting on its second surface. A tubular member is then placed onto the reinforcing ring from above, with its vertical axis concentric or nearly concentric with the vertical central axis of the reinforcing ring. Because the vertical axes of the tubular member and reinforcing ring are concentric, the tubular member rests on the first surface of the reinforcing ring. In this position, the outer periphery of the first edge of the tubular member is within the outer periphery of the first surface of the reinforcing ring, and the inner periphery of the first edge of the tubular member is outside the inner periphery of the first surface of the reinforcing ring. In this position, the tubular member and the reinforcing ring are joined by welding, forming a waterproof seam.

[0016] Because the outer periphery of the first edge of the tubular member is within the outer periphery of the first surface of the reinforcing ring and the inner periphery of the first edge of the tubular member is outside the inner periphery of the first surface of the reinforcing ring, the weld is of the fillet weld type, which can be performed with or without full penetration. Due to the orientation of the vertical axes of the tubular member and the reinforcing ring, the weld is performed in a horizontal position, which is very convenient to perform.

[0017] After completion of the manufacturing of the tank segment, when the tubular member and reinforcing ring are joined, the tank segment is rotated 180 degrees about a horizontal axis. While the reinforcing ring was installed below the tubular member during the manufacturing of the segment, the reinforcing ring is positioned above the tubular member after the rotation. Here, the segment rests on the downward-facing second edge of the tubular member, and here, the second surface of the reinforcing ring forms the upper surface of the tank segment.

[0018] The tank segments are assembled by placing the second segment on top of the first segment. The second segment is placed from above, its vertical axis concentric or nearly concentric with the vertical axis of the second segment, and the second edge of its tubular member rests on the second surface of the reinforcing ring of the first segment. Because the vertical axes are concentric, the second segment is placed in the following position: In this position, the outer periphery of the second edge of the second tubular member is within the outer periphery of the second surface of the reinforcing ring of the first segment, and the inner periphery of the second edge of the tubular member of the second segment is outside the inner periphery of the second surface of the reinforcing ring of the first segment. In this position, the tubular member of the second segment and the reinforcing ring of the first segment are joined by welding, forming a waterproof seam.

[0019] Since the outer periphery of the second edge of the tubular member of the first segment is within the outer periphery of the second surface of the reinforcing ring of the second segment and the inner periphery of the second edge of the tubular member of the first segment is outside the inner periphery of the second surface of the reinforcing ring of the second segment, the weld is of the fillet weld type, which can be performed with or without full penetration. Due to the orientation of the vertical axes of the tubular member and the reinforcing ring, the weld is performed in a horizontal position, which is very convenient to perform.

[0020] This method of manufacturing and assembling tank segments provides several advantages over the prior art.

[0021] Because the weld is applied to each reinforcing ring segment instead of the ring being inserted into the segment, time is saved and there are fewer tolerance requirements between the tubular member and the reinforcing ring, making manufacturing significantly easier.

[0022] Similarly, due to the placement of the tubular members on top of the reinforcing ring during segment manufacturing, the tolerance requirements between the individual tubular members are significantly reduced. In conventional manufacturing methods, tubular members are placed directly on top of each other, but the diameter and roundness of two adjacent tubular members must be the same to obtain a joint without stress concentrations resulting from misalignment between the tubular members. In the manufacturing method according to the present invention, certain variations in the diameter and roundness of two adjacent tubular members are acceptable because the reinforcing ring inserted between the tubular members significantly reduces stress concentrations resulting from misalignment between the tubular members.

[0023] Overall, the method, when used to assemble buoyancy modules of, for example, a tubular floating wind turbine offshore structure, provides an improved assembly of buoyancy elements for offshore structures.

[0024] In some specific embodiments, a first welding station is provided, the first welding station including a plurality of rollers arranged in a circular configuration and configured to rotatably support the first reinforcing ring on the rollers in a horizontal orientation during welding between the first tubular member and the first reinforcing ring. As will become apparent below, this first station is used to weld subsequent tubular members onto each ring to provide additional segments for assembling a multi-segment tube. At the first welding station, one or more welding machines are provided for welding.

[0025] In some embodiments, one or more welding machines are located on both the outside and inside of the tubular member, thereby facilitating simultaneous welding on both sides of the weld seam.

[0026] The welding machine is advantageously provided in a fixed location at the first welding station, and welding of the tubular member to the reinforcing ring is performed by rotating the combination of tubular member and reinforcing ring about its vertical central axis instead of moving the head along the edge.

[0027] This practical embodiment has the advantage that a stationary welding machine requires minimal and simple mechanical support compared to a welding machine that moves around a ring, where precision can be an issue when the head movements are large. This is especially true when the segments have diameters in the range of 5 to 15 meters.

[0028] In an advantageous embodiment, a second welding station is provided that includes a plurality of rollers arranged in a circular configuration and configured to rotatably support the first segment with the second ring-free edge when each first reinforcing ring is oriented upward and horizontally.

[0029] In practice, after welding the first tubular member to the first reinforcing ring at the first welding station to provide the first segment, the resulting first segment is turned upside down so that the first reinforcing ring faces upward, and the first segment is lifted upward into the second welding station, with rollers rotatably supporting the second edge of the first segment.

[0030] Optionally, a support ring or support plate is provided between the downward facing edge and the roller to protect the roller from potentially sharp downward facing edges.

[0031] After welding the second tubular member to the second reinforcing ring at the first welding station, the resulting second segment is turned upside down so that the second ring faces upward, and then the second segment is raised above the first ring of the first segment at the second welding station to form a double segment.

[0032] Advantageously, as described for the first welding station, one or more welding machines are installed on both the outside and inside of the tubular member, thereby facilitating simultaneous welding on both sides of the weld seam. The welding machines are advantageously provided in fixed locations at the second welding station, and welding of the segments to the ring is performed by rotating the two segments about their vertical central axes instead of by moving a head along the edges.

[0033] Optionally, the welding machine's welding head is height adjustable, for example by being mounted on the arm of a welding robot, so that the height of the welding head can be adjusted to match the height of a single segment. However, if all segments have a single standard height, head height adjustment is not necessary.

[0034] To further extend the length of the multi-segment structure, as is typically done in practice to build a buoyancy module of a desired height, additional segments can be manufactured and joined to the already joined segments by welding.

[0035] In a preferred embodiment, the additional segment is manufactured using the same method used to manufacture the first segment. After manufacturing, the additional segment is rotated upside down and lifted over a second welding station. The already assembled structure, which includes two or more segments, is then placed from above on top of the additional segment, with its vertical axis concentric or nearly concentric with that of the additional segment. In this position, the tubular member of the first segment and the reinforcing ring of the second segment are joined by welding, which forms a waterproof seam.

[0036] This method can be repeated for as many segments as desired to achieve the desired height.

[0037] It should be noted here that lifting a multi-segment already assembled with two or more segments above an additional segment may seem counterintuitive compared to lifting a single segment one after the other on top of an already welded multi-segment. However, as explained below, this arrangement is justified because it eliminates the need to lift the welding head upward with each additional segment. Instead, by first lifting the already welded multi-segment to a storage station and then always pointing only at a single segment for the next weld, the welding head does not need to be raised higher than the height of the single segment, which is typically in the range of 2 to 10 meters.

[0038] As mentioned above, to protect the rollers, the second welding station optionally includes a support ring or support plate between the rollers and the second downwardly facing edge of the single segment as it is elevated from the first welding station onto the second welding station, which becomes more important as the number of segments welded together into the elongated tube increases, as the weight increases proportionately.

[0039] Advantageously, one welding station, or rather both welding stations, not only have a first roller supporting the segment and ring combination from below, but also a second roller abutting the combination laterally to accurately position and guide the ring and tubular member during rotation and simultaneous welding.

[0040] The invention will now be explained in more detail with reference to the drawings. [Brief explanation of the drawings]

[0041] [Figure 1] 1 shows the arrangement of the rotary support for the welding station. [Figure 2] Three stations for welding are shown. [Figure 3A] The first assembly step is shown in a perspective view. [Figure 3B] The first assembly step is shown in side view. [Figure 4] 10 shows the subsequent steps for assembling the double segments. [Figure 5] 10 shows the subsequent steps for assembling the double segments. [Figure 6] 10 shows the subsequent steps for assembling the double segments. [Figure 7] 10 shows the subsequent steps for assembling the double segments. [Figure 8] 10 shows the subsequent steps for assembling the double segments. [Figure 9] 10 shows the subsequent steps for assembling the double segments. [Figure 10A] An additional assembly step using the third segment is shown in side view. [Figure 10B] 10 shows a perspective view of an additional assembly step with a third segment in preparation. [Figure 11A] The triple segment assembly is shown in side view. [Figure 11B] 1 shows a perspective view of the triple segment assembly. [Figure 12] 10 shows a side view illustrating the movement of the triple segments of the storage station. [Figure 13] A side view of a triple segment of a storage station is shown. [Figure 14] 1 shows a perspective view of a triple segment storage station and the preparation of a fourth segment at a first welding station. [Figure 15A] 1 shows a perspective view of a welding machine at a first welding station and a second welding station; [Figure 15B] 1 shows an enlarged cross section of the welding machine at the first welding station. DETAILED DESCRIPTION OF THE INVENTION

[0042] FIG. 1 shows a rotary support arrangement for welding station 1. Welding station 1 includes a plurality of first rollers 5 on a corresponding first frame 4 for rotatably supporting circular tubular segments from below for welding. The first frames 4 and first rollers 5 are arranged in a circular configuration to support the corresponding circular structures. Welding station 1 also includes second rollers 6 on a corresponding second frame 7 for abutting such circular tubular structures from the side, properly guiding the circular tubular structures in a rotational movement about a vertical central axis.

[0043] Optionally, the second roller 6 is movable radially in and out in the horizontal direction, which is also useful for easily fitting the ring-shaped segments into the roller station 1 if the segment diameter varies and even if it deviates slightly from a circle.

[0044] FIG. 2 shows three stations for welding. The first welding station 1 and the second welding station 1′ are provided in addition to a third station, which is a storage station 1″, which is provided with a fixed support ring 9′. The support ring 9 is provided at the second welding station 1′, for example, similar to the support ring 9′ at the storage station 1″. Further referring to FIG. 1, the support ring 9 is supported by the first roller 5 and fixed so as to be guided in a circle by the second roller 6. Instead of the support ring 9, a support plate is optionally used at the second welding station 1′.

[0045] 3A (perspective view) and 3B (side view) show a first assembly step using a first welding station 1 and a second welding station 1'. A reinforcing ring 10 is placed on a support roller 5 of the first welding station 1 and is guided by a second roller 6 abutting its outer periphery for rotation about a vertical axis X.

[0046] 4 illustrates the placement of the first tubular member 11 on the reinforcing ring 10, with the first edge 11A of the first tubular member 11 abutting the top surface of the reinforcing ring 10. Advantageously, the first edge 11A has a smaller diameter than the reinforcing ring 10, to ensure that even if the first edge 11A deviates slightly from round due to deformation, for example, during shipping and handling, the entire first edge 11A rests on the reinforcing ring 10, leaving sufficient space for a fillet weld. The orientation of the first tubular member 11 positioned on top of the reinforcing ring 10 provides advantages, particularly in that welding can be performed from above, which is easier than welding from below, due to the melting of the metal during welding.

[0047] FIG. 5A shows the rotation and movement of a first segment produced by welding a tubular member 11 and a reinforcing ring 10 from a first welding station 1 to a second welding station 1'. The final result of the first segment rotated onto the second welding station 1' is shown in FIG. 5B. Arrow 8 indicates the orientation of the segment relative to the vertical direction in FIG. 5A, with arrow 8 pointing downward. While a first edge 11A of the first tubular member 11 is being welded to the first reinforcing ring 10, a second edge 11B of the first tubular member 11 rests on, but is not fixed to, the support ring 9. This is because the support ring 9 remains on the rollers 5 of the second support station 1' to support the various segments, and the segments then rest their downward-facing edges on the support ring 9.

[0048] 6 illustrates the preparation of the second segment, in which the first edge 12A of the second tubular member 12 is welded to the second reinforcing ring 10 at the first welding station 1. The second reinforcing ring 10 is similar in size to the first reinforcing ring 10 in the illustrative case of the present invention, although this is not essential. The procedure is identical to that of the first segment shown in FIG. 4 and described above.

[0049] As shown in FIG. 7A, once welding is completed at the first welding station 1, the second segment 12 rotates and is lifted toward the top of the first segment at the second welding station 1'. As a result, the downward-facing second edge 12B of the second segment 12 abuts the first reinforcing ring 10 of the first segment 11 for welding, as shown in FIG. 7B. By welding at the second welding station 1', the two segments form a double segment 12 / 11, in which the two tubular segments 11, 12 are fixed to each other, and the first reinforcing ring 10 is positioned as a single ring between the two adjacent tubular members 11, 12, with the second reinforcing ring 10 on top. The second edge 11B of the first segment 11 rests on the support ring 9.

[0050] In the procedure shown, the first segment is lifted over the second welding station 1', and the second segment is lifted over the top of the first segment. Alternatively, the first segment can be lifted from the first welding station 1 over the storage station 1'', the second segment can be welded and then lifted from the first welding station 1 over the second welding station 1', and then the first segment can be lifted from the storage station 1' over the second segment at the second welding station 1'. While this is possible, it requires additional lifting operations and is therefore not preferred. Considering the relatively large size of the segments, typically 5-10 meters in diameter, the number of operations is advantageously minimized.

[0051] The double segment 12 / 11 is then lifted from the second welding station 1' and stored in the storage station 1'' with the downwardly facing second edge 11B of the first tubular member 11 resting on the support ring 9' of the storage station 1'', as shown in Figure 8.

[0052] 9 shows the welding of the third tubular member 13 to the third reinforcing ring 10. As shown in FIG. 10A, the resulting third segment is lifted from the first welding station 1, rotated, and lifted so that the downward-facing second edge 13B of the third tubular member 13 is positioned on the top surface of the support ring 9 of the second welding station 1′, with the reinforcing ring 10 facing upward, as shown in FIG. 10B.

[0053] As shown in FIG. 11A, the double segment 12 / 11 is then lifted from the storage station 1'' and the downward-facing second edge 11B of the first tubular member 11 is placed on the third support reinforcing ring 10 at the top of the third tubular member 13, resulting in the configuration shown in FIG. 11B. At the second welding station 1', the downward-facing second edge 11B of the first tubular member 11 is welded on the third support reinforcing ring 10 at the top of the third tubular member 13 to form the triple segment 12 / 11 / 13.

[0054] As shown in Figure 12, the triple segment 12 / 11 / 13 is lifted from the second welding station 1' and stored in a storage station 1'', as shown in Figure 13. As shown in Figure 14, a fourth segment is produced at the first welding station 1 by using an additional tubular member 14 and an additional reinforcing ring 10, and the procedure described is repeated for as many segments as desired to form the final buoyant structure.

[0055] Although an additional lifting step is required, the procedure shown offers several advantages over the following alternative: In this alternative, the double segment 12 / 11 is not lifted from the second welding station 1', but the third segment 13 is lifted toward the top of the double segment 12 / 11, and the fourth segment 14 is lifted toward the top of the triple segment. By lifting and moving the double segment 12 / 11 and its corresponding triple segment 12 / 11 / 13 twice, i.e., from the second welding station 1' to the storage station 1' and then back to the second welding station 1' when an additional single segment is installed on top of it, it is always the bottom segment that is welded at the second welding station 1'. Therefore, adding a segment does not require the welding head at the second welding station 1' to be lifted upward. Because the tubular members 11, 12, 13, and 14 of the segments usually have the same height, there is no need to move the welding head to assemble all the added rings upward. This in particular allows lifting and welding at the two stations 1, 1' to be carried out simultaneously, minimizing the complexity of the structure and operation and increasing speed.

[0056] The welding machine 15 is shown in Figure 15A and in an enlarged view in Figure 15B. As shown in Figure 15A, the welding of the third tubular member 13 onto the corresponding reinforcing ring 10 can be performed simultaneously with the welding of the second tubular member 12 onto the reinforcing ring 10 already welded to the first tubular member 11 of the first segment.

[0057] As shown in FIG. 15B, the welding machine 15 has a fixed base 16 and welds the third tubular member 13 onto the third reinforcing ring 10 from above. The welding machine 15 has a connecting arm 17 or moves a welding head 18 to the welding location. The distance of the welding head 18 from the fixed base 16 is adjustable to accommodate slight variations in the welding position and angle, but the welding machine 15 is not configured to reach the upper edge 13B of the third tubular member 13. This was explained above for the purpose of simplifying the welding station 15. However, as explained in detail above, it is necessary to move a long multi-segment onto the storage station 1″ and then move from the storage station 1″ a segment with only a single tubular member toward the top of the reinforcing ring 10. This becomes necessary when an additional single segment is fabricated at the first welding station 1 and moved to the second welding station 1′.

Claims

1. A method for assembling buoyancy modules for a tubular floating offshore structure, the method comprising providing a first tubular member (11) and a first stiffening ring (10) for a first segment, and a second tubular member (12) and a second stiffening ring (10) for a second segment, each of the first and second tubular members (11, 12) having a first edge (11A, 12A) and an opposing second edge (11B, 12B); The method further includes providing, for each of the first and second segments, a corresponding reinforcing ring (10) that is arranged flat and has an outer periphery that is greater than the circumference of the corresponding tubular member (11, 12) of the first edge (11A, 12A); placing the tubular member (11, 12) with the first edge (11A, 12A) on the reinforcing ring (10) within the outer periphery; and welding the first edge (11A, 12A) to the reinforcing ring (10) from above, so that the corresponding reinforcing ring (10) is facing upward. and then lifting one of the segments with the second edge (11B, 12B) of the tubular member (11, 12) above the reinforcing ring (10) of the other of the segments, after turning both welded segments upside down so that the reinforcing ring (10) of the other of the segments is welded from above, and welding the second edge (11B, 12B) to the reinforcing ring (10) from above, thereby forming a double segment (12 / 11) with one of the reinforcing rings (10) at the top and a downward-facing second edge (11B, 12B) without a reinforcing ring (10) at the bottom.

2. The method further includes providing a third reinforcing ring (10) that is laid flat and has a third outer circumference that is greater than the circumference of a first edge (13A) of a third tubular member (13); placing the third tubular member (13) with the first edge (13A) over the third reinforcing ring (10) within the third outer circumference; and welding the first edge (13A) of the third tubular member (13) to the third reinforcing ring (10) to provide a third segment.

2. The method of claim 1, further comprising: turning the third segment upside down so that the third reinforcing ring (10) faces upward, then lifting the double segment (12 / 11) with the second edge (11B, 12B) on the underside of the segment towards the top of the third reinforcing ring (10); and welding the second edge (11B, 12B) to the third reinforcing ring (10) from above to provide a triple segment (12 / 11 / 13).

3. 3. The method according to claim 1, wherein the method includes providing a first welding station (1) having a plurality of rollers (5, 6) arranged in a circular configuration during welding between the first tubular member (11) and the first reinforcing ring (10) and configured to rotatably support the first reinforcing ring (10) in a horizontal orientation on the rollers (5, 6), and the method includes maintaining a first welding machine (15) for welding at a fixed location at the first welding station (1); and welding the first tubular member (11) to the first reinforcing ring (10) while rotating the first ring (11) about a vertical central axis (X).

4. The method includes providing a second welding station (1') comprising a plurality of other rollers (5, 6) arranged in a circular configuration and configured to rotatably support the first tubular member (11) with the second edge (11B) facing downwards when each of the first reinforcing rings (10) faces upwards, the method comprising: - after welding the first tubular member (11) to the first reinforcing ring (10) at the first welding station (1) to provide the first segment, lifting the first segment from the first welding station (1) and turning it upside down so that the first reinforcing ring (10) faces upwards; - after welding the second tubular member (12) to the second reinforcing ring (10) at the first welding station (1) to provide the second segment, lifting the second segment from the first welding station (1) and turning the second segment upside down so that the second reinforcing ring (10) faces upwards; - lifting the first and second segments above each other above the second welding station (1') after turning them upside down, and welding the upper second edges (11B, 12B) of the two segments (11, 12) to the lower reinforcing ring (10) of the two segments (11, 12) at the second welding station (1') while the rollers (5, 6) rotatably support the lower second edges (11B, 12B) of the two segments (11, 12), thereby forming a double segment (12 / 11) with an upper segment and a lower segment; - maintaining a second welding station (15) in a fixed position on the second welding station (1') and rotating the double segment (12 / 11) about the vertical central axis while welding the undersides of the two reinforcing rings (10) from above; The method of claim 3, comprising:

5. - lifting the double segment (12 / 11) from the second welding station (1') onto a storage station (1''); - welding the third tubular member (13) to the third reinforcing ring (10) at the first welding station (1) to provide the third segment, then turning the third segment upside down so that the third reinforcing ring (10) faces upwards, and then lifting the third segment above the second welding station (1'); - then lifting the double segment (12 / 11) from the storage station (1'') onto the third reinforcing ring (10) at the second welding station (1') and welding the lower second edges (11B, 12B) of the tubular members (11, 12) of the double segment (12 / 11) onto the third reinforcing ring (10) to form a triple segment (12 / 11 / 13) consisting of the first segment, the second segment and the third segment; - lifting the formed triple segment (12 / 11 / 13) from the second welding station (1'); 5. The method of claim 4 when dependent on claim 2, comprising:

6. 6. The method according to claim 4 or 5, wherein the second welding station (1′) comprises a support ring (9) or a support plate between the rollers (5, 6) and the second edge (11B) of the first tubular member (11), and the method comprises lifting the first segment from the first welding station (1), turning the first segment upside down, and lifting the first segment onto the support ring (9) or the support plate of the second welding station (1′) before welding the double segment (12 / 11) at the second station (1′).

7. 7. The method according to claim 3, wherein the rollers (5, 6) of at least one of the first and second welding stations (1, 1') comprise a first roller (5) supporting the combination of the tubular member (11, 12, 13, 14) and the reinforcing ring (10) from below and a second roller (6) abutting laterally against the combination, the method comprising guiding the combination by means of the second roller (6) during welding, which is carried out simultaneously with rotation.

8. Use of the method according to any of claims 1 to 7 for assembling buoyancy modules of a tubular floating wind turbine offshore structure.

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