Method of assembling tubular floating structure and use thereof

Abstract

Methods of assembling tubular floating structures and uses thereof are provided. The first and second tubular members (11, 12) are welded to opposite sides of the reinforcing ring (10) to obtain a double segment (12 / 11). Additional segments (13, 14) may be added to form a tubular multi-segment with a reinforcing ring (10) between adjacent five tubular members (11, 12, 13). The resulting multi-segment (12 / 11 / 13) is used as a tubular buoyancy module in a floating offshore structure.

Description

Technical Field

[0001] The present invention relates to a method of assembling a tubular floating structure for offshore support, for example for offshore wind turbines. Background Art

[0002] Offshore wind turbine support platforms (e.g., as disclosed in U.S. patent application US2020 / 269960) and other types of support platforms in the offshore industry (e.g., support platforms for floating fish farms as disclosed in international patent application WO2021 / 053361) include buoyancy tanks that are moored to the seabed to keep the structure in a desired position.

[0003] For large platforms, buoyancy tanks are correspondingly large and can be challenging to manufacture. Typically, buoyancy tanks are manually assembled and welded from bent steel plates supported by reinforcing rings and longitudinal beams in a process similar to shipbuilding and highly labor-intensive. In a more industrialized process, buoyancy tanks can be manufactured by assembling and welding complete prefabricated tubular elements that are welded together edge to edge in rows so that they form a tank with the desired tubular length. In order for the tubular member to maintain its tubular shape when in the water, reinforcing rings are inserted into the tubular member and welded to the inner surface of the tubular member as a measure to resist hydrostatic and hydrodynamic pressures when installed in offshore conditions.

[0004] Reinforcement rings are heavy, increase costs, and installation takes time, so it is desirable to reduce their number and facilitate production and shorten production time. In addition, the insertion of reinforcement rings requires that the inner circle of the tubular member matches the outer circle of the reinforcement ring with a small tolerance. However, due to the large size of the tubular member, there is a risk that its diameter changes or the shape of the segment deviates slightly from the circular shape and becomes elliptical, such as the risk caused by the handling and transportation of the segment. This deviation in diameter and the deviation from the circular shape may cause difficulties when inserting the circular reinforcement ring. This is particularly problematic when the segment is oriented horizontally with its central axis. Therefore, it is best to insert the ring when the axis of the segment is oriented vertically. However, in this case, when welding is performed along the two edges of the ring, it is necessary to perform a single weld from the bottom of the ring, which increases the difficulty of the welding process. Each method has its disadvantages.

[0005] Therefore, there is a need to find improved assembly methods that overcome these disadvantages.

[0006] In other technical fields, the assembly of tubular elements into elongated tanks is implemented as standard, for example when assembling silos in agriculture. In some silo structures, the segments are provided with inner rings for assembly with bolts. Other examples can be found in French patent document FR2395903, in which the segments are provided with rings at their opposite ends, then stacked step by step, and adjacent rings are welded to each other by welding from the side. However, side welding of such rings is difficult, especially if the weld must be waterproof. Therefore, the methods known from silo production do not seem to be successfully applied to the production of large buoyancy tanks for floating offshore structures.

[0007] Therefore, alternative and improved assembly principles are needed. Summary of the invention

[0008] It is therefore an object of the present invention to provide an improvement in the art. In particular, the object is to provide an assembly method for a buoyancy tank in an offshore structure, in particular a buoyancy tank for an offshore wind turbine. This object and other advantages are achieved by an assembly method and its use as described below and in the claims.

[0009] In short, two tubular members are welded to opposite sides of a reinforcement ring to obtain a double segment. Other segments can be added to form a tubular multi-segment with a reinforcement ring between adjacent tubular members, which is a structural stabilizing ring. The resulting multi-segment is used as a tubular buoyancy module in a floating offshore structure.

[0010] In the following the term tank is used together with the term tubular buoyancy module as this is the terminology according to the technical field. Similarly, the segments for the tubular buoyancy modules will also be referred to as tank segments or simply segments.

[0011] The assembly method includes the following two main steps:

[0012] 1. Manufacturing of tank segments

[0013] 2. Assemble the tank segments to form a complete tank

[0014] The tank segment includes a cylindrical tubular member and a reinforcement ring. The tubular member forms the wall of the segment and ultimately the complete tank. Both components are made of steel. The tubular member has a first edge and an opposite second edge at opposite ends of the tubular member. The reinforcement ring has a first surface and an opposite second surface on opposite sides of the reinforcement ring. The reinforcement ring also has an outer circumference that is set larger than the outer circumference of the first edge of the tubular member, and an inner circumference that is set smaller than the inner circumference of the first edge of the tubular member. As such, there is some tolerance when positioning the tubular member on the reinforcement ring.

[0015] In the manufacture of the tank segment, the reinforcement ring is placed horizontally with the central axis oriented vertically, with its first surface facing upward and resting on its second surface. The tubular member is then placed onto the reinforcement ring from above, with the vertical axis of the tubular member being concentric or approximately concentric with the vertical central axis of the reinforcement ring. Due to the concentricity of the vertical axes of the tubular member and the reinforcement ring, the tubular member will rest on the first surface of the reinforcement ring in a position where the outer circumference of the first edge of the tubular member is within the outer circumference of the first surface of the reinforcement ring and the inner circumference of the first edge of the tubular member is outside the inner circumference of the first surface of the reinforcement ring. In this position, the tubular member and the reinforcement ring are joined by welding, which forms a waterproof seam.

[0016] Since the outer circumference of the first edge of the tubular member is within the outer circumference of the first surface of the reinforcement ring, and the inner circumference of the first edge of the tubular member is outside the inner circumference of the first surface of the reinforcement ring, the weld is a fillet weld type, which can be performed with full penetration or incomplete penetration. Due to the vertical axis orientation of the tubular member and the reinforcement ring, the weld is performed in a horizontal position, which is very convenient to perform.

[0017] After completing the manufacture of the tank segment, in which the tubular member and the reinforcement ring have been joined, the tank segment is rotated 180 degrees about the horizontal axis. Although the reinforcement ring has been placed below the tubular member during the manufacture of the segment, it is positioned above the tubular member after the rotation. The segment now rests on the downwardly facing second edge of the tubular member, and the second surface of the reinforcement ring now forms the upper surface of the tank segment.

[0018] The assembly of the tank segments is performed by placing the second segment on top of the first segment. The second segment is placed from above with its vertical axis concentric or approximately concentric with the vertical axis of the first segment and the second edge of its tubular member resting on the second surface of the reinforcement ring of the first segment. Due to the concentricity of the vertical axis, the second segment will be placed in a position where the outer circumference of the second edge of the second tubular member is within the outer circumference of the second surface of the reinforcement ring of the first segment and the inner circumference of the second edge of the tubular member of the second segment is outside the inner circumference of the second surface of the reinforcement ring of the first segment. In this position, the tubular member of the second segment and the reinforcement ring of the first segment are joined by welding, which forms a waterproof seam.

[0019] Since the outer circumference of the second edge of the tubular member of the first segment is within the outer circumference of the second surface of the reinforcement ring of the second segment, and the inner circumference of the second edge of the tubular member of the first segment is outside the inner circumference of the second surface of the reinforcement ring of the second segment, the weld is a fillet weld type, which can be performed with full penetration or incomplete penetration. Due to the vertical axis orientation of the tubular member and the reinforcement ring, the weld is performed in a horizontal position, which is very convenient to perform.

[0020] This method of manufacturing and assembling tank segments has many advantages over conventional techniques.

[0021] Since the segments are welded on the respective reinforcement rings instead of inserting the rings into the segments, time is saved and less tolerance is required between the tubular member and the reinforcement rings, which greatly simplifies manufacturing.

[0022] Similarly, since the tubular members are placed on top of the reinforcement rings during the manufacture of the segments, the tolerance requirements between the individual tubular members are significantly reduced. In conventional manufacturing methods where the tubular members are placed directly on top of each other, the diameter and roundness of two adjacent tubular members need to be the same in order to obtain a joint that does not generate stress concentrations due to misalignment between the tubular members. In the manufacturing method according to the invention, some variation in the diameter and roundness of two adjacent tubular members is allowed, since the reinforcement ring inserted between the tubular members will significantly reduce the stress concentrations generated due to misalignment between the tubular members.

[0023] In summary, the method is an improvement in the assembly of buoyancy elements for offshore structures, for example when used to assemble buoyancy modules of tubular floating wind turbine 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 reinforcement ring in a horizontal orientation on the rollers during welding between the first tubular member and the first reinforcement ring. As will become apparent below, the first station is used to weld subsequent tubular members to corresponding rings to provide additional segments for assembling a multi-segmented pipe. In the first welding station, one or more welding machines are provided for welding.

[0025] In some embodiments, one or more welders are placed on the outside and inside of the tubular member to facilitate simultaneous welding on both sides of the weld.

[0026] The welding machine is advantageously arranged at a fixed position at the first welding station and the welding of the tubular member to the reinforcement ring is accomplished while the tubular member and reinforcement ring combination is rotated about its vertical center axis, rather than moving the head along the edge.

[0027] The advantage of this practical embodiment is that the stationary welding machine requires minimal and only simple mechanical support compared to a welding machine that moves around the ring, since accuracy can be a challenge with large movements of the head. This is especially true when the diameter of the segment is in the range of 5 to 15 meters.

[0028] In an advantageous embodiment, a second welding station is provided, comprising a plurality of rollers arranged in a circular configuration and configured for rotatably supporting the first segment with its second non-ringed edge when the corresponding first ring faces upward and is in a horizontal orientation.

[0029] In practice, after welding the first tubular member to the first reinforcement ring in a first welding station to obtain the first segment, the resulting first segment is inverted so that the first reinforcement ring faces upward, and the first segment is lifted onto a second welding station, where rollers rotatably support the second edge of the first segment.

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

[0031] After welding the second tubular member to the second reinforcement ring in the first welding station, the resulting second segment is inverted so that the second ring faces upward. The second segment is lifted onto the first ring of the first segment in the second welding station to form a double segment.

[0032] Advantageously, as explained for the first welding station, one or more welding machines are placed on the outside and inside of the tubular member, thereby facilitating simultaneous welding on both sides of the weld. The welding machines are advantageously arranged at fixed positions at the second welding station, and the welding of the segments to the ring is done while the two segments are rotated about their vertical axes, rather than moving the head along the edge.

[0033] Optionally, the height of the welding head of the welding machine is adjustable, for example by being mounted on the arm of a welding robot. Thus, the height of the welding head can be adjusted to match the height of a single segment. However, if all segments have a single standardized height, then the height of the head does not need to be adjusted.

[0034] To extend the length of the multi-segment structure even further (which is often done in practice to construct a buoyancy module of a desired height), additional segments may be manufactured and joined to segments already joined by welding.

[0035] In a preferred embodiment, the additional segment is manufactured using the same method as used to manufacture the first segment. After manufacture, the additional segment is inverted and lifted onto a second welding station. Then, the already assembled structure comprising two or more segments is placed from above on top of the additional segment, with its vertical axis concentric or approximately concentric with the vertical axis 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 joint.

[0036] The method may be repeated with as many relevant segments as necessary to achieve the desired height.

[0037] It should be noted here that the method of lifting an already combined multi-section with two or more sections onto additional sections may seem counterintuitive compared to the method of lifting individual sections one by one onto the top of the already welded multi-section. However, as will be explained below, there are good reasons for this arrangement, because the welding head does not have to be lifted upwards with each added section. Instead, by first lifting the already welded multi-section to a storage station and then always lifting only onto a single section for the next weld, the welding head does not need to be lifted above the height of the single section, 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 plate between the rollers and the second downwardly facing edge of the individual segments that are lifted off the first welding station and onto the second welding station. This becomes more important the more segments are welded together into an elongated tube, as weight increases proportionally.

[0039] Advantageously, one welding station instead of two comprises not only a first roller supporting the segment and ring combination from below, but also a second roller laterally adjoining the combination for correctly positioning and guiding the ring and the tubular element during rotation and simultaneous welding. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The present invention will be described in more detail with reference to the accompanying drawings, in which

[0041] Figure 1 A rotary support device for a welding station is shown;

[0042] Figure 2 Three stations for welding are shown;

[0043] Figure 3A A first assembly step is shown in perspective; Figure 3B A first assembly step is shown in side view;

[0044] Figures 4 to 9 The subsequent steps for the assembly of the double segment are shown;

[0045] Fig. 10A Another assembly step is shown in perspective view, wherein the third segment is shown in side view;

[0046] Fig. 10B A further assembly step is shown in perspective, wherein the third segment is in preparation;

[0047] Fig.11A The three-segment assembly is shown in side view;

[0048] Fig. 11BThe three-segment assembly is shown in perspective view;

[0049] Fig.12 A side view showing the movement of three segments to a storage station;

[0050] Fig.13 A side view of three sections in a storage station is shown;

[0051] Fig.14 a perspective view showing three segments in a storage station and the preparation of a fourth segment in a first welding station;

[0052] Fig.15A The welding machines in the first welding station and the second welding station are shown in perspective view;

[0053] Fig. 15B An enlarged cross section of a welding machine in a first welding station is shown. DETAILED DESCRIPTION

[0054] Figure 1 A rotary support device for a welding station 1 is shown. It comprises a plurality of first rollers 5 on respective first frames 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 for supporting respective circular structures. It also comprises second rollers 6 on respective second frames 7 for abutting such circular tubular structures from the side and properly guiding them in rotational movement around a vertical central axis.

[0055] Optionally, the second roller 6 can be moved radially in and out in the horizontal direction. This is useful if the segment diameter varies and also in order to make it easier to fit the ring segment into the roller station 1 , even if the ring segment deviates slightly from a circular shape.

[0056] Figure 2 Three stations for welding are shown. A first welding station 1 and a second welding station 1 ' are provided in addition to the third station, which is a storage station 1 '', the latter comprising a fixed support ring 9'. The support ring 9 is arranged on the second welding station 1 ', for example similar to the support ring 9' of the storage station 1 '. Further reference Figure 1 , a support ring 9 is supported by the first roller 5 and fixed to be guided into a circular shape by the second roller 6. Instead of the support ring 9, a support plate is optionally used on the second welding station 1'.

[0057] Figure 3A Perspective drawing and Figure 3B The side view of shows a first assembly step using a first welding station 1 and a second welding station 1 '. The reinforcement ring 10 is placed on the support rollers 5 of the first welding station 1 to rotate around the vertical axis X, guided by the second rollers 6 abutting its periphery.

[0058] Figure 4The first tubular member 11 is shown placed onto the reinforcement ring 10, wherein the first edge 11A of the first tubular member 11 abuts the upper surface of the reinforcement ring 10. Advantageously, the first edge 11A has a smaller diameter than the reinforcement ring 10 to ensure that the entire first edge 11A rests on the reinforcement ring 10 and leaves enough room for the fillet weld, even if the first edge 11A deviates slightly from a circular shape, for example due to deformation caused by transportation and handling. The orientation of the first tubular member 11 on top of the reinforcement ring 10 has the advantage that welding can be performed from above, which is easier than welding from below, in particular due to the melting of the metal during the welding process.

[0059] Figure 5A The first section manufactured by welding the tubular member 11 and the reinforcement ring 10 is shown rotating and moving from the first welding station 1 to the second welding station 1'. Figure 5B The final result of the first segment being rotated to the second welding station 1' is shown in FIG. Arrow 8 shows the relative rotation of the segment to the second welding station 1'. Figure 5A , with arrow 8 pointing downwards. When the first edge 11A of the first tubular member 11 is welded to the first reinforcement ring 10, the second edge 11B of the first tubular member 11 rests on the support ring 9 but is not fastened to the support ring 9, because the support ring 9 is held on the rollers 5 of the second support station 1' for supporting the individual segments, which are then placed on the support ring 9 with their edges facing downwards.

[0060] Figure 6 The preparation of the second segment is shown, wherein the first edge 12A of the second tubular member 12 is welded to the second reinforcement ring 10 in the first welding station 1. In this exemplary case, the second reinforcement ring 10 is similar in size to the first reinforcement ring 10, but this is not strictly necessary. The process is similar to Figure 4 The process is the same as the first section shown in and explained above.

[0061] like Fig. 7A As shown, once the welding in the first welding station 1 is completed, the second segment is rotated and lifted onto the top of the first segment in the second welding station 1' so that the second downwardly facing edge 12B of the second segment 12 abuts the first reinforcement ring 10 of the first segment 11 for welding. Figure 7B By welding in the second welding station 1 ', the two segments form a double segment 12 / 11, wherein the two tubular segments 11, 12 are fastened to each other, wherein the first reinforcement ring 10 is located as a single ring between the two mutually adjacent tubular members 11, 12, and the second reinforcement ring 10 is located on top. The second edge 11B of the first segment 11 rests on the support ring 9.

[0062] In the process shown, the first segment is lifted onto the second welding station 1' and the second segment is lifted on top of the first segment. Alternatively, the first segment is lifted off the first welding station 1 and onto the storage station 1", and the second segment after welding is lifted from the first welding station 1 to the second welding station 1', after which the first segment is lifted from the storage station 1" onto the second segment in the second welding station 1'. This is possible but not preferred, as it requires additional lifting operations. Note that the segments are large in size, typically 5-10 meters in diameter, which helps to minimize the number of operations.

[0063] Subsequently, the double segment 12 / 11 is lifted away from the second welding station 1' and Figure 8 As shown, stored in a storage station 1 ″, wherein the downwardly facing second edge 11B of the first tubular member 11 rests on a support ring 9 ′ of the storage station 1 ″.

[0064] Fig. 9 FIG. 1 shows the welding of the third tubular member 13 and the third reinforcement ring 10. Fig. 10A As shown, the resulting third segment is lifted away from the first welding station 1, rotated, and lifted onto the upper surface of the support ring 9 of the second welding station 1' with the second edge 13B of the third tubular member 13 facing downwards, and with its reinforcement ring 10 facing upwards, as shown in FIG. Fig. 10B shown.

[0065] like Fig.11A As shown, the double segment 12 / 11 is then lifted away from the storage station 1", and the downwardly facing second edge 11B of the first tubular member 11 is lifted onto the third support reinforcement ring 10 on top of the third tubular member 13, thereby forming Fig. 11B Configuration shown. In the second welding station 1 ', the downwardly facing second edge 11B of the first tubular member 11 is welded to the third support reinforcement ring 10 on top of the third tubular member 13 to form three sections 12 / 11 / 13.

[0066] like Fig.12 As shown, the three segments 12 / 11 / 13 are lifted away from the second welding station 1' and as shown in FIG. Fig.13 As shown, it is stored in storage station 1". Fig.14 As shown, a fourth segment is produced in the first welding station 1 by using another tubular member 14 and another reinforcement ring 10, and the described process is repeated for the required number of segments to form the final buoyant structure.

[0067] Despite the need for an additional lifting step, the process shown has some advantages over the alternative in which the double segment 12 / 11 is not lifted off the second welding station 1', but rather the third segment 13 is lifted on top of the double segment 12 / 11 and the fourth segment 14 is lifted on top of the triple segment. By lifting and moving the double segment 12 / 11 and the corresponding triple segment 12 / 11 / 13 twice, namely from the second welding station 1' to the storage station 1", and back to the second welding station 1' when another single segment has been placed in the second welding station 1', the lowest segment in the second welding station 1' is always welded. Therefore, the welding head in the second welding station 1' does not need to be lifted upwards due to the addition of segments. Since the tubular members 11, 12, 13, 14 of the segments are generally of the same height, there is no need to move the welding head for assembly upwards with each added ring, which minimizes the complexity and speed of construction and operation, especially since the lifting and welding at the two stations 1, 1' can be done simultaneously.

[0068] Welding machine 15 Fig.15A is shown in Fig. 15B A close-up view is shown in FIG. Fig.15A As shown, welding the third tubular member 13 to the corresponding reinforcement ring 10 may be performed simultaneously with welding the second tubular member 12 to the reinforcement ring 10 that has been welded to the first tubular member 11 of the first section.

[0069] like Fig. 15B As shown, the welding machine 15 has a fixed base 16 and welds the third tubular member 13 to the third reinforcement ring 10 from above. The welding machine 15 has a link arm 17 that moves the welding head 18 to the welding position. The distance of the welding head 18 from the fixed base 16 is adjustable to slightly change 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 is explained above for the purpose of simplifying the welding station 15. However, as explained in detail above, once the additional single segment has been manufactured in the first welding station 1 and moved to the second welding station 1', the longer multi-segment must be moved to the storage station 1 "and then moved from the storage station 1 "to the top of the reinforcement ring 10 with only the segment of a single tubular member.

Claims

1. A method for assembling a buoyancy module of a tubular floating offshore structure, wherein the method comprises providing a first tubular member (11) and a first reinforcement ring (10) for a first segment and a second tubular member (12) and a second reinforcement ring (10) for a second segment, each of the first tubular member and the second tubular member (11, 12) comprising a first edge (11A, 12A) and an opposite second edge (11B, 12B); wherein the method further comprises providing, for each of the first segment and the second segment, a respective reinforcement ring (10), the respective reinforcement ring lying flat and having an outer circumference larger than the circumference of the first edge (11A, 12A) of the respective tubular member (11, 12), within which the tubular member (11, 12) is assembled. The components (11, 12) are placed onto the reinforcement ring (10) with their first edges (11A, 12A) and the first edges (11A, 12A) are welded to the reinforcement ring (10) from above; after the two welded segments are inverted so that their corresponding reinforcement rings (10) face upward, one of the segments is lifted onto the reinforcement ring (10) of the other segment with its second edge (11B, 12B) of the tubular component (11, 12) and the second edge (11B, 12B) is welded to the reinforcement ring (10) from above to form a double segment (12 / 11), wherein one of the reinforcement rings (10) is located at the top and the second edge (11B, 12B) facing downward without the reinforcement ring (10) is located at the bottom.

2. The method according to claim 1, wherein the method comprises providing a third reinforcement ring (10), the third reinforcement ring being flat and having a third outer circumference larger than the circumference of the first edge (13A) of the third tubular member (13), placing the third tubular member (13) with its first edge (13A) onto the third reinforcement ring (10) within the third outer circumference, and welding the first edge (13A) of the third tubular member (13) to the third reinforcement ring (10) to provide a third segment; after inverting the third segment so that the third reinforcement ring (10) faces upward, lifting the double segment (12 / 11) onto the third reinforcement ring (10) with the second edge (11B, 12B) of the lower segment of the segments, and welding it to the third reinforcement ring (10) from above to provide a three-segment (12 / 11 / 13).

3. A method according to any preceding claim, wherein the method comprises providing a first welding station (1), the first welding station comprising a plurality of rollers (5, 6), the plurality of rollers being arranged in a circular configuration and being configured for rotatably supporting the first reinforcement ring (10) in a horizontal orientation on the rollers (5, 6) during the welding between the first tubular member (11) and the first reinforcement ring (10), wherein the method comprises maintaining a first welding machine (15) for the welding at a fixed position at the first welding station (1) and welding the first tubular member (11) to the first reinforcement ring (10) while rotating the first ring (11) about its vertical center axis (X).

4. A method according to claim 3, wherein the method comprises providing a second welding station (1'), the second welding station comprising a plurality of other rollers (5, 6) arranged in a circular configuration and configured to rotatably support the first tubular member (11) with its second edge (11B) facing downwards when the corresponding first reinforcement ring (10) faces upwards; wherein the method comprises, - after welding the first tubular member (11) to the first reinforcement ring (10) in the first welding station (1) to provide the first segment, lifting the first segment out of the first welding station (1) and turning the first segment upside down so that the first reinforcement ring (10) faces upwards; - after welding the second tubular member (12) to the second reinforcement ring (10) in the first welding station (1) to provide the second segment, lifting the second segment out of the first welding station (1) and inverting the second segment so that the second reinforcement ring (10) faces upwards; - after the rotation, the first segment and the second segment are lifted one above the other to the second welding station (1') and a double segment (12 / 11) having the upper segment and the lower segment is formed by welding the second edge (11B, 12B) of the upper segment of the two segments (11, 12) to the reinforcement ring (10) of the lower segment of the two segments (11, 12) in the second welding station (1'), wherein the rollers (5, 6) rotatably support the second edge (11B, 12B) of the lower segment of the two segments (11, 12); - The second welding station (15) is kept in a fixed position of the second welding station (1') and welding is performed from above the lower one of the two reinforcement rings (10) while rotating the double segment (12 / 11) about its vertical center axis.

5. A method according to claim 4, when dependent on claim 2, comprising: - lifting the double segment (12 / 11) out of the second welding station (1') and onto the storage station (1"), - after welding the third tubular member (13) to the third reinforcement ring (10) in the first welding station (1) to provide the third segment, and after inverting the third segment with the third reinforcement ring (10) facing upwards, lifting the third segment onto the second welding station (1'), - Then, in the second welding station (1'), the double segment (12 / 11) is lifted from the storage station (1") to the third reinforcement ring (10), and the second edge (11B, 12B) of the lower tubular member of the tubular members (11, 12) of the double segment (12 / 11) is welded to the third reinforcement ring (10), and three segments (12 / 11 / 13) of the first segment, the second segment and the third segment are formed, - The three segments (12 / 11 / 13) formed are lifted away from the second welding station (1').

6. A 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), wherein the method comprises, before welding the double segment (12 / 11) in the second welding station (1'), lifting the first segment out of the first welding station (1) and inverting the first segment and lifting the first segment onto the support ring (9) or the support plate of the second welding station (1').

7. A method according to any one of claims 3 to 6, wherein the rollers (5, 6) of at least one of the first welding station (1) and the second welding station (1') comprise a first roller (5) supporting the combination of the tubular member (11, 12, 13, 14) and the reinforcement ring (10) from below and a second roller (6) adjoining the combination from the side, and wherein the method comprises guiding the combination by means of the second roller (6) during rotation and simultaneous welding.

8. Use of a method according to any preceding claim for assembling buoyancy modules of a tubular floating wind turbine offshore structure.

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