A hollow ring flange connection for a wind turbine tower

Abstract

The invention relates to a ring flange with a hollow cross section for connecting tubular sections of wind turbine towers. The invention provides a realistic, easy to fabricate and structurally efficient circumferential connection between tubular sections of wind turbine towers which is particularly suitable for towers with very large height. The hollow ring flange according to the invention can be employed in a similar manner to the conventional solid ring flanges while avoiding the need for prohibitively thick flange plates associated with increased tower height and swept area. As a result, the hollow ring flange allows flange weight savings, bringing direct and indirect benefits with respect to overall cost, increases procurement alternatives needed for the sustainability of the supply chain.

Description

[0001] A HOLLOW RING FLANGE CONNECTION FOR A WIND TURBINE TOWER

[0002] Technical Field

[0003] The invention relates to a hollow ring flange for connecting tubular sections of wind turbine towers.

[0004] Prior Art

[0005] Wind turbine output can be increased by employing longer turbine blades and positioning the rotor of the turbines at larger heights. This requires the construction of stiffer and stronger towers. Such towers, especially onshore wind turbine towers, are constructed by onsite assembly of tubular sections. In the state of the art, tubular tower sections are connected using ring flanges. However, in order to withstand the large bending moments of the cantilever tower under operational loads, said ring flanges need to have a thickness considerably larger than that of the tower shell, thus increasing the weight of the tower and complicating procurement and welding of the flanges.

[0006] The document numbered DE2838514A1 discloses a hollow ring flange for pipes. The flanges are formed by joining two rings. A filling of plastic foam inside the flange is also disclosed.

[0007] The document numbered CN214660604U discloses double ring flanges with intermediate vertical stiffeners to be employed on wind turbine towers. The flanges are welded to the edge of the tubular sections and then bolted to each other.

[0008] The document numbered EP3339636A1 discloses a ring flange structure to be employed on wind turbine towers. The flange according to this document is first welded on a tubular element which is then divided, later to be bolted during assembly. This document doesn’t allow forming a flange as a separate part. The use of spacing elements on the bolts between flange faces is also disclosed.

[0009] The document numbered CN205207395U discloses a bolt sleeve to be employed on wind turbine towers. It is mentioned that the sleeve protects the bolt holes on the flanges. Object and Brief Description of the Invention

[0010] The object of the invention is to provide a realistic, easy to fabricate and structurally efficient circumferential connection between tubular sections of wind turbine towers, which is particularly suitable for towers with very large height. The hollow ring flange according to the invention can be employed in a similar manner to the conventional solid ring flanges, while avoiding the need for prohibitively thick flange plates associated with increased tower height and swept area, thus increased loads. As a result, the hollow ring flange brings direct and indirect benefits with respect to overall cost, facilitates procurement, mitigates special needs for transportation of the raw material as well as delivery lead times, provides flange weight savings and increases the alternatives in supply chain for sustainability.

[0011] Another benefit of the hollow ring flanges according to the invention in comparison to the conventional solid ring flanges will be the easier manufacturing of the tower sections that form the wind turbine tower. Current manufacturing process of the sections involves the welding of cold rolled shell cans one to another and to two flanges on each side. The large mass of the conventional solid ring flange requires a constant monitoring of the shell canflange welding process. Given the relatively large thicknesses of the rolled steel sheets used in the shell cans, a shell can-flange welding is rather thick and associated with a large heat input. The relatively large mass of the conventional solid ring flange (when compared to the rolled shell can) may cause large geometrical distortions during the manufacturing of tower sections. A commonly known such geometric deformation is a tilt of the flange, which requires machining of the flange post welding. Lower mass of the hollow ring flange eliminates such adverse effects, simplifying the manufacturing process of the tower sections and improving their final quality.

[0012] A ring flange according to the invention comprises a hollow cross section. These hollow ring flanges are welded to the edges of the tubular tower sections, positioned on the inside or outside, or extending to both the inside and the outside of the tubular tower sections. During assembly, the successive hollow flanges are bolted together through the holes drilled on the hollow flanges.

[0013] The hollow flange according to the invention can be formed by rolling an extruded member with a rectangular hollow section and welding the ends, welding together two circular planar strips and two rolled strips, or welding together some combination of rolled profiles forming a rectangular hollow section. In an embodiment of the invention, the face of the hollow flange that is connected to the tubular tower shell is formed by the shell itself.

[0014] The hollow flange can be fitted with stiffening tubes at the bolt holes to axially resist the force due to the bolts.

[0015] The hollow flange can be filled with a filler such as concrete or high strength grout to decrease the required flange thickness and stiffening tube thickness.

[0016] Detailed Description of the Invention

[0017] The flange according to the objects of the invention is described with the use of the attached figures.

[0018] Figure 1 is a front view of a wind turbine tower assembly consisting of tubular sections.

[0019] Figure 2 is a perspective view of a circumferential connection between two tubular tower sections.

[0020] Figure 3 is a perspective exploded view of the connection shown in Figure 2, revealing the ring flanges of the upper and lower tubular tower sections.

[0021] Figure 4 is a closeup view of a circumferential connection established using hollow ring flanges.

[0022] Figure 5 is a closeup view of a circumferential connection established using hollow ring flanges with stiffening tubes around the bolt holes according to the invention.

[0023] Figure 6 is a cross section of a circumferential connection according to the invention employing a standard rectangular hollow section welded inside the tower section shell.

[0024] Figure 7 is a cross section of a circumferential connection according to the invention employing a standard rectangular hollow section welded at the edge of the tower section shell.

[0025] Figure 8 is a cross section of a circumferential connection according to the invention using a built-up rectangular hollow section consisting of individual plates.

[0026] Figure 9 is a cross section of a circumferential connection according to the invention using a built-up rectangular hollow section consisting of angled plates.

[0027] Figure 10 is a cross section of a circumferential connection according to the invention extending inside and outside of the tower section shell.

[0028] Figure 11 is a cross section of a circumferential connection according to the invention with ring flanges incorporating a filler. The features in the figures have been numbered and corresponding numbers are defined below.

[0029] 100. Wind turbine tower

[0030] 101. Tubular section

[0031] 102. Shell can

[0032] 103. Ring flange

[0033] 104. Rectangular hollow section

[0034] 105. Bolt

[0035] 106. Stiffening tube

[0036] 107. Upper face

[0037] 108. Lower face

[0038] 109. Internal face

[0039] 110. External face

[0040] 111. Weld

[0041] 112. Bolt hole

[0042] 113. Bolt head

[0043] 114. Nut

[0044] 115. Washer

[0045] 116. Angle section

[0046] 117. Filler

[0047] The ring flange (103) for circumferential connection between tubular sections (101) of wind turbine towers (100) according to the invention essentially comprises a hollow ring-shaped member with a hollow cross section at any plane defined by a radius and a height with respect to the axis of said tubular sections, and further having two flat faces each lying in a plane defined by a height with respect to the axis of said tubular sections (101), a plurality of bolt holes (112) on said flat faces, such that each bolt hole on a upper face (107) is aligned with a bolt hole (112) on a lower face (108) with respect to a line parallel to the axis of said tubular sections (101) a plurality of stiffening tubes (106) each having an axis parallel to the axis of said tubular sections (101), that are positioned inside the hollow ring-shaped member extending between said flat surfaces and are each aligned with one bolt hole (112). A wind turbine tower (100) assembly consists of individual conventional tubular sections (101) made of steel as seen in Fig. 1. Each tubular section (101) comprises one or more cylindrical shell cans (102), fabricated by roller bending of flat plates and subsequent longitudinal welding along their common meridional edges. Adjacent shell cans (102) are then held in place next to each other and welded together along their common circumferential edges. Multiple shell cans (102) are thus joined to produce a tubular section (101), with such length that the section fits in a track for transportation from the factory to the wind farm site.

[0048] In the factory, tubular sections (101) are fitted at their ends with ring flanges (103) featuring predrilled bolt holes (112). Conventional solid ring flanges comprise a solid rectangular cross section and are, in most cases, internal with respect to the cylindrical shell can (102), or sometimes project both internally and externally. Such solid ring flanges are commonly produced by forging and may have a neck that is welded to the adjacent shell can (102). During erection on the wind farm site the continuity between adjacent tubular sections (101) is ensured by means of connections between ring flanges (103). To realize this connection, a crane lifts an upper tubular section (101) and directs it so that its ring flange (103) is held opposite of the corresponding ring flange (103) of a lower tubular section (101), which has already been installed. The installation personnel pass bolts (105) through the opposing bolt holes (112) of the two ring flanges (103) and pretension them with proper wrenching devices as seen in Figs. 2 and 3.

[0049] The ring flanges (103) according to the invention have a hollow cross section instead of the solid cross section of conventional solid ring flanges. Bolts (105) are used to connect the ring flanges (103) of two adjacent tubular sections (101) as seen in Fig. 4, in a similar manner with the conventional solid ring flanges. Stiffening tubes (106) are placed around the bolt holes, as seen in Fig. 5.

[0050] The hollow cross section is preferably rectangular. However, the hollow cross section may have a different shape such as a right trapezoid with the inclined side facing away from the surface of the tubular section (101) shell.

[0051] The cross section of the ring flange (103) according to some embodiments of the invention can be formed of a rectangular hollow section (104) consisting of an upper face (107), a lower face (108), a vertical internal face (109) and a vertical external face (110). Fig. 6 is a schematic representation of such an embodiment of this invention. This hollow ring flange (103) is fabricated by roller bending a straight member with a standard rectangular hollow section (104) into a ring-shaped member. Such straight members are commercially available in two variations, hot-rolled and cold-formed. Roller bending takes place in steel fabrication yards by means of press brake machines. Considering the relatively large diameter of wind turbine towers (100), considerably large rectangular hollow sections (104) can be bent by this process into the desirable diameter, to enable the fabrication of hollow ring flanges (103) according to the invention. After bending to a full 360° circular shape, the continuity of the ring flange (103) is ensured by welds (111) between its two ends.

[0052] The upper face (107) and lower face (108) of the hollow ring flange (103) feature bolt holes (112), spaced at regular distances, depending on the number of bolts (105) that are needed to connect the two adjacent tubular sections (101).

[0053] Depending on the dimensions, most notably the thickness of the upper face (107) and lower face (108) of this embodiment, significant local bending deformations of the upper face

[0054] (107) and the lower face (108) may appear during bolt (105) pretensioning and operation of the ring flange (103), particularly in the tensile region of the connection. This may lead to large plate thickness requirements for the upper face (107) and lower face (108). The stiffening tubes (106) according to the invention allow overcoming this problem.

[0055] The ring flange (103) may be stiffened with stiffening tubes (106) having the same or slightly smaller external diameter than the bolt holes (112), a slightly larger internal diameter than the bolts and a height equal to the distance between the upper face (107) and the lower face

[0056] (108) of the ring flange (103). The stiffening tubes (106) are inserted between two opposing bolt holes (112) and welded to each face by peripheral fillet welds (111). The stiffening tubes (106) resist axially the forces exerted by the bolt head (113) and the bolt nut (114) during bolt (105) pretensioning and operation, alleviating the local bending deformation of the upper face (107) and lower face (108), thus minimizing thickness requirements.

[0057] The stiffening tubes (106) can be made of steel.

[0058] In addition to stiffness improvement, stiffening tubes (106) offer improved corrosion protection.

[0059] In this embodiment, after bending and drilling of the bolt holes (112), and welding of the stiffening tubes (106) to the upper face (107) and lower face (108), the hollow ring flange (103) is welded to the edge of the last cylindrical shell can (102) of the tubular section (101) by means of double welds (111) on the vertical external face (110) of the hollow ring flange (103). The tubular section (101) is then painted and fitted with internals before being transported to the wind farm site.

[0060] During erection the tubular section (101) is lifted by cranes and the bolt holes (112) of its lower hollow ring flange (103) are placed opposite the corresponding bolt holes (112) of the upper hollow ring flange (103) of the lower tubular section (101), which has already been installed. Bolts (105) are placed through the bolt holes (112) and the stiffening tubes (106) and tightened by nuts (114), using washers (115) to distribute stresses at the nuts (114) and the bolt heads (113). The bolts (105) are pretensioned by hydraulic wrenches to ensure proper connection.

[0061] Another embodiment of the invention is schematically shown in Fig. 7. A similar arrangement to the embodiment disclosed above is presented, but in this embodiment the hollow ring flange (103) is welded to the last cylindrical shell can (102) of the tubular section (101) by means of full penetration butt welds (111) to the upper face (107) or lower face (108) of the ring flange (103).

[0062] In another embodiment of the invention, which is represented schematically in Fig. 8, a built- up ring-shaped member is used for the hollow ring flange (103). This embodiment may be preferred in situations where a heavy rectangular hollow section (104) must be used as a ring flange (103) due to structural demands, so that roller bending of a straight member into the ring-shaped member with the desirable diameter is not possible due to fabrication limitations.

[0063] In this case, a part of the last cylindrical shell can (102) of the tubular section (101) may be extended to form a vertical external face (110) of the ring flange (103). The upper face (107) and lower face (108) of the ring flange (103) may be directly cut from flat plates into their desired shape, either in one piece, or most likely - to optimize cutting patterns and make best use of the flat plates - in multiple pieces that are then butt welded together. After drilling the necessary bolt holes (112), the upper face (107) and lower face (108) are welded to an inner surface of the last cylindrical shell can (102) of the tubular section (101), serving also as the vertical external face (110) of the ring flange (103), by means of butt welds (111). The vertical internal face (109) of the ring flange (103) may be easily bent from a flat plate and welded to the upper face (107) and lower face (108), also by butt welds (111), to form the entire hollow ring flange (103). The stiffening tubes (106) are also welded to the upper face (107) and lower face (108) around the bolt holes (112). In this embodiment, with a part of the tubular section (101) acting as an external face, a ring flange (103) for use on the inner surface of the tubular section (101) having a U-shaped cross section with a vertical internal face (109) is obtained.

[0064] In another embodiment of the invention, in a similar manner to the previously disclosed embodiment, a part of the last cylindrical shell can (102) of the tubular section (101) may be extended to form a vertical internal face (109) of the ring flange (103). The upper face (107) and lower face (108) are welded to an outer surface of the last cylindrical shell can (102) of the tubular section (101), by means of butt welds (111). The vertical external face (110) of the ring flange (103) may be easily bent from a flat plate and welded to the upper face (107) and lower face (108), also by butt welds (111), to form the entire hollow ring flange (103). In this embodiment, with a part of the tubular section (101) acting as an internal face, a ring flange (103) for use on the outer surface of the tubular section (101) having a U-shaped cross section with a vertical external face (110) is obtained.

[0065] In another embodiment of the invention, which is represented schematically in Fig. 9, a built- up rectangular hollow section (104) composed by two angle sections (116) is used for the ring flange (103). The two angle sections (116) are welded together by means of full penetration butt welds (111). This embodiment eliminates some of the welding that is necessary for the previously disclosed embodiments employing built-up rectangular hollow sections (104), and may be more cost effective in terms of material used for upper face (107) and lower face (108). In a similar embodiment, the leg of the angle section forming the vertical external face (110) of the hollow ring flange (103) may extend to constitute part of the tubular section (101) shell, so that the weld (111) between the ring flange (103) and the adjacent shell can (102) is moved away from the ring flange (103). Similar embodiments may make use of U-shaped sections or other readily available standard sections that may be suitable for reducing welding, simplifying fabrication and obtaining appropriate overall hollow sections.

[0066] In another embodiment of the invention, shown in Fig. 10, hollow ring flanges (103) may be used both on an inner and an outer surface of the tubular sections (101), acting as a T-flange. To further protect the upper face (107) and lower face (108) from bending deformations, the hollow cross section may, in a further embodiment of the invention, be filled with a filler (117) such as concrete or other high-strength grout, as shown in Fig. 11. The filler (117) can be filled using properly drilled auxiliary holes. The use of a filler (117) allows smaller thickness requirements of the stiffening tubes (106), the upper face (107) and lower face (108), as well as smaller height of the rectangular hollow section (104), hence shorter bolts (105).

[0067] Further to connections between adjacent tubular sections (101), all alternatives of the hollow ring flange (103) connection may be employed at the bottom of a tubular wind turbine tower (100), to enable the anchorage of the wind turbine tower (100) to a foundation, in which case anchor bolts are used instead of structural bolts (105).

Claims

CLAIMS1. A ring flange (103) for circumferential connection between tubular sections (101) of wind turbine towers (100) comprising a hollow ring-shaped member with a hollow cross section at any plane defined by a radius and a height with respect to the axis of said tubular sections, and further having two flat faces each lying in a plane defined by a height with respect to the axis of said tubular sections (101), a plurality of bolt holes (112) on said flat faces, such that each bolt hole on a upper face (107) is aligned with a bolt hole (112) on a lower face (108) with respect to a line parallel to the axis of said tubular sections (101) characterized by further comprising a plurality of stiffening tubes (106) each having an axis parallel to the axis of said tubular sections (101), that are positioned inside the hollow ring-shaped member extending between said flat surfaces and are each aligned with one bolt hole (112).

2. A ring flange (103) according to claim 1, characterized in that the hollow cross section contains a filler (117).

3. A ring flange (103) according to claim 1 for use on the inner surface of a tubular section (101) characterized by having a U-shaped cross section with a vertical internal face (109).

4. A ring flange (103) according to claim 1 for use on the outer surface of a tubular section (101) characterized by having a U-shaped cross section with a vertical external face (110).

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