WO2015169968A1

WO2015169968A1 - Reinforcement of an access-way to a tower

Info

Publication number: WO2015169968A1
Application number: PCT/EP2015/060374
Authority: WO
Inventors: Steen KAASGAARD
Original assignee: Doxatech Aps
Priority date: 2014-05-09
Filing date: 2015-05-11
Publication date: 2015-11-12

Abstract

The present invention relates to a method of installing a doorway frame (40) in a tower segment (10) for a tower (1 10) comprising at least one tower segment (10, 10'), wherein said tower segment (10) comprises a tubular steel wall (1 1 ), and where said method comprises the steps of: - in a first production site assembling a doorway frame (40) and an arched wall section (23) into a doorway wall section (20) by welding said doorway frame (40) and said arched wall section (23) together, said arched wall section (23) having a wall thickness (d₁), and defining a rim (24, 25, 26, 27); - at a second production site, cutting a portion of said tubular tower segment (10), to form an opening (20') corresponding in size and form to said doorway wall section (20), said tower segment (10) having wall thickness (d₂) being equal to the wall thickness (d₁) of the arched wall section (23), said opening (20') defining a rim (14, 15, 16, 17); s - welding the rim (14, 15) of said doorway wall section (20) to said rim (24, 25) defined in said opening (20') cut in said tubular tower segment (10).

Description

Reinforcement of an access-way to a tower

The present invention relates to a method of manufacturing a tower with a reinforced doorway of the type being formed from one or more tubular tower segments formed in steel. The present invention also relates to a tower segment for a tower with a reinforced passage-way.

Background of the invention

Wind turbines and consequently wind turbine towers become ever larger. While the towers must be strong and stable to be able to carry the weight of the constituent parts of the wind turbine and to endure the forces acting thereon, access to the interior of the wind turbine tower must be provided, e.g. for electrical cables to and from the nacelle, which are led through openings in the tower wall. Further, accesses ways for maintenance personnel is provided in the tower walls. The access-ways, forming openings in the tower wall, causes a weakening of the tower structure, and therefore reinforcement in the vicinity of the access ways is often required.

Typically, wind turbine towers are constructed from a number of tubular tower segments that are stacked on top of each other to form an elongated tubular structure. The tower segments are provided with flanges at the top and bottom rims and are bolted together at a tower erection site. If the towers are small the entire tower may be provided by a single segment. However, in the case of larger towers, due to transport requirements, the towers need to be segmented during transport. The segments may then be assembled into a tower structure at the site of erection of the wind turbine. Such tower segments of e.g. 18-21 meters are often manufactured from sub-segments formed as steel rings that may be assembled into a tower segment by joining individual rings/sub-segments in extension of each other. The segments are transported to a tower erection site and stacked on top of each other to form towers up to the order of 100 meters high, and formed from 3-6 segments.

The joining of the segments at the erection site is done by bolting them together. The joining of the sub-sections into sections may be provided by e.g. welding the rings together, or by any other suitable means. Access-ways to such wind turbine towers are typically provided at a tower section site/production hall, where the subsections may be formed from steel plates e.g. 3 by 18 meters into rings or cylinders 3 meters high and 6 meters in diameter. Where a doorway/passage-way for equipment and/or personnel is desirable, an opening is cut in the steel tower segment (formed from sub- segments) in the shape of a doorway, and a door or hatch is mounted in the opening. Due to the considerable forces acting on the tower, the weakening caused by the opening needs to be alleviated by providing reinforcement at or in the vicinity of the passageway to counter the effects of the weakening. Firstly, it is well known that a circular or oval opening provides the best force distribution around the opening. Therefore, especially at places where large loads must be sustained (larger wind turbines), such as at the bottom of the tower, the passageways are mostly provided as circular or oval passageways.

To strengthen the weakened areas of the tower/tower segment, it is known in the art to provide reinforcement ribs on an internal wall of the tower in the vicinity of the opening.

Also known in the art, is a reinforced tower segment, where a passageway is provided with a door frame of a heavier material quality and/or thickness than the surrounding steel wall of the tower segment, to counter the weakening caused by the removal of the material, when making the opening in the steel wall. This is e.g. disclosed in DE 10 2012 019 695.

Also known in the art is to provide a plate with an opening corresponding to the opening in the tower segment on the outside or inside of the tower wall. The plate extends from the hole, and is attached to the outer or inner surface of the steel wall of the tower segment. Thus, when mounted, it provides an enlarged thickness of the tower segment wall in the vicinity of the wall. Such a reinforcement is known from DE 20 2009 015 675 U1 .

Also, known in the art is to provide a section in the form of a rectangular plate with a larger thickness than the thickness of the wall of the tower segment, and with an oval passageway provided centrally in the plate. The section may be welded to a rectangular opening provided in the wall of tower. Such a reinforcement is known from EP 1 856 410. It is a problem of the prior art solutions that it is difficult to weld surface to surface, and in particular welding along curved rims, or welding rims of plates having different thicknesses.

Summary of the invention

On this background, it is an object of the present invention to provide a more efficient and reliable method of providing passage-ways through tower segments, for segmented towers, such as wind turbine towers.

In an aspect, these objects are achieved by providing a method of manufacturing a wind turbine tower segment for a wind turbine tower comprising at least one tower segment, wherein said tower segment comprises a tubular steel wall, and where said method comprises the steps of:

- in a first production site assembling a doorway frame and an arched wall section into a doorway wall section by welding said doorway frame and said arched wall section together, said arched wall section having a wall thickness (di), and defining a rim;

- at a second production site, cutting away a portion of said tubular tower segment to form an opening corresponding in size and form to said doorway wall section, , said tower segment having wall thickness (d₂) being equal to the wall thickness (di) of the arched wall section, said opening defining a rim;

- welding the rim of said doorway wall section to said rim defined in said opening cut in said tubular tower segment.

In another aspect, the objects of the invention are achieved by providing a method of manufacturing a plurality of wind turbine tower segment for wind turbine towers, each tower comprising at least one tower segment, wherein each of said tower segments comprises a tubular steel wall, where said method comprises the steps of

- in a first production site assembling a plurality of doorway wall sections, for each doorway wall section welding a doorway frame and an arched wall section together, each of said arched wall sections having a wall thickness di and defining a rim, and producing first and second sets Si, S₂ of doorway wall sections having different wall thickness disi, di_Ss;

- at a second production site, cutting a portion of said tubular tower segment, to form an opening corresponding in size and form to a doorway wall section of one of said first and second sets Si, S₂, said tower segment having wall thickness d₂ being equal to the wall thickness disi of the arched wall section of said first set Si of doorway wall sections, said opening defining a rim;

- welding the rim of said doorway wall section to said rim defined in said opening cut in said tubular tower segment;

- at a third production site, cutting a portion of said tubular tower segment, to form an opening corresponding in size and form to a doorway wall section of the other of said first and second sets Si, S₂, said tower segment having wall thickness d₂ being equal to the wall thickness dis₂ of the arched wall section of said second set S₂ of doorway wall sections, said opening defining a rim; and - welding the rim of said doorway wall section to said rim defined in said opening cut in said tubular tower segment.

In another aspect, the objects of the invention are achieved by providing a method of providing a passageway in a tower segment for a tower comprising at least one tower segment, wherein said tower segment comprises a tubular steel wall, and where said method comprises the steps of:

- at a second production site, cutting a portion of said tubular tower segment, to form an opening corresponding in size and form to one said doorway wall section, when said tubular tower segment is arranged in a stack of other tower segments to form a tower, said tower segment having wall thickness (d₂) being equal to the wall thickness (di) of the arched wall section, said opening defining a rim;

In a further aspect, the objects of the invention are achieved by providing a method of installing a doorway frame in a tower segment for a tower comprising at least one tower segment, wherein said tower segment comprises a tubular steel wall, and where said method comprises the steps of:

- in a production facility assembling a doorway frame and an arched wall section into a doorway wall section by welding said doorway frame and said arched wall section together, said arched wall section having a wall thickness (di), and defining a rim; - at a second production site, cutting a portion of said tubular tower segment, to form an opening corresponding in size and form to said doorway wall section, when said tubular tower segment is arranged in a stack of other tower segments to form a tower, said tower segment having wall thickness (d₂) being equal to the wall thickness (di) of the arched wall section, said opening defining a rim;

In either of the above mentioned aspects of the invention the method may further comprise arranging an inner surface of said doorway wall section flush with an inner surface of said tubular steel wall, and an outer surface of said doorway wall section flush with an outer surface of said tubular steel wall, upon welding the rim of the doorway wall section to the rim defined in said opening cut in said tubular tower segment.

In either of the above mentioned aspects or the above mentioned embodiment, the step of welding said doorway frame and said arched wall section together, is performed by an automated welding robot.

According to another aspect of the invention the objects may be achieved by a tower segment for a tower comprising a plurality of tower segments stacked on top of each other, wherein at least one of the tower segment comprises

- a tubular steel wall having a wall thickness (d₂), an opening, said opening defining at least a portion of a rim; and

- a doorway wall section including a doorway frame and an arched wall section with a wall thickness (di), said arched wall having a rim, wherein said arched wall section is mounted in the opening provided in said tubular steel wall, wherein the a wall thickness (di) of said arched wall section is the same as the a wall thickness (d₂) of said tubular steel wall; and wherein said tower segment further comprises a welding seam provided between the rim of the arched wall section and the rim of the opening in the tubular steel wall. The inner surface of said doorway wall section is arranged to be flush with an inner surface of said tubular steel wall, and an outer surface of said doorway wall section is arranged to flush with an outer surface of said tubular steel wall. In the context of the present application, by first production site is meant a factory or production hall/production facility, adapted for industrial production of scale. In any case the production facility is meant to be geographically distinct from the second and third production site. The second or third production site may be a wind turbine erection site, or a tower section assembly site. Tower sections are typically formed in large factories/production halls, where the tower sections are assembled from sub segments. The sub-segments are produced from sheet steel bend into a ring. A number of rings may be welded to each other (in extension of each other in the direction of the longitudinal axis of the tubular rings forming the sub- segments). Each tower segment is equipped with a flange at a lower and /or an upper rim, to allow tower segments to be stacked and bolted together to form a tower (such as a wind turbine tower). From the tower segment assembly site the tower segments are transported to a tower erection site, where the tower segments are stacked and joined, typically by bolting the flanges together. Even though, in many cases the first and second sites will be remote form each other, this may not always be the case, since in some cases wind turbines could e.g. be erected close to a production facility. In other cases mobile production facilities could be brought close to a wind turbine erection site, e.g. if a production facility for doorway wall sections was installed in a truck. The point is that the doorway wall sections are produced in a controlled or controllable production site, whereas the tower sections are assembled at dedicated larger sites or at a wind turbine erection site, "on location" and the doorway wall section is mounted either in the tower section assembly site or "on location" of the wind turbine erection site. By the various aspects of the invention a considerable reduction of time used at the tower section assembly site or at the tower erection site may be achieved. With prior art techniques providing a passageway in a steel tower or steel tower segment may take in the order of 170 hours at the tower construction/erection site. By the present invention the time use at the tower segment site or at the tower erection site may be reduced to the order of 4 hours, while increasing the quality of the welding, and the strength of the reinforcement. The method further allows the more complicated production of doorway wall sections to be made under controlled automated conditions, which improves the quality considerably, while the overall production time is dramatically improved.

Further objects, features, advantages and properties of the method for rinsing metallographic samples according to the invention will become apparent from the detailed description.

Brief description of the drawings

In the following detailed portion of the description, the invention will be explained in more detail with reference to the exemplary embodiments shown in the drawings, in which:

- Fig. 1 , in a perspective view, shows a wind turbine with a tower formed by a plurality of tower segments arranged one on top of the other, each tower segment being formed by a number of sub-segments; - Fig. 2, in a perspective view, shows a doorway wall section for providing a passageway in a wind turbine tower segment, according to the invention and illustrating a method of manufacturing such a segment according to the invention;

- Fig. 3, in a horizontal sectional view, shows the doorway wall section of Fig. 2.

- Figs. 4A and 4B, in a perspective view, shows steps of a method of assembling a tower segment with a passageway, Fig. 4A showing an opening provided in a segment, and Fig. 4B showing a doorway wall section mounted in the opening shown in Fig. 4A;

- Fig. 5, in a perspective view, shows a doorway wall section arranged in a tower segment, or a tower sub segment, according to another embodiment; and

- Fig. 6 in a horizontal sectional view, shows details of a tower segment with a doorway wall section mounted.

Detailed description of the invention

Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. In the following detailed description, the method of manufacturing a wind turbine tower segment 10 according to the invention will be described by the preferred embodiments. The present invention relates to various aspects of a wind turbine 100, such as a horizontal axis wind turbine (HAWT) as illustrated in FIG. 1 , or at least to any wind turbine comprising a vertically arranged tower. The wind turbine 100 comprises a generally tubular tower 1 10, which may be manufactured of steel, concrete or combinations thereof. The tower 1 10 in Fig.1 is of a type that is erected by stacking multiple tower segments 10, 10' formed in steel on top of each other. The tower 1 10 supports the weight of the nacelle 120, blades 130 and hub 140. Depending on size, etc., such towers for wind turbines may comprise segments of a lattice (or truss) type, and towers may alternatively be formed of concrete or concrete segments. Alternatively, towers may comprise segments of different types. The present invention relates a tower 1 10, such as a wind turbine tower, being formed from a plurality of tower 10, 10' segments stacked on top of each other and where at least one tower segment 10 is formed as a tubular steel structure. The nacelle 120 typically houses the drive train (e.g., gearbox, shafts, couplings, generator, etc.), as well as the main frame (also called bedplate) and yaw drives. Other items such as the control electronics may be housed within the nacelle 120 as well.

In the exemplary embodiment, tower 1 10 is fabricated from tubular segments 10, 10' formed from tubular steel rings defining a wall, and such that an internal cavity 150 (see Fig. 4B) is defined within the wall, between a supporting surface 200 (on which the tower is erected) and the nacelle 120. Each of the segments 10, 10' may be formed from one or more sub- segments 101 , 101 '. A height of tower 1 10 may be any suitable height enabling wind turbine 100 to function as known in the art. One or more passageways 30 is provided through the wall of one or more segments 10, 10' or sub segments 101 , 101 ' into the cavity 150 of the tower 1 10. In Fig .1 , one passageway 30 provides a doorway formed in the lowermost sub segment 101 of the lowermost tower segment 10. In this case the passageway 30 is provided to give access for e.g. maintenance personnel into the tower 1 10 structure, where typically a ladder, stairs or elevator may be provided to allow access to the upper parts of the tower 1 10 and to the nacelle 120. Passageways 30 may also be provided for cables and other functional equipment, such as electrical power cables, generator etc. The passageways 30 according to the invention may be provided at any height of the tower 1 10, and may be sized to fit various purposes, e.g. man sized passageways 30, where personnel access is required, and e.g. smaller passageways for passing electrical power and control cables trough the tower wall, or larger passageways 30 for larger objects.

The wind turbine tower 1 10 thus comprises a plurality of tower segments 10, 10' stacked on top of each other, each of the tower segments 10 comprising a tubular steel wall 1 1 , see Figs 4A and 4B. The tower segments 10,10' are permanently joined to each other by suitable means, e.g. by bolting upper and lower flanges on neighboring segments 10, 10' together, or by welding. The tower segments 10, 10', e.g. of 18-21 meters height, may be manufactured from sub-segments 101 , 101 ' formed as steel rings that may be assembled into a tower segment 10, 10' by joining individual rings/sub- segments 101 , 101 ' in extension of each other. A tower 1 10 is assembled by transporting tower segments 10, 10' to a tower erection site, and stacked on top of each other to form towers 1 10 up to the order of 100 meters high, and formed from 3-6 segments. The joining of the segments 10, 10' at the erection site is typically done by bolting them together. The joining of the subsections 101 , 101 ' into sections 10, 10' may preferably be provided by e.g. welding the rings together at a tower segment production facility. In Fig. 1 , the assembled tower 1 10 is formed from three tower segments 10, 10', as indicated by the heavy lines in Fig .1 , and each of these tower segments 10, 10' are formed from three sub-segments 101 , 101 ', as indicated by the finer line. In the figures we have used the reference number 10 for tower segments wherein a passageway 30 is formed, and the reference number 10' to designate tower segments without passageways. It is however clear that, in Fig. 1 , one or both of the upper tower segments 10' may also comprise one or more passageways. Further, in the figures we have used the reference number 101 for sub-segments wherein a passageway 30 is formed or where a main portions of a passageway 30 is formed, and the reference number 101 ' to designate tower segments without passageways, or a neighboring sub-segment into which the passageway partly extends. The sub-segment 101 , 101 ' rings are formed from flat, typically rectangular sheets of steel-plate bend into ring-shaped elements, and joined where ends of the plate meet, e.g. by welding, or the ends may be joined by bolting or by other means known in the art. Fig. 2, in a perspective view, shows a doorway wall section 20 for providing a passageway/an access-way 30 for personnel, equipment, cables or the like through a wall of a tubular steel tower segment 10, a sub segment 101 , 101 ' and consequently - when assembled - the tower 1 10 as whole. Fig. 3 shows the doorway wall section 20 of Fig. 2 in a sectional view.

The doorway wall section 20 comprises a doorway frame 40 and an arched wall section 23 in the form of an arched steel plate. The arched wall section 23 is adapted to replace a similar size and shaped portion or cut-out of a wall 1 1 of a tower segment 10. The doorway frame 40 is preferably formed generally as an oval structure of a heavy material quality steel frame, in one piece or assembled from parts. The doorway frame 40 is arranged in an opening 23" in the arched wall section 23, the opening 23" corresponding in shape and size to an outer perimeter of the doorway frame 40. Preferably, the doorway frame 40 is welded to the arched wall section 23 along a rim 23' of the opening 23", creating a welding seam. The internal rim 23' the opening 23" of the arched wall section 23 is preferably shaped in U or V shape (seen in cross-section) to provide a basis for providing a welding seam 41 on an external/outer/convex side of the arched wall section 23, and a welding seam 42 on the internal/inner/concave side of the arched wall section 23, see Fig. 3.

The arched wall section 23 is preferably formed from a steel plate having a thickness di . The arched wall section 23 is preferably formed by bending a rectangular flat sheet of steel plate. The doorway frame 40 is preferably also made from steel and has a thickness d₄ (in the same direction as the thickness di of the arched wall section 23, when mounted) and a breadth d3 (in a direction perpendicular to di and d₄). The thickness d₄ of the doorway frame 40 is preferably at least 3 times as large as the thickness di of the arched wall section 23, such as 3-8 times, such as 3-6 times, such as 3-5 times.

The breadth d3 of the doorway frame 40 is preferably at least 2 times as large as the thickness di of the arched wall section 23, such as 2-5 times, such as

2-4 times, such as 3 times.

By the doorway frame 40 being formed generally as an oval structure is meant that it may have an overall oval structure. However, portions of the doorway frame may be straight. E.g. a portion of the doorway frame that may be intended to function as a doorstep may be straight. Further, portions at the (vertical) sides of the doorway frame may be straight and in parallel. In other embodiments, the doorway frame 40 may have other shapes, e.g. circular or rectangular. The opening 23" in the arched wall section 23 is preferably made to correspond to the doorway frame 40 prior to assembling the two.

The doorway wall section 20 may be manufactured by providing an arched wall section 23, cutting an opening 23" in the arched wall section 23 corresponding in size and shape to a doorway frame 40, thereby creating an internal rim 23' of the opening 23", and welding the doorway frame 40 to the internal rim 23' of the arched wall section 23.

The manufacture of the doorway wall section 20 is preferably performed in a production facility (a factory, permanent workshop) using an automated welding robot. Thereby, the complicated welding of the arched connection between the rim 23' of the opening 23" of the arched wall section 23 to the doorway frame 40, and the welding of the thicker doorway frame 40 to the thinner arched wall section 23 may be performed under controlled conditions, whereby the process may applied in an automated production line, providing a more uniform doorway wall section 20 production. Further, testing of the quality of the welding seams 41 , 42 is more efficient when performed at a designated production facility, and the overall procedure becomes more cost efficient.

Thus, the doorway wall section 20 has an outer rim 24, 25, 26, 27 having four sides or edges. Preferably, at the production facility, the rim 24, 25, 26, 27 is made U or V shaped (in cross-section) to provide room for welding seams, to weld the doorway wall section 20 to a tower segment 10 or one or more tower sub segments 101 , 101 '. The arched wall section 23 is preferably generally rectangular, and formed from a rectangular steel sheet material /plate and arched to form an arched plate adapted to replace an arched portion cut away from a typically cylindrical tower wall 1 1 . The tower wall 1 1 usually is cylindrical. But it may be formed as a truncated cone. Also, other shapes may be conceivable such as having a hexagonal, heptagonal or octagonal horizontal cross section.

The doorway/passageway 30, including an outer rim of the doorway frame 40 has a width l_i and a height Hi .

The doorway wall section 20 has a width L₃ and height H₃.

The width L₃ of the doorway wall section 20 is preferably in the range of 1 .1 - 5 times the width l_i of the doorway. The height H₃ of the doorway wall section 20 is preferably in the range of 1 .1 -3 times the height Hi of the doorway.

When assembled, the arched wall section 23 of the doorway wall section 20 extend from the doorway frame 40 by at least 10 cm, in the (arched) plane of the arched wall section 23, which corresponds to a circumferential direction of tower segments 10. In Figs. 2 and 3 this extension from the outer periphery of the doorway frame 40 is designated H₂ in the vertical direction (height) and L₂ in the horizontal direction (width). Thus H₂ is equal to or larger than 10 cm, and L₂ is equal to or larger than 10 cm. In other embodiments H₂ is equal to or larger than 10 cm, and L₂ is equal to or larger than 10 cm.

However, the vertical and horizontal extensions (H₂ and L₂ respectively) formed by the arched wall section 23, may each extend several meters from the outer periphery of the doorway frame 40 depending on the size of the tower segment in which the doorway wall section 20 is intended to be mounted, and the size of the passageway 30. It is clear that the vertical and horizontal extensions (H₂ and L₂ respectively) do not need to be the same but may be varied, depending on the size of the doorway wall section 20 and the size of the tower segment in which the doorway wall section 20 is intended to be mounted. A typical doorway wall section 20 according to the invention extends over 60° of the circumference of the tower 1 10/ tower segment 10. However, in other embodiments the doorway wall section 20 may extend over 20-90° of the circumference of the tower 1 10/ tower segment 10, such as 30-80°, such as 40-70°, such as 50-65°.

Turning now to Figs. 4 and 5 further steps of a method of manufacturing a tower segment 10 for a tower 1 10 such as a wind turbine tower is described.

A doorway wall section 20 as in any embodiment described above is transported to a tower segment assembly site, such as a wind turbine tower segment assembly site or to a tower erection site, such as a wind turbine tower erection site. When erected, the tower 1 10 comprises at least one ring- shaped/tubular steel tower segment 10, in which a passageway is intended to be provided. Each tower segment 10 may or may not be formed from sub- segments 101 , 101 '.

At the tower segment assembly site or at the tower erection site, a portion of the tubular tower segment 10 is cut away, to form an opening 20' in the tower segment 10 or sub segment 101 , the opening 20' corresponding in size and form to said doorway wall section 20, and a doorway wall section 20 is mounted in the opening 20'.

The opening 20' cut in the tower segment 10 is preferably rectangular. The opening 20' defines a rim 14, 15, 16, 17 in the tubular tower segment 10. The tubular tower segment 10 is formed in a metal, preferably in steel sheet material. The tubular tower segment 10 has wall thickness 02.

The wall thickness di of the arched wall section 23 of the doorway wall section 20 is chosen to be equal to the wall thickness 02 of the tower segment 10, in which the opening 20' is cut.

A doorway wall section 20 with wall thickness di equal to the wall thickness 02 of the tower segment 10, in which the opening 20' is cut, is arranged in said opening 20' such that the sides/edges of the rim 14, 15, 16, 17 of the opening 20' is aligned adjacent to the corresponding sides/edges of the rim 24, 25, 26, 27 of the doorway wall section 20. Then the doorway wall section 20 is welded to the tower segment 10 by providing at least one welding seam 60 (Fig. 6) between the rim 14, 15, 16, 17 of the opening 20' and the rim 24, 25, 26, 27 of the doorway wall section 20.

The inner surface 21 of said doorway wall section 20 is made flush with an inner surface 12 of said tubular steel wall 1 1 , and an outer surface 22 of said doorway wall section 20 is made flush with an outer surface 13 of said tubular steel wall 1 1 , upon welding the rim 24, 25, 26, 27 of the doorway wall section 20 to the rim 14, 15, 16, 17 defined in said opening 20' cut in said tubular tower segment 10, see Fig .6.

As mentioned above, each tower segment 10, 10' may be formed from a number of sub-segments 101 , 101 ', see further below.

The doorway wall section 20 may be welded to the opening 20' in the tubular tower segment 10, e.g. at a tower erection site, or it may be welded to an opening 20' in a tower segment 10 or a tubular sub-segment 101 in a tower segment assembly site, where said sub-segment 101 is assembled to other sub-segments 101 ' to form a tower segment 10. In Fig. 4A it is indicated that the opening 20' may be formed in a sub segment 101 of a tower segment 10, the tower segment 10 in this case being formed from three sub-segments 101 , 101 '. The doorway wall section 20 may thus be mountes either in the tubular/ring shaped elements called sub-segments 101 , 101 ' before assembling the sub segments 101 , 101 ' in into a tower segment 10, or the doorway wall section 20 may be mounted in an assembled tower segment 10 formed from sub segments 101 , 101 '. Further, it is possible that the doorway wall section 20 may is formed in the assembled tower 1 10. It will be appreciated that this depend on the tower size, and in the access to the site how large the tower segments to be transported may be.

In Figs. 4A and 4B the sub-segment 101 , in which to provide a passageway 30, is indicated by the reference number 101 and the neighboring sub- segments 101 ' of a tower segment 10 are shown in dashed line and designated 101 '. In Figs. 4A and 4B, sub-segments 101 ' are shown above and below the sub-segment 101 with the passageway 30, however, it may be appreciated that the sub-segment 101 in which the passageway 30 is to be arranged/is arranged may be the lowermost or the topmost sub-segment of a tower segment 10. It may also be appreciated that in some embodiments the tower 100 may be comprised by a single tower segment 10, and that this may not be formed by sub-segments. This will usually be the case if the wind turbine is of a smaller type.

In Fig. 5, an embodiment is illustrated, where the opening 20' is provided entirely within a single sub-segment 101 of a tower segment 10. In this case the rim 14, 15, 16, 17 of the opening 20' is provided entirely in a single sub- segment 101 . In the embodiment, shown in Figs.4A-4B, the opening removes a portion of the sub-segment 101 from its top to its bottom. Thus, in the Fig. 4 embodiment, the upper rim portion 17 is defined by a portion of the lower rim of the above sub-segment 101 ', and the lower rim portion 16 is defined by a portion of the upper rim of the below sub-segment 101 '. It will be appreciated that the embodiment shown in Fig. 5 may be used in combination with the sub-segments 101 , 101 ' as shown and described in relation to Figs. 4A-4B.

In other not shown embodiments (not shown), the opening 20' may extend between two neighboring tubular sub-segments 101 , 101 ' of a tower segment 10, both formed as steel sub-segments 101 , 101 ', and having the same thickness, 02. Thus a portion of the opening 20' may be formed in one sub- segment 101 , and another portion of the opening 20' may be formed in another, neighboring, tower sub-segment 101 ' of a tower segment 10. Depending on the height of the sub-segment 101 or segments 10 and the size of the desired passageway 30, an opening 20' may be also be provided such that it extends over 3 or more sub-segments 101 , such that the middle sub-segment 101 or middle sub-segments 101 are entirely cut from top to bottom rims and a top and bottom portion of the opening 20' are cut in partly in a sub-segment 101 neighboring at the top and bottom of the fully cut sub- segment 101 respectively. It will be appreciated that it will also be possible that an opening 20' extending over more than two sections will have an upper rim provided by a lower rim of an above tower segment, and/or a lower rim provided by an upper rim of a lower tower segment.

In one further embodiment (not shown), one portion of an opening 20' may be formed in one tower segment 10, and another portion of the opening 20' may be formed in another tower segment 10'. A typical sub-segment 101 ,

101 ' may be 3 meters in height. An opening 20' and a corresponding doorway wall section 20 may in that case be up to 6 meters in height H₃.

Fig. 4A shows a single sub-segment 101 in which an opening 20' has been provided by removing a portion of the tubular steel wall 1 1 of the tower segment 10. The opening 20' is provided by cutting a portion of the side wall 1 1 of the tower segment 10 away, e.g. by using a blow-torch. It will be appreciated that the removed/cut away portion, i.e. the opening 20' should be corresponding in the size and shape to the doorway wall section 20 intended to be mounted in the sub-segment 101 of the tower segment 10 opening 20'. Fig. 4B shows the tower segment 10 with a doorway wall section 20 installed.

As described, the doorway wall section 20 is preferably welded to the rim 14, 15, 16, 17 of the opening 20'. As shown in Fig. 6, in a preferred embodiment, the rim (or at least portions thereof) may be provided with a V-shape or a U- shape (seen in a cross section of the wall) in order to allow a welding seem to be provided in connection with both the inner surface 12 and the outer surface 13 of the wall 1 1 of the tower section 10. In Fig. 6, a welding seam 62 is provided in the notch provided by the V shape of the rim 14, 15 of the doorway wall section 20, and on/in connection with the inner side surface 12 of the wall 1 1 of the tower section 10, and in connection with the inner surface 21 of the doorway wall section 20. Also, Fig. 6 shows a welding seam

61 provided in the notch provided by the V shape of the rim 14, 15 of the doorway wall section 20, and in connection with the outer side surface 12 of the wall 1 1 of the tower section 10, and in connection with the outer surface 22 of the doorway wall section 20. It will be appreciated, that in alternative embodiments (not shown) a welding seam 60 may be provided also on just one side.

When above it is mentioned that the inner 12, 21 and outer 13, 22 surfaces are flush after welding, it will be appreciated that any welding seams 60, 61 ,

62 may protrude from the mentioned surface, and that this does not mean that the respective inner surfaces 12, 21 and respective outer surface 13, 22 are not flush. The teaching of this invention has numerous advantages. Different embodiments or implementations may yield one or more of the following advantages. It should be noted that this is not an exhaustive list and there may be other advantages which are not described herein. One advantage of the teaching of this method is that it provides a great flexibility in designing and operating a rinsing or rinsing and grinding system.

Although the teaching of this application has been described in detail for purpose of illustration, it is understood that such detail is solely for that purpose, and variations can be made therein by those skilled in the art without departing from the scope of the teaching of this application.

The term "comprising" as used in the claims does not exclude other elements or steps. The term "a" or "an" as used in the claims does not exclude a plurality. The single processor or other unit may fulfill the functions of several means recited in the claims.

Claims

1 . A method of manufacturing a wind turbine tower segment (10) for a wind turbine tower (100) comprising at least one tower segment (10, 10'), wherein said tower segment (10) comprises a tubular steel wall (1 1 ), and where said method comprises the steps of:

- in a first production site, assembling a doorway frame (40) and an arched wall section (23) into a doorway wall section (20) by welding said doorway frame (40) and said arched wall section (23) together, said arched wall section (23) having a wall thickness (di), and defining a rim (24, 25, 26, 27);

- at a second production site, separate from said first production site, cutting a portion of said tubular tower segment (10), to form an opening (20') corresponding in size and form to said doorway wall section (20), said tower segment (10) having wall thickness (d₂) being equal to the wall thickness (di) of the arched wall section (23), said opening (20') defining a rim (14, 15, 16, 17);

- welding the rim (24, 25, 26, 27) of said doorway wall section (20) to said rim (14, 15, 16, 17) defined in said opening (20') cut in said tubular tower segment (10).

2. A method according to claim 1 , wherein an inner surface (21 ) of said doorway wall section (20) is flush with an inner surface (12) of said tubular steel wall (1 1 ), and an outer surface (22) of said doorway wall section (20) is flush with an outer surface (13) of said tubular steel wall (1 1 ), upon welding the rim (24, 25, 26, 27) of the doorway wall section (20) to the rim (14, 15, 16, 17) defined in said opening (20') cut in said tubular tower segment (10).

3. A method according to claim 1 or 2, wherein the step of welding said doorway frame (40) and said arched wall section (23) together, is performed by an automated welding robot.

4. A method of manufacturing a plurality of wind turbine tower segment (10) for wind turbine towers (1 10), each tower (1 10) comprising at least one tower segment (10, 10'), wherein each of said tower segments (10) comprises a tubular steel wall (1 1 ), where said method comprises the steps of

- in a first production site assembling a plurality of doorway wall sections (20), for each doorway wall section (20) welding a doorway frame (40) and an arched wall section (23) together, each of said arched wall section (23) having a wall thickness (di) and defining a rim (24, 25, 26, 27), and producing first and second sets (Si, S2) of doorway wall sections (20) having different wall thickness (disi, dis_s);

- at a second production site, cutting a portion of said tubular tower segment (10), to form an opening (20') corresponding in size and form to a doorway wall section (20) of one of said first and second sets (Si, S2), said tower segment (10) having wall thickness (d2) being equal to the wall thickness (disi) of the arched wall section (23) of said first set (disi) of doorway wall sections (20), said opening (20') defining a rim (14, 15, 16, 17);

- welding the rim (24, 25, 26, 27) of said doorway wall section (20) to said rim (14, 15, 16, 17) defined in said opening (20') cut in said tubular tower segment (10);

- at a third production site, cutting a portion of said tubular tower segment (10), to form an opening (20') corresponding in size and form to a doorway wall section (20) of the other of said first and second sets (Si, S2), said tower segment (10) having wall thickness (d2) being equal to the wall thickness (dis2) of the arched wall section (23) of said second set (disi) of doorway wall sections (20), said opening (20') defining a rim (14, 15, 16, 17); and

5. A method according to claim 4, wherein an inner surface of each of said doorway wall sections (20) is arranged to flush with an inner surface of each of said tubular steel walls (1 1 ), and an outer surface of each of said doorway wall sections (20) is arranged to be flush with an outer surface of each said tubular steel wall (1 1 ), upon welding the rim (24, 25, 26, 27) of the doorway wall section (20) to the rim (14, 15, 16, 17) defined in said opening (20') cut in said tubular tower segment (10).

6. A method according to claim 5 or 6, wherein the step of welding said doorway frames (40) and said arched wall sections (23) together, is performed by an automated welding robot.

7. A wind turbine tower segment (10) for a wind turbine tower (1 10) said tower (1 10) comprising at least one tower segment (10, 10'), wherein at least one of the tower segment (10) comprises

- a tubular steel wall (1 1 ) having a wall thickness (d₂), an opening (20'), said opening defining at least a portion of a rim (14, 15, 16, 17); and

- a doorway wall section (20) including a doorway frame (40) and an arched wall section (23) with a wall thickness (di), said arched wall having a rim (24, 25, 26, 27),

wherein said arched wall section (23) is mounted in the opening (20') provided in said tubular steel wall (1 1 ),

wherein the a wall thickness (di) of said arched wall section (23) is the same as the a wall thickness (d₂) of said tubular steel wall (1 1 ); and

wherein said tower segment (10) further comprises a welding seam (60) provided between the rim (24, 25, 26, 27) of the arched wall section (23) and the rim (14, 15, 16, 17) of the opening in the tubular steel wall (1 1 ).

8. A wind turbine tower segment (10) according to claim 7, wherein an inner surface of said doorway wall section (20) is flush with an inner surface of said tubular steel wall (1 1 ), and an outer surface of said doorway wall section (20) is flush with an outer surface of said tubular steel wall (1 1 ).

9. A method of providing a passageway in a tower segment (10) for a tower (1 10) comprising at least one tower segment (10, 10'), wherein said tower segment (10) comprises a tubular steel wall (1 1 ), and where said method comprises the steps of:

- in a first production site assembling a doorway frame (40) and an arched wall section (23) into a doorway wall section (20) by welding said doorway frame (40) and said arched wall section (23) together, said arched wall section (23) having a wall thickness (di), and defining a rim (24, 25, 26, 27);

- at a second production site, cutting a portion of said tubular tower segment (10), to form an opening (20') corresponding in size and form to said doorway wall section (20), said tower segment (10) having wall thickness (d₂) being equal to the wall thickness (di) of the arched wall section (23), said opening (20') defining a rim (14, 15, 16, 17);

- welding the rim (14, 15) of said doorway wall section (20) to said rim (24, 25) defined in said opening (20') cut in said tubular tower segment (10).

10. A method of installing a doorway frame (40) in a tower segment (10) for a tower (1 10) comprising at least one tower segment (10, 10'), wherein said tower segment (10) comprises a tubular steel wall (1 1 ), and where said method comprises the steps of:

- in a first production site assembling a doorway frame (40) and an arched wall section (23) into a doorway wall section (20) by welding said doorway frame (40) and said arched wall section (23) together, said arched wall section (23) having a wall thickness (di), and defining a rim (24, 25, 26, 27); - at a second production site, cutting a portion of said tubular tower segment (10), to form an opening (20') corresponding in size and form to said doorway wall section (20), said tower segment (10) having wall thickness (d₂) being equal to the wall thickness (di) of the arched wall section (23), said opening (20') defining a rim (14, 15, 16, 17); s