Patent Description:
Wind turbines may comprise a tower made of several support structures sections. Flange connections may be used to connect the individual support structure sections. Examples of such support structure sections are disclosed in <CIT>.

<CIT> relates to a flange assembly, a coupling flange and an assembly method thereof. A plenty of reinforced plates are located on the front side of the flange plate. Each front end face of the reinforced plates is provided with a balancing contact surface. The bending moment produced by the compressive stress of the balancing contact surface serves to counteract the tensile stress acted on the pipe wall by the bolts, thus reducing the circumferential tensile stress, achieving a reliable coupling strength and keeping a constant flexural rigidity under persistent circulating dynamic load. So they are suited to the connection of large-scale steel pipes such as the connection of tower pillars of circular pipe type of large-scale wind-driven generators.

Another prior art example of a flange assembly is disclosed in <CIT>.

Flanges of wind turbine support structures, in particular connecting tower sections or between Monopiles (MPs) and Transition Pieces (TPs), are typically large diameter structures, which makes fulfilling fabrication tolerances very challenging. In particular flatness requirements, which are required in order to limit the size of flange gaps, are critical. Even small gaps between flanges may be critical for the fatigue life of bolts connecting the flanges.

Hence, there may be a need for a flange, a support structure section comprising such a flange, in particular for wind turbines, and a method for connecting the flange allowing for the reduction of gaps.

This need has been addressed with the subject-matter of the independent claims. Advantageous embodiments are described in the dependent claims.

It is proposed a flange, wherein the flange is configured for being mounted to a counter flange with bolts extending through a plurality of through holes distributed along a circumference of at least one of the flange and the counter flange, wherein the flange comprises a ring-shaped contact surface, wherein the flange comprises a ring-shaped discontinuous contact surface, wherein the ring-shaped contact surface and the ring-shaped discontinuous contact surface are arranged such that the plurality of through holes is arranged between the ring-shaped contact surface and the ring-shaped discontinuous contact surface, and wherein at least one of the plurality of through holes is provided between a contact section of the ring-shaped discontinuous contact surface and the first ring-shaped contact surface.

The ring-shaped contact surface may typically be a continuous contact surface. Thus, in the following it will also be referred to the ring-shaped contact surface as continuous contact surface. However, it is also possible that the ring-shaped contact surface is a discontinuous contact surface.

The ring-shaped continuous contact surface and the ring-shaped discontinuous contact surface may allow for providing defined contact between the flange and the counter flange.

Typically, the flange and the counter flange both comprise through holes and the bolts are provided separately. However, the bolts may also be fixed to one of the flange and the counter flange before assembling the flanges.

In an embodiment, an opening between contact sections of the discontinuous contact surface allows for inserting shims between the ring-shaped continuous contact surface and the counter flange in a semi-mounted state of the flange.

The shims may be used to provide contact between the flange and the counter flange in regions, where a gap is present due to unavoidable manufacturing tolerances. Well defined contacts may reduce fatigue of the bolts.

The semi-mounted state may refer to a state, in which the flange and the counter flange are arranged such that the bolts may be inserted into the through holes. It may also refer to a state, in which only some of the bolts are inserted into the through holes. At least some of the inserted bolts may be pre-tensioned in a semi-mounted state.

According to embodiments, the openings may have a height in a direction perpendicular to the ring-shaped discontinuous contact surface greater or equal than <NUM>, in particular greater or equal than <NUM>.

Said height may be sufficient for inserting shims between the ring-shaped continuous contact surface and the counter flange from a side of the ring-shape discontinuous contact surface.

According to embodiments, the height may be less than <NUM>, in particular, less than <NUM> to reduce the material required for forming the ring-shaped discontinuous contact surface.

According to embodiments, the flange may be an L-flange or a T-flange.

In an embodiment, the ring-shaped continuous contact surface may surround the ring-shaped discontinuous contact surface. Thus, in case the flange is a flange of a support structure section of a wind turbine tower, the shims may be inserted from the inside of the tower.

According to embodiments, the flange may comprise a body and a contact ring, wherein the contact ring comprises the ring-shaped continuous contact surface and/or the ring-shaped discontinuous contact surface. Typically, one contact ring comprises the ring-shaped continuous contact surface and another contact ring comprises the ring-shaped discontinuous contact surface. However, it may also be possible to provide both the ring-shaped continuous contact surface and the ring-shaped discontinuous contact surface within a common contact ring, which has holes to allow bolts to pass through.

The contact ring and the body may be formed as one piece. Alternatively, the contact ring may be provided separately and maybe glued to the body. In other embodiments, the contact ring may be welded to the body. It is also possible that the contact ring is fixed to the body using bolts, for example by means of counter-sunk bolts.

In addition, it is provided a support structure section comprising one of the aforementioned flanges and a wind turbine comprising such a support structure section.

Furthermore, it is proposed a method for mounting a flange according to one of the aforementioned embodiments to a counter flange. The method comprises inserting bolts through at least some of the through holes, preloading the inserted bolts with a first preload, identifying one or more gaps between the ring-shaped continuous contact surface and the counter flange, and inserting one or more shim(s) into at least one of the one or more gaps through an opening between to contact sections of the ring-shaped discontinuous contact surface.

The shims may have predetermined heights. Thus, for a given gap, one or more shims may be inserted.

The bolts may be preloaded by applying a well-defined torque or by using pre-tensioning techniques.

In an embodiment, the first preload corresponds to more than <NUM> percent, in particular more than <NUM> percent, of their nominal final tensile load.

Embodiments of the method may prescribe that the method comprises before inserting the shim, preloading at least some of the inserted bolts with a second preload after identifying the one or more gaps, and identifying one or more gaps between the ring-shaped continuous contact surface and the counter flange.

Thus, it is proposed a method for mounting a flange according to one of the aforementioned embodiments to a counter flange, wherein the method comprises inserting bolts through at least some of the through holes, preloading the inserted bolts with a first preload, identifying one or more gaps between the ring-shaped continuous contact surface and the counter flange, preloading at least some of the inserted bolts with a second preload after identifying one or more gaps, in particular long gaps, between the ring-shaped continuous contact surface and the counter flange. Thereafter, one or more (remaining) gaps may be identified and the method may prescribe inserting a shim into at least one of the one or more (remaining) gaps through an opening between to contact sections of the ring-shaped discontinuous contact surface.

Preloading at least some of the inserted bolts with a second preload may allow for closing some of the gaps before inserting shims. Thus, unnecessary shimming may be avoided.

In an embodiment, the through holes of the flange are arranged circularly.

Inserting bolts may comprise inserting bolts at least every <NUM>°. According to further embodiments, inserting bolts comprises inserting bolts through through holes provided between the ring-shaped continuous contact surface and a contact section of the ring-shaped discontinuous contact surface.

Thus, an opening may remain between the other parts of the discontinuous contact surface for inserting shims.

The invention may be better understood by reference to the drawings. The drawings are incorporated into, and form part of, the specification. They illustrate embodiments of the present disclosure and, along with the description, serve to explain the principles of the disclosure. The drawings are only illustrative of certain embodiments and do not limit the disclosure. In the drawings:.

<FIG> shows a wind turbine <NUM> comprising a tower <NUM> supporting a nacelle <NUM> which supports a wind turbine rotor <NUM>. The wind turbine tower comprises several support structures sections <NUM>, <NUM>, <NUM>, which are connected to each other using flange connections <NUM>.

Large diameter structures up to <NUM> and above make fulfilling fabrication tolerances very challenging. In particular, flatness requirements, which are required in order to limit the size of flange gaps are very difficult to comply with. <FIG> illustrate several types of flange gaps, which may arise in practice.

<FIG> shows a flange connection <NUM> formed by a flange <NUM> and a counter flange <NUM>. The two flanges <NUM> and <NUM> are connected to each other using bolts <NUM>. A gap is observable between the flange <NUM> and the counter flange <NUM> at a side opposite to the part of the flange <NUM> extending in the same direction as the bolt <NUM>. The flanges <NUM> and <NUM> may be called L-flanges. The part of the flange <NUM> perpendicular to the bolt <NUM> may be directed to the center of the flange as shown in <FIG>, for example. However, it is also conceivable that said part extends to the outside of the flange.

<FIG> shows another flange connection <NUM> formed by a flange <NUM> and a counter flange <NUM>, which are connected by bolts <NUM>. Here, the gap exists between the sections of the flange <NUM> and the counter flange <NUM> which extent parallel to the bolts <NUM>.

<FIG> shows a further flange connection <NUM>. The flanges <NUM> and <NUM> may be considered as T-flanges. Two groups of bolts <NUM> and <NUM> are provided for connecting the flanges. Gaps may be observed at parts of the flanges <NUM> and <NUM> facing away from the part of the flanges <NUM>, <NUM>, extending parallel to the bolt <NUM> and <NUM>.

<FIG> shows another T-flange connection <NUM> comprising flange <NUM> and counter flange <NUM>. Two bolts, <NUM> and <NUM>, are provided for establishing the connection. Here, a gap exists in the middle of the connection. The lack of contact in the center region may lead to fluctuating loads on the bolts when forces perpendicular to the bolt extensions are applied to the support structure of which the flange <NUM> forms a part.

<FIG> shows a further flange connection <NUM>. The flange connection comprises a flange <NUM> and a counter flange <NUM>. The flange <NUM> includes two contact rings <NUM> and <NUM> which provide a ring-formed discontinuous contact surface and ring-formed continuous contact surface. Moreover, <FIG> shows that the flange connection <NUM> may comprise a sealing <NUM>, which may prevent moisture upon entering the flange connection from the left side.

<FIG> shows a bottom view of a flange <NUM>. The flange comprises a base <NUM>, a ring-shaped continuous contact surface <NUM> and a ring-shaped discontinuous contact surface <NUM>. The ring-shaped discontinuous contact surface <NUM> comprises several contact sections <NUM> - <NUM>.

Between the ring-shaped continuous contact surface <NUM> and the ring-shaped discontinuous contact surface <NUM> through holes <NUM> are provided. Some through holes <NUM> are provided between contact sections of the ring-shaped discontinuous contact surface <NUM> and the first ring-shaped contact surface <NUM>. Said arrangement may in particular allow for proper pre-loading inserted bolts with a first pre-load before inserting one or more shim(s) as will be explained further below.

<FIG> shows a cross-section of the flange <NUM> along the line A-A of <FIG> shows the through hole <NUM> formed in the base <NUM> and a contact ring <NUM> welded to the base <NUM>, wherein the contact ring <NUM> provides the continuous contact surface <NUM>.

<FIG> shows a cross-section of the flange <NUM> along the line B-B shown in <FIG> illustrates that a further contact ring <NUM> may provide the discontinuous contact surface <NUM>. Moreover, the through hole <NUM> is shown. The quotient of an area of the ring-shaped discontinuous contact surface <NUM>, the sum of the areas of all contact sections <NUM>,. , <NUM> of the ring-shaped discontinuous contact surface <NUM>, and an area of the first ring-shaped contact surface <NUM> may be larger than <NUM>:<NUM>, in particular larger than <NUM>:<NUM>. Thus, a two large difference in contact pressure experienced by the flange at the ring-shaped discontinuous contact surface in comparison to the contact pressure experienced by the flange at the first ring-shaped contact surface may be avoided.

Although the flange <NUM> is shown with the contact ring <NUM> and the contact ring <NUM> facing upwards in the <FIG>, it may be preferred that the upper flange of a flange connection is provided with the contact ring <NUM> and/or <NUM>. Thus, an essentially even surface may be provided at the counter-flange, which may facilitate moving shims in the gaps.

<FIG> illustrate a method for establishing a flange connection. The flange is shown from the outside. The flange may comprise a base <NUM> and a contact ring <NUM> providing the outer ring-shaped continuous contact surface. The flange may be connected to a counter flange <NUM>. As shown in <FIG>, a gap may exist after the two flanges have been brought into contact with one another and bolts <NUM>, <NUM>, <NUM> and <NUM> have been inserted into through holes at a position between contact sections of the contact ring <NUM> providing the ring-shaped discontinuous contact surface (with respect to <FIG>, this may correspond to inserting bolts into the hole <NUM>) and the counter flange <NUM>. Between the protrusions of the contact ring providing the ring-shaped discontinuous contact surface, an opening <NUM> may exist. As shown in <FIG>, unavoidable manufacturing tolerances may lead to a long gap between the two flanges. This gap may even exist, when the bolts <NUM>, <NUM>, <NUM> and <NUM> have been pre-tensioned to a first pretension value.

In an embodiment of the proposed method, some bolts, for example the bolts <NUM>, <NUM>, <NUM> and <NUM>, may be tensioned to a higher second pretension value. As shown in <FIG>, this may close the long gap such that only a small gap remains.

The opening <NUM> may allow for inserting a shim <NUM> from the inside of the flange as shown in <FIG>.

Claim 1:
Flange (<NUM>),
wherein the flange (<NUM>) is configured for being mounted to a counter-flange with bolts (<NUM>) extending through a plurality of through holes (<NUM>, <NUM>) distributed along a circumference of at least one of the flange (<NUM>) and the counter flange,
wherein the flange (<NUM>) comprises a first ring-shaped contact surface (<NUM>),
wherein the flange (<NUM>) comprises a ring-shaped discontinuous contact surface (<NUM>),
wherein the first ring-shaped contact surface (<NUM>) and the ring-shaped discontinuous contact surface (<NUM>) are arranged such that the plurality of through holes (<NUM>, <NUM>) is arranged between the first ring-shaped contact surface (<NUM>) and the ring-shaped discontinuous contact surface (<NUM>),
characterized in that
at least one of the plurality of through holes (<NUM>, <NUM>) is provided between a contact section (<NUM>) of the ring-shaped discontinuous contact surface (<NUM>) and the first ring-shaped contact surface (<NUM>).