Flange Element

Abstract

The present invention relates to an annular flange element (20) for connection of a tubular element (26), the annular flange element (20) including an outer flange portion (44) with an outer forward side (28) extending radially outwardly and having an outer front face (31) for connection to a cooperating structure. The flange element (20) further includes an inner forward side (29) extending radially inwardly and having an inner front face (30) for connection to a cooperating structure, and an attachment portion (22) extending from the rear side (25) and adapted for secure attachment to the tubular element (26). The inner and outer flange portions (21, 44) are partially divided by at least one annular groove (70) extending between the inner and outer flange portions (21, 44) from a position between the inner and outer front faces (30, 31) toward a position away from the rear side (22).

Description

[Technical field]

[0001] The present invention relates primarily to flange elements for flange connections designed for connecting pipes, tubulars or conical shells that are subjected to high dynamic forces. [Background technology]

[0002] Freestanding tower structures, such as wind turbine towers, are often large and therefore constructed by rigidly connecting two or more sections of the tower together. The tower sections are usually constructed at a practical length for transporting to and lifting at the building site. Wind turbine towers and similar tower structures are often constructed by flange-fitting conical sections of the tower together. Loads on the bolted joints joining the sections are of a dynamic nature due to daily wind-induced loads and vibrations. In addition, extreme short-term high loads can be experienced during storms. Because the most practical way to assemble tower sections is with bolted flange connections, over the years many different designs have been developed, built and installed. However, the industry still experiences challenges with existing bolted connections for such tower structures. In offshore installed wind turbine towers, as well as at the interface between the tower and the supporting structure, and in the load-bearing structure itself, dynamic loads on the structure can come from wave and current induced dynamic responses.

[0003] The most important challenges for bolted flange connections of large tower structures such as wind turbine towers relate to the structural strength of the flange connections connecting the tower sections, fatigue resistance of the flange connections due to their dynamic response to wind loads, and loosening of bolts and nuts of the flange connections during operation due to vibrations and global dynamic excitations induced by wind flow past the tower structure including the large turbine blades and, in the case of offshore, waves on the supporting structure.

[0004] Tower sections are usually connected by providing flanges on the tower section and connecting two corresponding flanges on two adjacent sections using a number of bolts. The loads on the bolts of the joints formed by connecting two adjacent sections of such tower structures are dynamic in nature due to constantly changing loads induced by wind and / or water. As a result, there are several problems with this type of bolted connection. For example, there is a problem of bolt fatigue since the bolt stress is dynamic as a function of the dynamic loads of the tower. There can also be problems due to additional bolt loads from the prying effect on the bolts and local bending of the bolts as the flanges start to separate partially or totally under extreme tower loads. Furthermore, there are problems with loosening of the nuts caused by vibration and dynamic loads. There are also problems with water ingress into the bolts causing corrosion of the bolts. T-shaped flanges with inner and outer bolt circles offer better performance than L-shaped flanges. Prior art flanges are not usually used in areas that are inaccessible for inspection and maintenance and the outer bolt circle is often inaccessible.

[0005] It is an object of the present invention to alleviate at least one or several of the problems associated with the prior art solutions.

[0006] It is a further object of the present invention to provide a novel flange connection for large tower structures that can handle dynamic loads due to wind and / or water passing through the tower structure.

[0007] It is a further object of the present invention to reduce problems associated with corrosion of bolts connecting tower sections of a tower structure. Summary of the Invention

[0008] The present invention describes an annular flange element for the connection of tubular elements. The flange element has an inner periphery arranged around a central axis A, an outer periphery arranged around the central axis A and an outer flange portion extending radially outward towards the outer periphery. The outer flange portion comprises an outer section at a rear side and an outer front side with an outer front surface for connection to a cooperating structure. The flange element further comprises an inner flange portion extending radially inward towards the inner periphery, the inner flange portion comprising an inner section at the rear side and an inner front side with an inner front surface for connection to a cooperating structure. The flange element further comprises an attachment portion extending from the rear side in a direction opposite to the inner and outer front sides, the attachment portion being adapted for secure attachment to a tubular element. In this document, a tubular element is understood to mean any kind of elongated hollow object having a rim suitable for connection to the flange element. The cross section of the tubular element can be circular, elliptical, polygonal, and other shapes, and the tubular element can have a conical shape.

[0009] In accordance with the present invention, the inner and outer flange portions are partially divided by at least one annular groove extending between the inner and outer flange portions from a location between the inner and outer forward faces toward a location away from the aft side.

[0010] In one embodiment of the flange element, at least a portion of the outer front surface and the inner front surface have a non-zero angle with respect to a plane P perpendicular to the central axis A.

[0011] In another embodiment of the flange element, the groove is configured to allow for flexible displacement between the inner and outer front faces, such that the non-zero angle of the inner and outer front faces relative to plane P can change from non-zero to zero during connection to a cooperating structure.

[0012] In yet another embodiment of the flange element, the groove is provided such that, when connected to a cooperating structure, the attachment portion is in a fixed position during displacement of the inner and outer front faces.

[0013] In yet another embodiment of the flange element, the outer flange portion further comprises an outer flange wedge with an outer flange wedge surface disposed on the outermost section of the outer front face, and an outer flange heel with an outer flange heel surface disposed on the innermost section of the outer front face. The inner flange portion further comprises an inner flange wedge with an inner flange wedge surface disposed on the innermost section of the inner front face, and an inner flange heel with an inner flange heel surface disposed on the outermost section of the inner front face. The inner and outer flange wedge surfaces respectively form wedge surface angles γ1 and γ2 with the plane P, the inner and outer flange heel surfaces respectively form inner and outer heel surface angles β1 and β2 with the plane P, the inner and outer abutment surfaces are disposed near the annular groove on respective sides of the annular groove, and the inner and outer flange closure surface angles α1 and α2 are defined by the angles between the plane P and a straight line between the inner and outer abutment surfaces respectively and the inner and outer flange wedge surfaces respectively. The angles are positive in the sense that the apex of the angles is closest to the annular groove (not the wedge surface). In other words, it is the inner and outer abutment surfaces, which are the portions of the inner and outer heel surfaces closest to the annular groove, that come into contact with the cooperating structure first (before the bolts are tightened) when connecting two tubulars, said tubulars having flange elements according to the invention attached to their ends.

[0014] The wedge face angle controls the rotation of the inner and outer flanges during bolt pre-loading and has several advantages. The wedge face angle causes the flanges to deflect like a Belleville spring during assembly of the flange connection, which causes the flanges to be pre-stressed and subject to hoop stress. The deflection pre-stress of the flanges ensures that for any tower design load, the flanges will not loosen contact outside the flange recesses where the bolt fastenings are located, thereby preventing water from entering the annular openings formed by the flange recesses and causing corrosion of the bolts located in the bolt holes. Furthermore, the internal pre-stress of the flanges creates a separation force for the nuts that are threaded onto the bolts in the flange connection, so that the nuts will not self-loosen due to vibration or other dynamic loads. The bolt pre-stress is static and provides superior fatigue properties. The static bolt stress allows for higher bolt pre-stress and higher design load resistance of the flange elements. Furthermore, there is no prying effect on the bolts before flange separation occurs; the prying effect occurs when the load exceeds the design load of the flange connection.

[0015] In yet another embodiment of the flange element, the inner flange portion includes a plurality of inner bolt holes evenly distributed about the central axis A, and the outer flange portion further includes a plurality of outer bolt holes evenly distributed about the central axis A. The bolt holes extend in a direction substantially parallel to the central axis.

[0016] In yet another embodiment of the flange element, the outer flange portion includes an outer annular recess disposed between the outer flange heel and the outer flange wedge, with the plurality of outer bolt holes disposed within the recess, and the inner flange portion further includes an inner annular recess disposed between the inner flange heel and the inner flange wedge, with the plurality of inner bolt holes disposed within the inner flange recess.

[0017] In yet another embodiment of the flange element, the at least one annular groove includes one annular groove extending in a direction parallel to the central axis A from a position between the inner and outer front faces toward a position away from the mounting portion.

[0018] In yet another embodiment of the flange element, the width (W) of the annular groove at any depth is at least W=D×sin(β1)+D×sin(β2), where D is the distance from the any depth to the inner edge of the annular groove.

[0019] In yet another embodiment of the flange element, a plurality of inner and outer bolt holes have radial increments Δri and Δro, respectively, to facilitate insertion and allow rotation of the inner and outer flange portions (30, 31) without bending the bolts, where Δri of the inner bolt holes is at least Δri=Ti×sin(α1) and Δro of the outer bolt holes is at least Δro=To×sin(α2), where Ti and To are the thicknesses of the inner and outer flange elements, respectively, and α1 and α2 are the inner and outer closure angles, respectively.

[0020] In yet another embodiment of the flange element, the annular groove extends at least half, and more preferably substantially two-thirds, of the path from the inner and outer front faces toward the rearward surface.

[0021] In yet another embodiment of the flange element, the at least one annular groove comprises an inner groove having an inwardly oriented element and an outer groove having an outwardly oriented element, both grooves having a common opening between the inner and outer flange heel surfaces.

[0022] In yet another embodiment of the flange element, the surfaces of the rearward inner and outer sections have angles relative to the plane P that correspond to the angles α1 and α2 of the inner and outer closure surfaces.

[0023] In yet another embodiment of the flange element, the pressure test channel extends from an outer surface of the flange element to a portion of the annular groove that is fluidly isolated from the surroundings when the flange element is fully installed.

[0024] In yet another embodiment of the flange element, a portion of the annular groove is fluidly isolated from the surroundings when the flange element is fully installed. The annular groove may be isolated from the surroundings by being blocked by the base element or by being fluidly connected only to the annular groove of the cooperating flange element. While the annular groove often comprises one continuous groove, in some embodiments segmented grooves are contemplated.

[0025] In another aspect of the invention, a method for connecting a flange element to a cooperating structure is described. The cooperating structure has inner and outer rings of bolts that fit with bolt holes of an annular flange element. Examples of such a cooperating structure may be a base element for connecting to a first tubular body of a wind turbine tower, or a bottom of a wind turbine housing designed for mounting to the top of a wind turbine tower. The method relates to a flange element as described in paragraph

[0013] and includes the steps of aligning the flange element and the cooperating structure such that the ring of bolts is aligned with the ring of bolt holes, and displacing the flange element and the cooperating structure toward each other such that the inner and outer abutment surfaces contact against the cooperating structure and the ring of bolts enters the ring of bolt holes. The method further includes the step of tightening the bolts such that the inner and outer wedge surface angles γ1 and γ2, the inner and outer closing surface angles α1 and α2, and the inner and outer heel surface angles β1 and β2 are all zero.

[0026] In another aspect of the invention, a method for connecting a flange element to a cooperating structure is described. The cooperating structure has inner and outer rings of bolt holes that mate with the bolt holes of the flange element. Preferably, the cooperating structure is an annular flange element according to the invention as described in paragraph 0013. It is also conceivable that the cooperating structure is a prior art flange connection with matching bolt holes. The method includes the steps of aligning the flange element and the cooperating structure such that the rings of bolt holes of the flange element are aligned with the rings of bolt holes of the cooperating structure, displacing the flange element towards the cooperating structure such that the inner and outer abutment surfaces contact against the cooperating structure, and entering the bolts into the bolt holes. The method further includes the steps of tightening the bolts such that the inner and outer wedge surface angles α1 and α2, the inner and outer closing surface angles γ1 and γ2, and the inner and outer heel surface angles β1 and β2 are all zero.

[0027] In another aspect of the invention, a method is described for testing the integrity of a connection between a flange element and a cooperating structure, where at least a portion of the annular groove must be fluidly isolated from the environment, the method including applying pressure to a portion of the annular groove through a pressure test channel until the pressure in the annular groove reaches a predetermined test pressure, and observing whether the pressure decreases over time. [Brief description of the drawings]

[0028] [Figure 1] FIG. 2 is a radial cross-sectional view of a flange element according to the invention; [Figure 2a] FIG. 13 is a radial cross-sectional view of an embodiment of a flange element where the critical angles are shown and the wedge face angle and the closure face angle are identical. [Figure 2b] 11A-11C are radial cross-sectional views of embodiments of flange elements in which the wedge face angle and the flange closure face angle are different. [Diagram 3] 13A-13D show embodiments of a base element to which embodiments of a flange element can be fastened. [Figure 4]FIG. 13 is a cross-sectional view of a flange element resting on a base element before the bolts are tightened. [Diagram 5] 5 is a cross-sectional view of the flange element of FIG. 4 after the bolts have been tightened. [Figure 6] FIG. 1 is a cross-sectional view of two flange elements attached together prior to final tightening of the bolts. [Figure 7a] FIG. 7 is a cross-sectional view of the two flange elements of FIG. 6 after the bolts have been tightened. [Figure 7b] FIG. 13 illustrates the increased radius of the bolt holes. [Figure 8] 13A-13C illustrate an embodiment of a pressure test channel for testing the pressure within the annular groove cavity. [Figure 9] 1A-1C show an embodiment of a flange element having inner and outer flange portions with different features. [Figure 10a] FIG. 2 shows the rear side of a complete flange element according to the present invention. [Figure 10b] FIG. 2 shows the front side of a complete flange element according to the invention. [Figure 11a] 1 shows a wind turbine and a floating body structure suitable for connecting tubular components using a flange element according to the invention; [Figure 11b] 1 shows a wind turbine and a floating body structure suitable for connecting tubular components using a flange element according to the invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] In order to enhance the understanding of the present invention, the drawings are utilized and like reference numerals are used to denote like features in all the drawings.

[0030] An annular flange element 20 according to the present invention will be described hereinafter using terms such as outward and outermost, which herein refer to a radial direction outward from a central axis A of the flange element as shown in Figures 10a and 10b. Inward and innermost refer to a radial direction toward the central axis A. The central axis A extends longitudinally through the center point of the annular shape represented by the flange element.

[0031] The present invention relates to an annular flange element 20 for the connection of tubular elements. Primarily the flange element is designed for large tubular bodies, such as those for offshore wind turbines, which are subjected to high dynamic forces from wind and waves. An example of which can be seen in figures 11a and 11b.

[0032] The annular flange element 20 shown in Figure 1 has a central axis A shown in Figures 10a and 10b, and for ease of description of the flange element defines an outer periphery 108 and an inner periphery 109, which are simply the outermost and innermost surfaces of the flange element. By annular we mean any shape that represents a complete loop. This may be a circle, an ellipse, a polygon, or other shape.

[0033] The annular flange element 20 has an outer flange portion 44 extending radially outwardly toward the outer periphery 109, the outer flange portion 44 having an outer rear section 25a of the rear side 25 and an outer forward side 28 having an outer front surface 31 for connection to cooperating structure.

[0034] The annular flange element further includes an inner flange portion 21 extending radially inwardly toward the inner periphery 108. The inner flange portion 21 includes an inner aft section 25b of the aft side 25 and an inner forward side 29 having an inner front face 30 for connection to a cooperating structure. The aft side 25, including the inner aft section 25b and the outer aft section 25a, faces away from the inner and outer front faces which are the surfaces that contact the cooperating structure when the flange element 20 is connected to the cooperating structure.

[0035] The annular flange element further comprises an attachment portion 22 extending from the rear side 25 substantially opposite the inner and outer front faces 30, 31, the attachment portion being adapted for secure attachment to the tubular element. Preferably, the attachment portion comprises at least one welding bevel 23, but preferably two welding bevels, which extend partially or preferably over the entire circumference of the flange element, so that the attachment portion can be welded to the tubular element.

[0036] The inner and outer flange portions 21, 44 are partially divided by at least one annular groove 70 extending between the inner and outer flange portions 21, 44 from a position between the inner and outer front faces 30, 31 toward a position away from the mounting portion 22. The purpose of the annular groove 70 is to provide greater flexibility to the inner and outer flange portions 21, 44, thus allowing for a more uniform distribution of clamping forces on the inner and outer front faces. Preferably, the at least one annular groove is one annular groove 70 extending in a direction parallel to the central axis A from a position between the inner and outer front faces 30, 31 toward a position away from the mounting portion 22.

[0037] In a preferred embodiment, at least a portion of the outer anterior surface 31 and the inner anterior surface 30 have a non-zero angle relative to a plane P that is perpendicular to the central axis A. The grooves 70 are configured to allow for flexible displacement between the inner and outer anterior surfaces such that the non-zero angle of the inner and outer anterior surfaces relative to the plane P can change from non-zero to zero during connection to a cooperating structure.

[0038] 1 and 2, the outer flange portion 44 further comprises an outer flange wedge 40 having an outer flange wedge surface 41 disposed on the outermost section of the outer front face 31. The flange portion further comprises an outer flange heel 42 having an outer flange heel surface 43 disposed on the outer front face 31 on its innermost section.

[0039] In a preferred embodiment, the inner flange portion 21 further comprises an inner flange wedge 32 having an inner flange wedge surface 33 located on the innermost section of the inner front surface 30, and the flange portion further comprises an inner flange heel 34 having an inner flange heel surface 35 located on the outermost section of the inner front surface 30.

[0040] As shown in Figures 2a and 2b, the inner flange wedge surface 33 and the outer flange wedge surface 41 form wedge surface angles γl and γ2, respectively, with the plane P. Also, the inner flange heel surface 35 and the outer flange heel surface 43 form heel surface angles β1 and β2, respectively, with the plane P. Furthermore, the inner and outer flange portions have inner and outer flange closure surface angles α1 and α2, which are defined by the angles between the plane P and the straight lines leading from the inner and outer abutment surfaces 45, 46, respectively, to the inner and outer wedge surfaces 33, 41, respectively. In some embodiments, the wedge surface angles and the flange closure surface angles are the same, as seen in Figure 2a. In other embodiments, the wedge surface angles and the flange closure surface angles are different, as seen in Figure 2b. For example, the outer flange wedge surface angle γ2 can be applied, as seen in Figure 2b, to ensure a permanent and strong closure of the two connected outer flange wedges to avoid salt water from entering the bolt.

[0041] In a preferred embodiment, the inner flange portion 21 includes a plurality of inner bolt holes 39 evenly distributed about the central axis A, and the outer flange portion 44 further includes a plurality of outer bolt holes 38 evenly distributed about the central axis A. The outer flange portion 44 further includes an outer annular recess 37 disposed between the outer flange heel 42 and each of the outer flange wedges 40, with the plurality of outer bolt holes 38 disposed within the outer annular recess. The inner flange portion 44 further includes an inner annular recess 36 disposed between the inner flange heel 34 and the inner flange wedge 32, with the plurality of inner bolt holes 39 disposed within the inner flange recess 36.

[0042] To reduce the prying effect on the bolts 72, 73 and increase the static window of the bolted connection, the bolts and bolt holes should be as close to the center of the flange element 20 as possible. In a preferred embodiment, the radial width of the flange heel surfaces 35, 43 should be less than the thickness of the tubular wall and the radial width of the flange wedge surfaces 33, 40 should be less than half the thickness of the flange heel surfaces 35, 43. The thickness (in a direction parallel to the central axis A) of the inner and outer flange portions 21, 44 should be at least as thick as the annular wall, preferably 1.5 to 2 times thicker than the tubular wall in the tubular bodies to be connected.

[0043] In many cases, the cooperating structure to which the flange element 20 according to the invention is connected is another flange element, as shown in Figures 6 and 7a. Alternatively, the flange element may be connected to a base element having a flat contact surface for contacting the flange element, as shown in Figures 4 and 5. Typically, the inner and outer flange closure surface angles α1 and α2, as well as the inner and outer wedge surface angles, are greater than 0 degrees and in the range of 0.1° to 3°. The inner and outer heel surface angles β1 and β2, respectively, are greater than 0 degrees and typically in the range of 0.15° to 5°. It should be noted that in many cases, the inner flange portion 21 differs from the outer flange portion 44 in terms of flange thickness, flange width, bolt configuration including bolt material, bolt diameter and number of bolts, wedge surface angle and heel surface angle. Such an embodiment is shown in Figure 9. This is due to different exposure to moisture, salt, UV, temperature, and forces from weather and wind turbine operation, as well as practical issues regarding handling, installation, and preloading of the bolts.

[0044] FIG. 4 shows one flange element 20 disposed on bolts extending from a base element 74 with the bolts tightened, and FIG. 5 shows the flange element of FIG. 4 prior to tightening of the bolts.

[0045] FIG. 6 shows two flange elements according to the invention in contact only at the inner and outer abutment surfaces 45, 46 and 45', 46' prior to tightening of the bolts. The parts of the cooperating structure (in this case the flange elements) have the same reference numbers but with an apostrophe. The angle is rather small and is more clearly shown in FIG. 2a and FIG. 2b. When the bolts are tightened, the annular groove 70 and the cooperating annular groove 70' allow the respective inner and outer flange portions 21, 44 and their cooperating counterparts 21' and 44' to be displaced synchronously until the inner flange wedge surface 33 abuts against the cooperating counterpart 33', as shown in FIG. 7. Although the angle is small, it can be seen that both sides of the annular flexible groove are curved and are on the verge of contacting the opposite side in the vicinity of the inner and outer abutment surfaces 45, 46. The minimum width W of the annular flexible groove at any position B inside the annular groove 70 must be wide enough to allow this displacement. FIG. 8 shows these relationships. During tightening of the bolts, each flange portion rotates about a respective rotation area, labeled R in Figure 8. The width W is the distance D from any position B inside the annular groove 70 to the inner edge 71 of the annular groove multiplied by the sine of β1 plus the distance D from any position B within the annular groove 70 to the inner edge 71 of the annular groove multiplied by the sine of β2. More precisely, W = D x sin(β1) + D x sin(β2), where β1 and β2 are the inner and outer flange heel surface angles, respectively.

[0046] Preferably, the inner section 25a of the rear side 25 makes an angle α1 with the plane P, which is the same as the inner flange closing plane angle. Similarly, the outer section 25b of the rear side 25 makes an angle α2 with the plane P, which is the same as the outer flange closing plane angle. This ensures that the nut or bolt head fastened to the bolt has a horizontal position on the surface of the rear side 25 and the cooperating rear side 25' when the inner or outer flange wedge surface 33, 41 abuts against the cooperating inner and outer flange wedge surfaces 33', 41'. The depth of the annular groove 70 must be sufficiently deep and the width of the annular groove 70 must be sufficiently wide to allow for these displacements. The groove end 71 must be located between the middle of the flange portion and the rear side 25. More preferably, the inner groove end is located in a third of the path toward the rear side 25, which corresponds to two-thirds of the path toward the attachment portion 22.

[0047] In the preferred embodiment shown in FIG. 7b, the plurality of inner and outer bolt holes 39, 38 each have a radius increment Δri, Δro to allow rotation of the inner and outer flange portions 21, 44, respectively, without bending the bolt, which would cause the bolt hole to change angle as the bolt is tightened. Additional width is also required to insert the bolt into the flange element and the bolt hole of the cooperating flange element. The Δri of the inner bolt hole 39 is at least Δri=Ti×sin(α1), and the Δro of the outer bolt hole 38 is at least Δro=To×sin(α2), where Ti and To are the thicknesses of the inner and outer flange elements (30, 31), respectively, and α1 and α2 are the inner and outer closure surface angles, respectively, as clearly shown in FIG. 2a and FIG. 2b.

[0048] In one embodiment, the at least one annular groove 70 comprises an inwardly tapered inner annular groove 77 and an outwardly tapered outer annular groove 78, both having a common opening between the inner and outer flange heel surfaces 35, 43. The two grooves form a V-shape and should have a steep angle with respect to a plane P perpendicular to the central axis A.

[0049] In one embodiment, the flange element includes a pressure test channel 75 that extends from the outer surface of the flange element 20 to the annular groove 70 that is fluidly isolated from the surroundings when the flange element is fully installed and the bolts are tightened. The annular groove may be blocked by the base element 74 or may be fluidly connected to the annular groove 70' of the cooperating flange element 20' to form a fluidly isolated cavity of the two annular grooves 70, 70'. If the annular cavity cannot hold the pressure supplied to the annular groove cavity 76, the operator knows that the integrity of the flange connection has been compromised and that the bolts 38, 39 and the flange elements 20, 20' are subject to deterioration.

[0050] In the following, a method for connecting a flange element 20 to a cooperating structure having inner and outer rings of bolts 73', 72' mating with bolt holes 39, 38 of the flange element is described. The method relates to a flange element according to the invention, in which the outer flange portion includes an outer flange wedge 40 with an outer flange wedge surface 41 located on the outermost section of the outer front face 31 and an outer flange heel 42 with an outer flange heel surface 43 located on the innermost section of the outer front face 31. The method further relates to a flange element as described above, in which the inner flange portion 21 includes an inner flange wedge 32 with an inner flange wedge surface 33 located on the innermost section of the inner front face 30 and an inner flange heel 34 with an inner flange heel surface 35 located on the outermost section of the inner front face 30. The inner and outer flange wedge surfaces 33, 41 form wedge surface angles γ1 and γ2, respectively, with the plane P, and the inner and outer flange heel surfaces 35, 43 form inner and outer heel surface angles β1 and β2, respectively. The inner and outer flange closure surface angles α1 and α2 are defined by the angle between plane P and a straight line between the inner and outer abutment surfaces 45, 46, respectively, and the inner and outer flange wedge surfaces 33, 41, respectively.

[0051] The method includes the step of aligning the flange element 20 and cooperating structure so that the rings of the inner and outer bolts 73,72 are aligned with the rings of the inner and outer bolt holes 39,38.

[0052] One step of the method is to displace the flange element 20 towards (or away from) the cooperating structure so that the inner and outer abutment surfaces 45, 46 contact the cooperating structure and the rings of the bolts 73', 72' enter the rings of the bolt holes 38, 39.

[0053] One step in the method is to tighten the bolts so that the inner and outer flange closure surface angles (α1, α2), the inner and outer wedge surface angles (γ1, γ2), and the inner and outer heel surface angles (β1, β2) are all zero or close to zero.

[0054] Below, a method is described for connecting the flange element 20 described in paragraph 0050 to a cooperating structure having inner and outer rings of bolt holes 39', 38' that mate with the inner and outer bolt holes 39, 38 of the flange element. In a preferred embodiment, the cooperating structure is a flange element according to the invention. The method includes the step of aligning the flange element 29 with the cooperating structure such that the ring of inner and outer bolt holes (39, 38) matches with the ring of inner and outer bolt holes (39', 38') in the cooperating structure.

[0055] One step of the method is to displace the flange element towards the cooperating structure such that the inner and outer abutment surfaces (45, 46) contact the cooperating structure.

[0056] One step in the method is to insert a bolt into a bolt hole.

[0057] One step in the method is to tighten the bolts so that the inner and outer closure surface angles (α1, α2), the inner and outer wedge surface angles (γ1, γ2), and the inner and outer heel surface angles (β1, β2) are all zero or close to zero.

[0058] A method for testing the integrity of a connection between a flange element 20 and a cooperating structure according to the present invention will now be described.

[0059] One step of the method is to supply pressure to the annular groove 70 via the pressure test channel 74 until the pressure in the annular groove reaches a predetermined test pressure, and then in another step observe whether the pressure decreases over time. If the pressure does not decrease, the integrity of the connection between the flange element 20 and the cooperating structure according to the present invention is not compromised. [Explanation of symbols]

[0060] 20 T-flange element 21 Inner flange 22 Mounting part 23 Welding bevel 24 Elliptical transition region 25 Rear side 25a Rear inner section 25b Rear outer section 26 Tubular elements 28 lateral anterior side 29 Inner front side 30 Inside front 31 Outer front 32 Inner flange wedge 33 Inner flange wedge surface 34 Inner flange heel 35 Inner flange heel surface 36 Inner flange recess 37 Outer flange recess 38 Outer Bolt Holes 39 Inner Bolt Hole 40 Outer flange wedge 41 Outer flange wedge surface 42 Outer flange heel 43 Outer flange heel surface 44 Outer flange 45 Inner contact surface 46 Outer contact surface 70 Flexible Groove 71 Groove End 72 Outer bolt 73 Inner bolt 74 Tower Base 75 Pressure Test Channel 76 Annular groove cavity 108 Inner circumference 109 Outer periphery

Claims

1. An annular flange element (20) for connecting a tubular element (26), said flange element (20) comprising: an inner circumferential surface (108) disposed about a central axis (A); an outer peripheral surface (109) disposed around the central axis (A); an outer flange portion (44) extending radially outwardly towards said outer circumferential surface (109), said outer flange portion (44) comprising an outer section (25a) of an aft side (25) and an outer forward side (28) having an outer front surface (31) for connection to a cooperating structure; an inner flange portion (21) extending radially inwardly towards said inner circumferential surface (108), said inner flange portion (21) comprising an inner section (25b) of said rear side (25) and an inner forward side (29) having an inner front surface (30) for connection to said cooperating structure; a mounting portion (22) extending from said rear side (25) in a direction opposite said inner and outer front faces (30, 31), said mounting portion being adapted for secure attachment to a tubular element (26); an annular flange element (20), wherein the inner and outer flange portions (21, 44) are partially divided by at least one annular groove (70) extending between the inner and outer flange portions (21, 44) from a position between the inner and outer front faces (30, 31) toward a position away from the rear side (25).

2. 2. The flange element (20) of claim 1, wherein at least a portion of the outer front surface (31) and the inner front surface (30) have a non-zero angle with respect to a plane (P) perpendicular to the central axis (A).

3. 3. The flange element (20) of claim 2, wherein the at least one annular groove (70) is configured to permit flexible displacement between the inner front surface and the outer front surface, and the non-zero angle of the inner and outer front surfaces relative to the plane (P) can change from non-zero to zero during connection to the cooperating structure.

4. A flange element according to any one of the preceding claims, wherein the groove is provided such that, when connected to the cooperating structure, the attachment portion is in a fixed position during displacement of the inner and outer front faces.

5. The outer flange portion (44) is an outer flange wedge (40) having an outer flange wedge surface (41) disposed on the outermost section of said outer front surface (31); an outer flange heel (42) having an outer flange heel surface (43) disposed on an innermost section of said outer front surface (31); The inner flange portion (21) is an inner flange wedge (32) having an inner flange wedge surface (33) disposed on an innermost section of the inner front surface (30); an inner flange heel (34) having an inner flange heel surface (35) disposed on an outermost section of said inner front surface (30); 5. A flange element (20) according to any one of claims 1 to 4, wherein the inner and outer flange wedge surfaces (33, 41) respectively form wedge surface angles (γ1, γ2) with a plane (P), the inner and outer flange heel surfaces (35, 43) respectively form inner and outer heel surface angles (β1, β2) with a plane (P), inner and outer abutment surfaces (45, 46) are disposed on each side of the annular groove near said groove, and inner and outer flange closure surface angles (α1, α2) are defined by the angle between the plane (P) and a straight line between each of the inner and outer abutment surfaces (45, 46) and each of the inner and outer flange wedge surfaces (33, 41).

6. 6. A flange element (20) according to any one of claims 1 to 5, wherein the inner flange portion (21) comprises a plurality of inner bolt holes (38) evenly distributed about the central axis A, and the outer flange portion (44) further comprises a plurality of outer bolt holes (39) evenly distributed about the central axis A.

7. 6. A flange element (20) as set forth in claim 5, wherein the outer flange portion (44) comprises an outer annular recess (37) disposed between the outer flange heel (42) and the outer flange wedge (40), and the plurality of outer bolt holes (38) are disposed within the outer annular recess, and the inner flange portion (44) further comprises an inner annular recess (36) disposed between the inner flange heel (34) and the inner flange wedge (32), and the plurality of inner bolt holes (39) are disposed within the inner flange recess (36).

8. The flange element (20) according to any one of claims 1 to 7, wherein the at least one annular groove includes one annular groove (70) extending in a direction parallel to the central axis A from a position between the inner and outer front faces (30, 31) towards a position away from the mounting portion (22).

9. 8. The flange element (20) of claim 5 or 7, wherein the width (W) of the annular groove (70) at any depth is at least W = D x sin(β1) + D x sin(β2), where D is the distance from the any depth to an inner end (71) of the annular groove (70).

10. 8. A flange element (20) according to claim 4 or 7, wherein the plurality of inner and outer bolt holes (38, 39) respectively have radial increments Δri and Δro to facilitate bolt insertion and to allow rotation of the inner and outer flange portions (30, 31) without bending the bolts, and wherein Δri of the inner bolt holes is at least Δri=Ti×sin(α1) and Δro of the outer bolt holes is at least Δro=To×sin(α2), where Ti and To are thicknesses of the inner and outer flange elements (30, 31), respectively, and α1 and α2 are the inner and outer flange closure plane angles, respectively.

11. 11. The flange element (20) according to any one of the preceding claims, wherein the annular groove (70) extends at least half, more preferably substantially two-thirds, of the path from the inner and outer front faces (30, 31) towards the surface of the rear side (22).

12. 12. A flange element (20) according to any one of claims 1 to 11, wherein the at least one annular groove (70) comprises an inwardly inclined inner groove and an outwardly inclined outer groove, the inner groove and the outer groove having a common opening between the inner and outer flange heel surfaces (35, 43).

13. 6. A flange element according to claim 5, wherein surfaces of the inner and outer sections (25a, 25b) of the rear side (25) have angles relative to a plane (P) corresponding to the inner and outer flange closure surface angles (α1, α2), respectively.

14. 14. The flange element (20) of any one of claims 1 to 13, wherein a pressure test channel (75) extends from an outer surface of the flange element to a section of the annular groove (70) that is fluidly isolated from the surroundings when the flange element is fully installed.

15. 6. A method for connecting a flange element (20) to a cooperating structure having inner and outer rings of bolts (73', 72') mating with the bolt holes (39, 38) of the flange element, the method comprising: aligning said flange element (20) and said cooperating structure such that said ring of said bolts (73', 72') is aligned with said ring of said bolt holes (39, 38); - displacing said flange element and said cooperating structure towards each other such that said inner and outer abutment surfaces (45, 46) contact said cooperating structure and said ring of said bolts (39, 38) enters said ring of said bolt holes (39, 38); and tightening the bolts so that the inner and outer flange closure surface angles (α1, α2), the inner and outer wedge surface angles (γl, γ2), and the inner and outer heel surface angles (βl, β2) are all zero.

16. 6. A method for connecting a flange element (20) according to claim 5 to a cooperating structure having inner and outer rings of bolt holes (39', 38') mating with bolt holes (39, 38) of said flange element, comprising: aligning said flange element (20) with said cooperating structure such that the ring of bolt holes (39, 38) is aligned with the ring of bolt holes (39', 38') of the cooperating structure; displacing the flange element towards the cooperating structure such that the inner and outer abutment surfaces (45, 46) contact the cooperating structure; inserting a bolt into the bolt hole; and tightening the bolts so that the inner and outer flange closure surface angles (α1, α2), the inner and outer wedge surface angles (γl, γ2), and the inner and outer heel surface angles (βl, β2) are all zero.

17. applying pressure to the annular groove (70) via a pressure test channel until pressure within the annular groove reaches a predetermined test pressure; 15. A method for testing the integrity of a connection between a flange element (20) and a cooperating structure as claimed in claim 14, comprising the step of observing whether said pressure decreases over time.

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