POWER PYLON WITH FLANGE CONNECTED TUBULAR SEGMENTS

Abstract

 A power pylon comprises at least two tubular segments interconnected by two opposing annular flanges which are attached to the respective ends of the tubular segments. The annular flanges extend radially inwards and each having an end face that faces the end face of the opposing flange. The annular flanges have through bores distributed in a circle.
The through bores of the two opposing flanges are aligned and bolts pass through said aligned through bores, wherein nuts cooperate with said bolts to bolt the opposing flanges together. The end face of at least one of the opposing annular flanges has a central annular recessed zone that is machined in said end face. The central annular recessed zone is flanked by a radially outward engagement surface and a radially inward engagement surface, which form the interface with the opposing flange.

Description

[0001] The invention relates to a power pylon comprising at least two tubular segments which are interconnected by an annular flange connection, the annular flange connection comprising two opposing annular flanges which are attached to the respective ends of the tubular segments, said annular flanges extending radially inwards and each having an end face that faces the end face of the opposing flange, the annular flanges each having through bores distributed in a circle, wherein the through bores of the two opposing flanges are aligned, wherein the annular flange connections furthermore comprise bolts that pass through said aligned through bores, and nuts cooperating with said bolts so as to bolt the opposing flanges together.

[0002] An example of such a pylon is known as "Wintrack pylon", which comprises two steel tubular segments with each a length of about 30m. The outer diameter of this known pylon tapers from about 2,4m at the bottom to 0,5m at the top. The wall thickness of the two tubular segments is about 16 mm. The upper segment has a weight of about 13 tons and the lower segment has a weight of about 40 tons. At the location of the flange connection the pylon has an outer diameter of about 1,2m.

[0003] The upper tubulars segment of the "Wintrack pylon" has a flange attached (welded) at its lower end, which flange extends radially inwards. The lower tubular segment has a flange attached (welded) at its upper end which also extends radially inwards. The flanges are each provided with for example twenty-four through bores aranged in a circle. The bores of the opposing flanges are aligned and bolted together by bolts and nuts.

[0004] Although the known pylons have been successfully built, there have occurred some problems with the sealing between the flanges. A defect in the sealing between the flanges may increase the risk of corrosion of the bolts due to exposure to moist/water.

[0005] From EP 1 514 029 it is known to provide a layer of a thermoplastic material between the flanges to compensate for surface unevenness and, additionally with silicone filling mass to prevent moisture from entering between the flanges. This solution however requires additional parts and complication during installation (heat the thermoplastic layer).

[0006] The present invention has for an object to mitigate the problem of exposure of the bolts to moist in a simple but effective manner.

[0007] This object is achieved by a pylon according to the preamble of claim 1, wherein the end face of at least one of the opposing annular flanges has a central annular recessed zone that is machined in said end face, said central annular recessed zone being flanked by a radially outward engagement surface and a radially inward engagement surface which form the interface with the opposing flange.

[0008] This connection structure according to the invention achieves that two radially spaced relatively narrow coaxial annular interfaces are created between the two opposing flanges. Thereby any unevenness in the flange surfaces is compensated.

[0009] In a practical embodiment the central annular recessed zone has a width that is between 70% - 75%, preferably around 73% of the width of the end face of the annular flange.

[0010] Preferably the radially outward engagement surface and the radially inward engagement surface have substantially the same width.

[0011] Thereby, in the mentioned practical embodiment, the two radially spaced relatively narrow coaxial annular interfaces between the opposing flanges each have width that is about 12,5% -15% of the total flange width. By such a width of the interfaces a good compromise is achieved between the load distribution at the interfaces, and on the other hand the approximation of a two-point load which mitigates the unevenness problem of the interfaces.

[0012] In a preferred embodiment the end face of both of the opposing annular flanges have an annular recessed zone that is machined in the end face. The flanges are manufactured separately from the tubular walls of the tubular pylon segments and are then attached to the respective tubular walls by welding. It is advantageous to manufacture only one single type of flange both for the upper and the lower pylon segment. This prevents that the wrong flange can be welded to the tubular wall and two opposing flanges can be of the type having no recess.

[0013] In a possible practical embodiment the annular flange has a thickness and the central annular recessed zone has a depth with respect to the radially outward and radially inward engagement surfaces, wherein the ratio between said depth and said thickness is within the range 0,02 - 0,03, preferably around 0,027.

[0014] In a possible practical embodiment the flange has an outer diameter and the central annular recessed zone has a depth with respect to the radially outward and radially inward engagement surfaces, wherein the ratio between said depth and an outer diameter of the flange is between 0,001 - 0,002, preferably between 0,0015 and 0,0020, more preferably around 0,0017.

[0015] In a preferred embodiment the bolts have a head which is arranged against the lower annular flange of the flange connection.

[0016] In a preferred embodiment the connection furthermore comprises washers arranged between the flange surface and the bolt heads and nuts, wherein the washer at the lower flange has a radial groove extending from the inner side of the washer to the outer side of the groove.

[0017] The radial groove may have a depth that corresponds to about half of the thickness of the washer. In a practical embodiment the washer may have a thickness of about 8mm and the groove may have depth of about 4mm.

[0018] The radial groove, in the mounted state of the washer, preferably faces the flange surface.

[0019] The groove in the washer at the lower flange of the connection serves as a drainage for water/moist that for some reason has entered in the through bores. If the water would stay in the bores the bolts might get exposed too long to the moist and get corroded, whereby the risk of failure of the bolt increases. By draining the possible water from the bores through the groove this risk is reduced.

[0020] The invention will be further elucidated in the following description with reference to the drawing, wherein:

Fig. 1

shows in a view from above a flange connection of a pylon according to the invention,

Fig. 2

shows a cross section according to C-C as indicated in Fig. 1,

Fig. 3

shows in a view from above one of the flanges of the connection of Fig. 1,

Fig. 4

shows a cross section according to A-A in Fig. 3,

Fig. 5

shows a detail of Fig. 4, and

Fig. 6

shows a view in perspective of a washer for a connection shown in Fig. 1.

[0021] In Figs 1 and 2 is illustrated a flange connection to connect two tubular segments 1 and 2 of a power pylon. Such a power pylon carries overhead power lines. The tubular segments 1, 2 each have a tubular wall indicated by reference numerals 3, 4 respectively. In a practical embodiment of the pylon the tubular walls of the pylon may have an outer diameter of about 1,1 - 1,2 m at the location of the flanged connection. The outer diameter D_o (cf. Fig. 3) of the flanges corresponds to the outer diameter of the tubular walls

[0022] The upper tubular segment 1 has an upper flange 5, which is attached to the lower end of the upper tubular wall 3. The flange 5 is attached to the tubular wall by welding and extends radially inwards therefrom. The weld is indicated by reference numeral 7.

[0023] The lower tubular segment 2 has a lower flange 6, which is attached to the upper end of the lower tubular wall 4. The flange 6 is attached to the tubular wall by welding and extends radially inwards therefrom. The weld is indicated by reference numeral 8.

[0024] The flanges 5, 6 have an upstanding circumferential rim 19, at which the flange is welded to the tubular walls. The rim 19 may have a height of about 25 mm. This rim 19 has the advantage that the welding heat is applied at some distance of the flanges 5, 6 whereby the effect of deformation, thermal tension and additional unevenness of the flanges 5, 6 is reduced.

[0025] In the preferred embodiment the flanges 5 and 6 are identical. The separate flange 5, 6 is shown in Fig. 3 and 4. Identical flanges 5, 6 results in that all flanges can be made by the same forming and machining process and no mistakes can be made regarding which flange has to be welded to which tubular wall 3, 4.

[0026] For a pylon according to the invention the flanges 5, 6 may have thickness t ≥ 30 mm, for example 60 - 80 mm. The flanges 5, 6 may have an inner diameter D_i of 700 - 800 mm.

[0027] The flanges 5, 6 are provided with through bores 9 distributed over the circumference of the flange, as can be seen in Figs 3 and 4.

[0028] In the particular embodiment shown in the figures there are twenty-four bores 9 provided in the flange 5, 6. Bolts 10 with a threaded shank are inserted through the aligned bores 9 of the two opposing flanges 5, 6. The bolts 10 are inserted from below such that the bolt head 10A is located at the lower flange 6. Nuts 11 are screwed on the bolts 10 to tighten the flanges 5, 6 together. For the pylon according to the invention M48 bolts can be used.

[0029] Between the nut 11 and the upper flange a washer 13 is arranged. Also between the bolt head 10A and the lower flange a washer 12 is arranged. The lower washer 12 is shown separately in Fig. 6. The washer 12 has an upper surface 12A in which a radial groove 14 is formed. When mounted the upper surface 12A is facing the flange 6. The radial groove 14 forms with the flange surface a channel that communicates with the bore 9. This has as an advantage that if moist/water somehow ends up in the bore 9, it will be able to drain at the lower side from the bore 9 through the formed channel. In this way a retention of water in the bores 9, which is potentially detrimental for the bolt 10, is prevented.

[0030] In a practical embodiment the washer 12 may have a thickness of about 8mm and the groove 14 may have a depth of about 4mm.

[0031] The opposing annular flanges 5, 6 each have an end face 15, which faces the end face 15 of the other one of the flanges 5, 6. The end face 15 has a central annular recessed zone 16 that extends circumferentially. The annular recessed zone 16 is machined in said end face 15. The central annular recessed zone 16 is flanked by a radially outward engagement surface 17 and a radially inward engagement surface 18. The radially outward engagement surface 17 and radially inward engagement surface 18 form the interface with the same surfaces 17, 18 of the opposing flange 5, 6 when the flanges 5, 6 are clamped together (cf. Fig. 2). These surfaces 17, 18 are machined such that they each form an even plane. The radially inward engagement surface 18 may be a little recessed with respect to the outward engagement surface 17.

[0032] The central annular zone 16 has a depth d of about 2mm with regard to the outer and inner engagement surfaces 17, 18.

[0033] By providing the recessed central annular zone 16 the contact surface between the engaging flanges 5, 6 is reduced whereby the evenness and thus the tightness between the opposing contacting surfaces 17, 18 can be better guaranteed. This has a positive influence on the prevention of water penetration between the flanges without the use of a separate sealing gasket or the like between the flanges.

[0034] The total flange width Wt may be about 185 mm. The width W_cz of the recessed annular zone 16 may be about 130mm. The width W_eso, W_esi, of the engagement surfaces 17, 18 may be 25-30mm.

Claims

1. Power pylon comprising at least two tubular segments which are interconnected by an annular flange connection,
the annular flange connection comprising two opposing annular flanges (5, 6) which are attached to the respective ends of the tubular segments, said annular flanges extending radially inwards and each having an end face (15) that faces the end face (15) of the opposing flange (5, 6),
the annular flanges (5, 6) each having through bores (9) distributed in a circle, wherein the through bores (9) of the two opposing flanges (5, 6) are aligned,
wherein the annular flange connection furthermore comprises bolts (10) that pass through said aligned through bores (9), and nuts (11) cooperating with said bolts (10) so as to bolt the opposing flanges (5, 6) together,
characterised in that the end face (15) of at least one of the opposing annular flanges (5, 6) has a central annular recessed zone (16) that is machined in said end face (15), said central annular recessed zone (16) being flanked by a radially outward engagement surface (17) and a radially inward engagement surface (18) which form the interface with the opposing flange (5, 6).

2. Power pylon according to claim 1, wherein the end face (15) of both of the opposing annular flanges (5, 6) have a central annular recessed zone (16) that is machined in the end face.

3. Power pylon according to claim 1 or 2, wherein the central annular recessed zone (16) has a width (W_cz) that is between 70% - 75%, preferably around 73% of the width (W_t) of the end face of the annular flange.

4. Power pylon according to any of the preceding claims, wherein the radially outward engagement surface (17) and the radially inward engagement surface (18) have substantially the same width.

5. Power pylon according to any of the preceding claims, wherein the flange (5, 6) has a thickness (t) and the central annular recessed zone (16) has a depth (d) with respect to the radially outward and radially inward engagement surfaces, wherein the ratio (d/t) between said depth (d) and said thickness (t) is within the range 0,02 - 0,03, preferably around 0,027.

6. Power pylon according to any of the preceding claims, wherein the flange (5, 6) has an outer diameter (D_o) and the central annular recessed zone (16) has a depth (d) with respect to the radially outward and radially inward engagement surfaces (17, 18), wherein the ratio (d/D_o)between said depth (d) and an outer diameter (D_o) of the flange (5, 6) is between 0,001 - 0,002, preferably between 0,0015 and 0,0020, more preferably around 0,0017.

7. Power pylon according to any of the preceding claims, wherein the bolts (10) have a head (10A) which is arranged against the lower annular flange (6) of the flange connection.

8. Power pylon according to any of the preceding claims, wherein the connection furthermore comprises washers (12, 13) arranged between the flange surface and the bolt heads (10A and nuts (11), wherein the washer (12) at the lower flange (6) has a radial groove (14) extending from the inner side of the washer (12) to the outer side of the washer (12).

9. Power pylon according to claim 8, wherein the radial groove (14) has a depth that corresponds to about half of the thickness of the washer (12).

10. Power pylon according to claim 8 or 9, wherein the radial groove (14), in the mounted state of the washer (12), faces the flange surface.

Drawing