Field of the invention The present invention concerns a bolted flange coupling and a method for making up the flange coupling.

Background In the processing industry, bolted flange couplings are a common method of coupling two sections of pipes, blinding of a pipe or for coupling a pipe to a rigid interface, such as a manifold block or other equipment to which a pipe is to be connected. An example of a bolted flange coupling is disclosed in for instance US 6561521 B2.

The present application provides a flanged bolt coupling, wherein at least some of the disadvantages of the prior art couplings are removed or minimized. Summary of the invention

The bolted flange coupling of the present invention is defined by the appended claims and in the following: In a first embodiment, the present invention provides a bolted flange coupling comprising a first coupling half, a second coupling half and a cylindrical metal seal, wherein the metal seal has an outer surface comprising a first inclined annular sealing section, a second inclined annular sealing section, a first annular recess, a second annular recess and an inner annular surface; the first coupling half comprises a first connecting element, a bore comprising a first recess half comprising an annular seal surface for sealing against the first annular sealing section;

- the second coupling half comprises a second connecting element, a bore comprising a second recess half comprising an annular seal surface for sealing against the second annular sealing section; the first and the second connecting element comprises a cooperating first connection surface and second connection surface, respectively, for connecting the coupling halves by use of connecting bolts, and at least one of the connecting elements comprises a flange having through-holes for the connecting bolts; and - the first and the second recess halves form a common annular recess when the coupling halves are connected; and wherein the common annular recess is arranged to accommodate the metal seal, such that the inclined annular sealing sections of the metal seal are sealing against the respective annular seal surfaces of the common annular recess when the coupling halves are connected, and the inner annular surface of the metal seal has a minimum diameter being equal to or larger than a minimum diameter of the bores, such that the inner annular surface and the bores form parts of a conduit having a minimum diameter equal to the minimum diameter of the bores; wherein the first annular recess is arranged between the first and the second annular sealing sections to accommodate a retainer ring arranged between the outer surface of the metal seal and a surface of the first recess half, and the first recess half comprises a holding element arranged to interact with the retainer ring, such that the metal seal is retained when introduced into the first recess half; and the second annular recess is arranged between the first and the second sealing sections to accommodate a seal ring arranged to seal between the outer surface of the metal seal and a surface of the first recess half and the second recess half.

The first coupling half being a flanged pipe end, wherein the flanged part comprises through going holes for the bolts connecting the coupling halves, and the second coupling half may be a flanged pipe end, a blind end, or a block element, which all comprises cooperating means for the bolts.

The cylindrical metal seal being formed with the inner annular surface having an inner diameter, and the inner annular surface of the metal seal has a minimum diameter being equal to or larger than a minimum diameter of the bores, such that the inner annular surface and the bores form parts of a conduit having a minimum diameter equal to the diameter of the bores. The metal seal and the bores of the coupling halves in a connected stated having a common center axis.

The annular seal surfaces of the first and second coupling halves, and the corresponding first and second annular sealing section of the metal seal, are inclined such that they are forced/pushed into sealing contact when the coupling halves are connected. The annular seal surfaces and sealing sections are formed such that the metal seal is wedged between the two coupling halves when these are connected. The bores of the coupling halves and the metal seal form together a continuous bore with no protruding elements from the metal seal.

When stated that both coupling halves are formed with bores, this should be understood to include an embodiment, wherein one of the coupling halves is in the form of an end cap/blinding element. This coupling half will then be formed with a bore having a depth from the connecting surface that is shallow. The depth would in one embodiment be the depth of the recess half of the coupling half. When the two coupling halves are connected, or prior to connection, the retainer ring is arranged between the outer surface of the metal seal and a surface of the first recess half. The retainer ring is preferably made in an elastic material, such as a suitable elastomer, or formed by an elastic metal element, but any suitable material may be used.

In an embodiment, the holding element, is an annular rib. Alternatively, the holding element is annularly arranged knobs or similar elements providing the same holding function as the annular rib without forming a continuous element, but rather multiple separate elements. The annular rib or other holding elements may be attached to the first recess half, for instance by threads or screws. Thereby, the holding element may be replaced if damaged.

The annular rib (or inner circumference of the holding element) has an inner diameter smaller than the outer diameter of the retainer ring. The surface of the first recess half against which the retainer ring abuts is arranged between the annular rib and the annular seal surface.

In one embodiment of the bolted flange coupling, the outer surface of the metal seal comprises a second annular recess, arranged between the first and the second sealing sections, for accommodating a secondary seal ring, the secondary seal ring is arranged to seal between the outer surface of the metal seal and a surface of the first recess half and the second recess half, preferably the second annular recess is arranged between the second annular sealing section and the first annular recess. The secondary seal ring is preferably made in an elastomeric material, but may also be made in a suitable soft metal. In addition to allow for back pressure test of the flanged coupling, the secondary seal ring also functions as a secondary seal

(environmental seal).

In one embodiment of the bolted flange coupling, an annular guiding rib is arranged at the first connection surface and an annular guiding recess for accommodating the annular guiding rib is arranged at the second connection surface. The height of the guiding rib, extending from the first connection surface, is such that the metal seal is shielded during connection of the coupling. Preferably, the height of the guiding rib, i.e. the length the guiding rib extend from the first connection surface, is substantially equal to the length which the metal seal extends from the first connection surface when arranged in the first recess half. The length of the guiding rid is preferably equal to half the length of the cylindrical metal seal, or longer.

In one embodiment of the bolted flange coupling, the annular guiding rib has a height being at least equal to the length that the metal seal extends from the first connection surface.

In one embodiment of the bolted flange coupling, the part of the metal seal to be accommodated in the second recess half extends a distance from the first connection surface in the longitudinal direction of the coupling, and the height of the annular guiding rib is at least equal to the distance or longer.

In one embodiment of the bolted flange coupling, the connection surface, of the at least one connecting element being a flange, comprises an inner annular section which is flat and an outer annular section which is convex, such that an annular gap is formed between the first and the second connection surfaces before the connecting bolts are tightened, the width of the gap increasing in the radial direction from the centerline of the coupling. In other words, the connection surface of at least one of the connecting elements comprises a convex annular surface. When the coupling halves are connected and the bolt connection is tightened, the gap between the coupling halves is reduced. When the bolt connection is fully tightened, the gap is closed and the connecting surfaces are in full contact.

In one embodiment, the inner annular section extends from an end of the first or second recess half to the guiding rib or guiding recess. In one embodiment of the bolted flange coupling, the annular gap has a wedge- shaped cross-section, the cross-section in a plane containing the centerline of the flanged coupling, having a wedge angle within the range of 0.2-1.2°. The annular gap is present when the coupling is assembled but not made up, i.e. the bolts are not tightened. The annular gap widening in a direction away from the centerline of the coupling. The annular gap is formed between the connection surfaces before the coupling is made up by tightening the connecting bolts.

In one embodiment of the bolted flange coupling, the convex annular surface is at an angle with respect to a plane being perpendicular to the centerline of the coupling, the angle being in the range of 0.1-0.6°. In one embodiment of the bolted flange coupling, at least one of the width of the annular gap, the wedge angle and the angle of the convex connection surface is dimensioned such that the first and the second connection surface is in full contact when the coupling is fully made up, i.e. the connecting bolts are fully tightened.

In one embodiment of the bolted flange coupling, the first or the second connecting element is part of a rigid interface, such as a manifold block or hub, providing a connection surface. In one embodiment of the bolted flange coupling, the first and the second connecting element is a flange comprising through-holes for the connecting bolts.

The first and second connecting element may optionally be an extension, or part, of a pipe weld neck, a manifold, a hub on any suitable equipment etc.

The first and the second coupling halves may be parts of any type of fluid transport structure wherein a metal seal is desired, provided that at least one of the coupling halves comprises a flange as the connecting element. The bores of the first and the second coupling halves are usually through-bores forming a continuous fluid path/conduit when connected. However, in some instances one of the bores may be a blind bore providing a closed off coupling.

The coupling halves are described as having or comprising a bore. In some embodiments, each of the coupling halves may comprise several bores, forming several paths/conduits when the coupling halves are connected. In such instances, each bore that needs sealing is provided with a metal seal comprising any of the technical features described above. For instance, one bore may have all the technical features while another may have only some of the technical features.

The shape of the flange, i.e. the circumference or cross-section perpendicular to the centerline of the coupling half, may be of any suitable design, such as circular or oval, as well as any suitable polygon, such as a square or hexagon. The term "convex" and "convex surface" is in the present application intended to encompass both a curved and a straight angled surface. An example of a surface encompassed by the term "convex surface" is the lateral surface of a conical frustum. Short description of the drawings

The present invention is described in detail by reference to the following drawings: Figs, la-l c are cross-sectional views of a bolted flange coupling according to the invention. Figs. 2a-2c are cross-sectional views of a first coupling half of the bolted flange coupling in figs, la-lc.

Figs. 3a-3d are cross-sectional views of a second coupling half of the bolted flange coupling in figs, l a-l c.

Fig. 4 show an exploded view of the coupling in figs, l a-lc.

Fig. 5 show the first coupling half in figs. 2a-2c, wherein the angle of the connection surface is illustrated.

Fig. 6 is a cross-sectional view of an embodiment of the bolted flange coupling according to the invention, wherein each coupling half is flanged and comprises a pipe weld neck. Fig. 7 is a cross-sectional view of a bolted flange coupling according to the invention, wherein one of the coupling halves is blind.

Fig. 8 is a cross-sectional view of a coupling half according to the invention featuring multiple bores.

Detailed description of the drawings

An embodiment of a bolted flange coupling according to the invention is shown in figs, l a-lc. The bolted flange coupling comprises a first coupling half 1 (or coupling member), a second coupling half 2 (or second coupling member) and a cylindrical metal seal assembly (i.e. a metal seal 3) arranged to seal between the two coupling halves. The metal seal 3 has an outer surface comprising a first annular sealing section 4 and a second annular sealing section 5, and an inner annular surface 29.

The first coupling half 1 comprises a first connecting element 6 (i.e. the flange 17), a bore 7, a first recess half 8 (or recess section) and a pipe weld neck 30, see figs. 2a-2c (shown as a mirror image of the first coupling half in figs. la-c). The first recess half features an annular seal surface 9 for sealing against the first annular sealing section 4 of the metal seal. The second coupling half 2, see figs. 3a-3d comprises a second connecting element 10, a bore 11 and a second recess half 12 (or recess section) comprising an annular seal surface 13 for sealing against the second annular sealing section 5. In this embodiment, the second coupling half 2 is a manifold block, but may in other embodiments comprise a pipe weld neck similar to the first coupling half 1 , a blind, or be a part of any type of hub to which a bolted flange coupling is desired. The first and second annular sealing section and the respective annular seal surfaces of the first and second recess halves provides the main metal/metal sealing of the coupling.

The first and the second connecting element 6,10 comprises a cooperating first connection surface 14 and second connection surface 15, respectively, for connecting the coupling halves 1 ,2 by use of threaded connecting bolts 16/nuts 28. The first connecting element 6 (i.e. flange 17) features through-holes 26 for the connecting bolts, while the second connecting element may optionally comprise threaded through-holes 31 or threaded blind holes.

When the first and the second coupling halves are connected, the first and the second recess halves 8, 12 form an annular recess 18. The annular recess 18 is arranged to accommodate the metal seal 3. The inner annular surface of the metal seal has a minimum diameter being equal to or larger than the diameter of the bores 7, 1 1 such that the inner annular surface and the bores form parts of a conduit 19 having a minimum diameter equal to the diameter of the bores. Preferably, the minimum diameter is slightly larger than the diameter of the bores to minimize wear of the metal seal.

The annular seal surfaces 9, 13 of the first and second coupling halves, and the corresponding first and second annular sealing section 4,5 of the metal seal, are inclined such that they are forced into sealing contact when the coupling halves are connected. The sealing contact provides the primary metal-metal seal of the coupling.

Further, the outer surface of the metal seal comprises a first annular recess 20, arranged between the first and the second annular sealing sections 4,5, for accommodating an elastic ring 21 (i.e. retainer ring), the elastic ring is arranged between the outer surface of the metal seal and a surface of the first recess half 8. The first recess half 8 features an annular rib 22 arranged to interact with the elastic ring 21 such that the metal seal 3 is retained in the first recess half 8 after being introduced therein. The annular rib 22 has an inner diameter smaller than the outer diameter of the elastic ring 21.

In addition to the first annular recess, the outer surface of the metal seal 3 comprises a second annular recess 27 arranged between the first and the second sealing sections. The second annular recess is for accommodating an elastomeric seal ring 23 (i.e. a secondary seal ring) arranged to seal between the outer surface of the metal seal and a surface of the first recess half 8 and the second recess half 12. The second annular recess 27 is arranged between the second annular sealing section and the first annular recess. The elastomeric seal ring 23 allows for backpressure testing of the metal seal. To provide the made-up coupling with increased resistance to shear forces and guidance of the coupling halves during connection, the first coupling half features an annular guiding rib 24 at the first connection surface 14 and a cooperating annular guiding recess 25 at the second connection surface 15. The annular guiding recess is arranged to accommodate the annular guiding rib. During connection of the bolted flange coupling the metal seal 3 is initially introduced into the first recess half 8 of the first coupling half 1 and retained or kept in place by the interaction between the annular rib 22 and the elastic ring 22 (retainer ring). To protect the section of the metal seal to be accommodated within the second recess half 8, the guiding rib has a height HI (i.e. the distance the guiding rib extend from the first connection surface, see fig. 2c) which is equal to, or larger than, the height H2 of said section (i.e. the distance the seal extends from the first connection surface, see fig. lc).

An exploded view of the bolted flange coupling described above is shown in fig. 4 for illustrative purposes.

An expanded view of the first coupling half 1 is shown in fig. 5 to better illustrate an important feature of the bolted flange coupling. To obtain a

preloading/pretensioning of the metal seal against the corresponding annular seal surfaces 9, 13 of the first and second recess halves 8,12, the first connection surface 14, that is the connection surface of the flange 17, has an outer annular section 34 having a slightly convex shape. The convex shape ensures that a gap is formed between the first connection surface and the second connection surface before the bolts/nuts are tightened and the coupling made up. The gap becomes increasingly larger, i.e. is widening, in the radial direction away from the centerline C. The size or width of the gap is such that it is fully closed, and the connection surfaces 14,15 are in contact, when the bolts/nuts are tightened and the coupling made up. The first connection surface 14 also comprises an inner annular section 33 being flat, i.e. the surface of the inner annular section is in a plane P being perpendicular to the centerline C. In the embodiment of fig. 5, the inner annular section is interrupted by the annular guiding rib 24. However, in other embodiments the inner annular section 33 may for instance extend from the end 35 of the recess half 8 to the guiding rib 24, while the convex outer annular section extends from the guiding rib and radially outwards. The main requirement is that the first connection surface has a flat annular section extending a given distance from a metal seal accommodated in the first recess half. The feature of having a flat inner annular section 33 provides several advantages compared to a coupling wherein the whole first connection surface is convex. First of all, the flat annular section improves the load carrying capability of the coupling, since local yields are avoided. Local yields are a potential problem when the initial contact area (i.e. the contact area between the first and second connection surface before the bolts/nuts are tightened and the coupling made up) between the coupling halves is small, as would be the case if the whole connection surface was convex. Further, the flat annular section 33 may also serve as a reference plane when machining the coupling half.

As illustrated in fig. 5, the outer annular section 34 has a radial angle a relative to the plane P being perpendicular to the centerline C of the first coupling half (or the of made up coupling). The optimum angle a will depend on the flange dimensions, such as thickness, and/or the expected maximum bending moment exerted on the coupling during use. The angle a is commonly in the range of 0.1-0.6°. As mentioned above, the effect of this feature is that a pretension/preloading of the metal seal 3 is obtained. The pretension/preloading provides for a lighter and/or stronger coupling since a separation of the main metal/metal sealing, i.e. the sealing provided by the cylindrical metal seal 3, is prevented over a larger range of bending moment. In other words, a coupling having the described pretension will tolerate a higher bending moment compared to a coupling having the same dimensions, but without pretension.

A further embodiment of the bolted flange coupling is shown in fig. 6. In this embodiment, both the first coupling half 1 and the second coupling half 2 have a flange 17, 17' as the connecting element. The remaining technical features correspond to the features described for the embodiment of figs. 1-5.

In some cases, the bolted flange coupling is blinded, i.e. the coupling is closed off. An example of a blinded flange coupling is shown in fig. 7. The second coupling half 2 of the flange coupling in fig. 7 is identical to the second coupling half shown in figs. 1 and 3. However, as opposed to the coupling in fig. 1 , the first coupling half 1 of the coupling in fig. 7 features a blinded bore 32, such that fluid entering the bore 1 1 of the second coupling half is prevented from exiting through the bore of the first coupling half 1.

Each of the coupling halves 1 ,2 may comprise multiple cooperating bores 7, 1 1 to provide a flanged coupling having multiple separate fluid conduits. A first coupling half 1 for such a coupling is shown in fig. 8. The first coupling half features multiple bores 7 and corresponding first recess halves 8. By use of multiple cylindrical metal seals 3 (not shown), one metal seal for each bore 7, the first coupling half may be connected to a second coupling half (not shown) featuring multiple cooperating bores 1 1. A bolted flange coupling made up of coupling halves having multiple cooperating bores features multiple separate fluid conduits.

Other embodiments of the bolted flange coupling may be used to couple pipelines to various equipment, such as compact manifolds, production flowlines, metering equipment, valves, pumps, XT's and similar. In addition, one of the coupling halves may be a blind to close off a coupling site. In the latter instance, one of the coupling halves will not comprise a bore. In all embodiments, one of the coupling halves will always have a flange as the connecting element.