WO2014038955A1

WO2014038955A1 - Seal assembly

Info

Publication number: WO2014038955A1
Application number: PCT/NO2013/050153
Authority: WO
Inventors: Lars Timberlid LUNDHEIM; Viktor GRENNBERG; Daniel Vik SKOGEN; Hongzhou HU; Ernst Folke Leif CEDERSTRÖM
Original assignee: Aker Subsea As
Priority date: 2012-09-07
Filing date: 2013-09-06
Publication date: 2014-03-13
Also published as: NO20130545A1; NO340035B1

Abstract

Seal assembly sealing an annulus between an inner tubular member (5) and an outer tubular member (7), comprising a seal (50) arranged in the annulus (19) and an activation assembly (70) arranged on an axial side of the seal (50). The activation assembly (70) is axially movable in such way that it activates the seal (50) to an activated mode when moving axially towards it and wherein the seal (50) is adapted to move to a deactivated mode when the activation assembly (70) is moving axially away from it. The inner or outer tubular member (5, 7) comprises an angled shoulder (51). The seal (50) comprises an inclined sliding face (52) in abutment with the angled shoulder (51). A spring assembly (60) is arranged between the seal (50) and the activation assembly (70).

Description

Seal assembly

The present invention relates to a seal assembly adapted to seal the annulus between two coaxially arranged tubular members. In particular the seal assembly is adapted to provide complete sealing function for a pressure drop over the seal assembly in a first direction, while yielding at a pressure drop of a certain value in a second direction, the first and second directions being opposite directions. The seal assembly according to the present invention thus functions like an annular check valve. Background

Particularly in the field of subsea wells and equipment related to subsea hydrocarbon production, a vast amount of seals are known which are adapted to seal in the annulus between tubular metal members. In such subsea wells large pressures may appear, such as from the well itself (well pressure) and ambient pressures due to large sea depths.

Patent application publication GB2434607 describes an annular seal which is adapted to take a radial inner position in which it does not seal, and a radial outer position in which it seals against the inner face of a tubular element. In the sealing position the annular seal is biased radially outwards by means of radially functioning springs that forces the seal outwards.

The invention

According to the invention there is provided a seal assembly adapted to seal an annulus between an inner tubular member and an outer tubular member. The seal assembly comprises a seal which is arranged in the annulus and an activation assembly arranged on an axial side of the seal. The activation assembly is axially movable in such way that it activates the seal to an activated mode when moving axially towards it, and that the seal moves back to a deactivated mode when the activation assembly moves axially away from it. According to the invention, the inner or outer tubular member comprises an angled shoulder. The seal comprises an inclined sliding face in abutment with the angled shoulder. Furthermore, a spring assembly is arranged between the seal and the activation assembly. In a preferred embodiment, the spring assembly is axially compressible when the seal assembly is in the activated mode. I.e. the spring assembly can still be compressed further in the axial direction when in the activated and sealing mode. This will typically take place when a pressure on the opposite side of the seal, with respect to the side of the spring assembly, is so large that the resulting force on the seal from the pressure will force the seal in the axial direction and thereby compress the spring assembly further. If this happens, a fluid path will arise past the seal.

The spring assembly, arranged between the activation assembly and the seal, transmits axial force from the activation assembly onto the seal. Thus, the spring assembly needs not become compressed in order to transmit these forces. The degree of compression will depend upon the stiffness of the spring assembly and the transmitted axial force.

As mentioned, when in the activated mode, the spring assembly can be compressible by movement of the seal towards the spring assembly to such extent that a fluid path is provided past the seal. This also will typically take place when excessive pressure exists on the side of the seal which is opposite of the spring assembly. Or more precisely when an excessive pressure drop over the seal assembly is present. The force from this pressure will move the seal against and compress the seal assembly, thereby letting the fluid flow past the seal. As the seal is moved it will slide along the angled shoulder. Tension in the seal will seek to alter the seal diameter towards the original diameter, i.e. towards the diameter of the seal when the seal is in the deactivated mode.

The spring assembly can advantageously comprise a wave spring arranged between an upper force distribution element and a lower force distribution element. Such force distribution elements can be metal rings.

The activation assembly can comprise a plurality of activation heads adapted to exert axial force onto the spring assembly. The activation heads can be distributed along the extension of the upper force distribution element. It should be noted that the term upper and lower (force distribution elements) are meant to designate that the force distribution elements are on respective sides of the wave spring. Hence, they should not be strictly interpreted to above and below, as in a vertical stack. Indeed, the seal assembly according to the invention may take a horizontal or inclined orientation.

The angled shoulder can advantageously be a part of the inner tubular member and when in the deactivated mode, the angled shoulder can extend beyond the extension of the seal in the radial direction.

In yet an embodiment the inner tubular member comprises a radially external face portion which, when the seal assembly is in the deactivated mode, extends radially beyond the radially outermost portion of the seal. In this embodiment, when in the activated mode, the radially outermost portion of the seal extends beyond the radially external face portion.

The seal can comprise a first main section and a second main section, wherein the material of the first main section is softer than the material of the second main section and wherein the first main section is arranged axially closer to the spring assembly than the second main section.

Example of embodiment

While the invention has been described in general terms above, a more detailed example of embodiment will be presented below with reference to the drawings, in which

Fig. 1 is a cross section perspective view of an internal tree cap which is

provided with a seal assembly according to the invention;

Fig. 2 is a principle view of the seal assembly according to the invention in a deactivated mode;

Fig. 3 is a principle view corresponding to Fig. 2, however in an activated mode; Fig. 4 is yet a principle view corresponding to Fig. 3, however wherein the seal is forced by a pressure to open for a fluid path past the seal; Fig. 5 is a principle drawing corresponding to Fig. 2, however wherein the seal is arranged on the inner face of an outer tubular member;

Fig. 6 is an enlarged perspective view of a portion of the seal assembly and the internal tree cap;

Fig. 7 is an enlarged perspective view corresponding to Fig. 6, however

showing the seal assembly in an activated mode, such as in Fig. 1 ;

Fig. 8 is an enlarged cross section view through the seal assembly, showing the seal assembly in a deactivated mode;

Fig. 9 is an enlarged cross section view through the seal assembly, showing the seal assembly in an activated mode; and

Fig. 10 is a principle cross section view through a segment of the seal.

Fig. 1 is a cross section perspective view of an internal tree cap (ITC) 1 which is adapted to be locked inside the spool of a subsea Xmas tree (not shown in Fig. 1 ). The ITC 1 comprises a plurality of movable components having various functions such as a locking ring for locking the ITC 1 to the Xmas tree and a metal seal adapted to seal between the ITC 1 and the inner bore of the Xmas tree spool. These functions will however not be described herein. On its outer face, the ITC 1 is provided with a seal 50 which is adapted to seal against the inner surface of the Xmas tree spool. The seal 50 exhibits sealing surfaces which are made of non-metal materials. The principle function of the seal 50 will be described in the following with reference to Fig. 2 to Fig. 5. Fig. 2 shows a principle view of a seal assembly according to the present invention. The seal 50 is part of a seal assembly, and is arranged in the annulus 19 between an inner tubular member 5 (such as the ITC 1 shown in Fig. 1 ) and an outer tubular member 7 (such as the Xmas tree discussed above). Fig. 2 shows the seal assembly in a deactivated state, wherein fluid may flow past the seal 50 in the axial direction. Axially above the seal 50 is an activation assembly 70. The activation assembly 70 is adapted to move axially in both axial directions, thereby exerting an axial force onto the seal and relieving such force. Between the activation assembly 70 and the seal 50 there is arranged a spring assembly 60. When the activation assembly 70 is moved axially towards the seal 50, the spring assembly 60 transmits force onto the seal 50. The spring assembly 60 exhibits sufficient stiffness so that the seal 50 is moved along an angled shoulder 51 on the inner tubular member 5. During this activation of the seal 50 the spring assembly 60 may become compressed to some extent, however not fully compressed. The seal 50 exhibits a sliding face 52 that abuts the tapered shape of the angled shoulder 52. Fig. 3 shows the seal assembly in an activated mode. In this mode, the spring assembly 60 has forced the seal 50 into sealing engagement with the inner surface of the outer tubular element 7 and with the outer surface of the inner tubular element 5. As can be appreciated by comparison with the sketch in Fig. 2, the seal has moved both axially and radially, as indicated with the bowed arrow drawn on the seal 50. Since the seal 50 has the shape of a ring, its diameter and circumference has been changed. The seal 50 shown in this example is adapted to slide on an angled shoulder 51 and the circumference of the seal 50 will increase when it is moved into the activated mode (Fig. 3). In other

embodiments, the seal 50 could be made to attain a smaller circumference when being forced into the activated mode (cf. Fig. 5).

Still referring to Fig. 3, since the circumference of the ring-shaped seal 50 has been increased, a tensile stress exists in the seal 50. As a result, if the force from the spring assembly 60 is removed, the seal 50 will move back along the angled shoulder 51 by itself, towards the deactivated mode.

Fig. 4 shows the same parts as Fig. 2 and Fig. 3 in a principle view. In this situation, the activation assembly 70 is in the same position as in Fig. 3, thus in an activated mode position. Fig. 4 illustrates how a pressure on the side of the seal 50 which is opposite with respect to the spring assembly 60 forces the seal 50 back towards the spring assembly 60. In other words, the pressure moves the seal 50 along the angled shoulder 51 and thereby provides a fluid path past the seal 50. The spring assembly 60 thus exhibits sufficient stiffness to activate the seal 50 into the activated mode, however also sufficient compliance to let pressure above a threshold value move the seal 50 so as to provide said fluid path.

As will be appreciated by the person skilled in the art, a fluid pressure on the same side of the seal 50 as the spring assembly 60 will increase the sealing contact between the seal 50 and the surfaces of the inner and outer tubular elements 7, 5.

Fig. 5 illustrates an embodiment corresponding to the one shown in Fig. 2 to Fig. 4, however wherein the seal is arranged on an outer tubular member, abutting an angled shoulder which is part of the outer tubular member. In this embodiment the circumference of the seal will become reduced when being moved along the angled shoulder towards an activated mode. Fig. 6 illustrates a realistic embodiment of the present invention in a cross section perspective view, showing a portion of the view of the ITC shown in Fig. 1 , however in a deactivated mode. In this embodiment, the spring assembly 60 comprises a wave spring 62 interposed between an upper force distribution ring 61 and a lower force distribution ring 63. The wave spring 62 is an elongated metal member that encircles the inner tubular member 5 twice. Differing from the upper force distribution ring 61 and the lower force distribution ring 63 which each extend along one plane, the wave spring 62 exhibits a plurality of wave shapes. When compressed, the wave shapes of the wave spring 62 become bent towards a straighter shape. The function of a wave spring is known to the person skilled in the art and needs not be discussed in more detail herein. The number of turns of the wave spring can also be one or more than two.

In order to exert force onto the seal 50 via the spring assembly 60, the activation assembly 70 is arranged on the opposite side of the spring assembly 60 with respect to the seal 50. In this embodiment the activation assembly 70 comprises a plurality of activation heads, here in the form of bolt heads 71 , which are attached to an axially movable activation sleeve 73. The bolt heads 71 are distributed about the perimeter of the inner tubular element 5 (ITC 1 ) and are adapted to abut against the upper force distribution ring 61 when the activation sleeve 73 is moved towards the activated mode (i.e. downwards in Fig. 6).

Fig. 7 is a view corresponding to the view in Fig. 6, however with the seal assembly in the activated mode (the outer tubular element is not shown in Fig. 6 and Fig. 7 for illustrational purpose). As can be appreciated from Fig. 7, the bolt heads 71 of the activation assembly have forced the upper distribution ring 61 an axial distance towards the seal 50. As a result the spring assembly 60, or more precisely its wave spring 62, has become compressed and the seal 50 has moved partially axially and partially radially along the angled shoulder 51 . It should be noted that the spring assembly 60 has not been fully compressed, i.e. it may still be compressed further. This makes it possible for an excessive pressure to move the seal 50 back along the angled shoulder 51 thereby compressing the seal assembly 60 further and providing a fluid path past the seal 50.

Fig. 8 and Fig. 9 are enlarged cross section views through the sealing assembly in the deactivated mode and the activated mode, respectively, hence

corresponding to the situations shown in Fig. 6 and Fig. 7. The shown

components of the seal assembly according to the invention are discussed above with reference to the preceding figures.

Still referring to Fig. 8 and Fig. 9. The inner tubular member 5, on the outer surface of which the seal 50 is arranged, has a radially external face portion 59. When the seal 50 is in the deactivated mode, as depicted in Fig. 8, the radially outermost portion of the seal 50 is positioned radially within the radial position of the radially external face portion 59. Furthermore, when the seal 50 is in the activated mode the radially outermost portion of the seal 50 is positioned radially beyond the radial position of the radially external face portion 59. Advantageously the radially external face portion 59 can be located adjacent to the radially outermost portion of the angled shoulder 51 .

Fig. 10 is a principle cross section perspective view through a segment of the seal 50. In this embodiment the ring shaped seal 50 comprises two main sections which are of different materials. The cross section has a generally wedge-shaped form. A first main section 55, which is the section closest to the spring assembly 60, comprises a soft material adapted to provide sealing engagement with the facing surfaces of the inner tubular element 5 and the outer tubular element 7. A second main section 57 is attached to the first main section 55 and is arranged axially on the other side of the first main section 55 with respect to the spring assembly 60. The second main section 57 comprises a hard material which provides a certain stiffness in the ring-shaped seal 50. That is, the material in the second main section 57 is sufficiently stiff so that when it is elastically deformed, by movement along the angled shoulder 51 , it will ensure that the seal 50 moves back to the deactivated mode upon retraction of the activation assembly 70.

Moreover, the material in the second main section 57 prevents extrusion of the seal 50 to occur when it is forced into the cleavage between the inner and outer tubular members 5, 7.

With the terms "soft material" and "hard material" is meant herein that the material in the first main section 55 is softer than the material in the second main section 57. An appropriate example of a material in the first main section is rubber. An example of an appropriate rubber is a hydrogenated version of nitrile rubber (HNBR). An example of an appropriate material in the second main section is a thermoplastic, such PEEK plastic (polyether ether ketone). The soft rubber would then provide the sealing engagement with the abutting surfaces, while the PEEK plastic would prevent the seal 50 from being extruded and provide for the seal 50 to move back towards its shape in the deactivated mode (cf. Fig. 6 and Fig. 8).

As a hard material in the second main section 57, one could also use metal, for instance as a metal split ring.

When using a rubber material in the first main section 55, tests have shown that when deactivating the seal assembly, a rubber ring which is not attached to the second main section 57 will need some time before contracting to a reduced circumference. Hence, when using rubber or similar materials having such property, the first main section 55 should preferably be attached to the second main section 57. However, if a soft material used in the first main section 55 is of a type that will contract by it self, one could also employ a seal 50 comprising a first main section 55 which is not attached to the second main section 57. In such a case, the second main section 57 would push the first main section 55 in the axial direction, however the first main section 55 would contract its circumference by itself.

Claims

1 . Seal assembly adapted to seal an annulus between an inner tubular member (5) and an outer tubular member (7), comprising a seal (50) arranged in the annulus (19) and an activation assembly (70) arranged on an axial side of the seal (50), the activation assembly (70) being axially movable in such way that it activates the seal (50) to an activated mode when moving axially towards it and wherein the seal (50) is adapted to move to a deactivated mode when the activation assembly (70) is moving axially away from it, characterized in that

- the inner or outer tubular member (5, 7) comprises an angled shoulder (51 );

- the seal (50) comprises an inclined sliding face (52) in abutment with the angled shoulder (51 ); and that

- a spring assembly (60) is arranged between the seal (50) and the activation assembly (70).

2. Seal assembly according to claim 1 , characterized in that the spring assembly (60) is axially compressible when the seal assembly is in the activated mode.

3. Seal assembly according to claim 2, characterized in that in the activated mode, the spring assembly (60) is compressible by movement of the seal (50) towards the spring assembly (60) to such extent that a fluid path is provided past the seal (50).

4. Seal assembly according to one of the preceding claims, characterized in that the spring assembly (60) comprises a wave spring (62) arranged between an upper force distribution element (61 ) and a lower force distribution element (63).

5. Seal assembly according to one of the preceding claims, characterized in that the activation assembly (70) comprises a plurality of activation heads (71 ) adapted to exert axial force onto the spring assembly (60).

6. Seal assembly according to one of the preceding claims, characterized in that the angled shoulder (51 ) is a part of the inner tubular member (5) and that when in the deactivated mode, the angled shoulder (51 ) extends beyond the extension of the seal (50) in the radial direction.

7. Seal assembly according to one of the preceding claims, characterized in that the inner tubular member (5) comprises a radially external face portion (59) which, when the seal assembly is in the deactivated mode, extends radially beyond the radially outermost portion of the seal (50), wherein when in the activated mode the radially outermost portion of the seal (50) extends beyond the radially external face portion (59).

8. Seal assembly according to one of the preceding claims, characterized in that the seal (50) comprises a first main section (55) and a second main section (57), wherein the material of the first main section (55) is softer than the material of the second main section (57) and wherein the first main section (55) is arranged axially closer to the spring assembly (60) than the second main section (57).