Rotating stack for transferring fluids across a rotating interface and method for making such a rotating stack

Abstract

A rotating stack, for conveying fluid through a rotating interface around a rotation axis between an incoming flow line and an outgoing flow line, comprises: a group of lower annular elements, upper annular elements and a central annular element; the lower annular element, the upper annular element and the central annular element are each centered on the axis; the central annular element is located between the lower annular element and the upper annular element; an outer annular element is located between the lower annular element and the upper annular element with the axis as the center; an annular chamber is located between the central annular element and the outer annular element; the downward facing surface and the upward facing surface of the outer annular element are adjacent to the upward facing surface of the lower annular element and the downward facing surface of the upper annular element; the upward facing surface of the lower annular element and the downward facing surface of the upper annular element have a first stepped surface, and the upward facing surface and the downward facing surface of the outer annular element have a second stepped surface, so as to provide at least two annular cavities centered on the rotation axis.

Description

Technical Field

[0001] The present invention relates to a rotating stack for conveying a fluid through a rotating interface about an axis of rotation between an incoming flow line and an outgoing flow line.

[0002] Furthermore, the invention relates to a turret mooring system comprising such a rotating stack. Furthermore, the invention relates to a floating offshore structure provided with such a rotating stack and a method for manufacturing such a rotating stack. Background Art

[0003] Annular fluid swivels are known in the art for conveying high pressure fluids through a rotating interface between an incoming fluid line and an outgoing product pipeline. Applications of such swivels include, for example, offshore oil and gas exploration, where high pressure oil and / or gas streams are transferred from a (deep sea) offshore well to a floating vessel, such as a floating production storage and offloading (FPSO) vessel. Typically, such floating vessels are equipped with a turret mooring system that is capable of coupling a mooring buoy or "mooring structure" and holding one or more riser lines from the well to a product pipeline on board the vessel. Since a turret mooring system should allow some rotation between the vessel and the buoy, the swivel is also suitable for providing rotation between the incoming flow line and the product pipeline.

[0004] In the design of rotating devices, the rotating interface is provided with seals to prevent leakage. In the rotating interface, the seals are subjected to the high pressure difference between the high pressure fluid flowing through the rotating device and the surrounding environment.

[0005] In addition, the seals are subject to mechanical wear due to the rotation of the interface. Thus, in the prior art, rotating devices (rotating stacks) face several problems that affect their performance and reliability; the main problem being that the dynamic seals cannot be replaced on site due to the relatively large size of the rotating parts.

[0006] Another major problem is that it is difficult to meet seal design criteria, especially as seal diameter, temperature range or fluid pressure increases.It is an object of the present invention to overcome or alleviate the deficiencies of the prior art. Summary of the invention

[0007] This object is achieved by a rotating stack according to the attached claim 1. The structure of the rotating stack allows a relatively simple way of assembly or disassembly, which also enhances the process of replacing any seal in the rotating stack.

[0008] Furthermore, the present invention relates to a turret mooring system equipped with a rotating stack as defined above, a floating offshore structure equipped with a rotating stack as defined above, and a method for manufacturing a rotating stack as defined above. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The present invention will be explained in more detail below with reference to the accompanying drawings, in which exemplary embodiments of the present invention are shown. The drawings are for illustrative purposes only and are not intended to limit the concept of the present invention. The scope of the present invention is defined by the appended claims.

[0010] Figure 1 shows a perspective view of a rotating stack according to an embodiment of the present invention;

[0011] Figure 2 shows a detailed cross-sectional view of a rotating interface of a rotating stack according to an embodiment of the present invention;

[0012] Figure 3 shows a detailed cross-sectional view of a rotating interface of a rotating stack according to an embodiment of the present invention;

[0013] Figure 4A and Figure 4B shows a detailed cross-sectional view of a piercing tube for use in a rotating stack according to an embodiment of the present invention;

[0014] Figure 5 shows a perspective view of a rotating stack according to an embodiment of the present invention;

[0015] Figure 6 a perspective view showing a portion of a manifold block according to an embodiment of the present invention; and

[0016] Figure 7 A floating offshore structure equipped with a rotating stack according to an embodiment of the invention is schematically shown.

[0017] In the following description of the embodiments, items denoted by the same reference numerals refer to the same or similar items. DETAILED DESCRIPTION

[0018] Figure 1 A perspective cutaway view of a rotating stack according to an embodiment of the present invention is shown.

[0019] The rotating interface 72 of the rotating stack 10 according to the present invention is composed of a plurality of annular elements including a set of inner and outer annular elements, each centered on a common axis of rotation A.

[0020] In this rotational interface, the outer ring element is configured to rotate about an axis of rotation A relative to the inner ring element group.

[0021] The rotation interface comprises a set of inner ring elements 12, 14, 16 and an outer ring element 18. The set of inner ring elements comprises a lower ring element 12, a central ring element 14 and an upper ring element 16.

[0022] Each of the inner annular elements 12, 14, 16 has a cylindrical inner surface at an inner radius RI1. Each of the lower annular element 12 and the upper annular element 16 has a cylindrical outer surface at a first outer radius RO1. The central annular element 14 has a cylindrical outer surface at a second outer radius RO2. The second outer radius RO2 is smaller than the first outer radius RO1.

[0023] When the inner ring element, the central ring element and the outer ring element are stacked on each other, with the central ring element 14 located between the lower ring element 12 and the upper ring element 16, there is a circular groove between the relative surfaces 12a, 16a of the lower ring element and the upper ring element, which surfaces are basically perpendicular to the rotation axis A.

[0024] The outer ring element 18 has a cylindrical inner surface at a second inner radius RI2 and a cylindrical outer surface at a third outer radius RO3 and is also centered on the rotation axis A. The second inner radius RI2 of the outer ring element 18 is slightly larger than the second outer radius RO2 of the central inner ring element 14, so that there is a radial gap G of about 1 mm between the central inner ring element and the outer ring element (see Figure 2 and Figure 3 ). The outer ring element 18 is arranged in a circular groove between the lower inner ring element 12 and the upper inner ring element 16, so that the cylindrical inner surface 22 of the outer ring element abuts the outer cylindrical surface 20 of the central inner ring element. A recess 24 is provided along the circumference of the cylindrical inner surface of the outer ring element, so that an annular chamber 24a is formed between the cylindrical outer surface 20 of the central inner ring element and the cylindrical inner surface 22 of the outer ring element 18.

[0025] In the outer annular member 18, a conduit 26 is provided in the radial direction between the recess 24 and the outer circumference to provide an outlet (or inlet) of the annular chamber 24a.

[0026] The upward surface 12a of the lower ring element 12 and the downward surface 16a of the upper ring element 16 are provided with a first stepped surface, wherein the upward surface 12a and the downward surface 16a each extend outwardly beyond the cylindrical outer surface 20 of the central ring element 14 at a second outer radius RO2. The outer ring element 18 includes an upward surface 18a and a downward surface 18b with a second stepped surface, the second stepped surface being complementary to the first stepped surface.

[0027] Between the downwardly facing surface 16a of the upper annular element 16 and the upwardly facing surface 18b of the outer annular element 18, and between the upwardly facing surface 12a of the lower annular element 12 and the downwardly facing surface 18a of the outer annular element 18, annular cavities 28, 30, 32, 34 are formed, in which face-seal type sealing rings (not shown here) are arranged. Figure 2 The arrangement of the annular chamber and the sealing ring will be described in more detail.

[0028] Reference Figure 1 , the rotating stack may include multiple rotating interfaces. To simplify stacking, the lower ring element 12 and the upper ring element 16 are designed to have the same shape of their upper surface 12a and lower surface 16a (perpendicular to the rotation axis A). In this way, the upper ring element 16 of the first rotating interface can be used as the lower ring element 12 of the second rotating interface stacked on top of the first rotating interface.

[0029] Between each pair of stacked outer ring elements is placed a coupling ring or drive ring 36. The coupling ring is configured to couple the outer ring elements in pairs for joint rotation. One of the coupling rings is equipped with a pair of lugs (not shown) designed to accommodate a pair of drive arms 38 for coupling to an external structure (not shown) on a floating structure (not shown).

[0030] The rotating stack 10 comprises a base ring element 40 on which a lower supporting ring element 42 is arranged. The lower supporting ring element 42 has an upwardly facing surface 42a having the same shape as the upwardly facing surface 12a of the lower ring element 12 as described above. The lower supporting ring element 42 has a stepped upwardly facing surface on which the outer ring element 18 can be arranged in such a way that an annular chamber exists between the ring elements 42, 18.

[0031] The base ring element 40 is provided with inlet ports 44 (and / or outlet ports) in the radial direction on its circumference, and the inlet ports 44 (and / or outlet ports) are each configured to be connected to the inflow flow line 46 or the outflow flow line, respectively. In addition, each inlet port or outlet port 44 is connected to a conduit 48 in the base ring element 40, and the conduit 48 extends upward and parallel to the rotation axis A.

[0032] Each of the inner annular elements 12 , 14 , 16 is provided with at least one through hole 50 for conveying (hydrocarbon) fluid parallel to the rotation axis A. In each inner annular element 12 , 14 , 16 , the at least one through hole 50 is located at a position corresponding to the position of the duct 48 in the base annular element 40 .

[0033] At the top of the rotating stack 10, a closed ring element 52 can optionally be arranged. The closed ring element 52 can also serve as a support or a (fluid) connector for other rotating stacks located above.

[0034] In the rotating stack 10, the inner ring elements 12, 14, 16 are connected between the base ring element 40 and the closing ring element 52 by a plurality of bolt rods 54 extending through holes arranged on the pitch diameter DP of the ring elements. Figure 2 Give a more detailed description.

[0035] Figure 2 A detailed cross-sectional view of a rotational interface of a rotational stack according to an embodiment of the present invention is shown.

[0036] The first stepped surface and the second stepped surface have a layout in which four annular cavities 28, 30, 32, 34 are centered on the rotation axis A. The first stepped surface and the second stepped surface have a rectangular cross-section and are arranged between the central outer annular element 18 and the lower inner annular element 12 and the upper inner annular element 16. Two of the annular cavities 28, 30 are arranged at the first interface A1 between the facing surfaces 16a, 18b of the upper annular element 16 and the outer annular element 18. The other two annular chambers 32, 34 are arranged at the second interface A2 between the facing surfaces 12a, 18a of the lower annular element 12 and the outer annular element 18. A face seal type sealing ring 56 is installed in each of the annular cavities 28, 30, 32, 34.

[0037] exist Figure 2 , a portion of the arrangement of the combination of the lower annular element 12, the central annular element 14, the upper annular element 16 and the outer annular element 18 is shown. In addition, a portion of the bolt rod 54 is shown, which extends through the lower annular element, the central annular element and the upper annular element.

[0038] Above and below the annular chamber 24a, annular cavities 28, 30, 32, 34 are arranged at first and second interfaces A1 and A2 between the outer and upper annular elements 18, 16 and the central and lower annular elements 14, 12, respectively.

[0039] At both the first interface A1 and the second interface A2, the hydraulic area H, i.e. the radial area H where the annular chambers and the corresponding sealing rings are located, is kept to a minimum. That is, each of the annular chambers has a radial width W, and each sealing ring has a corresponding width when placed in the associated annular chamber. In each of the first interface A1 and the second interface A2, a non-zero gap X is arranged between the two annular cavities 28, 30; 32, 34. Thus, the width of the radial area H is equal to the width W of the two annular cavities 28, 30; 32, 34 plus the gap X in the same interface A1, A2.

[0040] Furthermore, in order to keep the hydraulic area H to a minimum, in each interface one of the two annular cavities 28 ; 32 is arranged directly adjacent to the cylindrical outer end face 15 of the central annular element 14 .

[0041] The radial width B of the annular chamber 24a is equal to or less than the height C of the annular chamber 24a. In addition, the radial width B of the annular chamber is less than the width of the hydraulic area H (i.e. the width W of the two annular cavities 28, 30; 32, 34 combined plus the gap X in the same interface A1; A2). At the same time, the inner diameter of the radially inner sealing ring is substantially equal to the inner diameter of the annular chamber. When the annular chamber is under operating pressure, these measures have the following effect: the vertical force F2 on the seal in the first interface A1 and the second interface A2 is less than the vertical force F1 on the upper and lower radial walls of the annular chamber 24a.

[0042] Furthermore, in each of the upwardly and downwardly facing surfaces 18 a , 18 b of the outer ring element 18 , a bushing 58 (sliding bearing) is located outside the hydraulic region H and thus at a radius greater than that of the sealing ring 56 .

[0043] In an embodiment, the bolt rod 54 is located at a distance from the second outer radius RO2 to leave a gap of 5 mm to 10 mm between the bolt hole and the O-ring seal groove 60, wherein the O-ring seal groove 60 maintains the O-ring seal to ensure tightness between the central annular element 14 and the lower / upper inner annular element 12; 16. To achieve this, the center of each rod is toward the outer radius RO1 and away from the inner radius RI1 in the central annular element.

[0044] In this way, the clamping force acting on each of the inner annular elements 12, 14, 16 acts primarily on the O-ring seal groove 60 to limit the risk of opening and squeezing the O-ring seal out of the O-ring seal groove 60 when the associated flow lines and annular chambers in the rotating stack 10 are under high operating pressures. This technique attempts to minimize the prying effect on the bolt shank (see below).

[0045] It can be appreciated that the pressure induced end cap force acts on the hydraulic area H, from the inner diameter of the O-ring seal groove 60 to the outer diameter of the outer annular chamber groove (retaining face seal). This force tends to open both the interface between the central annular element and the lower annular element and the interface between the central annular element and the upper annular element. The pressure induced end cap force is increased by the ratio of the distance of the hydraulic area H to the inner diameter RI1 and the distance of the bolt 54 to the same inner diameter RI1 (prying effect): obviously, the greater the distance of the bolt 54 to the inner diameter RI1, the smaller the tensile load on the bolt 54. This property is critical for this type of design.

[0046] According to an embodiment, the first stepped surface and the second stepped surface have a layout in which at least two annular cavities 28, 30, 32, 34 are centered on the rotation axis A, wherein half of at least two of the annular chambers are located at a first interface between the downward facing surface of the upper annular element and the upward facing surface of the outer annular element, and the other half of at least two of the annular chambers are located at a second interface between the upward facing surface of the lower annular element and the downward facing surface of the outer annular element.

[0047] Figure 3 A detailed cross-sectional view of a rotational interface of a rotational stack according to an embodiment of the present invention is shown.

[0048] Figure 3 The rotation interface shown is similar to Figure 2 The rotation interface shown is basically the same. Figure 2 Features with the same reference numerals.

[0049] exist Figure 3 In the interface shown, further recesses 62 are provided in the outer ring element 18 on either side of the annular chamber 24a to accommodate two additional sealing rings 64, piston oriented. The additional sealing rings 64 may be referred to as isolation seals, thereby providing further isolation of the annular chamber 24a in the circumferential direction of the rotating interface.

[0050] Figure 4A and Figure 4B Shown are details of a penetration tube 66 used in a rotating stack 10 according to an embodiment of the present invention.

[0051] In the through-holes 50 extending through the inner annular elements 12, 14, 16 of the rotating stack 10, a stab tube 66 may be placed to provide a conduit extending between the base annular element 40 and the central annular element 18 which is associated with a corresponding through-hole of the radial conduit 26 connected to the central annular element.

[0052] The piercing tube 66 has a closed end cap 68 and is provided with openings 70a, 70b in its side wall at the level of the radial ducts 44 of the base annular element 40 and at the level of the radial ducts 26 in the central annular element 18, respectively.

[0053] In this way, a flow path is obtained for the fluid flowing through the puncture tube which is leak-proof.

[0054] Figure 4A A cross-sectional view of the penetration tube 66 is shown. Figure 4B A cross-sectional view of a rotating stack with a penetration tube 66 mounted in the through hole 50 of the inner ring element 12 , 14 , 16 is shown.

[0055] Figure 5 A perspective view of a rotating stack according to an embodiment of the present invention is shown.

[0056] The rotating stack 10 shown here includes a base ring element 40 , a plurality of rotating interfaces 72 , 74 , 76 , 78 , and a closing ring element 52 .

[0057] Additionally, the rotating stack 10 includes a pair of coupling arms 30 attached to one of the coupling rings 36. The coupling arms are configured to couple to a vessel (not shown) in which the rotating stack is mounted. The coupling arms provide a fixed orientation of the rotating interface relative to the vessel.

[0058] On the outer cylindrical end face of each rotational interface there may be an additional detection port 80 providing access to a leakage port in the hydraulic region H (not shown).

[0059] Figure 6 A perspective view of a manifold block according to an embodiment of the present invention is shown.

[0060] When the rotating stack 10 is arranged on a turret mooring system on a floating object such as a vessel, the ports 44 for inflow / outflow fluids on the base annular element 40 of the rotating stack can be connected to riser lines 82, which are attached to a manifold structure (grounded portion) within the turret of the turret mooring system.

[0061] According to an embodiment, the riser line 82 is provided with a pipe flange 84. The pipe flange 84 of the riser line 82 is then coupled to the associated port 44 on the base ring element 40 via a pipe segment 86 or a flange 88 of a connecting pipe. The pipe segment 86 is provided with a pipe segment flange 89 configured for connection to the pipe flange 84 of the riser line 82. Pipe segments of different lengths and with connectors of different orientations on the flanges 88, 89 can be used to form a fluid connection between the riser line 82 and the port 44 for inflow / outflow of fluid.

[0062] Figure 7 An example of a floating offshore structure equipped with a rotating stack according to an embodiment of the invention is schematically shown.

[0063] A floating production unit 1, such as an FPSO vessel, or generally an offshore vessel, is moored at an offshore location near a reservoir R in the seabed. Process equipment 2 on board the vessel is schematically shown in the figure.

[0064] Floating production unit 1 is turret moored. Figure 7 In the drawings, according to an embodiment, a floating production unit is shown as being turret moored by a turret mooring system.

[0065] The turret mooring system provides a turret mooring structure, which includes a turret structure 3 such as a mooring buoy and a support structure installed outside or inside the floating production unit 1. The turret structure 3 is anchored to the seabed with anchor lines 5. The riser line 82 (and other pipelines and other equipment 90, such as umbilical lines, gas / water injection lines, power lines, valves / gates, etc.) extends between the reservoir R below the seabed and the turret structure 3. The support structure provided on the floating production unit 1 has a container for accommodating the turret structure 3, so that the floating production unit 1 can still rotate around the turret structure 3. In this way, the floating production unit 1 can show the wind direction under the influence of wind, waves, currents and / or drifting ice, and adopt a position of least resistance relative to the environment, while the riser line maintains its unrotated position.

[0066] A rotation stack 10 according to an embodiment of the present invention is arranged in a turret mooring system to provide one or more rotational interfaces between a riser line 82 on a floating vessel and the processing facility 2 .

[0067] According to an embodiment, the inner and outer annular elements are obtained from steel forgings and machined to the desired final shape. The steel forgings may be based on carbon steel or stainless steel.

[0068] The invention has been described with reference to a few embodiments. The rotating stack shown is described here by way of example. Structures having a different number of rotating interfaces may be constructed within the scope of the invention.

[0069] Those skilled in the art will appreciate obvious modifications and alternatives after reading and understanding the foregoing detailed description, which are considered to be illustrative rather than restrictive in all respects. The present invention is intended to be interpreted to include all such modifications and variations, as long as such modifications and variations are within the scope of the appended claims. Therefore, the scope of the present invention is limited by the appended claims, rather than by the foregoing description.

[0070] Description of Reference Numerals

[0071] Floating Production Unit 1

[0072] Processing equipment 2

[0073] Turret structure 3

[0074] Anchor Rope 5

[0075] Rotating stack 10

[0076] Inner annular elements 12, 14, 16

[0077] Cylindrical outer end surface 15

[0078] Upward surface 12a

[0079] Downward surface 16a

[0080] Outer ring element 18

[0081] The downwardly facing surface 18a

[0082] Upward facing surface 18b

[0083] Outer cylindrical surface 20

[0084] Cylindrical inner surface 22

[0085] Recess 24

[0086] Annular chamber 24a

[0087] Catheter 26

[0088] Annular cavities 28, 30, 32, 34

[0089] Coupling ring or drive ring 36

[0090] A pair of drive arms 38

[0091] Base ring element 40

[0092] Lower supporting ring element 42

[0093] Port 44 for inflow / outflow of fluid

[0094] Flow line 46

[0095] Through hole 50

[0096] Closed loop element 52

[0097] Bolt 54

[0098] Face seal seal 56

[0099] Bushing 58

[0100] O-ring groove 60

[0101] Additional recess 62

[0102] Isolation seal 64

[0103] Piercing tube 66

[0104] Openings 70a, 70b

[0105] Rotation interface 72, 74, 76, 78

[0106] Probe port 80

[0107] Riser line 82

[0108] Pipe flange 84

[0109] Pipe section 86

[0110] Pipe flange 88

[0111] Equipment 90

[0112] Interface A1, A2

[0113] Rotation axis A

[0114] Pitch diameter DP

[0115] Radial clearance G

[0116] Hydraulic area H

[0117] Cavity radial width B

[0118] Cavity height C

[0119] Vertical forces F1, F2

[0120] Reservoir R

[0121] First outer radius RO1

[0122] Second outer radius RO2

[0123] The third outer radius RO3

[0124] First inner diameter RI1

[0125] Second inner diameter RI2

[0126] Radial width W

[0127] GapX

Claims

1. A rotating stack for conveying a fluid through a rotating interface about an axis of rotation between an inlet flow line and an outlet flow line, the rotating stack comprising: a set of inner annular elements, including a lower annular element, an upper annular element and a central annular element; The lower annular element is centered about the rotation axis and has an inner radius and a first outer radius; The upper annular element is centered on the rotation axis and has the inner radius and the first outer radius; the central annular element being centered on the rotation axis and having an outer cylindrical end surface located between the lower annular element and the upper annular element, the central annular element having the inner radius and a second outer radius, wherein the second outer radius is between the inner radius and the first outer radius, so that a circular groove exists between an upwardly facing surface of the lower annular element and a downwardly facing surface of the upper annular element, the upwardly facing surface and the downwardly facing surface are each perpendicular to the rotation axis; The rotating stack also includes: an outer annular element centered on the axis of rotation and having an inner end surface, the outer annular element having a second inner radius and a third outer radius, wherein the third outer radius is greater than the first outer radius and the second inner radius is slightly greater than the second outer radius, so that there is a radial gap of about 1 mm between the outer annular element and the central annular element; the downwardly facing surface and the upwardly facing surface of the outer annular element are directly adjacent to the upwardly facing surface of the lower annular element and the downwardly facing surface of the upper annular element, respectively; The inner end surface of the outer annular element is adjacent to the flat cylindrical end surface of the central annular element and is provided with a circular groove so that an annular chamber is formed between the central annular element and the outer annular element. wherein the upward-facing surface of the lower annular element and the downward-facing surface of the upper annular element have a first stepped surface, and the upward-facing surface and the downward-facing surface of the outer annular element have a second stepped surface, and the first stepped surface and the second stepped surface are configured so as to provide at least two annular cavities, the at least two annular cavities being centered on the rotation axis and having a rectangular cross-section, respectively, at least two of the annular cavities have half at a first interface between the downward-facing surface of the upper annular element and the upward-facing surface of the outer annular element, and the other half of the at least two of the annular cavities are at a second interface between the upward-facing surface of the lower annular element and the downward-facing surface of the outer annular element, and Wherein, the radial width of the annular chamber is equal to or smaller than the height of the annular chamber, and the radial width of the annular chamber is smaller than the width of the two annular cavities combined.

2. The rotating stack according to claim 1, wherein: A face-seal type sealing ring is arranged in each of the at least two annular cavities.

3. The rotating stack according to claim 1 or 2, wherein: In each interface, the halves of the at least two annular cavities are separated from one another in the radial direction by a gap.

4. The rotating stacking element according to claim 1 or 2, wherein: In the radial direction, each of the annular cavities is defined between an outward edge on an annular element selected from the set of inner annular elements and an inward edge on the outer annular element; The surfaces of the inward edge and the outward edge are parallel to the direction of the rotation axis, and In a direction parallel to the rotation axis, each of the annular cavities is defined at the first interface and the second interface, wherein the first interface is between the upward facing surface of the outer annular element and the downward facing surface of the upper annular element, and the second interface is between the downward facing surface of the outer annular element and the upward facing surface of the lower annular element.

5. The rotating stack according to claim 1 or 2, wherein: Each of the annular cavities is defined by a width WS in the radial direction and a depth HS in a direction parallel to the rotation axis.

6. The rotating stacker according to claim 1 or 2, wherein: An annular additional recess is provided above the circular groove in the inner end face of the outer annular element and an annular additional recess is provided below the circular groove in the inner end face of the outer annular element; each additional recess is equipped with a piston-oriented sealing ring.

7. The rotating stacker according to claim 1 or 2, wherein: An annular bushing is arranged in each interface, and the radially outermost annular cavity is separated from the annular bushing in the radial direction by a second gap.

8. The rotating stacker according to claim 1 or 2, wherein: Each of the lower annular element, the upper annular element and the central annular element is configured with at least one through hole extending in a direction parallel to the rotation axis, and the at least one through hole has a corresponding position in each of the lower annular element, the upper annular element and the central annular element.

9. The rotating stacker according to claim 8, wherein: The central annular element is provided with at least one radial duct extending from one of the at least one through hole to the outer cylindrical end face, the radial duct being arranged in fluid communication with the annular chamber.

10. The rotating stack according to claim 1 or 2, further comprising a base annular element having at least one through hole, the position of the at least one through hole of the base annular element corresponding to the position of the at least one through hole in each of the lower annular element, the upper annular element and the central annular element, and Also included is a radial conduit extending from the through hole to a port on the outer cylindrical end surface of the base annular element.

11. The rotating stacker according to claim 9, wherein: The outer ring element also has at least one radial conduit extending from the through hole to a port on the outer cylindrical end surface of the outer ring element.

12. The rotating stacker according to claim 10, wherein: The outer ring element also has at least one radial conduit extending from the through hole to a port on the outer cylindrical end surface of the outer ring element.

13. The rotating stacker according to claim 10, wherein: A puncture tube is arranged in the correspondingly positioned through holes of the lower annular element, the upper annular element and the central annular element, the puncture tube extending between the radial ducts of the base annular element and the radial ducts of the central annular element.

14. A turret mooring system comprising a rotating stack according to any one of the preceding claims 1 to 13 for conveying a fluid through a rotating interface about an axis of rotation between an incoming flow line and an outgoing flow line.

15. A floating offshore structure provided with a rotating stack according to any one of the preceding claims 1 to 13, or comprising a turret mooring system according to claim 14, wherein the rotating stack is used to convey fluid through a rotating interface about an axis of rotation between an incoming flow line and an outgoing flow line.

16. A method for making a rotating stack for conveying a fluid through a rotating interface about an axis of rotation between an incoming flow line and an outgoing flow line, The method comprises: A set of inner annular elements is provided, including a lower annular element, an upper annular element and a central annular element; The lower annular element is centered on the rotation axis and has an inner radius Rl1 and a first outer radius; The upper annular element is centered on the rotation axis and has the inner radius Rl1 and the first outer radius; Centering the central annular element on the rotation axis and providing the central annular element with an outer cylindrical end surface; positioning the central annular element between the lower annular element and the upper annular element, the central annular element having the inner radius and a second outer radius, wherein the second outer radius is between the inner radius and the first outer radius, such that a circular groove exists between an upwardly facing surface of the lower annular element and a downwardly facing surface of the upper annular element, the upwardly facing surface and the downwardly facing surface being each perpendicular to the axis of rotation; The method further comprises: An outer annular element is centered on the rotation axis, the outer annular element has an inner end surface, the outer annular element has a second inner radius and a third outer radius, wherein the third outer radius is greater than the first outer radius, and the second inner radius is slightly greater than the second outer radius, so that there is a radial gap of about 1 mm between the outer annular element and the central annular element; the downward facing surface and the upward facing surface of the outer annular element are directly adjacent to the upward facing surface of the lower annular element and the downward facing surface of the upper annular element, respectively; positioning the inner end surface of the outer annular element adjacent to the flat cylindrical end surface of the central annular element, A circular groove is provided in the inner end surface of the outer annular element so that an annular chamber is formed between the central annular element and the outer annular element, providing a first stepped surface on an upwardly facing surface of the lower annular element and a downwardly facing surface of the upper annular element; A second stepped surface is provided on the upward surface and the downward surface of the outer annular element; the first stepped surface and the second stepped surface are configured to provide at least two annular cavities, the at least two annular cavities are centered on the rotation axis and have a rectangular cross-section, respectively, half of the at least two annular cavities are at a first interface between the upward surface of the outer annular element and the downward surface of the lower annular element, and the other half of the at least two annular cavities are at a second interface between the upward surface of the lower annular element and the downward surface of the outer annular element, wherein the radial width of the annular chamber is equal to or less than the height of the annular chamber, and the radial width of the annular chamber is less than the width of the two annular cavities combined.

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