Active deformation control for a swivel and method therefor

Abstract

A swivel (10) includes a rotary interface around a rotation axis having an inner annular part (2) and an outer annular part (1), the outer annular part being concentric with and rotatable relative to the inner annular part around the rotation axis; a toroidal cavity (5) being defined between an outer surface of the inner annular part and an inner surface of the outer annular part, the swivel being provided with a heating system including at least one heating element (30) and at least two temperature sensors (32, 34), the at least one heating element being thermally coupled to either the inner annular part or the outer annual part or to a support (11; 12) of either the inner annular part or the outer annular part; each of the at least two temperature sensors being thermally coupled to either the inner annular part or the outer annual part or the support (11; 12) of either the inner annular part or the outer annular part.

Description

[0001] Active deformation control for a swivel and method therefor

[0002] Field of the invention

[0003] The present invention relates to a swivel provided with a thermal compensation system. Moreover, the invention relates to a method for active deformation control for a swivel by means of the thermal compensation system.

[0004] Background

[0005] In offshore industry, swivels or swivel stacks are known for transfer of fluids or electrical power between a floating vessel such as a FPSO / FLNG (Floating Production Storage and Offloading I Floating Liquefied Natural Gas) vessel and associated equipment on a sea bed. Typically, such a floating vessel is equipped with a turret mooring system that can couple one or more lines from the equipment on the sea bed to processing devices on the vessel. Since the turret mooring system should allow weathervaning of the moored vessel, the swivel is likewise adapted to provide rotation between the incoming lines and the processing devices.

[0006] Toroidal fluid swivels are known in the art for transfer of high-pressure fluids across a rotary interface between an incoming fluid line from a well on the sea bed and an outgoing product piping on the floating vessel. Applications for such a swivel include for example offshore oil and gas explorations where high-pressure flows of oil and / or gas are transferred from a (deep-sea) offshore well to the floating vessel.

[0007] In particular for deep-sea applications there is a need for swivels that can withstand design pressures well over 500 atm for incoming fluid while at the same time, a high flow of the fluid should be transferred.

[0008] In addition, electric connections are guided through the turret mooring system by means of a swivel mechanism. Electric swivels are used for transmitting electrical information and power from rotating to fixed parts of a swivel stack located on a FPSO / FLNG Turret. Electric swivel enclosures use bearings between the fixed and rotating part, ensuring free rotation.

[0009] A well-known issue in designing and manufacturing a swivel is to have minimal deformation of the swivel during operations. In particular, deformations that interfere with proper functioning of seal in the swivel or create metal-on-metal contact between static and rotating parts of the swivel, should be kept to a minimum. Mechanical compensation of deformation due to high pressure of the fluid is for example known from European patents EP 966630 and EP 2539221.

[0010] A different type deformation of the swivel can occur across the swivel due to the temperature of the fluid passing through the swivel relative to the temperature at the rotary interface of the swivel. A similar problem can occur due to resistive heating in electric swivels created by relatively high current across the rotary interface. Such thermal deformations are not easily compensated.

[0011] It is well-known to apply encapsulation of the swivel which can reduce heat exchange to the environment and thus thermal gradients in parts of the swivel. However, under some circumstances the temperature difference may be too large or the swivel configuration too complex, that no acceptable reduction of deformation can be achieved. Also, encapsulation may not be practical in swivel stacks as it impacts maintenance.

[0012] It is an object of the present invention to overcome or mitigate temperature based deformations of the swivel.

[0013] Summary of the invention

[0014] The object is achieved by a swivel comprising a rotary interface around a rotation axis having an inner annular part and an outer annular part, the outer annular part being concentric with and rotatable relative to the inner annular part around the rotation axis; a toroidal cavity being defined between an outer surface of the inner annular part and an inner surface of the outer annular part, the swivel being provided with a heating system comprising at least one heating element and at least two temperature sensors, the at least one heating element being thermally coupled to either the inner annular part or the outer annual part or to a support of either the inner annular part or the outer annular part; each of the at least two temperature sensors being thermally coupled to either the inner annular part or the outer annual part, or the support of either the inner annular part or the outer annular part.

[0015] Advantageously, the invention provides an active system configured for counteracting deformations of the swivel by reducing the thermal gradient across the swivel.

[0016] By providing a heating element on one or more parts of the swivel the thermal gradient between the various parts can be reduced. As a result, heat dissipation by thermal convection and corresponding thermal stresses and deformations will be reduced. Improved long-term operation of seals in the swivel can be obtained. The thermal compensation also prevents metal-metal contact between moving parts in the swivel due to thermal deformation.

[0017] According to an aspect, the invention provides a turret mooring system for a floating object comprising a swivel as described above. According to an aspect, the invention provides a floating production storage and offloading, FPSO, vessel provided with a swivel as described above.

[0018] According to an aspect, the invention provides a method for manufacturing a swivel comprising a rotary interface around a rotation axis having an inner annular part and an outer annular part, the outer annular part being concentric with and rotatable relative to the inner annular part around the rotation axis; a toroidal cavity being defined between an outer surface of the inner annular part and an inner surface of the outer annular part, the method comprising: providing the swivel; providing a heating system comprising at least one heating element and at least two temperature sensors, arranging the at least one heating element on either the inner annular part or the outer annual part or a support of either the inner annular part or the outer annular part; to obtain a thermal coupling between the at least one heating element and either the inner annular part or the outer annual part or the support of either the inner annular part or the outer annular part; arranging each of the at least two temperature sensors on either the inner annular part or the outer annual part or the support of either the inner annular part or the outer annular part to obtain a thermal coupling between each of the temperature sensors and either the inner annular part or the outer annual part or the support of either the inner annular part or the outer annular part.

[0019] Brief description of drawings

[0020] Embodiments of the present invention will be described hereinafter, by way of example only, with reference to the accompanying drawings which are schematic in nature and therefore not necessarily drawn to scale.

[0021] In the drawings, identical or similar elements are indicated by the same reference sign. Figure 1 shows a schematical cross-section of a swivel for fluid transfer;

[0022] Figure 2 shows a schematical cross-section of a swivel according to an embodiment;

[0023] Figure 3 shows a schematical cross-section of a swivel according to an embodiment;

[0024] Figure 4 shows a schematical cross-section of a swivel according to an embodiment, and

[0025] Figure 5 shows a schematical cross-section of a swivel according to an embodiment;

[0026] Detailed description of embodiments

[0027] Figure 1 shows a schematical cross-section of a swivel for fluid transfer. The cross-section shows a part of a swivel 10 having a rotary interface having an annular space 5 between an inner and outer swivel member 2, 1 for transferring a fluid, e g., a liquid such as LNG or liquid mixture of hydrocarbons, from a fluid path defined by an inlet (not shown), which is connected to a riser or the like, to a fluid path defined by an outlet (not shown), which is connected to a storage facility on a vessel weathervaning around said riser. The swivel 10 comprises sealing arrangements 20 for preventing leakage of the annular space 5, which sealing arrangements 20 are positioned on both sides of and parallel to the annular space 5 in a gap between the inner and outer swivel members 2, 1. The inner and outer swivel members 2, 1 are tubular members which are arranged coaxially around a longitudinal axis of rotation V, with both the annular space 5 and sealing arrangements 20 extending along the complete circumference of an outer wall of the inner swivel member 2 and an inner wall of the outer swivel member 1 . The sealing arrangements 20 above and below the annular space 5 are located in such a manner that they perform a sealing function in the operative position of the swivel.

[0028] Furthermore, the swivel 10 may comprise annular shaped support portions 11 , 12 below and / or above the rotary interface.

[0029] Now referring to Figures 2 - 5, to avoid that during operation a deformation of the swivel or a part thereof would become unacceptably large, such that the operation becomes adversely affected, the invention provides a thermal compensation system. The thermal compensation system is configured to locally heat a portion of the swivel such that the deformation is counteracted by elastic deformation due to thermal expansion or thermal stress created in the portion of the swivel.

[0030] According to an embodiment, the thermal compensation system comprises at least one heating element, preferably an electric heating element, and at least two temperature measurement devices. The at least one heating element is configured to be attached and be in thermal contact to a predetermined portion of the swivel. The temperature measurement devices each are thermal sensors such as thermocouples, resistive temperature detectors and thermistors that are configured to be attached and in thermal contact with a predetermined measuring location on the swivel.

[0031] In addition, according to an embodiment, the thermal compensation system comprises a thermal controller that is configured to connect to the at least one heating element and to the temperature measurement devices. The thermal controller is configured to receive temperature related signal(s) from the temperature measurement devices and to control the amount of power to supply to the at least one heating element based on the received temperature related signal(s) and / or a difference between the received temperature related signals. In this manner, a temperature difference can be compensated (reduced) between different locations on the swivel, i.e., the portion of the swivel heated by the heating element and an unheated remainder portion of the swivel. Additionally, thermal deformation(s) of the swivel due to operation conditions can be counteracted and reduced.

[0032] Figure 2 shows a schematical cross-section of a swivel according to an embodiment. The thermal compensation system in this embodiment has an heating element 30 that is attached to the outer annular part 1 of the swivel. Thus, the outer annular part can be heated relative to the inner annular part 2 and the support 11 , 12 of the swivel.

[0033] Further, a first temperature measurement device 32 is attached to the outer annular part 1 , located near or at the heating element 30 at a distance for example in a range between zero and about 100 cm, and a second temperature measurement device 34 is attached to the inner annular part 2. It is noted that the second temperature measurement device may be located alternatively either at a location on the outer annular part 1 spaced away from the location of the first temperature measurement device 32, or at another location on the unheated portion of the swivel, for example on a portion of the support 11 , 12.

[0034] The thermal compensation system comprises a power supply 42 connected to the heating element 30 and a controller 40 that is connected to the temperature measurement devices 32, 34 so as to receive measured temperature data and to the power supply 42 for controlling output power to the heating element 30. In an embodiment the controller 40 provides that an output power of the power supply 42 is proportional to a measured temperature difference between the two temperature measurement devices 32, 34.

[0035] In yet a further embodiment, the swivel is provided with a heading sensor 50 that is configured to measure a heading (i.e., an orientation) of the outer annular part relative to the inner annular part. Since the heading may have influence on the temperature distribution in the swivel, the controller in such a case is configured to receive a value of the heading and adapt the output power to the heating element accordingly.

[0036] Figure 3 shows a schematical cross-section of a swivel according to an embodiment. The thermal compensation system in this embodiment has a heating element 30 that is attached to the inner annular part 2 of the swivel. Thus, the inner annular part 2 can be heated relative to the outer annular part 1 and the support 11 , 12 of the swivel.

[0037] The first temperature measurement device 32 is attached to the inner annular part 2, at or near the heating element 30 and the second temperature measurement device 34 to the outer annular part 1 or in general a location on either a part of the swivel other than the inner annular part 2 whereon the heating element 30 is arranged, or at location on the inner annular part 2 spaced away from the location of the first temperature measurement device Figure 4 shows a schematical cross-section of a swivel according to an embodiment.

[0038] The thermal compensation system in this embodiment has an heating element 30 that is attached to a support 11 ; 12 of the inner annular part 2 of the swivel. Thus, the support of the inner annular part can be heated relative to both the outer and inner annular parts 1 , 2 of the swivel.

[0039] The first temperature measurement device 32 is attached to the inner annular part or at the support 11 ; 12 of the inner annular part at or near the location of the heating element 30. The second temperature measurement device 34 is attached to the outer annular part 1 or in general a location on an outer part of the swivel that is not in direct contact with the heating element, i.e., on a part of the swivel other than the support whereon the heating element 30 is arranged. Alternatively, the second temperature measurement device 34 may be attached to the same part of the swivel where the first temperature measurement device 32 is located at a location spaced way therefrom.

[0040] Alternatively in this embodiment, the heating element 30 can be attached to a support of the outer annular part instead of the support of the inner annular part.

[0041] Figure 5 shows a schematical cross-section of a swivel according to an embodiment. In this embodiment, the thermal compensation system comprises the heating element 30 and an additional heating element 31. Both the heating element 30 and the additional heating element 31 are attached to the inner annular part 2 and the outer annular part 1 of the swivel, respectively and are preferably controlled individually by the thermal controller (not shown) to create a respective temperature difference between either the inner annular part 2 or the outer annular part 1 and an unheated portion of the swivel which is not in contact with the heating element 30; 31, or the support 11 ; 12 of the swivel. This embodiment allows to controllably reduce a first temperature difference between the inner annular part and the outer annular part of the swivel, and a further temperature difference between each of the inner annular part and the outer annular part of the swivel and the unheated portion of the swivel.

[0042] Depending on the expected deformation during operation, the thermal compensation system is configured to control a temperature difference between the portion of the swivel exposed to heating by the heating element and the unheated portion of the swivel that creates a local thermal compensation which is directed to sufficiently reduce the process-induced deformation created by the transfer of fluids across the rotary interface between the incoming fluid line and the outgoing product piping on the floating vessel. The thermal compensation system is designed to output an amount of electrical power for heating, relative to the mass and heat capacitance of the swivel and to the temperature difference created by the transferred fluid flowing through the swivel, to create a thermal expansion which reduces the process induced deformation and achieves sufficient compensation thereof. The location of the heating element on the swivel relative to the incoming fluid line may be determined by a direction of the thermal gradient caused by the transferred fluid flowing through the swivel under given operational conditions.

[0043] The invention has been described with reference to some embodiments. Obvious modifications and alterations will occur to the skilled in the art upon reading the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims.

Claims

Claims1. A swivel (10) comprising a rotary interface around a rotation axis having an inner annular part (2) and an outer annular part (1), the outer annular part being concentric with and rotatable relative to the inner annular part around the rotation axis; a toroidal cavity (5) being defined between an outer surface of the inner annular part and an inner surface of the outer annular part, the swivel being provided with a heating system comprising at least one heating element(30) and at least two temperature sensors (32, 34), the at least one heating element being thermally coupled to either the inner annular part or the outer annual part or to a support (11 ; 12) of either the inner annular part or the outer annular part; each of the at least two temperature sensors being thermally coupled to either the inner annular part or the outer annual part or the support (11 ; 12) of either the inner annular part or the outer annular part.

2. The swivel according to claim 1 , wherein the at least one heating element is thermally coupled to an inner surface of the inner annular part.

3. The swivel according to claim 1 , wherein the at least one heating element is thermally coupled to an outer surface of the outer annular part.

4. The swivel according to claim 1 , wherein the at least one heating element is thermally coupled to the support (11 ; 12) of either the inner annular part or the outer annular part.

5. The swivel according to claim 1 , wherein at least one of the temperature sensors is thermally coupled to the inner annular part or the outer annular part.

6. The swivel according to claim 1 , wherein at least one of the temperature sensors is thermally coupled to the support (11 ; 12) of either the inner annular part or the outer annular part.

7. The swivel according to any one of the preceding claims, further comprising a power supply (42) and a controller (40); the power supply configured to be electrically coupled with the at least one heating element (30) for supplying power to the heating element; the controller (40) configured to be connected to the power supply and further configured tocontrol output of the power supply to the heating element.

8. The swivel according to claim 7, wherein the controller is coupled to the at least two temperature sensors and configured to receive a respective temperature signal from each of the temperature sensors; the controller being configured to control the power supply to supply an amount of power to the at least one heating element based on the measured respective temperature signals.

9. The swivel according to claim 7 or claim 8, wherein the swivel comprises a heading sensor (50) for determining a heading value for a heading of the inner annular part relative to the outer annular part and the controller is configured to be connected to the heading sensor for receiving a heading signal corresponding with the heading value and to control output of the power supply to the at least one heating element based on the heading value.

10. The swivel according to any one of the preceding claims 1 - 9, wherein the swivel is configured as a swivel for hydrocarbons transfer.11 . The swivel according to any one of the preceding claims 1 - 9, wherein the swivel is configured as an electric swivel.

12. The swivel according to any one of the preceding claims, configured to be mounted on a floating object and to provide a rotary interface around a rotation axis between a first part rotatable relative to the floating object and a second part attached to the floating object.

13. A turret mooring system for a floating object comprising a swivel according to any one of the preceding claims 1 - 11.

14. A floating production storage and offloading, FPSO, vessel provided with a swivel according to any one of the preceding claims 1 - 11.

15. A method for manufacturing a swivel (10) comprising a rotary interface around a rotation axis having an inner annular part (2) and an outer annular part (1), the outer annular part being concentric with and rotatable relative to the inner annular part around the rotation axis; a toroidal cavity (5) being defined between an outer surface of the inner annular part and an inner surface of the outer annular part, the method comprising:providing the swivel; providing a heating system comprising at least one heating element (30) and at least two temperature sensors (32, 34), arranging the at least one heating element on either the inner annular part or the outer annual part or a support (11 ; 12) of either the inner annular part or the outer annular part to obtain a thermal coupling between the at least one heating element and either the inner annular part or the outer annual part or the support (11 ; 12) of either the inner annular part or the outer annular part; arranging each of the at least two temperature sensors on either the inner annular part or the outer annual part or the support (11; 12) of either the inner annular part or the outer annular part to obtain a thermal coupling between each of the temperature sensors and either the inner annular part or the outer annual part or the support (11 ; 12) of either the inner annular part or the outer annular part.

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