Field of the invention

The present invention relates to a swivel joint for transfer of cryogenic fluid, in particular for cooling a loading/offloading system of an offshore transfer terminal. Typically, when a cryogenic fluid, such as liquefied natural gas (LNG), is to be transferred between a carrier and a further terminal or vessel via the transfer terminal, the fluid connections between the transfer terminal and carrier and between the transfer terminal and the further terminal or vessel have to be cooled in advance so that stress and strain of cooling down can be avoided during actual transfer of cryogenic fluid. The invention further relates to an offshore transfer terminal provided with a swivel according to the invention, and to a method for transfer of cryogenic fluid between a carrier and such an offshore transfer terminal.

Background art

US 2008/0277928A1 describes a design for a weathervaning offshore cold fluid (e.g. LNG or liquefied petroleum gas) transfer system which includes at least one cryogenic toroidal swivel that has a design that reduces deformations resulting from low temperature cryogenic fluids. The known low pressure cryogenic toroidal fluid swivel consists of an outer ring-shaped part which rotates about an inner ring-shaped part. The two structures form an annular chamber between them for the distribution and transfer of cryogenic fluids, which chamber is sealed by multiple ring seals between the two swivel parts, above and below the chamber. Though such a toroidal swivel to a large extent reduces deformation of the swivel due to temperature differences, this comes at the price of a relatively complex construction of the swivel.

US 3,984,059 relates to a marine loading system for cryogenic material, wherein the system is provided with coaxial ducting having a plurality of rigid coaxial pipes which have inner and outer coaxial ducts extending in coaxial relationship along substantially the whole length of the respective pipes, the inner duct for transfer of liquid material between material handling stations, and the outer duct for pressure equalization return flow of vapour of said material. The inner and outer coaxial ducts are maintained at a constant spacing by annular plates which are spaced axially from each other and joined together by axial spacer rods or plates. Insulated anchor point may be provided at each end of a pipe length, to prevent relative axial movement of the inner and outer walls of the pipes at those points. It is an object of the invention to provide a cryogenic swivel joint which allows weathervaning of a vessel and which has a simple construction.

It is a further object of the invention to provide an offshore transfer terminal comprising such a swivel, and a method for transferring cryogenic fluid between a carrier and such an offshore transfer terminal. Summary of the invention

To this end, according to a first aspect, the invention provides a cryogenic swivel joint comprising: a first conduit and a second conduit, and a first inline swivel rotatably connecting the first conduit to the second conduit, together defining a first path for passage of cryogenic fluid through the swivel joint; a third conduit and a fourth conduit, and a second inline swivel rotatably connecting the third conduit to the fourth conduit, together defining a second path, separate from the first path, for passage of cryogenic fluid through the swivel joint; wherein the fourth conduit extends at least partially within the first and second conduit, the swivel joint further comprising a third swivel rotatably connecting the first conduit to the fourth conduit, wherein the first, second and third inline swivel are adapted for allowing the first conduit and the third conduit to rotate around an axis of rotation independent from the second conduit and the fourth conduit. As the respective conduits are connect to each other by inline swivels, the swivel joint can be constructed without a toroidal chamber to allow a relatively simple construction of the swivel joint. The swivel joint provides two separate paths for flow of cryogenic fluid. For instance, cool (e.g. vaporized) fluid may be circulated through the first and second conduit in the first path in order to cool the fourth conduit. Likewise, vaporized fluid may be transported through the third and fourth conduits in the second path for cooling the third and fourth conduits. In general, when vaporized fluid is used to cool a loading/offloading system, the vaporized fluid will circulated in a loop which includes both the first and second path as well as other parts of the loading/offloading system which come into contact with the cryogenic fluid, such as valves and hoses.

When the fourth conduit and/or the whole system has been sufficiently cooled, cryogenic liquid may be transported through the first and second conduit, and the third and fourth conduit can be used as return path, for instance for boil off gas. The inline swivels allow rotation of the first conduit independent from the second conduit, while also allowing the third conduit to rotate independent from the fourth conduit.

The first, second, third and fourth conduits typically comprise or are substantially made of a metal or metal alloy.

The fourth conduit is preferably rotation fixedly attached with respect to the second conduit. To achieve this, a drive system may be arranged within the second conduit and connected to the inner wall of the second conduit and the outer wall of the fourth conduit, wherein the drive system is adapted for allowing some axial movement between these conduits while substantially blocking rotational movement of these conduits relative to each other.

By cryogenic fluid herein is meant a fluid which, when at a pressure of 1 atm, has a boiling point below - 100°C, e.g. below - 150°C. For instance, at 1 atm, natural gas typically becomes a liquid at approximately - 162 °C, and at or below this temperature the LNG is cryogenic.

In an embodiment the first, second and third inline swivel are adapted for allowing the first conduit, second conduit and third conduit to rotate independently from each other around the axis of rotation. In an embodiment, a portion of the fourth conduit extends through an opening in a circumferential wall of the second conduit.

In an embodiment a portion of the fourth conduit is substantially fixed to a portion of the second conduit. The fourth conduit is thus at least partially supported by the second conduit. Preferably, the portion of the fourth conduit is fixed in and extends through an opening in a circumferential wall of the second conduit.

In an embodiment the fourth conduit comprises a first end connected to the second inline swivel and an opposite second end, wherein along a portion of its length between the third swivel and the second end the fourth conduit is provided with a bend or meandering portion adapted for accommodating a change in vertical distance between the first end and the second end. The bend or meandering portion enables the swivel joint to cope with more deformation of the fourth conduit, e.g. due to temperature differences or inaccuracies during manufacturing of the swivel joint, than if the fourth conduit were completely straight. The bend or meandering portion is preferably arranged between the first inline swivel and the second end of the fourth conduit.

In an embodiment wherein the bend or meandering portion is arranged within the second conduit, preferably wherein the bend or meandering portion extends in a direction non-parallel to the axis of rotation and has a length greater than the internal diameter of the second conduit.

In an embodiment the outer surface of the fourth conduit, at least between the first end and the bend or meandering portion, is spaced apart from the inner surfaces of the sidewalls of the first and second conduits. It can thus be substantially prevented that deformation of the fourth conduit will result in a corresponding deformation of the first and second conduit.

In an embodiment, the outer surface of the sidewall of the fourth conduit is apart from the inner surfaces of the sidewalls of the first and second conduits along at least 70%, preferably at least 95%, of the length of the fourth conduit. Thermal deformation of the first and/or second conduit due to changes in temperature of the fourth conduit is thus substantially reduced.

In an embodiment the bend or meandering portion bends or meanders over an arc of at least 180 degrees with respect to the axis of rotation. For instance, the bend or meandering portion may comprise or have an S-shape or a U-shape.

In an embodiment the fourth conduit is provided with a bellows or telescopic pipes, for allowing some deformation of the fourth conduit along the axis of rotation. This allows the swivel joint to cope with deformations due to temperature differences or inaccuracies during manufacturing of the swivel joint and conduits or parts thereof. The fourth conduit is preferably substantially rigid for the remaining part of the fourth conduit which extends with its center axis parallel to, or substantially coinciding with, the axis of rotation. The bellows or telescopic pipes may be provided with one or more a seals, and are preferably part of, or used with, a drive system as described above. In an embodiment the second conduit is provided with a first opening at or near the first inline swivel and a second opening at an opposite end of the second conduit, the first path extending through the first and second opening, wherein the second conduit is further provided with another opening in a circumferential sidewall of the second conduit and through which the second path extends. A first fluid stream that is to follow the first path can thus easily be connected to the second opening of the second conduit, and a second fluid stream that is to follow the second path can be connected to the another opening. Fluid from the first stream which follows the first path does not pass through the another opening.

In an embodiment, the first conduit is provided with a first opening at or near the first inline swivel and a second opening in a circumferential sidewall of the first conduit, the first path extending through the first and second opening.

In an embodiment, the second and third conduits are formed as substantially cylindrical pipes having substantially closed circumferential walls. Thus, the second and third conduits allow fluid to pass there through along the axial directions of the pipes, but do not allow fluid to exit the pipes through their circumferential walls.

In an embodiment the first inline swivel and the third swivel are adapted for substantially preventing translational movement of the first conduit along the axis of rotation relative to both the first inline swivel and the third swivel. For instance, the inline swivels may each comprise a first part and a second part that is rotatable relative to the first part, wherein the first part and second part are held within a predetermined axial distance to each other. Several manners to keep first parts and second parts of a swivel within a predetermined axial distance from each other are known in the art, e.g. by placing both parts in a common housing and/or clamping the parts towards each other.

In an embodiment the first inline swivel, the second inline swivel and/or the third swivel are provided with face seals or with piston seals. Preferably all of the inline swivels are provided with face seals.

In an embodiment the first inline swivel, the second inline swivel and/or the third swivel are provided with axial seals.

In an embodiment the first inline swivel, the second inline swivel and the third swivel together allow the first and third conduit to rotate at least a complete revolution around the axis of rotation relative to the second and fourth conduit. This allows the swivel joint to be used in applications in which a vessel weathervanes around the swivel joint.

In an embodiment the swivel joint further comprises a transition piece which extends substantially normal to the axis of rotation and is fixed to the third swivel and to the fourth conduit, and wherein the fourth conduit extends through the transition piece. The transition piece, which may comprise or a plate, substantially closes off the first conduit at or near an end of the first conduit that is connected to the third inline swivel, in this manner preventing fluid from the first path from passing beyond the third inline swivel. The transition piece preferably at least partially supports the weight of the fourth conduit, e.g. such that the fourth conduit is substantially supported by the transition piece and the circumferential sidewall of the second conduit. The transition piece is typically welded and/or bolted to the fourth conduit and/or to the third inline swivel.

In an embodiment the third and fourth conduits are adapted for allowing passage there through of liquefied natural or petroleum gas, and wherein the first and second conduits are adapted for passage there through of vaporized natural or petroleum gas. Vaporized gas passing through the first and second conduits can thus be used to cool the fourth conduit.

According to a second aspect the invention provides an offshore transfer terminal for transfer of Liquefied Natural or Petroleum Gas (LNG or LPG) to and/or from a floating carrier vessel, the transfer terminal comprising a loading/offloading system for LNG or LPG that is provided with a cryogenic swivel joint according to any one of the preceding claims, the transfer terminal further comprising: a base; a loading / offloading hose coupled on one end to the first or second conduit and provided on another end with a connector for coupling with the carrier vessel; a return hose, coupled on one end to the third or fourth conduit and provided on another end with a connector for coupling with the carrier vessel; and an arm, extending above the sea surface and rotatable relative to the base around the axis of rotation, the arm carrying the loading/offloading hose as well as the return hose. The loading/offloading hose and the return hose of the offshore transfer terminal can both be connected, via the swivel joint, with the floating carrier vessel, the arm and swivel joint allowing the carrier vessel to rotate around the axis of rotation. Typically, either the first and third conduit are rotation fixedly connected to the base and the second and fourth conduit are rotatable relative to the base around the axis of rotation, or the second and fourth conduit are rotation fixedly connected to the base and the first and third conduit are rotatable relative to the based around the axis of rotation.

According to a third aspect the present invention provides a method for transferring liquefied natural or petroleum gas (LNG or LPG) between a floating carrier vessel and an offshore transfer terminal as described above, the method comprising the steps of: connecting the carrier vessel to the connector of the loading/offloading hose; connecting the carrier vessel to the connector of the return hose; cooling the loading / offloading system by supplying vaporized LNG or LPG through the loading/offloading hose; and returning the supplied vaporized LNG or LPG, after it has passed through the loading/offloading system, to the carrier vessel via the return hose.

In an embodiment the method further comprises the subsequent step: transferring liquefied LNG or LPG between the carrier vessel and the offshore transfer terminal via the loading/offloading hose and the first and second conduit of the swivel joint.

Short description of drawings

The present invention will be discussed in more detail below, with reference to the attached drawings, in which Fig. 1 schematically shows a cross-sectional view of a swivel joint according to the invention;

Figs. 2A - 2D schematically show view of a swivel joint according to another embodiment of the invention; and

Fig. 3 shows a side view of an offshore transfer terminal that is provided with a swivel joint according to the invention.

Description of embodiments Fig. 1 schematically shows a cross-sectional view of a swivel joint 1 according a first embodiment of the invention, as may be used for transport of a cryogenic fluid such as LNG or LPG. The swivel joint defines two different flow paths P1 ,P2 along which the fluid can be transported. The swivel joint comprises a first conduit 10 and a second conduit 20, and a first inline swivel 15 rotatably connecting the first conduit to the second conduit, together defining the first path P1 for passage of cryogenic fluid through the swivel joint. The first path P1 passes through a branch port 13 that is connected to an opening in the circumferential sidewall of the first conduit, through a portion of the first conduit which runs parallel to the axis of rotation and subsequently through the second conduit 20 which also runs parallel to the axis of rotation. The inline swivel 15 allows the second conduit to rotate around the axis of rotation V relative to the first conduit.

The swivel joint further comprises a third conduit 30 and a fourth conduit 40, and a second inline swivel 35 rotatably connecting the third conduit to the fourth conduit, together defining a second path P2, separate from the first path P1 , for passage of cryogenic fluid through the swivel joint. A first end 31 of the third conduit may be connected to another conduit or hose, and an opposite second end 32 of the third conduit is fixed to the second inline swivel 35. The fourth conduit 40 is fixed at its first end 41 to the second inline swivel 35, and is attached near its second end 42 to a circumferential sidewall of the second conduit 20. The fourth and second conduits in this manner are coupled rotation-fixed ly to each other. The first conduit 10 is fixed at a first end 1 1 to a third inline swivel 55 and at an opposite second end 12 to the first inline swivel 15, so that the first conduit can rotate around the axis of rotation V with respect to the second and fourth conduits.

A plate 60, which is welded to the third inline swivel 55 and to the fourth conduit, closes off the first end 1 1 of the first conduit from passage of cryogenic fluid flowing along the first path P1. The fourth conduit extends through the plate 60, allowing passage of cryogenic fluid through the plate 60 along the second path P2. Reference numeral 70 schematically indicates a toroidal swivel, e.g. an electric swivel or hydraulic swivel, through which the swivel joint 1 extends.

The second conduit 20 is attached with a first end thereof to the first inline swivel 15. Cryogenic fluid may enter or leave the path P1 at a second end 22 and at the branch port 13.

The first and second conduit have substantially equal inner diameters D1 in planes normal to the axis of rotation V. The fourth conduit, which partially extends within the first and second conduits, has a significantly smaller outer diameter D2, allowing the fourth conduit to be spaced apart from the inner circumferential walls of the first and second conduits. In the example shown, diameter D1 lies in the range of 10 inch to 37 inch (25.4 cm to 93.98 cm) , and diameter D2 is typically of 5 inch (12.7 cm) or less. Though the fourth conduit, near its second end 42, is in contact with the second conduit at the location where it passes through an opening in the circumferential side wall of the second conduit, the fourth conduit is spaced apart from the first and second conduits over at least 90% of the length of the fourth conduit.

The fourth conduit is provided near its second end with an S-shaped meandering portion 44. Upon deformation of the fourth conduit, this meandering portion 44 reduces axial stress on the fourth conduit between the point where the fourth conduit is fixed to the second conduit and the point where the fourth conduit is fixed to the plate 60. Though in the orientation of the swivel joint shown in Fig. 1 the fourth conduit is at least partially suspended from the plate 60 and the first end 31 of the third conduit 30 lies vertically above the second end of the second conduit, it will be appreciated that the same swivel joint may be used in an orientation in which the second end 22 of the second conduit 20 lies vertically above the first end of the third conduit 31.

Figs. 2A-2D schematically illustrate a second embodiment of a swivel joint of the invention. The swivel joint 200 comprises a first conduit 210 that is connected to a second conduit 220 via a first inline swivel 215. A third conduit 230 is connected to a fourth conduit 240 via a second inline swivel 235. A third inline swivel 255 connects the fourth conduit 240 to the third conduit 230 and allows the fourth conduit to route through the first conduit 210. A plate 260 is fixed to the third swivel 255 and to the fourth conduit, with the fourth conduit 240 extending through the plate. The inline swivels, each of which comprises face seals, allow rotation of the conduits connected thereto around axis of rotation V. Conduits 210, 220, 230 and 240 have respective first and second distal ends 21 1 ,212, 221 ,222, 231 ,232 and, 241 ,242.

A toroidal swivel 270 may be provided around the swivel joint 200, though the toroidal swivel does not form part of the swivel joint 200.

The fourth conduit extends partially within the first and second conduits, and is provided with a U-shaped bend near second end 242 of the fourth conduit 240. The U-shaped bend provides a 180 degree change in direction for fluid passing through the fourth conduit 240, and also allows changes in length of the fourth conduit 240 to be compensated for by flexing of the bend portion. In general, the longer the horizontal portion of the U-shaped bend, the greater the flexibility of the bend portion will be. The second conduit is provided with a bend portion 224 across an arc of about 90 degrees, and surrounds a 90 degree arc portion of the U-shaped bend of the fourth conduit. The second end 222 of the second conduit 220 extends substantially normal to the axis of rotation V, whereas the second end 242 of the fourth conduit 240 extends substantially parallel to the axis of rotation V.

Fig. 2B shows a side view of the swivel joint 200. Fig. 2C shows a cross-section through plane ll-C of Fig. 2B, showing a drive system 247 which is coupled to the outer wall of the fourth conduit and is connected via radial spacers 248 to the inner wall of the second conduit. The drive system is adapted for restraining rotation of the second conduit relative to the fourth conduit around the axis of rotation V, while allowing some axial movement of the fourth duct relative to the second duct along the axis V. A top view of the swivel joint 200 is shown in Fig. 2D.

Fig. 3 shows an LNG carrier vessel 390 floating on the water W moored close to an offshore transfer terminal 300 according to the invention. The transfer terminal 300 comprises the swivel joint 200 of Fig. 2A. The swivel 200 is at least partially arranged above a base 380 of the transfer terminal. For reasons of clarity the details of the swivel 200 are not shown again in Fig. 3.

The base 380 is supported on a foundation 301 of the transfer terminal 300, the base and foundation being substantially rotationally fixed with respect to the sea floor 391 1. An arm 310 which extends above the water line W is rotatable relative to the base 380 around the axis of rotation V. The arm carries a loading/offloading hose 310 that is connected at one end to the second conduit 220 (via second end 222 thereof shown in Fig. 2) of the swivel joint 200. At the other end 312 the hose 310 is provided with a connector 313 that is coupled with the carrier vessel 390. The arm further carries a return hose 320 that is connected at one end to the fourth conduit of the swivel joint 200, via second end 242 of the fourth conduit. At the other end 322 the hose 320 is provided with a connector 323 that is coupled with the carrier vessel 390. As the arm is rotatable around the axis of rotation V and both hoses are connected to the swivel joint, the vessel 390 can weathervane around the axis V. The hoses, swivel joint and further conduits connected to the swivel joint form a loading/offloading for LNG or LPG.

When transferring the LNG or LPG between the vessel 390 and the transfer terminal 300, first the connectors of the loading/offloading hose and of the return hose are connected to the carrier vessel. Next the loading/offloading system is cooled by supplying vaporized LNG or LPG and circulating the vaporized fluid through the loading/offloading hose all conduits of the swivel joint.

The vaporized LNG or LPG that has been used to cool the loading/offloading system is subsequently returned to the carrier vessel via the return hose. In this manner a loop for the vaporized fluid is created which permits the vaporized fluid to be recirculated until a predetermined temperature is reached for the loading/offloading system.

Once the loading/offloading system has been sufficiently cooled to allow transfer of liquefied LNG or LPG there through, the return hose may optionally be closed off, and liquefied LNG or LPG is transferred between the carrier vessel and the transfer terminal through the loading/offloading hose and the swivel joint.

The present invention has been described above with reference to a number of exemplary embodiments as shown in the drawings. Modifications and alternative implementations of some parts or elements are possible, and are included in the scope of protection as defined in the appended claims.