The invention relates to a coupling device for rotatable coupling of fluid conduits for cryogenic fluids, comprising an annular outer body and an annular inner body rotatable relative thereto, a first flange of a first fluid conduit coupled to the inner body and a second flange of a second fluid conduit coupled to the outer body, bearing rings with balls, provided between the outer body and the inner body, and sealing means for providing a fluid-tight seal between the outer body and the inner body.

A rotatable coupling for connecting a pair of pipes and for transferring fluid between the pipes at ambient

temperature and cryogenic temperatures is known from the American patent US 4 355 827. A cryogenic seal between relatively rotatable inner and outer elements of the coupling prevents leakage at cryogenic temperatures, and an ambient temperature seal between the joint elements ensures a seal at ambient temperatures and prevents fluids coming into contact with the cryogenic seal. At ambient temperature the seal assembly comprises an elastomer O-ring retained in the outer element and an annular sealing ring fastened to the inner element and spring-biased toward the O-ring. At ambient temperatures the sealing ring is held against the O-ring in a fluid-tight manner. As the temperature decreases, a number of rods or wires, or an annular sleeve having a high coefficient of linear expansion, pulls the annular sealing ring away from the adjacent O-ring to prevent wear thereof, and other damage thereto, at low temperatures. The relative rotatability of the inner and outer elements is provided by a bearing of a number of, in this case three, annular tracks with balls. An axial bore provides fluids, which could possibly leak along the sealing means, with an escape to the outside world in order to prevent these fluids coming to lie in the ball space and there possibly contaminating the bearing. The known rotatable coupling has a number of drawbacks. The different sealing systems for ambient temperature and cryogenic temperatures, and particularly an annular pipe or an assembly of rods or wires for retracting or pressing an annular sealing ring, result in a complex and thereby expensive construction. The extent to which this complex construction can meet demands in respect of reliability in the longer term and the amount of maintenance required by the construction are unknown. The presence of an axial bore as escape channel for leaked fluids to prevent contamination of lubricants for the bearing is likewise considered a drawback.

It is an object of the invention to provide a coupling device for cryogenic fluid conduits which is suitable for coupling conduits for cryogenic liquids with a temperature below -160°C, for instance liquid natural gas. The coupling has to have a relatively simple construction, be low- maintenance and thereby be relatively inexpensive to operate.

These objects are achieved, and other advantages gained, with a coupling device of the type stated in the preamble, wherein the balls are provided according to the invention between an outer ring and an inner ring of a single-row ball bearing which is received between the outer body and the inner body and which is bounded by an annular outer gland arranged against the outer body and an annular inner gland arranged against the inner body.

In the manufacture of such a coupling device a ready- made single-row ball bearing is inserted between the outer body and the inner body and, other than in a prior art coupling device, no balls are inserted individually and in direct contact with the outer body and the inner body. The invention thus provides a coupling device with reliable seals which can be arranged in simple manner, wherein lubricants for the bearing and an escape channel for leaked fluids can be dispensed with.

An embodiment of such a coupling device, wherein the first flange is statically coupled to the inner gland, which is in turn statically coupled to the inner body, and the second flange is statically coupled to the outer body which is in turn dynamically coupled to the inner body, comprises first static sealing means between the first flange and the inner gland, second static sealing means between the inner gland and the inner body, first dynamic sealing means between the second flange and the inner body and second dynamic sealing means between the second flange and the inner body.

At least one of the first static sealing means, the second static sealing means, the first dynamic sealing means and the second dynamic sealing means comprises for instance a sealing ring manufactured from a polyethylene with ultra-high molecular weight (UHMW PE) .

At least one of the first static sealing means, the second static sealing means, the first dynamic sealing means and the second dynamic sealing means comprises for instance a pressure ring manufactured from an austenitic superalloy on the basis of nickel-chromium.

At least one of the first static sealing means, the second static sealing means, the first dynamic sealing means and the second dynamic sealing means comprises for instance a spacer ring manufactured from a corrosion-resistant stainless steel .

In an advantageous embodiment of a coupling device according to the invention at least one of the outer ring and the inner ring of the ball bearing is manufactured from a hardened martensitic steel.

The bearing ring of the outer ring and the bearing ring of the inner ring are preferably each provided with a friction-reducing coating which inhibits wear.

In a coupling device according to the invention the balls are preferably manufactured from a ceramic material, for instance from silicon nitride (Si ₃ N ₄ ) .

With a suitable choice of ceramic material, balls having a hardness greater than that of stainless steel balls are obtained, and it is possible to construct a lubrication-free bearing .

In order to minimize effects of an axial load on the coupling device the balls are preferably received in a four- point contact between the bearing ring of the outer ring and the bearing ring of the inner ring of the ball bearing.

The invention will be elucidated hereinbelow on the basis of an exemplary embodiment, with reference to the drawings .

In the drawings

Fig. la is a perspective view of an embodiment of a coupling device according to the invention, as seen on the front side, with a first flange,

Fig. lb is a cut-away perspective view of the coupling device shown in fig. la,

Fig. lc is a perspective view of the coupling device shown in fig. la, as seen on the rear side, with a second flange,

Fig. Id is the coupling device shown in fig. la in front view,

Fig. le is the coupling device shown in fig. Id in a cross-section along the line E-E,

Fig. If is the coupling device shown in fig. la in rear view, and

Fig. 2 is a cross-sectional view of a seal for a coupling device according to the invention.

Corresponding components are designated in the figures with the same reference numerals.

Figures la-f show a coupling device 10 formed from an annular outer body 1 and an annular inner body 2 rotatable relative thereto. A first flange 3 is fixedly coupled with bolts 5 to an annular gland innerbody 6, which is in turn fixedly coupled with bolts 7 to inner body 2. A second flange 4 is fixedly coupled with bolts 8 to outer body 1. Received between outer body 1 and inner body 2 is a ready-made ball bearing, with an outer ring 9 and an inner ring 11 between which balls 12 of silicon nitride (S13N ₄ ) are enclosed in a brass bearing cage 13. Ball bearing 9, 11, 12, 13 is further bounded by the gland innerbody 6 and an annular gland outerbody 14, which is fixedly coupled with bolts 15 to outer body 1. The bearing ring of outer ring 9 and the bearing ring of inner ring 11 are each provided with a friction-reducing Xylan coating which inhibits wear. An annular seal 16 is arranged between first flange 3 and gland innerbody 6 for a first fluid-tight static seal. An annular seal 17 is arranged between gland innerbody 6 and inner body 2 for a second fluid-tight static seal. An annular seal 18 is arranged between second flange 4 and inner body 2 for a first fluid- tight dynamic seal. An annular seal 19 is arranged between second flange 4 and inner body 2 for a second fluid-tight dynamic seal. The figure further also shows a seal 20 which provides access to a channel through which a purge gas, for instance nitrogen, can be guided through the ball bearing.

Fig. 2 shows in detail the annular seal 18 shown in fig. le, which is formed from a jacket 21 of UHMW PE which is U- shaped in cross-section, a spring 22 of an austenitic superalloy (Iconel) on the basis of nickel-chromium which is V-shaped in cross-section for exerting a force on jacket 21 in axial direction, and a spacer 23 of a corrosion-resistant stainless steel (AISI) which is rectangular in cross-section for exerting a force on jacket 21 in radial direction.

The shown coupling device enables coupling of conduits for cryogenic liquids with a temperature below -160 °C and an internal pressure between 2.5 and 3.5 barg, wherein a number of at least 400,000 rotations through an angle of between 6 and 10 degrees can be performed without disturbance.