High pressure fluid swivel

Abstract

A fluid swivel that includes a stationary annular structure defining upper and lower annular seal recesses, and a rotatable outer housing operatively connected to the stationary annular structure, the outer housing defining an annular passage that has upper and lower surfaces. Upper and lower seals are positioned between the stationary annular structure and the rotatable outer housing and disposed in the upper and lower seal recesses. An inner housing bore is disposed in the stationary annular structure and arranged to provide fluid of pressure P to the annular passage, the fluid exerting a first force (Fv.sub.1) longitudinally inwardly on the outer surface of the outer housing, and a second force (Fv.sub.2) longitudinally outwardly on the upper and lower surfaces of the annular passage, the second force (Fv.sub.2) having a greater magnitude than the first force (Fv.sub.1) so the outer housing deflects outwardly, pushing the upper and lower seals into the upper and lower seal recesses.

Claims

1. A sealed fluid swivel comprising: an inner housing assembly positioned coaxially about a longitudinal axis; an outer housing positioned coaxially about the inner housing assembly and arranged and designed to rotate relative to the inner housing assembly about the longitudinal axis, the outer housing including: a radially inward-facing annular surface defining an innermost diameter of the outer housing; an radially inward-facing annular passage having a radial width and an axial height; a radial flow passage having an internal diameter and communicating with the annular passage; upper and lower annular seal recesses, the upper annular seal recess is above the annular passage and the lower annular seal recess is below the annular passage; an upper seal disposed in the upper annular seal recess and a lower seal disposed in the lower annular seal recess, the upper and lower seals for sealing between the outer housing and annular, axially-facing surfaces of the inner housing assembly; an inner housing bore disposed in the inner housing assembly and communicating with the annular passage, the inner housing bore arranged to carry fluid having a fluid pressure to the annular passage, the fluid allowed to fill a small space between the inner housing assembly and outer housing from the radially inward-facing annular surface of the outer housing to the upper and lower seals; wherein the axial height of the annular passage is smaller than the internal diameter of the radial flow passage, the width being about twice the axial height of the annular passage, thereby allowing the axial distance between the upper and lower seals to be minimized to reduce the effective pressure height (H.sub.eff) of the outer housing on which the pressurized fluid outwardly acts.

2. A fluid swivel comprising: a stationary inner housing assembly; a rotatable outer housing operatively connected to the stationary inner housing assembly and defining upper and lower annular seal recesses, the outer housing having an annular passage that has upper and lower surfaces and a radially inward-facing annular surface defining an innermost diameter of the outer housing; upper and lower seals positioned between the stationary inner housing assembly and the rotatable outer housing and disposed in the upper and lower annular seal recesses; and an inner housing bore disposed in the stationary inner housing assembly and arranged to provide fluid having a fluid pressure (P) to the annular passage, the fluid allowed to fill a small space between the inner housing assembly and the outer housing from the radially inward-facing annular surface to the upper and lower seals, the fluid exerting a first axial force (Fv.sub.1) on an outer upper surface of the outer housing, and a second axial force (Fv.sub.2) on the upper surface of the annular passage, the second force (Fv.sub.2) having a greater magnitude than the first force (Fv.sub.1) so that the outer housing deflects axially upward.

3. The fluid swivel of claim 2, wherein the fluid exerts a third axial force (Fv.sub.1) on an outer lower surface of the outer housing, and a fourth axial force (Fv.sub.2) on the lower surface of the annular passage, the fourth axial force (Fv.sub.2) having a greater magnitude than the third axial force (Fv.sub.1) so that the outer housing deflects axially downward.

4. The fluid swivel of claim 3, wherein the third axial force is equal to the first axial force but in the opposite direction and the fourth axial force is equal to the second axial force but in the opposite direction.

5. The fluid swivel of claim 2, wherein the outer housing and the stationary inner housing assembly are separated by at least two axial thrust bearings and at least one radial bearing.

6. The fluid swivel of claim 2, further comprising backup seals, secondary seals, and backup secondary seals, positioned between the outer housing and the stationary inner housing assembly.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The objects, advantages, and features of the invention will become more apparent by reference to the drawings which are appended hereto, wherein like reference numbers indicate like parts, and wherein an illustrative embodiment of the invention is shown, of which:

(2) FIG. 1 is a cross section of an illustrative swivel stack assembly with two swivels, each according to the invention, stacked on a swivel base with one inlet of the base fluidly coupled to an outlet of one swivel and a second inlet of the base fluidly coupled to an outlet of a second swivel;

(3) FIG. 2 is a top view of the swivel stack assembly of FIG. 1 with section line 1-1 indicating the cross section view of the top swivel of the assembly of FIG. 1;

(4) FIG. 3 is an enlarged sectional view of a swivel according to the invention;

(5) FIG. 4 is an enlarged sectional view showing stair stepped dynamic face seals between inner and outer housings with an annular groove in the outer housing, with arrows showing forces on the swivel parts caused by pressure in the swivel; and

(6) FIG. 5 is another diagrammatic illustration of FIG. 4 showing effective pressure height area in the swivel according to the invention.

DESCRIPTION OF THE INVENTION

(7) The aspects, features, and advantages of the invention mentioned above are described in more detail by reference to the drawings wherein like reference numerals represent like elements. The following table provides a list of reference numerals used throughout the specification and the features that they represent:

(8) TABLE-US-00001 Figures where Reference Reference Numeral Feature Numeral Appears 5 Longitudinal axis 1 10A Upper swivel 1, 3, 4, 5 10B Lower swivel 1 16A Upper swivel inner housing 1, 3, 4, 5 16B Lower swivel inner housing 1 17A Upper swivel seal plate 1, 3, 4, 5 17B Lower swivel seal plate 1 18 Upper ring portion 4 18A Threaded bolts 1 19 Lower ring portion 4 20A Upper swivel outer housing 1, 3, 4, 5 20B Lower swivel outer housing 1 21A Upper swivel upper bearing 1, 3, 4 21B Lower swivel upper bearing 1 22A Upper swivel lower bearing 1, 3, 4 22B Lower swivel lower bearing 1 23A Upper swivel radial bearing 1, 3, 4 23B Lower swivel radial bearing 1 26A Upper inner housing bore 1 26B Lower inner housing bore 1 30 Annular passsage 1, 3, 4 30A Radial flow outlet 2 40 Upper dynamic seal 3, 4, 5 41 Lower dynamic seal 3, 4, 5 42 Backup upper dynamic seal 3, 4, 5 43 Backup lower dynamic seal 3, 4, 5 44 Upper secondary dynamic seal 3, 4, 5 45 Lower secondary dynamic seal 3, 4, 5 46 Backup secondary upper dynamic seal 3, 4, 5 47 Backup secondary lower dynamic seal 3, 4, 5 52 Swivel connectors 1 52A Upper shoulder 4, 5 52B Lower shoulder 4, 5 54 Base housing 1 56 Fixed spools 1 58A Upper swivel base inlet 1 58B Lower swivel base inlet 1 60A Upper spool 1, 2 60B Lower Spool 1, 2 61 First upper annular seal recess 4 62 First lower annular seal recess 4 63 Second upper annular seal recess 4 64 Second lower annular seal recess 4 70 Bolts 1 98 Primary static seal 4 99 Secondary static seal 4 100 Swivel Base 1 105 Space 4 120 Pick-up arms 2 200 Swivel stack 1 A.sub.1 Lateral component of the circumferential 4 sealed area of the outer housing D.sub.P Internal diameter of upper spool 1 F.sub.H Horizontal force 4 F.sub.v1 Inward vertical force 4 F.sub.v2 Outward vertical force 4 H.sub.eff Effective height 5 P Pressure in annular groove 4, 5

(9) The invention is for a novel high pressure swivel where two of the novel swivels are illustrated in FIG. 1 stacked on top of each other. Two swivels, including upper swivel 10A and lower swivel 10B of swivel stack 200 are shown stacked on top of a fixed swivel base 100. Two swivels are shown for illustrative purposes in FIG. 1, but a single swivel could be provided or more inner housing bases may be provided to accommodate several swivels. As shown in FIG. 1, an upper swivel inner housing 16A, and a lower swivel inner housing 16B are secured by bolts 70 extending from the top of upper swivel 10A through lower swivel 10B, through swivel connector 52 and into base housing 54.

(10) The swivel base 100 is fixed to a substantially geostationary point (not shown) of an offshore mooring terminal. Fixed spools 56, arranged and designed to carry high pressure fluids, enter upper and lower swivel base inlets 58A, 58B of base housing 54. Of course other spools can be provided about the circumference of the base housing 54 to provide fluid communication to other swivels in a stack. An upper spool 60A provides fluid communication between base inlet 58A and upper inner housing inlet 26A of upper swivel 10A. Lower spool 60B provides fluid communication between base inlet 58B and lower inner housing inlet 26B of lower swivel 10B. Spools 60A, 60B are spaced about a longitudinal axis 5 of the stack of swivels.

(11) Upper swivel 10A is constructed with an upper swivel inner housing 16A having an upper swivel seal plate 17A attached to its top by means of threaded bolts 18A. Upper swivel outer housing 20A is rotatively carried on inner housing components 16A, 17A by means of upper swivel upper and lower bearings 21A, 22A and upper swivel radial bearing 23A.

(12) As illustrated in FIG. 1, the lower swivel 10B may be constructed similarly to upper swivel 10A, with the two swivel assemblies bolted together. Lower swivel 10B may be constructed much like upper swivel 10A with lower swivel upper and lower bearings 21B and 22B, and lower swivel radial bearing 23B, providing rotational support of the lower swivel outer housing 20B to the lower swivel inner housing 16B and a lower swivel seal plate 17B. As mentioned above, upper swivel 10A and lower swivel 10B are coupled together, and to the base housing 54, by threaded bolts 70. Although much of the following disclosure references upper swivel 10A and its parts, it is to be understood that the features and principles discussed apply equally to the lower swivel 10B. In addition, a swivel stack according to the present invention may have additional swivels, each sharing features and characteristics in common with those discussed herein.

(13) In the upper swivel 10A, a radial flow outlet 30A in the upper swivel outer housing 20A is radially aligned with an annular passage 30, which extends circumferentially about the upper swivel outer housing 20A. When upper swivel outer housing 20A turns about upper swivel inner housing members 16A/17A, annular passage 30 is always in fluid communication with the upper inner housing inlet 26A, which fluidly connects to spool 60A and base inlet 58A.

(14) FIG. 2 is a top view of the swivel stack of an embodiment of the present invention. Spools 60A, 60B positioned 180 degrees from each other. A single radial flow outlet 30A is illustrated for fluid communication with spool 60A, but multiple radial outlet passages can be provided about the outer housing. Pick-up arms 120 may be mounted to the top of the swivel stack assembly.

(15) FIG. 3 is a perspective view of the upper swivel 10A illustrating the upper swivel inner housing 16A and upper swivel seal plate 17A in registration with the upper swivel outer housing 20A and rotatively supported thereto by bearings 21A, and 22A, as well as lower radial bearing 23A. An upper radial bearing (not shown) can be provided corresponding to bearing 23A. Dynamic seal pairs 40, 42; 41, 43; 44, 46; 45, 47 provide sealing of the inner and outer housing in response to high pressure fluid in inner housing bore 26A and annular passage 30.

(16) FIG. 4 shows an enlarged partial cross section of the upper swivel 10A, including upper swivel inner housing components 16A and 17A, and upper swivel outer housing 20A rotatively supported by upper swivel upper and lower bearings 21A, 22A, and upper swivel radial bearing 23A. Static seals 98, 99 are positioned between inner housing 16A and seal plate 17A to prevent high pressure fluid in annular passage 30 from passing therebetween. Components 16A and 17A are static; they are bolted together and move together as one unit. A first set of upper and lower annular dynamic face seals 40, 41 are placed in first upper and lower annular seal recesses 61, 62. A backup secondary set of upper and lower annular dynamic face seals 42, 43 are placed in second upper and lower annular seal recesses 63, 64, which are of greater diameter than the first upper and lower annular seal recesses 61, 62.

(17) FIG. 4 further illustrates the forces on the upper swivel outer housing 20A caused by high fluid pressure in annular passage 30, as well as the space 105 between upper swivel inner components 16A, 17A and upper swivel outer housing 20A. FIG. 4 exaggerates space 105 to illustrate that high pressure acts behind dynamic seals 40 and 41, including over upper and lower shoulders 52A and 52B, to force dynamic seal 40 into face seal recess 61 and to force dynamic seal 41 into face seal recess 62. In other words, an inward vertical force F.sub.v1 is applied behind dynamic seals 40 and 41 toward the upper swivel outer housing 20A by virtue of the fluid pressure. The total inward force F.sub.v1 is equal to the fluid pressure P times the circumferential sealed area of the outer housing, the lateral component of which is identified as A.sub.1 in FIG. 4.

(18) The annular passage 30 is shaped so as to cause upper and lower ring portions 18, 19, which face opposite to the dynamic seals 40, 41, to deflect outward and spread apart under the force of pressure P in the annular passage 30. See the arrows labeled DEFLECTION DIRECTION of FIG. 4. These deflections partially compensate for any detrimental deflections of the upper swivel seal plate 17A above and the upper swivel inner housing 16A below.

(19) The outward deflections of upper and lower ring portions 18, 19 are caused by pressure P acting on the surfaces of annular passage 30. The circumferential area of the surfaces of the groove on which the pressure P acts, or circumferential groove area, is designed to be greater than the circumferential seal area discussed above. The outward vertical force F.sub.v2, which is generated by pressure P, acts to deflect the upper and lower ring portions 18, 19 in opposition to inward force F.sub.v1. The force F.sub.v2 is greater than F.sub.v1. The net force F.sub.v2 - F.sub.v1 deflects the upper ring portion 18 outward and upward and the lower ring portion 19 outward and downward. As a result, the clearances of the seal recesses 61, 63 and 62, 64 remain substantially constant with pressure increasing to very high levels.

(20) A horizontal force F.sub.H causes upper swivel outer housing 20A to deflect outwardly but has little effect on the clearances of the seal recesses 61, 63 and 62, 64.

(21) FIG. 5 is the same cross section of a portion of a swivel, but illustrates the shortened radial internal pressure height, or effective height H.sub.eff, on which fluid pressure in the swivel is acting. This tends to force upper swivel outer housing 20A outwardly from the upper swivel inner housing members 16A, 17A. The effective height H.sub.eff of the pressure area on which pressure P is acting is the height acting around the groove of the outer housing and upper and lower shoulders 52A and 52B. The area may be reduced by the placement of seals 40, 41 in a stair-step arrangement, bringing them as close together as practical. A reduction in the pressure area results in a reduction of the compressive load and stresses in the inner housing. Further, the reduced effective height H.sub.eff reduces the radial force applied to the upper swivel outer housing 20A so that its diameter and weight can be reduced, resulting in a lighter, smaller swivel.

(22) Additional Features

(23) The invention embodied in the swivel illustrated in FIGS. 1-5 is characterized by additional features, including:

(24) (1) The dynamic seals discussed above may include as primary seals an upper seal 40, a lower seal 41, a backup upper seal 42, and a backup lower seal 43 to seal between upper swivel inner housing components 16A, 17A and outer housing 20A. See FIGS. 4 and 5. A secondary seal system, including an upper secondary seal 44, a lower secondary seal 45, a backup secondary upper seal 46, and a backup secondary lower seal 47 may also be provided.

(25) (2) The static seals of FIGS. 4 and 5 may include a primary static seal 98 and a secondary static seal 99.

(26) Separate oil barrier systems may be provided on the primary dynamic seals 40, 42 and 41, 43 and on the secondary dynamic seals 44, 46, and 45, 47.

(27) (3) The upper dynamic seals 40, 42 and 44, 46, that radially surround the inner housing components 16A, 17A, may be of a slightly larger diameter than the corresponding opposing lower dynamic seals 41, 43 and 45, 46. Such larger diameter of the upper dynamic seals as compared to the lower dynamic seals produces a positive downward force that minimizes upper swivel outer housing 20A from floating upward and excessively forcing the seals vertically.

(28) (4) The radial groove annular passage 30 in the upper swivel outer housing 20A is wide and of short height, as illustrated in FIG. 4, with the height being about 50% to 60% of the internal diameter D.sub.p of the inner housing inlet (26A). As described above, the dynamic seals 40, 42; 41, 43; 44, 46; 45, 47 are preferably placed as close together as practical in a stair step arrangement. Such geometries contribute to the reduction of pressure height in the area acting on the upper swivel outer housing 20A. (See, e.g., effective height H.sub.eff in FIG. 5). With a predetermined internal pressure rating, that pressure acts on a smaller pressure area, resulting in a smaller radial force. As a consequence, the diameter and weight of the outer housing is reduced, compared to prior swivels of the same pressure rating. The shorter effective pressure height H.sub.eff area also reduces the compressive load and stresses in the upper swivel inner housing components 16A and 17A.