Sealing arrangement

Details Sealing arrangement Sealing arrangement

1999-11-15

2001-05-22

Knight, Anthony (Department: 3626)

Pipe joints or couplings

With fluid pressure seal

Swivel with flange in socket

C285S121100, C285S121500, C403S078000, C277S558000, C277S572000

Reexamination Certificate

active

06234540

ABSTRACT:

The invention relates to a sealing arrangement, in particular for use in fluid swivels, which are used in offshore installations to transfer fluids between fixed underwater pipe lines and floating vessels which may weathervane around earth-fixed installations. The sealing arrangement according to the invention, makes it possible to pressurize the fluid to be sealed to a relatively high pressure between the two swivel members without extrusion of the seals and at pressures fluctuating from ambient to a relatively high pressure without crazing or cracking of the seals.
BACKGROUND OF THE INVENTION
Sealing arrangements are used in fluid swivels. Such fluid swivels are used in offshore installations to transfer fluids between fixed underwater pipe lines and floating vessels which may weathervane around earth-fixed installations. Fluids can be withdrawn from a well head or can be introduced or can be loaded/offloaded or used for power and control of equipment.
A typical fluid swivel includes at least two swivel members comprising ring-shaped inner and outer walls forming an annular chamber between them and forming cylindrical clearances at each side of the chamber between the fixed and rotating wall members. Several circular grooves are provided in the cylindrical clearances to hold an arrangement of piston or rod seals at each side of the fluid chamber.
In order to transfer a large number of separate fluid lines of small to large pipe diameter sizes, several swivel modules are assembled together in a stack. The lowest swivel path of a swivel assembly requires a relatively large sealing diameter to provide sufficient space in the centre of its inner ring to guide the entry piping of the above situated swivels. This sealing diameter of the lowest swivel path increases with the total fluid throughput of a complete swivel assembly.
The first point at which problems occur during increasing of the pressure is at the sealing of the clearance between the two swivel members. The seal grooves and the clearances widen as the fluid pressure increases, because the inner and outer walls of the swivel are driven apart by the fluid pressure. The growth of seal groove widths and the clearances may lead to the allowable extrusion gap size of the seals being exceeded and consequently result in extrusion of the seal in the extrusion gap and/or in cracking of the seals.
It is possible to address the extrusion problem by decreasing the initial clearance between the two members in the none-pressurized condition and by making the inner and outer swivel rings sufficiently rigid. However, this will result in a risk of interference during differential temperatures of the inner and outer parts, a sharp increase of material costs because the stiffening results in very massive swivels, which jeopardises the feasibility particularly when a large sealing diameter is required.
From U.S. Pat. No. 4,828,292 and U.S. Pat. No. 4,925,219 a sealing assembly is known wherein face seals are used. Face seals engage to opposite surfaces being parallel to the direction of displacement of the two swivel members and a surface of one of the swivel members, said surface being parallel to the axis, so that the face seals are oriented between flat surfaces rather than cylindrical surfaces as piston or rod seals. The axial distance between the sealing surfaces remains essentially constant despite any radial deflection of the inner and outer swivel part caused by increase or decrease of fluid pressure, so that the extrusion gaps of the face seals are hardly affected by the fluid pressure. For this reason, swivel designs using these face seals do not require large wall section thicknesses to limit the radial deflections and can, therefore, be designed for strength rather than for stiffness.
Swivels based on face seals, however, require several inner and outer rings to create the grooves for their seals. These rings and the swivel bearing are to be machined with very high axial tolerances to limit the initial seal gap tolerances as result of the accumulated machining tolerances. The large number of swivel rings and the high machining tolerances result in high fabrication costs.
SUMMARY OF THE INVENTION
The invention aims to provide a sealing arrangement for two adjacent members being displaceable with regard to each other, such as a swivel. It must be possible to pressurize the fluid to be sealed to a relatively high pressure between the two swivel members without extrusion of the seals and at pressures fluctuating from ambient to a relatively high pressure of 2000 psi or more without crazing or cracking of the seals.
According to the present invention a sealing arrangement is provided between an inner member and a outer member of the swivel. The members are adjacent and can be rotated with respect to one and another around a common central axis. The members define between them at least one circumferentially extending torroidal fluid cavity which is in communication with fluid lines through inner and outer members respectively. A circumferential gap between the inner and outer member is in communication with the fluid cavity and has two gap sections each located at a different distance from the central axis. An intermediate gap section connects the first and second gap sections and extends in a generally radial direction. The sealing means are located in the groove of the inner and/or outer member and bridge the gap section to seal the cavity. The improvement is that the inner and the outer member in the area of the circumferential gap each comprise a radially extending arm. The arms overlap both in the axial and in the radial direction and define the intermediate gap section there between. The intermediate gap section at least partly extends in the axial direction at is bridged by the sealing means such that widening of the upstream part of the gap by pressure in the cavity reduces the width of the intermediate gap section and increases the pressure on the sealing means.
According to a further aspect of the invention the circumferentially extending space or gap for the sealing means has an additional space upstream of the sealing means between sealing means and cavity, within which a double sealing means assembly has been provided of the type with U-shaped means spaced apart from each other and with in between a space connected to a source of pressure via a bore, wherein the space of the gap between the sealing means and the double sealing means assembly might be connected as well to a pressure source via a bore. The increased pressure on the double sealing means provides for improved gas tightness, a clean environment (i.e. without hydrocarbons being present), lubrication and hence contributes to an increase seal life.
According to a further aspect of the invention each arm of the sealing arrangement comprises an axially extending free leg. The sealing means can be placed at least partly between said legs. To provide the improved sealing, two sealing means may be present on each side of at least one leg such that a primary seal and a secondary seal are formed. The free legs may have a stepped surface such that recesses or cavities are formed wherein the sealing means can be positioned.
The opposing surfaces of the arms need not extend completely in the axial direction, but each arm may alternatively comprise a substantially wedge-shaped portion having a slanting surface, the intermediate gap section being formed between the slanting surfaces of the arms. By increasing or decreasing the angle of the slanting surfaces, the amount by which the gap section is closed upon pressure variations in the fluid can be adjusted.
The legs of the substantially L-shaped extension can enclose an angle of substantially 90° or an angle substantially less than 90°. The sealing means can comprise a rod seal, piston seal, face seal or conical seal or a combination of them.


REFERENCES:
patent: 3279806 (1966-10-01), Bialkowski
patent: 4555118 (1985-11-01), Saliger
patent: 4602806 (1986-07-01), Saliger
patent: 4626003 (1986-12-01), Williams et al.
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