Pipe joints or couplings – Having plural independent paths – Allowing relative motion of pipes
Reexamination Certificate
1999-10-07
2002-03-12
Dayoan, B. (Department: 3627)
Pipe joints or couplings
Having plural independent paths
Allowing relative motion of pipes
C285S121400, C285S121500, C285S121600, C285S272000, C285S190000
Reexamination Certificate
active
06354633
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a high pressure swivel comprising an inner annular wall and an outer annular wall concentric with said inner wall and rotatable relative to said inner wall. Each annular wall has an outer surface and an inner surface and comprises an aperture extending in a radial direction from the inner surface towards the outer surface. The apertures in the walls are in mutual fluid communication, the inner surfaces of the walls facing each other in close proximity and defining an annular gap extending in an axial direction on each side of the apertures. At least one flexible sealing element is comprised in the annular gap on each side of the aperture in each annular wall. The apertures are respectively in fluid communication with a fluid inlet or is a fluid outlet.
BACKGROUND OF THE INVENTION
Such high pressure swivels are known from EP-B-0013454 and EP-B-0013455. For the purpose of the present invention the term “high pressure” is intended to include pressures of about 50 bar and higher. In the known high pressure swivels, a toroidal chamber is defined between the inner, stationary annular wall, or ring, of the swivel and the outer annular wall or ring. In the following description the terms “annular walls” and “rings” will be used in an interchangeable manner. Conduits which convey high pressure hydrocarbons such as oil or gas at pressures of between 100 and 300 bar, extend through the central space of the inner, stationary ring. Through the inlets of the inner ring, the conduits connect to the toroidal chamber. The rotating outer ring that defines one half of the toroidal chamber, comprising one or more outlets that are connected to said toroidal chamber. On either side of the toroidal chamber of the known swivels, the sealing elements are located in the annular gap, also called the “seal extrusion gap”.
The sealing of swivels handling liquids or crude oils with limited gas content is achieved with a double sealing arrangement on either side of the toroidal chamber. The so-called primary seals are positioned closest to the toroidal chamber and carry the full pressure, while the secondary seals are positioned behind the primary seals to back-up the primary sealing function in an event of primary seal rupture.
The sealing of gas or crude with high gas content is more difficult due to the low viscosity of the gas and the danger of fire and explosions in case of leakage. Therefore, for such an application a different sealing concept is used. The primary seals are replaced by two pairs of seals facing each other. Within these two pairs of seals, a barrier of liquid is maintained at a higher pressure than the gas to be sealed, such that an absolute gas tightness is achieved. Leakages of seals in this configuration will only result in internal leakages of the barrier liquid to the gas line or to a leak recuperation tank.
Defects in the known swivels occur when the width of the annular gap in which the seals are located exceeds a certain level such that the seals are extruded from the annular gap by the high pressure acting upon them. The design of the known swivels has concentrated on minimizing the seal extrusion gap opening. On the other hand, a minimum gap width must be maintained such that deflections of the inner and outer rings of the swivel will not cause the two parts to contact one another and do thus prevent rotation. In order to minimize the deformations of the inner and outer ring due to pressure effects, the known rings are made of cast steel, with a wall thickness of about 240 mm for a 2 m diameter swivel. Deformations are prevented by the heavy masses of the inner and outer rings. A single swivel of a seal diameter of 1980 milimeters suitable for operating at pressures of 100 bar may weigh 20 tons or more.
Not only should the deformations of the inner and outer rings be minimized, but known swivels are also designed in such a way that stresses remain within the limits which are imposed by the Pressure Vessel Codes. The known swivel units are often stacked one on top of the other. The hydrocarbons supplied to the swivels often have temperatures between 20 and 120° C. During transfer of these fluids, the outer ring of the swivel is cooled by the external ambient air, whereas the inner ring remains relatively hot. This is especially so when the swivel is exposed to outside weather conditions and when a wind blows against a swivel stack. The temperature difference between the concentric rings of the swivel generates deformations of the extrusion gap as the inner ring expands more than the outer ring. To avoid contact between the rotating parts of the swivel due to temperature fluctuations, when a pressure drop occurs, the initial extrusion gap should be wide enough to accommodate these temperature deformations. The width of the initial extrusion gap that is required to accommodate the thermal deformations reduces the allowable deformations due to pressurization.
In order to minimize the variations in the extrusion gap dimensions due to temperature effects, the outer ring of the swivel is often insulated by a suitable insulating material such as rubber. These insulations often cause problems as the design of the swivel stack becomes more complicated and inspection of the swivel unit becomes difficult.
Finally, to further increase the stiffness of the inner and outer rings in the areas of the inlets and outlets, reinforcements are attached to the inner and outer rings around the inlets and outlets of the known swivels. These reinforcements again add to the weight of the swivel.
It is therefore an object of the present invention to provide a high pressure swivel which is relatively insensitive to pressure variations and which can transfer high pressure fluids while using a relatively light weight construction.
It is a further object of the present invention to provide a swivel for transferring high pressure fluids, in which temperature fluctuations of the inner and outer ring are reduced.
It is a further object of the present invention to provide a swivel which can be combined with other swivels of similar shape in a number of different configurations.
It is again an object of the present invention to provide a swivel which is of a relatively small size, which is of a simple construction, which is relatively maintenance free and which can be easily manufactured at relatively low cost.
SUMMARY OF THE INVENTION
Thereto the swivel according to the present invention is characterized in that the apertures in the inner and the outer annular walls are connected to the fluid inlet or the fluid outlet via a respective first and second distribution member, the apertures having a smaller axial dimension than the diameter of the fluid inlet and/or the fluid outlet.
Because the axial dimension of each aperture in the inner and outer ring is significantly reduced compared to the dimensions of the fluid inlet and the fluid outlet, the pressure area between the sealing elements, on which the forces act that tend to separate the inner and the outer rings, is also significantly decreased in size. In this way a very small size and light weight swivel can be constructed. The invention is based on the principle of connecting two relatively big pressure vessels, formed by the inlet and the outlet, via the distribution members, to a rotatable connecting element (inner and outer annular walls) of reduced pressure area. Thereby, the forces on the connecting element remain limited and this element can consequently be constructed with reduced dimensions. The distribution members may be formed by a plurality of individual conduits, by distribution chambers or by a combination thereof.
In one embodiment, the apertures have a smaller axial dimension than the axial dimension of the distribution members. In this way, fluids are passed to the relatively large size distribution members for distribution of the fluids towards or away from the apertures along the circumference of the inner and outer rings.
In another embodiment of a swivel according to the present invention
Dayoan B.
Lugo Carlos
Single Buoy Moorings INC
Young & Thompson
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