Patent Application
20080048443
By way of illustration and not limitation, the invention is described in detail hereinafter on the basis of the embodiments represented in the accompanying figures, in which:
The preferred embodiment of the invention is a bore seal which alleviates one or more of the deficiencies described in the prior art and incorporates one or more of the objects previously identified. The bore seal of the present invention is a compression ring disposed and compressed between the opposing ends of the oil and gas well tubular members to be joined. The bore seal of the preferred embodiment has an internal diameter/shape arranged and designed to match the bores of tubular members and equipment to be joined and sealed, including commercially available profiles, such as AX, CX, DX, LX, NX, VX, etc. The ring is about four inches long (measured in its axial direction) and is machined externally to provide two conical faces tapering towards each end at about a twenty-three degree angle to the axis. The ends of the connecting components are machined to open outwardly in order to provide tapering conical seats for the ring at the same angle but with a slightly smaller diameter. Seating of the ring requires bringing the opposing tubular members and the bore seal together with considerable force. This is achieved using one of three methods: (1) hydraulic actuators in one of the opposing components, (2) stud bolts and flanges, or (3) hubs and clamps.
In a preferred embodiment, the bore seal has a metal core constructed from a high yield strength ferrous material including, but not limited to, low alloy steels and martensitic stainless steel. These materials are in the range of yield strength up to a maximum of 180,000 lbf/in2 at room temperature and have outstanding strength retention at temperatures up to 450° F. However, the hardness level of the metal core which accompanies the high strength of the steel precludes its use in direct contact with corrosive well fluids. The bore seal metal core is therefore protected by a layer of stainless steel or nickel-based corrosion resistant alloy which provides a hardness limit specified by NACE International for sour well service. The stainless steel or nickel-based corrosion resistant alloy is applied to the outer surface of the bore seal metal core using a metal thermal spraying process.
The metal thermal spraying process generally uses a thermal spraying device, or gun, to heat the coating metal into a molten or semi-molten state. Compressed gas then atomizes and deposits the molten, atomized metal onto the surface to be coated at a high velocity to form a dense adherent coating of any desired thickness. The molten, atomized metal is uniformly deposited as rapidly quenched splats, which are single sprayed particles that, under magnification, resemble thin, flattened drops of liquid. The coating is formed on the sprayed surface through the aggregation of these splats. Thus, the microstructure of a thermal spray coating differs from the microstructure of coatings produced by other methods, such as dipping/immersion, brush painting, etc.
Three different types of thermal spraying devices—plasma, combustion-flame, and two-wire electric arc—are employed for melting and depositing the molten, atomized metal coating onto the surface to be coated. The plasma thermal spraying gun uses a plasma flame, wherein the plasma gas (generally, argon or other inert gas) is elevated to temperatures well above its ordinary gaseous state by an electric arc or other heat source. Typically, the coating metal is fed through the plasma gun as a powder, melted by the plasma flame, and blown onto the surface to be coated at a high velocity (usually greater than 200 meters/second) to form a highly dense adherent coating. The plasma thermal spraying gun is the most versatile thermal spraying device because virtually any metal or metal alloy can be melted and applied to a surface to be coated.
The combustion-flame thermal spraying gun, which uses an oxyacetylene-generated flame to melt a metal powder or wire, is easier to operate than the plasma thermal spraying gun. Unlike the plasma flame, however, the oxyacetylene flame has a much lower temperature which causes the molten metal powder or wire to be deposited onto the surface to be coated at a lower velocity and with lower density. But, the recent development and use of a high velocity oxygen fuel (HVOF) gun makes the combustion-flame thermal spraying techniques equal to or better than the plasma thermal spraying technique with respect to the final coating properties. Like the plasma thermal spraying gun, the HVOF gun causes the molten coating metal to be deposited onto the surface to be coated at high velocity to form a highly dense and adherent coating. This is achieved using specially-sized metal powder particles and a specially-designed gun nozzle which creates hypersonic flame gas velocities.
The two-wire electric arc technique is the least expensive metal thermal spraying process. In this technique, an electric current is passed through two metal wires to generate an electric arc at the point where the two wires intersect. The electric arc melts the ends of the metal wire and compressed air then blows the atomized metal through the nozzle of the spray gun onto the surface to be coated.
In the metal thermal spray process, the molten metal solidifies quickly on the applied surface by dissipating heat via conduction through the underlying surface. An advantage of the metal thermal spray process over traditional welding techniques is that the temperature of the bore seal core metal does not generally exceed 200° F. when the overlay coating material is applied to the core metal surface. Thus, the metal thermal spray process mitigates thermal degradation and/or thermal stress of the underlying bore seal metal core.
The metal thermal spray process, as briefly disclosed above, is well known in the art and therefore will not be further discussed herein.
A preferred embodiment of the invention is shown in
The basis for the bore seal's 10 external pressure rating is the minimum value of its resistance when unaided by internal pressure 34 within the connection 30 (i.e. the resistance provided solely by the seat/seal interference). The resistance to external pressure 32 is related to the compressive hoop stress developed in the seal 10 by the seat/seal interference. To ensure reliability of its rated resistance, the seal 10 is designed such that the minimum seat/seal interference does not deteriorate due to variations in the bore diameter from operational fluctuations of temperature and pressure. The nominal seat/seal interference is set so that the seal's 10 preload stress at minimum seat/seal interference produces the desired external pressure resistance consistent with a stress at maximum seat/seal interference that is below the material's yield stress at the maximum design temperature. The arrangement of interferences and stresses thus developed avoids permanent strain in the seal 10 which would reduce the minimum interference, and as a consequence, its external pressure rating.
The service limits for the embodiment shown in
In a preferred alternative embodiment of the invention, as shown in
The alternative embodiments of the invention, illustrated in
The abstract of the disclosure is written solely for providing the United States Patent and Trademark Office and the public at large with a description to determine quickly from a cursory inspection the nature and gist of the technical disclosure, and it represents solely a preferred embodiment and is not indicative of the nature of the invention as a whole.
While the preferred embodiment of the invention has been illustrated in detail, it is apparent that modifications and adaptations of the preferred embodiment will occur to those skilled in the art. Such modifications and adaptations are in the spirit and scope of the invention as set forth in the following claims:
| Number | Date | Country | Kind |
|---|---|---|---|
| 0610786.6 | Jun 2006 | GB | national |
