The present disclosure relates generally to riser tensioners for use on floating platforms and, more particularly, to an improved ram-style riser tensioner cylinder.
Various types of riser tensioners have been devised for use in the oil and gas industry. These tensioners help to maintain a desired tension on a riser extending between a subsea oil well and a surface (e.g., floating) drilling or production platform. Ram-style riser tensioners are often used to provide tension to risers used in spar and tension leg platform (TLP) applications. Ram-style riser tensioners may also be used as wireline tensioners in applications with marine drilling risers. Ram-style tensioners include hydro-pneumatic cylinders used to maintain a nearly constant tension on production risers or drilling risers as the floating platform moves in the ocean due to waves, current, and other factors.
In conventional ram-style tensioners, the cylinders typically include a cylinder barrel and a rod barrel that are able to slide, sweep, or stroke relative to one another to lengthen or compress the cylinder. Seals are placed between the barrels at their ends to prevent high pressure fluid from escaping the cylinder, to lubricate and enable the barrels to sweep relative to each other. The hydro-pneumatic cylinders are often filled with hydraulic fluid or oil to keep the seals lubricated, while compressed air or nitrogen is used as a gas spring to maintain tension in the riser. The cylinders are typically connected to an external gas accumulator, which is sized to provide a spring constant within a range that is conducive to the riser design.
Some applications for ram-style riser tensioners (e.g., spar and marine drilling riser applications) tend to produce long strokes on the cylinder compared to other applications (e.g., TLP applications). Thus, spar and marine drilling riser tensioners often utilize large sources of compressed air or nitrogen to maintain a sufficiently soft system during the long cylinder strokes. The swept volume in these cylinders can be quite large, often exceeding 200 gallons. Large volumes of hydraulic fluid are desirable for maintaining the seals on these long-stroking cylinders, since the fluid volume must have space to flow as the cylinder compresses. This fluid is generally contained within the cylinder and/or an accumulator, and large accumulators are often used to provide this volume of fluid. Unfortunately, large accumulators can take up a large amount of deck space and add undesirable weight to the cylinder assembly.
For a more complete understanding of the present disclosure and its features and advantages, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which:
Illustrative embodiments of the present disclosure are described in detail herein. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation specific decisions must be made to achieve developers'specific goals, such as compliance with system related and business related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of the present disclosure. Furthermore, in no way should the following examples be read to limit, or define, the scope of the disclosure.
Certain embodiments according to the present disclosure may be directed to an enhanced ram-style riser tensioner cylinder. In accordance with embodiments of the present disclosure, the tensioner cylinder includes an outer cylinder barrel and an inner rod barrel disposed within and extending in a first direction from the outer cylinder barrel. The cylinder also includes a high pressure seal disposed along a sliding interface between an end of the inner rod barrel and an inner wall of the outer cylinder barrel. In addition, the cylinder includes an end cap (e.g., top cap) coupled to an end of the inner rod barrel extending from the outer cylinder barrel, and a fluid reservoir disposed in the end cap. The fluid reservoir may be used to store and communicate fluid from the fluid reservoir to the high pressure seal for lubricating the high pressure seal.
The disclosed ram-style riser tensioner cylinder assembly is designed to store lubricating fluid within an end cap of the cylinder assembly, and to maintain a pressure of the fluid reservoir at approximately the same pressure as gas being stored in an internal accumulator of the cylinder. To accomplish this, some embodiments may include a piston that is open to the fluid reservoir on one side and to the pressurized gas of the internal accumulator on the opposite side. The piston may push the lubrication fluid from the reservoir through a fluid communication tube into the high pressure seal toward the bottom of the cylinder, in response to the cylinder being compressed. In other embodiments, the end cap may include a relatively small pressure communication port disposed between a port open to the pressurized gas and the fluid reservoir. Other arrangements may be utilized in other embodiments as well, as described in detail below. The disclosed cylinder assembly may provide an efficient use of space within the cylinder. In addition, the fluid reservoir may be readily accessible to operators, making it relatively easy to refill when the lubrication fluid store runs low.
Turning now to the drawings,
The tensioner 110 may include a plurality of gas accumulators to provide a desired amount of gas for maintaining a desired tension on the riser 114 as the cylinders 10 are stroked. As illustrated, the primary gas accumulators may be internal volumes 20 of gas within the cylinder barrel 12 and/or the rod barrel 14 of each cylinder 10. Each cylinder 10 may be maintained in a certain range of tensions by appropriately sizing the corresponding gas accumulator 20. This sizing of the accumulator 20 may be determined based on a desired stroke and stiffness for the cylinder 10.
In some embodiments, the amount of pressurized gas needed to maintain the tension in the riser 114 as the cylinder 10 strokes may exceed the volume available in the internal as volume 20 of the cylinder 10. Thus, the tensioner 110 may include an external accumulator 120 for each cylinder 10 that is manifolded to the appropriate cylinder 10 to provide the desired gas volume. An example of the external accumulator 120 and a corresponding manifold 122 for connecting the external accumulator 120 to the cylinder gas volume 20 are illustrated schematically in
The ram-style tensioner 110 is generally coupled to a floating platform (not shown) where drilling and production operations are performed. As the floating platform moves in response to waves, current, and other factors, the cylinders 10 of the tensioner 110 lengthen or compress while maintaining a desired tension on the riser 114. In some embodiments, the cylinders 10 may be mounted either directly into the hull of the floating platform, or to a structural frame 124 that mounts to the hull. As illustrated in
The presently disclosed embodiments are directed to an improved riser tensioner cylinder 10 that can be used, for example, in the above described ram-style riser tensioner 110.
As described above, the cylinder 10 generally includes the outer cylinder barrel 12 and the inner rod barrel 14 (or piston barrel). In the illustrated embodiment, the inner rod barrel 14 is disposed within and extending upward from the outer cylinder barrel 12. The cylinder 10 may be closed at opposing ends via end caps (e.g., bottom cap 16 and top cap 18). For example, the outer cylinder barrel 12 may be closed at one end with the bottom cap 16, as illustrated. Similarly, the rod barrel 14 may be closed at the opposite end from the cylinder barrel 12 with the top cap 18. It should be noted that, in other embodiments, the arrangement of the outer cylinder barrel 12 and the inner rod barrel 14 may be reversed such that the inner rod barrel 14 is disposed within and extending downward from the outer cylindrical barrel 12. In such a case, the inner rod barrel 14 would be closed off by the bottom cap 16, and the outer cylinder barrel 12 would be closed off by the top cap 18.
The cylinder barrel 12 and rod barrel 14 are designed to slide relative to one another in response to changes in movement of a component (e.g., floating platform/structural frame 124 of
The cylinder 10 may also include a cylinder flange 24 that attaches to an open end 26 (e.g., top end) of the cylinder barrel 12. The cylinder flange 24 may include a low pressure dynamic sealing arrangement 28 to close an annulus 30 between the cylinder barrel 12 and the rod barrel 14. A high pressure seal arrangement 32 is generally located near an open end 34 (e.g., bottom end) of the rod barrel 14 to separate high pressure and low pressure circuits. The “high pressure” circuit may refer to the internal volume 20 within the cylinder 10 along with the external gas accumulator (120), and the “low pressure” circuit may refer to the annulus 30 between the cylinder barrel 12 and the rod barrel 14 along with an external low pressure accumulator (not shown). The high pressure seals 32 may be installed either directly into the rod barrel 14 (
The presently disclosed cylinder assembly 10 includes a fluid reservoir 38 for holding lubricating fluid, and this fluid reservoir 38 may be disposed in an end cap of the cylinder 10. For example, as shown, the fluid reservoir 38 may be disposed in the top cap 18. In other embodiments, the fluid reservoir 38 may be disposed in the bottom cap 16. The reservoir 38 is used to maintain lubrication to the high pressure seals 32 between the cylinder barrel 12 and the rod barrel 14.
In some embodiments, the cylinder 10 may include a piston 46 internal to the top cap 18, with lubrication fluid being on one side 48 of the piston and pressurized gas on the opposite side 50. This may help to maintain the fluid and the gas at approximately the same pressure. Such embodiments are illustrated in
In
In
In other embodiments, the cylinder 10 may not include a piston for pushing fluid into the fluid communication tube 42. Instead, as shown in
The pressure communication tube 64 may include a much smaller tube (relative to the port 22) disposed between the port 22 and an upper surface of the reservoir 38 to maintain a desired pressure in the reservoir 38. As the pressure from the pressure communication tube 64 increases due to compression of the cylinder 10, the increased pressure in the reservoir 38 may force the fluid into the fluid communication tube 42 and toward the high pressure seal arrangement 32 to lubricate the seal 32 being moved along the outer cylinder barrel 12.
By disposing the fluid reservoir 38 in the top cap of the cylinder 10, present embodiments may enable a relatively efficient use of space within the cylinder 10. The disclosed cylinders 10 may utilize relatively less lubricating fluid to maintain proper lubrication of the high pressure seal arrangement 32, compared to existing systems that fill an annulus between the barrels with fluid. By using a smaller volume for the fluid reservoir 38, the disclosed cylinder 10 may provide an increased volume 20 available for the internal accumulator. In addition, by storing the fluid in a reservoir 38 in the top cap 18, present embodiments may provide easier and more direct access to the reservoir 38 than would be available in designs having a reservoir positioned lower in the cylinder.
Although the present disclosure and its advantages have been described in detail, it should be understood that changes, substitutions and alterations can be made herein without departing from the spirit and scope of the disclosure as defined by the following claims.
The present application is a non-provisional patent application of U.S. provisional application Ser. No. 62/082,989, entitled “Enhanced Ram-Style Riser Tensioner Cylinder”, filed on Nov. 21, 2014.
Number | Date | Country | |
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62082989 | Nov 2014 | US |