Patent Abstract:
Certain types of riser tensioner arrangements include a high-pressure accumulator; a pusher-type hydraulic cylinder; a first flow path coupling the high-pressure accumulator with a first volume of the cylinder to enable a first high-pressure fluid to flow therebetween; and a second flow path coupling the high-pressure accumulator with a second volume of the cylinder to enable a second high-pressure fluid to flow therebetween. The piston includes a seat and a hollow extension that defines part of the second volume of the cylinder.

Full Description:
This application is a National Stage Application of PCT/US2012/033317, filed 12 Apr. 2012, and which application is incorporated herein by reference. To the extent appropriate, a claim of priority is made to the above disclosed application. 
     BACKGROUND 
     Offshore oil drilling and production operations are conducted through a pipe, called a riser, running from a subsea wellhead to a surface platform or floating vessel. In order to support the weight of these risers and to control the stresses induced by ocean currents and vessel motions, the upper end of the riser is connected to a tensioning device. This riser tensioner maintains a predetermined range of tension throughout a range of vertical and lateral motions of the drilling or production rig. 
     The conventional approach to tensioning risers is to use a combination of a hydraulic or pneumatic mechanical cylinder, pressurized using a compressed gas, to apply the tensioning forces to the riser. Each riser tensioner is located on a deck of the floating platform or floating vessel and is structurally connected through its cylinders to the riser. The cylinders may be connected to the risers with wire rope or chain or directly connected through cylinder rods. The pressurized gas volume is typically contained in a separate pressure vessel referred to as an “accumulator”, positioned alongside the cylinder, which supplies sufficient gas volume to act as a gas spring. This combination of cylinder and accumulator acts to compress or expand the gas in response to vessel or riser movements, thereby maintaining a relatively uniform tension level in the riser. 
     For example,  FIG. 1  illustrates a conventional wire riser tensioner system  100  including a double-acting hydraulic cylinder  110 , a high-pressure accumulator  130 , and a low-pressure accumulator  140 . A piston  120  is disposed within an interior of the hydraulic cylinder  110  and configured to slide along an axial direction therein. The piston  120  includes a piston seat  122  and a piston extension  124 . The piston seat  122  divides the interior of the cylinder  110  into a first variable-volume section  112  and a second variable-volume section  114 . The volumes of the sections  112 ,  114  vary based on the position of the piston seat  122  within the cylinder  110 . The piston extension  124  extends upwardly through the second section  114  of the cylinder  110 . In certain implementations, the piston extension  124  may be hollow to reduce the weight of the piston  120 . 
     A first sealing arrangement  127  is disposed at the piston seat  122  of the piston  120  to provide a seal between the first and section sections  112 ,  114  of the cylinder  110 . A second sealing arrangement  129  is disposed between the piston extension  124  and an exterior of the cylinder  110  to seal the interior of the cylinder  110  as the piston  120  is slid therein. The second sealing arrangement  129  is located at an opposite end of the piston  120  from the first sealing arrangement  127 . 
     The high-pressure accumulator  130  defines an interior  132  in which a first high pressure fluid (e.g., oil) may be stored. The high-pressure accumulator  130  is coupled to the cylinder  110  via a first flow path  150 . The first flow path  150  provides a fluid pathway between the high-pressure accumulator  130  and the first variable volume section  112  of the cylinder  110 . In certain implementations, the first flow path  150  extends between a bottom of the high-pressure accumulator  130  and a bottom of the cylinder  110 . In certain implementations, a valve (e.g., an anti-recoil valve, a flow shut-off valve, etc.)  155  is disposed in the first flow path  150 . 
     The high-pressure accumulator  130  also is configured to hold a second high-pressure fluid (e.g., compressed air, compressed nitrogen, or other gas). One or more air pressure vessels (APV&#39;s)  170  may be coupled to the high-pressure accumulator  130  via piping  175 . Each APV  170  provides additional volume in which to store the second high-pressure fluid. In certain implementations, the APVs  170  are coupled to the high-pressure accumulator  130  using a ball-valve  172  or other valve arrangement. Providing additional volume in which the second high-pressure fluid may be contained aids in stabilizing the pressure of the second high-pressure fluid across the system  100 . 
     The low-pressure accumulator  140  defines an interior  142  in which a low-pressure fluid (e.g., a lubricant) may be stored. The low-pressure accumulator  140  is coupled to the cylinder  110  via a second flow path  160 . The second flow path  160  provides a fluid pathway between the low-pressure accumulator  140  and the second variable volume section  114  of the cylinder  110 . For example, the second flow path  160  provides a fluid pathway between the low-pressure accumulator  140  and an annulus area around the piston extension  124 . In certain implementations, the second flow path  160  extends between a top of the low-pressure accumulator  140  and a top of the cylinder  110 . The low-pressure accumulator  140  is isolated from the high-pressure accumulator  130 . 
     Accordingly, as the piston  120  is moved within the cylinder  110 , the first high-pressure fluid is moved between the high-pressure accumulator  130  and the first variable-volume section  112  of the cylinder  110  through the first flow path  150 . In addition, the low-pressure fluid is moved between the low-pressure accumulator  140  and the second variable volume section  114  of the cylinder  110  through the second flow path  160  as the piston  120  moves in the cylinder  110 . 
     SUMMARY 
     Aspects of the present disclosure relate to a riser tensioner arrangement including a high-pressure accumulator; a cylinder; a piston slidingly disposed within an interior volume of the cylinder; a first flow path coupling an interior volume of the high-pressure accumulator with a first volume of the cylinder to enable a first high-pressure fluid to flow therebetween; and a second flow path coupling the interior volume of the high-pressure accumulator with a second volume of the cylinder to enable a second high-pressure fluid to flow therebetween. The piston includes a seat and an extension. The piston seat separates the interior volume of the cylinder into the first volume and the second volume. The extension extends upwardly from the seat through the second volume. The extension defines a hollow interior that is coupled to the second volume of the cylinder via at least one aperture. 
     Other aspects of the present disclosure related to a method of manufacturing a riser tensioner including a high-pressure accumulator and a pusher-type cylinder. The method includes hollowing an interior of a piston-rod to provide an interior volume; defining at least one aperture through a sidewall of the piston-rod to provide access to the interior volume of the piston-rod; and positioning the piston-rod within a cylinder to separate an interior volume of the cylinder into first and second variable-volume sections. The second variable-volume section includes the hollow interior of the piston-rod and a volume of an annulus area around the piston-rod. In certain implementations, the method also may include coupling a first end of the high-pressure accumulator to the first variable-volume section of the cylinder via a first flow path; and coupling a second end of the high-pressure accumulator to the second variable-volume section of the cylinder via a second flow path. 
     A variety of additional aspects will be set forth in the description that follows. These aspects can relate to individual features and to combinations of features. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the broad concepts upon which the embodiments disclosed herein are based. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of the description, illustrate several aspects of the present disclosure. A brief description of the drawings is as follows: 
         FIG. 1  is a schematic diagram of a conventional riser tensioner system; 
         FIG. 2  is a schematic diagram of an example riser tensioner system including a hydraulic cylinder having a piston defining a hollow space accessible through apertures defined in a sidewall of the piston; 
         FIG. 3  is a schematic diagram of the example riser tensioner system of  FIG. 2  showing the piston moved to a second position; and 
         FIG. 4  is a diagram of another example riser tensioner system having features that are examples of inventive aspects of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the exemplary aspects of the present disclosure that are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like structure. 
       FIG. 2  illustrates an example riser tensioner system  200  including a hydraulic cylinder  210  and a high-pressure accumulator  230 . The riser tensioner system  200  does not include a low-pressure accumulator. A piston  220  is disposed within an interior of the hydraulic cylinder  210  and is configured to slide along an axial direction A therein. The piston  220  includes a piston seat  222  and a piston extension  224 . The piston seat  222  divides the interior of the cylinder  210  into a first variable-volume section  212  and a second variable-volume section  214 . The volumes of the sections  212 ,  214  vary based on the position of the piston seat  222  within the cylinder  210 . 
     The piston extension  224  includes a sidewall  226  that extends upwardly from the piston seat  222  through the cylinder  210  to define an annular region  223  around the sidewall  226 . As the piston  220  slides within the cylinder  210 , the annular region  223  around the piston extension  224  grows and shrinks (e.g., compare  FIGS. 2 and 3 ). The piston sidewall  226  defines a hollow interior  225  that is accessible from the annular region  223  through one or more apertures  228  defined in the sidewall  226 . Accordingly, the second variable-volume section  214  of the cylinder  210  is defined by the annular region  223  around the piston extension  224  and the hollow interior  225  of the piston extension  224 . 
     The one or more apertures  228  are disposed in the sidewall  226  above the piston seat  222 . In certain implementations, multiple apertures  228  are circumferentially spaced in a ring around the piston extension  224 . In certain implementations, the apertures  228  are disposed in a ring disposed directly above the piston seat  222 . In certain implementations, the apertures  228  include a single row of circumferentially spaced apertures  228 . In other implementations, additional rings of apertures  228  may be provided. 
     A first sealing arrangement  227  is disposed at the piston seat  222  of the piston  220  to provide a seal between the first and second variable-volume sections  212 ,  214  of the cylinder  210 . The first sealing arrangement  227  is configured to slide with the piston seat  222  along an inner wall of the cylinder  210 . A second sealing arrangement  229  is disposed between the sidewall  226  of the piston extension  224  and an exterior of the cylinder  210  to seal the interior of the cylinder  210  as the piston  220  is slid therethrough. The second sealing arrangement  229  is located at an opposite end of the piston  220  from the first sealing arrangement  227 . Each sealing arrangement  227 ,  229  may include one or more O-rings or other sealing structures. 
     To aid in lubricating the first sealing arrangement  227  of the piston  220  when the piston  220  slides within the cylinder  210 , a lubricant bath  290  may be supplied in the second variable-volume section  214  of the cylinder  210 . The lubricant bath  290  includes a volume of lubricant disposed on the piston seat  222  to provide lubrication to the first sealing arrangement  227  as the piston  220  slides within the cylinder  210 . In certain implementations, the lubricant bath  290  only partially fills the cylinder  210 . In certain implementations, the lubricant bath  290  has a volume that is substantially smaller than the second variable-volume section  214  of the cylinder  210 . In the example shown, the lubricant bath  290  has a height H 2  that is less than a height H 1  of the apertures  228  extending through the sidewall  226  of the piston  220  (see  FIG. 2 ). 
     In some implementations, a lubrication tank  295  is coupled to the cylinder  210  to provide lubricant to the second sealing arrangement  229  of the piston  220 . In certain implementations, the lubrication tank  295  is isolated from the second variable-volume section  214  of the cylinder  210 . The lubrication tank  295  is substantially smaller than the low pressure accumulator  140  of  FIG. 1 . In certain implementations, the lubrication tank  295  is substantially smaller than the second variable-volume section  214  of the cylinder  210 . In the example shown, the lubrication tank  295  is substantially smaller than annular region  223  extending between the sidewalls  226  of the piston  220  and the inner surface of the cylinder  210 . 
     A first high pressure fluid (e.g., a non-compressible fluid such as oil or other liquid) may flow between the first variable-volume section  212  of the cylinder  210  and an interior  232  of the high-pressure accumulator  230 . In certain implementations, the high-pressure accumulator  230  is coupled to the cylinder  210  via a first flow path  250 . The first flow path  250  provides a fluid pathway between the interior  232  of the high-pressure accumulator  230  and the first variable-volume section  212  of the cylinder  210 . In certain implementations, the first flow path  250  extends between a bottom of the high-pressure accumulator  230  and a bottom of the cylinder  210 . In certain implementations, a valve (e.g., an anti-recoil valve)  255  is disposed in the first flow path  250  to control fluid flow between the cylinder  210  and the accumulator  230 . 
     The high-pressure accumulator  230  also is configured to hold a second high-pressure fluid (e.g., a compressible fluid such as compressed air, compressed nitrogen, or other gas). The second high-pressure fluid acts as a spring (e.g., via compression and decompression) against the first high-pressure fluid. A second flow path  280  extends between the high-pressure accumulator  230  and the cylinder  210  for passage of the second high-pressure fluid therebetween. In particular, the second flow path  280  provides a fluid pathway between the high-pressure accumulator  230  and the second variable volume section  214  of the cylinder  210 . In certain implementations, the second flow path  280  extends between a location towards a top of the high-pressure accumulator  230  and a location towards a top of the cylinder  210 . 
     One or more air pressure vessels (APV&#39;s)  270  may be coupled to the high-pressure accumulator  230  via piping  275 . Each APV  270  provides additional volume in which to store the second high-pressure fluid. In certain implementations, the APVs  270  are coupled to the high-pressure accumulator  230  using a ball-valve  272  or other valve arrangement. The extra volume gained from the piston extension interior  225  and annulus space around the piston extension  224  of the cylinder  210  increases the total gas capacity of the system without enlarging the volume of the high-pressure accumulator  230  or adding additional APV&#39;s  270 . In certain implementations, the number of APV&#39;s  270  utilized in a system may be reduced, thereby reducing cost and the spatial footprint of the system. In the example shown in  FIG. 2 , the riser tensioner system  200  includes fewer APV&#39;s  270  than the conventional riser tensioner system  100  of  FIG. 1 . 
       FIG. 3  illustrates example fluid flow of the first high-pressure fluid along the first flow path  250  between the accumulator  230  and the cylinder  210 .  FIG. 3  also illustrates example fluid flow of the second high-pressure fluid along the second flow path  280  between the accumulator  230  and the cylinder  210 . As the piston  220  slides upwardly along the axis A, the first high-pressure fluid stored in the accumulator  230  flows into the first variable-volume section  212  of the cylinder  210  through the first flow path  250 . The annular region  223  in the second variable-volume section  214  of the cylinder  210  shrinks. Accordingly, the second high-pressure fluid compresses. The pressure of the second fluid stabilizes across the system including the hollow interior  225  of the piston extension  224 , the annular region  223  of the cylinder  210 , the interior  232  of the accumulator  230 , and any connected APVs. 
     As the piston  220  slides downwardly along the axis A, the piston seat  222  pushes the first high-pressure fluid back into the accumulator  230  through the first flow path  250 . The piston seat  222  may draw the second fluid into the second variable-volume section  214  from the accumulator  230  through the second flow path  280 . The pressure of the second fluid stabilizes across the system including the hollow interior  225  of the piston extension  224 , the annular region  223  of the cylinder  210 , the interior  232  of the accumulator  230 , and any connected APVs. 
       FIG. 4  illustrates another example implementation of a riser tensioner system  300  including a hydraulic cylinder  310  and a high-pressure accumulator  330 . The riser tensioner system  300  does not include a low-pressure accumulator. A piston  320  is disposed within an interior of the hydraulic cylinder  310  and is configured to slide along an axial direction therethrough. The piston  320  includes a piston seat  322  and a piston extension  324 . The piston seat  322  divides the interior of the cylinder  310  into a first variable-volume section  312  and a second variable-volume section  314 . The volumes of the sections  312 ,  314  vary based on the position of the piston seat  322  within the cylinder  310 . 
     The piston extension  324  includes a sidewall  326  that extends upwardly from the piston seat  322  through the cylinder  310  to define an annular region  323  around the sidewall  326 . As the piston  320  slides within the cylinder  310 , the annular region  323  around the piston extension  324  grows and shrinks. In the example shown, the annular region  323  has substantially less volume than the hollow interior  325  of the piston extension  324 . In other implementations, however, piston extension  324  may be sized so that the annular region  323  has a greater or lesser volume. The piston sidewall  326  defines a hollow interior  325  that is accessible from the annular region  323  through one or more apertures  328  defined in the sidewall  326 . Accordingly, the second variable-volume section  314  of the cylinder  310  is defined by the annular region  323  around the piston extension  324  and the hollow interior  325  of the piston extension  324 . In the example shown, four apertures  328  are visible extending through the piston sidewall  326  in a ring. In other implementations, a greater or lesser number of apertures  328  may be provided in the piston  320 . 
     A first sealing arrangement  327  is disposed at the piston seat  322  of the piston  320  to provide a seal between the first and second variable-volume sections  312 ,  314  of the cylinder  310 . The example piston seat  322  shown in  FIG. 4  is taller than the piston seat  222  shown in  FIGS. 2 and 3 . A second sealing arrangement  329  is disposed between the piston extension  324  and an exterior of the cylinder  310  to seal the interior of the cylinder  310  as the piston  320  is slid therethrough. The second sealing arrangement  329  is located at an opposite end of the piston  320  from the first sealing arrangement  327 . A conduit  397  for connection to a lubrication tank port is provided at the second sealing arrangement  329 . 
     A valve conduit  372  also is provided at the top of the high-pressure accumulator  330  for receiving piping to connect one or more APVs. First and second fluid conduits  350 ,  380  also are shown extending between the cylinder  310  and the high-pressure accumulator  330 . In the example shown, the first flow path  350  has a larger cross-dimension (e.g., diameter) than the second flow path  380 . In other implementations, each of the flow paths  350 ,  380  may have a greater or lesser cross-dimension. In certain implementations, the first flow path  350  passes through a valve  355  and the second flow path  380  is open. 
     Having described the preferred aspects and implementations of the present disclosure, modifications and equivalents of the disclosed concepts may readily occur to one skilled in the art. However, it is intended that such modifications and equivalents be included within the scope of the claims which are appended hereto.

Technology Classification (CPC): 5