PATENT ABSTRACT
A pressure gradient rotary sealing system is described which uses a pressure-reducing piston in several configurations with surface area differentials thereby reducing the pressure times velocity (PV) value for each of the sequential seals to extend seal system life and provide early indication of impending seal failure.

PATENT DESCRIPTION
[0001]     The present invention generally relates to a rotary seal that is used in a high speed, high pressure, high temperature environment where seal life and seal life predictability are very important. A more specific and typical application is with a wash pipe used in a drilling rig where a seal failure requires system shutdown. Seal life is a function of wear. The lower the pressure velocity (PV) value, the longer the seal life. PV is seal contact pressure multiplied by the velocity for a rotary seal. At high pressures the seals are energized by the operating pressure. This invention provides for increasing seal life by the use of multiple tandem mounted seals and reducing the pressure (i.e. PV values) sequentially for each seal. The invention configuration provides for detecting incipient seal failure so that otherwise required and untimely maintenance shutdown can anticipate and schedule as routine maintenance.  
       SUMMARY OF THE INVENTION  
       [0002]     A pressure differential sealing system in accordance with this invention for providing sealing between a rotating member and a stationary member that includes an excluder seal and one or more pressure-reduction pistons that are used to reduce the pressure between sealing stages. The sealing system is lubricated by grease packs. The excluder seal is designed to protect the sealing system from the media, which in the case of drilling operations can be very abrasive and under pressures as high as 7500 lb/square inch and temperatures as high as 360 Fahrenheit. The excluder seal isolates the rest of the sealing system from the media. The subsequent seals in the system are exposed only to the grease pack and are lubricated by the grease pack which results in lower friction and longer seal life.  
         [0003]     A floating pressure-reducing piston reduces the pressure drop across one or more sequential sealing stages and thus each seal in those stages experiences a lower PV thereby increasing seal life. The pressure-reducing piston has an area differential between two ends of the piston to produce the pressure drop.  
         [0004]     The rear seals have metal retaining rings to prevent rotation and provide retention. All seals in the system are energized by canted coil springs and by the media pressure. A canted coil retaining spring is provided to retain the sealing system in place during assembly.  
         [0005]     The grease packs have pressure monitors. Under normal operation, the system will have a standard pressure differential. As the sealing system wears to the extent that fluid leakage into the system is encountered, that pressure differential will be reduced. This reduced pressure differential provides an early indication of seal wear and thus system shutdown for maintenance can be scheduled instead of having an unplanned event.  
         [0006]     Various embodiments of the present invention include the following:  
         [0007]     A) The seals can be arranged sequentially, in tandem and coaxial about the rotating shaft (see  FIGS. 2   a  and  2   b ); in such case using first a balanced-pressure floating-excluder seal, next the pressure reducing step-piston, and then two tandem rotary pressure seals.  
         [0008]     B) The seals can be arranged sequentially in tandem about the rotating shaft ( FIGS. 3   a  and  3   b ), in such case using first a balanced-pressure floating-excluder seal, next two sequential pressure reducing step-piston arrangements, and then two tandem rotary pressure seals.  
         [0009]     C) The seals can be arranged sequentially in tandem about the rotating shaft ( FIGS. 4   a  and  4   b ), in such case using first a balanced-pressure floating-excluder seal, and then two tandem rotary pressure seals, and the pressure reducing piston are arranged as three or more small pressure-step pistons located around the circumference and ported so as to decrease the system pressure to each successive level of pressure seals.  
         [0010]     D) The seals can be arranged sequentially in tandem about the rotating shaft ( FIGS. 5   a  and  5   b ), in such case using first a balanced-pressure floating-excluder seal, and then two tandem rotary pressure seals, and the pressure reducing piston are arranged as a larger piston located concentrically about the fluid seal system, ported so as to decrease the system pressure to each successive level of pressure seals. Seals can also be arranged sequentially in tandem about the rotating shaft, in such case using first a balanced-pressure floating-excluder seal, and then two tandem rotary pressure seals, and the pressure reducing pistons are arranged as three or more small pressure-step pistons located around the circumference and ported so as to decrease the system pressure to each successive level of pressure seals, and in this case, two stages of pressure reducing pistons are used. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The present invention may be more clearly understood with reference to the following detailed description when taken in conjunction with the appended drawings, in which:  
         [0012]      FIG. 1  is an elevation view illustrating a wash pipe and a system in accordance with the present invention for providing sealing between a rotatable conduit and a stationary member;  
         [0013]      FIGS. 2   a  and  2   b  shows one embodiment of the present invention utilizing a single pressure reducing piston;  
         [0014]      FIGS. 3   a  and  3   b  shows another embodiment of the present invention similar to that shown in  FIG. 2   a , but with two pressure reductions stages;  
         [0015]      FIGS. 4   a  and  4   b  show a pressure gradient sealing system in accordance with the present invention with one or more side mounted pressure reducing pistons; and  
         [0016]      FIGS. 5   a  and  5   b  show a pressure gradient rotary sealing system in accordance with the present invention utilizing annular ring pressure-reducing piston. 
     
    
     DETAILED DESCRIPTION  
       [0017]     With reference to  FIG. 1 , there is shown a pressure gradient sealing system  10  as it may be installed on an oil rig top drive  12 .  
         [0018]     Embodiment  20  for a sealing system in accordance with the present invention as shown in  FIG. 2   a  generally includes a rear sealing system cartridge housing  22 , a sealing assembly guide bushing  24 , a rear fixed seal housing  26 , a rear fixed seal  28 ; a front fixed seal housing  30  and a front fixed seal  32 , the fixed seal  28  being disposed proximate an atmosphere pressure end of the system  20 .  
         [0019]     A rear grease pack  34  is provided along with a rear seal  36  abutting a floating pressure reducing piston  38 .  
         [0020]     A front sealing cartridge housing  40  is provided along with a front seal  42  for the floating piston  38 .  
         [0021]     A grease pack  44  is disposed between the front seal  42  and a floating excluder seal  46 . As will be described hereinafter in greater detail the system  20  also includes a plurality of static system O-rings  48  and all of the seals utilized canted coil springs  22  and seals  28 ,  32  include metal retaining rings  51 .  
         [0022]     A cartridge assembly canted coil spring  50  is shown along with a threaded ring  52 , a tightening washer  54 , locking ring  56 , and locking bolt  58 .  
         [0023]     A front pressure port  60  is provided and interconnected with the front grease pack  44  along with a middle pressure port  62  and an rear pressure port  64  interconnected with the rear grease pack  34 .  
         [0024]     The wash pipe attachment  52  is coupled into a wash pipe tube  66  via threads  68 , the tube  66  having drilling mud (not shown) flowing inside at high pressure. Drilling mud is usually a mixture of clay chemicals and water or oil and thus is an abrasive slurry.  
         [0025]     The sealing system in accordance with the present invention has several functions in order to accomplish extended seal life. 
        1 First, the seal system  20  isolates the harsh abrasive media by utilizing a floating pressure-balanced excluder seal  46 . The subsequent seals seals  28 ,  32 ,  42 ) in the system  20  are exposed only to the grease pack  34 ,  44  fluid, which is a design benefit because this provides lower friction and longer seal life.     2. The fluid sealing system effectively reduces the pressure across one or more sequential sealing zones in a state of force-equilibrium, therefore each seal experiences a lower PV and increasing the life of the sealing system. This is accomplished by the floating piston  38  having a smaller area on the energizing end. The pressure transferred is lower in direct proportion to the projected area differential of each end of the piston  38 .     3. The rear seals  28 ,  32  support the remaining pressure differential with a tandem seal combination. This redundant seal provided added life to the sealing system.     4. The rear seals  28 ,  32  are mounted with metal retaining rings  51  to help prevent rotation in the mounting glands  26 ,  30 , and to prevent OD shrinkage upon after a high temperature cycle.     5. All the seals utilize a filled polymer or PTFE material, which has lower friction, and can withstand higher temperatures that typical elastomers.     6. The polymer seals are energized with the canted coil spring technology to better energize the seals to close the seal gap after seal wear occurs, to ensure proper energizing with the media pressure.     7. In order to provide the user a prediction of the seal condition, the transducer/sensor  67  is the grease packs  34 ,  44 , from the front to the rear, monitors for pressure and temperature. Under normal operation, the pressure will have a predicted pressure differential as described in paragraph 2) above. Failures of the portions of the seal system will be detected with the monitoring equipment (not shown).     8. A guide bushing  2  at the rear helps hold the assembly concentric with the rotary shaft  66 , and also provides a method for pushing out the seal cartridge.     9. A canted coil spring  50  provides a positive retention of the seal system cartridge into the seal housing  1 .     10. O-rings  48  provide static sealing on the seal cartridge OD to prevent flow-around leakage.        
 
         [0036]     With reference to  FIG. 2   b , there is shown the pressure gradient sealing system  10  with many of the character references not shown in order to more clearly illustrate the pressures areas and forces.  
         [0037]     High pressure P 1  pushes the floating extruder seal  46  until equilibrium is achieved with pressure P 2  in the grease pack  44 . Pressure P 2  in the grease pack  44  produces a force F 1  on a surface area A 1  of the pressure reducing piston  38  which produces a force F 2  over area A 2  of an appropriate end of the piston  38 , which provides a reduced pressure P 3  on the rear grease pack  34 . The pressure P 3  activates a seal  32  at the reduced pressure P 3  thereby providing lower PV and longer seal life.  
         [0038]     A pressure transducer/temperature sensor  67  ( FIG. 2   a ) is interconnected with the pressure ports  60 ,  64  for determining a pressure differential therebetween which, in turn, provides incipient seal failure detection as hereinafter discussed in greater detail.  
         [0039]     With reference to  FIGS. 3   a  and  3   b , there is shown a pressure gradient rotary sealing system  100  with two pressure reduction stages. In this embodiment  100 , a rear sealing cartridge assembly housing  102  is provided along with a guide bushing  104 , a rear fixed seal housing  106 , a rear fixed seal  108 , a front fixed seal housing  110 , and a front fixed seal  112 .  
         [0040]     A grease pack  114  is disposed between the front seal  112  and a rear seal  116  for a rear floating pressure reducing piston  118 . A front seal  120  for the piston  118  abuts a middle grease pack  122  which, in turn, abuts a rear seal  124  for a front pressure reducing piston  126 .  
         [0041]     A cartridge housing  128  for the floating seals  118 ,  128  is provided along with a front seal  130  separated from a front floating excluder seal  132  by a front grease pack  134 .  
         [0042]     As in the embodiment  20 , a plurality of static system o-rings  136  are provided. A cartridge assembly retaining canted coil spring  140  is provided along with a locking ring  142  and locking bolt  144 . A center vent  146  for the front floating piston  126  is provided along with a center vent port  148  for the floating piston  118 .  
         [0043]     A pressure port  150  for the rear grease pack  114  is provided along with a pressure port  152  for the middle grease pack  122  and a pressure port  154  communicates with the front grease pack  134 . A tightening washer  156  is provided along with a pressure transducer  158 , which is in communication with the pressure ports  150 ,  152 , and  154  for determining pressure differential useful for determining seal life.  
         [0044]      FIG. 3   b  shows the pressures, areas and forces for the pressure gradient rotary sealing system  100  with two-pressure-reducing stages. The pressure P 1  pushes the seal  46  to provide the pressure P 2  in the front grease pack  134 . Pressure on the grease pack P 2  then produces a force F 1  on a surface area A 1  of the first pressure reducing piston  126 . The force acting over the area A 2  produces a reduced pressure P 3 , F 2  which is the force acting over the area A 2  producing a reduced pressure P 3  in the middle grease pack  122 . Pressure P 3  on the grease pack  122  produces a force F 3  on surface area A 3  of the second pressure reducing piston  118 . F 4  is the force acting over the area A 3  producing a further reduced pressure P 4  in the rear grease pack  114 . A pressure P 2  thereafter activates the seal  112  with the further reduced pressure with resulting lower PV and longer seal life.  
         [0045]     With reference to  FIG. 4   a , there is shown an alternative embodiment  200  of the pressure-gradient sealing system in accordance with the present invention utilizing a one or more side mounted pressure producing pistons  202 .  
         [0046]     More particularly, in this embodiment  200 , a rear seal cartridge system housing  204  is provided along with a sealing system guide bushing  206 , a rear seal support housing  208  along with a rear fixed seal  210 .  
         [0047]     A rear grease pack  212  is disposed between the rear fixed seal  210  and a center seal fixed-support housing  214  which abuts a center fixed seal  216  adjoining a front grease pack  218  which, in turn is disposed between a wash tube  220  and a sealing system cartridge housing  222 . Also shown is a front floating extruder seal  224  along with a plurality of static o-rings  226 .  
         [0048]     Also shown in the  FIG. 4   a  is a wash pipe attachment retaining threaded ring  228 , a tightening washer  230 , a tension ring  232 , and retention-ring bolts  234 .  
         [0049]     Associated with the side mounted pressure reducing piston  202  is a rear cylinder plug  236  and a front cylinder plug  238 , a rear cover seal  240 , and a front cover seal  242 .  
         [0050]     Disposed between the guide bushing  206  and rear seal housing  208  is a spacer washer  204 .  
         [0051]     A front pressure port  246  and a rear pressure port  248  are provided and interconnected with a pressure transducer  250 .  
         [0052]     Also shown in  FIG. 4   a  is a cartridge assembly retaining canted coil spring  252 , and a vent port  254  disposed during a center  256  of the side mounted piston  202 .  
         [0053]      FIG. 4   b  shows pressures areas and forces for the sealing system  200  with the side mounted pressure producing piston  202 . A pressure P 1  on the excluder seal  224  pushes the seal  224  to produce an equilibrium pressure P 2  in the front grease pack  218 , i.e. P 1 =P 2 .  
         [0054]     This pressure P 2  is translated through the front pressure port  246  to a pressure P 3  (P 3 =P 2 ) against an area A 1  of the piston  202  creating a force F 1  through a change in diameter of the piston  202 . The force F 2  acting over the area A 2  on the piston  202 , produces a reduced pressure P 4  which translates through the port  248  to a pressure P 5 , which is equal to pressure P 4 , on the grease pack  212  producing the reduce pressure P 5  on the rear seal  210  thus providing longer seal life.  
         [0055]     With the reference now to  FIG. 5   a , there is shown yet another embodiment  300  of a pressure-gradient rotary sealing system in accordance with the present invention utilizing an annular ring pressure-reducing piston  302  for a wash pipe attachment  304  having a wash tube  306 .  
         [0056]     As shown in  FIG. 5   a , the system  300  includes a rear sealing housing  308 , spacer washer  310 , a rear seal housing  312  and a rear fixed seal  314  abutting a rear grease pack  316  which, in turn, abuts a center seal fixed port housing  318  and a center fixed seal  320 . A front grease pack  322  is disposed between the fixed seal  320  and a front floating excluder seal  324 .  
         [0057]     A with previous embodiments  20 ,  100  and  200 , the system includes a plurality of o-rings  326 . Also, a sealing system cartridge retention canted coil spring  328  is provided along with a tightening washer  330 , retaining ring  332 , and retaining bolts  334 .  
         [0058]     A pressure port  336  is interconnected with the front grease pack  322 , which is supported by a housing  338 . A front cover seal  340 , and a rear cover seal  342  are provided for the annular ring piston  302  and a rear pressure port  344  is provided for the rear grease pack  316 , the port  344  being formed in a rear housing attached to a cylinder cap  348  by bolt  350 . A vent  352  is provided for the piston  302 .  
         [0059]      FIG. 5   b  shows the pressures, areas, and forces for the pressure gradient rotary sealing system  300  shown in  FIG. 5   a . Pressure P 1  pushes the excluder seal  324  to produce the pressure P 2  in the front grease pack  322  with P 1 =P 2 .  
         [0060]     The pressure P 2  translated through the fort  336  so that P 2 =P 3 . This produces a force F 1  on the area A 1  of the annular reducing piston  302  which then produces a force F 2  acting on area A 2  of the piston  302  to produce a reduced pressure P 4  which is forwarded to the rear grease pack  316  and seal  314  through the port  344 , producing a pressure P 5  in the grease pack P 5 =P 4 .  
         [0061]     This reduced pressure P 5  provides for a longer seal life as hereinabove discussed. The pressure differentials is measured by a pressure transducer  346  similar to the embodiments hereinbefore described.  
         [0062]     The purpose of the sealing system invention in accordance with the present invention is to provide a longer and more predictable seal-life solution to prevent fluid-media leakage through an interface between the sealing system  20 ,  100 ,  200 ,  300  and a wash pipe. The configuration illustrated in  FIG. 2   a  sealing system includes of a two-piece housing. The pieces are held together during assembly by the retention canted-coil spring,  FIG. 2  item  50 . Five O-rings  48 ,  FIG. 2   a  are used to block any leakage around the static periphery. The system  20  is mounted in place by the locking ring  56  and for locking bolts  58  tightening washers  54  which are used to prevent any distortion when the unit is assembled.  
         [0063]     The front floating excluder seal  46  prevents any media from entering the sealing system. Grease packs  34 ,  49  are used to lubricate the seals  32 ,  42  and to transfer the pressures as herein described earlier. Media pressure will push the front floating excluder seal  46  against the grease pack  44  producing pressure, P 1  shown in  FIG. 2   b . Pressure P 1  acting against area A 1  will produce a force F 1  as shown in  FIG. 2   b.    
         [0064]     The piston is a pressure-reduction piston that will move until forces F 1  and F 2  shown in  FIG. 2   b  are in equilibrium. The front piston seal  42  exerts pressure P 2  shown in  FIG. 2   b  against the front of the pressure-reducing piston  38 .  
         [0065]     The pressure-reducing piston will move until forces F 1  and F 2  shown in  FIG. 2   b  are in equilibrium. F 1  is equal to P 1 ×A 1 . P 2  is equal to F 2  divided by A 2 . Since A 1  is less than A 2 , P 2  will be less that P 1 . The ratio between P 1  and P 2  is directly proportional to the ratio between A 1  and A 2 .  
         [0066]     A 50% ratio between A 1  and A 2  will provide a 50% reduction in pressure from P 1  to P 2  resulting in a 50% reduction in PV for seal  32 . Pressures P 1  and P 2  are measured by the pressure transducer  66  that is connected to the pressure ports  62 ,  64 .  
         [0067]     Note that the pressure-reduction piston  38  can move in either direction until the forces are in equilibrium. Under normal operations the pressure differential will remain constant. As the seals wear, grease will be extruded from the grease pack until the grease pack  34  volume approaches zero. As that happens the pressure differential will decrease indicating seal wear and a reduced seal life expectancy as the seal lubricate is extruded. Therefore this pressure differential value can be monitored and used as a tool to predict seal life.  
         [0068]     With reference to  FIGS. 3   a  and  3   b , the pressure gradient pressure reduction system  100  can have multiple pressure reduction stages for further reductions in PV values. For example,  FIG. 3   a  shows a system  100  with two pressure reduction stages produced by pressure-reducing pistons  118 ,  126 . System pressures, areas, and forces are shown in  FIG. 3   b . The excluder seal  132  is a floating seal, so the pressure, P 1  shown in  FIG. 3   b  will be the same on both sides of the seal. Due to the difference in area from the front to the rear of the pressure-reduction pistons, pressure P 2  will be less than P 1 , and P 3  will be less than P 2 .  
         [0069]     With reference to  FIGS. 4   a  and  4   b , a pressure reducing system  200  utilizes a side-mounted pressure-reducing piston, or multiple pistons  202 , than can be spaced around a periphery of the system  200 . Here the pressure-reduction piston, or pistons  200  have front areas, A 1  as shown in  FIG. 4   b  that are less than the rear area, A 2  of the piston or pistons. The piston will move until the forces, F 1  and F 2  are in equilibrium. The pressure, P 3  will be less than the pressure P 2  thus reducing the seal PV for seal  210 .  
         [0070]      FIG. 5   a  shows a pressure gradient rotary seal system  300  with an annular ring pressure-reduction piston  302 . Here again, the area difference between the front and the rear of the piston-seal will reduce the pressure P 4  shown in  FIG. 4   b . The use of the annular ring-floating piston permits an increase in the volume of the grease pack without increasing the length of the sealing system.  
         [0071]     It should be appreciated that a plurality of side mounted or annular pressure reducing pistons may be employed in accordance with the present invention.  
         [0072]     Although there has been hereinabove described a specific pressure gradient rotary sealing system in accordance with the present invention for the purpose of illustrating the manner in which the invention may be used to advantage, it should be appreciated that the invention is not limited thereto. That is, the present invention may suitably comprise, consist of, or consist essentially of the recited elements. Further, the invention illustratively disclosed herein suitably may be practiced in the absence of any element which is not specifically disclosed herein. Accordingly, any and all modifications, variations or equivalent arrangements which may occur to those skilled in the art, should be considered to be within the scope of the present invention as defined in the appended claims.