Patent Publication Number: US-11377939-B1

Title: Interlocking diffuser arrangement in electrical submersible pump

Description:
FIELD OF THE DISCLOSURE 
     This disclosure relates in general to electrical submersible well pumps (ESP), particularly to a centrifugal pump having diffusers with an interlocking arrangement. 
     BACKGROUND 
     Electrical submersible well pumps are often used to pump well fluid from hydrocarbon producing wells. A typical ESP has a centrifugal pump with many stages, each stage having a diffuser and an impeller. The diffusers are stacked together in a pump housing and prevented from rotation. Each diffuser has a downward-facing shoulder that abuts an upward-facing shoulder of the diffuser directly below. A bearing at the top of the diffuser stack has threads that engage the pump housing, and when tightened, exert a compressive force on the stack of diffusers. The mating diffuser shoulders are perpendicular to the longitudinal axis of the pump housing. 
     In one type, each impeller and diffuser stage has an abrasion-resistant stage bearing that rotates with the shaft and typically transfers down thrust and up thrust to a mating diffuser. The abrasion-resistant components serve to resist abrasion when the pump is pumping sandy well fluid. Each stage bearing has a rotating component that fits within a non-rotating bushing of a mating diffuser. In another type, hubs of the impellers contact each other to transfer down thrust and up thrust to impellers above and below. The bushings and the rotating portions of the bearing that engages them are usually made of tungsten carbide. The bushings are normally pressed into a receptacle in each diffuser. To further prevent rotation an upper portion of each diffuser is staked or deformed over a top of the bushing. 
     The impeller and diffuser are normally castings from an iron-nickel alloy. The hardness of the alloy is much less than the hardness of the abrasion-resistant components. Making the impeller and diffuser of harder material would reduce erosion from sand-laden well fluid. However, harder material is normally more brittle. Compressing the diffusers in a stack to an extent as is done in the prior art can cause cracking. Also, staking the bushings into the diffusers creates difficulties with more brittle diffusers. 
     SUMMARY 
     An electrical submersible well pump has a tubular housing having a longitudinal axis. An upper and a lower diffuser are non-rotatably mounted in the housing. Each of the diffusers has an outer wall in close reception with an inner wall of the housing. A shaft extends through the diffusers on the axis. An impeller between the upper and lower diffusers mounts to the shaft for rotation in unison. The impeller has a bottom shroud with a skirt that fits within and engages a cavity in the lower diffuser in rotating sliding engagement. An outward-facing wall on an upper end of the lower diffuser has an outer diameter less than the outer wall of the lower diffuser, defining an upward-facing shoulder. A lower end of the upper diffuser has an inward-facing wall that fits over the outward-facing wall of the lower diffuser. The lower end of the upper diffuser abuts the upward-facing shoulder of the lower diffuser. A key mounted between the inward-facing wall and the outward-facing wall prevents relative rotation between the upper and lower diffusers. The key extends axially above an upper end of the neck and radially inward from the inward-facing wall of the upper diffuser into close proximity to the bottom shroud, creating a sand dam to retard swirling of sand-laden water surrounding the bottom shroud. 
     In the embodiment shown, the key has an upper end that is closer to the bottom shroud than to an upper end of the lower diffuser. The key may be rectangular when viewed in a transverse cross section. 
     In the embodiment shown, an inward-facing slot is formed in the inward-facing wall and an outward-facing slot is formed in the outward-facing wall. The key has an outer side that fits within the inward-facing slot and an inner side that fits within the outward-facing slot. An axial length of the key is no greater than an axial length of the inward-facing slot. The axial length of the key is greater than an axial length of the outward-facing slot. 
     An intake in the upper diffuser has an intake wall facing inward and converging in an upward direction. The inward-facing wall joins and extends downward from the intake wall. The inward-facing wall is cylindrical and has an axial dimension greater than an axial dimension of the outward-facing wall. The upper end of the key is below a junction between the intake wall and the inward-facing wall. 
     The key has an axial dimension greater than an axial dimension of the outward-facing wall. This axial dimension may be less than an axial distance from the upward-facing shoulder to the bottom shroud. 
     A bushing may be secured with an interference fit within a receptacle of the lower diffuser for receiving down thrust from the impeller. In the embodiment shown, an anti-rotation pin extends between the bushing and the receptacle to enhance non-rotation of the bushing relative to the lower diffuser. The receptacle has a counterbore with an upward facing base. The bushing may have an upper end with an external flange that lands on the base. In the embodiment shown, the pin is secured to and protrudes upward from the base. The flange has an aperture that receives the pin. The aperture may have an elongated circumferential dimension and a radial dimension that is less than the circumferential dimension. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic side view of an electrical submersible pump assembly in accordance with this disclosure. 
         FIG. 2  is an axial sectional of two of the stages of the pump of  FIG. 1 . 
         FIG. 3  is an enlarged view of a key and a portion of one of the stages of  FIG. 2 . 
         FIG. 4  is a sectional view of the key and a portion of one of the stages of  FIG. 2  taken along the line  4 - 4  of  FIG. 3 . 
         FIG. 5  is a top view of one of the bushings shown in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     The method and system of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. The method and system of the present disclosure may be in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey its scope to those skilled in the art. Like numbers refer to like elements throughout. In an embodiment, usage of the term “about” includes +/−5% of the cited magnitude. In an embodiment, usage of the term “substantially” includes +/−5% of the cited magnitude. The terms “upper” and “lower” and the like bare used only for convenience as the well pump may operate in positions other than vertical, including in horizontal sections of a well. 
     It is to be further understood that the scope of the present disclosure is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. 
       FIG. 1  illustrates an electrical well pump assembly (ESP)  11  of a type typically used for oil well pumping operations. ESP  11  includes a centrifugal pump  12  having a large number of stages, each of the stages having an impeller and a diffuser. Pump  12  may be suspended in a well on a string of production tubing  13 . Pump  12  has an intake  15  and discharges into production tubing  13 . Alternatively, pump  12  could be suspended on coiled tubing, in which case the discharge would be in an annulus surrounding the coiled tubing. 
     ESP  11  also includes an electrical motor  17  for driving pump  12 . Motor  17  connects to pump  12  via a seal section  19 . Motor  17  is filled with a dielectric lubricant, and a pressure equalizer reduces a pressure differential between the dielectric lubricant and well fluid on the exterior. The pressure equalizer may be within seal section  19  or in a separate module. Intake  15  may be at the lower end of pump  12 , in the upper end of seal section  19 , or in a separate module. Also, ESP  11  may also include a gas separator, and if so, intake  15  would be in the gas separator. 
     Referring to  FIG. 2 , pump  12  has a cylindrical housing  20  with a bore through which a drive shaft  21  extends along a longitudinal axis  23 . Motor  17  ( FIG. 1 ) operatively couples to drive shaft  21  for causing drive shaft  21  to rotate. 
     Pump  12  has a non-rotating stack of diffusers  25  that may be identical to each other.  FIG. 2  shows only two diffusers  25 , but most well pumps will have many more. Each diffuser  25  has diffuser passages  27  that extend upward or downstream and curve inward relative to axis  23 . An impeller  29  that rotates with shaft  21  locates between each of the diffusers  25 . Diffusers  25  and impellers  29  may be manufactured with a much greater hardness than in the past, such as between 40 and 70 Rockwell C. Each impeller  29  has impeller passages  31  that extend upward and curve outward relative to axis  23 . Impeller passages  31  receive well fluid from diffuser passages  27  of a next lower diffuser  25  and deliver the well fluid to diffuser passages  27  of a next upper diffuser  25 . A key and slot arrangement between impellers  29  and shaft  21  causes impellers  29  to rotate with shaft  21  but allows slight upward and downward movement of impellers  29  on shaft  21 . 
     Each diffuser  25  has an outer wall  33  that is cylindrical and fits closely within the inner diameter of housing  20 . A seal ring  35  optionally fits within an annular groove in outer wall  33  for sealing engagement with the inner diameter of housing  20 . Outer wall  33  has an upward facing shoulder  37  below an upper end or upper rim  39  of diffuser  25 . Diffuser  25  has a cylindrical outward-facing wall or neck  40  between upward-facing shoulder  37  and upper end  39  that is smaller in diameter than diffuser outer wall  33 . In this example, upward-facing shoulder  37  is a conical surface, taper or chamfer. Upward-facing shoulder  37  tapers downward or upstream and outward from neck  40  to outer wall  33 . 
     The lower end portion of each diffuser  25  has a cylindrical inward-facing wall  41  that slides over and fits tightly around outward-facing wall  40  of the next lower diffuser  25 . The lower end or lower rim of inward-facing wall  41  abuts in flush contact with upward-facing shoulder  37  of the next lower diffuser  25 . In this embodiment, the lower end of inward-facing wall  41  is also a conical surface and has a taper angle that is the same as the taper angle of upward-facing shoulder  37 . The axial dimension of inward-facing wall  41  is greater than the axial dimension of outward-facing wall  40  in this example. 
     Each impeller  29  has a skirt  43  on its lower end with a cylindrical outward-facing surface that rotates in sliding engagement with a receptacle  45  in the next lower diffuser  25 . Skirt  43  is a lower portion of a bottom shroud  47 , which extends upward and outward from skirt  43 . This upper portion of bottom shroud  47  is conical and encloses the lower sides of impeller passages  31 . 
     Impeller passages  31  discharge into a diffuser intake  49  that leads to diffuser passages  27 . Diffuser intake  49  is a space or chamber surrounding the discharge ends of impeller passages  31  and bottom shroud  47 . Diffuser intake  49  has an inward-facing intake wall  51  that is conical, converging in an upward direction. The lower end of intake wall  51  joins an upper termination of inward-facing wall  41 . The upper outer end of impeller  29  is spaced closely to intake wall  51 , but does not touch it. 
     Diffusers  25  may be stacked with a compressive force within housing  20 , which tends to resist rotation relative to each other. If diffusers  25  are of a much harder material than the prior art nickel-alloy used, the amount of the compressive force should be less than previously employed to avoid cracking. In this embodiment, a plurality of keys  53  also secure diffusers  25  together to prevent rotation. Each key  53  extends between outward-facing wall  40  of the next lower diffuser  25  and inward-facing wall  41  of the next upper diffuser  25 . Each key  53  protrudes above the next lower diffuser upper end  39  into diffuser intake  49  of the next upward diffuser  25 . This protruding portion of key  53  also extends radially inward from diffuser inward-facing wall  41  into diffuser intake  49 , creating a dam on lower diffuser upper end  39  to retard swirling of sand laden well fluid in the portion of diffuser intake  49  below impeller bottom shroud  47 . 
     Key  53  may be secured between inward-facing wall  41  of the next upper diffuser  25  and outward-facing wall  40  of the next lower diffuser  25  in various manners. Referring to  FIGS. 3 and 4 , in this embodiment, diffuser inward-facing wall  41  has an axially extending inward-facing slot  55 . Outward-facing wall  40  has an axially extending outward-facing slot  57 . In this example, the radial depth of inward-facing slot  55  in less than the radial depth of outward-facing slot  57 , but it could be greater. The axial length of inward-facing slot  55  is slightly less than the axial length of inward-facing wall  41  and greater than the axial length of outward-facing slot  57 . Outward-facing slot  57  extends from upward-facing shoulder  37  to lower diffuser upper end  39 . 
     Key  53  has an outer portion that fits within inward-facing slot  55  and an inner portion that fits within outward-facing slot  57 . Key  53  has an upper end  59  that is above the upper end of outward-facing slot  57  and in close proximity with impeller bottom shroud  47 . The axial distance from diffuser upper end  39  to key upper end  59  in this example is less than the axial length of outward-facing slot  57 , but it could be greater. Key upper end  59  is slightly below a junction of intake wall  51  with inward-facing wall  41 . Key  53  is rectangular in this example, but the shape could differ. Key  53  has an inner edge  61  that is parallel to axis  23  and parallel to the outer side of key  53 . 
     As shown in  FIG. 4 , key  53  has flat clockwise and counterclockwise sides  62  that may be parallel with each other and face into and away from the direction of rotation of impeller  29 . Sand from the well fluid may accumulate against the side  62  that faces against the direction of rotation of impeller  29 . Each clockwise and counterclockwise side  62  is in a plane that is slightly offset from axis  23  ( FIG. 3 ). 
     The distance from inward-facing wall  41  to key inner edge  61  may be greater than the radial depth of inward-facing slot  55  so as to create a wide dam with key  53 . Also, a radial dimension of key  53  from the outer portion to inner edge  61  may be more than a radial depth of either inward-facing slot  55  or outward-facing slot  57 . The upper inner corner of key  53  at the junction of upper end  59  with inner side  61  is spaced from bottom shroud  47  by a small distance or gap  63 . Gap  63  is much smaller than the axial distance from the upper outer tip of bottom shroud  47  to lower diffuser upper end  39 . 
     For assembly, a slight annular clearance may exist between outward-facing wall  40  of a next lower diffuser  25  and inward-facing wall  41  of the next upward diffuser  25 . During assembly, an assembler will slide the next upper diffuser  25  into engagement with the next lower diffuser  25 . Key  53  will be initially installed in one of the slots  55 ,  57 , and in this example, it is installed in inward-facing slot  55 . The assembler aligns key  53  with outward-facing slot  57  and forces the next upper diffuser  25  onto the next lower diffuser  25 . The conical shape of upward-facing shoulder  37  causes the next upper diffuser  25  to self-align with pump axis  23  as its conical lower end mates with shoulder  37 . Axial compression may be applied to the stack of diffusers  25 . 
     Referring to  FIG. 2 , a shaft bearing assembly fits within a diffuser shaft bore  69 . In this embodiment, the shaft bearing assembly includes a thrust runner  65  that rotates with shaft  21  and is axially slidable relative to shaft  21  to exert down thrust from a next upper impeller  29 . Thrust runner  65  slides in rotational engagement with a bushing  67  mounted in the next lower diffuser  25 . Bushing  67  is secured against rotation within diffuser shaft bore  69 . Bushing  67  may be press-fitted into diffuser shaft bore  69 . However, if diffuser  25  is formed of a much harder material than previously used, the amount of interference should be less to avoid cracking of diffuser  25 . 
     An anti-rotation pin arrangement may be employed in addition to an interference fit to prevent rotation of bushing  67  with diffuser shaft bore  69 . In this example, bushing  67  has an upper end that is a T-shaped external flange  71  when viewed in axial cross-section for receiving down thrust from thrust runner  65 . The lower side of flange  71  abuts a counterbore base  73  in diffuser  25 . 
     The anti-rotation pin arrangement in this example includes a cylindrical pin  75  that is secured in a hole and protrudes upward from base  73 . Pin  75  may be secured in the hole in base  73  in various manners. Bushing flange  71  has an aperture  77  that receives pin  75  to prevent rotation of bushing  67  in diffuser bore  69 . 
     A bearing sleeve  79  that rotates with shaft  21  slides in rotating engagement with the inner diameter of bushing  67 . Bearing sleeve  79  engages a hub of a next lower impeller  29  and may move upward relative to shaft  21  during up thrust into engagement with an inner portion of bushing flange  71  to transfer up thrust. Thrust runner  65 , bearing sleeve  79  and bushing  67  may be formed of an abrasion resistant material, such as tungsten carbide, that is harder than diffusers  25  and impellers  29 . 
     Referring to  FIG. 5 , to facilitate assembly, aperture  75  is circumferentially elongated, having two ends  81  circumferentially spaced from each other a selected degree. In this example, ends  81  are about 30 degrees apart, but that could differ. Also, aperture  81  extends completely to the outer diameter of bushing flange  71 , thus is open on its outer side. The radial depth of aperture  77  is much less than its circumferential length between circumferential ends  81 . 
     During assembly, an assembler will align aperture  81  with pin  75  and press-fit bushing  67  into diffuser bore  69 . The combination of the interference fit and pin  75  eliminate a need for staking or deforming portions of the lower end of diffuser bore  69  against and over portions of bushing  67 , as is done in prior art techniques. Diffusers  25  may be much harder and more wear resistant than in the past because staking deformation is not required. Also, the amount of interference can be less. 
     The present disclosure described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While only two embodiments of the disclosure has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the scope of the appended claims.