Patent Publication Number: US-2018045209-A1

Title: Torque transmitting key for electric submersible pumps

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 62/375,272 to Nowitzki et al., filed Aug. 15, 2016 and entitled “TORQUE TRANSMITTING KEY FOR ELECTRIC SUBMERSIBLE PUMPS,” which is hereby incorporated by reference in its entirety 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Embodiments of the invention described herein pertain to the field of electric submersible pumps. More particularly, but not by way of limitation, one or more embodiments of the invention enable a torque transmitting key for electric submersible pumps. 
     2. Description of the Related Art 
     Fluid, such as natural gas, oil or water, is often located in underground formations. In such situations, the fluid is often pumped to the surface so that it can be collected, separated, refined, distributed and/or sold. Centrifugal pumps are typically used in electric submersible pump (ESP) applications for lifting well fluid to the surface. Centrifugal pumps accelerate a working fluid through a rotating impeller paired with a stationary diffuser. In multistage centrifugal pumps, multiple impeller and diffuser stages are stacked around the pump shaft, with each successive impeller sitting on a diffuser of the previous stage. The shaft runs longitudinally through the center of the stacked pump stages. The shaft rotates and the impeller is keyed to the shaft causing it to rotate with the shaft. 
     A conventional vertical ESP assembly includes, from bottom to top, a motor, seal section, intake section, and multi-stage centrifugal pump. Production tubing carries the production fluid from the centrifugal pump to the well&#39;s surface. The assembly components each have a shaft running longitudinally through their centers. The shafts are all splined together and rotated by the motor shaft. In gassy wells, a gas separator or charge pump may also be included in the assembly, typically between the intake and the pump, or in place of the intake. For example, a gas separator may act as the intake of the assembly. In such instances, the gas separator compresses the gaseous fluid and then attempts to separate any unsaturated gas before the fluid passes into the centrifugal pump. Gas separators sometimes include impeller and diffuser stages to increase the pressure of the fluid during compression and separation of gas. Similarly, charge pumps are also sometimes used in tandem with a primary centrifugal pump in gassy wells, and may also employ stages. 
     A conventional ESP assembly sometimes includes bearing sets to carry radial and thrust forces acting on the pump during operation. The bearing set traditionally consists of a sleeve and bushing. The rotating sleeve is keyed to the shaft, rotating with the shaft. The bushing mates with the sleeve and should not rotate. Typically the bushing is pressed into the diffuser and extends around the sleeve. 
     The production fluid passing through the pump often contains solid abrasives, such as sand, rock, rock particles, soils, proppants or slurries that can cause damage to the pump components. In order to combat abrasion, the rotatable sleeve and bushing of the bearing set are conventionally made of tungsten carbide or a tungsten carbide cobalt composite that includes 6% cobalt. The tungsten carbide cobalt composite is a hard, brittle material having a hardness value ranging from 90-100 HRA. The hardened sleeve and bushing is often referred to in the ESP industry as abrasion resistant trim, or “AR trim.” 
     The key that secures the sleeve to the ESP shaft is conventionally a skinny, long rectangular strip (square prism) about 36 inches in length, with a square cross-sectional shape, and made of treated steel or an austenite alloy having a hardness of about 40-60 HRC (72 HRA). The key is conventionally formed in a drawn mandrel process, and the mandrel dictates the shape of the conventional key. The key secures into keyways in both the sleeve and the shaft, causing the sleeve to rotate with the shaft. Materials with a hardness of 40-60 HRC (72 HRA) are typically used for ESP keys because they are more ductile than harder, more brittle materials and therefore are simple to fabricate and permit the key to withstand shaft twist. A typical key ESP may twist an entire revolution around the pump shaft over the length of the pump. 
     A problem that arises with conventional keys is fretting of the key. During operation of the ESP assembly, the shaft vibrates inside the sleeve. This results in the hard sleeve knocking against the softer key, causing fretting of the key. Since the key is so long and skinny, the key may break all the way through as a result of the fretting. A broken key will not transfer torque between the shaft and sleeve, causing failure of the bearing set and shortening the operational life of the pump. 
     Key fretting may also be exacerbated by shaft twist, since shaft twist can lead to the key resting unevenly against the sleeve. Shaft twist may cause the square-in-cross section key to rest unevenly in the sleeve&#39;s keyway, which may force a corner and/or edge of the softer key against the side of a harder sleeve. These high points in the key may exacerbate fretting of the key, leading to premature failure of the bearing set and pump since the forces exerted on the key during operation are not distributed uniformly along the key&#39;s surface. 
     As is apparent from the above, current ESP keys suffer from many deficiencies. Therefore, there is a need for an improved torque transmitting key for electric submersible pumps. 
     BRIEF SUMMARY OF THE INVENTION 
     One or more embodiments of the invention enable a torque transmitting key for electrical submersible pumps (ESP). 
     A torque transmitting key for electric submersible pumps (ESP) is described. An illustrative embodiment of an electric submersible pump (ESP) system includes a rotatable shaft extending longitudinally through at least one impeller and diffuser stage and at least one bearing set, each of the at least one bearing set including a sleeve and a bushing, the sleeve coupled to the rotatable shaft by an elongate key such that the sleeve rotates with the rotatable shaft, and the elongate key made of a carbide composite material, the carbide composite material including a carbide selected from the group consisting of tungsten carbide, titanium carbide and silicon carbide, and a composite material selected from the group consisting of cobalt, nickel and a combination of cobalt and nickel. In some embodiments, the composite material includes between 6% and 10% by mass of one of cobalt, nickel or a combination thereof. In certain embodiments, the elongate key has one of an arch or tee cross-sectional shape. In some embodiments, the elongate key has an arch cross-sectional shape and a rounded portion of the arch is seated in a keyway extending along an inner diameter of the sleeve. In certain embodiments, the keyway extending along the inner diameter of the sleeve is rounded to match the rounded portion of the arch. In some embodiments, the elongate key has a tee cross-sectional shape and a cross of the tee is seated in a keyway in one of the shaft or the sleeve. In certain embodiments, the elongate key has a tee cross-sectional shape and each stepped side of the tee is seated in a keyway in one of the shaft or the sleeve. In some embodiments, at least one of the keyways is stepped to match the stepped side of the tee seated in the at least one keyway. In certain embodiments, the elongate key has a hardness of 86 HRA or greater. In some embodiments, the elongate key is about 18 inches in length. 
     An illustrative embodiment of an electric submersible pump (ESP) system includes an elongate torque transmitting key, the elongate torque transmitting key coupling an ESP rotatable component to an ESP shaft such that the ESP rotatable component rotates with the ESP shaft, a first side of the elongate torque transmitting key seated in a keyway of the ESP rotatable component and a second side of the elongate torque transmitting key seated in a keyway of the ESP shaft, the elongate torque transmitting key having a load optimizing cross-sectional shape. In some embodiments, the elongate torque transmitting key is 18 inches in length and the load optimizing cross sectional shape remains constant along the length of the elongate torque transmitting key. In some embodiments, the ESP rotatable component is a sleeve of a bearing set, the elongate torque transmitting key has a partially rounded load optimizing cross sectional shape, and wherein a rounded portion is the first side of the elongate torque transmitting key seated in the keyway of the sleeve. In certain embodiments, the keyway of the sleeve is rounded to match the rounded portion of the first side of the elongate torque transmitting key. In some embodiments, the ESP shaft extends longitudinally through a plurality of impeller and diffuser stages, and at least one impeller of the plurality of impeller and diffuser stages are keyed to the ESP shaft by the elongate torque transmitting key. In certain embodiments, the ESP rotatable component is a sleeve of a bearing set, the elongate torque transmitting key has a load optimizing cross sectional shape of a tee, and wherein a stepped side of the tee is the first side of the elongate torque transmitting key seated in the keyway of the sleeve, and wherein the keyway of the sleeve is stepped to match the stepped side of the tee seated in the keyway of the sleeve. In some embodiments, the elongate torque transmitting key consists of tungsten carbide cobalt composite. In certain embodiments, the tungsten carbide cobalt composite is greater than 6% cobalt by mass. In some embodiments, the load optimizing cross sectional shape is one of arched, round, tee, asymmetrical tee or L shaped. 
     An illustrative embodiment of a method of making a torque transmitting key for an electric submersible pump (ESP) includes extruding a carbide composite material through a die having a die shape to form an elongate key having a cross sectional shape of the die shape, heat treating the elongate key to harden the carbide composite material, and mating the hardened elongate key to an ESP shaft on a first side and a sleeve on a second side. In some embodiments, the cross sectional shape of the elongate key is an arch and a rounded top of the arch is the second side of the hardened elongate key mated to the sleeve. In certain embodiments, mating the hardened elongate key to the ESP shaft further includes mating the rounded top of the arch to a rounded keyway in the sleeve. In some embodiments, the cross sectional shape of the elongate key is a tee and a cross of the tee is the second side of the hardened elongate key mated to the sleeve. In certain embodiments, mating the hardened elongate key to the ESP shaft further includes mating a post of the tee to a stepped keyway in the sleeve. In some embodiments, the carbide composite material includes a composite material and a carbide, the composite material one of nickel, cobalt or a combination of nickel and cobalt, and wherein the carbide is one of tungsten carbide, silicon carbide or titanium carbide. In certain embodiments, the sleeve is a rotatable member of a bearing set and the sleeve is made of same carbide composite material as the hardened elongate key. In some embodiments, the cross sectional shape of the elongate key is one of round, arch, tee, asymmetrical tee or L shaped and the cross sectional shape of the elongate key optimizes loading zones on the elongate key. 
     In further embodiments, features from specific embodiments may be combined with features from other embodiments. For example, features from one embodiment may be combined with features from any of the other embodiments. In further embodiments, additional features may be added to the specific embodiments described herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Advantages of the present invention may become apparent to those skilled in the art with the benefit of the following detailed description and upon reference to the accompanying drawings in which: 
         FIG. 1A  is a perspective view of an ESP system of an illustrative embodiment. 
         FIG. 1B  is a cross sectional view across line  1 B- 1 B of  FIG. 1A  of an ESP system of an illustrative embodiment. 
         FIG. 2A  is a cross sectional view of a torque transmitting key of an illustrative embodiment having a square cross sectional shape. 
         FIG. 2B  is a cross sectional view across line  2 B- 2 B of  FIG. 3  of a partially rounded, arch-shaped torque transmitting key of an illustrative embodiment. 
         FIG. 2C  is a cross sectional view across line  2 C- 2 C of  FIG. 4  of a torque transmitting key having a tee cross sectional shape of an illustrative embodiment. 
         FIG. 2D  is a cross sectional view of a torque transmitting key having an L-shape of an illustrative embodiment. 
         FIG. 2E  is a cross sectional view of a round torque transmitting key of an illustrative embodiment. 
         FIG. 2F  is a cross sectional view of an asymmetrical tee shaped key of an illustrative embodiment. 
         FIG. 3  is a perspective view of a torque transmitting key having a partially rounded, arch-shape of an illustrative embodiment. 
         FIG. 4  is a perspective view of a torque transmitting key having a tee shape of an illustrative embodiment. 
         FIG. 5A  is a perspective view of an ESP system having a partially rounded, arch-shaped key of an illustrative embodiment. 
         FIG. 5B  is a cross sectional view across line  5 B- 5 B of  FIG. 5A  of an ESP system having a partially rounded, arch-shaped key of an illustrative embodiment. 
         FIG. 6A  is a perspective view of an ESP system having a tee shaped key of an illustrative embodiment. 
         FIG. 6B  is a cross sectional view across line  6 B- 6 B of  FIG. 6A  of an ESP system having a tee shaped key of an illustrative embodiment. 
         FIG. 7A  is a perspective view of a tee shaped key of an illustrative embodiment having a cross of the tee seated in an exemplary shaft keyway and a post of the tee seated in an exemplary sleeve keyway. 
         FIG. 7B  is a perspective view of a tee shaped key of an illustrative embodiment having a cross of the tee seated in an exemplary sleeve keyway and a post of the tee seated in an exemplary shaft keyway. 
         FIG. 7C  is a perspective view of a tee shaped key of an illustrative embodiment having opposing stepped sides of the tee seated in an exemplary shaft keyway and an exemplary sleeve keyway. 
         FIG. 8  is a flowchart of a method of making a torque transmitting key of an illustrative embodiment. 
     
    
    
     While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and may herein be described in detail. The drawings may not be to scale. It should be understood, however, that the embodiments described herein and shown in the drawings are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the scope of the present invention as defined by the appended claims. 
     DETAILED DESCRIPTION 
     A torque transmitting key for electric submersible pumps (ESP) is described. In the following exemplary description, numerous specific details are set forth in order to provide a more thorough understanding of embodiments of the invention. It will be apparent, however, to an artisan of ordinary skill that the present invention may be practiced without incorporating all aspects of the specific details described herein. In other instances, specific features, quantities, or measurements well known to those of ordinary skill in the art have not been described in detail so as not to obscure the invention. Readers should note that although examples of the invention are set forth herein, the claims, and the full scope of any equivalents, are what define the metes and bounds of the invention. 
     As used in this specification and the appended claims, the singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to a key includes one or more keys. 
     “Coupled” refers to either a direct connection or an indirect connection (e.g., at least one intervening connection) between one or more objects or components. The phrase “directly attached” means a direct connection between objects or components. 
     As used herein, the term “outer,” “outside” or “outward” means the radial direction away from the center of the shaft of the ESP and/or the opening of a component through which the shaft would extend. In the art, “outer diameter” and “outer circumference” are sometimes used equivalently. As used herein, the outer diameter is used to describe what might otherwise be called the outer circumference of a pump component such as a sleeve. 
     As used herein, the term “inner”, “inside” or “inward” means the radial direction toward the center of the shaft of the ESP and/or the opening of a component through which the shaft would extend. In the art, “inner diameter” and “inner circumference” are sometimes used equivalently. As used herein, the inner diameter is used to describe what might otherwise be called the inner circumference of a pump component, such as a sleeve. 
     As used herein the terms “axial”, “axially”, “longitudinal” and “longitudinally” refer interchangeably to the direction extending along the length of the shaft of an ESP assembly component such as a multi-stage centrifugal pump, seal section, gas separator or charge pump. 
     For ease of description and so as not to obscure the invention, illustrative embodiments are primarily described in terms of a hard, abrasion resistant sleeve (AR trim) keyed to an ESP shaft. However, illustrative embodiments are not so limited and may be employed where it is desirable to transfer torque loads in a rotatable pump assembly. In one example, the key of illustrative embodiments may be used to mate a rotating shaft or rotor to a rotatable component such as a sleeve or impeller, and/or where non-uniform loads are distributed on rotatable components coupled by the torque-transmitting key. Illustrative embodiments may be equally employed in multi-stage centrifugal pumps, charge pumps and/or gas separators, radial-flow pumps, axial-flow pumps, horizontal pumps, or regenerative-turbine pumps. 
     Illustrative embodiments may provide a torque transmitting ESP key with improved fretting and wear resistance and/or torque transmitting capability. In a departure from conventional keys, the key of illustrative embodiment may be made of a hard material such as titanium carbide, tungsten carbide, silicon carbide, a cobalt and/or nickel composite of any of those carbides, or another material having similar hardness on the Rockwell scale (e.g., 90-100 HRA) and conventionally believed to be too brittle to function as key material. The key of illustrative embodiments may match or approach within 5 HRA, the hardness of a hardened AR Trim sleeve mated to a rotatable shaft by the key. For example the key of illustrative embodiments may have a hardness of 86 HRA (69 HRC) or greater, improving fretting resistance of the key. The hard-material key of illustrative embodiments may be shorter in length than conventional keys, which shortened length may provide manufacturing benefits. 
     In addition to a square or rectangular cross-sectional shape, the key of illustrative embodiments may be shaped to optimize loading zones on the key. Key shape may be selected based on stress calculations and/or observed wear patterns. The key of illustrative embodiments may have a novel tee (T), asymmetrical tee, round, arched (partially rounded) and/or L cross sectional shape that may reinforce and/or deflect the key in areas where the key may be most vulnerable to fretting. For example, the novel shapes of illustrative embodiments may reinforce sections of the key, counteract high points on the key such as high points resulting from shaft twist and/or deflect forces acting on the key. One or more key shapes of illustrative embodiments may prevent corners and/or edges of the key from pressing against the sleeve or hardened keyway, which would otherwise cause wear and/or damage to sections of the key. Where the portion of the key having a modified shape is mated to a keyway, the mated keyway may similarly be modified in shape to match the novel shape of the key. 
     Illustrative embodiments may include an extrusion and heat treatment method for formation of a key of illustrative embodiments. The extrusion and heat treatment method may allow the key of illustrative embodiments to be formed in novel shapes that may improve fretting resistance of the key. 
     Illustrative embodiments may include a key composed of, consisting of, made of and/or including a hard carbide material such as tungsten carbide, silicon carbide, titanium carbide, a cobalt and/or nickel composite of any of the aforementioned carbides, or another material having similar properties and/or at least as hard, or approaching the hardness of the AR trim employed within the pump. Conventionally, experts have believed that it is not possible to create an ESP key of a hard brittle material such as tungsten carbide, silicon carbide or titanium carbide. One of skill in the art would expect that a key made from such long, thin brittle materials would break too readily during transportation and/or operation of the pump. In addition, these hard and brittle materials are difficult to work with, cut and shape to form. Contrary to what is expected, the inventors have successfully implemented an ESP key made of a hardened material that may reduce the risk of damage from fretting. In some embodiments, an increased cobalt and/or nickel percentage may increase the total rupture strength of the key of illustrative embodiments as compared to a conventional sleeve having 6% cobalt and/or compared to the cobalt percentage in the sleeve to which the key is mated. The elongate key may be formed with lengths varying from traditional keys, such as 18 inches in length rather than the conventional 36 inches in length, with multiple keys stacked along the length of the shaft one above the next. Where the length of the key of illustrative embodiments is shortened to 18 inches (from 36 inches), twice as many keys may be employed so as to run the length of the pump, shaft and/or the longitudinal distance desired for keyed components. 
     When installed, several keys of illustrative embodiments may be stacked axially along the shaft. One long side of each key may fit into an axially extending keyway on the outer diameter (OD) of the shaft, and the opposing long side of each key may be seated into a keyway extending along an inner diameter (ID) of a sleeve of a bearing set, impeller and/or other rotatable pump component.  FIG. 1A  and  FIG. 1B  illustrate an exemplary ESP system having a torque transmitting key of an illustrative embodiment. Key  100  may be made of, comprise and/or consist of a cobalt and/or nickel composite of a carbide, such as tungsten carbide, titanium carbide or silicon carbide. For example, fine ceramic tungsten carbide particles may be embedded in metallic cobalt binder forming a metal matrix composite of tungsten carbide cobalt composite. One long side of key  100  may seat into female shaft keyway  105  on the outer diameter of shaft  110 , and the opposing long side of key  100  may seat into female sleeve keyway  130  on the inner diameter of sleeve  115 , such that key  100  may transfer torque from shaft  110  to sleeve  115 . Sleeve  115  may be abrasion resistant trim (AR trim) and may be made of a material similar to the material of key  100 , for example tungsten carbide and/or a tungsten carbide cobalt composite, or another one of the aforementioned carbides and/or carbide composite materials. Sleeve  115  may be the rotating member of a radial and/or thrust support bearing set, with a non-rotatable bushing (not shown) surrounding sleeve  115  and pressed into and/or secured to non-rotating diffuser  120 . As shown in  FIG. 1A  and  FIG. 1B , sleeve may include flange  140  to provide thrust support. Shaft  110  may include spines  145  at one or both ends such that shaft  110  may be connected to and rotate with shafts above and/or below shaft  110 , such as the shaft of an ESP seal section or ESP motor. 
     Where the ESP system includes stages  135  of impeller  125  and diffuser  120  pairs, impellers  125  may similarly include a keyway so as to be rotatably coupled to key  100  above and/or below sleeve  115 . The keyways  105 ,  130  included on the surfaces of shaft  110 , sleeve  115  and/or impeller  125  may be female receptacles for key  100  and may be shaped and sized to accommodate the dimensions of key  100  to be inserted into keyways  105 ,  130 . Particularly, keyways  105 ,  130  may be shaped to mate with the side of key  100  seated within the respective keyway  105 ,  130 . Key  100  may be installed axially along shaft  110  and may extend through one or more stages  135  of impellers  125  and diffusers  120  and/or along one or more sleeves  115 . Keys  100  with shorter lengths, such as 9, 16, 18 or 20 inches in length may be stacked the length of the stages  135 . Keys  100  of shorter lengths may simplify manufacture of hardened, carbide composite key  100  and may improve ease of transport and installation. In some embodiments, the length of key  100  may be 36 inches consistent with conventional keys. In one example, a single key  100  may extend through three stages  135 , each stage including an impeller  125  and diffuser  120  pair stacked around shaft  110 . AR trim including sleeve  115  may be employed as desired for thrust and/or radial support, above, below or interspersed within the stages. 
     Key  100  may be made of a material that matches or approaches the hardness of the hardest rotatable component that may be keyed to shaft  110  with key  100 . Where sleeve  115  is made of tungsten carbide, silicon carbide, titanium carbide or a cobalt composite of any of those carbides, key  100  may similarly comprise one or more of tungsten carbide, silicon carbide, titanium carbide or a cobalt and/or nickel composite of any of those carbides. Forming key  100  of material matching and/or approaching (e.g., within 5 HRA) the hardness of sleeve  115  may reduce fretting of key  100  resulting from key  100  repeatedly bumping up against sleeve keyway  130  during ESP operation. In some embodiments, the cobalt and/or nickel percentage may be higher than 6% by mass in order to increase total rupture strength as compared to composites having only 6% cobalt by mass. For example, key  100  may include 8% cobalt, 10% cobalt or 12% cobalt by mass. Key  100  may be made of the same material as the rotatable component to which it transfers torque (e.g., sleeve  115 ), or may be made of another material with similar hardness to the rotatable component to which key  100  transfers torque. In an illustrative example, key  100  may comprise tungsten carbide cobalt composite and have a hardness of 86 HRA (69 HRC) or greater. In some embodiments, key  100  may precisely match the hardness of the rotatable component. In certain embodiments, key  100  may not precisely match the hardness of the rotatable component, but may be close to the hardness or substantially match the hardness, such as for example within 5-10 HRA of the hardness of sleeve  115 . 
       FIGS. 2A-2F  illustrate torque transmitting keys of illustrative embodiments. In some embodiments key  100  may have a square cross sectional shape as shown in  FIG. 2A , and may be made of a hardened carbide composite material as described herein. In some embodiments, key may have a novel cross sectional shape that may optimize loading zones on key  100 , as shown in  FIGS. 2B-2F . For example, key  100  may have a tee, asymmetrical tee, L, round, arch and/or partially rounded cross sectional shape.  FIG. 2B  illustrates an exemplary arch-shaped and/or partially rounded key  100  of illustrative embodiments.  FIG. 2C  illustrates a tee shaped key of illustrative embodiments.  FIG. 2F  illustrates an asymmetrical tee and/or step-shaped key of illustrative embodiments.  FIG. 2D  illustrates an L shape key of illustrative embodiments, and  FIG. 2E  illustrates a round key of illustrative embodiments. The length of key  100  may be shorter than conventional keys that are typically 36 inches in length in ESP applications. For example, key  100  may be 9 inches, 18 inches or 36 inches in length. Keys  100  may be stacked one above another when installed in an ESP system with one long side of each key  100  seated in sleeve keyway  130 , and the opposing long side seated in shaft keyway  105  such that torque may be transferred to from shaft  110  to sleeve  115  along the length of the shaft  110  and/or sleeve  115 .  FIGS. 2B-2F  illustrate exemplary load optimizing cross sectional shapes of key  100 . Tee, offset tee, L-shaped, round, arch and/or partially rounded cross sectional shapes of key  100  may reinforce key  100  in areas prone to fretting, may counteract high points in key  100  due to shaft twist and/or may cause deflection rather than fretting, such as for example, by rounding a keyed side of key  100  seated in sleeve keyway  130 . 
       FIG. 3  shows an exemplary key with an arch and/or partially rounded cross-sectional shape of an illustrative embodiment. As shown in  FIG. 3 , key  100  may have an arch shaped cross section that may be asymmetrical about a horizontal axis. The cross-sectional shape of key  100  may be constant throughout length  310  of key  100 . The arched cross-sectional shape may include a portion of a circle atop a portion of a square like a loaf of bread or a half of an oval. In the example of  FIG. 3 , rounded portion  300  extends halfway around and/or about halfway around key  100  to form an arch shape. In some embodiments, rounded portion  300  may extend more or less than halfway around key  100 , such as 25% or 75% around key  100 . Key  100  may have rounded portion  300  opposite a squared base  305 . Rounded portion  300  may be rounded, curved, parabolic, semicircular, elliptical or oval-shaped and may run along length  310  of key  100 . Rounded portion  300  of key  100  may lie in either one of sleeve keyway  130  or shaft keyway  105  in order to transfer torque from shaft  110  to sleeve  115 . In one example, rounded portion  300  of key  100  may be seated in sleeve keyway  130  to reduce fretting of key  100  due to contact with sleeve  115 . When placed in sleeve keyway  130 , rounded portion  300  may allow rocking and/or deflection of key  100  inside sleeve keyway  130 , which may reduce fretting during operational vibrations of the ESP assembly and/or counteract high points due to shaft twist. In some embodiments, where for example rounded portion  300  of key  100  is mated to sleeve keyway  130 , sleeve keyway  130  may be rounded to match arched portion  300  of key  100 . In some embodiments, key  100  may be seated such that opposing arch sides  315  lie in sleeve keyway  130  and shaft keyway  105  respectively. In this example, both sleeve keyway  130  and shaft keyway  105  may be partially rounded on the side of the respective keyway contacting rounded section of arch sides  315 . In some embodiments, rather than being partially rounded, key  100  may be entirely round, as illustrated in  FIG. 2E . 
       FIG. 4  shows a key with a tee cross sectional shape of an illustrative embodiment. The tee cross-sectional shape of key  100  may be similar to a capital “T” shape with a central post  400  and cross  405  that extends perpendicularly to post  400  and overhangs symmetrically on both sides of central post  400 . The side of key  100  having cross  405  may be wider than the side of key  100  having central post  400 , similar to the shape of a square positioned centrally below a rectangle or a larger square. Side portions  410  of cross  405 , perpendicular and/or adjacent to the top of cross  405  may be the same length, shorter or longer than the top of cross  405 , and may form stepped sides of tee shaped key  100 . In some embodiments, rather than post  400  being placed centrally beneath cross  405 , key may be an asymmetrical tee shape, as shown in  FIG. 2F , where post  400  is offset to one side of cross  405  in a stepped fashion. In certain embodiments, post  400  may be placed above cross  405  and offset to one side of cross  405  to form an L shape, as shown in  FIG. 2D . In the embodiment of  FIG. 2D , any of post  400 , cross  405 , long L side  200  and/or stepped L side  205  may be seated in keyways  105 ,  130 . 
       FIG. 7A-7C  illustrate alternative orientations of key  100  seated within shaft keyway  105  and sleeve keyway  130  to transfer torque between shaft  110  and sleeve  115 . As shown in  FIG. 7C , when installed between shaft  110  and sleeve  115 , key  100  may lie with stepped, side portions  410  of cross  405  seated within opposing shaft keyway  105  and sleeve keyway  130 . In the example of  FIG. 7C , both sleeve keyway  130  and shaft keyway  105  are shown stepped to match the change in height and/or depth of key  100  seated within shaft  110  and/or sleeve  115 . As shown, key  100  and keyways  130 ,  105  are mated and/or inversely shaped to one another so as to form a matched connection. In other illustrative embodiments, key  100  may be seated with post  400  in one of shaft keyway  105  or sleeve keyway  130 . In  FIG. 7A , post  400  is mated to sleeve keyway  130  and cross  405  is mated to shaft keyway  105 . In this example, sleeve keyway  130  may be stepped to match the change in width of key  100  as sleeve keyway  130  extends outwards. Shaft keyway  105  may be wide enough to accommodate cross  405  of key  100 . In  FIG. 7B , cross  405  is mated to sleeve keyway  130  and post  400  is mated to shaft keyway  105 . Shaft keyway  105  is shown stepped to narrow keyway  105  as keyway  105  extends inwards, to match the shape of post  400  and then follow the bottom side of cross  405 , as shown. The tee shaped profile of key  100  may allow a range of orientations with which key  100  can sit in sleeve keyway  130 , which may deflect and/or reinforce sections of key  100  that otherwise may be vulnerable to fret, wear or break. The orientation of tee shaped key  100  may be adjusted based on observed or anticipated wear patterns on key  100 . 
       FIGS. 5A and 5B  show an exemplary ESP stage having AR trim and employing a partially rounded and/or arched key  100  of an illustrative embodiment. Rounded arch portion  300  of key  100  may seat into sleeve keyway  130 , and square base  305  may seat into shaft keyway  105 . In some embodiments, the shape of sleeve keyway  130  and/or shaft keyway  105  may be modified to match the shape of the side of key  100  that seats into the respective keyway. For example, as shown in  FIG. 5A  and  FIG. 5B , rounded portion  300  of key  100  is seated in sleeve keyway  130 , and sleeve keyway  130  is rounded to match rounded portion  300  of key  100 . Base  305  is seated in shaft keyway  105  and shaft keyway  105  remains square in cross sectional shape to mate with base  305 . In certain embodiments, the shape of sleeve keyway  130  may remain unchanged from a conventional rectangular shape despite rounded portion  300  seated therein. Multiple keys  100  may be stacked along the length of shaft  110 . In some embodiments, rounded portion  300  may mate with shaft keyway  105  or key  100  may be rotated 90 degrees such that arch sides  315  mate into keyways  105 ,  130 . 
     As shown in  FIG. 5B , partially rounded key  100  may extend through several impeller-diffuser stages  135  and/or through one or more sleeves  115 . As shown in  FIG. 6A  and  FIG. 6B , tee shaped key  100  may extend through several impeller-diffuser stages  135  and/or through one or more sleeves  115 . For example, key  100  may extend through three stages  135 , each comprised of impeller  125  and diffuser  120 , as well as through sleeve  115  secured below stages  135 . The hard material of key  100  may match or approach the hardness of sleeve  115  and/or the hardest component to which key  100  may be mated. The cross-sectional shape and/or material of key  100  of illustrative embodiments may prevent operation-prohibitive damage to key  100  caused by fretting and/or twisting. 
     Illustrative embodiments include a method of making a torque transmitting key of illustrative embodiments.  FIG. 8  is a flowchart of an exemplary method of making a torque transmitting key of an illustrative embodiment. The method of illustrative embodiments may permit key  100  to be formed, made and/or manufactured in the carbide composite materials and/or the cross-sectional shapes described herein. First, the material for key  100  may be selected at material selection step  800 . The material may be selected based on the hardness of the AR trim or other rotatable component to be keyed to shaft  110  by key  100 . Exemplary materials may be carbide ceramics and/or composite materials such as tungsten carbide, titanium carbide, silicon carbide, cobalt and/or nickel composites of any of those carbides, or another material with similar properties. At shape selection step  805 , the cross sectional shape for key  100  may be selected. The cross-sectional shape may be selected to optimize loading zones on key  100  based on the anticipated fretting pattern and/or observed wear on key  100  in similar applications. For example, key  100  may be formed in an arch, tee, rounded, partially rounded, square, rectangle or other cross sectional shape. The length of key  100  may also be selected at shape selection step  805 . For example, the length of key  100  may be selected to simplify transport and manufacture and/or reduce the effects of brittleness of hardened key  100 . 
     To make key  100  having the selected profile and length, the key  100  material may first be extrusion formed at extrusion step  810 . Extrusion may be hot or cold extrusion depending the application and the key material chosen during material selection step  800 . During extrusion step  810  the key  100  material may be pushed through a die having the desired cross-sectional shape. The cross-sectional shape of key  100  may be modified by customizing the shape of the die or mold through which the key material is pushed and/or drawn. For example, the die may have an arch, rounded, square, cross, tee, L, rounded, and/or partially rounded shape to create a customized key cross sectional shape. Extrusion step  810  may result in an asymmetrical cross sectional shape of key  100 , if desired. The length of key  100  may also be set during extrusion step  810 . The extruded key  100  may be heat treated at heating step  815 . After extrusion forming, key  100  may still be brittle. Heat treatment step  815  may result in curing to produce an elevated hardness and/or strength of key  100 . Heating may be performed at the desired temperature and duration such that the cobalt and/or nickel composite material binds to the carbide material of key  100 . The shrinkage rate may be monitored during heating, since in some embodiments, key  100  may not be ground subsequent to heat treatment. Once key  100  is formed, key  100  may be mated into an ESP primary pump, charge pump, gas separator, centrifugal pump, stage or any other ESP system location where torque may be transmitted by a key between a rotatable shaft and a hard rotatable component, at mating step  820 . Key  100  may be mated to shaft  110  or a rotor on the one hand, and sleeve  115 , impeller  125  or other rotatable component on the other hand as described herein. The process used in formation of key  100  may result in key  100  of novel material, shape and/or improved fretting resistance. 
     Illustrative embodiments may reduce the likelihood of key damage due to fretting and/or twisting in a torque transmitting key, such as a key that transmits torque from a shaft to a sleeve of an ESP assembly stage. The key of illustrative embodiment may be constructed of a hard ceramic material like tungsten carbide, titanium carbide or silicon carbide or a cobalt and/or nickel composite of any of those carbides, which material may more closely match the hardness of the pump components mated to the key. The key of illustrative embodiments may include a higher percentage of cobalt and/or nickel than the rotatable pump component to increase total rupture strength of the key, such as up to 10% cobalt and/or nickel. The hardness of the key material may reduce the likelihood of fretting of the key material. The key of illustrative embodiments may include a load optimizing cross sectional shape to improve fretting resistance by reinforcing and/or deflecting the key in areas subject to damage, and for example may be round, arch shaped, tee shaped, L shaped, partially rounded, or may include other shapes that may cradle, deflect and/or reinforce the key against fretting. The key of illustrative embodiments may be shorter than that of conventional keys, such as 18 inches in length, to improve manufacture and transport. An extrusion and heat treatment process may be used to form the improved key of illustrative embodiments. 
     Further modifications and alternative embodiments of various aspects of the invention may be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the general manner of carrying out the invention. It is to be understood that the forms of the invention shown and described herein are to be taken as the presently preferred embodiments. Elements and materials may be substituted for those illustrated and described herein, parts and processes may be reversed, and certain features of the invention may be utilized independently, all as would be apparent to one skilled in the art after having the benefit of this description of the invention. Changes may be made in the elements described herein without departing from the scope and range of equivalents as described in the following claims. In addition, it is to be understood that features described herein independently may, in certain embodiments, be combined.