Patent Publication Number: US-2013251572-A1

Title: Methods and Apparatus for Enhancing Elastomeric Stator Insert Material Properties with Radiation

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a 35 U.S.C. §371 national stage application of PCT/US2011/061782 filed Nov. 22, 2011, which claims the benefit of U.S. Provisional Application No. 61/416,589 filed Nov. 23, 2010, both of which are hereby incorporated herein by reference in their entireties for all purposes. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     BACKGROUND 
     1. Field of the Invention 
     The invention relates generally to progressive cavity pumps and motors. Still more particularly, the present invention relates to the treatment of elastomeric stator inserts with ionizing radiation to enhance the material properties of the elastomeric material. 
     2. Background of the Technology 
     A progressive cavity pump (PC pump) transfers fluid by means of a sequence of discrete cavities that move through the pump as a rotor is turned within a stator. The transfer of fluid in this manner results in a volumetric flow rate proportional to the rotational speed of the rotor within the stator, as well as relatively low levels of shearing applied to the fluid. Consequently, progressive cavity pumps are typically used in fluid metering and pumping of viscous or shear sensitive fluids, particularly in downhole operations for the ultimate recovery of oil and gas. Progressive cavity pumps may also be referred to as PC pumps, progressing cavity pumps, “Moineau” pumps, eccentric screw pumps, or cavity pumps. 
     A PC pump may be used in reverse as a positive displacement motor (PD motor) by passing fluid through the cavities between the rotor and stator to power the rotation of the rotor relative to the stator, thereby converting the hydraulic energy of a high pressure fluid into mechanical energy in the form of speed and torque output, which may be harnessed for a variety of applications, including downhole drilling. Progressive cavity motors may also be referred to as progressing cavity motors (PC motors), positive displacement motors (PD motors), eccentric screw motors, or cavity motors. 
     Progressive cavity devices (e.g., progressive cavity pumps and motors) include a stator having a helical internal bore and a helical rotor rotatably disposed within the stator bore. An interference fit between the helical outer surface of the rotor and the helical inner surface of the stator results in a plurality of circumferentially spaced hollow cavities in which fluid can travel. During rotation of the rotor, these hollow cavities advance from one end of the stator towards the other end of the stator. Each of these hollow cavities is isolated and sealed from the other cavities. 
     Since a PC motors have few components, they can be made to have a relative small outer diameter while being able to generate considerable torque. This design can be applied to subsurface boring motors (i.e. mud motors) for the drilling of wellbores. In such applications, the drilling mud that is used to cool and lubricate the drill bit and to bring cuttings to the surface up the annulus area between the drill string and the wellbore is typically used as the drive fluid for the downhole PC motor. The drilling fluid or mud may contain a certain amount of solid particles without risking damage to the motor, which is another advantage of utilizing eccentric screw motors in the drilling of wellbores. 
     Conventional stators often comprise a radially outer tubular housing and a radially inner component disposed within the housing. The inner component has a cylindrical outer surface that is bonded to the cylindrical inner surface of the housing and a helical inner surface that defines the helical bore of the stator. Alternatively, the housing may have a helical bore and the inner component may comprise a relatively thin, uniform thickness coating on the helical inner surface of the housing. In either case, the inner component is typically made of an elastomeric material and is disposed within the stator housing, and thus, may also be referred to as an elastomeric stator liner or insert. The elastomeric stator insert provides a surface having some resilience to facilitate the interference fit between the stator and the rotor. 
     Typically, stator manufacturers use an injection molding process to form the elastomeric stator insert. The injection molding process requires a relatively low viscosity elastomeric material, which often limit the ultimate stiffness and resilience of the material. During operation, the rotor and stator insert are in constant frictional engagement along a plurality of sealing lines defining the fluid filled cavities. Materials with low stiffness, strength, and/or resilience may wear quickly, thereby reducing the efficiency, power, and useful life of the PC device. Thermally curing injection molded elastomers is known to enhance certain elastomeric properties, but may also detrimentally affect other elastomeric properties. 
     Accordingly, there remains a need in the art for progressive cavity devices exhibiting reduced friction between the rotor and the stator insert to enhance efficiency, power, and durability. It would be desirable to increase the efficiency, power, and durability of the progressive cavity device by enhancing the resilience, strength, and resistance to stress cracking of device components such as the elastomeric stator insert. Such improvements in the stator insert would be particularly well-received if they could be achieved in addition to or separate from the thermal curing process. 
     BRIEF SUMMARY OF THE DISCLOSURE 
     These and other needs in the art are addressed in one embodiment by a method for manufacturing a stator for a progressive cavity motor or pump. In an embodiment, the method comprises (a) forming an elastomeric stator insert. In addition, the method comprises (b) exposing the elastomeric stator insert to ionizing radiation. Further, the method comprises (c) positioning the elastomeric stator insert in a stator housing to form a stator. 
     These and other needs in the art are addressed in another embodiment by a method for manufacturing a stator for a progressive cavity motor or pump. In an embodiment, the method comprises (a) generating a beam of electrons. In addition, the method comprises (b) positioning a target between the beam of electrons and an elastomeric stator insert. Further, the method comprises (c) emitting ionizing X-ray radiation from the target after (b). Still further, the method comprises (d) exposing the elastomeric stator insert to at least 100 KiloGrays of the ionizing X-ray radiation. Moreover, the method comprises (e) forming a plurality of polymer cross-links in the elastomeric stator insert with the ionizing X-ray radiation during (d). 
     These and other needs in the art are addressed in another embodiment by a progressive cavity pump or motor. In an embodiment, the progressive cavity pump or motor comprises a stator having a central axis and including a stator housing and a stator insert disposed within the stator housing, wherein the stator includes a helical bore defined by the elastomeric stator insert. In addition, the progressive cavity pump or motor comprises a rotor rotatably disposed within the helical bore of the stator. The rotor has a radially outer helical surface. The stator insert comprises an elastomeric material including a plurality of polymer chains connected by a plurality of cross-links induced by ionizing radiation. 
     Thus, embodiments described herein comprise a combination of features and advantages intended to address various shortcomings associated with certain prior devices, systems, and methods. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description, and by referring to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a detailed description of the preferred embodiments of the invention, reference will now be made to the accompanying drawings in which: 
         FIG. 1  is a perspective, partial cut-away view of an embodiment of a progressive cavity device in accordance with the principles described herein; 
         FIG. 2  is an end view of the progressive cavity device of  FIG. 1 ; 
         FIG. 3  is a schematic view of a system for treating the elastomeric stator insert of  FIGS. 1 and 2  with ionizing radiation; and 
         FIGS. 4 and 5  are graphical illustration of results from the test described in Example 1. 
     
    
    
     DETAILED DESCRIPTION OF SOME OF THE PREFERRED EMBODIMENTS 
     The following discussion is directed to various embodiments of the invention. Although one or more of these embodiments may be preferred, the embodiments disclosed should not be interpreted, or otherwise used, as limiting the scope of the disclosure, including the claims. In addition, one skilled in the art will understand that the following description has broad application, and the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to intimate that the scope of the disclosure, including the claims, is limited to that embodiment. 
     Certain terms are used throughout the following description and claims to refer to particular features or components. As one skilled in the art will appreciate, different persons may refer to the same feature or component by different names. This document does not intend to distinguish between components or features that differ in name but not function. The drawing figures are not necessarily to scale. Certain features and components herein may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in interest of clarity and conciseness. 
     In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . .” Also, the term “couple” or “couples” is intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, that connection may be through a direct connection, or through an indirect connection via other devices, components, and connections. In addition, as used herein, the terms “axial” and “axially” generally mean along or parallel to a central axis (e.g., central axis of a body or a port), while the terms “radial” and “radially” generally mean perpendicular to the central axis. For instance, an axial distance refers to a distance measured along or parallel to the central axis, and a radial distance means a distance measured perpendicular to the central axis. 
     Referring now to  FIGS. 1 and 2 , an embodiment of a progressive cavity (PC) device  10  is shown. In general, PC device  10  may be employed as a progressive cavity pump or a progressive cavity motor. PC device  10  comprises a rotor  30  rotatably disposed within a stator  20 . Rotor  30  has a central or longitudinal axis  38  and helical-shaped radially outer surface  33  defining a plurality of circumferentially spaced rotor lobes  37 . Rotor  30  is preferably made of steel and may be chrome-plated or coated for wear and corrosion resistance. 
     Stator  20  has a central or longitudinal axis  28  and comprises a housing  25  and an elastomeric stator insert  21  coaxially disposed within housing  25 . In this embodiment, housing  25  is a tubular (e.g., heat-treated steel tube) having a radially inner cylindrical surface  26 , and insert  21  has a radially outer cylindrical surface  22  engaging surface  26 . Surfaces  22 ,  26  are fixed and secured to each other such that insert  21  does not move rotationally or translationally relative to housing  25 . For example, surfaces  22 ,  26  may be bonded together and/or surfaces  22 ,  26  may include interlocking mechanical features (e.g., surface  22  may include a plurality of radial extensions that positively engage mating recesses in surface  26 ). Insert  21  includes a helical through bore  24  defining a radially inner helical surface  23  that faces rotor  30 . Although housing  25  and insert  21  have mating inner and outer cylindrical surfaces  26 ,  22 , respectively, in this embodiment, in other embodiments, the stator housing (e.g., housing  25 ) may have a helical-shaped radially inner surface defined by a helical bore extending axially through the housing, and the elastomeric insert may be a thin, uniform radial thickness elastomeric layer or coating disposed on the helical inner surface of the housing. 
     Referring still to  FIGS. 1 and 2 , rotor lobes  37  intermesh with a set of circumferentially spaced stator lobes  27  defined by helical bore  24  in insert  21 . As best shown in  FIG. 2 , the number of lobes  37  formed on rotor  30  is one fewer than the number of lobes  27  on stator  20 . When rotor  30  and the stator  20  are assembled, a series of cavities  40  are formed between the helical-shaped outer surface  33  of rotor  30  and the helical-shaped inner surface  23  of stator  20 . Each cavity  40  is sealed from adjacent cavities  40  by seals formed along the contact lines between rotor  30  and stator  20 . The central axis  38  of rotor  30  is parallel to and radially offset from the central axis  28  of stator  20  by a fixed value known as the “eccentricity” of PC device  10 . 
     The manner and method in which a PC device  10  operates is well known in the art. In general, the intermeshing stator insert  21  and rotor  30  generate a plurality of cavities  40  separated in the circumferential and longitudinal directions. When PC device  10  is operated as a pump, the rotation of rotor  30  relative to stator  20  drives the axial movement of cavities  40  through device  10  in the direction towards the end with the higher fluid pressure, and when PC device  10  is operated as a motor, the flow of fluid through cavities  40  from the end with a high fluid pressure to the end with the lower fluid pressure drives the rotation of rotor  30  relative to stator  20 . 
     In general, elastomeric stator insert  21  may be constructed from any suitable elastomer or mixture of elastomers. In embodiments described herein, the elastomeric stator insert (e.g., stator insert  21  or uniform radial thickness stator insert disposed on the inner surface of the stator housing) is preferably made from nitrile rubber, hydrogenated nitrile (HNBR), ethylene propylene diene monomer rubber (EPDM rubber), Chloroprene (neoprene), fluoroelastomers (FKM), epichlorohydrin rubber (ECO), natural rubber (NR), or combinations thereof. In general, elastomeric stator insert  21  may be formed by any suitable means known in the art including, without limitation, injection molding, transfer molding, extrusion, compression molding, or any other molding method. 
     An elastomer is a polymer with the property of viscoelasticity (i.e., elasticity), generally having notably low Young&#39;s modulus and high yield strain compared with other materials. In particular, an elastomer is composed of a plurality of hydrocarbon polymer chains, which may have the same general orientation (e.g., substantially parallel). Cross-links may be formed between polymer chains when one polymer chain bonds with an adjacent polymer chain. Such cross-links may occur naturally or may be initiated by a variety of means including, without limitation, exposing the elastomer to heat, pressure, radiation, or changes in pH; curing the elastomer; reacting the elastomer with catalysts; or combinations thereof. Without being limited by this or any particular theory, the density of the cross-links in an elastomeric material impacts the physical properties of the elastomeric material. For example, increasing the number of cross-links between polymer chains may increase the tensile strength, Young&#39;s modulus, and resilience of the elastomeric material. Increasing the number of cross-links may also increase the resistance to stress cracks, deformation, and abrasion. 
     In embodiments described herein, the elastomeric stator insert (e.g., stator insert  21  or uniform radial thickness stator insert disposed on the inner surface of the stator housing) is exposed to ionizing radiation. In particular, the elastomeric stator insert is preferably exposed to at least 100 KiloGrays of ionizing radiation, at least 500 KiloGrays of ionizing radiation, at least 1000 KiloGrays of ionizing radiation, at least 2500 KiloGrays of ionizing radiation, at least 5000 KiloGrays of ionizing radiation, at least 7500 KiloGrays of ionizing radiation, or at least 10,000 KiloGrays of ionizing radiation. As is known in the art, a “gray” is a unit of absorbed radiation dose of ionizing radiation, and is defined as the absorption of one joule of ionizing radiation by one kilogram of matter (e.g., elastomeric material). 
     Without being limited to this or any particular theory, exposing the elastomer stator insert to ionizing radiation increases the polymer chain cross-linking in the elastomeric material by breaking some polymer chains and forming cross-links with other polymer chains within the elastomeric material, thereby offering the potential to increase one or more of the following properties of the elastomeric material—the tensile strength, the Young&#39;s modulus, the resilience, the stiffness, the resistance to stress cracks, the resistance to deformation, and the resistance to abrasion. For example, ionizing radiation may increase the tensile strength of the elastomeric material to 20 MPa (or by about 50% as compared to the same elastomeric material prior to treatment with the ionizing radiation), increase the modulus to 10 MPa (or by about 100% as compared to the same elastomeric material prior to treatment with the ionizing radiation), increase the hardness to 90 Shore A (as compared to the same elastomeric material prior to treatment with the ionizing radiation), or combinations thereof. Depending on the composition of the elastomeric material of the stator insert, the formation of cross-links in response to a given level of radiation exposure (e.g., 1000 KiloGrays) may occur at different rates, and the formation of cross-links in response to radiation exposure may occur at different levels of radiation exposure (e.g., 500 KiloGrays vs. 7500 KiloGrays). 
     In generally, any type of ionizing radiation may be applied to the elastomeric stator inserts described herein including, without limitation, alpha rays, beta rays, gamma rays, neutron rays, proton rays, UV rays, X-rays, and combinations thereof. Moreover, the ionizing radiation may be generated by any suitable means. For example, a relatively high-flux neutron source may serve as a neutron generator. As another example, the ionizing radiation source may be a DC accelerator such as a Dynamitron that directs an electron beam at a target to produce high-energy X-rays. 
     Referring now to  FIG. 3 , an embodiment of a system  100  for treating elastomeric stator insert  21  (or any other elastomeric stator insert) with ionizing radiation is shown. In this embodiment, system  100  includes a DC accelerator  110 , an electron beam acceleration tube  118 , an electron scan magnet  120 , and a target  130 . DC accelerator  110  generates a stream or beam of electrons  115  via thermionic emission from a heated filament or cathode  111  in an electron gun  112 . Within gun  112 , electrodes generate an electric field that focuses the stream of electrons  115 , and one or more anode electrodes accelerate and further focus the stream of electrons  115 . A relatively large voltage differential is applied to accelerates the electron  115  from gun  112  through beam tube  118  and scan magnet  120 . Scan magnet  120  provides an oscillating magnetic field that sweeps electrons  115  back and forth across a scan window  121 . The beam of electrons  115  is directed toward target  130 , which is positioned between scan magnet  120  and elastomeric stator insert  21 . Target  130  is made of an element with a Z-number sufficient to produce high-energy X-rays  122  capable of forming polymer cross-linking within elastomeric stator insert  21 . In this embodiment, target  130  is a water-cooled tantalum plate. Thus, electrons  115  impact target  130 , and in response, target  130  emits X-rays  122  to which elastomeric stator insert  21  is exposed. 
     In some embodiments, the elastomeric material of the stator insert (e.g., stator insert  21 ) and/or the stator housing (e.g., housing  25 ) may incorporate one or more energy activated elements that influence how the ionizing radiation affects the elastomeric material of the stator insert. The energy activated elements may enhance the ionizing radiation effects, increasing the formation rate of polymer cross-linking, increase the strength of the polymer cross-links, or combinations thereof. In an embodiment, the energy activated elements comprise a material capable of emitting secondary ionizing or non-ionizing radiation, upon exposure to the initial ionizing radiation. In another embodiment, the energy activated element material is a material that increases the capture efficiency of the ionizing radiation within the stator. The energy activated element(s) may be positioned in any suitable location(s) including, without limitation, incorporated within the elastomeric material, incorporated within the stator housing, incorporate in any other stator component, formed as an insert, lining, coating, or film on the stator insert, formed as an insert lining, coating, or film on the stator housing, or combinations thereof. Materials that may be employed as energy activated elements include, without limitation, peroxides, coagents, vinyl containing acrylates and methacrylates, modified bismaleimides, and combinations thereof. 
     In general, the elastomeric stator insert (e.g., stator insert  21 ) may be exposed to the ionizing radiation before or after being positioned (e.g., injected or installed) in the stator housing (e.g., housing  25 ), and before or after complete assembly of the PC device (e.g., PC device  10 ). Since the density of polymer cross-linking in an elastomeric material is generally directly proportional to elastomer viscosity, it may be preferable to maintain the cross-link density, and hence elastomer viscosity, relatively low prior to injection molding, transfer molding, extrusion, or compression molding of the stator insert. However, once the elastomeric stator insert is formed, the cross-link density, viscosity, and other properties may be enhanced by exposure to ionizing radiation. 
     Embodiments of elastomeric stator inserts described herein (e.g., stator insert  21 ) may be subject to additional processes to increase the polymer cross-linking density including, without limitation, thermal cure, pressure cure, or pH cure. In particular, embodiments of elastomeric stator inserts described herein are preferably peroxide cured to further enhance polymer cross-linking. These additional processes may be applied to the elastomeric stator insert before or after exposure to ionizing radiation. Thus, exposing the elastomeric stator insert to ionizing radiation may be the only process applied to increase polymer cross-linking density within the elastomeric stator insert, or may be one of many process applied to the elastomeric stator insert to increase polymer cross-linking density. 
     It should be appreciated that the ionizing radiation employed in embodiments described herein may damage molecules in addition to causing cross-linking. Such damage may increase elastomeric rigidity by breaking of polymer chains. However, such destruction of polymer chains and chemical retarders may increase the mechanical strength of the elastomeric stator insert. 
     Increased polymer cross-linking density induced by the ionizing radiation offers the potential to increase the strength, resilience, and stiffness of elastomeric stator inserts (e.g., elastomeric insert  21 ), as well as increase resistance to stress cracking and abrasion. In addition, added cross-linking induced by ionizing radiation offers the potential to decrease wear of the stator insert due to frictional engagement with the rotor, thereby increasing the efficiency of the PC device (e.g., PC device  10 ) and durability of the stator insert. 
     EXAMPLE 
     To assess and quantify the effect of ionizing radiation exposure to an elastomeric stator insert, two B3000 stators with standard nitrile elastomeric insert were sent to the IBA Industrial Inc.&#39;s facility in Edgewood, N.Y. to be exposed to ionizing radiation. At the facility, a 3 MeV Dynamitron directed a high energy electron beam at each stator. A water cooled tantalum plate was interposed between the electron beam and each B3000 stator to expose each B3000 stator to ionizing X-ray radiation. A first of the two B3000 stators was exposed to 180 KiloGray of ionizing radiation and a second of the two B3000 stators was exposed to 250 KiloGray of ionizing radiation. 
     Each irradiated B3000 stator was then employed in a PC motor, which was subjected to testing by way of a dynamometer and compared to a PC motor including a standard non-irradiated B3000 stator having a nitrile elastomeric insert. The three PC motors tested (i.e., the PC motor including the B3000 stator exposed to 180 KiloGray of ionizing X-ray radiation, the PC motor including the B3000 stator exposed to 250 KiloGray of ionizing X-ray radiation, and the PC motor including the non-irradiated B3000 stator) were identical with the exception of the ionizing radiation treatment. 
       FIG. 4  graphically displays test results showing the power produced by each PC motor tested (i.e., the PC motor including the non-irratiated B3000 stator, the PC motor including the B3000 stator exposed to 180 KiloGray of ionizing X-ray radiation, and the PC motor including the B3000 stator exposed to 250 KiloGray of ionizing X-ray radiation) at various differential operating pressures between 0 psi and about 500 psi. The power output of the PC motor including the non-irradiated B3000 stator is labeled “PC Motor w/ Non-Irradiated Stator” in the legend of  FIG. 4 ; the power output of the PC motor including the irradiated B3000 stator exposed to 180 KiloGray of ionizing X-ray radiation is labeled “PC Motor w/ Irradiated Stator (180 KiloGray)” in  FIG. 4 ; and the power output of the PC motor including the irradiated B3000 stator exposed to 250 KiloGray of ionizing X-ray radiation is labeled “PC Motor w/Irradiated Stator (250 KiloGray)” in  FIG. 4 . As shown in  FIG. 4 , for differential operating pressures greater than about 115 psi, the power output of the PC motor including the non-irradiated B3000 stator was lower than the power output of each PC motor including an irradiated B3000 stator. Thus, both PC motors including X-ray treated B3000 stators exhibited a higher power output than the PC motor including the non-irradiated B3000 stator for differential operating pressures greater than about 115 psi. 
       FIG. 5  graphically displays test results showing the rotational speed of the rotor of each PC motor tested and the torque output of each PC motor tested (i.e., the PC motor including the non-irratiated B3000 stator, the PC motor including the B3000 stator exposed to 180 KiloGray of ionizing X-ray radiation, and the PC motor including the B3000 stator exposed to 250 KiloGray of ionizing X-ray radiation) at various differential operating pressures between 0 psi and about 500 psi. The torque output of PC motor including the non-irradiated B3000 stator is labeled “PC Motor w/ Non-Irradiated Stator—Torque” in the legend of  FIG. 5 ; the torque output of the PC motor including the irradiated B3000 stator exposed to 180 KiloGray of ionizing X-ray radiation is labeled “PC Motor w/ Irradiated Stator (180 KiloGray)—Torque” in the legend of  FIG. 5 ; and the torque output of the PC motor including the irradiated B3000 stator exposed to 250 KiloGray of ionizing X-ray radiation is labeled “PC Motor w/ Irradiated Stator (250 KiloGray)-Torque” in the legend of  FIG. 5 . The rotational speed of the rotor of the PC motor including the non-irradiated B3000 stator is labeled “PC Motor w/ Non-Irradiated Stator—Speed” in the legend of  FIG. 5 ; the rotational speed of the rotor of the PC motor including the irradiated B3000 stator exposed to 180 KiloGray of ionizing X-ray radiation is labeled “PC Motor w/Irradiated Stator (180 KiloGray)—Speed” in the legend of  FIG. 5 ; and the rotational speed of the rotor of the PC motor including the irradiated B3000 stator exposed to 250 KiloGray of ionizing X-ray radiation is labeled “PC Motor w/ Irradiated Stator (250 KiloGray)—Speed” in the legend of  FIG. 5 . As shown in  FIG. 5 , for differential operating pressure greater than about 115 psi, the rotational speed of the rotor of the PC motor including the non-irradiated B3000 stator was lower than the rotational speed of the rotor of each PC motor including an irradiated B3000 stator. Thus, the rotors of both PC motors including X-ray treated B3000 stators exhibited higher rotational speeds than the rotor of the PC motor including the non-irradiated B3000 stator for differential operating pressures greater than about 115 psi. In addition, for differential operating pressure greater than about 115 psi, the torque output of the PC motor including the non-irradiated B3000 stator was lower than the torque output of each PC motor including an irradiated B3000 stator. Thus, both PC motors including X-ray treated B3000 stators exhibited a higher torque output than the PC motor including the non-irradiated B3000 stator for differential operating pressures greater than about 115 psi. 
     The trend lines on  FIGS. 4 and 5  connecting the actual data points are for visualization of the data trends and are not meant to mean that actual data points were taken at each location on the trend lines. The actual testing measurements are shown in Table 1 below. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Differential 
                 Rotational 
                   
                   
                   
               
               
                 Operating 
                 Speed 
                 Torque Output 
                 Power Output 
                 Temp 
               
               
                 Pressure (psi) 
                 (rpm) 
                 (ft-lbs) 
                 (bhp) 
                 (° C.) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 Non-Irradiated B3000 Stator 
               
            
           
           
               
               
               
               
               
            
               
                 374 
                 123 
                 1020 
                 23.9 
                 70.3 
               
               
                 268 
                 138 
                 860 
                 22.61 
                 66.5 
               
               
                 166 
                 157 
                 600 
                 17.94 
                 70.6 
               
               
                 118 
                 161 
                 450 
                 13.8 
                 70.9 
               
               
                 76 
                 164 
                 300 
                 9.37 
                 70.4 
               
               
                 33 
                 165 
                 150 
                 4.71 
                 69.4 
               
               
                 0 
                 168 
                 0 
                 0 
                 69.3 
               
            
           
           
               
            
               
                 Irradiated B3000 Stator (180 KiloGray) 
               
            
           
           
               
               
               
               
               
            
               
                 464 
                 113 
                 1250 
                 26.9 
                 71.2 
               
               
                 331 
                 133 
                 1030 
                 26.09 
                 67.5 
               
               
                 168 
                 159 
                 620 
                 18.78 
                 72.2 
               
               
                 113 
                 161 
                 440 
                 13.49 
                 72.2 
               
               
                 76 
                 165 
                 300 
                 9.43 
                 71.8 
               
               
                 32 
                 165 
                 150 
                 4.71 
                 70.6 
               
               
                 0 
                 169 
                 0 
                 0 
                 70 
               
            
           
           
               
            
               
                 Irradiated B3000 Stator (250 KiloGray) 
               
            
           
           
               
               
               
               
               
            
               
                 425 
                 118 
                 1160 
                 26.07 
                 76.7 
               
               
                 342 
                 135 
                 1030 
                 26.49 
                 72.2 
               
               
                 165 
                 159 
                 610 
                 18.47 
                 75.6 
               
               
                 117 
                 161 
                 460 
                 14.11 
                 75.4 
               
               
                 58 
                 165 
                 250 
                 7.86 
                 73.8 
               
               
                 31 
                 165 
                 150 
                 4.71 
                 73.5 
               
               
                 0 
                 169 
                 0 
                 0 
                 72.8 
               
               
                   
               
            
           
         
       
     
     While preferred embodiments have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teachings herein. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of the systems, apparatus, and processes described herein are possible and are within the scope of the invention. For example, the relative dimensions of various parts, the materials from which the various parts are made, and other parameters can be varied. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims. Unless expressly stated otherwise, the steps in a method claim may be performed in any order. The recitation of identifiers such as (a), (b), (c) or (1), (2), (3) before steps in a method claim are not intended to and do not specify a particular order to the steps, but rather are used to simply subsequent reference to such steps.