Abstract:
A magnetic retrieval tool for retrieving devices, such as probes, from a pressurized system. The retrieval tool uses a magnetic coupling to transfer movement of an external mechanism (i.e. external to the pressurized system), such as by an operator&#39;s manual movement, a motor or other drive, to an internal mechanism (i.e. internal to the pressurized system). The magnetic coupling may be through a wall of a pressure vessel using an outer magnetic core coupled to the outside of the pressure vessel which magnetically couples to an inner magnetic core disposed on the inside of the pressure vessel, such that translational or rotational movement of the outer magnetic core cause substantially simultaneous and corresponding translational and/or rotational movement of the inner magnetic core. An end effector tool is coupled to the inner magnetic core to engage and retrieve or insert the device into the pressurized system.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of PCT/US2013/038507, filed Apr. 26, 2013, which claims the benefit of U.S. provisional Application No. 61/639,807, filed on Apr. 27, 2012, and U.S. provisional Application No. 61/640,861, filed May 1, 2012. Priority to the aforementioned application is hereby expressly claimed in accordance with 35 U.S.C. §§119, 120, 365 and 371 and any other applicable laws. The contents of the aforementioned application(s) are hereby incorporated herein by reference in their entirety as if set forth fully herein. 
     
    
     BACKGROUND 
       [0002]    The field of the invention generally relates to retrieval tools such as those used in the oil, gas and chemical process industries, and more specifically to retrieval tools for retrieving items and devices in a pressurized system without releasing the system pressure. 
         [0003]    In a number of applications it is desirable, or necessary, to be able to insert items and devices into a system of pipes or vessels under pressure without releasing the system pressure and/or having to shut down the system. This may be required because the system is too expensive to shut down, or for other convenience or safety reasons. 
         [0004]    Special retrieval tools are used for this purpose, and are generally utilized in the oil and gas, and other chemical process industries. Typically, the retrieval tools are used to insert and remove devices such as metal corrosion coupons, mechanical and electronic monitoring probes, chemical injection nozzles, and the like, installed inside pipes and vessels under pressure while the plant or system is still operating. These retrieval devices are typically used in conjunction with a special access fitting, such as a COSASCO® fitting, and a separate isolating service valve which contains system pressure while the probe or device is being inserted into, or removed from, the system. 
         [0005]    These retrieval devices typically contain system pressure and allow manipulation of the internal mechanisms of the pressurized access fitting that is under pressure by an operator on the outside of the pressure barrier. Many retrievers use mechanical coupling mechanisms and mechanical seals to connect from the internal pressurized operated parts of the retriever to the external parts manipulated by the operator, to provide both translational and rotational control. Other retrievers use hydraulic systems to control the internal parts from the outside, typically where only a translational motion is required. 
         [0006]    A typical access fitting assembly  10  is shown in  FIG. 1 . The access fitting assembly  10  comprises an access fitting  12  which is mounted on the pipe  14  or vessel, usually with a welded, flanged or other high pressure coupling. The devices, such as an electronic probe  16  or mechanical probe  18 , to be inserted inside the pipe  14  through the access fitting  12  are sealed to an access plug  22  which seals to access fitting body  12 , so that once in place there is no isolating valve. The retriever and service valve then allow the inserted devices  16  or  18  to be removed and installed without shutting down the system operation and pressurization. 
         [0007]    Some typical prior mechanical configuration retrievers  26  and  28  are shown in  FIG. 2  and  FIG. 3 , respectively. The typical sequence of operations for use of both retrievers  26 ,  28  in  FIG. 2  and  FIG. 3 , respectfully, is as follows: 
         [0008]    First, as shown in diagram  1  of  FIGS. 2 and 3 , a protection plug  24  is removed from access plug  22  and a service valve  30  is attached to the access fitting  12 . The service valve  30  is open at this point to allow access to the plug  22  in the access fitting  12 . As shown in diagram  2 , the retriever  26 ,  28  is attached to the service valve  30  or directly to the access fitting. 
         [0009]    Also shown in diagram  2 , the retriever  26 ,  28  is manipulated to longitudinally move the end effector tool  32  of the retriever  26 ,  28  to engage the plug  22  in the access fitting  12 . 
         [0010]    Further shown in step  2 , the retriever  26 ,  28  is then manipulated to rotate the end effector tool  32  to unscrew the plug  22 . 
         [0011]    As the plug  22  is removed, the system pressure within the pipe  14  passes the plug  22  with device  16  or  18  and pressurizes the internal chamber of the retriever  26 ,  28 . The retriever  26 ,  28  is further manipulated to rotate the end effector tool  32  to completely unscrew the plug  22  with device  16  or  18  from the access fitting  12 . 
         [0012]    Next, as shown in Diagram  3 , the retriever  26 ,  28  is manipulated to longitudinally retract the end effector tool  32 , the plug  22  with device  16  or  18  being removed from the pipe  14 . Also, the service valve  30  is closed to seal the pressure within the pipe  14  and at the same time isolate the retriever from the pressurized pipe  14 . The retriever  26 ,  28  is then de-pressurized and removed from the access fitting  12 . 
         [0013]    The plug  22  and device  16  or  18  may then be removed from the retriever  26 ,  28 , as shown in diagram  4 . 
         [0014]    The procedure is simply reversed in order to insert/install the plug  22  and device  16  or  18  into the pipe  14 . 
         [0015]    However, the sliding seals of the retriever in  FIG. 2  and the rotary seals and thrust bearings of the retriever in  FIG. 3  become a system pressure limitation. With dirty process conditions such as sand and debris, damage can be caused to the seals with consequential operational failure. 
       SUMMARY 
       [0016]    The present invention is directed to an innovative magnetic retrieval tool which uses a magnetic coupling to transfer movement of an external mechanism (i.e. external to the pressurized system), such as by an operator&#39;s manual movement, a motor or other drive, to an internal mechanism (i.e. internal to the pressurized system). For example, the magnetic coupling may be through a wall of a pressure vessel using one fixed magnetic configuration outside the pressure vessel which magnetically couples to a second fixed magnetic configuration inside the pressure vessel. This magnetic coupling removes the need for the mechanical seals required on existing mechanical coupled retrievers because there is no direct physical contact between the external mechanism and the internal mechanism, as with all mechanical configuration retrieval tools such as those described above with respect to  FIGS. 2 and 3 . Thus, the internal mechanism can be completely sealed within the pressure vessel with no structure such as a shaft, or even electrical wires, extending from the internal mechanism to outside the pressure vessel. 
         [0017]    In one embodiment, the magnetic retrieval tool comprises a pressure vessel having a vessel wall having a top and a bottom, a sealed top end at the top of the vessel wall and an open bottom end at the bottom of the vessel wall. The pressure vessel has a longitudinal axis extending from the top end to the bottom end. For instance, the pressure vessel may be an elongated cylindrical tube having a tube wall, a cap on the top end and an opening at the bottom end. The pressure vessel has an outer portion outside the vessel wall and an inner portion inside the vessel wall. 
         [0018]    The magnetic retrieval tool has an outer drive assembly mounted to the outer portion of the pressure vessel in a manner to allow movement of the outer drive assembly longitudinally along the longitudinal axis of the pressure vessel, and rotationally about the longitudinal axis of the pressure vessel. The outer drive assembly has an outer magnetic core mounted within a sleeve. The outer magnetic core comprises at least one outer core magnet(s) each having a magnetic pole(s) adjacent the vessel wall. The sleeve is coupled to an actuation mechanism, such as a handle or other drive system. 
         [0019]    An inner rotor is disposed within the inner portion of the pressure vessel, and is magnetically coupled to the outer drive assembly in a manner such that movement of the outer drive assembly causes substantially simultaneous and corresponding movement of the inner rotor. For instance, the inner rotor is positioned adjacent the outer drive assembly on the opposite side of the vessel wall. The inner rotor comprises an inner magnetic core mounted to a support core. The inner magnetic core comprises at least one inner core magnet(s) each having a magnetic pole(s) adjacent the vessel wall and substantially oppositely aligned with the magnetic pole(s) of the outer core magnet(s). The term “substantially oppositely aligned” means that the pole(s) of the outer core magnet(s) and the pole(s) of the inner core magnet(s) are positioned relative to one another to produce a significant coupling force (rotational torque and/or translational force) between the outer magnetic core and the inner magnetic core such that movement of the outer drive assembly causes substantially simultaneous and corresponding movement of the inner rotor. In this way, the magnetic field of the inner core magnet(s) and the magnetic field of the outer core magnet(s) create forces pulling together the opposing inner core magnet(s) and the outer core magnet(s). 
         [0020]    The inner core also has an end effector tool for engaging and manipulating an access plug and/or device (such as a probe) within the pressurized system. As an example, the end effector tool may comprise a wrench head for engaging a square or hex head of an access plug. 
         [0021]    In another aspect, the outer magnetic core may comprise a plurality of magnets having alternating magnetic poles adjacent to the vessel wall. In this configuration, the inner magnetic core also comprises a plurality of magnets having alternating magnetic poles adjacent the vessel wall, with the magnetic poles of the inner magnetic core oppositely aligned with the alternating magnetic poles of the outer magnetic core. 
         [0022]    In still another aspect, the outer magnetic core may comprise a plurality of magnets having all similar magnetic poles adjacent to the vessel wall. In this configuration, the inner magnetic core also comprises a plurality of magnets having all similar poles adjacent the vessel wall, with the magnetic poles of the inner magnetic core substantially oppositely aligned with the magnetic poles of the outer magnetic core. 
         [0023]    The operation and use of the magnetic retrieval tool to retrieve or insert a device into a pressurized system, without depressurizing the system, is fairly straightforward. The use of the magnetic retrieval tool to retrieve a device, such as a probe, from a pressurized system will be described first. In the typical situation, the device is installed behind an access plug of an access fitting mounted on a pipe or vessel of the pressurized system. If the access fitting is not already fitted with a service valve, then a service valve is first installed onto the access fitting providing a pressure tight seal between the access fitting and the service valve. The service valve is open at this point, as the system pressure is sealed by the access plug. 
         [0024]    Then, the magnetic retrieval tool is installed on the service valve, providing a pressure tight seal between the service valve and the magnetic retrieval tool. The outer drive assembly is actuated, such as by manually manipulating a handle or operating a driver, to move the outer magnetic core longitudinally proximally toward the access plug. The longitudinal movement of the outer magnetic core causes substantially simultaneous and corresponding longitudinal movement of the inner rotor and its inner magnetic core to move the end effector tool of the inner rotor through the service valve and into engagement with the access plug. 
         [0025]    The outer drive assembly is then manipulated to remove the plug from the access fitting. For instance, the outer drive assembly may be actuated to rotate the outer magnetic core about the longitudinal axis of the pressure vessel. The rotational movement of the outer magnetic core causes substantially simultaneous and corresponding rotation of the inner rotor and its inner magnetic core to rotate the end effector tool of the inner rotor. The rotation of the end effector tool unscrews the access plug from the access fitting. As the plug is partially unscrewed, the plug allows system pressure to pass the plug and pressurize the pressure vessel of the magnetic retrieval tool. 
         [0026]    Once the pressure vessel is pressurized, the outer drive assembly is manipulated to completely remove the plug and also the device (such as a probe) behind the plug. This may entail further rotation of the outer drive assembly, which drives the inner rotor and end effector tool. Once the plug and device are completely detached from the access fitting, the outer drive assembly is manipulated to move the outer magnetic core longitudinally distally away from the access fitting. The longitudinal movement of the outer magnetic core causes substantially simultaneous and corresponding longitudinal movement of the inner rotor and its inner magnetic core to move the end effector tool, plug and device out through the service valve and into the pressure vessel of the magnetic retrieval tool. 
         [0027]    The service valve is then shut to seal the system process pressure from the magnetic retrieval tool. The pressure vessel is de-pressurized. The magnetic retrieval tool is removed from the service valve. Finally, the access plug, and attached device may be removed from the end effector tool of the inner rotor. 
         [0028]    The procedure for using the magnetic retrieval tool to insert a device, such as a probe, into a pressurized system is basically the reverse order of the procedure to retrieve a device. The device is attached to the access plug. The access plug and attached device are coupled to the end effector tool of the magnetic retrieval device. If not already in place, a service valve is installed onto the access fitting providing a pressure tight seal between the access fitting and the service valve. If a plug is installed on the access fitting, then it is first removed using the magnetic retrieval tool, as described above. 
         [0029]    With the plug removed, and the service valve installed with the service valve closed at this point, the magnetic retrieval tool is installed on the service valve, providing a pressure tight seal between the service valve and the magnetic retrieval tool. A bypass valve on the service valve is opened to slowly pressurize the pressure vessel to the system pressure. 
         [0030]    The service valve is then opened, such as fully opened, to allow the device and plug to be inserted through the service valve to the access fitting. The outer drive assembly is actuated to move the outer magnetic core longitudinally proximally toward the access fitting. The longitudinal movement of the outer magnetic core causes substantially simultaneous and corresponding longitudinal movement of the inner rotor and its inner magnetic core to move the end effector tool, plug and attached device through the service valve to the access fitting. 
         [0031]    The outer drive assembly is then manipulated to engage the access plug and device into the access fitting. Similar to the removal step described above, except in the opposite direction, the outer drive assembly may be actuated to rotate the outer magnetic core about the longitudinal axis of the pressure vessel. The rotational movement of the outer magnetic core causes substantially simultaneous and corresponding rotation of the inner rotor and its inner magnetic core to rotate the end effector tool of the inner rotor. The rotation of the end effector tool screws the access plug into the access fitting. The outer drive assembly is manipulated to tighten the access plug and device sufficiently to provide a seal of the system pressure. 
         [0032]    The pressure vessel is slowly de-pressurized, and then is removed from the service valve. The service valve may then be removed from the access fitting. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]      FIG. 1  is a side perspective, exploded view of a typical access fitting assembly installed on a pressurized system pipe. 
           [0034]      FIG. 2  is a side, perspective view of a mechanical configuration retriever having sliding seals and showing the sequence of operations for use of the retriever to retrieve a device from a pressurized system. 
           [0035]      FIG. 3  is a side, perspective view of a mechanical configuration retriever having rotary seals and showing the sequence of operations for use of the retriever to retrieve a device from a pressurized system. 
           [0036]      FIG. 4  is a side, perspective view of a magnetic retrieval tool according to one embodiment of the present invention. 
           [0037]      FIG. 5  is a side, perspective view of the magnetic retrieval tool of  FIG. 4  showing exemplary dimensions. 
           [0038]      FIG. 6  is a partial, enlarged, side, perspective view of the magnetic retrieval tool of  FIG. 4 . 
           [0039]      FIG. 7  is a partial, enlarged, side, cut-away perspective view of the magnetic retrieval tool of  FIG. 4 . 
           [0040]      FIG. 8  is a table of magnetic force calculations for an 8-segment alternating magnet outer magnetic core and inner magnetic core configuration having an axial length of 4 inches and having the listed specifications. 
           [0041]      FIG. 9  is a cross-sectional dimensional schematic of the outer magnetic core and inner magnetic core configuration for the table of  FIG. 8 . 
           [0042]      FIG. 10  is a table of torque and axial force for the outer magnetic core and inner magnetic core configuration of  FIG. 8  for different rotational slip angles (offset) between the outer magnetic core and inner magnetic core. 
           [0043]      FIG. 11  is a magnetic fluxplot of an 8-segment outer magnetic core and inner magnetic core, thin-wall, configuration with 20 degrees radial offset between the outer magnetic core and inner magnetic core. 
           [0044]      FIG. 12  is a magnetic fluxplot of an 8-segment outer magnetic core and inner magnetic core, thick-wall, configuration with 20 degrees radial offset between the outer magnetic core and inner magnetic core, and a 6.00 inches outer diameter. 
           [0045]      FIG. 13  is a magnetic fluxplot of an 8-segment outer magnetic core and inner magnetic core, thin-wall, configuration with 20 degrees radial offset between the outer magnetic core and inner magnetic core, and a 5.50 inches outer diameter. 
       
    
    
     DETAILED DESCRIPTION 
       [0046]    Referring to  FIGS. 4-7 , one embodiment of a magnetic retrieval tool  50  according to the present invention is shown. The magnetic retrieval tool  50  comprises a main pressure vessel  52 . The pressure vessel  52  in this embodiment comprises an elongated cylindrical tube  53  having a tube wall  54 , a top end  56  and a bottom end  58 . The pressure vessel  52  also has a cap  55  on the top end  56  of the tube  53  sealing the top end  56  of the tube  53 . The bottom end  58  of the tube  53  has an opening  60 . The tube  53  defines a longitudinal axis  57  through the center of the circular cross-section of the tube  53 . The tube  53  may be formed of magnetic or non-magnetic materials and is preferably configured to withstand typical operating pressures (system pressures) of 6,000 to 10,000 psi. For example, the tube  53  may be made of light-weight but strong materials such as titanium or carbon fiber or a composite of titanium and carbon fiber. The pressure vessel  52  of this embodiment has a cap  55  to seal the top end  56  of the tube  53 , but alternatively, the tube  53  and closed top end  56  can be made from a solid, integral piece of material. The tube wall  54  is preferably as thin as possible, such as 0.31″ for 6,000 psi rated retriever, because the tube wall  54  is between outer magnetic core  64  and inner magnetic core  74  and the magnetic coupling forces between them varies according to the distance between them. 
         [0047]    The interior and exterior surfaces of the tube wall  54  may have a low friction coating or sleeve, such as TEFLON® or similar protective coating, to reduce the frictional forces between the tube wall  54  and the inner rotor assembly  72  and outer drive assembly  62  during rotation and translation of the inner rotor assembly  72  and outer drive assembly  62  relative to the tube wall  54 . 
         [0048]    An outer drive assembly  62  is slidably mounted to the outer portion (exterior surface) of the tube  53  such that the outer drive assembly  62  can move both longitudinally along the longitudinal axis  57  of the tube  53 , and rotationally about the longitudinal axis  57  of the tube  53 . Turning to  FIGS. 6 and 7 , the outer drive assembly  62  comprises an outer magnetic core  64  mounted within a sleeve  66 . 
         [0049]    The outer magnetic core  64  comprises one or more outer core magnet(s)  68 . In this exemplary embodiment, the outer magnetic core  64  has eight magnets  68 . The magnets  68  are fixed to the sleeve  66 , and are preferably permanent magnets. It should be understood that any suitable number of magnets  68  may be utilized, such as from 2 to 12 magnets  68 , or from 8 to 12 magnets  68 , or more. Each of the eight magnets  68  are in the shape of an annular sector of a cylinder such that the eight magnets  68  together form a cylinder (i.e. the magnets  68  have a cross-section in the shape of a sector of an annulus about the longitudinal axis  57 ). Each of the magnets  68  has a magnetic pole adjacent the exterior surface of the tube wall  54 , either the North pole (N) or the South pole (S). In the illustrated embodiment, the magnets  68  are oriented with alternating magnetic poles adjacent the tube wall  54  (i.e. N, S, N, S . . . ). In other embodiments, the magnets  68  may be oriented with all similar poles (either N or S) adjacent the tube wall  54 , or any other suitable arrangement, such as NN, SS, NN, SS . . . , etc. The outer magnetic core  64  and sleeve  66  each have an axial length  100  (see  FIG. 5 ) in the direction of the longitudinal axis  57  (i.e. the length of the cylinder formed by the magnets  68 ). The inner diameter surface of the outer magnetic core  64  may be coated with a low friction coating or sleeve, such as TEFLON® or similar protective coating, to reduce the frictional forces between the tube wall  54  and the outer magnetic core  64  during rotation and translation of the outer drive assembly  62  relative to the tube wall  54 . 
         [0050]    The sleeve  66  may be cylindrical and can be formed of a high magnetic permeability material to complete and enhance the magnetic field coupling between the outer magnetic core  64  and inner magnetic core  74 . For instance, the sleeve  66  may be made of carbon steel or other magnetic material base. The sleeve  66  also provides structure for coupling the outer drive assembly  62  to a drive system for manipulating the outer drive assembly to move it longitudinally and rotationally, such as one or more handles  70 . Alternatively, the drive system coupled to the outer drive assembly  62  may be a motor, hydraulic, mechanical or pneumatic drive for local or remote operation. This may also allow for surface and sub-sea operation under extreme external pressures. 
         [0051]    Still referring to  FIGS. 4-7 , the magnetic retrieval tool  50  further comprises an inner rotor assembly  72  disposed within the tube  53 . The rotor assembly  72  also has a cylindrical shape, and comprises an inner magnetic core  74  mounted to the exterior surface of a support core  76 . The inner magnetic core  74  comprises at least one inner core magnet  78 , in this exemplary embodiment, eight magnets  78 . The magnets  78  are fixed to the support core  76 , and are preferably permanent magnets. The number of inner core magnets  78  will typically be the same as the number of outer core magnets  68 , but it is also possible to use a different number of magnets  78  from the number of magnets  68 . Again, it should be understood that any suitable number of magnets  78  may be utilized, such as from 2 to 12 magnets  78 , or from 8 to 12 magnets  78 , or more. Each of the eight magnets  78  are in the shape of an annular sector of a cylinder such that the eight magnets  78  together form a cylinder (i.e. the magnets  78  have a cross-section in the shape of a sector of an annulus about the longitudinal axis  57 ). Since the inner magnetic core  74  is disposed within the tube  53 , the outer diameter of the cylinder formed by the inner magnetic core is smaller than the inner diameter of the cylinder formed by the outer magnetic core  64  by at least the thickness of the tube wall  54 . Each of the magnets  78  has a magnetic pole adjacent the interior surface of the tube wall  54 , either the North pole (N) or the South pole (S). In the illustrated embodiment, the magnets  78  are oriented with alternating magnetic poles adjacent the tube wall  54  (i.e. N, S, N, S . . . ). In other embodiments, the magnets  78  may be oriented with all similar poles (either N or S) adjacent the tube wall  54 , or other desired arrangement, such as NN, SS, NN, SS . . . , etc. The inner magnetic core  74  and support core  76  each have an axial length  100  (see  FIG. 5 ) in the direction of the longitudinal axis  57  (i.e. the length of the cylinder formed by the magnets  78 ). The outer diameter surface of the inner magnetic core  74  may be coated with a low friction coating or sleeve, such as TEFLON® or similar protective coating, to reduce the frictional forces between the tube wall  54  and the inner magnetic core  74  during rotation and translation of the inner rotor assembly  72  relative to the tube wall  54 . 
         [0052]    Like the sleeve  66 , the support core  76  may be cylindrical and, can be formed of a high magnetic permeability material, such as carbon steel or other magnetic material base, to complete and enhance the magnetic field coupling between the outer magnetic core  64  and inner magnetic core  74 . The support core  76  also has a pressure balance port  80  from the top end of the inner rotor assembly  72  to the bottom end of the inner rotor assembly  72 , which allows pressure balancing within the tube  53  across the inner rotor assembly  72  (i.e. allows pressure to pass across the inner rotor assembly  72  within the interior of the tube  53 ). The pressure balance port  80  may be a hole as shown, or it can be a slot, multiple holes and/or slots, or other suitable fluid pathway across the support core  76 . 
         [0053]    A coupling mechanism  82  is attached to the bottom end of the inner rotor  72 . The coupling mechanism  82  has an extension rod  84  which is attached to, and extends downward from, the bottom end of the support core  76 . The extension rod  84  has a plurality of openings  86  and an interior lumen in fluid communication with the openings  86  and the pressure balance port  80 . An end effector tool  88  is disposed on the bottom end of the extension rod  84 . The end effector tool  88  is configured to engage and manipulate an access plug and/or device (such as a probe) within a pressurized system. As an example, the end effector tool  88  may have a socket head for engaging a square or hex head of an access plug. The tool  88  may also have a threaded plug retaining device  120 , magnet or biasing device for retaining an access plug or probe once it has been disconnected. 
         [0054]    The magnetic retrieval tool  50  also has an interface coupling  92  for attaching the magnetic retrieval tool  50  to a service valve  30  attached to an access fitting  12  of a pressurized system. The top end of the interface coupling  92  is attached to the bottom portion of the pressure vessel  52  (such as the bottom portion of the tube  53 ) in a fluid tight manner. The bottom end of the interface coupling  92  is configured to couple to a service valve  30  on an access fitting  12  of a pressurized system in order to couple the magnetic retrieval tool  50  to the access fitting. For instance, the interface coupling  92  may be a threaded, flanged, Grayloc, remotely operated coupling or similar means of attaching a retrieval tool to a service valve  30  on an access fitting  12  installed on a pressurized system. The interface coupling  92  has a lumen through which the extension rod  84  of the end effector tool  88  extends. The interface coupling  92  may also have integral or separate seal(s) where it attaches to a service valve to contain internal system pressure without leakage. The interface coupling  92  should be configured to provide proper positioning and coupling of the end effector tool  88  to the target plug or device to be retrieved or inserted in the pressurized system. 
         [0055]    Turning to  FIG. 5 , some of the design dimensions for an exemplary magnetic retrieval tool  50  are shown. The axial length  102  from the bottom end of the interface coupling  92  to the top of the cap  55  may be about 33 inches, or longer. The axial length  100  of each of the outer magnetic core  64 , sleeve  66 , inner magnetic core  74  and support core  76  is about 4 inches. The outer diameter  104  of the sleeve  66  is about 5.5 inches. The outer diameter  106  of the tube  53  is about 3.12 inches. The inner diameter  108  of the tube  53  is about 2.5 inches. The thickness  110  of the tube wall  54  is about 0.31 inches for 6,000 psi rated retrieval tool  50 . The inside diameter  112  of the interface coupling  92  at the connection to the pressure vessel  52  is about 1.8 inches. The inside diameter  114  of the interface coupling  92  where it attaches to a service valve or access fitting of a pressurized system is about 2.365 inches. 
         [0056]    The operation and use of the magnetic retrieval tool  50  to retrieve a device, such as a probe, from a pressurized system, without depressurizing the system having an access fitting, will now be described. As discussed above, typically, the device is installed behind an access plug of an access fitting mounted on a pipe or vessel of the pressurized system. If the access fitting is not already fitted with a service valve, then a service valve  30  is first installed on the access fitting  12  providing a pressure tight seal between the access fitting, the service valve and the retrieval tool  50 . The service valve  30  is open at this point, as the system pressure is sealed by the access plug  22  and seal  23 . 
         [0057]    Then, the magnetic retrieval tool  50  is installed on the service valve, by attaching the interface coupling  92  to the service valve. Depending on the type of interface coupling  82 , this can be done by screwing the coupling  92 , remotely operating the coupling  92 , etc., to provide a pressure tight seal between the interface coupling  92  and the service valve. The service valve is open at this point, as the system pressure is sealed by the access plug. 
         [0058]    The outer drive assembly  62  is actuated, by manually manipulating the handles  70  or operating a driver, to move the outer magnetic core  64  longitudinally downward toward the access plug. The longitudinal movement of the outer magnetic core  64  causes substantially simultaneous and corresponding longitudinal movement of the inner rotor assembly  72  and its inner magnetic core  74  downward, thereby moving the end effector tool  88  of the coupling mechanism  82  through the service valve and into engagement with the access plug. 
         [0059]    The outer drive assembly  62  is then rotated thereby rotating the outer magnetic core  64  about the longitudinal axis  57  of the tube  53 . The rotational movement of the outer magnetic core  64  causes substantially simultaneous and corresponding rotation of the inner magnetic core  74  and the inner rotor assembly  72 , thereby rotating the end effector tool  88 . The rotation of the end effector tool  88  unscrews the access plug from the access fitting. As the plug is partially unscrewed, the plug allows system pressure to pass the plug, pass through the openings  86  in the extension rod  84  and the lumen of the extension rod  84 , then through the pressure balance port  80  and into the tube  53  of the magnetic retrieval tool  50 , thereby pressurizing the tube  53  (and consequently the pressure vessel  52 ). 
         [0060]    Once the tube  53  is pressurized to the system pressure, the outer drive assembly  62  is further rotated to completely remove the plug and also the device behind the plug. Once the plug and device are completely detached from the access fitting, the outer drive assembly  62  and outer magnetic core  64  are moved longitudinally away from the access fitting. The longitudinal movement of the outer magnetic core  64  causes substantially simultaneous and corresponding longitudinal movement of the inner magnetic core  74  and the inner rotor  72  thereby moving the end effector tool  88 , plug and device out through the service valve and into the tube  53  of the magnetic retrieval tool  50 . 
         [0061]    The service valve  30  is then shut to seal the system process pressure from the magnetic retrieval tool  50 . The tube  53  is de-pressurized, such as by partially removing the interface coupling  92  from the service valve to allow pressure to escape. The magnetic retrieval tool  50  is removed from the service valve by completely disconnecting the interface coupling  92  from the service valve  30 . Finally, the access plug, and attached device may be removed from the end effector tool  88 . 
         [0062]    The procedure for using the magnetic retrieval tool  50  to insert a device, such as a probe, into a pressurized system is basically the reverse order of the procedure to retrieve a device. The device is attached to the access plug. The access plug and attached device are coupled to the end effector tool  88  of the magnetic retrieval device  50 . If not already in place, a service valve is installed onto the access fitting providing a pressure tight seal between the access fitting and the service valve. If a plug is installed on the access fitting, then it is removed using the magnetic retrieval tool, as described above. 
         [0063]    With the plug removed, and the service valve installed with the service valve closed at this point, the magnetic retrieval tool  50  is installed on the service valve by attaching the interface coupling  92  to the service valve to provide a pressure tight seal between the service valve and the interface coupling  92 . The service valve bypass valve is opened to slowly pressurize the tube  53  to system pressure. 
         [0064]    The service valve is then opened, such as fully opened, to allow the device and plug attached to the end effector  88  to be inserted through the service valve to the access fitting. The outer drive assembly  62  is actuated to move the outer magnetic core  64  longitudinally proximally toward the access fitting. The longitudinal movement of the outer magnetic core  64  causes substantially simultaneous and corresponding longitudinal movement of the inner rotor assembly  72  and its inner magnetic core  74  to move the end effector tool  88 , plug and attached device through the service valve to the access fitting. 
         [0065]    The outer drive assembly  62  is then manipulated to engage the access plug and device into the access fitting. Similar to the removal step described above, except in the opposite direction, the outer drive assembly  62  may be actuated to rotate the outer magnetic core  64  about the longitudinal axis  57  of the tube  53 . The rotational movement of the outer magnetic core  64  causes substantially simultaneous and corresponding rotation of the inner rotor assembly  72  and its inner magnetic core  74  to rotate the end effector tool  88  and the attached access plug and device. The rotation of the end effector tool  88  screws the access plug into the access fitting. The outer drive assembly  62  is manipulated to tighten the access plug and device sufficiently to provide a seal of the system pressure. 
         [0066]    The tube  53  is slowly de-pressurized, such as by partially removing the interface coupling  92  from the service valve to allow pressure to escape. Once the tube  53  is de-pressurized, the magnetic retrieval tool  50  is removed from the service valve by completely disconnecting the interface coupling  92  from the service valve. Then, if desired, the service valve may be removed from the access fitting. 
         [0067]    Turning now to  FIGS. 8-10 , an analysis of the magnetic force characteristics of several exemplary design configurations of the outer magnetic core  64 , inner magnetic core  74 , and pressure vessel  52  for a magnetic retrieval tool  50  will be discussed and compared. The magnetic force analysis was performed using finite element analysis.  FIGS. 8 and 9  show the design characteristics for three different design configurations, which each have eight alternating pole magnets  68  in outer magnetic core and eight alternating pole magnets  78  in inner magnetic core  78 , but differing magnet sizes (i.e. different inner diameter and outer diameter for the cylinder sector magnets  68  and  78 ), as shown in the table of  FIG. 8  and the dimensional schematic of  FIG. 9 . Each of the designs has an axial length  100  of the outer magnetic core  64 , sleeve  66 , inner magnetic core  74  and support core  76  of 4 inches, and the other dimensions and properties as listed. Each of these designs is also configured for pressure ratings of from 6,000 psi to 10,000 psi. For this discussion, the design in column 4 of the table of  FIG. 8  will be called Design  1 , the design in column 5 of the table of  FIG. 8  will be called Design  2 , and the design in column 6 of the table of  FIG. 8  will be called Design  3 . 
         [0068]    From the table of  FIG. 8 , it can be seen that Design  1  uses the largest magnets  68  and  78  of the three designs, and thus the largest outer magnetic core  64  and inner magnetic core  74 , resulting in the heaviest design as well. Design  1  also provides the greatest maximum coupling radial torque per 1 inch of axial length (259 lbf-in), and the greatest maximum coupling axial force per 1 inch of axial length (108 lbf). 
         [0069]    On the other hand, Design  3  has the smallest and lightest magnets  68  and  78  of the three designs, and the smallest outer magnetic core  64  and inner magnetic core  74 , resulting in the lightest design as well. However, Design  3  has the lowest maximum coupling radial torque per 1 inch of axial length (76 lbf-in), and the lowest maximum coupling axial force per 1 inch of axial length (41 lbf). 
         [0070]    Design  2  is somewhere between Design  1  and Design  3  in weight, size and maximum coupling radial torque per 1 inch of axial length (194 lbf-in), and maximum coupling axial force per 1 inch of axial length (90 lbf). 
         [0071]    Referring now to  FIG. 10 , the table shows the torque per unit axial length  100  and axial force per unit axial length  100  of the outer magnetic core  64  and inner magnetic core  74  for Designs  1 ,  2  and  3  for different rotational slip angles (offset) between the outer magnetic core  64  and inner magnetic core  74 . The table shows the torque and axial force for offsets from 0.0 degrees to 30.0 degrees. It can be seen that the maximum torque per unit axial length  100  is generated at an offset of about 20-25 degrees, and the maximum axial force per unit axial length  100  is generated at an offset of 0.0 degrees. 
         [0072]      FIGS. 11 ,  12  and  13  show corresponding magnetic flux plots with different outer magnetic core diameters in order to consider configurations with lower weight from smaller diameter. The computations in the flux plots are shown per 1 inch of axial length of magnetic core. Typical designs may use an axial length  100  of approximately 4 inches to suit most applications. Of course, larger torque and axial force can be produced by using longer axial lengths and larger diameters of the magnetic cores, as required. 
         [0073]    Although particular embodiments have been shown and described, it is to be understood that the above description is not intended to limit the scope of these embodiments. While embodiments and variations of the many aspects of the invention have been disclosed and described herein, such disclosure is provided for purposes of explanation and illustration only. Thus, various changes and modifications may be made without departing from the scope of the claims. For example, not all of the components described in the embodiments are necessary, and the invention may include any suitable combinations of the described components, and the general shapes and relative sizes of the components of the invention may be modified. Accordingly, embodiments are intended to exemplify alternatives, modifications, and equivalents that may fall within the scope of the claims. The invention, therefore, should not be limited, except to the following claims, and their equivalents.