Abstract:
The apparatus, for re-machining safety valves in situ on high pressure/high temperature plant and pipework, comprises a first gearbox and a second gearbox. The first gearbox has a first centre of rotation associated therewith and is configured to receive a driving torque. The second gearbox has a second centre of rotation associated therewith, is coupled to and is configured to be driven by the first gearbox. Coupling means is provided for transferring the drive torque from the first gearbox to the second gearbox. The coupling means is configured to define the location of the second centre of rotation relative to the first centre of rotation. A removable accessory assembly is provided and is coupled to the second gearbox, for carrying out a cutting, grinding or lapping operation to recondition a surface of a safety valve.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority from PCT/GB/2010/050080 filed on Jan. 21, 2010 and from GB 0900949.9, filed Jan. 21, 2009, which are hereby incorporated by reference in their entireties. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to the field of machining of safety valves, and in particular apparatus for re-machining and reconditioning of safety valves, and the use of such apparatus. 
         [0004]    2. State of the Art 
         [0005]    Safety valves, especially for use in high pressure applications, such as in industrial plants operating with high pressure steam, operate in harsh environments. In use, therefore, co-operating surfaces of the valve, namely a sealing disc of an actuating member and a valve seat, may deteriorate through general wear and tear, or corrosion. As these co-operating surfaces deteriorate, they may deform and/or collect residue or deposits from a fluid passing through the valve during operation. Such deformation and/or deposits may cause contact between the co-operating surfaces to be imperfect, thus reducing the sealing performance provided by the valve. It therefore becomes necessary to recondition the valve apparatus in order to renew the profile of these co-operating surfaces such that they contact one another in a more complete manner thus providing an improved seal. 
         [0006]    Conventionally, equipment including the valve apparatus must be disassembled at least to the extent that the valve apparatus can be removed from the surrounding equipment. Once removed from the surrounding equipment the surfaces of the valve apparatus can be machined by conventional machining apparatus by mounting the individual components of the valve apparatus within the conventional machining apparatus. 
         [0007]    Where vessels or piping systems operate under extreme conditions, such as high pressures and high temperatures, they are generally provided with safety valves. For security and functional reasons, these safety valves are generally welded into the system. 
         [0008]    After welding, the joints must be heat treated and x-rayed to ensure that no imperfections or stress concentrators are retained within the joints which could lead to subsequent catastrophic failure of the apparatus. It is, therefore, difficult to disassemble the valve assembly, especially the valve seat, because this onerous process must be followed each time the apparatus is reassembled. The actuator of the valve can readily be disassembled and machined elsewhere if necessary. However, the valve seat is, conventionally, reconditioned in situ by hand. 
         [0009]    In the extreme environments in which safety valves operate, it is critical that exceptionally close contact is made between sealing surfaces of the valve. The tolerances associated with this fit, in terms of smoothness and flatness between cooperating components, are measured in terms of microns and lightbands, and are typically about 3 micrometres. 
         [0010]    Any imperfection that is present in one of the surfaces provides the superheated steam with a point focus at which pressure will be exerted and material will subsequently be removed due to mechanical wear by the high pressure steam. The valve will subsequently fail. 
         [0011]    The hand machining process to recondition a surface comprising a blemish in the order of 0.5 mm typically takes approximately 1 day to complete. The process is a multi stage process starting with a coarse grit followed by subsequently finer grits ending with a 3 micron diamond paste in order to achieve a mirror finish. These grits are applied to a lapping block which enables the technician to achieve a flat profile. The process must be repeated for the actuating member; however, the latter may be disassembled and carried out remotely from the safety equipment. 
         [0012]    Portable lathes are known, which can be mounted on shafts to re-turn shafts and roll journals and may be used to cut o-ring grooves or repair turbine spindles. However, although such in situ machining may occur, the apparatus used to carry out the machining is restricted in its functionality. The reconditioning of valve surfaces typically takes a series of operations which cannot be undertaken by a conventional portable lathe. The finish achieved by a lathe would be inaccurate and, therefore, inadequate for the tolerances required for safety valves. 
         [0013]    Conventional machines that are capable of some of the multifunctional machining processes required to re-condition a safety valve are very large. The bulk of these machines (typically of the order 0.5 tonne to several tonnes) prevents them from being transportable. They could not, therefore, be used in situ to recondition a valve seat face without removing the valve from its operational location; they thus still retain the disadvantageous need for re-welding etc. Furthermore, none of these conventional machines actually achieve each of the functions required for re-machining and reconditioning safety valves namely cutting, turning, grinding, lapping and polishing. 
         [0014]    Safety valves are generally serviced every 18 months to 3 years in order to maintain the certification to the required standard. Consequently, reconditioning of these valves is an on-going issue that is currently very labour intensive. It is desirable to provide machining apparatus to overcome some of the aforementioned disadvantages. 
       SUMMARY OF THE INVENTION 
       [0015]    According to a first aspect, the present invention provides apparatus for re-machining safety valves, which apparatus comprises:
       a first gear box having a first centre of rotation associated therewith, the first gear box being configured to receive a driving torque;   a second gear box having a second centre of rotation associated therewith, coupled to the first gearbox and configured to be driven thereby;   coupling means for transferring the drive torque from the first gear box to the second gear box and configured to define the location of the second centre of rotation relative to the first centre of rotation; and   a removable accessory assembly, coupled to the second gear box, for carrying out a respective machining (cutting, turning, grinding, lapping or polishing) operation to recondition a surface of a safety valve.       
 
         [0020]    The apparatus according to the invention can provide multiple functionality, whereby the accuracy of the reconditioning operation can be significantly enhanced. The apparatus is installed in situ on the valve body and a datum is set up. As the different cutting, grinding and polishing accessories are interchangeable, a single piece of equipment can be taken into the field of operation and used to recondition the valve without the need of very labour intensive manual finishing techniques. 
         [0021]    The present invention further comprises a method of re-machining a safety valve, which comprises providing apparatus according to the invention, attaching the removable assembly to the second gearbox, and carrying out a respective machining operation by means of the accessory assembly so as to recondition a surface of the safety valve. 
         [0022]    As previously indicated, the safety valve is preferably welded to a high temperature/high pressure vessel so that the machining operation is therefore carried out in situ, without removal of the valve. 
         [0023]    The coupling means may comprise a rotatable body, configured to be rotated by the first gear box. A clamping member may be attached to the rotatable body; such a clamping member may have a concave, lipped edge for receiving an adaptor plate and means for securely attaching the clamping member to the rotatable body. The coupling means may further comprise an adaptor plate, configured to be received by the clamping member. The adaptor plate may have a hole formed therein for receiving a locating collar of the second gearbox, the hole being offset from the centre of the adaptor plate so that angular displacement of the adaptor plate translates the centre of rotation of the second gearbox received thereby. 
         [0024]    The accessory assembly may be a cutting or turning tool assembly, a grinding tool assembly (for example, comprising a pneumatically driven grinding tool), and/or a lapping tool assembly. 
         [0025]    The apparatus may be configured to be mounted in situ, on equipment which includes the safety valve to be re-machined. Alternatively, it may be mounted remotely from such equipment and may comprise a lapping tool assembly that is configured to receive an actuating component of a safety valve. Such a lapping tool assembly comprises two lapping rings positioned concentrically on a lapping platter of the lapping tool assembly, such that the space between the lapping rings corresponds to a dimension of a protrusion of the actuating component. Furthermore, the lapping tool assembly may comprise a guide arm for engaging with and rotatably driving the actuating component to effect lapping of a surface thereof. 
         [0026]    The apparatus may be configured to be portable (that is, it may be disassembled for packing in packing cases or the like, for re-assembly when needed for use in a method according to the invention. 
         [0027]    Preferred features of the present invention will now be described, by way of example only, with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]      FIG. 1  is an isometric view of safety valve re-machining apparatus mounted in situ on a safety valve; 
           [0029]      FIG. 2  illustrates primary gearbox of the apparatus of  FIG. 1 ; 
           [0030]      FIG. 3  illustrates a secondary gearbox of the apparatus of  FIG. 1 ; 
           [0031]      FIG. 4  illustrates a grinding tool assembly for use with the apparatus of  FIG. 1 ; 
           [0032]      FIG. 5  illustrates a lapping tool assembly for use with the apparatus of  FIG. 1 ; 
           [0033]      FIG. 6  is an isometric view of a disc lapping assembly installed on the apparatus of  FIG. 1 ; and 
           [0034]      FIG. 7  is a side view of the apparatus shown in  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0035]      FIG. 1  illustrates a safety valve  10  comprising a valve body member  12  within which is located a valve seat  8  for receiving a disc of an actuable member (not shown), the valve seat  8  having a seat face  14  for interacting with the disc of the actuable member to form a seal therebetween. As illustrated, apparatus  20  for re-machining the safety valve  10  is mounted on an upper surface  16  of the valve body member  12 . 
         [0036]    A primary gearbox  22  is provided with coupling arrangement  24  for receiving a drive torque from an external drive (not shown). A secondary gearbox  26  is mounted upon the primary gearbox  22 . The secondary gearbox  26  is coupled to the primary gearbox  22  using a clamp  28 . A main drive shaft  30  extends through the centre of rotation of the secondary gearbox  26  and is rotated about this centre of rotation when its gears are driven by the external torque drive. 
         [0037]    The clamp  28  (as shown in  FIG. 2 ) comprises a crescent shaped clamping member  120  which sits within a recess  122  formed on the upper surface of the rotating member  124  of the primary gearbox  22 . The clamping member  28  is secured in place by a plurality of fixings  126  (in this example, three fixings  126  are shown). 
         [0038]    An internal curved edge  128  of the crescent shaped clamping member  120  is provided with a lipped profile such that a circular plate  130  can be located under the lip. In tightening fixings  126  so that the clamping member  120  is secured, the circular plate  130  is clamped and therefore also secured in place. The circular plate  130  is provided with a bore  132  at an eccentric location thereof. The bore  132  is so dimensioned to receive a locating collar  146  (shown in  FIG. 3 ) of the second gearbox  26  therewithin. 
         [0039]    By altering the orientation of the circular plate  130  with respect to the clamping member  120 , and subsequently tightening the fixings  126 , the axis of the centre of rotation of the secondary gearbox  26  and, therefore, the drive shaft  30  can be translated to an eccentric location with respect to the main gearbox  22 . 
         [0040]    The clamp  28 , therefore, permits the secondary gearbox  26  to be shifted laterally with respect to the primary gearbox  22 . In this way, the centres of rotation of the respective gearboxes  22 ,  26  can be offset from one another by a distance, say D. 
         [0041]    When the primary gearbox  22  and the secondary gearbox  26  are aligned so that their centres of rotation coincide, (i.e. D=0) the main drive shaft  30  is rotated at the centre of rotation of the primary gear box  22 . However, when the centres of rotation of the respective gear boxes  22 ,  26  are offset from one another using clamping  28 , the main drive shaft  30  describes an orbital motion during operation of the apparatus  20 . In other words, the main drive shaft  30  rotates about the centre of rotation of the secondary gearbox  26  but the secondary gearbox  26  itself is rotated at a distance D about the centre of rotation of the primary gearbox  22 . 
         [0042]    Returning to  FIG. 1 , the secondary gearbox  26  is provided with a vertical feed drive gear  32  which is configured to interact with a gear  34  mounted via an arm  36  and pillar  38  onto the primary gearbox  22 . During the interaction between gears  32  and  34 , the gear  32  is rotated, causing an internal mechanism of the secondary gearbox  26  to ratchet so that the main drive shaft  30  is progressively shifted in a vertical (ie longitudinal) direction with respect to the secondary gearbox  26 . 
         [0043]      FIG. 3  shows the internal mechanism of the secondary gearbox which comprises a toothed component  140  to be rotated about a finely threaded member  142  of main drive shaft  30  such that longitudinal translation or displacement can be achieved. After a period of continuous operation, the extent of the longitudinal displacement of the main drive shaft  30  may be significant. It is desirable to implement a means of rapidly returning the main drive shaft  30  to its original location to begin a subsequent cut. In order to achieve this rapid return, a quick-release mechanism is provided, whereby button  144  is actuated, to release a locking mechanism such that the main drive shaft  30  can be translated longitudinally without needing to undertake a laborious rotation process to reverse the travel along the thread of component  142  of main drive shaft  30 . 
         [0044]    Returning to  FIG. 1 , the main drive shaft  30  is hollow, and is configured to receive a feed shaft  40  therewithin. The feed shaft  40  is secured in place relative to the main drive shaft  30  through the action of clamp  42  located at an upper end of the main drive shaft  30  as illustrated in the figures and a further clamp (not shown) located at a lower end of the main drive shaft  30  within the secondary gear box  26 . 
         [0045]    A further clamp  46  is located at a lower end of the feed shaft  40  for securing a cutting accessory to the feed shaft  30 . The cutting accessory of the first embodiment, illustrated in  FIG. 1 , is a cutting tool assembly  48 . The cutting tool assembly  48  preferably comprises a tool post  50  having a tool holder  52  mounted therewithin, the tool holder being configured to accommodate a cutting tool  54 . 
         [0046]    It is necessary to be able to accurately position the accessory, in this example the cutting tool assembly  48 , relative to a surface to be cut, in this example the valve seat face  14 . In order to achieve this, the apparatus  20  comprises a mounting assembly  60 . The mounting assembly  60  comprises a support surface  62  upon which the primary gear box  22  is mounted. A plurality of legs  64 , in this example four, are attached to the underside of the support surface  62 , each respective leg  64  comprising a foot  66  connected at a distal portion of the leg. Each foot  66  is configured to be pivoted about a central axis of the respective leg  64 . A fastener  68  such as a threaded bolt and nut is provided at a distal end of each respective foot, the fastener  68  being configured to be connected to the upper surface  16  of the valve body  12 . 
         [0047]    In a first embodiment (as illustrated in  FIG. 1 ), during operation, a drive motor (not shown) for generating torque is connected to the coupling arrangement  24 . The rotary motion provided thereby is translated into a rotary motion about a longitudinal axis passing through the centre of rotation of the primary gearbox  22  through a gear assembly located therewithin. In this embodiment, the secondary gearbox  26  is not offset from the primary gearbox  22 . In other words, the centres of rotation of the two gearboxes  22 ,  26  are aligned and the drive shaft  30  and, consequently, the feed shaft  40  are caused to rotate about a central longitudinal axis of the apparatus  20 . The longitudinal axis passes through centres of rotation of each of the primary and secondary gearboxes  22 ,  26 . Upon application of torque via the coupling arrangement  24 ; the secondary gearbox  26 , the main drive shaft  30 , and the feed shaft  40  together with the cutting tool assembly  48  are all rotated about the central longitudinal axis of the apparatus  20 . The vertical feed drive gear  32  is offset from the centre of rotation of the secondary gearbox  26  and is rotated about the centre of rotation of the secondary gearbox  26  during operation. Once per revolution of the secondary gearbox  26  the vertical feed drive gear  32  comes into contact with gear  34 . Gear  32  is rotated by this interaction and a ratchet mechanism  140  is actuated such that the main drive shaft  30  is progressively displaced longitudinally towards the valve seat face  14 . As the main drive shaft  30  is so displaced, the feed shaft  40  connected thereto and the cutting tool assembly  48  are also urged towards the valve seat face  14 . Consequently, the cutting tool  54  is urged into the valve seat face  14  and material is subsequently removed from the surface of the valve seat face  14  as the secondary gearbox  26  is rotated. 
         [0048]    The radial extent of material to be removed may be too great to be achieved in a single cut. So once a first cut has been made the release button  144  is actuated and the main drive shaft  30  is returned to a longitudinal location above the valve seat face  14 . The cutting tool assembly  48  is then adjusted to reposition the cutting tool  54  at a greater radial extent and a subsequent cut is undertaken. 
         [0049]    In a second embodiment, the apparatus  20  is used to perform a grinding operation. The cutting tool assembly  48  from the first embodiment is replaced with a grinding tool assembly  70  as illustrated in  FIG. 4 . The grinding tool assembly  70  comprises a tool post  72  for connecting the grinding tool assembly to the feed shaft  40  using the accessory clamp  46 . A grinding motor  74  is accommodated within the tool post  72 . The grinding motor  74  is driven pneumatically and receives an air supply from coupling member  78  located at a remote end of the feed shaft  40  (see  FIG. 1 ). 
         [0050]    The pneumatically driven grinding motor  74  causes a grinding wheel  76  connected to the motor  74  to be rotated about a longitudinal axis of the tool post  72 . 
         [0051]    In operation, the secondary gearbox  26  is moved laterally relative to the primary gearbox  22 . The fixings  126  are released to unlock clamping means  28  and circular plate  130  is rotated within the crescent shaped clamping member  120  in order to displace the secondary gearbox  26  such that the grinding wheel  76  is positioned above a valve surface to be ground. The fixings  126  are then tightened to secure the clamp  28  and a relative offset, say D, is achieved between the centres of rotation of the primary and secondary gearboxes  22 ,  26 . During operation of the apparatus  20  the secondary gearbox  26 , and the main shaft  30 , feed shaft  40  and grinding tool assembly  70 , are rotated around the central longitudinal axis of the primary gear box  22  at a distance determined by the offset [D]. In addition to this rotary motion, the grinding wheel  76  of the grinding tool assembly  70  is rotated about its own axis by virtue of the pneumatic drive of the grinding motor  74 . Consequently, the grinding wheel  76  describes an orbital motion and, when brought into contact with a surface to be ground (eg valve seat face  14 ) removes material therefrom. As in the previous embodiment, once per revolution of the secondary gearbox  26 , the vertical feed drive gear  32  comes into contact with gear  34  causing rotary displacement of gear  32  so that the rotating internal ratchet mechanism  140  of secondary gearbox  26  causing drive shaft  30  to travel in a vertical direction to displace the feed shaft  40  and thus cause a further layer of material to be removed from the surface to be ground. 
         [0052]    Because distance D can be changed, the apparatus is particularly flexible and can be configured to recondition a large range in size of safety valve seats  8 . The apparatus can be scaled up to accommodate larger valve seats than can be machined by a given size of circular plate  130 . In the smaller range, the size of valve seat face  14  that can be reconditioned is only restricted by the diameter of the grinding tool  76 . 
         [0053]    In the smallest example, the grinding tool would rotate about its own axis and that would correspond with a central axis of the main gearbox. There would be no orbital motion. 
         [0054]    A third embodiment of the apparatus of  FIG. 1  comprises a lapping and/or polishing assembly  80  as illustrated in  FIG. 5 . The lapping assembly  80  comprises a tool post  82  having connected thereto a lapping plate  84 . 
         [0055]    The tool post  82  is inserted into the feed shaft  40  and secured thereto by tightening accessory clamp  46 . The main drive shaft  30  together with the feed shaft  40  are offset from the central axis of the apparatus  20  by releasing the clamp  28  in order to position the centre of rotation of the secondary gearbox  26  at a location offset, say a distance D, from that of the primary gearbox  22 . In other words, the centres of location of these two gearboxes are not coincident so that the secondary gear box  26 , together with the shafts  30 ,  40  and the lapping assembly  80  travel around the longitudinal axis of the apparatus  20  at a distance D, rather than rotating about their own axes. 
         [0056]    In operation, the lapping plate  84  is positioned over the surface to be polished by adjusting the offset, D, of the centres of rotation of the two gearboxes  22 ,  26  using clamp  28  as described above. The vertical location of the feed shaft  40  and, therefore, the lapping assembly  80  is adjusted by releasing clamps  42  and the lower clamp (not shown), relocating the secondary gearbox  26  and re-tightening the latter clamps once a desired location is established. Fine adjustment of the vertical location can be achieved by the manual adjustment of the vertical feed drive gear  32  to bring the lapping plate  84  into contact with the surface to be lapped and polished. The lapping plate  84  is charged with particulate matter, or grit, in a conventional manner prior to bringing the lapping plate  84  into contact with the surface to be polished. 
         [0057]    Starting with coarse grit and working in the range of say 200 microns, down in various stages to finally 3 microns (provided by silicon carbide patarticles), polishing to a mirror finish can be achieved. By using the apparatus of the present invention, the number of different stages that are used can be reduced in number. For example, an overall process that would have taken an entire day or more when lapping and polishing manually, for example to remove a blemish of 0.5 mm depth, can be achieved in less than an hour using exemplary apparatus according to the invention. 
         [0058]      FIGS. 6 and 7  illustrate a fourth embodiment of the apparatus  20 . In the fourth embodiment, the apparatus is configured to lap and polish a valve disc from the actuating member of the valve. 
         [0059]    The secondary gearbox  26  is removed from the primary gearbox  22  and a lapping platter  210  is installed onto the upper surface  124  of the main gearbox  22 . Lapping rings  212 ,  214  are mounted on the lapping platter  210  and are chosen to accommodate the size of the particular valve disc to be reconditioned. 
         [0060]    As illustrated in  FIG. 7  a valve disc  220  is supported by the inner lapping ring  214  and the outer lapping ring  212  at diametrically opposite regions of the disc  220 . This enables a protrusion  222  of the disc  220  to fall between the inner and outer lapping rings  212 ,  214  whilst maintaining contact between a surface to be ground  224  and an upper surface of each respective ring  214 ,  212 . 
         [0061]    A guide arm  216  is mounted on the main gearbox  22 . The guide arm  216  comprises drive member  218  which, in operation is brought into contact with valve disc  220  and causes the valve disc  220  to be rotated about its own central axis. This rotation of valve disc  220  causes surface  224  to come into moving contact with upper surfaces of lapping rings  212  and  214 . Lapping abrasives are charged as described above to the faces of lapping rings  212  and  214  such that lapping of surface  224  is achieved. Valve disc  220  therefore effectively undergoes orbital motion with respect to a central longitudinal axis of the primary gear box  22 . 
         [0062]    Apparatus  20  is mounted on a floor surface to undertake these lapping processes. The upper part of the valve is disassembled and the valve disc  220  is mounted onto apparatus  20 . 
         [0063]    The apparatus  20  and all its attachments can be readily disassembled and packed into three portable packing cases so that the apparatus  20  can readily be transported to any geographic location by a technician. 
         [0064]    In summary, a multi-functional apparatus is provided for reconditioning the profile of a seat face and a valve disc of a safety valve. The multi-functionality includes cutting, grinding and lapping operations. The apparatus is portable and can be taken on site and mounted in situ on equipment housing the safety valve.