Patent Application
20120291282
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.
1. Field of the Invention
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.
2. State of the Art
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
According to a first aspect, the present invention provides apparatus for re-machining safety valves, which apparatus comprises:
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.
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.
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.
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.
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.
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.
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.
Preferred features of the present invention will now be described, by way of example only, with reference to the accompanying drawings.
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.
The clamp 28 (as shown in
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
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.
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.
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.
Returning to
Returning to
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
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.
In a first embodiment (as illustrated in
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.
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
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.
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.
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.
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.
A third embodiment of the apparatus of
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.
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.
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.
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.
As illustrated in
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.
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.
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.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0900949.9 | Jan 2009 | GB | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/GB2010/050080 | 1/21/2010 | WO | 00 | 7/20/2011 |
