IMPROVEMENTS IN AND RELATING TO RUPTURE DISC ASSEMBLIES

Abstract: A rupture disc assembly comprises a holder member (4) of a substantially incomprenssible material one end face of which is recessed (8) to receive therein a rupture disc member including a disc portion (2) of a frangible ma­ terial such as resin-impregnated graphite. When located in position within the recessed holder member (4) the outer surface of the disc portion (2) of the rupture disc member is substantially co-planar with the one end face of the holder member whereby, an clamping the assembly in position on a system to be monitored, the clamping forces on the assembly are applied to the substantially incom­ pressible material of the holder member (4) and not to the frangible material of the disc portion (2).

Description: IMPROVEMENTS IN a TING RELATING TO RUPTURE DISC ASSEMBLIES TECHNICAL FIELD This invention relates to rupture disc assemblies for use as safety relief devices on pressurised systems such as pressure vessels. BACKGROUND ART It is common practice, and has been for'some time, to provide such rupture disc assemblies incorporating resin-impregnated graphite discs as the rupturing elements, the consistency in the mechanical properties of the frangible graphite and the economy of manufacture of such discs making them comnercially viable. However, thc established arrangements have certain disadvantages. In one known arnangement, an assembly includes an accurately-machined, flat disc of resinimpregnated graphite located in a holder member compris- ing opposed inlet and outlet supporting portions, with the interposition of sealing gasket(s) where necessary, the disc and holder member being connected into a pressure system or vessel by being clamped between, for example, inlet and outlet pipe flanges. If the flange bolts are overtorqued or torqued unevenly, or if the clamping surfaces are misaligned, there is a strong tendency for the graphite disc to crack because of tne excessive or uneven forces acting thereon. An alternative Icnown arrangement utilises a single block of graphite comprising a cylinder of resin impregnated graphite of substantial depth compared with the thickness of normal graphite discs, said cylinder being accurately and centrally recessed from one end face thereof to provide an integral rupture membrane at the other end thereof. Such a unit can be bolted directly between inlet and outlet pipe flanges in a pressurised system without the requirement for a separate holder member. However there is still a tendency for the graphite to crack when subjected to the above-detailed excessive or uneven forces, while the recessed cylindrical block has the additional disadvantage, particularly at higher pressures, of being susceptible to sideways rupture through tne annular wall thereof. The invention as claimed is intended to overcome these disadvantages. OF 0? XZ VE ICE according to the present invention there is provided a rupture disc assembly comprising an annular holder member of a substantially incompressible material for location on a pressurised system to be monitored and a rupture disc member including a disc portion of a frangible material, characterised in that one end face of said holder member is recessed to provide therein a seating for said rupture disc member such that the outer face of the disc portion of said rupture disc member is substantially co-planar with said one end face of she holler Lember. buch an arr###ement ensures that, if the assembly is subjected to excessive or uneven loading, any tendency for the assembly to deform is resisted b the material of tne holder member which can withstand the forces thereon, thereby protect nag the disc portion of the rupture disc member from possible distortion, creckir, or the like. Further, the provision of 2 holder member of a rigid, non-deformable material eliminates the possibility of sideways blow-out. 'the assembly may further comprise an annular spacer member seating in the recessed holder member to locate the rupture disc member within said holder member with the outer face of the disc portion thereof substantLally co-planar with said end face of the holder member. The spacer member may be of a substantially incompressible material and may be located to constitute an axial extension, from the inner face of the disc portion, of the annular outer regions of said disc portion, or, alternatively may comprise a ring of substantially the same thickness as the disc portion and surrounding said disc portion to form a radial extension thereof. In a further embodiment, the rupture disc member includes, integrally formed with the disc portion, a further portion of said frangible material forming an axial extension, from the inner face of the disc portion, of the annular outermost region of said disc portion, said further portion of the rupture disc member comprising said spacer member. The material of the disc portion is conveniently graphite, preferably resin-impregnated graphite, although other frangible materials such as glass or ceramics may be used, The holder member is conveniently of metal or metal alloy, for example zinc-plated carbon steel, although non-metallic materials having the necessary resistance to deformation may be used. The preferred assembly further comprises inlet and outlet sealing gaskets which may be secured, for example by an adhesive, to the end faces of the holder member. The assembly may be provided with identification mwans including a tag portion extending substantially radially outwardly from the assembly and on which is stamped or otherwise marked operative details of the assembly. Conveniently the tag portion is in#tegrally formed with or attached to the above-mentioned ring-shaped spacer member. The rupture disc assembly may be clamped directly between annular inlet and outlet flanges of the pressurised system to be monitored, or may be located in or form part of a further holder member itself clamped between said inlet and outlet flanges. BKIbF DESCRIPTION OF THE 10ìfl Fig. 1 shows, disassembled, a holder member and a rupture disc member of an assembly according to the invention; Big. 2 shows an assembly according to the invention; Fig. 3 shows the assembly of Fig. 2 in position between inlet and outlet flanges of a pressurised system; Figs. 4,5 and 6 show three further assemblies according to the invention, and Fig. 7 is a plan view from above of an assembly according to the invention which is a modification of that shown in Fig. 5 and including identification means. BESG P"iODI# OF CARRYIISG OUT THE i:N7Ei\TTIc;i# Referring to Figs. 1 to 3 of the drawings, the illustrated assembly includes a rupture disc member in the form of a flat disc 2 of resin-impregnated graphite, and an annular holler member indicated generally at 4. The bore 6 through the member corresponds in diameter with that of the bore to be monitored, while an end face of the holder member is accurately recessed at 8 to receive therein the disc 2 so that the upper or outer surface of said disc is substantially co-planar with said end face of the holder member 4. The assembly is completed by a pair of gaskets 10 one to each end of the holder member 4, said gaskets being secured, preferably by an adhesive, to the holder member 4 to retain the disc 2 within said member 4 and to provide an easily handleable unit as shown in Fig. 2. The holder member 4 is made from a material that is substantially incompressible when subjected to the clamping pressures involved and as will be explained in more detail below, which material is conveniently a metal such as carbon steel suitably protected against corrosion by, for example, zinc plating. However other metals, metal alloys or non-metallic materials incorporating the necessary resistance to deformation may be used. In use, the assembled unit is positioned between inlet and outlet pipe flanges 12,14 respectively of a pressurised system, said flanges being bolted together to locate the assembly in its operative position with the bore 6 of the holder member 4 forming a continuation of the pipe flange bores and with fluid pressure being applied, in the direction of arrow P, to that part of the disc within the bore as seen in Fig. 3. It will be appreciated that, on bolting the pipe flanges together, the major portion of the clamping pressure is exerted, through the sealing gaskets 10, on the end faces of the holder member 4, while pressurised sealing contact is also made with the radially outer annular region of the disc 2 the outer or upper surface of which is substantially co-planar with that of the upper end face of the holder member 4. However, any excess loading of the bolts is resisted by the substantially non-deformable nature of the material of the holder member and is not transmitted to the frangible disc 2 itself. When positioned in the recess 8 in the holder member 4, the upper surface of the disc 2 may be slightly proud of the upper end face of the holder member 4 (by of the order of 0.001 inches) to ensure a good seal when the clamping pressure is applied thereto through the upper gasket 10. However said upper surface of the disc could be slightly below said upper end face of the holder member 4 if, on application of the clamping torque, the -upper gasket 10 is sufficiently deformable to ensure a pressure-tight seal with the disc 2. Although described in relation to a rupture member of resin-impregnated graphite, the assembly of the invention may include rupture members of other frangible materials such as glass or ceramics. The provision of a holder member 4 of a rigid, nondeformable material eliminates the possibility of sideways blow-out, while the accurate machining of the recess 8 in the holder member 3 of Figs. 1 to 3 to suit a disc 2 of predetermined dimensions ensures that the upper surface of the disc 2 and the upper end face of the holder member 4 are maintained level to close tolerances, typically 0.001 inches, thereby ensuring a pressure seal between the disc 2 and the holder member 4. Referring to i'ig. 4, the holder member 4 includes a recess 8 the diameter of which corresponds with that of the disc 2 to be received therein but the depth of which is substantially greater than the thickness of the disc 2. An annular spacer member 16 of S substantially incompressible material, for example stainless steel, is located in the recess as shown so that the inner face thereof provides a continuation of the inner face of the non-recessed part of the holder member 4 and so that the upper end face of said spacer member 16 provides an accurately positioned seating for the disc 2 whereby the outer face of said disc is substantially co-planar with the recessed end face of the holder member 4. The disc 2 may or may not be bonded to the spacer member 16, while inlet and outlet sealing gaskets 10, as in the embodiment of Figs. 1 to 3, may or may not be bonded to the holder member 4 and disc 2. It will be appreciated that the provision of a spacer member 16 as shown in Fig. 4 enables discs 2 of different thickness to be received in the same holder member 4 whilst still maintaining the outer face of such discs substantially co-planar with the recessed end face of the holder member 4. It is merely necessary to provide a spacer member 16 of a depth such that the upper end face thereof provides a seating located at the desired position in the holder member 4 dependent upon the thickness of the disc to be used therewith. Fig. 5 illustrates an arrangement similar to that of Fig. 2 except that an annular spacer member 16 of a substantially incompressible material and of thickness substantially equal to that of the disc 2 surrounds said disc to form a radial extension thereof. The recess 8 in the holder member 4 is suitably dimensioned to receive the combination of disc 2 and spacer member 16, which components may or may not be bonded to one another. Inlet and outlet sealing gaskets 10 again complete the assembly. In the embodiment of Fig. 5, the major portion of the clamping load when tne assembly is located between inlet and outlet pipe flanges is exerted, through the gaskets 10, on the holder member 4 and spacer member 16 both of which are of a rigid, non-deformable material capable of withstanding the forces involved. Referring to Fig. 6 there is shown an embodiment similar in appearance to that of Fig. 4, but the spacer member 16 is integrally formed with the disc 2 to form part of the rupture disc member itself and is of the frangible material of said disc 2, preferably resinimpregnated graphite. As an alternative to this arrangement an annular spacer member 16 separate from the disc 2 may be provided in accordance with Fig. 4, but of a frangible material such as resin impregnated graphite. Such a spacer member may or may not be bonded to the disc 2. All the described assemblies may be clamped directly between inlet and outlet pipe flanges such as those shown at 12,14 in Fig. 3 or may themselves be located in, or form part of, further holder members prior to being clamped in the system to be monitored. In all cases, however, the major portion of any clamping load is taken by the substantially incompressible material of the holder member 4 or, in the embodiment of Fig. 5, by said holder member 4 and spacer member 16. It is preferable for rupture disc assemblies to include means thereon for identifying the characteristics of the assembly in question when said assembly is in position in te system to be monitored. This is readily achieved with metal discs which can be provided with tags integrally formed therewith or attached thereto and extending radially outwardly therefrom. However the attachment of such tags to graphite discs is not so readily achieved. he incorporation in the described assemblies of metal parts, however, enables the attachment thereto of identification tags. For example such tags may be fixed to, or formed as part of, the holder member 4 to project outwardly from the assembly. Alternatively, an additional component to the assembly may be provided in the form of an annuls, preferably metal, bonded to the face of the inlet sealing gasket 10 remote from the disc 2 and including a tag portion projecting radially outwardly therefrom for identification purposes. The inlet sealing gasket 10 may, in turn, be bonded to the disc 2. The embodiment of Fig. 5 provides a particularly convenient means of incorporating an identification tag and this is illustrated in Fig, 7. Referring to Fig. 7, the annular spacer member 16 is shown surrounding, to form a radial extension of, the disc 2, said spacer member 16 being formed of an incompressible metal. Integrally formed with the spacer member 16 is a tag portion 18 which extends radially outwardly from the spacer member 16 and from te assembly as a whole. A groove in the upper surface of the holder member 4 accommodates a reduced-thickness arm portion 20 of the tag portion 18. Clearly, the characteristics of the rupture disc member/ assembly can be stamped or otherwise marked on the tag portion 18. For ease. of handling it is preferable for at least the disc 2, inlet sealing gasket 1G and spacer member 1 and identification means if present to be secured together to form a single, readily handleable component for easy insertion into an associated holder member 4.

Claims: CLAIMS 1. A rupture disc assembly comprising an annular holder member (4) of a substantially incompressible material for location on a pressurised system to be monitored and a rupture disc member including a disc portion (2) of a frangible material, characterised in that one end face of said holder member (4) is recessed (8) to provide therein a seating for said rupture disc member such that the outer face of the disc portion of said rupture disc member is substantially co-planar with said one end face of the holder member (4). 2. A rupture disc assembly as claimed in claim 1 and further comprising an annular spacer member (16) seating in the recessed holder member (4) to locate the rupture disc member within said holder member with the outer face of the disc portion ( < ) thereof substantially co-planar with said one end of the holder member (4). 3. A rupture disc assembly as claimed in claim 2 in which the spacer member (16) is located to constitute an axial extension, from the inner face of the disc portion (2), of the annular outermost region of said disc portion. 4. A rupture disc assembly as claimed in claim 3 in which the spacer member (16) is of a substantially incompressible material. 5. A rupture disc assembly as claimed in claim 3 in which the rupture disc member includes, integrally formed with the disc portion (2), a further portion (16) of said frangible material forming an axial extension, from the inner face of the disc portion (2), of the annular outermost region of said disc portion (2), said further portion (16) of the rupture disc member comprising said spacer member. 6. A rupture disc assembly as claimed in claim 2 in which the spacer member (16) comprises a ring of substantially incompressible material of substantially the same thickness as the disc portion (2) and surrounding said disc portion (2) to form a radial extension thereof. 7. A rupture disc assembly as claimed in any one of claims 2,3,4 or 6 in which the spacer member (16) is bonded to the disc portion (2). So A rupture disc assembly as claimed in any one of claims 1 to 7 in which the frangible material is resinimpregnated graphite. 9. A rupture disc assembly as claimed in any one of claims 1 to 8 in which the substantially incompressible material is zinc-plated carbon steel. 10. A rupture disc assembly as claimed in any one of claims 1 to 9 and further comprising inlet and outlet sealing gaskets (10) one to each end of, and secured to, the holder member (4). 11. A rupture disc assembly as claimed in any one of claims 1 to 10 and further comprising identification means including a tag portion (18) extending substantially radially outwardly of the assembly and carrying operative details of the assembly. 12. A rupture disc assembly as claimed in claim 11 together wit claim 6 in which the tag portion (18) is integrally formed with or attached to said ring (16) of substantially incompressible material. 13. h rupture disc assembly as claimed in any one of claims 1 to 12 and clamped directly between annular inlet and outlet flanges (12,14) of the Bressurised system to be ulonitored. 14. A rupture disc assembly as chimed in any one of claims 1 to 12 and located in or forming art of a further holder member itself clamped between annular inlet ard outlet flanges (12,14) of the pressurised system to be monitored.

Inventors: BALFOUR, IAN DAVID, BUSH, MICHAEL EDWARD, CARBIN, DEREK CHARLES
Applicants: ELECTROFABRICATION & ENGINEERING COMPANY LIMITED
Application year: 1980
Main classification: F16J3
IPC codes: F16L29, F16K17