Low pressure non-fragmenting rupture disks

Abstract: The rupture disks are each basically comprised of a non-metallic rupture member (12) having one or more lines of weakness (14) formed by indentations therein which define blow-out portions (16) in the rupture member. The blow-out portions are moved outwardly upon rupture of the rupture member along the lines of weakness, but remain attached to the rupture member by non-weakened portions thereof. A non-metallic reinforcing member (18) having lines of weakness (20) is attached to the rupture member for preventing tearing of the non-weakened portions of the rupture member.

Description: The present invention relates generally to low pressure non-fragmenting rupture disks and assemblies. A variety of fluid pressure relief apparatus of the rupturable type have been developed and used heretofore. Such apparatus have generally included a metallic rupture disk which is supported between a pair of supporting members or flanges which are in turn connected in a relief connection of a vessel or system containing fluid pressure. When the fluid pressure within the vessel or system exceeds the design rupture pressure of the rupture disk, rupture occurs causing pressurized fluid to be relieved from the vessel or system. Metal rupture disks usually include one or more scores on a surface thereof which create lines of weakness, along which the disks tear upon rupture, to form one or more blow-out portions which remain attached to the disks at unscored areas, see US-A-3005573 - conventional scored rupture disk, and US-A-3484817 - scored reversed buckling rupture disk. The scores are in the form of continuous grooves or indentations in the metal forming the disks. While non-fragmenting scored metallic rupture disks of both the conventional and reverse buckling types have been utilized successfully, such use has generally been limited to applications where the differential pressure at which the disks are designed to rupture is not extremely low, for example as low as, say, 0.17 to 0.68 bar. The reason for such unsuitability is that the metal rupture disks must be extremely thin in order to rupture at such low pressure differentials making the scoring of the disks impossible or impractical. Thus, there is a need for rupture disks and assemblies containing such disks which are suitable for use in extremely low pressure applications and which are non-fragmenting fragmenting upon rupture. US4479587 shows a disc concerned with two-way rupture, and increasing the difference between the rupture pressures in either direction. A flexible sealing membrane is attached to a partial support, on the side opposite a rupture member. The rupture member strength defines the rupture pressure in one direction, and the flexibility of those parts of the sealing membrane not supported by the support defines the rupture pressure in the opposite direction, rupture occurring when the deformed parts of the membrane meet cutting blades. Accordingly, the second, lower rupture pressure is defined by the shape of the support, and the elasticity of the flexible sealing membrane. This means that at very low pressures, the predictability of the rupture pressure is poor (being dependent on unpredictable rupture of a membrane), and the system is reliant on a breaking knife, which must be positioned exactly for predictable performance. The precharacterising portion of claim 1 is based on this disclosure. According to the present invention there is provided a low pressure non-fragmenting rupture disk comprising: a non-metallic rupturable sealing member and a non-metallic reinforcing member attached to said rupture member, said non-metallic reinforcing member having slits formed therein; characterised in that (a) one or more lines of weakness are formed by indentations in the sealing member so as to define at least one blow out portion in said rupture member which is to be moved outwardly upon rupture of said rupture member along said lines of weakness, but which remains attached to said rupture member by a non-weakened portion thereof, and in that (b) the slits formed in the reinforcing member correspond generally to the lines of weakness formed in the rupture member. The rupture disks of the present invention are each basically comprised of a non-metallic rupture member having one or more lines of weakness formed by indentations therein which define one or more blow-out portions in the rupture member. Upon rupture of the rupture member along the lines of weakness, the blow-out portions are moved outwardly, but remain attached to the rupture member at non-weakened portions thereof. A non-metallic reinforcing member is attached to the rupture member for preventing tearing of the non-weakened portions of the rupture member. In a preferred embodiment, the non-metallic rupture member includes radially extending indentations therein which form lines of weakness defining sector-shaped blowout portions. In order that the present invention may more readily be understood, the following description is given, merely by way of example, reference being made to the accompanying drawings in which:- Figure 1 is a top plan view of one embodiment of low pressure non-fragmenting rupture disk assembly of the present invention; Figure 2 is a cross-sectional view taken along line 2-2 of Figure 1; Figure 3 is an exploded perspective view of the assembly of Figures 1 and 2; Figure 4 is a perspective view of an alternative form of reinforcing member; Figure 5 is an exploded perspective view of a further form of rupture member and reinforcing member; Figure 6 is a side cross-sectional view of the low pressure non-fragmenting rupture disk assembly of the present invention clamped between a pair of bolted flanges; and Figure 7 is a cross-sectional view similar to Figure 6, but illustrating the rupture disk assembly after rupture. Referring first to Figures 1-3, a low pressure non-fragmenting rupture disk assembly 10 illustrated includes a non-metallic circular rupture disk 11 comprising a rupture member 12 having four radial indentations 14 formed in a side thereof which extend from the centre of the rupture member 12 outwardly to near the periphery thereof. The indentations 14 can be formed in the rupture member 12 in various ways, but a presently preferred technique is to stamp the rupture member 12 with a relatively sharp blade whereby continuous indentations, i.e., depressions, are formed in one side thereof. The indentations 14 form lines of weakness in the rupture member 12 along which the rupture member 12 tears when ruptured as a result of fluid pressure exerted thereon. The lines of weakness formed by the indentations 14 define sector-shaped blow-out portions 16 in the rupture member 12 which are moved outwardly upon rupture, but which remain attached to the rupture member 12 by non-weakened portions thereof, i.e., the portions between the outer ends of the indentations 14. Suitable materials for forming the rupture member 12, which have integrity and resistance to rupture when low pressures are exerted thereon, include a variety of plastics, resins and other materials such as graphite which is presently preferred. A rupture member 12 formed of graphite foil having a diameter of 38.1 mm, a thickness of 1 mm and having indentations 14 formed therein approximately 2.5 mm wide, 19.0 mm long and 0,152 mm deep ruptures at a differential pressure in the range of from about 0.17 to about 0.24 bar. In order to prevent the rupture member 12 from fragmenting when ruptured, i.e., to prevent the sector-shaped portions 16 from fragmenting or tearing away, a non-metallic reinforcing member 18 (Figures 2 and 3) is attached to a side of the rupture member 12. The reinforcing member 18 includes slits 20 formed therein which generally correspond in number, location and length with the lines of weakness 14, with a slit 20 aligned with each indentation 14. The support member 18 is attached to the side of the rupture member 12 opposite the side thereof in which the indentations 14 are formed. The presence of the support member 18 attached to the rupture member 12 does not increase the pressure differential required to rupture the rupture member 12 because the slits 20 are connected at the centre of the reinforcing member 18, and no resistance to rupture is provided by the reinforcing member 18. However, the non-weakened portions of the rupture member 12 are reinforced and prevented from tearing or otherwise fragmenting by the reinforcing member 18. The reinforcing member 18 can be formed of a variety of non-metallic sheet materials which have sufficient tensile strength to resist tearing upon the rupture of the rupture member 12. Films formed of plastic materials such as polyethylene, polyurethane, polyester and the like are particularly suitable. A polyester adhesive backed film is presently preferred. The reinforcing member 18 is preferably bonded to the rupture member 12 by an adhesive. Acrylic adhesives are particularly suitable for this purpose due to their high strength, flexibility and temperature resistance. For the 38.1 mm graphite rupture member having a thickness of about 1 mm described above, a polyester film reinforcing member 18 having a thickness of about 0.79 mm bonded to the rupture member 12 by an acrylic adhesive effectively prevents the tearing or fragmentation of the rupture member 12. The rupture disk 11 formed of the rupture member 12 and the reinforcing member 18 attached thereto is clamped between a pair of annular support member 22 and 24. While the annular support members 22 and 24 can take various forms, one of the support members, i.e., the support member 24, preferably includes an annular recess 26 formed therein for receiving a peripheral portion of the rupture disk 11. The support member 24 also preferably includes a cylindrical portion 28 attached thereto for aligning the assembly 10 within and between a pair of conventional bolted flanges when clamped therebetween as illustrated in Figures 4 and 5. While the support members 22 and 24 can be formed of various materials, they are preferably formed of metal and are held together with the rupture disk 11 clamped therebetween by a plurality of spot welds 30. Referring now to Figure 4, a further form of reinforcing member 33 is shown which includes four radial slits 32 which are identical to the slits 20 of the reinforcing member 18. In addition, the reinforcing member 33 includes four arcuate slits 34 formed therein, each of which is positioned transversely to and intersects with an outer end of one of the radial slits 32. The arcuate slits 34 function to prevent tearing of the reinforcing member 33 when rupture of the rupture member to which it is attached occurs. If desired, the rupture member 12 can include a variety of indentation patterns forming lines of weakness which define various numbers and shapes of blow-out portions therein. For example, more or less than four radial indentations 14 can be included in the rupture member 12 whereby more or less than four sector-shaped blow-out portions 16 are defined therein. In every case, the reinforcing member 18 will include slits formed therein corresponding in number, location and length with the lines of weakness formed by the indentations. Furthermore, the indentations can include interruptions whereby they have the appearance of dashed lines rather than continuous lines. Referring now to Figure 5, a still further form of rupture disk 40 is illustrated, which is identical to the rupture disk 11 except that instead of a plurality of radial indentations forming sector-shaped blow-out portions, the rupture disk 40 includes a rupture member 42 having a single arcuate indentation 44, which forms a line of weakness which defines a substantially circular blow-out portion 46 in the rupture member 42. A reinforcing member 48 is attached to one side of the rupture member 42 which includes an arcuate slit formed therein generally corresponding in location and length with the indentation 44 in the rupture member 42. Upon rupture, the substantially circular blow-out portion 46 is opened in a fashion similar to the top of a tin can, but remains attached to the rupture member 42 by the non-weakened area between the ends of the indentation 44. The corresponding circular portion 52 of the reinforcing member 48 opens with the blow-out portion 46 of the rupture member 42 and remains attached thereto whereby tearing or fragmentation of the rupture member 42 does not result. Referring now to Figures 6 and 7, the rupture disk assembly 10 is illustrated clamped between a pair of bolted flanges 60 and 62. Typically, the flange 60 is welded to a conduit 64 which is in turn connected to a pressure vessel or system containing pressurized fluid (not shown) which is to be protected from over-pressure by the assembly 10. The outlet flange 62 is connected to a conduit 66 which, depending upon the particular type of pressurized fluid involved, may conduct relieved fluid through the assembly 10 to an atmospheric vent or to a vessel or other location for processing or disposing of the fluid (not shown). The flanges 60 and 62 are clamped together with the rupture disk assembly 10 therebetween by a plurality of studs 68 and nuts 70. In operation of the assembly 10 and the rupture disk 11 thereof, fluid pressure is exerted on the rupture disk 11 by way of the conduit 64 and inlet flange 60. As long as the pressure level is below the design rupture pressure of the rupture disk 11, the rupture disk 11 remains intact. However, when the fluid pressure exerted on the rupture disk 11 equals or exceeds the design rupture pressure, the rupture member 12 tears along the lines of weakness formed by the indentations 14 therein whereby the sector-shaped blow-out portions 16 are moved outwardly as shown in Figure 7. Pressurized fluid flows through the assembly 10 and excess fluid pressure within the pressure vessel or system being protected is relieved as a result. The reinforcing member 18 attached to the rupture member 12 prevents all or parts of the sector-shaped blow-out portions 16 from tearing away from the rupture disk 11. Because the rupture member 12 is formed of a non-metallic material, it can have a thickness sufficient for the indentations 14 to be formed therein, but still rupture at an extremely low pressure, i.e., a pressure differential exerted across the rupture disk 11 in the range of from about 0.17 to 0.68 bar.

Claims: A low pressure non-fragmenting rupture disc (11,40), comprising: a non-metallic rupturable sealing member (12,42) and a non-metallic reinforcing member (18,38,48) attached to said rupture member, said non-metallic reinforcing member having slits (20,32,50) formed therein; characterised in that (a) one or more lines of weakness (14,44) are formed by indentations in the sealing member so as to define at least one blow out portion (16,46) in said rupture member which is to be moved outwardly upon rupture of said rupture member along said lines of weakness, but which remains attached to said rupture member by a non-weakened portion thereof, and in that (b) the slits formed in the reinforcing member correspond generally to the lines of weakness formed in the rupture member. A rupture disk according to claim 1, characterised in that said reinforcing member is bonded to one side of said rupturable sealing member by an adhesive, e.g. an acrylic adhesive. A rupture disk according to claim 1 or 2, characterised in that said rupturable sealing member (12,42) includes radially extending indentations which form lines of weakness defining sector-shaped blow-out portions therein. A rupture disk according to claim 3, characterised in that an arcuate slit (34) is associated with each radial slit (32) in the reinforcing member and is positioned transversely to and intersecting an outer end of one of said radial slits. A rupture disk according to claim 1, 2 or 3, characterised in that said rupture member includes one or more arcuate lines of weakness (44) defining a single substantially circular blow-out portion (46) therein. A rupture disk according to claim 5, characterised in that said reinforcing member (48) includes a single circular slit (50) formed therein which generally corresponds in location and length with said line of weakness in said rupturable sealing member. A rupture disk according to any preceding claim, characterised in that said non-metallic rupture member is comprised of graphite. A rupture disk according to any preceding claim, characterised in that said non-metallic support member is comprised of polyester film. A low pressure non-fragmenting rupture disk assembly comprising a rupture disk according to any preceding claim and inlet and outlet annular supporting members (22,24) adapted to be sealingly clamped together with said rupture disk therebetween.

Inventors: FITZGERALD JOHN G, FITZGERALD, JOHN G.
Applicants: BS & B SAFETY SYSTEMS INC, BS & B SAFETY SYSTEMS, INC.
Application year: 1990
Main classification: F16K17
IPC codes: F16K17