REVERSE BUCKLING PRESSURE RELIEF DEVICE

Abstract: A safety pressure relief device and a rupture disc therefor, in which the relief device comprises inlet and outlet support members (12, 14) with the rupture disc (16) positioned therebetween. The rupture disc (16) has an annular outer flange portion (34) with a conical central portion (36) with the tip (40) of the conical portion being directed toward the inlet support member (12). Scoring may be provided on the onical portion for defining at least one line of weakness thereon.

Description: This invention relates to safety pressure relief devices having reverse buckling discs. Rupture discs have been used for many years to provide safety pressure relief for pressure vessels or pressurized systems. A problem with early rupture discs was fragmentation of the disc which requires cleaning of the fragments of the rupture disc from downstream portions of the system. As a result, discs adapted to rupture without fragmentation were designed. For relatively high pressure applications, knife blades were necessary to open the thicker rupture discs required. One such apparatus is disclosed in US-A-3294277 but a problem with this type of system is that the knife blade assemblies are costly. An apparatus providing rupture of a disc without fragmentation at relatively high presures and without the need of knife blades is disclosed US-A-3484817, which uses a rupture disc with an annular flat flange and a concave-convex centre portion which is positioned between two support members. The concave side of the rupture disc is directed toward the inlet support member and scoring is provided on the concave-convex centre portion for providing lines of weakness thereon. When the inlet pressure exerted on the convex side of the disc reaches a predetermined design level, the elastic stability of the disc becomes unstable causing it to reverse buckle. Upon reversal, the disc will tear along the scoring due to the tensile force exerted on it as a result of the reversing process. The disc thus opens, and, due to the fact that the tearing of the disc occurs along the scoring, no fragmentation occurs. One limitation of this design is that it is not well adapted for relatively low pressures. US 4436218 shows as defined in the preamble of claim 1 a pressure relief device comprising inlet and outlet support means with inlet and outlet openings and a rupture means including an intermediate part-conical portion and an annular flange portion. According to the present invention, there is provided a pressure relief device comprising inlet support means; outlet support means; reverse buckling rupture means comprising a disc having an annular flange portion adapted to be disposed between said inlet and outlet support means and supported thereby, characterized in that said rupture means comprises a completely conical portion disposed radially inwardly of the flange portion with a tip thereof generally facing said inlet support means. The conical configuration allows the reverse buckling disc to rupture without fragmentation at relatively lower pressures than previously known rupture discs. Scoring is preferably provided on the disc for creating a line of weakness therein, such that the disc is torn along the line of weakness, without fragmentation when the rupture means is reversed due to being subjected to a predetermined pressure. In one embodiment, the scoring comprises a plurality of scores extending radially from the tip of the conical portion. In another embodiment, the scoring comprises a curvilinear score adjacent a base of the conical portion, generally forming an incomplete circle. This curvilinear score may be on the conical portion spaced from the base or actually on the base. The inlet support means preferably comprises an inlet support member defining an inlet opening therethrough and adapted for attachment to a pressure vessel or system. The outlet support means preferably comprises an outlet support member positioned adjacent the inlet support member and defining an outlet opening therethrough substantially coaxial with the inlet opening, with the reverse buckling rupture means comprising a reverse buckling rupture disc having an annular flange portion radially outwardly of the conical portion, which extends across the inlet and outlet openings and is preferably substantially coaxial therewith. In order that the invention may more readily be understood, the following detailed description is given, merely by way of example, reference being made to the accompanying drawings, in which:- Figure 1 is a cross-sectional view of a first embodiment of the safety pressure relief device of the present invention; Figure 2 is a plan view of the outside of the rupture disc used in the embodiment shown in Figure 1; Figure 3 shows a cross-section of the device of Figure 1 after rupture of the disc has occurred; Figure 4 is a cross-sectional view of a second embodiment of the safety pressure relief device of the present invention; Figure 5 is a plan view of the outside of the rupture disc shown in the embodiment of Figure 4; Figure 5A shows an alternative construction of the rupture disc in Figure 5; and Figure 6 shows a cross-sectional view of the apparatus of Figure 4 after rupture of the disc has occurred. The safety pressure relief device 10 shown in Figures 1 to 3 includes an inlet support means (member) 12, an outlet support means (member) 14 adjacent thereto, and a rupture disc 16 disposed between the inlet and outlet support members, the inlet and outlet support members 12 defining an inlet opening 18 and an outlet opening 20 respectively therethrough, these openings being substantially coaxial. Inlet and outlet support members 12 and 14 are similar to pipe flanges in that they may have necks 22 and 24, respectively, suitable for welding to pipe of substantially the same diameter. Alternatively, inlet and outlet supporting members 12 and 14 may be threaded for receiving threaded pipe or may be constructed so that they may be inserted between two pipe flanges. In operation, inlet support member 12 is connected directly to a pressure vessel nozzle, or to a pipe which is in turn connected to a pressure system, so that fluid pressure within the vessel or system is exerted against rupture disc 16. Outlet support member 14 may be left open to the atmosphere or connected by a pipe to a second vessel or system at a lower pressure level. In the embodiment shown in Figure 1, the support members 12 and 14 are provided with a plurality of openings 26 and 28 through which pass bolts or studs 30, provided with nuts 32, to fasten the support members 12 and 14 together. Referring now also to Figure 2, rupture disc 16 comprises an annular flange portion 34 and a conical centre portion 36 disposed radially inwardly from the flange portion. A base 38 of conical portion 36 defines a transition between the conical portion and flange portion 34. Preferably, flange portion 34 and conical portion 36 are integrally formed, and rupture disc 16 has a substantially constant cross-sectional thickness. When positioned in relief device 10, flange portion 38 of rupture disc 16 is clamped between inlet and outlet support members 12 and 14 and supported thereby such that conical portion 36 extends across, and is preferably coaxial with, inlet and outlet openings 18 and 20. A tip 40 of conical portion 36 points in the direction of inlet support member 12, so that the outer side of conical portion 36 is directed toward the inlet of device 10 and subjected to fluid pressure, whereby the disc will be placed in a state of compression. Scoring is provided on disc 10 to provide at least one line of weakness thereon. In the first embodiment shown in Figures 1-3, the scoring comprises a plurality of substantially linear scores 42 extending radially on conical portion 36. Preferably, the ends of scores 42 terminate at a location spaced from base 38 and tip 40, so that they do not intersect at tip 40, whereby a high stress concentration is prevented at the tip. In the construction shown, four such scores 42 are used which substantially divide conical portion 36 of rupture disc 16 into quadrants. Disc 16 is preferably formed of sheet material that is self-supporting under normal operating pressures, but the disc will reverse itself and rupture when fluid pressures exerted on its outer side exceed those for which it was designed. Upon reversal, rupture disc 16 will tear along scores 42 due to the tensile force exerted on it as a result of the reversing process and open, forming a plurality of "petals" 43 in the manner illustrated in Figure 3. Due to the fact that the tearing of disc 16 occurs along scores 42, no fragmentation of the disc occurs. Outlet support member 14 includes, adjacent the inner end of outlet opening 20, a shoulder 44 having a diameter less than that of base 38 of conical portion 36 of disc 16, so that shoulder 44 is radially inwardly spaced from flange portion 34 of the rupture disc. Shoulder 44 provides support for the transition between conical portion 36 and flange portion 34 at base 38 and prevents premature failure of rupture disc 16 due to stress or fatigue. There may be conditions under which such a shoulder 44 is not required, so it may then be omitted. Referring now to Figure 4, a second embodiment 50 of the safety pressure relief device of the present invention is shown and includes a rupture disc 56 disposed between inlet and outlet support members 52 and 54, which define coaxial inlet and outlet openings 58 and 60 therethrough. The method of fastening inlet and outlet support members 52 and 54 together and the method of connecting device 50 to a pressure vessel or pressure system are substantially identical to that shown in the first embodiment. Referring also to Figure 5, rupture disc 56 comprises an annular flange portion 62 and a conical central portion 64 formed integrally therewith and disposed radially inwardly therefrom. A base 66 of conical portion 64 defines a transition between conical portion and flange portion 62. When installed as shown in Figure 4, conical portion 64 extends across inlet and outlet openings 58 and 60 and is substantially coaxial therewith. As with the first embodiment, a tip 68 of rupture disc 56 points in a direction toward inlet support member 52, so that the outer side of conical portion 64 is directed toward the inlet of device 50. Rupture disc 56 is substantially identical to rupture disc 16 of the first embodiment except that scoring on rupture disc 56 is in the form of curvilinear score 70. Preferably, curvilinear score 70 defines an incomplete circle on conical portion 64 adjacent base 66 so that an unscored gap or solid portion 72 is left. As shown in Figure 5, scoring 70 is spaced radially inwardly from base 66 on conical portion 64. Alternatively, a curvilinear score 70′ may be located in the transition with the base 66 as shown in Figure 5A. That is, score 70′ may be contiguous with base 66. As with the first embodiment, rupture disc 56 of the second embodiment is in compression when subjected to pressure on the inlet side of relief device 50. When the rated rupture pressure is reached, rupture disc 56 will reverse itself and then tear along curvilinear score 70 so that a radially inner portion 74 of rupture disc 56 will lift toward the outlet of device 10, as shown in Figure 6, in a fashion similar to the top of a "pop-top" can. Rupture disc 56 does not tear at solid portion 72, and thus inner portion 74 is prevented from detaching itself completely. In this way, rupture disc 56 will rupture at a predetermined pressure without fragmentation, just as with the first embodiment.

Claims: A pressure relief device comprising inlet support means (12,52); outlet support means (14,54); reverse buckling rupture means (16,56) comprising a disc having an annular flange portion (34,62) adapted to be disposed between said inlet and outlet support means and supported thereby, characterized in that said rupture means comprises a completely conical portion (36,64) disposed radially inwardly of the flange portion with a tip (40,68) thereof generally facing said inlet support means (12,52). A device according to claim 1 wherein said rupture portion (36,64) is integrally formed with said flange portion. A device according to claim 1 or 2 wherein said conical portion (36,64) and flange portion (34,62) are integrally formed of a material of substantially constant cross-sectional thickness. A device according to any preceding claim wherein scoring (42,70,76) is formed on said conical portion (36,64) for creating a line of weakness therein such that said conical portion is torn along said line of weakness when said rupture means is reversed due to being subjected to a predetermined pressure. A device according to claim 4 wherein said scoring (42) comprises a plurality of scores extending radially from said tip (40). A device according to claim 5 wherein each of said scores (42) is spaced from said tip (40). A device according to claim 5 wherein said scoring (70,70') comprises a curvilinear score adjacent a base (66) of said conical portion (68). A device according to claim 7 wherein said curvilinear score (70) is spaced from said base (66). A device according to claim 7 wherein said curvilinear score (70') is contiguous with said base (66). A device according to claim 7, 8, or 9 wherein said curvilinear score (70,70') defines an incomplete circle.

Inventors: WALKER, WILLIAM J.
Applicants: BS & B SAFETY SYSTEMS, INC.
Application year: 1988
Main classification: F16K17
IPC codes: F16K17