PRESSURE RELEASE BURSTING DISC

Abstract: This invention is a reverse buckling rupture disc (12) having a mounting flange (20) and a pressure rupturable member (24) where the rupturable member has a one piece rupture disc with a pair of dome shaped members (22,24) projecting outwardly from the flange and where both domes are lying in the same axial orientation. The first dome shaped member (22) comprises a lower, generally arcuately shaped, wall extending in the axial direction in an arcuately and inwardly oriented configuration. The second upper dome shaped member (24) is comprised by a second arcuately shaped and inwardly extending wall which has a diameter less than that of the first dome shaped member and where the second arcuately shaped wall extends from the first arcuately shaped wall. The rupture disc assembly has a support ring adapted to support the rupture by a central aperture and means adapted to initiate a tear in said rupture disc.

Description: PRESSURE RELEASE BURSTING DISC FIELD OF THE INVENTION The invention relates to a pressure relief device, and more particularly to a pressure relief valve having a metal rupture disc in the form of a thin rupturable member of a model structure. BACKGROUND OF THE INVENTION The present invention relates to safety pressure relief devices and, in particular, to rupture disc assemblies, including reverse buckling rupture discs, and also to methods of manufacturing such rupture discs and assemblies. Rupture discs have been known in this art for many years. Normally, rupture discs are manufactured to have a rupturable membrane to provide a safety mechanism to relieve excessive pressure within an over-pressurized system or vessel. The rupture disc and/or rupture disc assemblies are typically placed within such a system or vessel so as to prevent the flow of a liquid or a gas through such a device until the rupture disc ruptures through excessive or overpressure loads. Prior art rupture disc assemblies include a support ring providing cutting projections to initiate a tear or shear in the disc upon reverse buckling. However, such assemblies are generally restricted in their use in that they are generally capable of use with gases only and sometimes within a restricted pressure range. Further, such known arrangements tend to have a fairly high rate of failure to burst within a desired pressure range. There is a constant need for improvement in rupture discs having improved operating characteristics, including the ability to be used in a more precise pressure range, and further, with improved failure resistance characteristics, particularly for use with pressurized gases. There is also a need for a disc which may be used with a variety of fluids such as various gases and liquids. Reverse buckle (or inverting) rupture disc systems consist in general of a dome- shaped metal disc which is held in a sandwich-like arrangement between two annular retainers and a support ring. The convex side faces the pressurized gas. The retainers may include cutting members for assisting rupture of the disc. Upon being subjected to sufficient pressure, the disc inverts and ruptures to relieve the excess pressure. SUMMARY OF THE INVENTION With the present invention, it has been found that by providing a rupture disc assembly with a domed portion, the base of which flares outwardly, provides improved characteristics including ease of manufacturing characteristics, better operating characteristics, and more reliability in use compared to other rupture discs known in the art. According to one embodiment of the invention, there is provided an improvement in a reverse buckling rupture disc, in which the disc has a mounting flange and a pressure rupturable member. The improvement of the present invention, according to one aspect, is where there is provided a rupturable member comprising a one piece rupture disc having a dome-shaped member projecting outwardly from said flange comprising an outer skirt portion having a first taper merging at a merger region with an inner arcuately shaped and inwardly extending dome which has a diameter less than that of the diameter of said skirt portion. In another aspect, the rupturable member comprises a one piece rupture disc having dome- shape members projecting outwardly from said flange, with the base region is a skirt which flares outwardly in a generally arcuately shaped wall extending in said axial direction in an arcuately and inwardly oriented configuration (i.e. oppositely curved from the main domed portion). The inner main dome-shaped portion comprises a second oppositely arcuately shaped and inwardly extending wall which has a diameter less than that of the diameter of said first portion. The second arcuately shaped wall extends from said first arcuately shaped wall. Without wishing to be tied to theory, it is believed that the outwardly flared portion of the dome reduces the force required to invert the dome in a disc of any given set of dimensions. This results in a greater measure of precision in the pressure level required to invert and thereby burst the disc. In another aspect, the outwardly flared base region or skirt comprises a straight- sided truncated cone (i.e. has a frusto-conical shape) or bows convexly outwardly, provided however that the skirt flares outwardly at a shallower angle than the adjoining dome wall. A further aspect of the invention resides in the junction region between the skirt and dome forming a sharp change in angle relative to the curvature of the dome wall. In another aspect of this invention there is provided a method of forming a rupture disc by providing a sheet of deformable material, forming a flange adapted to surround a dome structure, deforming the deformable sheet to form an outer dome comprising an outer skirt portion merging with the flange, further deforming the sheet of material beyond the skirt portion to form an inner dome and in which the deformation is carried out to an extent such that the inner dome has a diameter less than that of the skirt portion. In a preferred embodiment, the rupture disc defined above has an inner dome having a steeper angle of inclination than the skirt portion where the inner dome merges with the outer skirt, relative to the angle of inclination between the skirt portion and the flange. Another aspect of the present invention consists of a rupture disc assembly with a support ring adapted to support the rupture disc of the type described above. The support ring has a central aperture and means to initiate a tear , shear or cut in the rupture disc upon the disc reversing. Preferably, the means to initiate the tear shear or cut comprises at least one projection mounted on or protruding from said support ring. A particularly preferred embodiment is where the projection comprises a plurality of contiguous cutting means projecting inwardly from the aperture, said cutting means being adapted to contact the skirt position upon reverse buckling of said disc. Most desirably, the above referenced cutting means comprises a plurality of arcuately contoured segments having an innermost arc portion and corresponding outer projections. In another embodiment of the invention, in the above described rupture disc, the first accurately shaped wall of said first dome includes a plurality of spaced apart inwardly and upwardly contoured recesses. In a still further embodiment, the rupture disc skirt member is generally polygon- shaped when viewed in plan view. As well, it is preferred that the inner dome portion comprise a continuous arc or curvature extending from said skirt to the top of said rupture disc. In the above described embodiments, the radius of curvature between the lower skirt portion and the flange, as well as the radius of curvature between the skirt and the upper dome portion, is not critical per se. It can vary from being a relatively smooth transition with a rounded contour to a sharp transition. The rupture disc and support ring may be made of any suitable material from which conventional rupture discs and supports are made. Normally such materials are various types of metals or alloys such as stainless steel. The thickness of the materials used to form and support the rupture disc determine the rupture characteristics, etc. and are also known in the art. The rupture disc may be formed by different techniques known to those skilled in the art, one preferred technique uses cold deformation of a sheet of metallic material by the action of a press to deform the material into a shaped die. Thus, a die of the desired shape is provided and by deforming the metal to assume the shape of the die, the double dome of the rupture disc can be generated. The support ring can likewise be formed by conventional means such as with the use of a die having the desired configuration of the cutting means or alternatively by punching out a sheet of metal so that the support ring has the desired configuration followed by a separate bending operation to deform the cutting means into the desired angle for contact with the rupture disc upon the disc reversing. The products of the present invention can be manufactured in various sizes ranging from relatively small discs for use in conventional fields to very large diameter discs for specialized industrial applications. In general, the discs of the present invention can be used for both gaseous and liquid applications, and find desirable use in low pressure applications. However, depending on the type of material used for the disc, and other factors relating to the size and thickness of the material, other applications are also contemplated. The discs of the present invention have the advantage that they are more reliable than prior art proposals relative to operating characteristics. BRIEF DESCRIPTION OF THE DRAWINGS Having thus generally described the present invention, reference will now be made to the accompanying drawings illustrating preferred embodiments and in which: Figure 1 is an exploded cross-sectional view of a bursting disc assembly; Figure 2 is a top view of a rupture disc; Figure 3 is a top view of a support ring; Figure 4 is a cross-section of the disc taken along the line A-A of Figure 2; Figure 5 is a cross-section taken along the line B-B of Figure 3; and Figure 6 is a perspective view of the rupture disc of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT For purposes of description herein the terms upper, lower, vertical and horizontal along with other directional references shall be relative to the invention as oriented in Figure 1 , as illustrated in a pressure to non-pressure flow direction. In a typical arrangement, the flow direction is indicated by the arrows shown in Figure 1 , when the assembly is used in a typical installation. Further, "convex" and "concave" are in reference to an observer looking at the dome from the view shown in Figure 6. A typical assembly is illustrated in Figure 1 incorporating the rupture disc of the present invention, indicated by reference numeral 12, together with a support ring indicated by reference numeral 14, in combination with upper and lower (outlet and inlet) holders 18 and 16 respectively. In use, the assembly consists of the above parts joined together with the rupture disc generally sitting in a recess 28 of the lower holder 16 and with the support ring 14 lying on the outer surface. Preferably, the outer rim 28 of the lower holder 16 is interrupted and provided with a gap or interruption 30. Most preferably the gap 30 is provided or interrupted by one or more projections in the outer rim or wall portion, each of which forms an upstanding tooth-like shape or member 32. The projections or members 32 are adapted to mate with or cooperate with a corresponding or mating portion on another component of the overall assembly as described hereinafter. In another preferred embodiment, the projection 32 is spaced midway between the outer rim 28 and an inner ring wall 24. By the mating arrangement just described one can ensure proper assembly of the components of the overall assembly. The upper holder 18 includes a corresponding or mating recessed shoulder portion 70 having a circumferential or annular seat to that of the outer rim of the lower holder 16. The mating portion 70 forms a seat in the upper holder 18, which is interrupted by spaced apart projections 74 and 76. Projections 74 and 76 are dimensioned to correspond with the gap portions 30 of the outer rim 28 of the lower holder. A recess 80 is provided in the upper holder 18 which mates with the projection 32 described above. The recess 80 is generally of a similar configuration or shape to the projection 32 in order to cooperate with the latter. The corresponding projections of the upper holder 18 aid in the proper seating and assembly of the rupture disc assembly, by ensuring that the gap portions and projections are mated correctly in an abutting relationship. If the upper and lower holders 18 and 16 are not properly assembled such that the upper and lower holders are properly aligned, the upper and lower parts will not properly mate, or seat, providing an obvious visual cue that the parts are misaligned. Once placed together and in use, the assembly may be inserted in a pressure line and clamped together by conventional means, normally between flanges of adjacent pipe sections. Thus, the outer surface 25 of lower holder 16 will normally rest on the face of a first flange of a pipe section (not shown), while the outer surface 66 of the upper holder 18 will rest on a separate adjacent flange of a second pipe section (not shown). Referring in greater detail to the rupture disc of the present invention and in particular Figures 1, 2, 4 and 6, the disc 12 includes a conventional flange 20 extending about the periphery of the disc and which is adapted to provide a seating surface for the disc with a flange, as well as to provide a surface engageable with the support ring 14. In accordance with the present invention, the rupture disc includes outer and inner dome sections referenced generally by numerals 22 and 24 respectively. Dome 22 is the lowermost outer dome and comprises a generally inwardly and concavely arcuately extending wall 26. As best seen in Figure 2, the lower wall 26 of the dome actually comprises a plurality of segments 26a, 26b etc. which are formed by concave recesses in the wall, extending interiorly of the dome and which provide a generally polygonally shaped outline to the first dome when viewed from a top plan view. The purpose of these recesses is to improve the structural rigidity and inverting characteristics of the disc since the first dome section is adapted to rupture upon the disc reversing in use and by contact with the cutting means of the support ring, which will be described hereinafter in greater detail. The inwardly and concavely arcuately tapering configuration of the wall 26 is preferably substantially uniform about the circumference of the wall 26 and typically if one were to measure the average diameter of the wall 26 where it intersects with the flange 20, the first dome section will cover approximately 2% to 25% of the diameter D as measured across the opening of the upper and lower holders 18 and 16; preferably the closure of the diameter of the opening of the upper and lower holders is between 5% and 20% formed by the lower wall of the rupture disc. Depending on various factors such as the thickness of the material used to form the disc, the type of metal, etc., the size (height) of the first or outer dome or skirt 22 relative to size (height) of the inner dome 24 will vary considerably. Expressed in terms of a height percentage of the lower or outer skirt 22 relative to the height of the second dome, as measured from the commencement of the flange or above the base of the first dome or skirt 22. The height of the lower dome can be, for example, from 0.9% to about 35% of the height of the total height of the combined first and second domes. In particularly preferred embodiments, this height for the outer dome ranges from about 1.0% to 30% of the height of both domes; other embodiments are where the height of the outer dome or skirt ranges from 1.2% to 28% of the total height of both components. The height of the respective domes will vary depending on the diameter of the rupture disc and its intended use in different industrial fields. In addition, as described herein, the outer wall 26 of the first dome or skirt 22 desirably inwardly and arcuately tapers; in practice, this wall 26 may extend inwardly, relative to the flange 20 of the disc 12, in an inclined relationship to the flange 20. The degree of inclination can be relatively shallow, e.g. 1 or 2 degrees, depending on manufacturing techniques and tolerances and properties desired in the rupture disc. On the other hand, the angle of inclination can be up to 45 degrees. Preferred ranges are from 5 degrees to 30 degrees and more desirably 6 to 15 degrees. In the embodiment illustrated, the second or upper (inner) dome 24 is preferably constituted by a continuous convexly curving wall merging on its lower end with the wall 26 of the lower dome in a generally constant radius of curvature (see e.g. Figures 4 and 6). This radius of curvature can vary considerably and although a relatively smooth and continuous radius is desired, it has been found that relatively sharp radii can be employed in products of the present invention without significant losses in product characteristics. The dome 24 will have a variable height depending on the burst characteristics desired for any given application. In some cases, the height of the dome may involve a wall structure which, rather than being of a constant curvature, may have differing non-constant curved sections for certain applications in different fields. In addition, the rupture disc of the present invention may also incorporate known features such as recesses or dents in the dome to modify the properties of the dome for various uses or different applications. The outer wall or skirt 26 may alternatively have a generally inwardly tapering, straight or planar wall as seen in Figure 1. In this version, the skirt defines a truncated cone, the angle of taper is which broader and shallower than the angle of inward tapering of the inner dome 24 at the point where the skirt 26 meets the dome 24. It is also within the scope of this invention for the skirt 26 to have a convex curvature, provided however that the skirt flares outwardly from the inner dome portion 24. In this invention, it will be seen that the point of intersection between the inner and outer portions 26 and 24 are characterized by a relatively sharp change or break in curvature. Thus, the outer skirt 26 has a relatively shallow angle at the point where it meets the inner dome 24, while the wall of the dome at this same point, being near the base of the dome has a relatively steep angle. Without wishing to be tied to any theory, it is believed that this relatively abrupt change in angle assists in providing superior rupturing characteristics. This effect may also be achieved by the relatively shallow angle of disposition of the outer skirt portion. Referring now to the support ring 14, (in particular Figures 1 , 3 and 5) the ring 14 includes a generally circular flange portion 25. The ring 14 generally has an aperture which is relatively close to the size of the aperture of the upper and lower holders but, includes a plurality of cutting means in the form of projections 72 which are actually spaced apart teeth 78 which extend downwardly and inwardly into proximity of the lower wall 26 of the rupture disc, when the supporting ring 14 is assembled with the rupture disc. The teeth 78 are in the form of relatively sharp points and while one version of the teeth can be seen from the drawings, it will be understood that other cutting means may be employed. Thus, different patterns of cutting means in place of the arcuately contoured embodiment illustrated may be used. For example, as known in the prior art, a knife assembly can be used to tear, cut or shear the rupture disc upon reversing. As will be seen from Figures 3 and 7, the tab 104 of the support ring includes an aperture 102 generally in the form of a rectangular opening. This aperture 102 is adapted to receive the projection 32 to position the support ring 12 in proper alignment with the lower holder 16 as described previously. It should also be understood that the various disclosed embodiments are merely exemplary and are utilized in a manner as would be readily understood by a person in the art.

Claims: CLAIMS: 1. In a reverse buckling rupture disc having a mounting flange and a pressure rupturable member, the improvement wherein the rupturable member comprises a one piece rupture disc having a dome-shaped member projecting outwardly from said flange comprising an outer skirt portion having a first taper merging at a merger region with an inner arcuately shaped and inwardly extending dome which has a diameter less than that of the diameter of said skirt portion. 2. A rupture disc according to claim 1 , wherein said inner dome has a steeper angle of inclination than said skirt portion where said inner dome merges with said outer skirt, relative to the angle of inclination between said skirt portion and said flange. 3. A rupture disc according to claim 1 , wherein the height of the outer skirt is from about 0.9% to about 35% of the total height of the structure. 4. A rupture disc as defined in claim 1 , wherein said skirt portion has an arcuate, convex shape. 5. A rupture disc as defined in claim 1 , wherein said skirt portion has an arcuate concave configuration. 6. A rupture disc as defined in claim 1 , wherein said skirt portion has the configuration of a truncated cone. 7. A reverse buckling rupture disc comprising an outermost mounting flange and a pressure rupturable generally dome-shaped member, said generally dome-shaped member comprising an outer skirt portion joining with said flange, merging at a merger region with a dome-shaped inner wall, said outer skirt portion having an average angle of inclination from the horizontal, comprising a first angle, said inner wall portion having an angle of inclination from the horizontal at said merger region comprising a second angle, said first angle being lesser than said second angle. 8. A rupture disc as defined in any one of claims 1 to 7, wherein said skirt portion has an arcuate, convex shape. 9. A rupture disc as defined in any one of claims 1 to 7, wherein said skirt portion has an arcuate, concave shape. 10. A rupture disc as defined in any one of claims 1 to 7, wherein said skirt portion has the shape of a truncated cone. 11. A rupture disc assembly having a support ring adapted to support the rupture disc in any one of claims 1 to 10, said support ring having a central aperture and means adapted to initiate a tear, shear or cut in said rupture disc. 12. A rupture disc assembly as defined in claim 11 , wherein said means for initiating a tear comprises at least one tear-initiation projection mounted by said support ring, or a knife assembly. 13. A rupture disc assembly as defined in claim 11 wherein said tear means comprises a plurality of arcuately contoured segments having an innermost arc portion and corresponding outer projections. 14. A rupture disc as defined in claim 7, wherein said outer skirt portion includes a plurality of spaced apart inwardly and upwardly contoured recesses. 15. A rupture disc as defined in any one of claims 1 to 7, wherein said skirt portion is generally polygon shaped when viewed in plan view. 16. A rupture disc as defined in claim 2, wherein said inner dome comprises as a continuous arc or curvature extending from skirt portion to the top of said rupture disc. 17. A rupture disc according to claim 1 , wherein said rupture disc comprises a thin metallic member. 18. A rupture disc as defined in claim 1 , 2 or 3, wherein the outer skirt portion has an inward inclination by an average of at least 2 degrees from the vertical relative to the horizontal plane of said disc. 19. A rupture disc as defined in claim 18, wherein the inclination is from about 5 degrees to about 30 degrees from the vertical relative to the horizontal plane of said disc. 20. A rupture disc as defined in claim 7, wherein the skirt portion has a height equal to 0.9% to 35% of the height of the rupture disc. 21. A rupture disc as defined in claim 20, wherein the skirt wall has a height equal to 1.2% to 30% of the height of the rupture disc. 22. A method of forming a rupture disc comprising providing a sheet of deformable material, forming a flange adapted to surround a dome structure, deforming the deformable sheet to form an outer dome comprising an outer skirt portion merging with said flange, further deforming the sheet of material beyond the skirt portion to form an inner dome and in which the deformation is carried out to an extent such that the inner dome has a diameter less than that of the skirt portion. 3. The method as defined in claim 22, wherein said deformable material is a metallic material.

Inventors: GODDARD JOHN, GODDARD, JOHN
Applicants: GODDARD JOHN, GODDARD, JOHN
Application year: 2001
Main classification: F16K17
IPC codes: F16K17