Abstract:
An improved reverse rupture disc for use as a safety pressure relief device is provided. The disc is defined by an annular flat flange region, a concave-convex disc dome region and a transition region that joins the disc-shaped flat flange region to the concave-convex disc dome region. One or more deformations may be formed at or near the apex of the disc dome region for weakening the disc to the point that incidental damage to the disc will not weaken the disc any further, thereby ensuring that the disc will reverse at a certain pressure, and no lower. The disc may also formed with one or more irregular transition regions at the base of the disc and a partial circular groove in the transition region. The irregular transition region of the disc cooperates with a shear enhancing means such as a protrusion or notch formed in a support ring or disc holder disposed downstream of the disc to sever the disc dome from the annular flat flange region along the groove in the transition region. A back pressure support means extends over the transition region and potentially over the dome region to prevent vacuum and forward to reverse cyclical pressures in the convex direction from damaging or destroying the disc. An ungrooved region of the transition region acts as a hinge holding the ruptured disc dome to the flat flange region after the disc has ruptured. The ruptured disc dome hangs over an arcuate projection formed in the support ring or disc holder, which helps to prevent the disc from fragmenting.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation in part of prior U.S. application Ser. No. 08/933,281 filed Sep. 18, 1997, now U.S. Pat. No. 6,006,938. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to safety pressure relief devices and more particularly to reverse buckling rupture discs which are designed to reverse and rupture at low bursting pressures and are highly reliable. 
     BACKGROUND OF THE INVENTION 
     Relief devices of the type commonly known as rupture discs have been utilized in industry for many years to provide a safety mechanism to relieve excess pressure from an overpressurized system or vessel in a reliable manner. The rupture disc is most frequently placed in a vent or a pressure vessel or the like so as to prevent flow of fluid through the vent until the disc ruptures. Through the years, numerous improvements have been made in the rupture disc concept in order to reduce the cost and improve the reliability of the disc. 
     A specific type of disc normally referred to as a reverse buckling rupture disc has also been utilized for a number of years and functions under the principle that a disc dome is formed in the disc which is positioned in the vent such that the disc dome points toward or faces the pressure side of the vent, i.e., the convex side of the disc dome faces the internal region or upstream side of the vent where pressurized fluid is likely to produce an overpressure that would be dangerous or destructive if not relieved. One advantage of reverse buckling type discs is that systems being protected by the discs can be operated at pressures relatively close to the bursting pressure of the disc without producing fatigue and failure which occurs in many forward acting bursting discs when operated for long periods of time near the rated bursting pressure of such devices. When fluid pressure reaches a preselected pressure for which the disc dome was designed to rupture, the disc dome starts to collapse, i.e., the column or arch of the disc dome on one side thereof starts to buckle. It is believed that as the arch on one side of the disc dome starts to collapse, a buckling-type wave typically propagates across the surface of the disc dome to the opposite side of the disc dome where total collapse eventually occurs. This buckling wave tends to create a whiplash effect on the opposite side of the disc dome so that the disc dome at this location is rather violently urged in the direction to which the concave region of the disc dome faces (i.e., the downstream side of the vent). 
     One disadvantage of some conventional reverse rupture discs is that if they are damaged during handling, installation, or otherwise, they can buckle at a pressure below the rated pressure for the disc. In some cases, the disc will buckle at a pressure of between 40 and 80 percent of the rated pressure. For example, if the rated pressure is 100 psi, a damaged disc may buckle at between 40 and 80 psi. While the reverse rupture disc may buckle or reverse at such pressures, it will not necessarily open at these pressures and once a reverse rupture disc becomes inverted, it thus acts as a forward acting rupture disc which will rupture at a higher pressure than the initial buckling pressure. For such discs the rupture pressure may be as much as three to ten times the rated pressure. 
     Another disadvantage of some conventional reverse rupture buckling devices is that they are incapable of reversing and rupturing at low bursting pressures. Bursting pressures are generally defined relative to the size of the disc. For example, 15 psig would be a low bursting pressure for a 2 inch diameter disc made of stainless steel. Conventional limitations to achieving low bursting pressures have been twofold (1) causing the rupture disc dome to reverse at a low pressure, and (2) being able to open the rupture disc at the lower reversal pressures. As previously mentioned, some damaged, conventional reverse buckling rupture discs may reverse at a low pressure but not rupture at that pressure. Also, it is more difficult to rupture conventional reverse buckling rupture discs at low pressures where the media is noncompressible (e.g., a liquid). This is because a noncompressible media such as a liquid does not impart the same dynamic energy to the dome during collapsing as a compressible media does. 
     Many of the conventional reverse buckling rupture discs include knife blades positioned on the concave side of the disc dome which are normally in spaced relationship to the disc dome, but which are engaged by the disc dome upon buckling. The knives cut the disc dome typically into quarter sections. Knife blade assemblies for reverse buckling rupture discs however add substantially to the cost of such discs and are subject to failure due to corrosive activities of the fluids within the vent system, damage during handling or simply because a mechanic forgets to install the knife assembly which in normal discs results in disc bursting pressures which are many times the rated pressures of such discs. It has, therefore, been a goal of the rupture disc industry to produce a disc of the reverse buckling type which does not include knife assemblies, but which is highly reliable. 
     One reverse buckling disc, which was specifically designed to rupture without use of knife blades, incorporates the concept of placing grooves, scores or etchings, especially in a criss-cross or circular patterns on concave or convex faces of a reverse buckling rupture disc dome. A disc dome of this type can be seen in U.S. Pat. No. 3,484,817 to Wood. In the Wood device, the rupture disc dome buckles, reverses and fractures along the lines of weakness produced by the grooves so as to form petals which are held to the remainder of the rupture disc assembly. 
     There is also a problem in some conventional systems with portions of the rupture disc being entrained with the fluid being relieved. Pieces of rupture discs can cause damage to pumps and the like if they are allowed to freely break away from the remainder of the rupture disc assembly upon rupture. Therefore, it is important that the rupture disc dome or petals of the rupture disc dome remain intact after rupture and that they remain attached to the remainder of the disc. 
     There has been a continuing desire in the rupture disc industry to produce new types of reverse buckling rupture discs which have properties that make them especially suitable for specific purposes, more cost efficient, and/or make the disc more reliable. In particular, new reverse buckling discs are desired which will function at lower burst pressures, and reliably open at or below the rated burst pressure if damaged, without the need for knife blades for cutting the disc on reversal, and yet which will remain attached after rupture to minimize possible damage to the system protected by the disc. 
     Another notable problem arises in rupture discs designed to rupture at lower pressures. Such discs become more susceptible to damage or destruction caused by induced back pressure. Vacuum pressure in the convex direction of the disc dome causes movement and fracturing at the score of a reverse rupturing disc. 
     The present application addresses shortcomings associated with the prior art. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an improved reverse buckling rupture disc that eliminates or at least minimizes the above-mentioned drawbacks of such prior art devices. The reverse buckling rupture disc according to the present invention includes a disc-shaped flat flange region, a concave-convex reversible disc dome and a transition region that joins the flat flange region to the disc dome region. The concave-convex reversible disc dome region has a thickness and a configuration such that the disc dome reverses when a predetermined fluid pressure is exerted on the convex side and ruptures upon reversal. The disc may have one or more deformations formed at or near the apex of the disc dome. The one or more deformations are provided to weaken the disc dome and thereby cause the disc to buckle or reverse at a lower pressure than a disc of similar thickness, diameter, crown height and material type not having the one or more deformations. This makes the disc suitable for low pressure applications. 
     In a second aspect of the invention, a reverse rupture disc according to the present invention includes at least one irregular transition region adjacent to the transition region and coplanar with the annular flat flange region of the disc. The disc further includes a groove which is formed along a substantial portion of the transition region of the disc. The irregular transition region of the disc dome facilitates rupturing of the disc along the groove. Preferably, the groove extends around an arc of approximately 330°, but may vary as desired. Similarly, the length or region without groove may vary as required in order to retain petal after burst. The ungrooved region of the disc forms a hinge about which the reversed and ruptured disc dome remains attached to the flat flange region of the disc after rupturing. This design prevents fragmentation of the disc dome. In a preferred embodiment of the present invention, the ungrooved portion of the disc is disposed a preselected distance from the irregular transition region. 
     In another aspect of the present invention, a shear enhancing means aids in the rupturing of the reversed disc. The shear enhancing means cooperates with the groove to facilitate rupturing of the disc along the groove upon the reverse buckling thereof. The shear enhancing means is preferably located to cooperate with the transition region, and more specifically with an irregular transition region. The shear enhancing means may consist of a protrusion or a notch which cooperates with the irregular transition. A shear enhancing means in the shape of a notch may provide better localized stress than a protrusion given the absence of support at only one location provided by a notch compared to the existence of support at only one location provided by a protrusion. The notch focuses localized stress on the groove at the corners of the notch, allowing the rupture disc dome to flex away from the pressure at the notch. More specifically, circular, triangular, rectangular, are among an infinite number of shapes of various sizes which can be employed to further control the pressure at which the disc fractures along the groove. The shear enhancing means may be a part of (e.g., affixed to) the reverse rupturing disc, although preferably the shear enhancing means is part of a support ring, or the rupture disc holder. The support ring further includes an arcuate projection which is located adjacent to the ungrooved region of the disc. The arcuate projection provides a support surface for the disc dome region of the disc after rupturing. Alternatively, the arcuate projection may be a part of a rupture disc ring or holder. 
     In another aspect of the present invention a back pressure support means protects the reverse rupture disc from damage or destruction potentially caused by induced vacuum or back pressure. The above enhancements alone, and in combination with annealing the rupture disc after forming and scoring the disc material, have enabled the design and manufacture of very low pressure reverse buckling rupture discs. However, such low pressure discs require support in the reverse direction to protect against back pressures caused, for example, by vacuum or forward to reverse pressure cyclical conditions. A back pressure support means provides additional support in the convex direction of the transition region of the disc, including support for any irregular transition region. The back pressure support means may also extend over a portion of the concave-convex disc dome, as required for functional or manufacturing purposes. The back pressure support means may be a part of the reverse rupture disc, a support ring, or the disc holder. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a reverse rupture disc according to the present invention. 
     FIG. 2 is a perspective view of another embodiment of the reverse rupture disc according to the present invention. 
     FIG. 3 a  is a perspective view of a reverse rupture disc assembly according to the present invention. 
     FIG. 3 b  is an exploded view of one embodiment of a reverse rupture disc provided with shear enhancing means and back pressure support means. 
     FIG. 3 c  is an exploded view of one embodiment of a reverse rupture disc provided with shear enhancing means and back pressure support means extending over a portion of the concave-convex disc dome region. 
     FIG. 3 d  is a cross-sectional view of back pressure support means extending over a portion of the concave-convex disc dome region. 
     FIG. 4 is a top view of the reverse rupture disc shown in FIG.  1 . 
     FIG. 5 is a cross-sectional view of the reverse rupture disc according to the present invention in an installed position. 
     FIG. 6 illustrates the reverse rupture disc according to the present invention after rupturing. 
     FIG. 7 is a perspective view of a planar material to be formed into a reverse buckling rupture disc according to the present invention. 
     FIG. 8 is a cross-sectional view of an apparatus used in forming the disc dome, deformation and irregular transition region of the reverse rupture disc according to the present invention. 
     FIG. 9 is an exploded cross-sectional view of a grooving apparatus having a knife blade for placing a circumferential groove in the transition region of the disc. 
     FIG. 10 is an enlarged fragmentary cross-sectional view of the apparatus and disc of FIG. 9 showing the disc during the actual process step of forming a groove in the transition region. 
     FIG. 11 is an exploded perspective view of the rupture disc and die from the grooving apparatus shown in FIG. 9 following the formation of a groove in the disc in the transition region. 
     FIG. 12 is a perspective view of a rupture disc holder in accordance with the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Turning now to the drawings and referring initially to FIG. 1, reference numeral  10  generally designates a reverse rupture disc according to the present invention. The disc  10  is defined by an annular flat flange region  12 , a transition region  14 , and a disc dome  16 , as is well understood by those skilled in the art. The reverse rupture disc  10  is formed of a metal material which may be made up of a number of compositions, including, for example, nickel, aluminum, gold, tantalum, and composite materials such as MONEL®, INCONEL®, or HASTELLOY C®. Alternatively, the reverse rupture disc may be formed from other suitable materials. In the presently preferred embodiment illustrated in FIG. 1, the disc dome region  16  of the rupture disc  10  has a deformation  18  formed at its geometric apex. Deformation as defined in this application refers to a weakening of the strength of the disc dome; one type of deformation may be a dimple. The deformation  18  is located in the rupture disc  10  and may have an irregular shape in the dome. The deformation  18  weakens the integrity of the disc dome  16  so that when pressure is applied to the disc  10 , it will buckle at a pressure which is lower than the rated pressure for the disc absent the deformation  18 . For example, assuming the rated burst pressure for the disc, absent any dimple, indentations, dents, or other damage, is 120 psi. The formation of the deformation  18  weakens the disc  10  so that it is likely to buckle at between approximately 40 to 80 percent of its rating pressure without the deformation (e.g., between approximately 48 to 96 psi). The depth of the deformation  18 , material thickness, and crown height may also be used to adjust or set the rated burst pressure of the disc  10 . 
     The theory behind placing the deformation  18  at the apex of the disc dome  16  is that it weakens the disc  10  at its most vulnerable location, so that the disc is less likely to buckle below its rated pressure, even if damaged. The reason that the apex of the disc dome  16  is believed to be the weakest point is because it is the thinnest region of the disc dome and it is at the geometric point on the disc dome which receives no vertical support from the disc dome column or arch. Tests have shown that incidental damage to the disc  10  in locations other than the apex does not cause the disc to buckle at a pressure lower than that required to make the disc  10  buckle with the deformation  18  formed at its apex. This design thus helps establish a minimum reliable pressure at which the reverse rupture disc  10  will buckle. With the deformation  18  being placed on the apex of the disc dome  16 , the disc  10  begins to buckle at the rated pressure at the location of the deformation  18 . Thus, the buckling initiates at the center of the disc dome  16  and propagates outward in a radial direction toward the transition region  14 . 
     In the preferred embodiment of the present invention, the annular flat flange region  12  connects to the dome  16  at an irregular transition region extending into the periphery of the dome as shown in FIG.  1 . The flat flange region  12  is located in the disc and may include an arch or cord extending in the same plane extending radially inward past the groove (as discussed further below) causing the dome to have an irregular inner diameter. This irregular transition region is indicated by the reference numeral  20  and is coplanar with the annular flat flange region  12  of the reverse rupture disc  10 . The disc dome  16  may be formed with one or more irregular transition regions  20  around the circumference of the base region of the disc dome  16 . FIG. 1 illustrates one irregular transition region  20 . FIG. 2 illustrates an alternate embodiment where multiple irregular transition regions  20  are disposed around the perimeter of the base region of the disc dome  16 . 
     Returning to the embodiment illustrated in FIG. 1, the transition region  14 , and more particularly the irregular transition region  20  of the disc dome  16 , cooperates with a shear enhancing means such as a protrusion  22  formed in support ring  24  (shown in FIG. 3 a ) or a notch  23  formed in outlet ring  25  (shown in FIG. 3 b ) to facilitate rupturing the disc  10 . Alternatively, the shear enhancing means could be part of the disc  10 , any support ring, or a rupture disc holder  27 . A shear enhancing means in the shape of a notch will provide better localized stress than a protrusion given the absence of support at one point rather than the existence of support at one point. A circular shape has been used successfully, but many shapes for the notch can be employed to channel sufficient stress to the irregular transition region  20  to meet design criteria. One skilled in the art will appreciate that single or multiple shear enhancing means with any number of shapes and locations may be employed with the multiple irregular transition regions  20  of FIG.  2 . 
     Discs designed to rupture at low pressures give rise to another aspect of the present invention, a back pressure support means which protects the reverse rupture disc  10  from damage or destruction potentially caused by induced back pressure. As illustrated in FIG. 3 b,  the back pressure support means may take the same dimensions as the transition region  14 , including the irregular transition region  20  as required for support. Alternatively, the support means may extend to a portion of the disc dome  16  in the form of a flange  29 , as shown in FIGS. 3 c  and  3   d.  The back pressure support means may be a part of the disc  10 , any support ring such as an inlet ring  21 , or disc holder  27 . One skilled in the art will appreciate that back pressure support means with any number of shapes and locations may be employed to protect the disc  10 . The embodiment illustrated in FIG. 1 b  shows a disc dome having a deformation  18 ; however, it is understood that the back pressure support means functions independently of the deformation and may be used with a standard disc dome. 
     With respect to back pressure support, the key area of the disc  10  in need of support is the scored, or grooved region  30 , to be discussed in greater detail below. The combination of employing disc grooving, deformation(s) at or near the apex of the dome, irregular transition region(s), shear enhancing means, and annealing the disc as the last step, has enabled production of very low burst pressure discs. Annealing the disc will relieve stresses incurred in the material during the forming and scoring processes, allowing the groove line to fracture more readily than without the annealing step. For example, such an annealed two inch disc, employing a notch as the shear enhancing means, will reverse and rupture at two psi. However, vacuum pressures of 15 psi are not uncommon forces in the convex direction of reverse rupturing discs. Therefore, additional support in the convex direction is required for such low pressure discs. 
     Vacuum pressure on the rupture disc dome causes it to move very slightly in the convex direction, thus flexing and fracturing the groove  30 . This is due to the very thin rupture disc material thickness remaining after being scored. The groove cannot resist much vacuum pressure and resulting movement in the convex direction before fracture. To solve this problem, an inlet ring  21  having dimensions similar to the flat flange region  12 , including any irregular transition region  20 , would sufficiently support the scored region to prevent movement of the dome  16  in the convex direction, in turn preventing undesirable score fatigue and premature failure at the groove  30 . Since the rupture disc dome  16  has rigidity from being formed, it is not required for the inlet ring  21  to support the rupture disc dome in more than the area of the irregular transition region  20 . However, for manufacturing or design requirements, or in embodiments without an irregular transition region, the inlet ring  21  may extend over a portion of the disc dome  16  in the form of a flange  29 , as shown in FIG. 3 c.  The inlet ring  21  will allow the rupture disc  10  to continue to perform satisfactorily after being exposed to full vacuum and cycling conditions of positive to vacuum pressure. 
     The rupture disc  10  further includes a partial groove  30 , which is formed in the transition region  14 . The partial circular groove  30  extends around a substantial portion of the perimeter of the disc dome  16  in an arc which is approximately 330°, as shown in FIG.  4 . The depth of the partial circular groove  30  is generally greater than 66 percent of the thickness of the disc  10  in the transition region  14 . The approximately 30° arcuate section where the partial circular groove  30  does not span is indicated generally by reference numeral  32 . One skilled in the art will appreciate that the size of the perimeter of the disc dome and the arcuate section may vary depending on design considerations. This region of the transition region  32  functions as a hinge or tab for the rupture disc  10  at the time of bursting. Upon bursting, the disc dome  16  tears away from the flange region  12  along the groove  30 , and remains intact or untorn in the tab region  32 . This design enables the disc  10  to open and retain the disc dome  16 , much like the way opening of a push-tab soda cans allows a region of the tab to remain connected. 
     FIG. 5 shows the disc  10  installed between two support rings, an upstream support ring  34  and a downstream support ring  24 . The upstream and downstream support rings  34 ,  24  hold the disc  10  in place between oppositely facing disc holders and vent pipe sections  4  and  5 , as shown in FIG. 1 of U.S. Pat. No. 4,669,626 issued to applicant, the disclosure of which is incorporated herein by reference. The upstream support ring  34  is disposed above the flat flange region  12  of the disc  10 . The inner edge of the upstream support ring  34  generally lies above the center of the partial circular groove  30 . The downstream support ring  24  is disposed below the flat flange region  12  of the disc  10 . The inner edge of the downstream support ring  24  generally lies below the center of the partial circular groove  30 . The inner edge of the downstream support ring  24  acts as a shearing edge for the groove  30 . 
     The downstream support ring  24  has a protrusion  22  and an arcuate projection  36 , best shown in FIG.  3 . It extends radially inward from the inner diameter and may vary in length or width. Alternatively, the downstream support ring  24  (e.g., outlet ring  25 ) has a notch  23  as shown in FIG. 3 b.  The protrusion  22 , or notch  23 , is located in the downstream support ring  24  or holder and may take the form of a spike, point of triangular shape, or other desirable shape. In an alternative embodiment, the protrusion  22 , or notch  23 , and the arcuate projection  36  are housed in a rupture disc holder  37  shown in FIG.  12 . In embodiments employing an irregular transition region as discussed above, the protrusion  22 , or notch  23 , cooperates with the irregular transition region  20  of the disc dome  16  to rupture the disc  10 . This occurs as follows. Once the overpressure reaches the rated pressure of the disc  10 , the disc begins to buckle and reverse. During reversal, a downward pressure is exerted on the disc  10  pushing the disc downstream. Meanwhile the protrusion  22  acts on the irregular transition region  20 , thus applying a localized, upwardly-directed counter force. Alternatively, the notch  23  would increase localized stress on the irregular transition region  20  by providing no counter force against the overpressure at one or more locations. The overpressure in combination with the oppositely directed forces due to the protrusion  22 , or the lack of counterforce due to the notch  23 , exert a stress on the partially circular groove  30 , which causes the disc  10  to initiate shearing along the groove  30 . Because the groove  30  is not formed in the tab region  32 , the disc  10  does not shear in that region. The tab region  32  thus acts as a hinge securing the ruptured disc  10  to the annular flat flange region  12 . 
     The arcuate projection  36  of the support ring  24  is downstream of, and preferably aligned with, the tab region  32  such that, when the rupture disc  10  bursts the disc dome  16  will pivot about the tab region  32  and engage the arcuate projection  36 , as shown in FIG.  6 . FIG. 6 illustrates the ruptured and somewhat crumpled disc dome, as indicated by the reference numeral  40 , wrapped about the projection  36 , especially in the area of the groove  30  that tore from the flange region  12 , but which was adjacent to the hinge region  32 . The projection  36  is arcuate along its radially inward edge. The arcuate projection  36  has radially outward ends thereof  44  and  46  which include the arch  48  therebetween (shown in FIG. 3) which is generally similar to but slightly larger than the arch encompassed by the tab region  32 . 
     The above-described design ensures that the disc  10  will not only reverse at the rated pressure (which is determined after the deformation  18  is formed therein), but also open at that pressure. The deformation  18  makes it less likely that any incidental damage to the disc  10  does not cause the disc to reverse at a pressure lower than the rated pressure. The groove  30  in combination with the irregular transition region  20  of the disc dome  16 , which cooperates with the protrusion  22 , or notch  23 , essentially ensures that the disc  10  opens at its rated pressure. 
     As discussed above, prior art discs, which have been incidentally damaged, may not both reverse and open at their rated pressure. They may reverse at a lower pressure but not open until a much higher pressure. The design of disc  10  described herein is intended to overcome these drawbacks. In addition, disc  10  can be designed to operate effectively as a reverse buckling rupture disc in a low pressure system. In this type of system, disc  10  would both reverse and rupture which is different from numerous prior art discs. Finally, the present invention does not require a knife assembly and which minimizes the likelihood of damage to the system. The disc  10  according to the present invention solves several of the problems of conventional discs. 
     FIGS. 7-11 illustrate different steps in the method of manufacture of a reverse rupture disc  10  according to the present invention and illustrate various structures utilized in the manufacture of the present invention. FIG. 7 illustrates a planar sheet of material (e.g., metal)  100  from which a reverse rupture disc, such as the previously described disc  10 , is manufactured. FIG. 8 illustrates an apparatus  102  for forming a rupture disc  10  from such a material  100 . The apparatus  102  includes an upper member  104  and a lower member  106  which generally mate together so as to define a chamber  108  therebetween. A protrusion  114  which is part of the upper member  104  is provided to form the irregular transition region  20  in the base of the disc dome  16 , as explained above and shown in FIG.  1 . 
     A fluid supply passage  116  communicates a suitable source of pressurized fluid from a hose  118  to a lower region  120  of the chamber  108 , in which chamber region  120  is shown below the material  100 . As fluid is supplied to the chamber  108  at sufficient pressure, the material  100  bulges, forming the disc dome  16 . A rod  122  having a rounded end  124  protrudes into the chamber  108  from the upper member  104  of the apparatus  102 . The rod  122  forms the deformation  18  in the disc dome  16  as the material  100  bulges under pressure. The rod  122  can be adjusted axially using a micrometer  126  which in turn adjusts the size and depth of the deformation  18 . Also, by adjusting the pressure of the fluid to the passage  116 , the height of the disc dome  16 , also known as the crown height, can be adjusted. 
     A grooving apparatus  200  for performing the grooving process is shown in FIGS. 9,  10  and  11 . The apparatus  200 , as shown in FIG. 9, includes a lower holder member  202 , an upper holder member  204 , which mates with the lower holder member  202 , a die or knife holding member  206 , and force exerting means such as the partially shown hydraulic press mechanism  208 . A prebulged disc  210  is placed in a seat  212  in the lower holder member  202 . The knife holding member  206  includes a circular knife  214  having an edge  216  having a radius which is slightly larger than the rupture disc dome radius, but the same size as the radius of the groove  30  of FIG.  1 . 
     The knife edge  216  is placed in engagement with the disc transition region  14 , as shown in FIG. 10, and force is applied by the press  208 . Stops  218  on the knife holding member  206 , shown in FIG. 9, engage the holder  202  to facilitate proper grooving of the disc  10  so that the groove  30 , as seen in FIG. 10, has a proper depth associated therewith. The knife  214 , shown in FIG. 11, is only partially circumferential and includes a sector  220  in which the knife  214  is omitted to leave a region of the disc transition region  14  ungrooved. The sector  220  occupies an arc of a preselected size (e.g., approximately 30°). The stops  218  are removed from the knife-holding member  206  to facilitate alternate use of the other stops specifically designed for other particular depths and/or other disc thicknesses. Alternatively, the knife  214  can be replaced by other types of knife members so as to the limit the depth of a groove in the region  220 . A final step after scoring may be to anneal the disc to allow the score line to fracture more readily. 
     While the present invention is susceptible to various modification in alternate forms, several of which have been discussed above, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.