Fluid handling – Destructible or deformable element controlled – Destructible element
Reexamination Certificate
1999-09-20
2001-02-27
Fox, John (Department: 3753)
Fluid handling
Destructible or deformable element controlled
Destructible element
C137S068210, C137S068270, C137S068290
Reexamination Certificate
active
06192914
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to rupture disk apparatus and manufacturing methods, and more particularly, to rupture disks, assemblies, and manufacturing methods wherein the rupture disks have an area or areas of weakness to facilitate opening of the disk.
2. Description of the Prior Art
A great many pressure relief devices of the rupture disk type have been developed and used. Generally, such devices include a rupture disk supported between a pair of support members or flanges, which are in turn connected to a relief connection in a vessel or system containing pressurized fluid. When the pressurized fluid within the vessel or system exceeds the design rupture pressure of the rupture disk, the disk ruptures causing pressurized fluid to be relieved from the vessel or system.
Rupture disks fall into the general categories of forward acting tension type disks and reverse acting disks. Certain forward acting tension type disks have been developed using a score line in the surface of the disk to ensure opening at a specific area. More recently, reverse buckling rupture disks have also included scores formed on a surface to define an area or areas of weakness such that upon reversal, the disk tears in such area or areas of weakness. Scored reverse buckling rupture disk manufacturing methods are described in U.S. Pat. No. 4,441,350 to Short et al. issued on Apr. 10, 1984 and U.S. Pat. No. 4,458,516 issued to Naumann on Jul. 10, 1984.
While scored reverse buckling rupture disks have been used successfully and have obviated the need for knife blades in a number of applications, fragmentation and/or tearing away of portions of the disks can still be a problem. That is, upon the reversal and rupture of the scored reverse buckling rupture disk in the area or areas of weakness defined by the scores, fragmentation and tearing away of parts from the disk can occur. These same fragmentation and tearing away problems may also occur in tension loaded rupture disks.
To reduce the chances of fragmentation upon rupture, C-scored techniques have been developed. Such disks include, but are not limited to, an area or areas of weakness formed by one or more scores which define a circular or similar blow-out portion hinged to the reminder of the disk by an unweakened hinge area. Also, with respect to reverse acting disks, rupture disk assemblies have been developed that include a support member to contact the disk as it reverses and thereby lessen the chance of tearing away. For example, U.S. Pat. No. 5,167,337 to Short et al. issued Dec. 1, 1992 describes a C-scored reverse buckling rupture disk assembly that includes an inwardly extending support member for preventing the blow-out portion of the disk from fragmenting or tearing away at the hinge upon rupture.
A general problem in the manufacture of scored rupture disks that has continued to exist is that the tooling used to form the scores can be and often is damaged when the disk material is scored too deeply. For example, score dies of the type described in U.S. Pat. Nos. 4,441,350 and 4,458,516 cited above can be and often are collided together which dulls or breaks the score blades requiring their repair or replacement. Yet another problem with conventional scoring techniques is that the material directly under the score blade becomes work hardened such that it may be difficult to score the disk to a desired thinness.
Another problem that has existed in scored rupture disks prior to the present invention is the premature failure of the disks due to pressure cycling. Pressure cycling occurs in many rupture disk applications and includes positive pressure variations, as well as going from a positive to a negative pressure. Fluctuation in the pressure of the pressurized fluid exerted on the rupture disks may cause them to flex, which in turn may cause the material forming the disks to fatigue and fail at the score or scores in the disks. This in turn results in the development of leaks and/or the premature failure of the disks. The industry has attempted to minimize this fatiguing problem by supporting the scored region with, for example, the rupture disk head. However, this approach has not completely relieved the problem.
Thus, there is a continuing need for improved rupture disks, assemblies and methods which obviate the above mentioned problems.
SUMMARY OF THE INVENTION
Improved rupture disks, rupture disk assemblies, and manufacturing methods are provided which meet the needs described above and overcome the shortcomings of the prior art. The improved rupture disks of this invention have an area or areas of weakness therein at which the disks rupture or open. The invention is comprised of a rupturable member formed of a material, preferably malleable, adapted to be sealingly engaged in a pressurized fluid passageway. The disk includes at least one weakened region comprised of material displaced by a partial shearing movement to thereby form a thinner cross section than the remainder of the disk, with the material being displaced in a shear direction. The weakened region is formed in or adjacent to the rupturable member such that it defines an area of weakness for opening, yet does not result in a region that is susceptible to fatigue failure. In this regard, the flange of the disk can act to support the weakened region and avoid the need to utilize a separate support member.
The rupture disk of the present invention may include a flange having an inner and outer peripheral edge, the flange being offset from the rupturable member of the disk to expose the peripheral edge of the rupturable member and the inner peripheral edge of the flange. The peripheral edge of the rupturable member and the inner peripheral edge of the flange will be exposed on opposite sides of the fluid passageway, i.e., on the inlet side of the disk and on the outlet side of the disk. The weakened area includes a thinner cross section than the flange and rupturable member.
The improved rupture disk assemblies of the present invention are comprised of inlet and outlet rupture disk support members, a rupture disk having an area or areas of weakness which define a blow-out portion in the rupture disk, and a safety member positioned between the rupture disk and the outlet support member having a configuration for preventing the blow-out portion of the rupture disk from fragmenting or tearing away upon rupture and having at least one rupture initiating, stress concentrating point positioned to contact the rupture disk upon reversal to ensure opening. The stress concentrating point(s) is preferably positioned to contact the rupture disk at the weakened area.
A method of producing improved rupture disks having an area or areas of weakness along which the disks rupture is also provided. The method comprises the steps of forming a rupturable member, preferably of malleable material, adapted to be sealingly engaged in a pressurized fluid passageway, and forming an area or areas of weakness in or adjacent to the rupturable member, by displacing material with a partial shearing motion. The weakened area or areas is/are preferably formed using dies which are offset and are incapable of colliding. The weakened area may be formed such that the flange of the rupture disk acts as a support for the weakened area. As such, the fatigue life of the disk is improved when subjected to pressure variations in the fluid passageway.
Finally, a method of ensuring that a reverse buckling rupture disk having an area or areas of weakness formed therein ruptures after reverse buckling. The method comprises placing a safety member adjacent to the rupture disk on the outlet side of the rupture disk, the safety member having at least one rupture initiating, stress concentrating point positioned to contact the rupture disk at the area of weakness when the rupture disk reverse buckles.
It is an object of the present invention to provide an improved weakened region in a rupture disk to facilitate opening of the disk at the predetermined pressure ra
BS&B Safety Systems, Inc.
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Fox John
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