Fluid handling – Destructible or deformable element controlled – Destructible element
Reexamination Certificate
2000-04-19
2002-04-30
Rivell, John (Department: 3753)
Fluid handling
Destructible or deformable element controlled
Destructible element
C137S625270, C137S910000
Reexamination Certificate
active
06378544
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a pressure relief device and method of using the same. The pressure relief device is useful in systems needing protection from overpressurization or underpressurization. The pressure relief device of the present invention is particularly useful in systems where an ultra-clean environment is desired.
BACKGROUND OF THE INVENTION
A wide variety of pressure relief devices for preventing overpressurization or underpressurization in systems have been developed. A pressure relief device generally operates by relieving fluid pressure when a predetermined pressure is reached in a system either through a part of the pressure relief device breaking, fragmenting, severing, etc., to create a path for fluid to escape. Pressure relief devices in use today include for example rupture disks, safety relief valves, safety heads, and explosion vents.
Pressure relief devices are currently made of common or exotic metals, such as stainless steel, nickel, inconel, monel, aluminum, Hastelloy C, or tantalum; carbon, such as graphite, baked carbon, or resin impregnated carbon; or rigid plastics such as polyphenylene sulfide. Pressure relief devices can also be made of a single part or several parts. For example, single part rupture disks are typically flat or domed-shaped, and typically are made of either metal or graphite. Rupture disks containing several parts (hereinafter referred to a “composite rupture disks”) include several different components made of the same or different materials. For example, a rupture disk may contain one or more reinforcing layers of plastic in combination with metal, or may include additional components such as vacuum supports or disk cutting elements.
Common rupture disk designs include domed shaped disks having concave and convex sides. Dome shaped rupture disks where the concave side is exposed to fluid pressure is commonly known as a “conventional rupture disk.” Conventional rupture disks are placed in tension by the force of fluids under pressure, and rupture occurs when the tensile strength of the disk material is exceeded. Dome shaped rupture disks where the convex side of the disk is exposed to fluid is known as a reverse buckling disk. Reverse buckling disks are placed in compression by fluid pressure and the concave-convex surface reverses and ruptures when a certain pressure is exceeded. Reverse buckling disks may also include cutting elements that puncture the disk when the disk reverses.
Carbon containing rupture disks (e.g., graphite) also have various designs. One common design is a monolithic type design. In a monolithic type design, a disk formed from carbon contains a central bore that is machined only partially through the thickness of the disk. The depth of the bore is such that the carbon between the bottom of the bore and the unmachined side of the disk is of a thickness and strength to rupture at a desired rupture pressure. The monolithic type disk is typically bolted between pipe flanges and the central portion of the disk between the bottom of the bore and the unmachined side blows out to relieve pressure. Another common design for a carbon containing rupture disk includes a holder and replaceable carbon disk. Upon rupture, only the carbon disk needs to be replaced. Carbon rupture disks and particularly graphite rupture disks have been found to have good chemical corrosion resistance.
However, in certain industries, pressure relief devices made of metals, carbon, and plastics materials are often unacceptable. For example, metallic pressure relief devices can withstand only a limited number of pressurization and depressurization cycles, after which the rating of the device will change or the device will burst at normal operating pressures due to metal fatigue.
Moreover, in industries where corrosive fluids are used, pressure relief devices made of metals, carbon or plastics may be weakened and/or have a shortened lifetime from contact with corrosive fluids. Additionally, the contact of the corrosive fluid with the pressure relief device can result in the formation of undesirable contaminants. These contaminants are especially a concern in systems where an ultraclean environment is needed (environment where there is minimal particle, metallic, or organic contamination). Examples of such systems are those used in the manufacture of electronic components, such as semiconductors, flat panel displays, and computer memory drive; satellite components; photolithography masks; pharmaceutical; and foods. In these systems, even minute levels of contaminants can have a detrimental effect on the product being produced. Thus, there have been attempts to develop pressure relief devices with improved corrosion resistance properties.
One solution that has been proposed is to line or coat the pressure relief device with a polymeric corrosion resistant material such as a fluoropolymer. Although fluoropolymer liners provide some degree of protection against corrosion of the pressure relief device and contamination of the process fluids used within the system, these liners have a limited life and can pass chemicals or vapors to the pressure relief device. For example, liners can fail via pinholes or tears thus allowing fluids in the system to directly contact the pressure relief device and cause corrosion. Even without such failures, liners can have some permeability to liquids, gases, and dissolved gases in liquids.
Another solution is proposed in U.S. Pat. No. 5,979,477 to Stillings (“Stillings”). Stillings discloses a high purity, non-contaminating, burst disk preferably made of quartz. However, quartz has the disadvantage of being etched by chemicals, such as hydrofluoric acid, that are commonly used in the semiconductor industry. Thus, a burst disk made of quartz will over time become weaker, leading to rupture at a lower pressure than the design rupture pressure.
It is therefore desirable to provide improved materials from which to form pressure relief devices that have greater resistant to corrosive fluids or do not cause significant contamination when in contact with corrosive fluids. It is also desirable to provide materials from which to form pressure relief devices that can better withstand pressurization and depressurization cycles.
SUMMARY OF THE INVENTION
The present invention provides a pressure relief device, designed to rupture at a design rupture pressure, that includes a rupture element having an inner layer that is formed from a nonferrous-based composition and that is the layer closest to the “fluid” side of the system. The nonferrous-based composition contains one or more compounds selected from oxides of aluminum, carbides of silicon or titanium, elemental silicon, elemental germanium or combinations thereof.
In a preferred embodiment of the present invention, the inner layer of the rupture element of the pressure relief device is made of aluminum oxide in single crystal form (sapphire). In a more preferred embodiment, the entire rupture element is made of sapphire.
The present invention also provides a method of relieving overpressurization or underpressurization of fluids in a system that includes installing in the system the pressure relief device of the present invention.
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CFMT, Inc.
Rivell John
Woodcock & Washburn LLP
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