Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Mechanical measurement system
Reexamination Certificate
2003-06-13
2004-08-31
Bui, Bryan (Department: 2863)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Mechanical measurement system
C702S035000, C702S047000, C702S138000
Reexamination Certificate
active
06785616
ABSTRACT:
FIELD OF INVENTION
The present invention relates to pressure vessels, and more particularly to pressure vessels having oscillator and sensor means, and to a method and apparatus for determining if there may be deterioration in the structural integrity of such pressure vessel.
BACKGROUND OF THE INVENTION
Due to the need of alternative fuelled vehicles, such as natural gas, propane, and potentially fuel-cell powered vehicles, to carry highly pressurized gaseous, or dual-phase (gaseous and liquid) fuels, pressure vessels containing such highly pressurized fuels for such vehicles must be structurally sound and be able to withstand such high pressures.
Up to the early 1990's, pressurized fuel tanks for alternative or dual fuel (propane or natural gas) vehicles were typically cylindrical steel tanks, located in the trunk or in the traditional gasoline tank location for such vehicle. In order to save weight, such tanks were typically of a limited thickness, and thus could only be pressurized to a pressure in the range of 3000-3600 psi (20.68-24.82 MPa), and to conserve weight, they were of a limited size. The range of travel of the vehicle on a single tank fill was accordingly very limited due to not being able to carry more gaseous fuel, resulting in limited range of such vehicles on a single tank fill.
A need arose to have such pressure tanks able to withstand greater pressures, without greatly increasing the weight of such tank, so as to be able to carry more fuel without greatly increasing the tank size (and thus weight). This need has become more acute with the likely and coming introduction of fuel cell vehicles, which require substantial quantities of hydrogen which can only be stored in a gaseous pressurized form. Due to the lesser energy density of hydrogen as compared with natural gas and gasoline, even greater quantities are needed to power a vehicle for the same distance, and thus tanks able to withstand even greater pressures (so as to certain even greater quantities) of such gas are required.
Companies such as Dynetek, Inc. of Calgary, Alberta have developed specialized carbon-fiber composite pressure vessels, which are specially adapted for containing gaseous fuels at high pressure, in the range of 3000-10,000 psi (20.68-68.95 MPa). These specialized tanks typically consist of a substantially cylindrical inner vessel, typically of aluminum or a plastic. To the exterior surface of such inner vessel is wound a plurality of carbon fiber strands embedded in a polymer composite (CFRP), which is cured to form an exterior, extremely lightweight shell (known as a CFRP shell), highly resistant to tensile and hoop stresses to which it is subjected to by the compressed gases within the inner vessel. The exterior CFRP shell, which is typically comprised of a series of strands of carbon fiber which are wound about the exterior surface of the inner pressure vessel and held together with a polymer resin, effectively bears the bulk of the hoop stresses exerted by the highly pressurized gases which are injected into the inner pressure vessel.
These CFRP pressure vessel fuel storage tanks are adapted for storing propane, methane and/or natural gas, but are particularly adapted for storing hydrogen for fuel cell vehicles.
These CFRP pressure vessels, like all other pressure vessels, can become weakened through fatigue due to cyclic stresses which arise due to the high pressures involved and the continual filling, exhausting, and re-filling such tanks. In addition, the structural integrity of such CRFP pressure vessels may be compromised as a result of structural damage to the exterior CFRP shell due to cuts, gouges, or deformation thereto arising in the handling, storage, or filling of such pressure vessel. Alternatively, such pressure vessels can become damaged through overpressure, if for example, the pressure relief valve which is typically installed on such tanks was to fail or become inoperative.
Importantly, due to the extremely flammable nature of stored gaseous fuels such as natural gas and hydrogen, and due to the extremely high pressures under which such gas is stored, it becomes of paramount importance that such pressure vessels be structurally sound. Otherwise, due to the intended application of such tanks for use in motor vehicles or bulk transportation of gases on public highways, structural damage of such tanks can result in catastrophic failure of such tanks, and ignition of the flammable contents upon release of such contents to the atmosphere, with likely resultant loss of human life as well as material and property damage. Accordingly, it is of paramount importance that damaged or structurally compromised tanks be immediately removed from service.
Unfortunately, it is not easy, and in most cases impossible to determine if the structural integrity of a CFRP pressure vessel has been compromised from a simple visual inspection of such pressure vessel.
Accordingly, a real and clear need exists for a method to determine if the structural integrity of a modern CFRP pressure vessels has been possibly compromised.
A further need exists for a pressure vessel which is able to self-monitor and warn when structural integrity thereof may have been compromised.
Lastly, a further need exists for an apparatus to be able to determine if the structural integrity of a pressure vessel has been compromised.
Fulfillment of these needs allows an important advance in the implementation of CFRP pressure vessels, and allows structurally-compromised pressure vessels to be withdrawn from use and thereby reduce i) the possibility of leakage from such pressure vessels and the consequent loss of such fuel, or, worse yet ii) catastrophic failure resulting in explosion due to the extremely high pressures to which the vessel is subject to.
U.S. Pat. No. 5,522,428 teaches a composite pressure vessel 20, having a three types of sensors, namely a pair of strain sensors 46, a pair of temperature sensors 48, and a pair of acoustical sensors 44, all of which are applied to the exterior of the load-bearing composite shell 28 of the composite vessel (ref. col. 3, lines
5
-
12
). All sensors are connected to a microprocessor (CPU)
32
, which is in turn connected to a solenoid valve 26, which controls flow of gas to/from the vessel. The strain sensors 46 permit the microprocessor to count the number of fill cycles to which the vessel is subject, to keep track of when the cyclic stresses on the vessel may be reaching the design limit thereof. The temperature sensors 48 allow over-temperature conditions (and thus possible structural degradation to the vessel) to be sensed. The acoustic emission sensors 44 count the sound emissions in a given time period above a trigger level intensity, which if above a certain level, may indicate imminent failure. If any of certain conditions are sensed, the microprocessor 32 may cause the solenoid 26 to prevent refill of the pressure vessel 20.
The aforesaid method disclosed in US '428 for monitoring pressure vessel integrity involves numerous types of different types of sensors, and as such does not provide a single sensor capable of determining in and by itself the tank integrity.
Moreover, acoustical sensors are relatively large in size, and are relatively expensive. Furthermore, in motor vehicle (ie. “noisy”) environments, acoustic sensors may be unreliable. Lastly, there is no teaching in such patent as to how the “count” of pressure cycles is to be maintained by the microprocessor in the event of interruption of electrical power to the microprocessor. Indeed, it seems clear from this patent that electrical power must continue to be supplied to the microprocessor (col. 5, line 15-16—“with current battery technology, it is likely that the CPU
32
can be maintained by an integral battery”).
Accordingly, a real need continues to exist for a lower cost method and apparatus for being able to determine pressure vessel structural integrity.
SUMMARY OF THE INVENTION
The present invention makes use of the concept that a structural change in a component (which may indica
Lung Brian
Wong Joe Y.
Bui Bryan
Cowling Lafleur Henderson LLP
Horne D. Doak
Saskatchewan Research Council
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