Receptacles – High-pressure-gas tank
Reexamination Certificate
2000-11-14
2003-04-15
Moy, Joseph M. (Department: 3727)
Receptacles
High-pressure-gas tank
C220S585000, C220S586000, C220S590000
Reexamination Certificate
active
06547092
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to pressure vessels and, in particular, it concerns a pressure vessel which has a thin unstressed metallic liner.
A number of different structures are known for containing fluids at elevated pressures. These structures are generally referred to as “pressure vessels”. Requirements of safety, as well as attempts to reduce weight, have lead away from the use of simple metallic pressure vessels towards use of reinforced composite materials. In order to provide the required sealing characteristics, however, an additional inner liner must be provided. Hence the two principal types of pressure vessel currently in use both employ reinforced composite containers with either a seamless metallic or thermoplastic liner.
The use of a metallic liner generally provides a much longer operational life, better resistance to harsh environments, and better sealing characteristics than thermoplastic liners. The design of pressure vessels with metallic liners, however, presents its own particular problems, as will now be described.
Composite pressure vessels with metallic liners are manufactured by filament winding of fibers impregnated with resin matrix, together forming the composite material, around the metallic liner. The metal liner of these structures bears part of the applied internal pressure. In addition, incompatibility of the ranges of elastic behavior of the metal liner and composite material lead to residual compression stresses in the liner as a result of the “proof pressure” test (“autofrittage phenomenon”).
During subsequent application of internal pressure, the liner stretches and experiences corresponding tensile stress. In order to withstand these tension/compression stresses through repeated filling cycles over an extended period of usage, the liner must be relatively thick. Besides the clear implications of a thick liner for the weight of the vessel, the presence of a thick metallic layer also leads to safety problems.
In an effort to address these problems, attempts have been made to develop an unstressed metallic liner in which a thin metallic layer provides sealing properties while transferring all of the pressure load to the surrounding primary vessel. An example of such a structure is described in U.S. Pat. No. 5,292,027 to Lueke.
In order to avoid stressing of the liner, Lueke suggests a complicated “herringbone” pattern of parallelogram-like elements which provides undulations in two orthogonal directions. As a result, the liner readily stretches in any direction to conform to the deformation of the primary vessel.
The structure suggested by Lueke presents numerous problems of practical implementation. Firstly, the liner appears to contact the primary vessel at isolated points. Pressure applied to such a structure would not be effectively transferred to the primary vessel walls, and would probably result in immediate destruction of the herringbone pattern. Furthermore, the complicated structure would be extremely difficult to manufacture.
Another reference, U.S. Pat. No. 1,968,088 to Mekler, although less relevant than the Lueke reference, will be mentioned for its superficial similarity to one embodiment of the present invention. Mekler, in a patent filed before the introduction of reinforced composite materials into the art, describes a freely-expanding, corrugated protective liner for reaction vessels subjected to rapidly varying temperatures. The corrugations serve to prevent distortion and damage to the liner under extreme heat stress, while insulating the main vessel from the most extreme of the temperature variations. The reference does not address issues of performance under elevated pressure.
The structure described by Mekler is not suitable for use with fluids at elevated pressures. Since no solution is suggested for accommodating heat stress along the direction of elongation of the corrugations, it would appear that the liner must have a clearance from the ends of the primary vessel. As a result, the liner must be designed to bear a large proportion of any internal pressure. Additionally, no support is provided for the corrugations of the liner. Thus, if the liner was made from thin materials, the corrugated structure would rapidly deform and collapse under internal pressure. Finally, since this reference pre-dates the use of reinforced composite materials, Mekler clearly fails to teach any synergy between a liner structure and specific configurations of such composite materials.
Finally, reference is made to U.S. Pat. No. 3,446,385 to Ponemon which proposes the concept of a relatively unstressed metallic liner within a fiber glass reinforced load-bearing container. Several examples given (
FIGS. 6 and 7
of the Ponemon reference) propose to achieve this using a bi-directional corrugated pattern, conceptually similar to, but less feasible than, that suggested by the aforementioned Lueke reference.
In the examples of
FIGS. 3-5
, Ponemon provides a liner structure which can accommodate stress in one direction only. With regard to stress in other directions, Ponemon suggests choosing a filament winding angle of slightly more than, or slightly less than, 54°45′ which, he claims, generates deformations selectively in the required directions.
In fact, the solution proposed by Ponemon is based upon a fallacy and is non-operative. Specifically, Ponemon states: “It is known that winding filaments at a helical angle of 54°45′ within a tolerance of 1 degree produces an elongation in the glass fibers that is oriented in only one direction. That is, if the winding helical angle is greater than 54°45′, the elongation of the glass fibers will be only in the longitudinal direction of the axis of the vessel; whereas, if the helical winding angle is less than 54°45′, the elongation of the glass fibers is in the transverse or hoop direction of the vessel.”
The angle of 54°45′ is indeed a well known winding angle: it is the angle at which axial and hoop deformations in a cylindrical pressure vessel are equal. However, the suggestion that pure axial or pure hoop deformations may be obtained by shifting one degree to either side of this value is completely fallacious. To the contrary, angles in the stated region to either side of the 54°45′ angle will typically give very significant though non-equal variations in deformation in both axial and hoop directions. Furthermore, this value corresponds to an unstable singularity around which small variations in angle give rise to large, non-linear variations in deformation, making it an angle to be avoided when self-cancellation of stresses is sought.
There is therefore a need for pressure vessels with thin unstressed metallic liners which are convenient to produce and which effectively transfer applied pressure to the walls of the primary container.
SUMMARY OF THE INVENTION
The present invention is a pressure vessel which has a thin unstressed metallic liner.
According to the teachings of the present invention there is provided, a pressure vessel for containing a fluid at elevated pressure, the pressure vessel comprising: (a) a primary load-bearing container formed with at least one wall made of fiber-reinforced composite material, the shape of the primary container and the reinforcing directions of the fiber-reinforced composite material being configured such that, under a given change in the pressure of the contained fluid, a strain of the wall in a first direction is at least one order of magnitude less than a corresponding strain in a second direction perpendicular to the first direction; (b) an unstressed corrugated metallic liner positioned adjacent to at least part of an inner surface of the wall and forming part of a hermetic seal within the primary container, the liner having corrugations extending substantially parallel to the first direction such that the liner conforms to deformation of the wall in the second direction; and (c) a filler layer of elastic material interposed between the liner and the wall so as to substantia
Friedman Mark M.
Moy Joseph M.
LandOfFree
Pressure vessel with thin unstressed metallic liner does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Pressure vessel with thin unstressed metallic liner, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Pressure vessel with thin unstressed metallic liner will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3017301