Cryogenic Storage Apparatus

Abstract

A double walled container having an inner vessel and an outer shell with an intervening vacuum insulation space, including a neck tube formed of certain gas impervious fiber reinforced plastic compositions having certain physical properties, the neck tube providing access to the inner vessel and also being loaded in tension by the inner vessel as the sole suspension means therefor.

Parent Case Text

This application is a continuation of Ser. No. 599,343, filed Dec. 1, 1966, now abandoned, which latter application is a continuation of Ser. No. 337,696, filed Dec. 26, 1963, now abandoned, said last mentioned application being a continuation-in-part of Ser. No. 149,356 filed Nov. 1, 1961, now abandoned.

Description

This invention relates to cryogenic storage apparatus and more particularly to a double-walled, vacuum insulated cryogenic storage container.

Heretofore, typical containers for storing cryogenic liquids such as liquid oxygen and liquid nitrogen in relatively small quantities of about 15-25 liters comprised an inner storage vessel, an outer protective shell which enclosed the inner vessel thereby forming an evacuable insulation therebetween, and a relatively long narrow neck tube which served as the entrance to the inner vessel. The inner vessel was usually supported entirely by suspension from the top of the outer shell by such neck tube. These containers were extremely fragile in that the inner vessel often ruptured at the neck tube-inner vessel joint due to impact and acceleration forces experienced during handling.

Another disadvantage of these containers was the relatively small diameter of the neck tube which hampered access to the inner vessel. Enlargement of the neck tube opening of these containers was no solution, however, since this increased the heat leakage into the inner vessel. Not only was a portion of an otherwise well-insulated area replaced by a larger uninsulated opening, but the heat leakage along the walls of the neck tube itself was significantly increased.

In order to preserve the liquefied gas with a minimum of evaporation due to excessive heat leakage and yet provide a relatively sturdy container, the prior art found it necessary to employ a neck tube constructed of a material such as stainless steel. These strength and heat leak requirements are conflicting in that a relatively strong material such as stainless steel is also a relatively high conductor of heat. Furthermore, the prior art found it necessary to employ a neck tube constructed of such material to ensure an effective seal of the evacuated insulation space surrounding the inner product liquid vessel. The gas imperviousness and high strength advantage of stainless steel was only obtained at the cost of gas loss due to the contribution to heat leakage into the inner vessel.

It is an object of this invention to provide a low-temperature storage container employing an improved neck tube constructed of high strength material which has the advantages of large access opening, strength, and vacuum tightness while substantially reducing the heat leakage into the inner vessel. Another object is to provide a low temperature liquefied gas storage container with an improved neck tube that is constructed of a gas impervious and low-heat conductive material. These and other objects of the invention will become apparent from the following discussion and the accompanying drawing in which:

The FIGURE is a view of a longitudinal cross-section of a low-boiling liquefied gas container embodying principles of the present invention.

While the invention will be described in conjunction with a low-boiling liquefied gas storage container, it is to be understood that it is equally well-suited for utilization in other type low-temperature storage containers such as those used for the preservation of materials such as biological substances where a low-boiling liquefied gas is employed as a refrigerant to surround such biological materials.

This invention is embodied in an improved vacuum-insulated, low temperature storage container having an outer protective shell, an inner product vessel, an evacuable insulation space therebetween, and a neck tube connecting the outer shell to the inner vessel large enough to provide access to the interior storage space of such inner vessel.

The neck tube of the container is constructed of a substantially gas impervious reinforced fibrous laminate impregnated with a thermosetting synthetic resin. The gas permeation rate of the neck tube material must be less than 1 .times. 10.sup.-.sup.10 cu. cm./sec. of helium at a pressure of one atm. as determined by testing a tube having a 11/2 inch inside diameter, a 1/16 inch wall thickness and a length of 2 inches in a Model MS-9A Veeco Mass Spectrometer Leak Detector. Hence the term "substantially gas impervious" as employed herein means those materials having a gas permeation rate of from zero to 1 .times. 10.sup.-.sup.10 cu. cm./sec. of helium. Preferably the permeation rate is zero. The laminates employed as the neck tube can be of any material or synthetic fiber in random or orderly manner, such as is found in paper, cloth, or the like or any reinforcing or rigidifying fiber such as cellulosic fibers, glass fibers, synthetic fibers or the like, and thoroughly impregnated with a cured thermosetting resin. The degree of impregnation of the reinforced laminate should be sufficient to produce, after curing of the resin to a thermoset condition, a substantially gas impervious neck tube. Phenolic resins, i.e., phenol-aldehyde condensates, and epoxy resins such as the polyglycidyl ethers of polyhydric phenols, serve excellently as the thermosetting resins of these laminates although other thermosetting resins such as polyester resins providing the same or equivalent degree of gas imperviousness can be employed. These resins can be applied to liquid resins or solvent solutions of solid resins to impregnate a preformed neck tube and the resin cured in situ by heating to elevated temperatures or by curing aids or hardeners, such as polyfunctional amines, or both to a thermoset condition. If desired the neck tube can be fabricated from preimpregnated and cured reinforced laminates in tubular form, or they can be prepared from partially cured resin-impregnated paper or cloth webs, and finally cured to a thermoset condition after forming. It has been found that gas impervious neck tubes constructed of thermoset resin impregnated fibrous laminates, in a manner to be described, effectively reduce vaporization losses of the liquefied gas due to atmospheric heat leakage into the inner vessel as well as maintain the insulation qualities of the evacuable insulation space surrounding the inner vessel by preventing loss of the vacuum therethrough.

To achieve these results, a gas impervious neck tube is preferably constructed of resin impregnated fibrous laminates having the following physical properties:

Specific Gravity between about 1.10-1.55 Compressive Strength at least 10,000 psi. Tensile Strength at least 8,500 psi. Specific Heat between about 0.26-0.40 Thermal Conductivity between about 0.0007-0.0012

cal/sec/cm.sup.2 /deg C/ cm. These thermoset resin impregnated laminates reduce liquified gas vaporization induced by heat leakage to less than about 70 percent of the loss attained by employing a stainless steel neck tube. For example a material known commercially as Synthane Grade X manufactured by the Synthane Corp. of Oaks, Penn., which comprised a paper tube of 11/2 inch inside diameter with a wall thickness of 1/16 inch, reinforced with a thermoset phenol-formaldehyde resin having the above physical characteristics and a zero gas transmission rate as hereinbefore described was subjected to a 3-month test as a neck tube in a double-walled vacuum insulated storage container during which it was found that the loss of liquefied gas through vaporization induced by heat leak was 1.4 lbs/day as compared to 2 lbs/day employing a stainless steel neck tube in the same type of container under similar conditions. Further, it was found that there was no gas leak to the evacuable insulation space surrounding the inner vessel. Similar tests were preformed employing materials known commercially as Synthane Grade G-10 and G-11 manufactured by the Synthane Corp. which comprised neck tubes of a glass fiber fabric reinforced with a thermoset epoxy resin. The insulation space was evacuated to an absolute pressure of below about 30 microns of mercury and, after 3 months of continuous testing, the vacuum therein was substantially identical to that at the beginning of the test. The gas imperviousness of neck tubes constructed from these resin impregnated fibrous laminates has been further proven by mass spectographic tests.

The preferred embodiment of this invention employs opacified insulation wherein such insulation substantially completely fills the evacuable insulation space between the outer shell and the inner vessel. However, lower quality insulating systems such as the powder-in-vacuum insulators or straight vacuum with highly polished outer shell inner and inner vessel outer surfaces may be alternately employed.

The term "opacified insulation" as used herein refers to a two-component insulating system comprising a low heat conductive, radiation permeable material and a radiant heat impervious material which is capable of reducing the passage of infrared rays without significantly increasing the thermal conductivity of the insulating system. Such opacified insulation is more fully described in U.S. Pat. No. 2,967,152 issued Jan. 3, 1961, and copending U.S. application Ser. No. 597,947, filed July 16, 1956, now U.S. Pat. No. 3,007,596 both in the name of L. C. Matsch.

The opacified insulation of the former incorporates the radiation impervious barrier directly into the low heat conductive material. For example, equal parts by weight of copper flakes and finely divided silica might be mixed. The latter material has a very low solid conductivity value but is quite transparent to radiation. The copper flakes serve to markedly reduce the radiant heat inleak.

The latter referenced opacified insulation takes the form of low heat conductive material separated by a multiplicity of radiation-impervious barriers. The low heat conductive material may be a fiber insulation produced in sheet form. Examples include a filamentary glass material such as glass wool and fiber glass, preferably having fiber diameters less than about 50 microns. Also, such fibrous materials preferably have a fiber orientation substantially perpendicular to the direction of heat flow across the insulation space. The spaced radiation-impervious barriers may comprise either a metal, metal oxide, or metal coated material, such as aluminum coated plastic film, or other radiation reflective or radiation adsorptive material or a suitable combination thereof. Radiation reflective material, comprising thin metal foils are particularly suited in the practice of the present invention, for example, reflective sheets of aluminum foil having a thickness between 0.2 millimeters and 0.002 millimeters. When fiber sheets are used as the low conductive material, they may additionally serve as a support means for the relatively fragile radiant heat impervious sheets. For example, it is preferred that an aluminum foil-fiber insulation be spirally wrapped around the inner vessel with one end of the insulation wrapping in contact with the inner vessel, and the other end nearest the outer shell, or in actual contact therewith.

Even though the previously described preferred opacified insulation is more effective than straight vacuum insulation at higher internal pressures (poorer vacuum), its effective thermal insulation life is extended if the vacuum pressure can be maintained at or below a desired level. A gas-removing material such as an adsorbent may be used in the insulation space to remove by adsorption any gas entering through the joints of the outer shell. In particular, crystalline zeolitic molecular sieves having pores of at least about 5 Angstrom units in size, as disclosed and claimed in U.S. Pat. No. 2,900,800 issued in the name of P. E. Loveday, are preferred as the adsorbent. They have extremely high adsorptive capacity at the temperature and pressure conditions existing in the insulation space and are chemically inert toward any gases which might leak into the insulation space.

In the preferred embodiment depicted in the FIGURE of the drawing, neck tube 10 is constructed of a paper or fabric tube impregnated with a thermoset epoxy or phenolic resin in a manner such that neck tube 10 has the aforementioned physical properties. Neck tube 10 is preferably joined to the outer shell 12 of container 14 and to the inner storage vessel 16 by means of rigid annular support rings 18 and 20 respectively. As shown, neck tube 10 is preferably positioned by annular grooves 17 and 19 in rings 18 and 20, and bonded therein. Rings 18 and 20 are employed to simplify joining the neck tube to the inner vessel and the outer shell inasmuch as it has been found that stronger joints may be constructed by bonding the neck tube in grooves. In this manner, the shear strength of the bonding resin is more fully utilized and a more leak tight joint is achieved. If a relatively weaker joint can be tolerated, the neck tube joints can be formed without the use of grooves. It has been found that "A-12" epoxy resin manufactured by Armstrong Products Co. of Warsaw, Ind., is a suitable bonding agent.

Inner vessel 16 is preferably supported in tension by neck tube 10 at one end, the tensile strength of said tube being sufficient to support the entire weight of said vessel and its contents. Insulation space 24 between outer shell 12 and inner vessel 16 is preferably substantially completely filled with an opacified insulation material. Such insulating material affords lateral support for inner vessel 16 but no appreciable vertical support.

Insulation space 24 is preferably evacuated to a low positive pressure of less than about 25 microns of mercury and preferably less than about 0.5 microns by a vacuum pump capable of being connected to pinch-off tube 25. Absorbent material 26 such as silica gel or sodium zeolite A is located within enclosure 28 attached to the bottom of inner vessel 16 to assist in preserving the low vacuum pressure within insulation space 24.

The access opening formed by neck tube 10 is substantially occupied by an annular low heat conductive plug 30 such that liquid vaporized by unavoidable heat leakage will flow out through the annular space between plug 30 and neck tube 10. The vaporized gas will absorb a substantial part of the heat which would otherwise be conducted into inner vessel 16 by neck tube 10. Low heat conductive plug 30 may be constructed of a material such as foam plastic or cork.

A neck tube constructed of a reinforced thermoset phenol-aldehyde or epoxy resin laminate will not creep or change its shape under varying the temperature conditions. In the preferred embodiment support rings 18 and 20 and neck tube 10 are designed to bear the vertical loads that are imposed upon the inner vessel and, since rigidity and dimensional stability are important, the properties exhibited, and mentioned above, by these reinforced thermoset resin laminates are desirable.

The bonded joints, between neck tube 10 and annular rings 18 and 20 are preferably formed by curing an application of epoxy resin, such as the previously noted A-12 brand resin, at a temperature of about 150.degree. F. In this respect, it should be noted that outer shell 12 and inner vessel 16 should be connected, by means such as welding to annular rings 18 and 20 prior to their assembly with neck tube 10 so that the heat necessary to form the weld joining rings 18 and 20 to outer shell 12 and inner vessel 16 will not damage the bonded joints in the annular grooves of rings 18 and 20. Therefore, to assemble this arrangement, inner vessel 16 with its welded ring 20 is first attached to the support member 22 within the lower section of outer shell 12. Neck tube 10 is then placed in the annular groove of ring 20 and an upper section of outer shell 12, with annular ring 18 attached, is placed into position, elastically elongated and preferably girth welded at 11 to its first lower segment. The resulting joints in the annular grooves 17 and 19 of rings 18 and 20 are then cured, employing the epoxy resin as the neck tube joint bonding agent. Insulation space 24 is preferably evacuated simultaneously with the curing process.

It has been found that the ends of the neck tube and the annular grooves should be sandblasted prior to bonding to provide sufficiently roughened surfaces for proper bonding thereof. The sandblasting may be accomplished by projecting 120-mesh aluminum oxide particles against the surfaces of the grooves at a velocity of about 500 fps.

Claims

What is claimed is:

1. In a low temperature storage container having an outer shell and an inner storage vessel each with an upper opening wherein the two openings are vertically aligned and with said inner storage vessel and outer shell sized to enclose an intervening vacuum insulation space, the improvement comprising a cylindrical neck tube with opposite ends respectively gas-tightly sealed to the edges of said upper openings in the outer shell and inner vessel so as to provide a relatively wide access hole from the atmosphere to the interior of said inner vessel, said neck tube being formed of a substantially gas impervious material with the outer wall thereof sealing said vacuum insulation space and selected from the group consisting of paper reinforced with a thermoset phenol-formaldehyde resin, glass fiber reinforced with a thermoset epoxy resin, and glass fiber reinforced with a thermoset polyester resin, said neck tube being loaded in tension by said inner vessel as the sole suspension means therefor and having the following physical properties:

2. A storage container according to claim 1 in which the neck tube is formed of paper reinforced with a thermoset phenol-formaldehyde resin.

3. A storage container according to claim 1 in which the neck tube is formed of glass fiber reinforced with a thermoset epoxy resin.

4. A storage container according to claim 1 in which the neck tube is formed of material having a specific gravity of at least 1.10.

5. In a low temperature vacuum insulated storage container having an outer shell and an inner storage vessel each with an upper opening wherein the two openings are vertically aligned, the improvement comprising a cylindrical neck tube with opposite ends respectively gas-tightly sealed to the edges of said upper openings in the outer shell and inner vessel so as to provide a relatively wide access hole from the atmosphere to the interior of said inner vessel, said neck tube being formed of a substantially gas impervious material selected from the group consisting of paper reinforced with a thermoset phenol-formaldehyde resin, glass fiber reinforced with a thermoset epoxy resin, and glass fiber reinforced with a thermoset polyester resin, said neck tube being loaded in tension by said inner vessel as the sole suspension means therefor and wherein support rings with grooves that face each other axially of the container are connected to the edges of said upper openings in the outer shell and inner vessel, and the opposite ends of said neck tube are positioned and gas-tightly sealed in said grooves.