US2971667A - Expansible-wall container for lowtemperature fluids - Google Patents

Description

Feb. 14, 1961 w. L. BENSON El'AL 2,971,667

EXPANSIBLE-WALL CONTAINER FOR LOW-TEMPERATURE FLUIDS Filed April s, 1958 A T TURN/5 Y United States Patent EXPANSIBLE-WALL CONTAINER FOR LOW- TEMPERATURE FLUIDS Walter L. Benson, Needham, and Norman C. Dahl, Lexington, Mass, assignors, by mesne assignments, to Conch International Methane Limited, Nassau, Bahamas, a corporation of the Bahamas Filed Apr. 3, 1958, Ser. No. 726,111

5 Claims. (Cl. 220-) This invention relates to storing and shipping liquefied gases at low temperatures and more particularly to the storing and handling of such liquefied gases in large metal tanks which are surrounded by insulating materials.

Many type of containers suitable for handling liquids which must be maintained at relatively low temperatures are known and used. One of the most common of these is the metal tank set completely within another tank or receptacle with insulation material placed in the space between the inside metal tank and the outside receptacle. Because the inside tank is metal, it possesses a coeflicient of thermal expansion and hence is subject to contraction and expansion when exposed to temperature changes. The problem of expansion and contraction becomes markedly acute at the temperatures normally encountered in the handling of liquefied gases because the temperature differential between the liquefied gas temperature and normal room temperature is very great.

' In the case where the inside tank, designed for storing or shipping liquefied gases, is completely surrounded by an insulating material, such as balsa or cellular glass for example, contraction of the tank walls when the liquefied gas is added means that the walls pull away from the insulating material leaving a void area between the outside wall of the tank and the insulation material. There are cases where it is desirable to design the inside tank, containing the liquefied gases, so that it will depend for structural support upon the insulating material and the outside wall of the receptacle surrounding the insulating material, as when the inside tank is constructed of thin gauge metal to house the liquid but wherein the metal would be incapable of maintaining its shape to contain the liquid Without support from the insulation layer. When this is desirable it may readily be seen that a gap between the Walls of the inside tank and insulating material would lead to stresses in the tank Walls brought about both by the removal of the needed structural support offered by the outside receptacle and insulating material and by the pressure of the liquid and of the gas within the inner tank. Repetition of the cooling-warming cycle, brought about by adding and removing the liquefied gas, and hence of the stresses set up, may cause the inner tank to fail after arelatively short period.

'Moreover, if the inner tank containing the liquefied gas is only partially filled a large temperature gradient will exist in the gas column above the liquid level. This means that the tank walls will also exhibit a marked temperature gradient approximating the temperature gradient in'the gas because of the very low thermalconductivity of metal walls at the low temperatures involved. The resulting temperature gradients introduce additional stresses in the walls which may be partially relieved by the tank design of this invention. V

It therefore becomes evident that it would be desir- 'able t'ohave metal storage tanks which are capable of relieving these stresses induced, and which may at the some time have relatively thin metal walls which can de- 7 2,971,667 Patented Feb. 14, 1961 pend upon the outside receptacle for structural support, thus reducing the weight and cost of the storage or ship'- ping tank. One way in which the tank may be made to meet these requirements is to make at least a portion of the tank expansible for self-adjustment to enable the walls of the tank to remain substantially continuously in contact throughout the major portion of its area with the insulation layer.

It is therefore an object of this invention to provide a tank, suitable for storing and shipping liquefied gases, which may be constructed of thin metal walls, thus resulting in lower construction costs. It is another object to provide receptacles, suitable for storing and shipping liquefied gases, which remain substantially continuously in contact with insulating material surrounding them and which employ, in combination therewith, a structurally strong insulation. It is another object to provide an inner receptacle for storing and shipping liquefied gases which depends for a portion of its structural support upon an outside receptacle. It is a further object of this invention to provide receptacles, suitable for storing and shipping liquefied gases, which are expansible under the hydrostatic load and under the pressure built up within the receptacle by the vaporization of the liquid into gas. It is another object to provide such receptacles which are not critically affected by the thermal gradients within the receptacle. These and other objects will appear in the following discussion Which is presented with re;ter'-' ence to the accompanying drawings in which- Fig. 1 represents a cross-sectional view of the type of tank construction to which this invention is applicable;

Fig. 2 is a detailview of several of the components which are combined to make up the expansible members of the tank; Fig. 3 is a detail drawing showing the intersection of the edges of two perpendicular surfaces made of the components illustrated in Fig. 2; and V Fig. 4 is a diagrammatic view of how four walls of a tank may be made in accordancewith this invention. 7

In accordance with this invention a tank, suitable for the storage or transportation of liquefied gases, is made expans'ible to allow the sides of the tank to remain sub-' stantially in continuous contact with the insulation and hence make full use of the additional structural support offered by the insulation and/or the outside receptacle: This is done by constructing at least a portion of each of the side walls of the tank of modularpan-shaped components welded in a manner as to impart a sufficient de-' gree of flexibility to the components with relation to each other. The tanks of this invention may be better dscribed in detail with reference to the figures.

In Fig. 1 there is shown a simplified cross-sectional view of the general type of tank used for'storing or ship ping liquefied gases. The tank will be a polyhedron configuration and preferably one which is a rectangular parallelepiped. Inner tank 10, designed to contain the liquefied gas 13, is placed within a surrounding vessel 11 and insulating material 12 placed between them.- Such a tank may be equipped with a filling line 24 in which is placed a pressure-regulating valve 23 to provide proper gas venting, and with a draw-off line 26 incorporating valve 25. When the sides, top and bottom of tank 10 press closely on the insulating material, tank 10 reins an integral unit with tank 11 and tank 10 may therefore be of a lighter-weight, thinner construction than if this integration did not exist. But when the walls of tank It) are cooled by the introduction of liquefied gas, the metal contracts and the walls would tend to'pull away from the supporting insulation layer. If formedqof a thin" metal wall incapable of withstanding the liquid-and would be" subject 'tocfailure without ducing the stresses which would otherwisebe present.

welds 21.

combinations.- j Thepan-type components making up the surfaces of the tanks of this invention may be conveniently coninsulation layer. In a tank such as shown in Fig. 1 the surrounding vessel 11 maybe eliminated where insulation 12 is of such structural material, such as cellular glass or balsa wood, that it forms a strong outside receptacle. In such acase by maintainingthe tank walls in contact with insulating material 12 a strong integral unit is achieved without the additional tank 11.

'Moreover, if tank 10 is only partially filled with liquefied gas, there will exist a large, non-linear temperature gradient from liquid gas interface 14 through the gas column 15. Due to the fact that metals exhibit very low thermal conductivities at these temperatures, the temperature gradient'in gas column 15 will be also exhibited by tank wall, thus setting up differentials in expansion and contraction with resulting additional stresses in that portion of the tank wall surrounding the gas column.

1 The individual components which make up one or more surfaces. of-the tanks of this invention, are constructed as pan-shaped units, six of which are shown in Fig. 2.. These pan components are Welded completely along each of their four edges'16, including the points 17. When pressure is applied in the direction 4 it is preferred to make use of such metals as aluminum, alloys of aluminum or stainless steels for the wall construction of the inner tank.

The degree of flexibility required will be an important factor in determining the numberof pan-type components required to make up a given area and hence also the size of the individual pan-type components. Generally, for

a given pan material thickness, the larger the number indicated by the arrows the welded edges will be sufficiently flexible to permit the pan to operate as a diaphragm and. hence permit a wall constructed of these pan-components to expand and contract. Likewise, when the surfaces are brought into contact with liquefied gas at low temperature, they can contract without in- A means of joining two perpendicular surfaces made up of these pan-type components is shown in Fig. 3; In this arrangement the pan components 22 which form the surface edge are cut away so that they may be welded along lines 21 as shown. the edges may be pressed or otherwise constructed initially to this design. Four walls of a tank built up of these pan-type components 22 is illustrated in Fig. 4. The perpendicular surfaces are joined as in Fig. 3 by 7 An alternative arrangement for joining two tank walls made of these pan-type components may consist of using a supporting frame construction of suitable angle irons, for example, to which the pans forming the edge of the tank are affixed.

The stresses, which would be induced in a rigid tank by reason of a temperature gradient existing in the gas column above the liquefied gas, and hence also in the tank walls themselves, are eliminated by the tank of this invention since the walls are given flexibility so they can contract non-uniformly without inducing stresses.

Tanks made in accordance with this invention may Of course, pans suitable for' have one or more sides or surfaces constructed from the pan-type components. For example, 'it may only. be

necessary to use a flexible flooring to reduce the stresses set up within the tank. 'With a flooring which is capable of contracting and expanding in two directions in the horizontal plane, the walls attached to it are given flexibility in the vertical planes. Such flexibility is sufficient to relieve some of the stresses set up within the tank. On the other hand, it may be desirable for two or four of the sides (and possibly the top) to be made of the pan-type components for lateral expansion to permit the side walls to remain continuously in substantial sura number of combinations are possible, thefinal design considerations governing the 'structed from stainless steel. However other suitable metals, such as aluminumand copper, or alloys, which possess the desired structural strength may be used. Where the contained liquid comprises a 'low boiling liquefied gas such'as liquefied natural gas having a boil- -poipt.of 25 0 at atmospheric pressure; it is d use of .non-austenitic steels and choice made from these inches while with pan material of the order of 0.125

inch thick, the pans may be about 45 inches in length assuming stress does not-exceed 20,000 p.s.i.

Although the pan-type components will normally be square (and this is preferred) the possibility of using pan components of a rectangular design is not excluded in the scope of this invention. Surfaces constructed of rectangular pan-type components would be desirable in applications where thestresses to be encountered are primarily in one direction. That is, the direction of the primary'stresses would be the direction in which the shorter of the pan component sides would be used.

The size of the tanks to which the expansible sides of this invention are applicable will vary with design conditions, particularly with the internal pressure in the tank. That is, the higher the internal pressure, the smaller the'tank should be to preventover-expansion of the expansible surfaces used. 0

The pan type components may conveniently be pressed out in'a conventional die press, a process which makes the production of the individual pan a relatively simple one. Although other means such as forms of crimping can be used to join the individual pan-type components, welding (as shown in Fig. 2) is preferable. The final tank will be so constructed as to afford a hermetically sealed container suitable for holding liquefied gas.

Thus, by the use of the expansible tanks. of this invention, there are provided means for continuously keeping the outside of the'tank walls in contact with the insulating material surrounding the tank and also for relieving the stresses which are set up in the tank walls when an applrfeciable temperature gradient exists'within the tank itse and shipping liquefied gases which maybe made of relatively light weight material and which is also .free of stresses caused by alternately filling and emptying.

We claimi a l. A tank in the shape of a'polyhedron completely enclosed by walls and provided with inlet and outlet means, at least'one of said walls being constructed of a plurality of rectangularly pan-shaped modular members curved outwardly and arranged in side-by-side and in end-to-end relation to provide a continuous wall therebetwecn having a plurality of'outwardly extending curvilinear pockets with rims of angular shape extending substantially perpendicularly inwardly from the edges with the rims extendin in .side-by-side relation having substantial distance. a

between adjacent. pans and joined one to the other along theirinner edges. only whereby. the rims of each panshaped member outwardlyfrom the edges is capable of movement toward and away from the adjacent rims of the adjacent pan members without disturbing the sealing connection between their edges. 5

2. 'A tank for the housing'of'a low boiling liquid comprising an inner. metallic shell and an outer housing of a structurally strong thermal insulating materialand in which the inner metallic shell isformed-of walls at least There results therefore a tank suitable for storing one of which is constructed of a plurality of rectangularly pan-shaped modular members curved outwardly and arranged in side-by-side and in end-to-end relation to provide a continuous wall therebetween having a plurality of outwardly extending curvilinear pockets with rims of angular shape extending substantially perpendicularly inwardly from the edges with the rims extending in side-by-side relation having substantial distance between adjacent pans and joined one to the other along their inner edges only whereby the rims of each panshaped member outwardly from the edges is capable of movement toward and away from the adjacent rims of the adjacent pan members without disturbing the sealing connection between their edges.

3. A tank as claimed in claim 2 wherein the tank com- 15 prises a rectangular parallelepiped.

5 of the tank is formed of the rectangular dish-shaped members.

References Cited in the file of this patent UNITED STATES PATENTS Shea June 24, 1930 2,354,691 Lebedetf Aug. 1, 1944 2,451,486 Horton Oct. 19, 1948 FOREIGN PATENTS 895,371 France Jan. 23, 1945

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