US3337079A - Stressed membrane liquified gas container - Google Patents

Description

22, 1967 J. 5. CLARKE E AL STRESSED MEMBRANE LIQUIFIED GAS CONTAINER 2 Sheets-Sheet 1.

Filed June INVENTORS JAMES S. CLARKE CHRISTOPHER E. LOESER ATTORNEY Aug. 22, 1967 J. s. CLARKE ET AL 3,337,079

STRESSED MEMBRANE LIQUIFIED GAS CONTAINER Filed June 4, 1965 2 Sheets-Sheet 2 INVENTORS JAMES S. CLARKE CHRISTOPHER E. LOESER ATTORNEY United States Patent ()fiice 3,337,079 Patented Aug. 22, 1967 3,337,079 STRESSED MEMBRANE LlQUIFlED GAS CONTAKNER James S. Clarke, Cranford, and Christopher E. Loeser, Scotch Plains, N.J., assignors to Esso Research and Engineering Company, a corporation of Delaware Filed June 4, 1965, Ser. No. 461,274 9 Claims. (Cl. 220-15) This invention relates in general to the storage of liquids at cryogenic temperatures and in particular to improvements in the construction of containers for the storage of liquified natural gas (LNG). The invention further relates to an improved insulated double walled container for the storage of LNG on board a tanker vessel.

In the handling of liquified natural gas at atmospheric pressure the severe low temperature environment introduces numerous critical structural and cost considerations into the design of stroage containers therefor. One of the particularly difficult structural problems centers about the need for providing for large thermal contractions and expansions, associated With the reduction of temperature from ambient temperature down to the service temperature of approximately -259 F. Further difiiculty centers about the choice of materials for the container walls which, of necessity, must be of a type which retain their structural properties at this low temperature. Normal carbon steels embrittle at cryogenic service temperatures and may not be employed for such use. Other materials such as aluminum, Invar, stainless steel, nickel, etc., while retaining their structural properties at the cryogenic service temperature of the stored material are costly.

Accordingly, it is the principal object of this invention to provide -a novel improved container capable of safely with standing the stresses induced by the thermal load of the stored material as well as a container which employs a minimum of high cost structural members such as Invar or stainless steel.

In accordance with the invention, a novel double walled container is provided wherein the inner walls or primary barrier of the container is formed of Invar or other similar property material. The walls of the primary barrier are formed as membranes and held in a relatively taut flat plane about their peripheries in a framework exterior of the cold temperature interior of the storage tank. The hydrostatic load of the stored material is supported by a secondary container wall outside of the membrane to which the load is transmitted by a layer of insulation material placed between the inner and outer walls.

A feature of the present invention is that it provides a novel means for producing a flat walled polygonal insulated container for the storage of cryogenic liquids with a minimum of high cost materials, such as Invar. Another novel feature is that the need for expansion joints in the inner wall of the container is eliminated due to the selection of a material with optimum thermal characteristics operating in a non-critical stressed condition. In accordance with the invention, the outer periphery of each of the inner walls of the container is provided with a plurality of protruding projections which extend through the plane of the adjacent walls. The outer edges of each of the projections are secured to an outer framework lying in the plane of each of the walls. The outer framework supporting the inner walls of the container absorbs the contractive thermal load of the inner membrane walls as it cools to the service temperature. The hydrostatic load of the stored cargo within the container is transmitted transversely first through the inner membrane, and then the insulation means to the outer container wall. Because the outer container wall is [fully insulated from the low temperature cargo, it may be made of any suitable structural carbon steel. In this way, a novel low cost insulated container may be constructed for the storage of liquids at cryogenic temperature.

Accordingly, it is a principal object of the present invention to provide a novel low cost storage container for liquids at cryogenic temperatures.

A further object of the invention is to provide a novel fiat walled polygonal container.

A further object of the invention is to provide a novel cryogenic container not requiring expansion and contraction joints.

A further object of the invention is to provide a novel container wherein the inner wall is of membrane thickness incapable of supporting the hydrostatic load of the stored liquid and wherein a layer of insulation exterior of the inner membrane wall transmits the hydrostatic load to the outer container walls.

These and other objects and advantages of the invention will become apparent and the invention will be understood from the following description and drawings in which:

FIGURE 1 is a cross-sectional view of one form of the invention as it would be located in a typical tanker vessel;

FIGURE 2 is a perspective view, with portions broken away, showing the corner construction of the invention; and

FIGURE 3 is a cross-sectional view similar to FIGURE 1 showing a modified form of the invention.

Referring to the drawings and FIGURES 1 and 2 in particular, a tanker vessel 10 shown schematically in crosssection includes an outer hull 12 and winner hull 14 spaced therefrom. An insulated cargo tank 16 in accordance with the invention is located within the hold of the tanker vessel and maintained in spaced relationship therefrom by a plurality of main structural members designated 18. In the form shown, the structural members 18 have a generally I-shaped cross-section, one end of which engages the inner hull 14 while the opposite end serves to secure portions of the outside container plating 26 of the insulated container. As will be explained hereafter, selected structural members 18 also serve to support and hold the inner membrane walls of the container in a stressed relationship. The cargo tank 16 includes a conventional riser portion designated generally at 20 through which loading and unloading may be accomplished.

The novel LNG storage tank in accordance with the invention includes -a plurality of inner membrane panels preferably made of Invar, a material capable of withstanding the service temperature and having a low coefficient of thermal expansion. Each of the inner membranes 22 defines a substantially fiat plane and includes a plurality of projecting tab portions 28 which extend through a surrounding layer of insulation 24 and are secured at their edge portions by welds 30 to the inner surface of the main structural frame member 18. As best seen in FIGURE 2, each of the projecting tabs 28 is rectangular in shape and is of substantially equal lateral width so that they interlock with the tabs of the adjacent intersecting membranes 22 to form an inner line of intersection on the interior of the cargo tank 16. An interior (or exterior) weld 32 is formed along this common intersection line to tightly seal the inner membranes 22 against liquid leakage.

In operation, each of the intersecting frame members 18 forms a generally rectangular outer boundary for its associated membrane. Each of the planes defined by the rectangular structure 18 serves to support the outer projections of its associated membrane wall 22. The structuralrnembers 18 also provide support for the outside plating or secondary barrier 26 which may be made of any suitable strong material such as carbon steel to withstand the hydrostatic load of the LNG cargo. Upon introduction of the LNG cargo, the lowering of temperature causes a contraction of the membranes 22 which due to the use of Invar is relatively minor in nature. Therefore, the structural stress limit of the inner membrane'ZZ is not exceeded and no plastic deformation thereof will occur. The insulation blanket 24 is designed to take the hydrostatic load of the cargo and transmit this force to the outer plating 26 which due to the insulation will not assume the low operating temperature of the LNG cargo. In this way, novel storage container arrangement has been provided for a cryogenic liquid employing a mini mum amount of relatively expensive material such as Invar or stainless steel. The secondary or outer barrier formed by the plating 26 is effective to take the hydrostatic load of the cargo. The thermal cool-down stresses are taken up by the inner membrane and transmitted to the main structural members 18 forming a framework about the periphery of the projections 28.

Referring to FIGURE 3, an alternate form of the invention is disclosed wherein a ships hull 34 includes an inner hull 36 and transverse bulkheads 40 of conventional form. The inner hull 36 and bulkhead carry a plurality of membrane supporting members 38 which extend through an insulation layer 42. The inner end of each of the membrane supports 38 is weldably secured at 46 to an inner membrane member 44, preferably made of Invar. In this embodiment it should be noted that the periodic rigid attachment of membrane 44 by welds 46 to the supports 38, and the choice of the membrane from a material such as Invar, avoids the need for provision of expansion and contraction joints. In this way, as in the embodiment of FIGURES 1 and 2, the inner membrane may be made of sufficiently thin structure so that it need only support the load due to the induced thermal stress of initial cooldown of the tank. All the hydrostatic loads are transmitted through the membrane 4-4- and insulation 42 to the outer carbon steel ships hull 36 and bulkhead members 40.

While two specific embodiments of the invention have been described and shown in detail to illustrate the application of the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles. For instance, while the invention has been described as having particular utility in association with tanker vessels, it will be readily seen that the invention has equal utility for shore based storage facilities of any polygonal shape.

What is claimed is:

1. A flat walled polygonal container for storage of liquids at cryogenic temperature comprising a plurality of first wall means defining an inner primary container, a plurality of second wall means surrounding and spaced from said inner primary container defining an outer secondary container thereabout, insulation means between said primary and secondary containers, and a plurality of frame means exterior of said primary container and lying in the respective planes of said first wall means, each of said first wall means including projecting edge portions extending through the planes defined by the adjacent intersecting wall means, said projections being secured to .said frame means.

2. A container in accordance with claim 1 wherein said secondary container is coextensive with the interior of said frame means.

3. A container in accordance with claim 1 wherein said projecting edge portions of said first wall means are generally rectangular in form and spaced from their adjacent projections a distance equal to the width of said projection.

4. A container in accordance with claim 3 including weld means forming a bead at the intersection of said wall means along the boundaries of said projections to thereby form a sealed primary container.

5. A container in accordance with claim '3 including weld means forming an inner bead at the intersection of said wall means along the innermost boundaries of said projections to thereby form a sealed primary container.

6. A flat walled polygonal container for storage of liquids at cryogenic temperature comprising a plurality of intersecting wall means defining a container, insulation means secured to the exterior surface of said container and a plurality of supporting frame means exterior of said container and lying in the respective planes of said wall means, each of said wall means including projecting edge portions extending through the plane defined by the adjacent intersecting wall means, said projections being weldedly secured to said frame means.

'7. A fiat walled polygonal container for storage of liquids at cryogenic temperature comprising a plurality of first Wall means defining an inner primary container, a plurality of second wall means surrounding and spaced from said inner primary container defining an outer secondary container thereabout, and a plurality of frame means exterior of said primary container and lying in the respective planes of said first Wall means, each of said first wall means including projecting edge portions extending through the planes defined by the adjacent intersecting wall means, said projections being secured to said frame means.

8. A container in accordance with claim 7 including insulation means between said primary and secondary containers, said insulating means substantially filling the space between said wall means to thereby transmit the hydrostatic load of the liquid within the container from the first wall means to the second wall means.

9. A container in accordance with claim 7 wherein said projecting edge portions of said first wall means are generally rectangular'in form and equally spaced from their adjacent projections a distance equal to the width of said projection.

References Cited UNITED STATES PATENTS 2,306,275 12/1942 Murray 22015 2,892,564 6/1959 Morrison 220-15 3,039,418 6/1962 Versluis. 3,104,025 9/1963 Dosker 22015 THERON E. CONDON, Primary Examiner.

JAMES R. GARRETT, Assistant Examiner.

Claims (1)

1. A FLAT WALLED POLYGONAL CONTAINER FOR STORAGE OF LIQUIDS AT CRYOGENIC TEMPERATURE COMPRISING A PLURALITY OF FIRST WALL MEANS DEFINING AN INNER PRIMARY CONTAINER, A PLURALITY OF SECOND WALL MEANS SURROUNDING AND SPACED FROM SAID INNER PRIMARY CONTAINER DEFINING AN OUTER SECONDARY CONTAINER THEREABOUT, INSULATION MEANS BETWEEN SAID PRIMARY AND SECONDARY CONTAINERS, AND A PLURALITY OF FRAME MEANS EXTERIOR OF SAID PRIMARY CONTAINER AND LYING IN THE RESPECTIVE PLANES OF SAID FIRST WALL MEANS, EACH OF SAID FIRST WALL MEANS INCLUDING PROJECTING EDGE PORTIONS EXTENDING THROUGH THE PLANES DEFINED BY THE ADJACENT INTERSECTING WALL MEANS, SAID PROJECTIONS BEING SECURED TO SAID FRAME MEANS.

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