US3363796A - Insulated cargo container - Google Patents

Description

Jan. 16, 1 968 G. R. PRINGLE INSULATED CARGO CONTAINER Filed Sept. 4, 1964 2 Sheets-Sheet 1 =|7 .2?" FIG. 4

INVENTOK GORDON R. PHI NGLE ATTORNEYS Jan. 16, 1968 G. R. PRINGLE 9 INSULATED CARGO CONTAINER Fil d Sept, 19 4 2 Sheets-Sheet 2 INVENTOR.

ATTORNEY GORDON R. PRINGLE United States Patent 3,363,796 INSULATED CARGO CONTAINER Gordon R. Pringie, Lower Bourne, Farnham, England, assignor to Esso Research and Engineering Company, a corporation of Delaware Filed Sept. 4, 1964, Ser. N 0. 394,587 4 Claims. (Cl. 220-9) ABSTRACT OF THE DISCLOSURE A cryogenic insulation system comprising a plurality of prestressed thermal insulation panels, the prestressing being sufficient to compensate for the contraction that would normally be induced in said panels at cryogenic temperatures. The cold faces of the panels are also provided with a predetermined configuration of stress relieving grooves, and are thereafter coated with a cargo impervious lining.

The present invention relates to new and improved cargo containers for ships or the like, particularly for tankers used for the transportation of liquefied gases, and the method of fabricating the same.

It has been established that the transportation of gases, such as natural gas, hydrogen, oxygen, methane, and the like, to remote locations, may best and most efficiently be accomplished by reducing the volume of the gas through its conversion into the liquid state. Such a conversion enables the storage volume requirements to be greatly reduced (approximately six-hundredfold for a given quantity of methane gas, for example) and, as should be appreciated, enables the most efficient transfer of the gas to a remote area.

In order to transfer liquefied gas in a practical and economical manner in relatively large volumes, it is necessary to store the liquefied gas at approximately atmospheric pressures, since large containers built to withstand superatmospheric pressures would be impractical, if not impos sible, to construct for use on seagoing tankers or the like. However, liquefied gases maintained at atmospheric pressures have extremely low vaporization points, ranging from about -435 F. for liquefied hydrogen, to -28 F. for liquefied ammonia, and these unusually low temperatures of the liquids present certain problems in the design and production of insulated cargo containers. Specifically, the containers must be capable of preventing heat losses which would lead to subsequent volatilization of the stored liquefied gas and of withstanding the internal stresses that may be induced therein by the large temperature gradient through the walls of the container. Typical arrangements for transporting liquefied gas have involved the use of aluminum storage tanks constituting primary barrier means independently supported within an insulated chamber separated from the primary barrier by a secondary liquid tight barrier.

The present invention represents a unique approach to and solution of the problem of safely and efficiently storing liquefied gas while compensating in an improved and simplified manner for the internal stresses to which the cargo container may be subjected by the extremely cold temperatures of the liquefied gas. As one important aspect of the invention, the new and improved cargo container enables the insulation employed in the construction of the container to serve the dual functions of insulator and liquid tight barrier, obviating the need for complicated expansion systems and independent tanks and insulators.

In accordance with the principles of the invention, the cargo storage container, itself, is constructed from a series of abutting, precompressed insulating blocks of novel and improved design. The blocks are prestrained beyond the amount of contraction that would be caused by the extremely cold temperature to which the container walls are to be subjected. By constructing the new cargo container from the insulator, itself, which insulator, by reason of the improvements of the invention, is able to be maintained under a predetermined precompression greater than the deleterious contraction forces to which it normally would be subjected in use. The insulating material is maintained effectively liquid tight so that the need for separate or independent storage tanks and insulators, as well as the need for expansion systems to accommodate relative expansion and contraction movements are obviated.

The new cargo container is constructed by cladding a cargo space such as the cargo hold of a ship with a plurality of discrete urethane foam blocks which are known excellent low temperature insulators and liquid tight barriers when intact. In accordance with One aspect of the invention, the blocks are precompressed lengthwise and WldthWi;6 and, while being maintained under the predetermined precompression, are transferred into special jack frames which maintain the blocks under [the predetermined precompression. The peripheral outer edges of the blocks are provided with dovetail slots or 'keyways, which edges project beyond the jack frames. Through cooperation with mating dovetails or keys fastened to the Walls of the hold, the blocks are anchored in place against the supporting ship structure.

Completion of the construction of an insulated cargo container may be accomplished by progressively abutting and anchoring pluralities of the frame and block combinations. The subsequent removal of the jack frames from blocks which are surrounded by other frames or blocks allows the precompressed insulated blocks to expand slightly into the gap created by the withdrawal of the frame and into liquid tight contact with one another and into more secure holding contact with the anchoring keys. Moreover, and as another important aspect of the invention, the amount of precompression remaining in the blocks after removal of the frames is sufiicient to compensate for any stresses of contraction that might be caused by the introduction of a material at cryogenic temperatures into the container, which stresses would otherwise cause cracking, and to maintain the blocks in liquid tight abutment at cryogenic temperatures.

It is to be understood that by fabricating a cargo container, in accordance with the principles of the invention, from precompressed insulating blocks which provide liquid tightness and resistance to cracking, the requirement of an independent cargo tank or an additional liquid tight barrier is substantially eliminated. However, to meet certain regulatory requirements, the inner surface of the precompressed, abutting blocks may be coated with a cargoimpermeable coating which will constitute a primary liquid barrier while the insulating blocks, themselves, will constitute a secondary liquid tight barrier capable of holding a liquid cargo for at least two weeks.

For a more complete understanding of the invention and its attendant advantages, reference should be made to the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic cross-sectional view of a portion of a tanker vessel incorporating a cargo container embodying the principles of the invention;

FIG. 2 is an enlarged, fragmentary cross-sectional view showing details of construction of the walls of the new cargo container;

FIG. 3 is an enlarged, fragmentary cross-sectional view showing details of construction of an inside corner of the new cargo container;

FIG. 4- is an enlarged, fragmentary cross-sectional view showing details of construction of an outside corner of the new cargo container;

FIG. 5 is a plan view of apparatus for precompressing an insulating block;

FIG. 6 is a cross-sectional view of apparatus for transferring a precompressed block to a jack frame;

FIG. 7 is a cross-sectional view of abutted block and frame combinations; and

FIG. 8 is a fragmentary elevational view of a wall of the new container in an intermediate state of construction.

Referring to FIG. 1, the new cargo container is indicated by the reference numeral 1t? and is shown in the general configuration of the cargo hold of a ship. In the illustrated embodiment, the container 113 includes a plurality of precompressed insulating blocks 11 in abutted end-to-end and side-to-side relationship (FlG. 8) anchored to a housing structure 12 which is typically a cargo hold of a tanker. A liquefied gas cargo is intended to be carried directly in the insulation-clad held without using an independent cargo tank. However, a separate liquid tight barrier may be utilized where appropriate.

In accordance with the invention a liquid tight cargo container is formed from square urethane foam blocks 11 which have been given an adequate compressive prestress to compensate for the internal stresses encountered when the blocks are subjected to low temperature liquefied gas cargoes, which stresses might otherwise cause the failure of the blocks by cracking, and to maintain the blocks in liquid tight abutment. As shown in FIG. 2, the foam wall blocks 11 have keyways 14- formed about their lower peripheral edges which are adapted to mate with elongate keys 15 extruded or otherwise formed from an aluminum, plastic or other suitable material. The keys 15 are fastened to hold walls 12 by bolts 16 or other suitable fastening means, to anchor the blocks to the ship structure 12.

As shown in detail in FIGS. 3 and 4, the corners of the new cargo container are constructed from special L-shaped urethane foam blocks 20, 21 which are respectively shaped for use in inside corners 25 and outside corners 26, the number and location of such corners being determined by the specific shape of the supporting structure. In ac cordance with the principles of the invention, the corner blocks 20, 21 are prestressed to substantially the same degree as the flat wall blocks 11 and are provided with keyways 14 which may be anchored to the ship structure 12 by keys 15.

As will be understood, the initial prestress in the insu lating blocks is sufficient to form liquid tight joints 17 between the adjacent sides 22 of the blocks and also to provide desired clamping action between the keyways 14 and the keys 15. However, where desired or necessary, the interfaces between adjacent blocks and between the blocks and the steel hull 12 may also be glued. Likewise, it may be found desirable or necessary to fill the voids in the keys 15 or otherwise effectively make the keys solid.

While the abutted, prestressed insulating blocks are of more than adequate liquid tightness and constitute a liquid tight barrier capable of retaining a liquefied cargo for at least two weeks, regulatory codes often require that at least two liquid barriers be provided. To this end, a cargo-impermeable coating 18 of urethane rubber may be applied directly over the faces of the foam blocks 11, 20, 21, which coating constitutes a primary barrier while the insulating blocks themselves constitute a secondary liquid tight barrier. When the insulating blocks are coated to form an additional liquid tight barrier, the faces are provided with V-shaped grooves 19 configured in rectangles (FIG. 8) or circles (not shown) on each block. As shown in FIG. 2, the depths of the grooves in adjacent blocks are unequal. The described and illustrated patterns of V- shaped grooves allow for stress relief of the coating 18 within the V-shaped grooves when the coating is ubjected to the contractive stresses of a supercooled cargo. Moreover, the staggered depths of the rectangular or circular patterns and the shapes of the patterns themselves, tend to localize and to reduce the shear stresses in each of the foam blocks 11 and precludes the build-up of concentrated, deleterious stresses in the corners of the completed cargo container during shrinkage or contraction of the coating 18.

Installation of the insulating blocks 11, 2t 21 in a cargo hold of a ship to form the new cargo container is relatively simple and may be expeditiously accomplished at a shipyard with facility. The individual wall blocks 11 are placed in a press 311 and are squeezed down from an initial unstressed size by platens 31 in the lengthwise and widthwise directions to an overcompressed, intermediate installation size, that of the inside dimensions of a jack frame 33. While maintained under the control of the platens 31 and bottom-supported by a plate 34, the compressed wall block 11 and the plate 34 are directly transferred into the jack frame 33 by an ejecting piston 35. As shown the jack frame 33 comprises a square frame, the outer dimensions of which coincide with the installed size of the insulation blocks 11, and a plurality of jack screws 36 operatively disposed therein.

Cladding of the cargo hold to create the new, closed container is done stepwise. Advantageously, starting at an inside corner, a corner block 20 is placed against the ship structure 12 and is compressed in situ by forces F applied by jacks or other suitable means (not shown). While under precompression and in accordance with the invention, the block 26 is then anchored by sliding a pair of keys 15' thereunder and bolting them to the supporting structure.

Thereafter, the walls of the cargo container are built up progressively and successively by abutting loaded jack frames 33, as shown in FIG. 8, and keying the blocks 11 to the structure 12 while they are held under compression by the frames 33. The frames are removed and the blocks 11 finally installed by tightening the jack screws 36 down against the plate 34, as shown in FIG. 7, to push the frame away from the block allowing the sides 22 of the block to expand slightly into its installed size against immediately adjacent installed blocks 11 and immediately adjacent unremoved frames 33, while retaining sufficient precompression to withstand and to compensate for any internal stresses and contraction that might otherwise be induced therein by a cold cargo of liquefied gas.

The construction of an outside corner is similar to that employed in building an inside corner, in that a preformed block is employed and the block is prestressed in situ. However, the necessary precompression in the outside corner blocks 21 may be provided by the use of a special compression plate 37 which is bolted to the supporting structure and drawn theretoward in conforming contact with the block 21 by a bolt 38.

The before-mentioned stress relieving grooves 19 are advantageously formed in the insulating blocks 11 by a suitable routing operation before cladding, but in some applications might be formed after the installation of the blocks. In any event, upon completion of the installation and routing of the insulating blocks to form a liquid tight and cold stress-resistant container, a urethane rubber coating, or other suitable cargo-impermeable coating of sufficient density to resist the hydrostatic pressure of the liquefied gas cargo in static and dynamic conditions, is applied over the surface of the compressed foam blocks 11, 20, 21. While not theoretically necessary for an operative cargo container, the coating 18 constitutes a primary liquid tight barrier, causing the precompressed blocks to become a secondary liquid tight barrier, and fulfills certain regulatory requirements.

It will be appreciated that the construction of containers with insulating blocks prestressed to a degree compensatory with the stresses that are normally induced therein by cold cargoes and to a degree compensatory with the contraction that would normally be expected enables the insulating material selected to be effectively unstressed and uncontracted during the actual storage of liquefied gas and to function in an additional capacity as a liquid tight barrier. Accordingly, new and significant economies in the manufacture of cargo containers, in accordance with the principles of the invention, will be realized by the elimination of at least one independent liquid barrier whose function may now be carried out by the insulation material, itself.

It should be understood that the specific method of construction and container structure herein illustrated and described are intended to be representative only, as certain changes may be made therein without departing from the clear teachings of the disclosure. Accordingly, reference should be made to the following appended claims in determining the full scope of the invention.

I claim:

1. A cargo container for liquefied gases and the like, comprising (a) a rigid supporting structure,

(b) a plurality of preformed, prestressed blocks of homogeneous insulating material, defining a closed geometric shape,

(0) means mounting said insulating blocks to said structure in abutting side-to-side and end-to-end relation,

(d) said abutted blocks having suflicient prestress to compensate for the contraction and to withstand the internal stresses that would normally be induced therein at cryogenic temperatures,

(e) whereby said blocks remain abutted and provide a liquid tight barrier for cargoes at cryogenic temperatures, the faces of said blocks including stress relieving grooves arrayed in predetermined configurations; a continuous, cargo-impervious coating of plastic material is supported by said faces, whereby stresses induced by changes in dimension of said coating will be non-deleteriously concentrated adjacent said grooves.

2. A container in accordance with claim 1, in which (a) said blocks define keyways about peripheral edges thereof,

(b) key means are fastened to said supporting structure and cooperate with said keyways to secure said blocks to said structure.

3. A closed cargo container comprising (a) a supporting structure and liquid tight walls mounted thereon, said supporting structure including a ship,

(b) said walls includinginsulating-blocks precompressed to a degree sufiicient to retain their strength, liquid tightness, and insulating properties when subjected to cargoes at cryogenic temperatures said blocks are urethane foam and include predetermined patterns of stress relieving grooves at the exposed surfaces thereof, a liquid tight coating of cargo impervious plastic is applied over said blocks and in contact with said grooves, said coating having a tensile strength greater than that of said foam and being of sufficient strength to retain its integrity at cryogenic temperatures, said grooves accommodating changes in dimension of said coating and preventing the undue stressing of said blocks by said coating.

4. The container of claim 1 wherein the depths of said grooves are unequal in adjacent abutted blocks.

References Cited UNITED STATES PATENTS 485,809 11/1892 Curtis et a1 2209 1,888,039 11/1932 Hufi 220 -9 2,552,641 5/1951 Morrison 220-9 2,889,953 6/1959 Morrison 220-9 2,896,271 7/1959 Kloote et al 2209 2,980,279 4/ 1961 Lueders 220-9 3,039,418 6/1962 Verluis 2209 3,044,617 7/1962 Morrison 220-9 3,106,307 10/1963 Morrison 2209 3,115,982 12/1963 Morrison 220-9 FOREIGN PATENTS 860,819 2/1961 Great Britain. 864,552 4/ 1961 Great Britain.

THERON E. CONDON, Primary Examiner. JAMES R. GARRETT, Examiner.

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