Securement System Using Loose Keys For Independent Storage Tanks

Abstract

An arrangement for securing independent storage tanks or containers in a tanker or other vehicle of transportation for transporting cargoes below or above ambient temperature wherein the arrangement comprises a system of key-keyway-bearer combinations removed from the neutral axis of the container, preferably located at the top and the bottom of the storage tank and utilizing loose keys, or in other words, keys that are detached from the surrounding keyway-bearer structure.

Description

BACKGROUND OF THE INVENTION

The present invention relates in the broadest sense to the storage and transportation of liquids such as liquefied natural gas, hereinafter referred to as LNG, at extremely low temperatures well below ambient temperature and at essentially atmospheric pressure. More particularly, the present invention is concerned with a novel and improved system for securing storage tanks carrying LNG or the like in large quantities within a moving vehicle such as a tanker and wherein the system uses loose keys.

It is well know in the art that the transportation of gasses, such as natural gas and the like, to locations remote from its source of origin 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 (e.g., approximately six-hundredfold for a given quantity of methane gas and, as will be appreciated by those skilled in the art, enables the most efficient and orderly transfer of the gas to the remote area.

In order to transfer LNG in a practical and economically feasible manner in relatively large volumes, it is necessary to store the liquefied natural gas at approximately atmospheric pressure, since large containers built to withstand superatmospheric pressures would be impractical, if not impossible, to construct for use on seagoing tankers or vessels and the like. The LNG now is kept in storage containers having exceptionally large capacities and these containers when transported by tanker are confined within the cargo hold space of the tanker. To prevent heat losses which would lead to excessive volatilization of the stored liquified gas, it is essential to provide proper thermal insulation for the containers. Also, the containers must be of sufficient strength to withstand the internal stresses that may be induced therein by large temperature gradients through the walls of the container. In using containers having such large capacity in a moving vehicle, it is desirable to maintain absolute control of the movements of the containers so as to avoid bumping or shifting movements thereof in response to the erratic movements of the transportation vehicle, such as the pitch and roll movements of a seagoing tanker. The problem of properly securing the containers in the cargo hold space provided therefor in the tanker further is increased by the need to compensate for movement of the storage containers caused by the expansion or contraction thereof that comes about due to the storage of the containers at a temperature well below that of ambient temperature. This change in temperature naturally will result in considerable contraction in the dimensions of the containers when filled with a material such as liquefied gas or the like, and in a corresponding expansion when the containers are emptied and allowed to rise in temperature. Heretofore, the solution to the problem of properly securing the containers in the tanker's cargo hold space has been the use of key-keyway systems employing keys formed integral with the tanker's hull.

The prior art securement arrangements have been found to be unsatisfactory in many respects. Frequently, prior art securement systems for mounting containers in a tanker have relied upon vertically disposed key-keyway arrangements. These prior art arrangements have not only been relatively complex and costly to construct, but have been ineffective in providing an equalized distribution of stress concentrations along the entire key-keyway structure. This is because the key-keyway is located at the vertical center of the container sidewalls and therefore, the stress is concentrated at one or two localized points which normally are at either end of the key. Thus, the possibility of local failure where greater stress concentrations occur is greatly increased. Since these arrangements are structurally inefficient the consequence is a substantial increase in the cost. Other prior art systems have used top and/or bottom key-keyway arrangements wherein the key is formed integral with the tanker's hull or the container. Since the key and key-way constructions are formed as an integral part of the container or the tanker's hull, the construction of the container is substantially more complicated and, also, it is substantially more difficult to inspect and repair the keys and the keyways. Further, the keys do not always properly mate with the keyways thereby requiring further modification at the site of the tanker or other vehicle of transportation.

SUMMARY OF THE INVENTION

The present invention overcomes both these and other prior art deficiencies by providing a novel and improved arrangement for securing independent storage tanks or containers in position in a tanker or vehicle of transportation, while allowing for contraction or expansion of the container caused by the loading of the cargoes, such as LNG, at lower than ambient temperature. The system comprises essentially an arrangement of keys, keyways and bearer supports located at the bottom of the container in directions corresponding to and along the longitudinal and transverse centerlines of the tank. Specifically, a lower keyway and container support pedestal are secured to the inner bottom wall of the tanker's hull. A matching keyway and container bearing member are secured to the underside of the container. A loose key, preferably made of fabricated steel, is fitted into the channel formed between the keyways to secure the container from undesirable lateral and longitudinal movement relative to the ship. The container's bottom or lower keyways are designed so that its width is wider than they key at ambient temperature by an amount carefully calculated to correspond to the amount of thermal contraction that occurs when the container is cooled to the temperature of the cargo. Thus, at operating temperature the key will fit neatly in the keyway. The containers may be further supported by additional bearer members and support pedestals located near the outboard sides of the container. To further secure the containers against any upsetting force that may result from the motion of the transportation vehicle, there is provided a second key and keyway system located at the top of the container extending in a direction on the longitudinal centerline thereof. As with the lower container keyways, the keyways secured to the top of the container are constructed to suit the dimension of the key when the container is cold. Matching keyways are secured to the underside of the deck and these upper keyways are fitted only in alternate bays formed between adjacent deck girders. The keys are designed to be shorter than the distance between the adjacent girders to facilitate their insertion into the keyway. Thus, installation of the containers, deck structure and keyways can be accomplished prior to the final fitting and insertion of the keys. The container securement of the present invention is more effective than that proposed by the prior art, since forces and therefore stress concentrations are equally distributed along the container, bearing areas are substantially reduced, and the key support structure can be less extensive than required heretofore. The use of a common structure for slidably mounting the keys and providing bearer support substantially reduces the construction costs and minimizes thermal losses. A significant feature of the present invention comprises the use of loose keys which permits the keys and keyways to be machine finished under workshop conditions prior to final installation. Also, the use of loose keys permits the withdrawal of the keys for inspection and repair if required. By virtue of the fact that the present arrangement provides for equal distribution of forces, the stress concentrations are evenly distributed on the container and consequently the possibilities of failure associated therewith are substantially reduced. Further, the use of loose keys as compared to integral formed male tenons simplifies and expedites construction of the storage containers.

Accordingly, it is a primary object of the present invention to provide a novel and improved system for securing storage containers in a transportation vehicle, such as a tanker, which is low in cost, economical in construction, and reliable in operation.

Another object of this invention is to provide a novel and improved system for securing independent storage container and which uses loose keys.

A further object of this invention is to provide a novel and improved key-keyway system for securing a storage container in a cargo hold of a vehicle and wherein there is equal distribution of stress concentrations along the container.

Having in mind the above and other objects that will be evident from an understanding of this disclosure, the invention comprises the devices, combinations construction, arrangements of parts as illustrated in the presently preferred embodiment of the invention which is hereinafter set forth in such detail as to enable those skilled in the art readily to understand the function, operation, construction, and advantages of it when read in conjunction with the accompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a transverse cross-sectional view taken substantially along the line 1--1 in FIG. 2 of a tanker in which the new and improved system for mounting a storage container according to the principles of the present invention has been installed;

FIG. 2 is a bottom plan view taken substantially along the line 2--2 in FIG. 1 of the storage container partially broken away;

FIG. 3 is a top plan view taken substantially along the line 3--3 in FIG. 1 illustrating a portion of the top of the storage container embodying the features of the present invention;

FIG. 4 is a enlarged cross-sectional view taken substantially along the line 4--4 in FIG. 3 showing details of construction of a top key-keyway arrangement constructed in accordance with the present invention;

FIG. 5 is an enlarged cross-sectional view taken substantially on the line 5--5 in FIG. 2 illustrating details of construction of a bottom key-keyway-bearer arrangement constructed in accordance with the present invention; and

FIG. 6 is an exploded perspective view illustrating a bottom key-keyway-bearer arrangement embodying the principles of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention is disclosed in combination with a cryogenic storage container for storing liquefied natural gas (LNG) or the like at atmospheric pressure, such as disclosed in the U.S. Pat. of Clarke et al., No. 3,319,431, issued May 16, 1967, and assigned to the assignee of the present invention, wherein the container is fully disclosed and to which reference may be had for a more complete understanding thereof.

Referring now to the drawings, there is illustrated in FIG. 1 a storage container 10 which is installed in a double-hulled tanker 11 (although a single-hulled tanker may be suitable) having an outer hull 12 and an inner hull 13 which are maintained in separated spaced relationship by structural members 14 and which defines a cargo hold space 15. The container 10 includes an inner tank 16 which constitutes a primary barrier having the general shape of the cargo hold 15 and which is fabricated from aluminum, stainless steel, high nickel steel, aluminum alloy or a like material which is capable of withstanding the thermal stresses induced by the cryogenic cargoes. The inner tank 16 is enclosed by a similarly shaped and designed outer tank 17 which constitutes an outer or secondary barrier and also, as with the inner tank 16, is fabricated from a material such as aluminum or the like which is not deleteriously affected by the extremely cold temperatures of the cryogenic cargoes. The tanks 16 and 17 are maintained in space relation by means of rigid spacing members 18 secured therebetween.

The double-walled tank or storage container 10 is provided about its outer surface with an exterior layer of thermal insulation 19. It will be understood by those skilled in the art that for purposes of the present invention the layer of insulation 10 may be located otherwise than as illustrated. For example, it may be situated along the inner hull of the tanker 11. Briefly referring to the internal construction of the tank 10, there is illustrated as impervious longitudinal bulkhead 20 that is effective to prevent sloshing of the LNG cargo from side-to-side within the tank. The tank also includes horizontal flats 21 and 22 which include a plurality of apertures 23 and 24, respectively, to permit drainage and circulation.

As shown in FIG. 1, the tank 10 properly is secured in position within the cargo hold 15 of the double-hulled tanker 11 by means of a bottom key-keyway-bearer system generally designated 25 and a top key-keyway system generally designated 26. Also, to further provide support for the tank 10 there is provided at the tank bottom a plurality of bearer/support arrangements generally designated 27 situated near the outboard sides of the tank. At the bottom of the tank 10 the system 25 comprises a plurality of keyway-bearer means 28, one pair being longitudinally disposed and a second pair being transversely or laterally disposed keyways, each of the pairs located along lines corresponding to the respective centerlines of the tank 10 as best illustrated in FIG. 2. Since each of these keyway-bearer means 28 are identical in their construction and arrangement, only one need be described for purposes of understanding the present invention. The keyway-bearer 28 comprises a lower keyway or elongated channel 29 secured to the underside of the tank 10. See FIGS. 2 and 5. The keyway 29 is formed by a pair of laterally spaced keyway vertical bearing members 30, which are made of balsa wood, fir or other suitable material, which extend the length of the members 30 and are located adjacent to tank bottom, and that properly are secured in place by means of support brackets 31 which are suitably fastened at one end to the bottom of tank 10 and at the other end to the vertical bearing member 30. These brackets 31 comprise the same material as that for the tank which may be made of aluminum, 9 percent nickel steel or any other suitable material. As shown in FIG. 5, at the lower end of the inner surface of each of the bearing members 30 there is provided a lateral bearing block 32, which is made of wood, laminated phenolic (micarta) or any other suitable material and has an outer contact bearing surface 33. At the bottom of each of the vertical bearing members 30 there is secured a contact bearing surface 34 made of a material such as micarta, stainless steel, or the like, to vertically provide support for the tank 10 and any cargo contained therein. To the inner bottom of the tanker and disposed for alignment with the foregoing keyway-bearer means 28 there are provided a pair of keyway-bearer support means 28', comprising a pair of laterally spaced elongated hollow keyway support stools 35, which comprise preferably 9 percent nickel steel or some other suitable material such as aluminum, etc. At the top or upper surface of each of the support stools 35 there is secured vertical contact bearing surfaces 36, which are similar to the bearing surfaces 34 described heretofore. The support stools 35 are properly secured in place adjacent the inner bottom of the tanker by means of support brackets 37, which are similar to the support brackets 31 for the bearer members 30. The support stools 35 are disposed such that when the tank 10 is mounted in the tanker's cargo hold 15 the bearing surfaces 36 of the stools 35 will align in contact with the corresponding bearing surfaces 34 of the vertical bearing member 30. On the inner surface at the upper end and extending the length of the support stools 35 there are provided a pair of opposing lateral bearing blocks 38, having outer contact surfaces 39, which are similar to the lateral bearing members 32. The spacing between the lateral bearing blocks 38--38, as illustrated in FIG. 5, defines an elongated channel or keyway 40 having a width that is slightly smaller than that between the lateral bearing blocks 32--32 for reasons to be described hereinafter. Also, disposed adjacent the inner bottom of the tanker are a pair of spaced support blocks 41 of suitable wood material which are located between opposing inner faces of the support stools 35 inwardly of the lateral contact surfaces 39. These blocks 41 provide vertical support for elongated hollow steel key 42 having a rectangular end cross section and which is to be slidably inserted into the channel formed by the keyways 29 and 40 upon mounting the tank 10 in the tanker's cargo hold 14. Once the tank 10 has been mounted with its bearer members 30 properly located relative to the support stools 35, as shown in FIG. 5, the loose key 42, made preferably of fabricated steel, is fitted into each of the channels thereby to secure the tank from lateral and longitudinal movement relative to the tank top. The spacing between lateral bearing blocks 38--38 is such as to provide a relatively close fit for the key 42. However, the keyway width defined between the lateral bearing blocks 32--32 secured to the tank 10 is such that it is wider than the corresponding key width at ambient temperature by an amount carefully calculated to correspond to the thermal contraction when the tank 10 is cooled to the temperature of the cryogenic cargo. Thus, when the tank 10 is at operating temperature the key 42 will fit neatly in the keyway 29 defined between lateral bearing blocks 32--32. In addition to the foregoing described combined bearing-support arrangements located at each of the key-keyway means 28, the tank 10 further is supported vertically by additional bearing members 43 (similar to bearing members 30) and support pedestals 44 (similar to support stools 35) which extend longitudinally near the outboard sides of the tank, as best illustrated in FIG. 2. Each of the bearing members 43 is suitably secured to the underside of the tank 10 and is provided with a contact bearing surface 45 that is similar to the bearing surfaced 34, and each of the support stools or pedestals 44 is provided with a contact bearing surface 46 which is similar to the bearing surfaces 36. As shown in FIG. 6, it is clearly apparent that by using an arrangement including a loose key 42, that is, one structurally separate from the surrounding keyway defining structure, the installation and repair of the keys and/or the keyways is greatly simplified. A modification of the foregoing described construction and arrangement that is within the scope of this invention may include making the bottom keys 42 in multiple lengths so that complete withdrawal thereof for purposes of inspection or otherwise is permitted. Thus, in the event of pitching or rolling movement of the tanker, the longitudinal and transverse key-keyway combinations properly will secure the tank in place in the cargo hold while permitting thermal expansion and contraction.

The tank 10 further is secured from undesirable movement by means of the longitudinal extending top key-keyway means 47 (secured to the tank) and 47' (secured to the deck 49) which comprise the system 26. The top or deck keyway 47' comprises a pair of laterally spaced support stools or pedestals 48 fastened adjacent the underside of the deck 49. Each inner surface of the support stools 48 at its bottom end is provided with a lateral bearing block 50 having an outer bearing contact surface 51, similar to the lateral bearing blocks 32 and 38. The stools 48 are secured to the underside of the deck 49 by means of metal support brackets 52 in a manner similar to that for the lower bearing and support members. The bearing blocks 50 define elongated channels or keyways 53. The keyways 53 may be located in alternate bays (see FIG. 3) formed between the downward extending transverse deck girders 54 so as to facilitate insertion and removal of the keys 42 therefrom. This is best illustrated in FIG. 3, wherein the key is shown in dotted lines prior to insertion into its keyway. At the top of the tank 10 there is secured the matching keyway 47 comprising a second pair of support stools 55 which are held in spaced relation by means of support brackets 56. A lateral bearing member 57 having a bearing contact surface 58 is secured to the inner surface at the upper end of each of the support stools 55. These members 55 extend longitudinally the length of the stools and define an upper tank keyway 59. Located and secured to the tank top wall between the opposing inner faces of the support stools 55 inwardly of the bearing members 57 are a pair of spaced support blocks 60, preferably of a wood material, which function in a manner similar to the support blocks 41. As with the lower tank keyways 29, the top tank keyway 59 is constructed to suit the dimension of the key 42 when the tank 10 is cold. Thus, as shown in FIG. 4, the spacing between the lateral bearing blocks 50 is less than the width between the lateral bearing members 57 so that when the key 42 slidably is inserted into register with the keyways 53 and 59 and the tank is cooled, the space between the upper tank bearing members 57 will contract laterally with corresponding contraction of the tank thereby to form a neat fit for the loose key 42. It is to be noted that when using a construction where the girders extend down, the keys 42 are shorter than the distance between adjacent deck girders 54 so that installation is made easier. It is apparent from the foregoing description that installation of the tanks, deck structure and keyways can be completed before final fitting and insertion of the keys into their corresponding keyways.

As an alternate arrangement to the above, both the top and bottom tank keyways may be recessed into the tank structure (that is, the top and bottom tank walls), thereby permitting an increase in the size of the tanks relative to their capacity.

Further numerous alterations of the structure herein disclosed will suggest themselves to those skilled in the art. However, it is to be understood that the present disclosure relates to a preferred embodiment of my invention which is for purpose of illustration only and is not to be construed as a limitation of the invention. All such modifications which do not depart from the spirit of the invention are intended to be included within the scope of the appended claims.

Claims

Having thus set forth the nature of the invention, what I claim herein is:

1. In the storage and transportation of a material having a temperature differing widely from ambient temperature, a container of large capacity formed of a material characterized by substantial expansion and contraction due to temperature changes and which has a substantially flat bottom, a supporting structure having a relatively flat floor, means for mounting said container within said supporting structure so that said flat bottom is disposed in spaced relation relative to said flat floor and in a manner to substantially stabilize the position of said container within said supporting structure while permitting free expansion and contraction thereof, said mounting means comprising a first and second plurality of longitudinally and transversely arranged elongated keyways provided on said flat bottom of said container and one said flat floor respectively, corresponding ones of said keyways of said first and second plurality being disposed in vertically aligned matched relation thereby to define a composite channel, an elongated key being slidably received in both of the keyways of each of said composite channels, whereby said container is stabilized against any undesirable movement relative to said supporting structure.

2. An assembly according to claim 1 wherein the width of said first plurality of keyways is greater than that of said second plurality of keyways by a predetermined amount corresponding to the amount of contraction of said container caused by the change from ambient temperature to storage temperature.

3. An assembly according to claim 1 wherein bearing means are operably associated with each of said keyways of said first and second plurality whereby said bearing means assists in maintaining said container in a stabilized position.

4. An assembly according to claim 3 wherein said bearing means for each of said keyways comprises a pair of laterally spaced horizontal bearing surfaces located on opposite sides of said keyway, wherein said bearing surfaces of said corresponding ones of said keyways are disposed in contact with each other.

5. An assembly according to claim 3 wherein said bearing means for each of said keyways comprises a pair of opposing bearing members extending laterally inward of each of said keyways for contact with said key.

6. An assembly according to claim 3 wherein additional bearing means are provided adjacent the periphery of said flat bottom of said container and support means for said bearing means are provided on said flat floor for further supporting said container within said supporting structure.

7. An assembly according to claim 1 wherein said container includes a relatively flat top portion and said supporting structure has a top wall, a third and forth plurality of longitudinally arranged elongated keyways provided on said flat top portion and on said top wall, respectively, corresponding ones of said keyways of said third and fourth plurality being disposed in vertically aligned matched relation.

8. An assembly according to claim 7 wherein the width of said keyways comprising said first and third plurality is greater than that of said keyways comprising said second and fourth plurality by a predetermined amount corresponding to the amount of contraction of said container caused by a change from ambient temperature to storage temperature.

9. An assembly according to claim 7 wherein bearing means are operably associated with said third and fourth plurality of said bearing means comprising a pair of opposing bearing members extending laterally inward of each of said keyways disposed for contact with said key.

10. In the storage and transportation in the cargo hold of a tanker of a material having a temperature differing widely from ambient temperature, a tank of large capacity formed of a material characterized by substantial expansion and contraction due to temperature changes, said tank having top and bottom walls, said cargo hold having a deck and a floor, means for securing said tank within said cargo hold so that said bottom wall is spaced from said floor, said securing means comprising a first and second plurality of opposing longitudinal and transverse keyways operably secured to said bottom wall and said floor respectively, a third and fourth plurality of opposing longitudinal keyways operably secured to said top and said deck respectively, key means separate from said keyways being slidably and removably disposed in opposing ones of said keyways thereby to stabilize and effectively isolate said tank from any movement transmitted by said tanker.

11. In the assembly of claim 10 wherein girders extend downward from said deck in a transversely spaced arrangement thereby to define a plurality of bays, said fourth plurality of keyways being secured to said deck in alternate bays between said girders, thereby to facilitate insertion of said key means into its corresponding keyways.

12. A tank of relatively large capacity for use in the storage and transportation of material having a temperature differing widely from ambient temperature and being formed of a material characterized by substantial expansion and contraction caused by temperature changes, said tank being adapted for securement within a cargo containing structure and having top, bottom and sidewalls, means adapted to securely position said tank within said enclosed area, said means comprising a first plurality of longitudinal and transverse extending elongated channels formed on said bottom of said tank and a second plurality of longitudinal extending elongated channels formed on said top of said tank, each of said channels being adapted to match with an opposing channel formed with the cargo containing structure thereby to form a composite keyway capable of slidably receiving a slidable and removable key, whereby said tank will be secured in position when placed within said cargo containing structure.