Abstract:
A low temperature liquified gas storage tank is supported in the hull of a ship by a plurality of chocks secured to and spaced peripherally around the tank and by chock engaging members carried by the ship&#39;s hull. Pressure resistant heat insulating pads disposed between the chocks and the chock engaging members are arranged to provide sliding surfaces which support the tank horizontally and vertically and permit thermal contracting and expanding movements of the tank relative to the ship&#39;s hull and which compensate for thermal expansion and contraction of the chocks and the chock engaging members.

Description:
SUMMARY OF THE INVENTION 
     The present invention relates to structure for supporting a spherical or cylindrical low temperature liquified gas storage tank with respect to the hull of a ship. 
     Conventional methods of mounting a spherical or cylindrical tank on a ship include one in which the tank is supported by attaching support members such as skirts or struts to the tank adjacent its intermediate height (at the equator in the case of a spherical tank). With such a conventional method, since the tank and the support members are rigidly fixed together, bending stresses are produced in the support members due to expansion and contraction of the tank, a fact which requires that the support members should have a high strength. The use of large support members, however, results in limiting the expansion and contraction of the tank, thus producing high stresses in the supported region of the tank and in the support members. Repetition of such stresses each time a low temperature liquid is charged or discharged will cause fatigue to the tank and support members. 
     Therefore, considering the expansion and contraction which takes place in this type of tank due to the large difference in the temperature of the tank when loaded and when not loaded, it is necessary to support the tank in such a manner as to allow expansion and contraction thereof and to avoid excessive stresses otherwise occurrable in the tank and in the support members. On the other hand, it is essential that the tank be prevented from being displaced relative to the ship by pitching and rolling of the latter. 
     The present invention provides a spherical or cylindrical tank support structure for a ship which meets the two conditions described above. 
     Thus, the present invention provides a spherical or cylindrical tank support structure including means disposed between the outer periphery of the tank and the tank support deck of a ship for supporting vertical loads on the tank, said structure comprising a plurality of chocks spaced apart from each other circumferentially of the tank, a plurality of pairs of opposed chock holding members disposed on said tank support deck in such a manner that said members in each pair are disposed on opposite sides of one of said chocks circumferentially of the tank, and pressure resistant heat insulating pads disposed between each chock and the associated opposed members holding said chock therebetween, said pressure resistant heat insulating pads abutting against either said chock or said opposed members in such a manner as to allow relative sliding movement radially of the tank. 
     According to such support structure of the present invention, without providing a special structural member such as a skirt or a column, it is possible to mount a tank on the support deck and to provide a horizontal tank displacement preventive function while allowing the radial movement of the tank caused by the thermal expansion and contraction of the tank. Further, by distributively supporting the tank circumferentially thereof, it is possible to prevent the horizontal movement of the tank without inducing an excessively high stress in the tank. 
     Other merits and features of the present invention will appear as the description proceeds, when taken in conjunction with the accompanying drawings illustrating preferred embodiments thereof. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic cross-sectional elevation showing the relation between a ship&#39;s hull and a spherical tank; 
     FIG. 2 is a schematic plan view showing said relation; 
     FIG. 3 is a detailed sectional elevation showing one of the supports of the tank; 
     FIG. 4 is a sectional plan view taken along the line A--A of FIG. 3; 
     FIG. 5 is a sectional elevation taken along the line B--B of FIG. 3; 
     FIGS. 6 and 7 are sectional elevations similar to FIG. 3 but showing other embodiments; 
     FIG. 8 is a sectional elevation taken along the line C--C of FIG. 7; 
     FIG. 9 is a sectional elevation of a further embodiment, showing the principal portions thereof; and 
     FIGS. 10 and 11 are schematic elevational views of still other embodiments. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIGS. 1 through 5, provided on and projecting from a spherical tank 1 at two vertically spaced positions adjacent its equator and therebelow are two horizontal support rings 2a and 2b. Also, provided on and projecting from the lower surface of the lower support ring 2b are a plurality of load support chocks 3 equally spaced around the periphery or circumference of the tank. Stiffeners 4 joined to the tank plate 1a are disposed between said upper and lower support rings 2a and 2b above said load support chocks 3, thereby providing a sufficient support strength. Pressure resistant pads 5a, 5b and 5c of heat insulating material are fixed to the lower surface of each load support chock 3 and to the opposite lateral surfaces 3b and 3c thereof circumferentially of the tank, and the external surfaces 6a, 6b and 6c of the pads form slides. 
     A ship&#39;s hull 7 in which said tank 1 is mounted is provided with a support deck 8 for supporting said tank 1 below the upper deck. Fixed on said support deck 8 are U-shaped support blocks 9, each associated with one of the load support chocks 3. Each U-shaped support block 9 comprises a horizontal portion disposed below the chock 3 to provide a tank weight support block 10, and a pair of portions projecting from opposite ends of said tank weight block 10 to provide a pair of opposed chock holding members 11a and 11b facing toward the opposite lateral surfaces 3b and 3c of the associated load support chock. The slide surfaces 6a, 6b and 6c abut against support surfaces 12a, 12b and 12c consisting of the upper surface of the tank weight support block 10 and the opposed lateral surfaces of the pair of opposed members 11a and 11b in such a manner as to allow relative sliding movement between each chock 3 and support block 9 radially of the tank. 
     Since the load support chocks 3 and the pressure resistant heat insulating pads 5b and 5c will thermally contract circumferentially of the tank upon thermal contraction of the tank 1, there will be the danger of a clearance being created between the slide surfaces 6b, 6c and the support surfaces 12b, 12c. In order to prevent this, the pairs of relatively slidable abutment surfaces 6b, 12b and 6c, 12c between said pressure resistant heat insulating pads 5b, 5c and the opposed members 11a and 11b are inclined at an angle of inclination α (FIG. 4) in such a manner that they gradually approach each other, or converge, as they extend toward the center of the tank 1. 
     In order to include the function of preventing upward floating movement of the tank in the U-shaped support block 9 (possessing both the function of supporting vertical loads on the tank and the function of preventing horizontal movement of the tank), said pairs of relatively slidable surfaces 6b, 12b and 6c, 12c may be inclined at an angle of inclination β in such a manner that they gradually approach each other, or converge, as they extend upwardly, as shown in FIG. 6. In this case, at least one of the opposed members 11a and 11b will be fixed on the tank weight support block 10 after mounting of the tank 1. 
     Other references included in the drawings are: 15, a heat insulating material applied to the outer surface of the tank; 16, the outer plate of the ship&#39;s hull; 17, a longitudinal partition wall; 18, a transverse partition wall; and, 19 a double bottom. 
     The operation will now be described. The weight of the tank 1 is distributively supported on the tank weight support blocks 10 by the chocks 3 through the intermediary of the pressure resistant heat insulating pads 5a. There is no possibility of the tank being restrained, since the support surfaces 12a and the slide surfaces 6a are slidable radially of the tank when the tank 1 expands or contracts due to a change in the temperature of the tank. There may be a force acting on the tank tending to move it horizontally. However, since the opposite lateral surfaces 3b and 3c of each load support chock 3 are held between the opposed pair of associated members 11a and 11b and there are many circumferentially disposed chocks 3, even if a horizontal force F (FIG. 2) acts on the tank, the tank can be distributively supported by the reactions f acting on the many chocks 3 so that its horizontal movement can be prevented. Moreover, because of the presence of the relatively slidable opposed surfaces 6b, 12b and 6c, 12c, the tank will not be restrained from its radial expansion and contraction. Further, in the case where such relatively slidable opposed surfaces 6b, 12b and 6c, 12c have a downwardly diverging angle of inclination β, as shown in FIG. 6, upward movement of the load support chocks 3 can be prevented and hence a tank floating-up preventing function is provided, in which case also the tank 1 is not restrained in its radial expansion and contraction. 
     FIGS. 7 and 8 illustrate another means for preventing the tank from floating up. In this example, a pressure resistant heat insulating pad 5d is fixed on the upper surface 3d of each load support chock 3, while the lower surface 12d of a retainer member 14 fixed to the lower end of a stiffener 13, projecting from the partition walls 17 and 18 of the hull 7, abuts against a slide surface 6d on the upper end of the pad, thereby preventing the load support chock 3 and hence the tank 1 from floating up. Of course, the slide surface 6d and the support surface 12d are slidable radially of the tank 1. In this case, since the load support chock 3 and the pressure resistant heat insulating pad 5d will thermally contract in the direction of height upon thermal contraction of the tank 1, there will be the danger of a clearance being created between the slide surface 6d and the support surface 12d. In order to prevent this, the relatively slidable opposed surfaces 6d and 12 d between the retainer member 14 and the pressure resistant heat insulating pad 5d may be provided with an inwardly descending angle of inclination B, as shown in FIG. 9. 
     In the embodiments described above, all of the pressure resistant heat insulating pads 5a - 5d have been fixed to the chock 3. However, they may be fixed to the opposed members 11a and 11b, to the support surface of the tank weight support block 10 and to the holder member 14 so that they relatively slidably abut against the surfaces 3a - 3d of the chock 3. Further, the horizontal support rings 2a and 2b are intended to increase the circumferential strength of the tank 1, and although it is desirable to attach the chocks 3 to the outer periphery of the tank thus reinforced by said rings 2a and 2b, the rings 2a and 2b are not essential for the construction of the present invention. Further, in the case of attaching the chocks 3 to the ring 2b, the chocks may be fixed to the lower side of the ring 2b rather than arranging them so that they constitute portions of the ring 2b in the illustrated manner. 
     A support device shown at 20 in FIG. 10 is such that the two opposed members 11a and 11b are fixed on the support deck 8 without using the U-shaped support block 9, with the pressure resistant heat insulating pad 5a interposed between the support deck 8 and the chock 3. A support device shown at 21 in FIG. 10 is a vertical load support means comprising a pressure resistant heat insulating pad 23 interposed between the ring 2b and a tank weight support block 22 fixed on the support deck 8. The support devices shown in FIGS. 3 - 5, in FIG. 6 and in FIGS. 7 and 8 and the support device 20 shown in FIG. 10 also serve as vertical load support means for the tank. Therefore, such support devices alone may be used to support the tank 1, but as shown in FIG. 10 a suitable number of support devices 21 designed for exclusive use for support of vertical loads on the tank may also be incorporated to support the tank. Further, a number of support devices having the additional function of preventing the upward floating of the tank, such as shown in FIGS. 6 through 9, may be combined with support devices which do not have this function, such as the devices shown in FIGS. 3 through 5, so as to support a single tank 1. 
     A support device shown at 24 in FIG. 11 has no pressure resistant heat insulating pad 5a and no function of supporting vertical loads on the tank. In this case, the support device 21 for exclusive use for support of vertical loads on the tank may, of course, be additionally used to support the tank 1. Further, the present invention is not limited in application to a spherical tank, but it may be applied to a vertically mountable cylindrical tank or to a horizontally mountable cylindrical tank, without any modification.