US2993460A - Tank support - Google Patents

Description

y 5, 1961 c. DREYER 2,993,460

TANK SUPPORT Filed May 29, 1958 TEM P. GRADKENT FIGS TEMP. (F.) -4o 0 +90 TEMP. GRAD3ENT FIG.

iNVENTOR CURTIS DREVER ATTORNEYS United States Patent 2,993,460 TANK SUPPORT Curtis Dreyer, Oakland, 'Calif., assignmto California Research Corporation, San Francisco, Calif., a corporation of Delaware Filed May 29, 1958, Ser. No. 738,774 3 Claims. (Cl. 114-74) This invention relates to insulated metal tanks of relatively large transverse or lateral dimensions, such as are to be secured to the bottom framing of a tankship for transporting refrigerated liquefied petroleum gases at temperatures ranging from 90 F. to -40 F. or lower, and particularly refers to improved flexible supports for the flat steel bottom of such a tank, to adapt it to expansion and contraction from temperature variations and also to resist lateral forces due to ships motion, wave action, etc., without introducing undue stresses or displacements either in the tank or in the ships framing.

A principal object is to provide a substantially symmetrical arrangement of independent vertical flat flexible plate supports, all oriented with their planes perpendicular or normal to radii extending from the center of the tank to points on its outer edge. Transverse shear forces from any source are transmitted through the stiff or longitudinal dimension of each plate, but radii changes of dimensions of the tank bottom from the center outwardly, as by the large temperature changes that are encountered in this service, are accommodated by a slight elastic distortion or bending of the separate support plates in the plane between their top edges, which are secured to the tank bottom, and their bottom edges, which are secured to a foundation or to the framing of the ship structure, at appropriate locations to carry the downward and lateral thrust of the tank and its contents.

An alternative construction, in which a small area of center portion of the tank is rigidly connected to the foundation or to the ships framing, may supplement the centering action of the circumferentially spaced rows of unconnected plates to keep the center of the tank aligned in its desired position, regardless of inward and outward motion of the tank walls due to expansion and contraction of the flat bottom. A variation of this arrangement, wherein the center of the tank is securely anchored as by a cylindrical skirt surrounding a central sump, for example, involves vertical and relatively stifi plates as supports, the upper and lower ends of which are unsecured and movably retained in an upper and a lower concave groove or saddle, so that the plates are free to rock and, hence, are not subject to any bending stresses. In this case the cylindrical skirt can be designed to act in much the same way as a plurality of flexible plates arranged in a circle. The skirt, too, will permit limited radial expansion while resisting lateral loads and maintaining tank center.

It is another object of the invention to provide such a structure that is adapted to the thickness of thermal insulation that is required for the economical operation of such a tankship.

Another object is to provide a tank support with no sliding, rolling, or articulating parts between the bottom and the supporting structure therefor.

These and other object and advantages will be further apparent from the following description of several alternative embodiments, taken in connection with the attached drawing, which illustrates preferred constructions involving the invention.

In the drawing, FIGURE 1 is a diagrammatic plan view of a rectangular tank for a tankship, showing an 2,993,460 Patented July 25,1961

oriented arrangement of independent vertical support plates.

FIGURE 2 is a diagrammatic vertical sectional view on line II-II of FIGURE 1, showing a preferred arrangement of plate supports, each with an insulating block separating its upper end from the metal tank bot tom.

FIGURE 3 is a diagrammatic plan view similar to the arrangement of FIGURE 1, but with a central skirt anchorage for the lateral restraint of the center of the tank bottom.

FIGURE 4 is a diagrammatic vertical sectional view on line IV-IV of the arrangement of FIGURE 3, showing an uninsulated connection between the tank bottom and the separate oriented vertical support plates, and with a central skirt anchorage.

FIGURE 5 is a diagrammatic plan view of a circular tank with concentric rows of oriented vertical flat rocker plate supports and a central skirt anchorage.

FIGURE 6 is a diagrammatic vertical sectional view on line VIVI of the arrangement of FIGURE 5, showing the oriented vertical rockers and their upper and lower saddles on the tank bottom and support, respectively.

FIGURE 7 is a detail front elevational and part sectional view of a simple vertical support plate and insulating block of the type shown in FIGURE 1.

FIGURE 8 is a transverse vertical sectional view on line VIIIVIII of the plate arrangement of FIGURE 7.

FIGURE 9 is a diagrammatic representation of the temperature gradient along the vertical length of the plate and insulating block support of the type shown in FIGURES l, 7, and 8.

FIGURE 10 is a detail vertical'transverse sectional view of the plate arrangement of FIGURE 4, illustrating a plate welded at its upper end directly to the metal tank bottom.

FIGURE =11 is a diagrammatic representation of the temperature gradient along the vertical length of the partially insulated plate support of FIGURES 4 and 10.

FIGURE 12 is a diagrammatic vertical sectional view of a welded plate arrangement similar to FIGURE 4, but with a-rsupport framing that is higher at the center than at the edge of the tank, so that longer or higher support plates may be used at the edge, where the horizontal cumulative deflections due to temperature change are greatest.

FIGURE 13 is a vertical sectional view on line XIII XIII of FIGURE 3 showing an arrangement of a circular centering and anchoring skirt for the tank.

FIGURE 14 is a detail front elevational and part sectional view of a stiif vertical plate rocker for the arrangement of FIGURE 6.

FIGURE 15 is a detail vertical sectional view on line XVXV of FIGURE 14, showing an arrangement of concave saddles for the stifi vertical plate rocker.

Referring to the drawings, and particularly to FIG- URES 1-4, reference numeral 10 designates generally the fiat bottom of a tank 11, usually provided with a central sump 12 to which piping connections (not shown) may be attached for filling or emptying the tank. Supporting the tank bottom '10 is a plurality of relatively long flat vertical plates 13, secured at their lower ends to a suitable foundation or support 14, which is the framing of a ship. Tank 11, in this example, is designed to carry liquefied petroleum gas (LPG) such as propane, butane, methane, etc., or mixtures of them at substantially atmospheric pressure and very low temperature,

3 ranging down to -40 F., or lower. Accordingly, the tank bottom and walls are quite heavily insulated (FIG- URE 8), usually externally as at 15, and it is desirable also to insulate thermally the top of each plate 13 from the tank bottom 10, as by a composition or wooden block 16.

Plates 13 are arranged so that each will carry its share ofthe downward load and also is oriented with itsplane face normal to a line extending radially from the center of the tank 11 toward the outer edge or shell (FIGURES l, 3, and By this arrangement, the bottom it} of the tank may expand and contract radially due to temperature changes ranging from atmospheric, which may be as high as i+90 F. to the temperature of the LPG, which may be as low as 40 F., or even lower. Each separate plate 13 will deflect by lateral deflection or bending between its top and bottom edges, as shown to an exaggerated scale in FIGURE 8, by the amount A, but

' will retain substantially all of its downward load-carrying ability. It has been found that the combined bending stresses in the plates 13 due to lateral deflections A and to axial eccentric loading do not add linearly, so that relatively high axial loads can be carried without buckling of the separate, unconnected plates. This unexpected result makes it possible to provide a support for a tank of this nature that is lighter and stronger than would be expected.

Referring now to FIGURES 7 and 8, there is shown in illustrative detail a preferred arrangement of plates 13 and insulating blocks 16. In this example, plate 13 is a conventional or built-up I section with upper flange 17 and lower flange 18 secured as by studs 19 and bolts 20 to the tank bottom and support 14. To accommodate the transverse force needed tohold tank 11 centered in its desired position during temperature changes or to resist horizontal accelerations due to the ships motion, the upper flange 17 has means such as a transverse, upwardly extending key member 21 on its upper face, fitting into an appropriate slot 22 in block 16, and the block is also held against endwise motion .by metal brackets 23 secured to the tank bottom 10. Internal stiffeners 24 and 25 are usually provided for the upper face tank bottom 10, as shown in this figure.

FIGURE 9, as has been stated, illustrates the approximate temperature gradient from the support 14 to the tank bottom 10, due to the insulated and uninsulated portions of this support plate.

Referring now to FIGURE 10, there is shown an alternative arrangement to that just described, in which the upper edge of the web of support 13 is welded as at 26 to the tank bottom It The upper portion of the web is desirably insulated and this results in the approximate temperature gradient of FIGURE 11. Actually, it is sometimes feasible to use a completely uninsulated web, as its normal resistance to heat flow will be adequate, under certain conditions, to prevent undue cooling of support 14 or heat addition to tank bottom 10. Approximate temperature gradient for such a case is indicated by dotted line on FIGURE 11.

The arrangement of FIGURE 4 differs from that of the figures so far discussed in providing a central anchorage for tank bottom 10, in the form of a continuous cylindrical skirt 27 that is secured around its entire periphery to both the tank bottom '10 and the support 14 (FIGURE 13). When such a central anchorage is used to keep the center of the tank 11 in its desired location, the vertical support members do not need to be flexible, but may be simple stiff plates 28 with rounded upper and lower ends retained in concave saddles 29 and 30 secured to tank'bottom 10 and support 14, respec tively (FIGURES 6, l4, and When radial expansion or contraction of the tank bottom 11 takes place, these plates do not bend, as in the case of those already discussed, but rock slightly through deflection A (FIGURE 15) while still carrying their downward load.

FIGURES 5 andfiillustrate this last-named arrangement as applied to a cylindrical tank, but it is obvious that it could also be used with the rectangular tanks of FIGURES 1 and 3.

FIGURE 12 shows an alternative embodiment of the arrangement of FIGURE 4 in which the support 141 is higher in the center than at the rim of tank 111, so that the oriented vertical support plates 131 are progressively longer as they approach the rim. This gives a longer length of web in which to accommodate the higher deflection that is encountered at increasing distance from the tank center, which is anchored as by skirt 271.

As an example of the practice of this invention, and assuming an LPG tank 60 ft. by ft., weighing a total of 15,360,000 pounds and supported on vertical, oriented plates (FIGURE 1), each plate would he so located as to carry a downward load of 153,600 pounds. Using well-known computation procedures, and assuming a temperature range of +70 F. to 40 F., the maximum horizontal deflection A of the upper end of any vertical .plate.13 due to expansion or contraction of the bottom 10 would be about 0.43 inch. If each plate 13 were 34inches square, it would need to be only 0.625 inch thick to be well within safe working ranges of stress due to the downward force of the tank and the combined bending and axial stress due to the displacement of the upper edge from the vertical.

In conclusion, it will be apparent that this invention comprehends broadly the provision of oriented, separate, unconnected, nominally vertical support plates for the bottom of a tank subject to wide temperature ranges and also to accommodate horizontal forces due to accelerations :ofits mass byv motion of its support, which may be a ship, the orientation being such that the plane of each support is normal or perpendicular to a radial line from the tank'center to a point on the tank rim. Such a structure is also of great utility where only expansion and contraction of the tank bottom, as for a tank supported on an earth foundation, is involved.

.Although several specific illustrations are given, both of flexible plates'secured at their top and bottom edges and those that 'are stiff and free to rock under load, it is obvious that numerous changes could be made'without departing from the essential features of the invention, and all those modifications that come within the scope of the appended claims are intended to be embraced thereby.

I claim:

1. In combination with an insulated metal tank for transporting liquefied petroleum gas or the like by ship, wherein said .ttank .is subject to .transverse accelerations during operationofsaideship and whose bottom is subject to lateral expansion and (contraction due to temperature changes, said Ltank being positioned in a substantially flat-bottomed ship structure, an anchorage rigidly connecting the center 'of said tank to said ship structure, and a plurality of concentric circular rows of separate, unconnected, substantially plane vertical metal plates forming the support of said tank bottom, the center of said circular rows of plates being coincident with the center of said tank and said plates in each of said circular rows being uniformly spaced over the whole of said tank bottom, the plane of each of said separate metal plates being normal to a line extending radially from said center of said tank bottom toward the outer periphery thereof, and each of said plates being rectangular and secured throughout its upper and lower edges to said tank bottom and said ship structure, respectively, the intermediate portion of said plates being unrestrained to bend in the direction of said line, and equally distributing the transverse acceleration forces to all of the plates in each of said circular rows.

2. The combination of claim 1, with the addition of an insulating block secured between the upper end of each of said vertical metal plate supports and the bottom of said tank, each of said supports being transversely secured to said block to transmit forces in the plane of said plates.

3. The combination of claim 1, in which said central anchorage for the center of said tank is a substantially uninterrupted circular sheet metal skirt connecting said tank bottom to said ship structure.

References Cited in the file of this patent UNITED STATES PATENTS Henry July 28, 1959

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