US2982441A - Liquid-storage tank - Google Patents

Description

May 2, 1961 J. H. FARRELI. ETAL 2,982,441

LIQUID-STORAGE TANK Filed Jan. 16, 1957 4 Sheets-Sheet 1 b Jr. Georg/CY@ ORS May 2, 1961 J. H. FARRELL ETAL v 2,982,441

LIQUID-STORAGE TANK Filed Jan. 16, 1957 4 Sheets-Sheet 3 hnzes frr'fll BY l .4

May 2, 1961 Filed Jan. 16, 1957 J. H. FARRELL ETAL LIQUID-STORAGE TANK 4 Sheets-Sheet 4 FI@ 6 ze INVENTORY United States Patent LIQUID-STORAGE TANK James H. Farrell, Cambridge, James Peter Hunsaker, Milton, and George Y. Robinson, Jr., West Acton, Mass., assignors, by mesnc assignments, to Couch International Methane Limited, Nassau, Bahamas, a corporation of the Bahamas l Filed Jan. r6, 1957, ser. No. 634,547

s claims. (c1. zzo-11) This invention relates to the transportation of liquids in large volume and at low temperature. lt relates more particularly to the structure of suitable tanks or containers for use as independent cargo kvessels to be carried in transportation by means such as a ship or the like.

Containers or tanks of the type embodying the features of this invention are adapted for use in applications such as described in the copending application Ser. No. 582,965, tiled May 7, 1956, wherein a cluster of such tanks or containers, as illustrated in Figure 1r of the drawing, `are arranged in closely spaced apart relation within the hold of a ship or the like conveying means for transportation from place to place. Unlike land storage or transportation, the pitch and roll of a ship causes such shifting movement of the effective load of cargo carried within the tanks that pro-blems peculiar to on-ship transportation develop. In general, it can be assumedthat the shifting of load responsive to the pitch or rollof a ship becomes somewhatuniformly distributed about the walls of the tank when the latter is formed of cylindrical sha-pe. However, the volume of liquid capable of being carried within a limited Vspace is an important factor in the commercial practice o-f the entire program and, for such purpose, cylindrical tanks have been found lto be impractical because of the large waste in space between the tanks. l Y

Maximum utilization of availablespace can be effected more by theuse of independent cargo'containers of polygonalshape, as represented by tanks of square, rectangular, or trapezoidal design, asillustrated in the drawings, the selectionY of shape depending upon the dimensional characteristics of the space between the walls Yand the bulkheads of the ship The diculty which arises in the use of such tanks of polygonal or prismatic shape for the storage and transportation rof large volumes of liquidv resides in the means for providingsufticient structural strength for serviceas independent cargo containers; that is, the ability to hold the liquid within the tank without depending uponvthe, structure of the-ship itself for aid in support of the tank.v` Y The :situation undersuch circumstancesis lfurtherlaggravatedb'y (l) the roll ,and pitch of the ship which creates unbalanced pressure in one or the other ,v of the Walls, of the tank, and (2) the thermal gradient which existsthroughout the length of the tank, especiallyV whenV from the topjof `the tank .to the liquid level -whichmay amount to asmuch as 260 F. whenas in 4the preferred practice, `the .content material in thetank constitutes Vlicpgeiied natural gas formed principally of vmethane Vboil- Aingaat abgut i258 F., at atmospheric ,pressure t' When used to transport large'gvolurnes ,oftaliqueted natural vidnalyvalls ofthe tankwhile at the `same/time perrnl 2,982,441 gatented May 2, 1961 to contain the liquid at pressures deviating widely from atmospheric 'pressure because the forces existing on the walls of the tank would be tremendous and incapable of being retained in a tank capable of economical or practical construction.

It has been common practice in polygonal tanks formed of flat plates to augment the structural strength of the tank by Vertical stifening beams or by a combination of vertical and horizontal beams but such arrange ment has been found to be unacceptable for use in independent cargo containers designed to handle large 'volumes of liquid at very lowtemperature. This is due to the fact that the vertical beams notv only become highly stressed in themselves but they also introduce additional stresses due to the thermal gradient in the tank in that they `do not permit the -bottom of the tank Vfreely to contractl or exp-and relative to the top of the `tank without introducing bending moments in the vertical beams.

vIt is an object of this inventionto provide tank structures of large capacity which are capable of serving as independent cargo containers mounted within a means of transportation such yas a ship and which are strong enough to stand unbalanced pressures on the walls such as are brought about by movement in one or more planes of the transportation means. i

Another object is to provide a tank structure of the type 'described which'is capable of serving as an independentcargo container and which is capable of withstanding the stresses induced in the side walls of the tank by reason of thermal gradients existing in the tank, particularly when the tankis partially filled with a cold liquid. 1

These and other objects and ladvantage-s of this invention will Yhereinafter appear and for purposes o-f illustration, but not of lim-itation, an embodiment of the invention is shown in the yaccompanying drawing, in Whichy y Figure 1 is a perspective elevational View lof `a group of tanks embodying the features of this invention with portions broken away to show the interior construction thereof; Y y

Figure 2 isa plan view of the bottomwall of a tank shown in Figure l; Y 1 y Figure 3 is a sectional View taken along the lines-"3f of Figure l;

Figure 4 is a sectional view taken along the line 4-,4V of Figure 1; f Figure 5 is a sectional view taken along the line Ses of Figurel';` l y. l n e i .l

,Figure 6'S aOP Plan View of the top wall of the tankshown in VFigure Vl with Iportions broken away totshow l the inner l:structure thereof;y Y 1 Figui-e7l is a'sectional view taken along the line 7.-'1 of Fgure', and Y Y A' Figure 8 is a sectional view taken along the line 8f8 i A 0f Figure 7,.v v Y f It has been found in accordance with the Vpracticefof this invention that the desired performance characteristics 1 1n a polygonal tankjof the type described for `containing l, large AVolumes of liquid at a low temperature canbe-` 'y achieved by the combination `which includesfa plurality ofV vertically spaced apart, horizontally arranged,frein#-`r 1 forcing and stitfening members which extend allabout interior Wall of the tank 4and which' are secured thereto for, purposes of Vstiifening andreinforcing the walls'fof the tank to resist deformation under load and to transrnlt stresses operative on one .wallj'to'othersadjacentt. theretofor distribution olflload or stresses which might'r suddenlybe brought about against" one'wallnof'the tank responsive to the pitch or roll of the ship. Such/internal; horizontal4 arranged ,bracing members stilfenifthe vertical temperature gradients to exist in the tank without inducing additional stresses characteristic of the previous use of vertical reinforcing members.-

It has been found further that the desired performance characteristic in a polygonal tank of the type described for the transportation of large volumes of a cold liquid can be further improved by the use of a plurality of vertically spaced apart horizontally arranged reinforcing and stiffening members of the type described in combination with a plurality of horizontally disposed cross tie members extending angularly between the adjacent sections of the horizontally arranged stiffening and reinforcing members and spaced inwardly from the corner therebetween to interconnect the sections with stiff arms which operate in tension to resist deformation of the walls of the tank and to distribute stresses and load from one wall to the others adjacent thereto in a manner to relieve the walls of the full force of existing pressures.

It has been found that the performance characteristics of the independent cargo container can be still further improved by the inclusion with the combination described of horizontally arranged cross brace members extending crosswise between the mid-sections of the opposite walls of the tank to restrict the spaced relation between the walls and to provide pivot points about which wall deections can take place to provide a combination of forces in effecting distribution of load and resistance to deformation. p

Referring now to the drawings for a fuller description of the invention, a tank embodying the features of this invention is schematically illustrated as indicated by the numeral 10. The tank structure, whichY may be of various dimensions and shape, is formed with upright side walls 12 and 14, front and back walls 16 and 18, a bottom wall 20 and a top wall or cover 22. The elements are preferably formed of metal or alloy of high structural strength such as aluminum and alloys of aluminum, capable of use under the temperature conditions which may range to below 300 F.

In the assembled relation, the tanks are confined by insulation and the like which separate the tanks from the walls of the ship and minimize the transfer of heat to the liquid contained in the tank.

A plurality of horizontally arranged, reinforcing and stiffening members 30 are secured, as by welding, in vertically spaced apart relation to the inner faces of the vertically disposed tank walls. The reinforcing of stiffening members 30, formed of rigid materials having high structural strength and preferably of metal plates, angle irons, l-beams, H-beams or the like, extend continuously about the interior surface of the tank to reinforce and stilfen the ywalls at vertically spaced apart portions. They operate to tie in the walls onewith another in a manner to resist deformation under load and to distribute load substantially uniformly to all of the adjacent vertical walls of the tank. Because of the horizontal relationship of the reinforcing and stiifening members 30, as distinguished fromthe vertical arrangement of beams as heretofore employed, temperature gradients through the length of the tank will have little, if any effect on the existing stress relationships 4which would otherwise become developed in the tank. As a result, the tank having its vertical walls reinforced with the horizontally arranged reinforcing and stiffening members will be free to expand 'or contract without the introduction of stresses by vertical supporting or reinforcing means. Y

A further concept of this invention resides in the moditication which makes use of cross ties 32, as illustrated in Figure 5 of the drawings. The cross ties extend angularly to interconnect the reinforcing and stiffening members 30 at the same level vbetween'the adjacent walls of the tank. These Vcross ties, which span the area between the adjacent sections of the reinforcing and stiffening members, comprise 'elongate metal or other sth strucim'ally strong members which are preferably spaced one 75 from the other inwardly from the corner defined by the adjacent walls. When more than one cross tie member is provided in each corner section, it is desirable to provide for a uniform spaced relation between the members and it is preferred to limit the distance from the corner so as not to bring the ends of the cross tie members beyond the centers of the adjacent walls thereby to avoid crossing over and interference with the cross tie members extending crosswise from other corners of the tank. Thus, in a rectangularly shaped tank, as illustrated in Figure 5, a section at the center of the tank wall of larger dimension will remain free of cross ties, as illustrated in Figure 5 of the drawings.

In addition to the horizontally arranged bracing and reinforcing members 30 and in addition to the cross ties 32 marked improvement in the characteristics of the tank will be secured by the use of cross brace members 34 and 36 which extend across the tank between opposite walls to tie in the walls in a manner to maintain a predetermined spaced relationship therebetween.

The cross ties take the balanced and unbalanced loads in the tank resulting from the ships motion and, combined with the horizontal bracing and reinforcing members about the walls of the tank, give the tank the necessary structural strength to withstand shifting movements of the liquid in the tank due to the pitching and rolling of the ship. It will be apparent from the description that by the combination of the horizontal bracing members, cross tie members and cross bracing members, the tank is suitably constructed to provide, if necessary, for large unbalanced pressures against any wall of the tank while at the same time remaining substantially unaffected by the thermal gradients which might exist in the vertical plane of the tank. This is because the various horizontally arranged bracing and reinforcing members will, in general, be at the same level and therefore approximately at the same temperature.

From the theoretical standpoint, a new and novel combination of force members is provided for minimizing the effect of unusual stresses placed against any one or more walls ofthe tank. When load suicient to cause deformation occurs, the force relationships developed through the described members are believed effective to place the adjacent cross ties under tension as the walls adjacent to the deformed wall are caused to utter about the pivot at the center which is held against deflection by the cross brace members 34 and 36. The combination of forces inthe cross tie members coupled with the stiffening and reinforcement available from the plurality of horizontally arranged stiiening and reinforcing members is effective to stabilize the tank under extreme load conditions thereby to make available a tank structure with maxamum capacity and maximum strength coupled with minimum cost and materials.

Where the spaced relation between the endsof the inner most cross brace members is greater than the spaced -'relation between the ends of adjacent cross brace members in any one wall, as in the walls 12 and 14 of larger dimension in the illustrated tank, it is desirable to make use of a number of cross brace members at the center spaced apart from each other and from the ends of the cross ties 32 by an amount corresponding to the spaced relationship between the ends of the cross ties to continue the'desired reinforcement throughout the wall of the tank for distribution of load, otherwise the central portion might become' unbalanced in load with respect to the adjacent end portions. Instead of making use of a plurality of cross brace members 36a and 36h, the end of the cross brace member 36 may be provided with legs 38 and- 40 that extend` angularly` outwardly to engage the wall 12, or corresponding portions of the attachedstilfening andreinforcing plate 30, at the desired spaced apart points, as illustrated in Figure 5. i i

While the foregoing defines the important'concepts embodied in the tank structure for strength and stability under load, the following will describe theother elements illustrated in the tank of the drawings. The top wall 22 is provided with stitfening 'and'reinforcing members on its underside by means of beams 4-2 which 'extendlengthwise of the tank in laterally spaced apart relation and a plurality of smaller ybeams 44 which extend crosswise rof the tank in longitudinally space apart relation. The'top wall 22 of the tank is provided with' an opening 46 fitted with a cover 48 having a plurality of openings extending therethrough for the insertion of the various pipings used `to introduce the liquid and to Aremove the liquid from the tank and to maintain various controls with respect to the pressure conditions existing within the tank. The numeral 50 indicates vertical members which, if desired, may be incorporated to tie in the top wall with the bottom wall of the tank.

The horizontal bracing members, the cross tie members and the cross brace members may be designed by conventional methods of stress analysis so that they will be of adequate strength and thickness to support such transmitted loads. It has been found that an aluminum alloy (particularly an aluminum-magnesium-chromiummanganese alloy) is well suited for the plates and the horizontal bracing members employed in the practice of this invention. This is because an aluminum-magnesium alloy gains strength and ductility at low temperatures and is not subject to brittle fracture. Such other materials as nickel-bearing steels would also be suitable; however, the aluminum-magnesium alloys appear to be the more economical for use. It will be understood that other metals of high structural strength capable of maintaining strength under the temperature conditions existing might also be used for the tank walls and for the various reinforcing and strengthening elements described.

The spacing of the horizontal bracing members may be determined by anyone skilled in the art by making a detailed stress analysis and by considering the fact that the spacing is dependent somewhat on the wall thickness. That is, the thicker the vertical walls of the tank, the farther apart the horizontal bracing members may be placed. As an example, in a tank 30 x 30' x 50 high, having a wall thickness of about 1/z", it has been found desirable to space the horizontal bracing members 30 about inches apart. ln this example, the horizontal bracing members were 5 x 3" x 3% angles. Y

The structural arrangement of the tank embodying the features of this invention will enable the entire tank to behave as a stiff box sections that is fully capable of supporting the imposed loads with a minimum amount of material. The tank will be capable of withstanding large unbalanced pressures caused by the shifting of liquid within the tank while, at the same time, showing no effect of any stresses in the vertical walls of the tank which might be induced by a vertical thermal gradient throughout the tank.

It will be understood that changes may be made in the details of construction, arrangement and shape of the tankand the elements embodied therein without departing from the spirit of the invention, especially as dened in the following claims.

We claim:

1. A liqueed gas storage apparatus comprising a tank in which liquefied gas is stored in direct contact with the surfacesV thereof at a temperature considerably below ambient temperature whereby the walls of the tank arev tinuously thereabout'. and arranged in` vertically spaced Y surfaces of the wallsthroughout their lengths to provide f vertically spaced apart, horizontally arranged sections reinforcing and stiffening the vertically disposed walls of Y the tank, cross tie members at each levelof the `stiffening and reinforcing members extendingjcrosswise between adjacent vertically disposed'wallsofV the tank with the ends of the cross tie members secured in relatively uniformly spaced apart relation tojthe stiifeningand reinforcing members for a distance short of the centers thereof, and cross brace members extending crosswise between opposite of the vertically disposed walls of the tank and connected at their ends to the reinforcing and stiifening members in spaced apart relation from each other corresponding to the spaced relationbetween the ends of the cross tie members.

2. A liquelied gas storage apparatus of large capacity comprising a tank in which liquefied gas is stored in direct contact with the surfaces thereof at a temperature ditering widely from the ambient temperature whereby the walls of the tank are subject to dimensional change responsive to expansions and contractions due to temperature change, comprising a completely enclosed tank of polygonal shape in horizontal cross-section and formed with vertically disposed walls of a high strength, fluid impervious material which does not lose its strength at the temperature of the liquid and reinforcing and stiffening means for the vertically disposed walls of the tank consisting essentially of horizontally disposed stiffening and reinforcing members joined to the inner surfaces of the vertically disposed walls of the tank to extend subdisposed elongate cross tie member interconnect'ng the vertically disposed Walls of the tank and extending angularly between and secured to the adjacent sections of the attached horizontally arranged and vertically spaced j apart reinforcing and stiffening members.V

3. A liquid storage tank as claimed in claim 2 in which the tank walls areformed of a metal having a relatively v.

high coeicient of expansion and contraction and wherein the stitfening and reinforcing members are fixed to the inner face of the vertically disposed Vwalls of the tank..

4. A'tank as claimed in claim 2 in which, when more than one cross tie member is provided between adjacent sections of the attached horizontally arranged'and vertically spaced apart reinforcing and stiffening members, the cross tie members are spaced one from the other inwardly from the corner for a distance less than that which positions the ends of the cross tie members'beyond the j centers ofthe adjacent wall sections.

subject tol dimensional lchange in response to. expansions and contractions due to wide temperature changes, comprising a completely enclosed tank of polygonal shape in horizontal cross-section having walls of a high strength, uid impervious material which does notlose its strength at the temperature of the liquid and-reinforcing means for the vertically disposed walls ofthe tank consisting essentially of horizontally disposedv stilening and rein' forcing members joined to inner surfaces of the vertically Y disposed walls of the tank to extend substantially lcon- 5.7A liqueed gas storage apparatus of large capacity comprising a tankfin which liquefied gas is, storedin di-k rect contact with the surfacesy thereofat a temperature differing widely from the ambient temperature whereby the Walls of the tank are subject to dimensional Vchange responsive to expansions and contractions "due to temperature change, comprising a completely enclosed ltank of polygonal shape in horizontal cross-section and formed with vertically disposed walls of a high strength, fluid impervious material vwhich does not lose its strength at the vertically disposed walls of the` tankl toextend substantially continuously vthereabout and arranged in vertically spacedapart-relation substantially throughoutjthe 8 References Cited in the file of this patent vUNITED STATES PATENTS GrammA July 1, 1930 Hathorn Apr. 26, 1938 Plummer Dec. 5, 1950 Jackson Aug. 7, 1951 Bruderer Feb.,28, 1956 FOREIGN PATENTS Great Britain Mar. 8, 1945 Australia Sept. 24, 1954

Images