US2532854A - Fluid storage tank - Google Patents

Description

Dec. 5, 1950 L M 2,532,854

FLUID STORAGE TANK Filed May 27, 1947 2 Sheets-Sheet 1 Fig. 6.

INVENTOR Fred L. Plummer BY WW ATTORNEY F. L. PLUMMER.

FLUID STORAGE TANK 2 Sheets-Sheet 2 Filed May 27, 1947 INVENTOR Fred L. Plummer BY WW ATTORNEY Patented Dec. 5, 19 50 FLUID STORAGE TANK Fred L. Hummer; Warren, Pa., assignor to Hal nmonfleirone Works, Warren; Pan la curpomatiom 'afwliennsylvania Application May'Zi', 1947,Seria1fNo; 75058279 'Ihisinventiomrelates to' closed storage-. tanks' for liquids and more particularly toroundsteel' tank constructions=of*=the-fiatbottomcylindrical shell-, and dome reef-type.

In such a tank-a horizontal flat bottom portion is connected as bywelding: to a vertical cylindrical'body-portion 'or" shell forming" therewith the peripheral bottom corner portion of-the* tank; whilethe top end'ofthe shell isconnected as by welding to an outwardly convex top or self -sustamed shallow dome port'ion forming with-the shell the peripheral top corner portion ofthe tank. i

If internal vapor pressure-as from volatile liquids develop ed 'in 'such" artank it may "subj eot certain portions thereof to unduly high or concentrated or unfavorable stresses which if unrestrained or not compensated for may produce structural deformatlons which may'lead'to failure of the tank or of parts thereof! Especially the peripheral top and bottom corner portionscf the tank'become vulnerablerenderingthe tank liable to' failure should internal super atmos pherimpressure prevail;

ofthe I tank structurer The general character of"? the fonces, stresses, strains; and potential deformationsvtoz which the I tank'i walls for 1- tank structure may be subjected" em" be understood from the fact that theinternal:v vapor: pressure tends -to deform thestraight i si'desot 'theetank towards assuming a: curved and nonestraight form; thereby subjecting especially the cornerportionsiof 'the tank:- to excessive, concentrated and. tun-favorablestresses andstrains through which-"undue deto'rmationuand failure may" ocour;

It is among the objects of this inventlolrtoprovide-simple and effective anti-deformation means for the tankanti more particularly for the corner portions thereof, so that a tank of the fiat ibot team; cylindrical shel1 and dome roof type may berenderedwafeeven though the operation of the tank involves internal super-atmospheric vapor pressure as a prevalent force:

The character endcorrectional nature ofthese stresses isomers-apparentandelearly understood, ifforexample, the top -portiorrot'the-tank: islooked upon as-"a dished or c iomed member that ma be subjeetew eitner to outwardly' directed radial fortiescreating tension stresses in the marginabtnnultrr portion on the member; or to inwardly-direeted rauiatrorees creatingicompression stresses in "the" marginal: annular portion of the member; I Aulsh'ed member 'thils sul'ajected' t'oftension'or compressiomin tue mareinal annular portion thereof may absorb tensicn stressesof a relatively high orderwithoutsufiering anyresult ant'ob'jectional deformation, yet-it may: "orumple, buckle and become' permanently deformed under relativelylight eontpresslom stresses; Therefore?- in the case of-euch members compreSSionstreSses are much more critical thamtension stresses'yanw toillustratethe present instah'ee the compressitn stressese -willherein -be 'term'ed the critical ones; while tension stresses will be referred' tonorr critical i Reverting to the tmk as such? it can be visu-f alized that the==peripherar top corner portion i is being subjected to non-criticai tension stresses when the press reinsiuetuetenk' is substantial-** 1y equal" tmtheter-the uter atniosphere; thestresses bein'g muined to be. caused by a roof" load such as may be due to the weight of't'he roof itself, asnow load; or' other "leads or equipment piaced upon the-root top portionorthe-tanIrQ such a load-upofi'the -roof tends to flatten the convex shape thereot; and tendstoforeethe pe ripheral portion er -the top; or rootoutwardly-"and torimposerediel"outwardlyuirected forces: 1

, the peripheral top comer portion oat-thetahltl Bye" eontrasw: whom? ihtemal upward vapor pressurefsubstantially exceeds 'the oppositely di j rected roof load, tension stresses are set-up in the top on rcofialong wlth the tendeney of-the t: dome tn bulfi upwardly end tit-accentuate the Upward internal vapor pressure in the tank also sets up deformational tendencies and strains in the lower peripheral corner portion at the bottom of the tank, especially when the liquid level in the tank is low. Such stresses are due to upward pull transmitted marginally from the.

bottom by providing efficient and simple. antideformation means in conjunction with antideformation means for the top corner portion.

I attain the foregoing objects by embodying in the top of r the tank a cup-shaped or cupped girder having an effective cross-sectional area that presents a relatively high moment of inertia to the compression or buckling forces; and by providing internal corner braces extending between the tank bottom and the shell, which afford efiicient force transmission between theshell area and the bottom area of the tank while neutralizingor side-tracking deformation-inducing forces from the peripheral corner portion, or preventing such forces or stresses from acting directly or unfavorably upon the corner portion.

The cupped girder according to this invention has embodied in the marginal annular portion and welded thereto a supplementary concentric steel ring or ring member of suitable steel profile spaced from the extreme edge of the tank top, that is from the peripheral juncture of the tank top with the shell. That is to say, the ring memher while unitary and concentric with the tank top is of a diameter significantly smaller than the peripheral or outer diameter of the top so that the ring member is spaced a significant distance from the periphery of the top. The cupped girder further comprises stiffening elements radially extending between the steel ring and the peripheral juncture of the tank top with the shell. 1 I

V In order to attain or stiffening interconnection between the respective horizontal and verticalareas of the bottom corner portion, there is provided a representative brace member comprising a foot portion having a radially extending vertical -rib or'flange the free edge of which is welded to the horizontal tank bottom, and a head portion having a vertically extending rib or flangethe free edge ofv which;

is welded to the vertical shell; I

v The invention possesses other objects and features of advantage, some of which with the foregoing will be set forth in the following description. In the following description and in the claims, parts will be identified byspecific names for convenience, but they are intended to be as generic in their application to similar parts as the art-will permit. In the accompanying drawings there has been illustrated the best embodiment of the invention known to me, but such embodi- The novel features considered characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as toits organizatign and its method of f general shape of a efiicient force transmission operation, together with additional objects and advantages thereof, will best be understood from the following description of a specific embodiment when read in connection with the accompanying drawings in which:

Fig. 1 is a diagrammatic part-sectional top view of the tank embodying top cornerand bottom corner anti-deformation means;

Fig. 2 is a vertical section of the tank taken upon the line 22 of Fig. 1;

Figs. 3 and 4 are diagrams illustrating tentative deformations of the tank due to exterior roof load and to internal super-atmospheric pressure respectively;

Fig. 5 is a detail perspective view of the bottom corner anti-deformation means enlarged relative to Figs. 1 and 2;

Fig. 6 is a further enlarged perspective detail View of'fa bottom corner brace member;

Fig. 7 is an enlargeddetail sectional View of the top corner portion of the tanktaken on line of Fig. 1; A

Fig. 8 is an external perspective view of the corner portion shown in Fig. 7; r

Fig. 9 is a sectional view of the top corner portion similar to Fig. 7 although modified with respect to the arrangement of the anti-deformation means;

Fig. 10 is an internal perspective view of the:

corner portion of Fig. 9; I

Fig. 11 is a sectionalview of a further modification of the anti-deformation means;

Fig. 12 is an internal perspective view of the corner portion of Fig. 11. 3

According to the semi-diagrammatic views of Figs. 1 and 2 the tank Trcompris es a horizontal fiat bottom Iii, a cylindrical vertical shell or body portion II of the diameter D rising from the bottom and'welded thereto, and a shallow outwardly convex top or dome portion 12 fixed to and connected with the top end of the shell by means of an annular connecting element l3 of obtuse angular cross-section and Welded to the shell and to the dome respectively. The peripheral bottom corner portion of the tank is provided with anti-deformation means as represented by radially and upwardly extending corner brace members l4 and 15, the members l4 being longerthan the members l5. A supplementary ring member It of angular cross-section is concentric with the shell I I although of a diameter d smaller than the diameter Dof the shell, and is welded to the top side of the domeand.

thus unitary therewith. i

The peripheral top corner portion of the tank thus comprises the annular connecting element I3, the supplementary ring element 56, and the marginal annular portion or peripheral. zone I! of the top or dome defined by the differential of the diameters D and d, that is Dd=2d1'.1 Fromi said tobe represented by the moment of inertia, of the cross-section of the component portions just enumerated.

Figs. Sand 4 illustrate in exag erated fashion.

potential deformations .(indicated in dot-anddash-lines) of the tank T2; when (a) an external vertical roof load prevails as indicated by arrows I8 in Fig. 3, and when (1)) internal super-at mospheric vapor pressure prevails as indicated by' arrows IS in Fig. 4. Y

.;n...F gw re: ba uett s. tentati e d The moment of inertia of ether. The roofis usually connected to the shell as by a continuous angle or angle profile shaped into a ring, the angle being of obtuse configuration. The tank bottom may rest directly on the ground or ona layer-of sand, gravel or crushed stone; A usual thickness found in the roof plates is about i to 4", bottom plates usually being. ,4 to thick, while the thickness of the shell plates depends upon the size of the tank and the weight of the stored fluid and ma vary from /4"' for .the top ring or course to l" or more for the bottom ring or course of welded plates;

. Let us assume. tank and the tank is filled with air or an airvapor mixture at cit-near outside atmospheric pressure. The weight of the roof plates and any.

such superimposed roof loads as snow or equipment create low compression stresses in the roof plates, let us say 300 pounds per square inch.

Because of such a load there is a tendency of the roof to flatten, andof the diameter of the roof to increase where it is connected to the top edge portion of the'shell. This tendency creates a relatively low tension stress in the peripheral top corner portion of the tank, that is in the connecting ring and the adjacent associated portions of the roof and of the shell which corner portion acts as a horizontal tension ring and counteracts or prevents the flattening of the roof. The weight of the roof, of the shell and of superimposed roof loads also creates relatively low compression stress, let' us say 300 pounds per square inch which act vertically in the cylindrical shell. These stresses together with the weight of the bottom'p lates are transmitted directly to that there be no liquid in the in the roof plates.

tendency of the roof to rise, while decreasing its the ground so that there are no significant.

stresses in the bottom plates.

Let us now assume the tank to be partially filled with liquidand to have the space above the liquid in the tank filled with air or an airvapor mixture-at or near the outside atmospheric pressure. The weight of the liquid imposes substantially no additional stress upon the bottom plates since thatweight is transmitted directly to the soil or foundation. However, additional stresses are those which are due to outward hydrostatic pressure. from the liquid tending to burst the vertical shell by creating therein horizontal or ring stresses. The thickness of the plates may 1 be determined so that a maximum stress does not exceed about 18,000 pounds per square inch.

A steel ring of thin plate can safely resist a uniform outwardly directed pressure creating a tension stress of thisintensity regardless of the diameter of the ring-,- since the internal pressure tends to hold the ring to a perfect circular form, or to change it to that form ifany small irregularities exist in its shape before the pressure is applied. Yet if the same ring is subjected to a uniform inwardly directed pressure creating a compression stress in the ring, even a ring of perfect circular form may buckle and fail at a relatively low stress intensity, while a ring having initial small irregularities will buckle and fail at even lower stress value. That is to say, theresistance of such a steel ring to buckling and failure depends upon (a) the diameter of the ring, (b) the area of .the cross-section of the ring, and (c) the lateral stiffness of the ring such as measured mathematically by the moment of inertia of the cross-sectional area of the ring (for a given area themoment of inertia increases as the depth of the cross-section in radial direction increases) V By comparison let us now consider stress conditions which develop in a tank of the above defined general type, when super-atmospheric gas pressure prevails in the tank:

7 Again we have a cylindrical, fiat bottom, dome roof type tank, however with a conservation vent set to operate at say 2.5 pounds per square inch (40 ounces per square inch pressure) and at 1 ounce per square inch vacuum. The problem of this invention is to utilize that general type of tank in spite of an internal vapor pressure which would normally endanger a tank of such a shape with the hazard of failure by crushing.

Let it be assumed that there is no liquid or very little liquid in the tank, the space within the tank being largely filled with an air-vapor.

sumed for this type of tank where internal vapor pressure approximately equals that of theouter atmosphere; However, upward pressure against the underside of the roof caused by the superatmospheric vapor pressure creates tension stresses, let us say 3,000 pounds per square inch, This is tantamount to a diameter at the periphery where it is connected to the shell. The tendency which under the assumed conditions is much greater than the opposite one resulting from the roof loads, creates compression stresses in the peripheral top corner portion of the tank and adjacent portions of the roof and shell plates. This top corner portion, therefore, is thus called upon to act as a horizontal ring under compression and to resist such against such happenings, this invention converts the peripheral top corner portion of the tankrinto a compressionor crush-resisting girder having sufficient radial width as well as adequate crosssectional area to afford sufficient moment of inertia to prevent the inward collapse of the top end-portion of the tank shell; Such a girder may ment such as exemplified above by the members l6, 2| and 22 respectively, the connecting ring or member exemplified above at 13, l3 'and [3 1 respectively, and adjacent portions of the dome and of the vertical tank shell respectively as far as they can be assumed to contribute to the crushresistance or moment of inertia of this girder,-

construction in the top corner portion of the, tank. a 1

Upward vapor pressure on the roof, in this instance well exceeding the weight of the roof and the'shell, also creates tension stresses of, say

upwardly and off the ground. This upward pull upon a shell according to this invention is to be neutralized by downward pressure upon the tank bottom, since the soil, in the absence of'special {anchoring means, cannot exert a downward pull upon the bottom along its periphery where the shell tends to pull it up.

In order to compensate for or neutralize this-v potential effect this invention provides radial; members upon and unitary with the bottom of:-

the tank to extend radially in that critical intermediate zone of the tank bottom where it is to be rendered resistant. These radial members are represented by the horizontal and radially extending foot portions 14 and 15 of the inclined brace members It and Hi, the length and spacing from one another of these horizontal radial members being such that the bottom plates are thereby given adequate strength and ability to transfer the .downward pressure from the shell to the bottom safely and without allowing critical deformations to occur. From the foot portions or base members extend the inclined brace members proper to transmit the downward forces acting upon the base members to a zone of the shell which is spaced an adequate distance upwardly from the bottom. The forces acting through the inclined brace members are thus well distributed to a cylindrical zone of the shell the height of which zone is defined by the height of the head portions N and 15 of the brace members I l and I5 respectively. Thus it will be visualized that the inclined brace members transfer the critical forces from an annular horizontal zone Z1 of the bottom area 20 to a vertical cylindrical zone Z2 of the shell area l9, these zones being defined by the length of the foot portions and the head portions respectively of the brace members.

By combining the cupped girder in the top and the bracing connections between zones Z1 and Z2 at the bottom portion of the tank one may utilize an otherwise standard tank safely under internal super-atmospheric pressure conditions Where this general type of tank would otherwise be unsafe or be liable to failure.

I claim: 7

1. In a closed liquid storage tank adapted to be subjected to internal super-atmospheric pressure, a top portion comprising a cylindrical shell portion, a convexly shaped sheet metal top fixed peripherally to the shell portion, reinforcing means for said top comprising a ring member of structural profile unitary and concentric with the top and of a diameter significantl smaller than the peripheral diameter of the top so that said ring is spaced at significant distance from the periphery of the top, said ring member in cross-section comprising .a vertically extending portion welded edgewise to said top and a free horizontal portion extending from said vertical portion at the end thereof which is pointing away from said top, said ring member being disposed at the underside of the top, with the addition of radial vertically curved reinforcing members of I-shaped profile extending between the ring and the shell.

2. In a closed liquid storage tank adapted to be subjected to internal super-atmospheric pressure, a top portion comprising a cylindrical shell portion, a c'onvexly shaped sheet metal top fixed peripherally to the shell portion, reinforcing means for said top comprising a ring member of structural profile unitary and concentric with the top and of a diameter significantly smaller than the peripheral diameter of the top so that said ring is spaced a significant distance from the periphery of the top, said ring member in crosssection comprising a vertically extending portion welded edgewise to said top and a free horizontal portion extending from said vertical portion at the end thereof which is pointing away from said top, said ring member having the profile of a structural channel disposed at the underside of the top and having inwardly directed free flanges, with the addition of radial vertically curved reinforcing members extending between the ring and the shell.

FRED L. PLUMMER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 720,924 Intze Feb. 17, 1903 1,513,605 Kramer Oct. 28, 1924 1,846,294 Wiggins Feb. 23, 1932 2,009,606 Diffenderfer July 30, 1935 2,201,652 Joor May 21, 1940 2,237,308 Larson l Apr. 8, 1941 2,333,792 Jackson M Nov. 9, 1943 2,395,685 Schmitz Feb. 26, 1946

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