US2947439A

US2947439A - Flat bottom pressure container

Info

Publication number: US2947439A
Application number: US702711A
Authority: US
Inventors: Raymund V Mcgrath
Original assignee: Chicago Bridge and Iron Co
Current assignee: Chicago Bridge and Iron Co
Priority date: 1957-12-13
Filing date: 1957-12-13
Publication date: 1960-08-02
Anticipated expiration: 1977-08-02

Description

Aug. 2, 1960 R. v. MGGRATH FLAT BOTTOM PRESSURE CONTAINER Original Filed May 22. 1953 2 Sheets-Sheet 1 Aug. 2, 1960 R. v. MGGRATH FLAT BoTToM PRESSURE CONTAINER Original Filed May 22, 1953.

2 Sheets-Sheet 2 United Stnits actuan FLAT-horror@ contraint R Raymond V. McGrath, Merrionctte Bark. Ill assiguor to Chicago Bridge tir Iron lttonnranp a corporation of nugois Continuation of application Ser. No. 356,723, May 22, 1953. This applic'onec. 13, 1957, Ser. No. 702,711

1 Claim. (ci. zzo-.13)

Thisinvontien relates to a pressure vessel... rnore particularly a vessel intended tor the .storage of large volurnes of volatile liquids and. .their vaporsy This applicationof rnv prior application Serial Nossofp/ZS nledMay 22. .1953., entitled Flat Bottorn Pressure Container, handoned- 'lhe pressure cont ers or tanks referred to herein are generally huilt off; lates including the bottoni, the

side Wall. usually a-eylindrical Wall. and the top so arranged as to withstand a. gas pressure in. the range between 1./1 ps-i.. to as much. as 1.5 pts-i.. which is the lower limit of; the A.S.M.E .code tor pressure vessels- The containers are `irsttendetl to hold large volumes of the order of. 30,000., 40,990 and 80,00() barrels or more. Such conttainers are etten used to store gasoline.

E conorny in construction of such large tanks dictates that the bottoni plate should. if possible. be built on llat grade. lt `should he understood that ordinarily these tanks are .con tructed in the open. on a prepared grade consisting `oli. afsand cushionln the pastz pressure tanks have been constructed which een withstand high Apressures but ordinarily these tanks have bottoms which are cusped and given an upwardly concave curvature so `that the bottom plates. may he placed in tension when the node circles are tied `to the top `of thovtank to withstand the gas pressures intended during. storage- The building of tanks .having 4such dished Vuuthorf `than dat bottom plates entails thePreParation of. amore errpensive foundation as well as .additional cost of fabrication and erection Instead of spreading a sand cushion on dat. ground as is possible with fiat bottoni tanks., the foundation has to he accurately scooped. outto the bottoni plate curvature- The dished plates have Yto' he. eatetully eornputed .and fabricated, Which radds substantially to the expense of the tanks.

Attempts have been `made in the Passt, to oonstr-llt tanks with substantially 4hat .bottoms to withstand relatively low .gas .pressures on he order ot V.to n-.siby tying the sides or the periphery of. the. side vtall to an anchoa In this vvay, all. ofthe gas nressureagainst the top of the tank tending to ,lift the side wall frein the grade has been transferred to the side wall and carried in tension to ananchorug .wall orother heavy objects at the periphery of, the tank, AA further attempt to cope with the .problem .has4 been by use of `a tank havingl an annular peripheral trough to contain liquid.. the weight of which resists the tendency .of the; gas pressure within the tank to lift .the side wall' ol `the `grade. Such `vessels are fully operative at storage gas pressures so. long as `liquid is maintained .the .trough 1ct the `prescribed level.

Afterthe liquid drained therefrom, there must be a venting of the tank to atmospherein order to .reduce the gas pressure .for unless `such venting takes. l Place the pressure within the tank would exceed `the Weight of `.the liquid remaining .thus lift. the side-wall :and part @of the hottdnt olf o i-tthetgratlecondition .is undesiraintended stresses and result in failure.

ble in. that it nray the bottom plates .beyond their s ice .Larson Patent 2 297t002 illustrates a Pressure. container capable of withstanding a maximum gas pressure of about 21/2 p.s.i. and` ordinarily intended for gas pressures iu the range of 1A psi. to 11/2 p.`s.i. This vessel utilizes a weighted trough at the tank periphery filled with liquid to withstand the uplift of the side wall o'f the tank. When the liquid in the trough is at a sulcient depth the Working gas pressure within the Vessel can'be at its maxmum'of approproximately 11/2 p.s.i but when the liquid is drained from the tank there must be a venting of the gas space therein to lower the gas pressure to Within the accepted standards of design and which will at lower capacities of the vessel be as low as 1A p.s.i.

The prosnt invention diisers from that shown by the cited patent, in that the gas pressure capable of being contained is not dependenty on the Volume of liquid Within the vessel since the vessel as designed can withstand the desired rnarrirnurn gas pressure through the range of liquid level Afrom full t empty. In other Words, the full operating gas pressure ofthe container may be utilized regardless of the amount of liquid Within the container. In carrying out the principles of the invention, a tank haviugV a dat bottom made of fiat plates laid directly on a Hat grade may be utilized thuslcutting down the expense of a molded foundation and also the expense .barrel hat bottoni tank costs approximately $494200. as

compared to $128,500 for a 5 p,s.i. noded s pheroid of 55.000 barrels capacity. Obviously, if a hat bottom tank could withstand 5 p si. pressure, the cost would be much lessthan the cost of the conventional spheroid. B y providing the tension rods and the ring wall or walls located inside `and spaced from the peripheral ring wall, this invention permits the use of the more econorncpl flat bottom at pressures heretofore impracticable. In addition,

A fr rrther savings can be achievedrhy using acylindrical sidewall as shown in Fig.- l in place of the `conve.ntional spheroidal side wall construction.

When Hat bottom plates are used design costs are lower and there is less waste metal, less plate edge prepara-tion and trimming, less fabrication, lower freight rates, lower cost for grade prparation and lower cost for assembly ond eld welding than is the case when dished plates are required. In fact, in some cases the flat detail permits the complete avoidance of shop fabrication, and pluies can be shipped directly to the `jobsite from the mill. `Single` curved plates, such as cylindrical plates, are likewise cheaper to prepare and erect than are double curved platos such as dished or spheroidal plates. Because of those economies the cost of a pressure tank of 55,000 barrels capacity made `in accordance with. the teachings herein disclosed, exclusivo of foundation costs, would'slge from $20,000 to $30,000 `less than `a conventional spheroidal tank of the same pressure and capacity. While `the foundation costs vary with the circumstances and are higher for the ringwalls, the dilference in foundation ycosts normally would not c xoeed $10,000 to $20,000. These economies bedtime more pronounced as capacities are. i..nercas.ed.

Other important practical advantages of this invention are the .reduced cost of maintenance of the tanks because the `.bottoms can he cleaned .tnueh more sirnply than where bottoms are cusped, the simplification of gauging structed of reinforced concrete.

procedures, and the reduction of ground water problems when a flat bottom is used.

In general, the container of the present invention utilizes a first anchoring ring Wall around the periphery of the bottom to which the side wall is tied lin an appropriate manner so that uplift of the side wall is transferred to the anchoring wall. In addition to the peripheral wall which has been known in such early structures as that of the Larson patent cited above, there i-s provided a means of tying the internal parts of the top of the vessel to one or more anchoring walls located appreciably within the confines of the bottom as will be understood from the following description. The inner anchoring walls used in tying the top of the container are spaced under the flat bottom and grade and appreciably within the outer or peripheral anchor wall (such as a distance of at least ten feet) and resist the uplift on the top of the vessel caused by internal product pressure, not only by the weight of the wall itself, but also by the earth above and about the wall and also by the downward force of the internal pressure over the anchoring wall.

Specific embodiments of the present invention are illustrated in the accompanying drawings in which:

Figure 1 is a vertical sectional view through the center of a container having the invention therein;

Figure 2 is a horizontal sectional view through the container of Figure 1 taken substantially along line 2-2 in Figure 1;

Figure 3 is a fragmentary enlarged view showing the connection of the tie members to the top of the container;

Figure 4 is a fragmentary broken view partly in section showing the details at the bottom of the tank;

Figure 5 is a vertical sectional View taken substantially through the center of another form of container having the invention therein;

Figure 6 is a horizontal sectional view through the container shown in Figure 5 and taken substantially along line 6--6 in Figure 5; and,

Figure 7 is a fragmentary sectional view through an alternative form of anchoring wall.

The vessel illustrated in Figures 1 and 2 includes a flat bottom 10 formed of at plates which usually are lapped at the seams and welded with a single pass on the inside. This bottom is placed on a level grade and preferably upon a'sand cushion. The side wall 11 is cylindrical in form and extends upwardly from the periphery of the bottom 10 to which it is joined as by welding and is generally set in from the edge of the plates at a distance as illustrated in Figure 4. The top 12 of the vessel includes curved plates which are noded. In effect, the top has a peripheral curved portion 13 and an inner curved portion 14 which join at the node circle 15. The

. plates 16 of the outer portion 13 extend toward the node circle in a horizontal direction so that gas pressure acting upon the top outside of the node circle 15 produces stresses some of which are transmitted by the plates to v the side wall 11.

The cylindrical side wall 11 is anchored to a ring wall 17 beneath the side wall and extending about the periphery of the tank. This ring Wall has a foot portion 18 and an upwardly extending neck portion 19 both con- Obviously, steel could be substituted for the neck portion 19 and also for the foot portion 18.

secured thereto to effect the tying of the side 'wall to the y' rin-g Wall 17. Any upward gas pressure on the outer curvedtop portion 13 is thus transmitted to the anchoring ring wall 17.

In order to effectively resist the internal gas pressure to which the container is subjected, the inner portion 14 of the top 12 is also tied to an anchoring wall. In the Brackets 20 are welded to the side wall 11 in a manner permitting a. tie rod 21 to be which tension members 23 may be Welded. These tension members extend downwardly inside the container and through the bottom 10 into an inner ring wall 24. Ring wall 24 lies appreciably Within the ring wall 17 and preferably has a diameter equal to or less than the diameter of the node circle 15V and the gird'er 22. This ring wall is usually similar to the ring wall 17 at the periphery of the vessel. The stresses produced by gas pressure acting upwardly on the central portion 14 of the top are thus transmitted through the tension members 23 to the inner ring wall 24. This wall is also provided with a foot portion 25 and an upwardly extending neck portion 26. `It will be noticed that these ring walls in cross section appear to have the shape of an inverted T.

The particular construction of this container permits the storage at full operating gas pressure of volatile liquids whether the tank contains a considerable depth of liquid or very little liquid. Each of the ring walls has a considerable weight which weight resists the tendency ofthe gas pressure within the container to lift the same off of the grade. In addition to this weight, the uplift is resisted by the weight of earth above the foot portions of the ring wall and some internal gas pressure acting downwardly on the bottom. It is ordinarily considered that the bottom plates have zero stress; that is, these plates are not in tension or compression in the direction of their greatest dimensions. The weight of liquid within the tank acting downwardly and in the direction of the thickness of the plates produces some compression which is negligible compared to the allowable stresses in the plates. For this reason, the tie members 23 extend through the bottom plates without stressing the same. In Figure 4, it will be noticed that the tie member 23 is attached to a T section 27 which is, in turn, attached to a tension bar 2S extending into the concrete ring wall. The T section 27 could be eliminated if desired.

In operation, the tendency of gas pressure to raise the top of the vessel also tends to lift the anchoring walls. 'Ihis tendency to lift involves not only the wall but the earth above it. The earth affected is that not only vertically above thevbase or foot of the wall but includes a much Vlarger area which might be separated from the unaffected earth by

imaginary lines

29 and 30 `of demarcation extending upwardlly and outwardly from the edges of the foot portion of the wall. The downward gas pressure within the container also acts over this enlarged area and at least some of that pressure will be transmitted to the ring wall thus opposing the upward gas pressure in the horizontal projection of that same area.

If the ring walls are of the same vertical'cross section, it is desirable to locate them relative to each other so that the allowable upward internal gas pressure or tendency to lift per foot of circumference is approximately equal on both walls. When this is done, the identical depths of excavation and the cross sections of the ring walls permits the use of one form for both walls and thereby greatly reduces the cost of their installation. Since the top portion 16 outside the node circle 15 is horizontal, only the gas pressure on the inner curved portion 14 of the top will produce tension in the tie rods 23.

While the roof of the tank shown is curved so that the plates may be placed in tension by internal gas pressure and thus transmit that pressure to the side wallsy and tension members, it should be understood that flat roofs properly braced by rafters or other stiffening beams could be substituted for the curved plate tops illustrated and described in detail. v g

In Figures 5 and 6, another container of slightly different form is illustrated. The operation of this container is the same as that illustrated in Figures 1 to 4, and the Y difference exists in the shape of the side walls of the conp 1. The side walls which are circular in plan have a curved section 41 joined directly with the top section 42.

This provides a container having the appearance of a spheroid. The overhanging portion of the periphery of the vessel may be internally trussed to support different levels of liquid if necessary.

The roof or top of the vessel shown is provided with a central section 44 and an intermediate section 43. A node circle 45 is provided between

sections

42 and 43. Another node circle 46 is provided between

sections

43 and 44. In each instance the high portion of that section of the roof or top coming into the node circle from the outside is substantially horizontal so that only gas pressure acting on the section inside the node circle produces tension in the tie rods connected to that node circle.

In accordance with the above, gas pressure on the top section 42 is transmitted through the side walls to the outer peripheral ring wall 47. Gas pressure on the annular section of the top designated 43 will be transmitted through tie rods 48 to a smaller ring wall 49 below the bottom 40 and preferably of no greater diameter than the outer diameter of section 43 whereby the ring wall 49 will be spaced well within the outer ring wall 47. These tie rods 48 are similarly connected to an annular gir-der 50 as illustrated in Figures 1 and 3. The inner tie rods 51 are connected to a girder 52 at the top and at the node circle 46 at the outer periphery of the top section 44 and to an annular ring wall 53 underlying the bottom of the tank beneath grade. Ring wall 53 is preferably of no greater diameter than node circle 46 and girder 52 so that the ring wall 53 lies appreciably within ring wall 49.

The ring walls may, as previously stated, be located so that the uplifts per foot of circumference are substantially equal. While the tie members illustrated in both Figures 1 and 5 are shown as extending downwardly at an inward slope i.e. the ring walls are of lesser diameter than the corresponding node circle girders, it should be understood that these ties can be arranged vertically if desired, i.e. the ring walls can be of equal diameter to the corresponding node circles or girders.

The ring walls illustrated in Figures 1 and 5 may be replaced by an equivalent buried slab as illustrated in Figure 7. In Figure 7, a bottom 60 is shown above a buried slab 61 of concrete and a tie member 62 extends to and through the bottom by means of a vertical extension connecting tie 63 into the slab 61. If desired, the horizontal extent of such a at slab 6 1 may be substantially equivalent to the extent of the bottom of the vessel. It is ordinarily preferred to form the ring walls in the inverted T shape since the upwardly extending neck portion acts as a stilening girder.

When the vessel is substantially full of liquid the downward weight of that liquid may be taken into consideration in the calculations of the permissible pressure within the vessel. When there is little or no liquid within the present container, it is still capable of withstanding the full operating pressure since removal of the liquid changes neither the weight of the ring walls and the earth above the ring walls nor the downward pressure of the gas over the effective area. Vessels with at bottoms are not ordinarily built for pressures over l5 p.s.i., since vessels for working pressures above this limit are better constructed under the A.S.M.E. code for pressure vessels which has a low pressure limit of l5 psi.

While this invention is susceptible of embodiment in many different forms as indicated in the drawings, it is to be understood that it is capable of many modifications. Changes, therefore, in the construction and arrangement may be made without departing from the spirit and scope of the invention as deined in the appended claims.

`I claim:

A pressure container for storing fluids in large volume, comprising a substantially ilat bottomed vessel resting directly on grade material, a cylindrical side wall secured to said bottom, a rigid top secured to said side wall, a circular anchor wall positioned below said bottom and beneath said grade, said anchor wall having a diameter substantially equal to that of the side wall and anchored thereto, a second anchor wall of appreciably smaller diameter than said rst anchor wall positioned beneath grade and lying appreciably within the periphery of said bottom and concentric with the side wall, and tension members inside the vessel converging downwardly from the top and connecting the top thereof to said second anchor wall, said anchor walls having substantial rigidity and Weight to resist the tendency of the internal pressure within the container to lift portions of the container and deform the bottom.

References Cited in the le of this patent UNITED STATES PATENTS 2,114,513 Wilkin Apr. 19, 1938 2,237,308 Larson Apr. 8, 1941 2,297,002 Larson Sept. 29, 1942.

2,351,509 Hammeren Iune13, 1944 2,593,153 Ioor Apr. 15, 1952 FOREIGN PATENTS 514,961 Belgium Nov. 14, 1952