US2635782A

US2635782A - Floating roof for liquid storage tanks

Info

Publication number: US2635782A
Application number: US751302A
Authority: US
Inventors: Clifford M Orr
Original assignee: Chicago Bridge and Iron Co
Current assignee: Chicago Bridge and Iron Co
Priority date: 1947-05-29
Filing date: 1947-05-29
Publication date: 1953-04-21
Anticipated expiration: 1970-04-21

Description

April 21, 1953 c. M. ORR 2,635,782

FLOATING ROOF FOR LIQUID STORAGE TANKS Filed May 29. 1947 2 SHEETS-SHEET l April 21, 1953 c. M. ORR

FLOATING ROOF FOR LIQUID STORAGE TANKS 2 SHEETS-SHEET 2 Filed May 29. 194'! L50 5 7? 3%0 Q7 07 7; M

Patented Apr. 21, 1953 FLOATING ROOF FOR LIQUID STORAGE TANKS Clifford M. Orr, Chicago, Ill., assignor to Chicago Bridge & Iron Company, a corporation of Illinois Application May 29, 1947, Serial No. 751,302

4 Claims. 1

This invention relates to liquid storage tanks, and more particularly to a roof for use in conjunction with a floating roof tank.

In the storage of volatile liquids, it has been found that evaporation losses can be reduced by the use of a tank in which the top closure is a roof adapted to float upon the surface of the liquid stored within the tank.

According to this invention, the floating roof comprises a deck, an outer annular pontoon and an intermediate annular pontoon positioned between the outer pontoon and the center of the deck. Radial rafters extend between a ring girder at the center of the deck and the inner pontoon. Additional radial rafters extend between the inner pontoon and the outer pontoon. The substantially circular sheet metal deck is positioned above and secured to the pontoons and rafters and a drain is provided at the center of the deck. The rafters carry the deck loads to the pontoons and serve to stiffen the deck in a manner to make it substantially inflexible. As

i will be hereafter more fully set forth, the rafters the patent to J. H. Wiggins issued May 12, 1942 as Number 2,282,772.

The principle of insuring an inflexible deck by the provision of radial rafters may be incorporated in a floating roof having a single annular pontoon with the rafters bridging the entire single deck portion of the roof. It may also be incorporated in a roof having an annular pontoon and a central pontoon with the rafters again bridging the entire single deck portion of the roof. In the first instance, the rafters would extend across the deck either as continuous rafters or joined by a ring girder or other structural support at the center, while in the second case, the rafters would extend from the annular pontoon to the central pontoon. The invention will be hereinafter described, however, as embodied in a floating roof having two annular pontoons.

In the preferred embodiment shown, the volume of the pontoons is so adjusted as to maintain the center portion of the deck just touching the surface of the liquid under normal con- "ditions.

However, the roof may be desizned'so that the central portion of the deck is somewhat above or below the liquid level, if so desired. A heavy load, whether of rain or snow, will, of course, tend to sink the deck somewhat lower in the liquid. The stiffness of the deck, of course, provides buoyancy for it. By virtue of the construction and arrangement of this roof I find that I can provide a steep slope to the deck from its outer edge to the center of the deck, which forms a sump. For example, in a foot diameter roof, I provide a downward pitch to the deck of 24 inches from its outer edge to the central sump. The effect of this comparatively steep pitch is to insure speedy and adequate drainage of the roof through drainage means located at the sump.

For purposes of disclosure, my invention will be described in conjunction with the accompanying drawings in which:

Fig. 1 is a plan view of a portion of the floating roof;

Fig. 2 is a sectional view taken on line 22 of Fig.

Fig. 3 is an enlarged detailed view of a portion of the pontoons with the roof removed; and

Fig. 4 is an enlarged sectional view through the pontoons similar to Fig. 2.

Referring now to the drawings, [0 indicates a liquid storage tank having a floating roof ll floating upon the surface of a liquid [2 stored within the tank. The floating roof includes an outer annular pontoon l3 positioned beneath the outer edge of the deck [4, as shown, and a central sump l5. An inner annular pontoon I6 is positioned intermediate the sump and the outer pontoon. The central sump includes a drain pipe I! for draining liquid from the surface of the deck. A ring girder l8 surrounds the central sump to which are attached the inner ends of a first plurality of radial rafters l9 radiating from the ring girder to the inner pontoon. In the embodiment shown, the rafters are channel members and are welded to the deck along their entire length. As shown in the drawings, the rafters l9 are attached to, but do not extend through, the inner pontoon. A second plurality of radial rafters 20 are attached to and extend from the outer edge of the inner pontoon to the inner edge of the outer pontoon, as shown. The deck l4 comprises a plurality of sheet metal plates secured together to form a substantially circular deck, and is secured to the upper sides of the pontoons and to all, or at least the major proportion, of the rafters.

A number of relatively small deck braces 2| are located within each pontoon to prevent sagging of that portion of the deck immediately above each pontoon. The deck braces are welded to the deck and to the sides of the pontoon, but it will be seen from the drawings that the braces have ends beveled to a point 22, and those points only are welded to the pontoons. This arrangement provides an adequate brace -fr the roof while permitting'somedegree of flexibility to that portion of the roof above each pontoon. The pontoons are open topped except for the deck. which closes them.

Sealing means of usual construction will; of course, be employed to seal the space between the roof and the side walls of the "tank.v

In a typical construction, a floating-roof embodying the invention having a diameter of 120 feet is provided with deck plates which weigh approximately 8 pounds to the square foot. The entire roof has an average weight of 1 6' pounds per square foot. If the'deck plates were not attaohed:to--theradial rafters, it is clear that the Iplates; would flex upwardly with a gas pressure in the space beneath the 'deck' in "excess of '8 pounds per square root. Accordingly, I weld the under side of. the-deck toall,-or;substantial1y all, of:theradial-rafters to prevent flexure of the rooifandto maintain the same substantially in- -fiexible, asipreviously described.

In lihGrB'VGl'It the :gas pressure beneath the roof in=thespace defined.-.by the inner pontoon and infith'e; spacewbetween the two pontoons exceeds apredetermined amount; emergency venting -means3-is provided. I 'he predetermined pressure at which the -emergency-vents will come into operation "will, offcourse,besomewhat less than 16- pounds-:per square --foot in excess of atmos- .pheric,,--but more thant pounds per square foot.

A vent pipe 23 connects the'gas-spacearound-the center; ofithe roof with the-gas space between'the pontoons to equalize the pressure beneath the roof. .An' emergency :ventipipe-Msis provided in the outer pontoon to permit gases to escape to the atmosphere'irombeneath therdeck when the )DI'ESVSUIB hasincreased: to the extent necessary to *l iftthe roofsuffici'ently to raise the inner end of that pipe out of' the liquid. inasmuch as gas :pressure under-the roof would cause the level of 'thevliquidsbelow therroof to be lower than the liquid level outside of the roof and adjacent the side-wallsof the tannthevent pipe 2 is inclined upwardly and outwardly to guard against. 'a liquid lock inthe vent. Under gas pressures-less than the predetermined -maximum, the :pipe =24 will, of course be'immersed inthe liquid and no venting :will :take place.

u -A n added teaturaof my invention isthe simplici by and economy with which the roof may be-erected. --It=has-been customary in the past, in the construction oil-floating -rocf tanks, first to fabricate a tank and then construct the roof within the tank. In the'usual-construction; temporaryerection framing isemployedwithin :the tank andthe floating roof-laid outandassembled upon. such temporary framing. -Aefter the roof has been-completed, the framingis removed and very-often is unusable in other construction and is: discarded. In the construction-of the roof shown herein, the need f or temporary erection framing is eliminated. The 213011 5001 and the ringgirder. may beassembled while resting upon thefbottoin of the tank and tied together by means of'theradialraf ters. -'I he-deck.plates are tllh assembled upon thexupper surfaces of the pontoons.andurafters-an-d welded or otherwise sethe radial rafters take the place of the temporary erection framing, but unlike such framing, are incorporated into the permanent and final structure, hence eliminating all waste of material.

While I have shown and described my invention in its preferred embodiment, it is to be understood that it is capableof many modifications. Changes, therefore, in the construction and arrangement may be made without departing from the spirit and scope of the invention as disclosed in the appended claims.

I claim:

1. In a liquid storage tank, a floating roof comprising, a substantially circular deck, an outer-annular pontoon positioned beneath the outer edge of the deck, a central sump in the deckandan inner annular pontoon beneath the deck between the outer pontoon and the sump, sai'dxpbntoons being closed on their upper sides only by said deck, a first plurality of radial rafters-beneath: the deck and extending from the sump to the inner pontoon, a second plurality of radial rafters-beneath the deck and extending ironithe inne1-.-pontoon to the-outer pontoon -said matters-being respectively secured at theirends tattle-sides of the sumpandporitoons along only az-portion of the-depthof thesump andpontoons, said deck and rafters comprising theonly structural ccnncction between-said pontoons and said -sump,;sa-id deck being secured to at least the entire len th ofsomeoi the rafters-torender the d'eck ovzer the rafters substantially inflexible, the side portions of the pontoonsat the rafter end connectionsbeing-structurallysupported only by the deck'and the 'bottomcf thepontoonsto .permi-t flexingof said portions to provide for relative vertical stress-avoiding movement of the pontoons -and inflexible deck portions under influence'ofnon-uniform loads-inthe roof and -unequalb-uoyancies ofthe ponteons,and-said deck having :asubstantially uniform slope from its outer-edge to the sump.

The floating roof ofcl-aim-l inwhich said -sump-incl-udes a ring girder andtheinner edges 0 ci-said first plurality of radial rafters-treattached to the -girder.

In a -1iquid storage tank, a fioating roof comprising, a substantially circular deck, an outer annular pontoon positioned beneath the outered-ge of the =deck, a central sump in the deckand aninner annular vpontoonbeneath the deck between the outer pontoon and the a sump, .a ring girder aroundthe-sump beneath the deck, said pontoons being closed on their upper-sides only by. said: deck, a first plurality of radial rafters having their inner edges secured to the girder and having their outer edges secured to the inner side of the inner pontoon, a-second plurality of radial rafters having their inner edges. secured vto the outer side of the I inner .pontoon and having-their outer edges secured to the inner side of the outer pontoon, said-rafters being respectively .secure'dto the sides er the pontoons along only aportion of-the depth ointhe pontoons, "saidde'c'k and rafters comprising -the only. "structural connection between said pont'o'oiis and "said ring girder, said deckbing-secured toat least theentirellength of-some of'the rafters torender the deckover the rafters substari'tially' 'ihfieklble, andlmeans permitting relative vertical stress-avoiding movement 'of' the p'o'nto'o'ns andliriflexible deck portions-under inilii'e'ncefofnon uniformloads on the roof andunequal buoyancies. 6f the pontoons including side 'iifdiilrposition. During the entire construction, 1 5 'f'sai d pontoons at the rafter en'd con- References Cited in the file of this patent UNITED STATES PATENTS Number Name Date Kimbell Feb. 251, 1930 Howard Feb. 23, 1937 Wiggins May 12, 1942 Wiggins June 23, 1942 Laird Aug. 156, 1944 Wiggins Nov. 11, 1947