US3057507A

US3057507A - Floating roof for a liquid storage tank

Info

Publication number: US3057507A
Application number: US84287A
Authority: US
Inventors: Frederick D Moyer; Clifford M Orr
Original assignee: Chicago Bridge and Iron Co
Current assignee: Chicago Bridge and Iron Co
Priority date: 1961-01-23
Filing date: 1961-01-23
Publication date: 1962-10-09
Anticipated expiration: 1979-10-09

Description

F. D. MOYER ET AL 3,057,507

FLOATING ROOF FOR A LIQUID STORAGE TANK Oct. 9, 1962 2 Sheets-Sheet 1 Filed Jan. 23, 1961 five 7%215: Wedera'cijjgyev;

Oct. 9, 1962 F. D. MOYER ET AL 3,057,507

FLOATING ROOF FOR A LIQUID STORAGE TANK Filed Jan. 23, 1961 2 Sheets-Sheet 2 I I Eva/$30245,

United States Patent 3,057,507 FLOATING ROOF FOR A LIQUID STORAGE TANK Frederick I). Moyer, Chicago, and Clifiord M. Orr, Western Springs, IiL, assignors to Chicago Bridge 3; Iron Company, Chicago, Ill., a corporation of Illinois Filed Jan. 23, 1961, Ser. No. 84,287 Claims. (Cl. 22026) This invention relates to a floating roof and more particularly to a roof used in a liquid storage tank of the field-erected type.

Floating roof storage tanks have been used particularly extensively in the petroleum industry to store exceedingly large amounts of product. The tank is an upwardly open circular shell with a bottom. The floating roof covers most of the liquid surface of the product, there being a slight annular opening between the roof and the shell which is sealed against escape of vapors by a curtain.

The floating roof structures must be made to withstand and hold considerable rain water, particularly in climates where rainfall is quite heavy in quantity during a short time. In order to withstand the stresses without collapsing, roofs have been made in the past quite heavy with sufficient bracing so that the roof may safely carry considerable loads. It is desirable to decrease the Weight of the roof in order that less steel be used in its manufacture. Stability under heavy rainfall conditions must be maintained however.

The present roof structure incorporates a simple design which acts differently under conditions of normal use and under the conditions of heavy rainfall upon the roof. The roof weighs considerably less than previous floating roofs for use in the same size tank. It is extremely stable both under conditions of trapped water on the roof or in the event of a rupture of a part of the roof which allows product to flow on top of the roof.

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

FIGURE 1 is a top plan view of a liquid storage tank having the roof of this invention mounted thereon (the roof is shown in a very small scale in order to show the whole structure);

FIGURE 2 is a vertical sectional view taken substantially through the center of the tank and roof shown in FIGURE 1;

FIGURE 3 is a fragmentary broken enlarged sectional view along a radial line through the roof showing the details thereof;

FIGURE 4 is a view similar to FIGURE 3 showing the roof under conditions of heavy rainfall thereon;

FIGURE 5 is a view similar to "FIGURE 2 of a slightly modified form of the roof;

FIGURE 6 is an enlarged fragmentary sectional view on a radial line through the roof shown in FIGURE 5;

FIGURE 7 is a fragmentary enlarged plan view of one end of the drain trough connection to the pontoon; and

FIGURE 8 is a fragmentary enlarged vertical sectional view through the structure illustrated in FIGURE 7.

The liquid storage tanks in which floating roofs are generally used in the petroleum industry include a plate bottom 9 (FIGURE 2) mounted upon a prepared grade of sand fill or similar foundation. The bottom may be coned slightly toward the center in order to drain any water which may settle from the petroleum product. The shell 10 of the tank is made of horizontal courses of butt welded or lapped plates, one upon the other to the desired height. Various appurtenances are used with the tanks such as the necessary piping and valves, gauging apparatus, access ladders and other equipment. These are not shown as they form no part of the present invention.

In FIGURE 2, stored liquid 11 is shown within the tank so that the floating roof, generally designated 12, floats on the liquid near the top of the tank.

The floating roof structure of the present invention in general includes an annular pontoon 13, which is spaced when the roof is centrally located within the tank a short distance from the inner surface of the sidewall 10 of the tank. The space within the pontoon is covered by a single deck portion formed of plates lapped and welded together and suitably secured to the inner periphery of the annular pontoon 13. A central sump 15 is formed by placing a plate ring 16 (FIGURE 3) in upstanding relation to the deck 14- substantially at the center of the deck. Radial drain troughs 1'7 connect the upper surface of the annular pontoon 13 with the sump 15 so that rainfall falling on the roof will be collected in the sump more rapidly than on the rest of the single deck portion of the roof. A drain basin 18 is connected with the sump and with the single deck portion outside the sump. With some products, rain water may be drained directly through the product to the bottom of the tank. With others, a flexible hose or swingable pipe drain may be connected to the drain basin and led outside.

Referring particularly to FIGURES 3 and 4, it will be noted that the annular pontoon 13 has an outer rim 19 extending substantially vertically and spaced a short distance from the wall 10 of the tank. This rim supports a conventional sealing structure (not shown), including, for example, shoes for sliding engagement with the tank sidewall and a curtain to seal the space against vapor loss. The bottom 24 of the pontoon is connected to the lower end of the rim l9 and the top and upper deck 21 is also connected to the rim so that it is pitched toward the center of the roof. An inner rim plate 22 joins the upper and lower decks of the pontoon and extends by a portion 23 above the upper deck 21. This annular extension 23 serves to keep rain water that falls on the pontoon from passing inwardly of the upper deck and onto the single deck portion 14 of the roof.

As previously stated, the single deck portion 14 is of single plate thickness. The sump is formed by the ring 16 suitably attached as by Welding to the surface of the single deck. As an example, the ring 16 may be of a size to enclose an area equal to about one-fifth of the annular pontoon area. The drain troughs 17 thus will serve to collect water within the sump six times as rapidly as water will be collected upon the single deck portion 14. The practical result of this operation is that the center of the deck is thus weighted by the collected water depressing the single deck deeper into the product so that the drainage pitch or slope of the single deck portion is increased.

Water collected on the single deck portion is conducted into the basin 18 through an opening 24 adjacent the upstanding rim 16. A smaller opening 25 may also be provided into the basin and communicating with the sump. However, an upstanding pipe 26 of much larger size than the opening 25 will serve to maintain most of the water in the sump until after the water has been drained from the single deck portion. The small opening 25 may be omitted and the drain pipe 26 will thus maintain water Within the sump during periods of no rainfall and the water will gradually evaporate. An

. emergency overflow pipe 27 may be provided communitakes up in ring compression the forces which the single deck imposes on the pontoon. The drainage troughs 17 are suitably connected to the pontoon inner rim 22 by a thin flexible metal angle 29 (FIGURES 7 and 8). The inner end 30 of the troughs merely rests upon the upstanding rim 16 in sliding engagement so that it may move with up and down movements of the single deck portion.

The pontoon 13 is designed to support the roof under the most severe conditions to which the roof may be subjected. This condition might exist should the drain become clogged or should the single deck portion be ruptured so as to permit product to flow onto the single deck portion.

The embodiment illustrated in FIGURES and 6 differs from that of FIGURES 3 and 4 in that a step is provided in the single deck portion. The single deck sump floor 31 is connected to the upstanding sump ring 16 at an elevation above the connection of the single deck portion 32 outside of the ring to provide a step in the single deck portion at the sump ring. The ring is made larger since the depth of liquid that can be collected inside the sump is less than in the case of the roof shown in FIGURES 3 and 4. This structure provides an even increased pitch to the single deck portion 32 when rain water is collected in the sump to depress the single deck portion. Additional stiffening angles 33 are required at the connection of the sump floor 31 to the ring and thus increase slightly the weight of the roof over that shown in FIGURES 3 and 4. The weight, however, is still considerably less than required in other roof designs.

In operation, both of the forms of the roof described above have the advantage of providing a Weight on the center of the roof to depress the single deck portion and increase the drainage characteristics during the time that such drainage is required in normal operation. In dry periods, the rain water is removed from the roof so that the single deck portion merely floats on the liquid without necessarily great slope or pitch toward the drain. This structure permits a substantial reduction in the overall weight of the roof without adverse effect on the performance thereof.

The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, for some modifications will be obvious to those skilled in the art.

We claim:

1. A floating roof for a liquid storage tank, comprising: an annular hollow pontoon having an inwardly sloping upper deck and an inner rim plate extending above said deck to trap rain water thereon; a relatively flexible single plate thickness deck secured to the pontoon below the inner edge of the sloping upper deck and covering the area Within the pontoon; an upstanding plate member secured to the single deck forming a sump generally centrally of the single deck; and a drain trough extending over the single deck from the pontoon upper deck to the sump to drain and collect rain water into the sump during rainfall more rapidly than on the single deck outside the sump.

2. A floating roof as specified in claim 1 wherein a drain is connected to the single deck outside the sump and an overflow drain is positioned in the sump with its inlet spaced above the bottom thereof so that rain water may collect in the sump to depress the central portion of the single deck to improve drain slope of the deck during rainfall.

3. A floating roof as specified in claim 1 wherein the plate member forming the sump is a ring secured to the single deck plate and extends upwardly from the deck forming said sump.

4. A floating roof as specified in claim 1 wherein the single deck portion outside the plate member forming said sump is secured to the lower end of the plate member and the single deck portion inside the plate member is secured thereto above the lower end to form a step in the single deck for sloping the outer single deck portion toward the sump.

5. A floating roof as specified in claim 1 wherein said drain trough is flexibly secured to the pontoon at its outer end and slidingly rests on the plate member at its inner end and extends in bridge fashion over the intervening single deck.

References Cited in the file of this patent UNITED STATES PATENTS 2,390,141 Wiggins Dec. 4, 1945 2,497,047 Prager et a1. Feb. 7, 1950 2,538,033 Orr Jan. 16, 1951 2,886,204 Moyer et a1 May 12, 1959