US2886204A

US2886204A - Single deck contact type floating roof

Info

Publication number: US2886204A
Application number: US461718A
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: 1954-10-12
Filing date: 1954-10-12
Publication date: 1959-05-12
Anticipated expiration: 1976-05-12

Description

y May 12, 1959 F.. D. MQYER ET AL SINGLE DECK CONTACT TYPE FLOATING ROOF Filed Oct. 12, 1954 4 Sheets-Sheet l Zeig l 75 //5 www: E W2 il .ZYZ' Q -f ,ZV/Zevg;

May 12, 1959 F. D. MOYR ET AL 2,885,204

SINGLE DECK c-oNTAcT TYPE FLOATING ROOF Filed oct. 1 2, 1954 v 4 sheets-Sheet 2 May 12, 1959 Filed oct. 12.- 1954 F. D. MOYER ET Al. 2,886,204

SINGLE DECK CONTACT TYPE FLOATINC ROOF 4 Sheets-Sheet 3 l Egg,

ZU Z6 May 12, 1959 -F. D. MOYER ETAAL v 2,886,204

SINGLE DECK CONTACT TYPE FLOATING ROOF Filed Oct. l2, 1954 4 Sheets-Sheet 4 Ain Figure 7 (stitfeners omitted) ;l

United, States Patenfolf SINGLE DECK coNTAcr TYPE ELoATrNG Roor Frederick D. Moyer, Chicago, and Clilford M.-rr, Western Springs, Ill., assignors to Chicago Bridge & Iron Company, a corporation of Illinois Application October 12, 1954, SeralNo. 461,718

s claims. (nizza-26) This invention relates to a tank floating roof ofthe single deck contact type.

In such a roof, the contour of the lower face of the deck, whichunder normal floating conditions is entirely in contact with the liquid upon which it oats, is the same as the upper drainage area orjsurface ofthe deck, the upper and'lower faces being separated onlyl by the thickness of the deck plates. y

One of the main problems with such a roof is drainage of surface rainfall. In order to have adequate drainage it is important to have` appropriate slope or pitch, but the pitch of the roof is limited specifically bythe Weight of the roof and the specic gravity o 'f any given liquid on which it'oats. This is because more liquid is displaced as the slope increases and with any given roof weight and any Igiven specific gravity of liquid, the entire under surface of the roof canno longer be immersed in the-liquid when the slope has been increasedl to an eicient pitch.v y v l f.

It has been suggested in the past that-heavyweights be concentrated at or fnear the .center ofthe roof so that .it canv be further immersed, but this adds ymore problems than it solves. y,

In the present invention the problem is solved', without the addition of unnecessary weight, by providing steps in vertical cross section to provide a pluralityof integrated drainage areas, the steepness of the 'slope in at least one of such areas, and preferably in all, substantially exceeding the steepness of the slope possible with a single drainagearea on a roof of the same size and weight.

In one form of the invention the drainage areas comprise a plurality of concentric annuli, with drains connecting the ring drainage area formed at the junctions of the annuli with a central drainage area. l a

In another form of the invention the drainage areas are radial, comprising radial wedges sloped to provide radial vdrainage areas between them.

It is also possible to'coinbine these forms of drainage areas. f v

The invention is illustrated in the drawings, in which:

Figure l is a partial plan Vview of one form of the roof (stifeners or trusses omitted);

Figure 2 is a vertical vsection taken .along the line 2--2 in Figure 1 (stieners or ytrusses omitted);

Figure 3 is a vertical section taken along the line 3-3 in Figure l (stiEeners or truss'es'omitted);

'Figure 4 is a developed vertical cylindrical section taken along the line 4--4 in-Figure l;

lFigure 5 is a partial plan view of a modified form of 'ure 5;

Figure 7 is a partial plan view of a modified form of the invention;

Figure 8 is a vertical section taken along the line ,t5- 8 2,886,204 y fffifel Mer, 12, 1,959

. 2 i Figure 9Vv is a partial plan View of aimodiiied form'of the invention; "v

Figure 10 is a'section taken along the line 10--10 m Figure/9 (stiifeners omitted); A i' Figure 11 is ay partial plan view-of another formof the invention (stiffeners included); and"l Q Figure 12 is a section taken along the line f12-12'in Figure 11. 'i i f The4 first successful'oating roofs were of the pan .or pontoon-less type. This is `the most economical type of vfloating roof and is widely Vused today'for crude oils and products o f "relatively low volatility whichy require reduction of lling losses, prevention of corrosionl from sour 'liquids and protectionagainst losses from fire,` but do not require the additional insulation of a pontoon lor double deck type of roof.

Such a roof must be of the fcontact type-'-that is', it must float with the entire underside of the roof wetted by the stored product, if lcorrosion of the roof is to be reduced to the minimum. It must falso be pitched for drainage of rain water vbecause the roof, having no stabilizing pontoons, is subject to tipping and even'sinking if a largevv quantity of water vis `allowedfto collecton the deck.

In the past mostpan roofs were .built withwthe singleof water, and since this simplest type of roof was rela-- tively light comparedy with pontoon-type ondouble-deckftypewroofs, the slope of 'the cone even when shaped'by the mentioned trusses, was .nevertheless quite .fiat and ydrainage of rain water was not always satisfactory.

Structurally, ther-,conical shape -Wasfar from ideaLyfor the heavy outer portion Vof the roof displaced ,much less than its weight while the central portion displaced more than its weight thus creating a tendencyfor. the center of the roof to -be displaced upwards compared with the outer portion, destroying adequate drainage. Thefioof, therefore, had to be held in this conical shape by heavy trusses.` f l As an example, ythe slopefrom rim `to center` for-a roof in a tank 140 feet in diameter vmight be' about 7inche`s, and the drainage pitch thus only 7 inches in approximately feet, or one-'inch Sin approximately 10 feet. Roofs usually were built ofv lap-jointed plates of 5716 Vinch thickness which, without ,any 'trussing or supports, weighed about 8 pounds per square foot and'thus tended to displacelmore than 1% inches of'aproduct weighing 54 pounds per cubic foot. Sincetthe slope of the conical deck was about one' inch in 10 feet, the weight of steel was greater than the'theoretical displacement for' an outer annular :portionxof the deck nearly 18 feet wide, and this portion tended'to sag between trusses. Furthermore, a large portion ofthe weight of a pan roof was made up of the devices used to .seal'the space between theouter rim of 'the roof and'the tank shell, and the outer rim itself was a'heavy plate, .so thetrusses had to lift these outer loads, includingthe'weightof the outer deck plates not balanced by displacement, land transfer them toward the center yof the roof where the displacement exceeded the weight.

The result was that not only did the roof drain lpoorly because of insuicient pitch and the other reasons listed, but also the `trussing provided for forcing the 'roof finto shapehad to be designed for largeloads.

vTherewere'other disadvantages vof* :the old design.

When a tankwas emptied, the roof could not be allowed to come to rest directly on the tank bottom because it was not the 4same shape as thegbottom, and'further because a drain pipe andother devices beneath they roof required clearance. Therefore, it was necessary to provide a structure forlanding the roof in its low position; and since -this supporting structure carried not only the weight of the roof but lalsothe weight of water, snow and ice that accumulated while the roof was landed, it was a heavy and costly structure. Usually'it consisted of a large number of individual leg supports, the large number being required becausecach leg was connected only to. thesingle-thickness deck plates andthe load per support waslimitedlby the strength of the deck plates and the firmness ofthe grade on which the deck plates rested.

Another disadvantage of theoriginal design of pan floating 'roof was the diliiculty of assembling .and joining the deck plates. Neither the trusses nor the supports, alone or in combination, could be used for supporting the -individual deck plates when `the roof was being built. The trusses were too widely spaced to hold the plates lin properl shape, and the leg supports tended to distort the unstitfened deck plates near the supports.

` The present floating roof design has the following advantages: f y

(1) Improved drainage with positive radial or circumferential pitch or both radial and circumferential pitch toward the sump.

(2) Improved `trussing with adequate circumferential as well as radial framing.'

(3) Reduced bending moments due to improved location of buoyancy with respect to weight. This is partially responsible for the reduction in the cost of trussing.

(4) Reduced erectioncost due to elimination of heavy temporary supports for construction.

(5) In some cases a smaller number of adjustable supports and more positive load distribution on supports resulting from use of circumferential framing.

It is contemplated that the high portions formed by the steps be vented since'it is not normally desired to collect gas in these high spots. The form of vents, however, is no part of the present invention.

l In Figures l, 2, 3 `ancl 4 the wedge-shaped stepping is illustrated.

`As there shown, a floating roof is divided into a number of pie-shaped wedges or segments 11. l These are .divided alternatelylby ridges`12. and valleys 13. In this form of the invention the drainage areas are generally warped having constantly changing pitch and all of the vdrainage follows the valleys; 13 to the central sump 14 from which a drain 15 leads to the bottom of the tank.

.In Figures 5 and 6, a form of the invention in which a plurality of annuli is used is illustrated. In this form the single deck portion is divided into an outer annulus and an inner annulus 21 .separated by the step 22.

Adrain trough 23 Vconnects the lowermost portion of the `tions'of theroof to the :sump do not a'dd significantly to the displacement of liquid.

In Figures 7 and 8, .a modified form is shown in which a pon-toon 25 is provided in combination with a single deck of the contact

type having annuli

20 and 21. Sim- `ilarly, ysingle decks of the contact type as shown in the other figures may be combined with a pontoon.

Figures 9 and `10 illustrate a combination form in .which the single1deckportion comprises a central con- CII ical portion 30, which may be considered as an annulus surrounding and sloping inwardly ltoward the sump 14 and the radial segments 32 which in combination with each other form alternate ridges 33 and valleys 34. Drainage of the radial segments 32 is to the ring drainage area 31 which is connected by a series of troughs 35 to the central sump. f f i Figures l1, and l2 are detailed fragmentary views i1- lustrating another form of the invention having three

anular areas

60, 61 and 62.separated by

steps

63, 64 and 65. Drainage is to the central sump 66. Y

Trussing is accomplished by means of the

rafters

70, 71 andL 72 andposts 73,*74 and 75. These are connected by

conventional rods

76, 77, 78 and 79. Similar trussing may be provided in the other forms of the invention though not shown.

In the particular form illustrated in Figures l1 and l2, the

annuli

60 and 61 are 20 feet wide; the annulus 62 is 25 feet wide; and the sump is 4 feet in radius. This roof will accommodate a foot tank.

The outer annulus 60 has pitch of 5 inches; annulus 61 has a pitch of 5 inches; and annulus 62 has a pitch of 7 inches. All of these are steeper than the pitch that could be accomplished by using a single cone of the same size and weight oating on the same liquid and in contact therewith and could be increased further by adding the ridge and valley construction shown in Figures l, 2, 3, 4, 8, 9 and 10.

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

We claim:

l. A oating roof of the contact type for a liquid storage tank comprising a single roof deck `portion to cover liquid in the tank, the lower surface of the roof deck being adapted to remain substantially completely incontact with the liquid in the tank, said roof deck having portions sloped transversely to a radius of the roof and portions sloped radially toward the center of the roof to divide the upper surface thereof into drainage areas converging toward the center of the roof, said drainage areas comprising a plurality of concentric annuli forming at least one ring-like drainage trough, a central outlet to receive the drainage from the converging drainage areas, a communicating passage from said trough to said central drainage outlet, said communicating passage being adapted to permit gravity flow of surface liquid from said trough to said outlet, the total eiective slope of each drainage area exceeding the maximum slope possible in a continuous single deck roof of substantially the same weight and size having its lower surface maintained substantially in contact with the liquid in the tank.

2. A oating roof `of the contact type for a liquid storage tank comprising a single roof deck portion to cover liquid in the tank, the lower surface of the roof deck being adapted to remain substantially completely in contact with the liquid in the tank, said roof deck having portions sloped transversely to a radius of the roof and portions sloped radially toward the center of the roof to divide the upper surface thereof into drainage areas converging toward the center of the roof, said drainage areas comprising a plurality of concentric annuli forming at least one ring-like drainage trough, a central outlet to receive the drainage from the converging drainage areas,

size having its lower surface maintained substantially in contact with the liquid in the tank.

3. A oating roof of the contact type for a liquid storage tank comprising a single roof deck portion to cover` liquid in the tank, the lower surface of the roof deck being adapted to remain substantially completely in contact with the liquid in the tank, said roof deck having portions adapted to be drained in directions transverse to a radius of the roof and portions adapted to be drained along radii toward the center of the roof to divide the upper surface thereof into drainage areas converging toward the center of the roof, said drainage areas comprising a plurality of concentric annuli forming at least one ring-like drainage trough, a central outlet to receive the drainage from the converging drainage areas, a communicating passage from said trough to said central drainage outlet, said communicating passage being adapted to permit gravity flow of surface liquid from said trough to said outlet, the total effective slope of each drainage area exceeding the maximum slope possible in a continuous single deck roof of substantially the same Weight and size having its lower surface maintained substantially in contact with the liquid in the tank.

4. A oating roof of the contact type for a liquid storage tank comprising a single roof deck portion to cover liquid in the tank, the lower surface of the roof deck being adapted to remain substantially completely in contact with the liquid in the tank, said roof deck having a plurality of concentric annular drainage troughs With the outer periphery of one adjacent to the inner periphery of the other, the outer annular trough being adapted to drain toward the roof center and to have the accumulation then drain transversely to a radius of the roof and turn downwardly toward the inner annular trough, said inner trough having portions sloped radially toward the center of the roof to divide the upper surface thereof into drainage areas converging toward the center of the roof, a central outlet to receive the drainage from the converging drainage areas, a communicating passage leading from the inner annular trough to said drainage outlet, the flow from each annular trough being gravitational to provide a final drainage of the roof at its center, the total effective slope of each drainage area exceeding the maximum. slope possible in a continuous single deck roof of substantially the same weight and size having its lower surface maintained substantially in contact with the liquid in the tank.

5. The lloating roof claimed in claim 4 comprising in addition a generally annularly shaped pontoon positioned in contact with the outer annular trough and having its inner periphery in engagement with the outer periphery of the outer trough.

References Cited in the le of this patent UNITED STATES PATENTS 1,886,131 Smith Nov. 1, 1932 2,282,772 Wiggins May 12, 1942 2,321,058 Wiggins .Tune 8, 1943 2,359,416 Hammeren Oct. 3, 1944 2,464,786 Allen Mar. 22, 1949 2,538,033 Orr Jan. 16, 1951 2,664,220 Cord et al. Dec. 29, 1953 2,750,067 Wiggins June 12, 1956