US2531898A - Floating roof with flexible deck and central weights - Google Patents

Description

Nov. 28, 1950 R. c. ULM

FLOATING ROOF WITH FLEXI DECK AND CENTRAL WEIGH 5 Sheets-Sheet 1 Filed Sept. 7, 1950 -l' WNW INVENTOR.

Nov. 28, 1950 R. c. ULM 2,531,898

FLOATING ROOF WITH FLEXIBLE DECK AND CENTRAL WEIGHTS Filed Sept. 7, 1950 3 Sheets-Sheet 2 W (9 LI INVENTORZ fay a Nov. 28, 1950 R. c. ULM 2,531,898

FLOATING ROOF WITH FLEXIBLE DECK AND CENTRAL WEIGHTS Filed Sept. 7, 1950 3 Sheets-Sheet 3 FIG. 4

IN V EN TOR.

Patented Nov. 28, 1950 FLOATING ROOF WITH FLEXIBLE iiEoK AND CENTRAL WEIGHTS Reign 0. Ulm, East Chicago, Ind., assignor to Graver Tank & Mfg. 00., Inc., East Chicago, Ind., a corporation of Delaware Application September 7, 1950, Serial No. 183,612

Claims. 1

Y This invention relates to floating roofs as used mainly for vapor conservation in the storage of gasoline and other volatile liquids. It provides greater efficiency and economy in floating roofs, particularly of the single-deck type. Basically, a floating roof according to this invention is an improvement over the floating roof disclosed and claimed in Patent No. 2,497,047 of Frank D. Prager and myself, hereinafter called the Prager-Ulm roof. The corrosionresisting self-draining nature of the Prager-Ulm roof, with a smooth inward-downward slope, is maintained more safely and more completely by means of the present invention.

The main part of such a roof, a substantially unreenforced, flexible, centrally weighted and centrally drained deck the underside of which contacts the liquid, is modified as to its operative and inoperative shapes, in accordance with this invention, whereby it is materially improved as to the safety, completeness and accuracy with which the roof maintains its corrosion-resisting, self-draining nature in its various operating that is, floatingconditions.

The shape of such a deck, in vertical crosssection, is not the same, under diiierent conditions, although the changes are seemingly small. As pointed out in Patent No. 2,497,047, such a deck is extremely flexible; if not held or tensioned in some manner it behaves almost like u tion curve, is influenced by the fact that the deck is shored up or supported, against its own weight, at distributed points or lines. The corresponding contour of the membrane deck, when in floating condition, is different, being subject to different factors and forces. This latter contour, hereinafter called the operating curve, is influenced by the fact that the deck tends to bulge or curve upwards due to the pressure of the displaced liquid; the deck being weighted down locally, by the central ballast weight and the peripheral rim and seal. Strictly speaking, different operating curves exist under different operating conditions. For instance, a snow load on the roof aflects this curve. Still another contour exists when the deck is not shored up and not supported by liquid; I call it the dry suspension curve.

The change of contour of thedeck, between these different curves, is allowed by the flexible,

substantially 'unreenforced deck construction.

2. However, I have discovered that it is desirable, and possible, to minimize this change, or the actual amount of flexing.

For this purpose I prefer to eliminate several factors present in the original Prager-Ulm design, which added to the actual amount of flexing in some important parts of the deck.

One such factor, eliminated in the roof as shown here, was the use of different andmore rigid plate material in the center of the roof. I prefer to construct a circular, flexible membrane deck comprising substantially the entire area of the floating roof, substantially unreenforced and unobstructed except at the required, peripheral, rigid, upstanding rim; and I usually employ lap-welded metal plate material of uniform thickness throughout this circular area. As a result the inward pull of the central ballast weight is imposed on the flexible membrane deck somewhat more directly.

This applies even in the event that the central, weight-supporting part of the deck is reenforced to some extent by drainage channels or the like, which may be welded to the top of the deck in this central part. However, I prefer to eliminate or modify such channels also; not so much for structural as for functional reasons connected with the prevention of trouble due to ice and the like. Still further flexibility of the central deck section results from this further change, although I may keep the central ballast weight rigid by reenforcements in its upper part.

The relatively flexible central part of my new and improved floating roof tends to curve downward, as a result of the Weight of the ballast material which is substantially distributed over the same. I may or may not counteract such downward curvature, depending on details of the central reenforcements which I will explain. Depending on such modifications the contour of the new roof may have different types of curvature, as will be explained hereinafter. A final factor of the original Prager-Ulm idea which added to the actual amount of flexing, had to do with the method of constructing the deck. The construction curve was a fiat, straight-sided cone. As pointed out in my copending application S. N. 122,639 filed October 21, 1949, I prefer to provide this construction curve with an upward curvature over a part of the radius between the inner and outer parts thereof, thereby making it very similar to the normal operative or floating shape of the deck.

The aforementioned modifications add to the construction curve in accordance herewith, in order to minimize the actual values of deflection Z as defined in Patent 2,497,047. By this expedient I also minimize the actual values of the radial elongation or strain in the plate material. This again minimizes the peripheral strain, and the peripheral stresses connected therewith. In this manner I minimizeperipheral compression forces in the body of the deck, which would otherwise tend to produce radial bulges or wrinkles. The theoretical shape of the construction curve, for deck I5, is shown by line A in Figure 3 hereof. It is theoretical insofar as it disregards the sudden steps due to the lapwelds between the plates. These are shown by line B. Of course, as mentioned initially, the figure exaggerates the thickness of the plates and therefore the magnitude of the sudden steps, nevertheless these steps have actually appreciable magnitude in proportion to the total rise of the line or curve. When reference is made to the construction curve, hereafter, the actual curve B is meant except if the context is diiferent. Lines A and B rise outwardly at least to some slight extent throughout the extent of the lines and the rise is such that the outer, annular part 23forming an integral part of the deck about thickis curved downwardly or con-' cave to the top. In some instances, if the rim l6 and the seal 2[ are relatively light, the outer annular part 23 may not be actually concave to the top, but it is never bulged upwards to the same degree as is the intermediate ring 24.

The innermost circular part IQ of the floating roof is another integral part of the deck, in

accordance herewith.

The original form of the Prager-Ulm roof was based on the use of special, strong plate means 36, 31, 38, 39 and 4! for these innermost and outermost parts of the deck. I have discovered that this is unnecessary, and I prefer to use steel plates of identical thicknessusually for the entire deck.

As in the earlier construction, the rim portion 26 of the deck [5 is reenforced by structural means, including gussets 21. The center portion l9, below the ballast material I8, may be reenforced by drain channels 28.

In the construction of the roof, the construction curve B is suitably impressed on the deck, for instance in the manner disclosed in my said copending application. This involves the use of suitable shoring-up supports (not shown). When these supports are removed, upon completion of the construction process, the deck tends to assume a contour defined'by the dry suspension curve E in Figure 3. Substantially the same curve is shown at a different scale, in Figure of the Prager-Ulm disclosure.

The tank is then filled and the normal operating curve C is gradually established thereby. It must be understood that in accordance with my new invention, this establishment of the normal operating curve C constitutes very nearly the reestablishment of the construction curve A. Due to the fact that the present deck tends to return from the dry suspension curve E to the construction curve B, and that the latter resembles the normal operating curve C, a minimum of distortion is involved in the full and extreme change between operative and inoperative (dry conditions. This minimum of distortion again, involves a relative minimum of stress differentials between said extreme conditions. Inasmuch as all stresses-whether. radial or annumb-increase and decrease togetheh'although not at the same rate, I provide a relative minimum of annular tension and compression, and a relative minimum of bending moment, between the extreme conditions.

Otherwise, very considerable bending moments could be developed, tending to seriously warp the deck and even the rim. I have determined this point by testing difierent floating roofs with central weights, and accurately measuring the stresses as well as deflections, along different radii.

The relative smallness of stresses and trains in my improved floating roof allows the use of relatively thinner, peripheral and central deck plates, as indicated above; also the use of a relatively weaker, lighter and cheaper rim and reenforcing system for the same. Moreover the new and improved deck surface is particularly smooth and free from local irregularities, such as the radial bulges, wrinkles or wavy surfaces mentioned above. 7

This absence of irregularities in the deck simplifies the maintenance of the floating roof. Corrosive accumulations are practically non-existent, above and below the deck. After a rain fall, and after the melting of snow, all of the water drains away; no residual pools are formed, which would be removed only by slow evaporation.

Equally no layers of vapor in gas phase are formed anywhere below the deck; at most, bubbles of vapor are formed, moving through the product in liquid phase. This, again, contributes to the vapor economy. Where extensive layers of vapor are formed under a metal deck, as in prior floating roofs'where vapor accumulating spaces were intentionally or inherently formed, such layers act as thermal insulators, postponing both the heating up and the cooling down of the product during the daily temperature cycle. However, such layers of vapor also promote evaporation; in fact the existence of an interface, between a body in liquid phase and one in vapor phase, is one of the main requirements for evaporation. Inasmuch as myim provement reduces the chance for the formation of such layers or bodies in vapor phase, it also resists the formation of such an interface, the evaporation of liquid, and the ultimate loss of vapor.

It will be noted that the present floating roof is more efficient than the original Prager-Ulm roof, due to the safe elimination of wavy surfaces, and that it is also more economical due to the simplification and savings in material provided by the use of uniformly thin, flexible, lapwelded plates of any suitable shape, throughout the deck, in the rim, intermediate and ballast weight areas.

The construction of the ballast weight area of the deck should be considered in further detail, with reference to Figures 4, 5and 6. These figures show a slight modification which is some- 7 drain channels 28 buried below the ballast material as in Figures '1, 2 and 3. Such open construction of the drain passages facilitates the removal of ice, dirt and the like; an operation which is sometimes necessary on all floating roof drains and which may be extremely ime 7 portant, since clogging up of the drain may cause the deck to in the product.

Incidental-1y such open constructionof the drain passages may also be cheaper, although it may require extra material for sidewalls 3| of the flume, in addition to the peripheral walls 32 surrounding the loose ballast weight material which is preferably used. The saving incident to the use of the open vilume construction is due to the fact that the cutting out, fitting up and welding of suitable ports in the wall 32, for the channels 28, can be eliminated.

The open fi-ume construction mentioned separates the center weight 18 into separate bodies oi. ballast material. A flu-me -30 of about one foot width will usually be provided, as suggested by the drawing. Thus the separate bodies of ballast material are spaced from one another by an appreciable distance and the ballast weight k8 is no longer a circular unit structure, unless some special provision is made to combine the parts into such a unit structure.

For this purpose I provide a bar 33, extending across each end of the Home 30 adjacent the top of the home. These bars are preferably buttwelded to the sidewalls 31, as shown at 34. They are installed so that their outsides are .ilush with the outside of the peripheral Wall '32, ,so that they structurally complete the circular "unit formed by the peripheral wall, while leaving :the drain flume 30 substantially unobstructed.

I prefer to cover each part of the ballast weight by a removable cover 35. I also prefer to facil- .itate access to the central drain 2!! by locating the drain sump 36 in a circular, central enlargement 31 of the diametrical flume 3t. This enlargement may have .a diameter of about 4 feet. It can be .formed by more or less semicylindrical walls 38, secured to the inner ends of the straight side walls 3|.

As mentioned above, the improved, circular deck l5 in accordance herewith can be constructed of uniformly thin, flexible plates, usually steel plates of 1% thickness. Any desired economical pattern of such plates can be used, for instance with plain, rectangular plates throughout, except for suitable sketch plates at the periphery. The plates can be secured together by lapwelding.

In Figure 3 numeral ll designates the outermost sketch plate of the deck. Numerals 42 and '43 designate intermediate, rectangular plates, curved upwards as explained above. Numerals 44 and 4.5 designate central plates. dhe same thickness and flexibility may be used in plates 44., &5 and -44 as in i2 and 43.

As shown in Figure 3, thecentraliplates 44 and 45 may have downward curvature, impressed thereon by the channels 328 welded thereto.

However, it is also possible, as shown in Figure '7, to construct the innermost part of the deck, generally designated by numeral 18, as a simple, flat, straightsided cone C. llhe upward pressure of the :liquid product, tending to raise the drain-sump 36 and the empty enlargement 31 of the dome an, will tend to impose a curvature similar to that shown in 'Figure :3, but'this tendency may 'ibe negligible, since :the area 31 \will generally be small compared with the roomplete central area 115 over which the ballast weight is distributed.

For the same --reason there is but little danger that the open-drain fhnne area i301will be raised, interfering with drainage. :Sudh raising up of 8 l the area as would have to be expected is" me come; as: mentioned, by the bars 33.

Various other modifications. will occur to per: sons skii led in this art, upon consideration of this disclosure, 7 I

This is a continuation part of my applica. tion S. N. 146,503, filed February 23 1950;. as a division of my said application .51. NJ. 122,639,1ild October 21, 1 949.

I claim:

In liquid storage apparatus, a substantially centrally drained floating roof having the entire underside immersed in the stored liquid and the deck portion thereof shaped by contour-controlling ballast weight means installed in a generally central, minor but substantial part of the area of the floating roof; comprising an outer, relatively narrow, upstanding, rigid, compression-resistin rim; a single, circular, flexible membrane deck, substantially unreeniorced and unobstructed at least throughout area between the rim and the ballast weight, having its outer part secured to andreenforced by the bottom part of the rim, comprising substantially the entire area of the floating roof and forming a flat, smooth solid of rotation a-ll vertica'lcross-sectional contours of which substantially coincide with a curve running outwardly-upwardly throughout the radial distance from the center to the periphery of the deck, with continuous upward curvature between said generally central part and said rim; and ballast weight means distributed over and limited to said generally central part and constituting a suificient part of the total weight of the floating roof for the purpose of immersing the entire underside of the roof in the .stored liquid and cooperating with the stored liquid in shaping the membrance deck into said smooth solid of rotation.

2. Apparatus according to .claim 1, wherein said ballast weight means comprises a plurality of bodies of loose material, and an enclosure for each of said bodies; each enclosure being formed by-a wall upstanding from said deck, which wall comprises an arc-shaped outer portion and a straight portion intermediate the ends of the arc shaped portion; a pair-of such straight wall portions being arranged in parallel and-separated by an open drain fi-ume, and a pair of such arcshaped wall portions being interconnected by rigid structural means extending acrossan upper, terminal part of the flume and secured to the -walls.

3. Apparatus according to claim 2, wherein said open drain 'fiume ext-ends diagonally of the ballast weight means and "has a central, generally circular enlargement, formed by arc-shaped inner portions of said wall of each enclosure.

4. In liquid storage apparatus, a substantially centrally drained floating roof having the entire underside immersed .in'the stored liquid and the .deck portion thererof shaped by contour-controlling ballast weightmeans installed .inagenerally central, minor Ibutlsrlbstantial part .of the area of the floating roof; comprising an outer, upstanding, rigid, compression-resisting rim; a single,

circular, flexible .membrane deck, unreenforced which "the outer part of the-deck [is secured, and

said ideck comprising substantially the entire ,a'reacof ith'e floating roof inside :the rigid rim and forming a fiat, smooth solid of rotation all vertical cross-sectional contours of which substantially coincide with a continuous curve running outwardly-upwardly throughout the radial distance from the center to the periphery of the deck, with downward curvature over said generally central part and with upward curvature between said generally central part and said rim; and ballast weight means distributed over and limited to said generally central part and constituting a suificient part of the total weight of the floating roof for the purpose of immersing the entire underside of the roof in the stored liquid and cooperating with the stored liquid in shaping the membrane deck into said smooth 15 solid of rotation.

5. Apparatus according to claim 4, wherein said deck forms a flat, smooth solid of rotation all vertical cross-sectional contours of which substantially coincide with a continuous curve running outwardly-upwardly throughout the radial distance from the center to the periphery of the deck, with downward curvature over said generally central part, upward curvature over an intermediate part, and downward curvature ad- 10 jacent said rim.

REIGN C. U'LM.

No references cited.

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