US1594487A - Tank cover - Google Patents

Description

Aug. 3 1926.

L. A. BALDWIN TANK COVER Aug. 3 1926.

L. A. BALDWINl 1925 I 2 Smeets-Sheet Patented Aug. 3, 1926.

UNITED STATES PATENT OFFICE.

LESLIE A. BALDWIN, 0F ST. LOUIS, MISSOURI, ASSIG'NOR TO JOHNSJIANVILLE, CORPORATED, OF NEW YORK, N. Y., A CORPORATION 0F NEW YORK.

TANK COVER.

Application filed November 16, 1923. Serial No. 675,140.

This invention relates -to tank covers comprising insulating materials and suitable for the roofs of out-of-door storage tanks for volatile liquids or lowpressure gases, or both, such as petroleum and refinery-products tanks.

Liquids of the kind referred to when stored in metallic tanks of usual types are subject to evaporation losses of serious volume selectively adeeting the most valuable constituents of materials stored, especially during such times as the tanks are subjected to Wide daily ranges of temperature, to heavy Winds, or to excessive mean temperatures for considerable periods. The losses result from induced evaporation due to permitted changes in the surface temperature of the liquid and the temperature ofthe vapors in the space above the stored liquid,

andV to convection and escape of the vapors; the freed vapors cause undue fire risks and odor nuisances.

The diurnal fluctuation of temperature in the vapor spaces of tanks of the kind referred to provided with the usual covers on sunny days has been found to be of the order of to 60 Fahrenheit, with corresponding fluctuation of temperature of the surface of the liquid (petroleum) of the order of 10 to 20 F., Whereas the liquid at slx inches to a foot beneath the surface remains at a temperature fairly constant, having a diurnal fluctuation of the order of 1 to 3 F. only. A consequence of the rising' and falling surface and vapor space temperatures is of course expansion and contraction of the collected vapors, With escape of the vapors through the necessary vent-pipes and the crevices of the cover during expansion, and the intrusion of unsaturated air, capable of taking up more vapor, during contraction. This phenomenon is commonly referred to as breathing in the oil industry. Typical cases of these losses have been measured and computed by competent authority to reach 1500 barrels annually, in the case 0f a 55,000 barrel tank holding midcontinent crude, with corresponding losses amounting annually to 3,500 barrels in the case of 58 BaumeJ motor fuel, with some recession from these values when tank-covers of certain types of metal or wood and metal construction, newly installed, are employed the best practice then resulting in annuai losses from average mid-continent crude of about 400 barrels and of about 750 barrels for motor-fuel. Losses as low as these minima are sel-dom attained in actual practice, the expansion ofwalls and cover and the filling and emptying stresses on and motions of the tank walls resulting inevitabl in crevices into and from which the windy-V draft of air and vapor is substantial and costly. The storage losses in practice, especially of the gasoline fraction, maybe assumed to average from three to four per centum.

Anobject of this invention is to provide for minimizing or preventing losses of stored liquids by evaporation or the ex lansion and escape of gases or vapors w ich may accumulate in the vapor space over the surface of such liquids, and for this urpose the invention provides a genus of eat refleeting and heat insulating gas-tight covers adapted for use with liquid storage tanks 'to cause the internal temperature of the contents of the tank to be maintained relatively constant and to prevent escape of vapors.

For example, the invention is exemplified by and will be described as applied to gastight heat-insulating roofand cover constructions adapted to enclose the tops of the storage tanks or chambers to be protected. to extend over the connections between'the roof and the side -wall of the storage tank, and to be joined to the side, walls of the tank by a gas-tight expansible joint, and having features causing all joints and connections to be gas-tight and weather roof, enabling the heat insulation to be ma e impervious to gases and liquids, and permitting the outer surface, if desired, to reflect radiantgheat, lwhile preventing the substan tial transmission of heat or passage of -gases through the cover. The new cover is applicable to existing tank roof constructions.

In the instances of embodiments of the in vention adapted for use with oil storage tanks illustrated in the accompanying draw- .ings

Fig. 1 is a vertical section representing a typical. application of the invention to an oil storage tank having a Wooden roof;

free joint between roof and walls.

Fig. 2 is a similar vertical section. representing a modification applied to ancil tank having a sheet or plate metal roof; and

Fig. 3 is a detail vertical section at one of the joints between the adjacent sheets of insulation according to the construction of Fi 2.

n the drawin Fig. 1 shows at 1 the side wall of an oil-tank of the usual cylindrical riveted-sheet metal type upon which the ordinary wooden roof 2 1s supported :by wood rafters or steel beams 3, in the common way. Attached to, and projecting over the edgeof said roof are fastened by means of broad-headed nails a sheets 6 of suitable material, for example, compressed libre board, metal, wood, or asbestos-wood, having their outer edges bent downwardly into a curved portion 7 These sheets merely rest upon or 'extend just above the rimstiening metallic cornice 1* of tank wall 1, and here provide the necessary slidingTgr e sheets 7 also support the overhanging flexible eaves sealing extension of the roo cover and prevent its becoming abraded or too sharp y iexed at the edge of the roof. Joints at this place have heretofore provided a lar e leakage space, whatever type of cover may ave been employed for the remainder of the wooden deck 2.

According to the present invention, a cover of s-tight and weather-proof materials having a flexible and slack eaves-section'to serve as an expansion joint is built in place about the top of the tank and on the deck 2. Preferred materials for this cover are l f laminated fabrics whose rincipal thickness is comprised of a non-con uctin felt or mat of suitable fibrous texture, suc as one or more sheets of a felt or bat of the well-known heat insulation materials, for example felted cattle-hair, asbestos, wood-fibre, vegetable fibre, mineral wool, cork, wool,cotton, diatomaceous earth, marsh ass or other or mixed coarse libres, not ereinv claimed as new. The recommended material is a wellknown fabric made up of a felted mat of cattle-hair with or without admixtures, enclosed between strong paper covers. For the purposes of the present invention, one of these covers is an asphalt saturated paper and the'other cover is impre ated with sodium silicate in aqueous so ution, or with` any other satisfacto flexible gas-resisting impre ant, "to lill interstices and aid in rendermg the aggregatelaminated fabric impervious to gases. At the eaves this felted layer or layers is exteriorly protected and rendered impervious to gases and water by one or more layers of impervious canvasasphalt, asbestos-asphalt, or other flexible sheet 9, lpreferably com rising a li ht canvas, clot of asbestos res, a flex-i' le fabric or an asbestos or other felt impregnated .by a layer of weather-resisting wall 1 of the tan with melted hard asphalt, fastened to the outside layer of insulating fabric orfelt by suitable fusible cement, preferably consisting of the same asphalt as the impregnant. This layer may in turn be rotected by a layer 29 comprising an asphalntic binder and mineral in edients, such as asbestos and any suitable fi ler, for example, sand, calcined or uncalcined powdered stone lime, ground calcareous matter or the like;A ut in the preferred construction, the greater part of the exposed surface of the roof, for example, the roof slope above line A, is finished by one or more lagers of impervious water-laid asbestos-asp alt sheets 32, (or other asphalted sheets, such as rag-felt sheets) followed white material 37, conveniently applied y attaching by suitable fusible cement, preferably asphalt to the upper-surfaces in overlapping relation, sheets of water-laid asbestos felt impregnated'with asphalt on their under sides Iiil order to construct this type of cover, the recommended procedure, referring to Fig. l, is first to apply about the top of the .in a line substantiall horizontal, a layer 11 of suitable cementitious adhesive, such as melted asphalt, into and by which the top'edge only of a strip of the impervious canvas asphalt, asbestos- .asphalt or other flexible fabric 9 is firmlyl embedded, any vertical seams being lapped and cemented. The strip 9 now hangs down from its horizontal upper edge and is washed over with a coating of melted asphalt 8, upon which is applied a layer 12 of the insulation fabric, which is 1n turn brushedwith asphalt, and a wider strip for a layer 13 of the insulation felt applied.

The belt of laminated material thus built about the cylindrical wall l is now reinforced to plrevent breaka e of its gas-tight contact wit the wall 1 y motions of the tank, wind or internal pressure. A preferred way of doing this is to encircle the whole tank and the applied fabric with a suitable compression binding, such as a metallic strip,

or, as shown, two or more runs of strong -per edge of the felt layer 19 with any suitable cement, such as silicate of soda. This keeps gases or oil out of the edges 14 of the 'cover material.

The eaves-plates 7 having been applied, the free lower edges of strips 9, 12 and 13 are now brought up over the edge, and severilo old the applied l ally fastened. The wider strip 13, which is preferably tapered in thickness to its edge 16, may be fastened to the wood deck with flat barbed nails 21 driven through flat metal caps 22. The edge 17 of the sheet 12 is similarly fastened, and forms a seat for the abutting edge of the next strip 18 of the felt material. The entire roof may be covered with two or more layers of the felt insula tion material laid with broken joints, but in the usual case two layers at the eaves and one on the roof slope are suliicient. The insulation sheets 13, 18 etc. may be laid in an asphaltic cement if desired, but in the usual case this is not necessary, the outer layers of the roof providing a suiiiciently impervi ous structure.

rlhe outer layer 9 at the eaves is laid, preferably over the layer of insulating felt material 12 and over the ioint at' edge' 17, in a liberal coat 3l of hot asphaltic cement and nailed at 21. v

The roof slope to the break of the eaves at A is now covered with overlapped sheets of the water-laid asphalt impregnated asbestos fclts, rag felts or other rooting sheets 32, laid in hot asphalt and preferably nailed frequently to the substructure through caps 22; over this, in layers. 31 of melted asphalt or asphaltic cement, a further weather-proofing and heat insulating layer 37 of sheets or strips of asbestos felt, rag felt or other felted roong sheets, preferably alread. impregnated on its under face only with t e asphal- 2 tic impregnant, and preferably white on its exposed surface, is now laid to the line A,

joints in this being overlapped, as at 38.

.The cover is completed by applying a relatively thick layer 29 of the plastic asphaltic cement, from the line A to the down-hang of the eaves, from which rain water dri s clear of the tank from the curved portion which ilexes slightly to accommodate the motions of the tank shell relative to its roof and cover.

Referring now to Fig. 2, tanks having metal roof-decks 43 may be protected according tothe same principles, with variation of the mode of attachment of ,the protective cover. An impervious strip or sheet 47, preferably of the canvasfasphalt, the asbestes-asphalt or other flexible' fabric material, is first fastened to the cylindrical wall 41 near the top by a belt of asphaltic cement 44 applied to the wall, and is then coated with a layer 46 of cement or melted asphalt, into which the lower edge of a relatively stiif sheet 49 of impregnatedasbestos felts,.asphalt saturated rag felts or a combination of both or other suitable material is embedded. Sheet 49 may be a flashing felt of well-known construction; any flexible protective material capable of supporting the remainder ofthe eaves section of the protective roof against the cutting and rubl bin stresses of the tank edges is suitable; a

after the impregnated strip 47 is attached at 44. A strip 51 of the above described in- Sula-ting felt sheet, preferably having' an edge tapered at 54, is now applied in a layer of hot asphalt 'at 52 and at 52, this strip beingof sufficient width to have its edge reach the illustrated position when bent over Vthe sheets 49. Upon the strip 51, in a layer of hot asphalt, a second strip of insulation felt 53 is now laid; and a binding 'wire 56 may now be wrapped about the tank to hold the lower edges of the insulation felt and form a guide, about which the impervious-- fabric strip 47 is now turned up andy over into a layer of hot asphalt 61. The layer 61 may extend over the down-hung part of sheet 53, but preferably the cement layer 43 on the now inner face of strip 47 is supple*- mented by a cementitious coat on this downhung art of the sheet 53, the hot asphalt layer eginning under the circumferential line B.

The strip 47 is wide enough to overlap the inward edge of the strip 43, and is sharply bent downwardly and then inwardly at 62 for attachment directly to the deck 43 by a layer of asphalt 55, and thus provides a seat for the abutting edge of the next strip 57 of insulation felt. A

At each radial and circumferential joint of the strips of insulation -felt 57, it is preferred to attach thetupp'er edge of the outer strip in this manner, as shown in Fig. 3,V in which a narrow strip 65 of thecanvas' asphalt, asbestos asphalt or other flexible fabric material is shown as applied to the top of an outer or lower strip, and bent downward at 59 and inward at 56, to form a seat' for the lower or outer edge of a felt strip 57. All crevices in this construction are filled at 58 with the attaching asphalt or a cement.

From the circumferential line B the remainder of the cover is built up of asphalt proof cement 70, referably the same material above descri layer 29, Fig. 1.

To accommodate varying conditions of d or preferred for' the 115 impregnated asbestos felts, rag felts or other tank structure it will be understood that the constructions exemplified by those shown in Fig. 1 or Fig. 2 may be interchangeably resorted to in whole or in part, depending upon the structure of the tank, to construct covers for wood or steel deck tanks of different kinds.

It will be understood that the elements of the improved cover are sufficiently ductile and extensible to enable them to be applied to conform to the large circumferential circles of the tank top without difiiculty, but for small tanks, the materials employed may comprise sheets lapped frequently at radial joints to permit edges of the sheets to lie on chords of the circles defined by their assembled positions.

In each instance of the invention, the necessary hatches and vent pipes may be sealed around by the cover materials. or otherwise, in order to assure a vapor-tight heat-resisting construction. At least one vent pipe is necessarily left open to prevent any considerable linternal pressure from building up. .But with eflicient heat and wind insulation and sealing,`as herein provided, the large breathing or diurnal expansion losses and the wind-drift losses are so nearly prevented by prevention of rapid variation of the internal temperature and eicient sealing that the output ofvapor through the ventpipe is reduced to a mere seasonal loss,- during rises of the mean temperature, and such incidents as the loss of lvapor during filling of the tank. These gf losses are not serious in volume or frequency.

It will be observed that this invention-provides a sealing and insulation cover capable of being applied to all types of existing tanks and serving to cause the interior temperature to be maintainednearly constant under diurnal temperature changes, and capable of resisting the effects of relative movement of the parts of the tank `which have heretofore resulted in of vapors.

I claim v 1. The combination of a tank having a roof and a Wall with a flexible cover adapted to seal spaces between the tank roof and its wall comprising a heat insulation layer and laminas of paper resistant to the penetration of hydrocarbon vapors, and having a lamina of a water-proof heat-resistant fabric mterpenetrated by a continuous asphaltic inclusion.

2. A tank of the kind having a wall and a roof, and having a flexible cover ada ted to seal spaces between the tank roof an its wall comprising a heat insulation layer and laminas of paper resistant to the enetration of hydrocarbon vapors, and having a. lamina of a water-proof heat-resistant fabric interpenetrated by a continuous asphaltic inclusion, and a lamina having a Whlte exterior face.

3. A roof construction for tanks comprising a flexible cover adapted to seal spaces between the roof of a roofed tank and its wall comprising a heat insulation layer and lamin of paper resistant to the penetration of hydrocarbon vapors` and having a lamina of a water-proof heat-resistant fabric 'interpenetratedby a continuous asphaltic inclusion, and a lamina havin 1 a weather-resistant white exterior face o asbestos fibre.

4. A flexible cover adapted to seal spaces between a tank roof and its wall com rlsing a heat insulation layer and laminas o paper impregnated with a flexible saturant adapted to render-the paper resistant to the penetration of hydrocarbon vapors, and having alamina of a water-proof heatfresistant fabric interpenetrated by a continuous asphaltic inclusion. .V f

Signed by me at St. Louis Missouri this First day of November, 1923.

LESLIE A. BALDWIN.

leakage and loss

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