Abstract:
The method of fabricating fire resistant tank apparatus for transportation and for installation above-ground to receive and dispense a liquid hydrocarbon or hydrocarbons, includes providing a metallic tank assembly having lightweight wall means defining inner wall means, intermediate wall means and outer wall means, and spacing the wall means to form primary space between the intermediate wall means and the inner wall means, and secondary space between the intermediate wall means and the outer wall means; providing access porting to a tank interior defined by the assembly; a bottom wall defined by the assembly located to support the assembly at an installation site; and providing thermal barrier material in one of the first and second spaces to effectively define a shell about the tank interior. In addition, fire resistant material may be applied to the outer side or sides of the outer walls and hardened to define a relatively lightweight shell enclosing the tank assembly. The method provides structure that resists severe heat invasion in the form of radiation, convection and conduction to maintain liquid hydrocarbon in the innermost tank isolated from such invasion, the structure also being bullet resistant.

Description:
This is a continuation, of application Ser. No. 514,544, filed Apr. 26, 1990, U.S. Pat. No. 5,038,056. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to tanks for flammable and combustible liquid, and more particularly concerns methods and means for making such tanks fire resistant in above-ground installation environments. 
     Tanks holding flammable or combustible liquids, such as new and used hydrocarbon products, if installed above ground, can be dangerous if not &#34;fireproofed&#34;, i.e., made &#34;fire resistant&#34;. For example, if the tanks leak flammable liquid, a fire danger will exist. Fire can weaken the lightweight tanks walls and lead to tank collapse and spillage of tank contents. Also, prior tanks were not, in general, bullet resistant. 
     In the past, such tanks were enclosed in concrete and transported to installation sites; however, the concrete is subject to cracking, which then can allow leakage to the exterior of flammable liquid leaking from the tank itself. Also, the concrete-enclosed tank is extremely heavy and difficult to transport. There is need for method and means to make such tanks fireproof and leak proof in such a way that a relatively lightweight unit is provided, for ease of transportation and installation, and subsequent safety. 
     SUMMARY OF THE INVENTION 
     It is a major object of the invention to provide an improved method of forming a tank assembly employing a thermal barrier or barriers between multiple tank walls, and meeting the above need. Basically, the method of the invention concerns forming of tank apparatus adapted for transportation for installation above-ground to receive and dispense a liquid hydrocarbon or hydrocarbons, and includes the following steps: 
     a) providing a metallic tank assembly having lightweight wall means defining inner walls means, intermediate wall means and outer wall means, and spacing the wall means to form primary space between the intermediate wall means and the inner walls means, and secondary space between the intermediate wall means and the outer wall means, 
     b) providing access porting to a tank interior defined by the assembly, 
     c) a bottom wall defined by the assembly located to support the assembly at an installation site, 
     d) and providing thermal barrier material in one of the first and second spaces to effectively define a shell about the tank interior. 
     As will be seen, the thermal barrier material may be filled into the second space, i.e., the space between the intermediate and outer walls of the assembly; and that barrier may be allowed to expand as a foam to enclose the tank interior the top, bottom and sides thereof. The first space closer to the liquids containing tank interior, may be maintained free of the barrier material. 
     Another object is to fabricate the inner wall means to define an inner tank forming the tank interior, and fabricating the intermediate wall means to define an intermediate tank extending about the inner tank; and also to fabricate the outer wall means to define an outer tank extending about the intermediate tank. 
     Yet another object is to provide the thermal barrier to include: 
     i) a per-formed block or blocks transmitting weight applied by the intermediate tank, 
     ii) a fill-in barrier extending about the block or blocks in the second space. 
     Also, fire-resistant material may be applied to an outer tank of the assembly defined by the outer wall means, with the thermal barrier means filling the space between the outer tank and an intermediate tank formed by the intermediate wall means. The fire-resistant material may be allowed to harden in situ to form a shell or shells, as will be explained. 
     Further, access porting may be provided at the top of the three wall tank assembly to enable access to the inner tank interior; the bottom wall of the inner tank may be supported by the bottom wall of the intermediate tank; and the latter may be supported by thermal barrier structure in the space between the bottom wall of the intermediate and the outer tanks. 
     These and other objects and advantages of the invention, as well as the details of an illustrative embodiment, will be more fully understood from the following specification and drawings, in which: 
    
    
     DRAWING DESCRIPTION 
     FIG. 1 is a perspective view of a metallic, three-wall tank assembly; 
     FIG. 2 is a fragmentary section showing multiple sub-shells of fire-resistant material applied to the outer tank of FIG. 1; 
     FIG. 3 is a side elevation showing the fireproofed tank supported in a shallow receptacle at an installation site; 
     FIG. 4 is a view of modified triple-hulled tank apparatus; and 
     FIG. 5 is an end view of the FIG. 4 apparatus. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows a tank assembly 210 having lightweight wall means defining inner wall means 211, intermediate wall means 214 and outer wall means 216. The inner wall means 211 typically forms an inner tank having a side wall or walls 211a, top wall 211b, and bottom wall 211c whereby an inner tank interior is formed at 212 for containing liquid hydrocarbon indicated at 213, or hydrocarbons, or the like. 
     The intermediate wall means typically form an intermediate tank having a side wall or walls 214a, a top wall 214b, and bottom wall 214c whereby the intermediate tank encloses the inner tank, and a first space or spacing 215 is formed between the inner and intermediate tanks. See space 215a, 215b and 215c. The outer wall means typically forms an outer tank having side wall or walls 216a, top wall 216b and bottom wall 216c whereby the outer tank encloses the intermediate tank, and a second space or spacing 217 is formed between the outer and intermediate tanks. See space 217a, 217b and 217c. 
     The three tanks may be cylindrical, or may have multiple flat, parallel side walls. Side walls 211a, 214a and 216a may be parallel, as shown; top walls 211b, 214b and 216b may be parallel, as shown; and hollow walls 211c, 214c and 216c may be parallel, as indicated. Such walls may consist of steel and be less than one inch thick, for lightweight tank construction enhancing portability, for installation above ground at different sites, as desired. Glass fiber walls, or reinforced walls, resin impregnated, are also contemplated. Typically, steel walls are used and are about 10 gauge (1/8 to 1/4 inch thick). The tank length may typically be about 5-20 feet. The walls are typically interconnected by welds at their junctions, and internal braces may be provided. The overall tank wall thickness is at least about two inches and is bullet (small caliber) resistant. 
     The weight of the inner tank and its liquid contents are transmitted to the intermediate tank, as via steel struts 219 in space 215c between bottom walls 211c and 214c. Such weight, together with the weight of the intermediate tank, is transmitted to the bottom wall 216c of the outer tank, as via thermal barrier blocks 220 assembled or positioned in second space 217c, as shown, when the tanks are being assembled. Side spacer struts may be provided, locally as at 208. After positioning of all three tanks as shown, expansible, thermal barrier material is injected, as via nozzle 244, into space 217a, 217b and 217c and may expand therein as foam, filling such space or spaces and including the intermediate tank. The barrier indicated at 221a, 221b and 221c fills the bottom space 217c about the thermal barrier (insulative) blocks 270, all such barrier means then blocking inwardly directed heat transmission to the intermediate steel tank. The barrier material cures in situ, after its injection and expansion. Usable thermal barrier materials include polyurethane foam, VERMICULITE, and the like. The final thermal barrier consists of the air and other gas in first space 215a, 215b and 215c, an prevents transmission to the contents of the inner tank of fire-generated heat which may for some reason have penetrated barrier foam 221a, 221b and 221c. 
     FIG. 1 also shows the provision of one or more pipe stubs 225 via which access may be gained to the tank assembly interior 212. As shown, the pipe 225 is connected to top walls 221b, 214b and 216b to extend through them, and above wall 211b. The pipe may be downwardly extended at 225b into the inner tank interior for remaining liquid from that interior, as well as filling liquid into that interior. One or more access ports may be provided to the spaces 215b, 217b, and to the interior space 212. Dipsticks may be inserted into the tank to measure the level of liquid hydrocarbon, i.e., flammable or combustible liquid (such as fuel) in the tank. Monitor means may be installed in the tank via one of the access ports to sense liquid level and transmit corresponding electrical signals to external apparatus that registers the liquid level for ready viewing. 
     Fire-resistant material is typically sprayed at 243, via a nozzle 242, onto the outermost tank walls 216a, 216b and 216c to form a first layer 250a which is allowed to harden or cure in situ. Then, if desired, a second nozzle, or the same nozzle, may be employed to spray the material onto layer 250a, forming a second layer 250b, also allowed to harden in situ. The combination of thus formed fire resistant sub-shells form a composite shell, leak resistant, fire resistant, and projectile resistant, typically having a thickness between 1/4 inch and 1 inch, an which chars when heated to elevated temperatures (1,000° F. to 2,000° F.) as by intense flames. 
     FIG. 2 shows a wire mesh 267 applied between layer or shells 250a and 250b for strengthening purposes. The application of fire-resistant material is preferably such as to coat the exposed pipe stub 225, and the supports 300 under the outer tank bottom wall 216c, as shown. An additional sub-shell of fire-resistant material may be used, as at 250c. 
     In order that the material 243 being sprayed on may cling to the upright metal walls without sagging out of position, and also to have optimum fireproofing effect, it typically has an epoxide resin base, and chars when exposed to flame. One example is the sprayable two component intumescent expoxy fireproofing system (CHARTEK) (liquid resin and hardener, mixed with methylene chloride, or 1,1,1-trichloroethane) supplied by Avco Specialty Materials, Lowell, Mass. 
     Further, prior to spraying the first layer 250a onto the outer tank walls, the latter are preferably sandblasted, and a primer coat applied to resist rusting. The primer coat may, for example, consist of polyamide epoxy resin, such as AMERON 71, SUBOX A8051, or VAL-CHEM 13-R-56, or ethyl silicate inorganic zinc (such as DIMETCOTE 6). 
     In FIG. 1, the tank assembly is supported by tank support 300 beneath bottom wall 216a and supported by exterior surface 301. The supports have lateral sides which are covered by the fire-resistant material, as at 250a&#39;. 
     Any fluid leaking from inner tank 211 via inner wall or walls 211a, 211b, 211c, or 211d passes first to space 215. Such leakage may be detected, as by a sensor 363 sensing volatile gases emitted, or liquids accumulating in space 215, as from a flammable hydrocarbon. The sensor is connected at 364 to an external monitoring device 365, as shown. 
     FIG. 3 shows a fireproof material coated tank, stub pipes, and supports, installed at a work site, in a basin 170 supported on the ground 171. The basin forms a collection zone 173 beneath the tank to collect any possible leakage of flammable liquid. A hood 176 may be provided over the tank and basin to prevent rainwater accumulation in the basin. 
     Properties of the &#34;CHARTEK&#34; fireproofing system or material are as follows: 
     
                       TABLE I______________________________________CHARTEKMECHANICAL PROPERTIES        ASTM        Ref-Property     erence   Value       Conditions______________________________________Tensile Strength        D638     2750 psi    Room Temp.                 19.0 × 10.sup.6 PAModulus               3.42 × 10.sup.5 psi                             Room Temp.                 2.36 × 10.sup.9 PACompressive Strength        D659     6342 psi    Room Temp.                 43.7 × 10.sup.6 PAModulus               1.89 × 10.sup.5 psi                             Room Temp.                 1.3 × 10.sup.9 PAImpact Strength        D256     0.42 ft lbs/in                             Room Temp.(unsupported,         0.22 J/cm   notchedunmeshed)             0.71 ft lbs/in                             Room Temp.                 0.38 J/cm   unnotchedFlexural Strength        D790     4290 psi    Room Temp.                 29.6 × 10.sup.6 PAModulus               3.32 × 10.sup.5 psi                             Room Temp.                 2.3 × 10.sup.9 PAHardness     Shore D  83          D ScaleBond Strength        D1002    1578 psi    Primed,                 10.9 × 10.sup.9 PA                             room temp.______________________________________ 
    
     
                                           TABLE II__________________________________________________________________________PHYSICAL PROPERTIES     ASTMProperty  Reference            Value          Conditions__________________________________________________________________________Density   D792   79 lbs/ft.sup.3                           After            1.27 g/cc      sprayingThermal   C177   2.10 BTU in/ft.sup.2 hr °F.                           At 68° F.Conductivity     0.302 W/m °C.                           At 20° C.            196 BTU in/ft.sup.2 hr °F.                           At 154° F.            0.283 W/m °C.                           At 68° C.Thermal Expansion     D696   20.5 × 10.sup.-6 in/in °F.                           From -70° F.With Mesh        36.9 × 10.sup.-6 cm/cm °C.                           (-57° C.) toThermal Expansion            36.4 × 10.sup.-6 in/in °F.                           150° F.Without Mesh     65.5 × 10.sup.-6 cm/cm °C.                           (66° C.)Specific Heat     Differential            0.33 BTU/lbm °F.                           At 86° F.     Scanning            1.38 j/Kg °C.                           At 30° C.     Calorimetry            0.23 BTU/lbm °F.                           At 500° F.            0.96 j/Kg °C.                           At 260° C.Oxygen    D2863  32IndexFlash Point     D92Component I      Over 200°  F. (93° C.)                           Open cupComponent II     Over 200° F. (93° C.)                           Open cupViscosityComponent I      285000 CPS     At 100° F.                           (37.8° C.)Component II     60000 CPS      At 100° F.                           (37.8° C.)Gas (Nitrogen) Permeability     D1434             ##STR1##      At 68° F., 1.51 Atm             ##STR2##      At 20° C., 1.53 BarWater Vapor     E96    1.013 × 10.sup.-3 gr/hr ft.sup.2                           At 73° F.                           (22.8° C.)Transmittance     Procedure B            4.07 × 10.sup.-1 g/hr m.sup.2                           and 50% RHPot Life         55 minutes     At 70° F.                           (21° C.)Gel Time         8 hours        At 60° F.                           (16° C.)            4 hours        At 80° F.                           (27° C.)Cure Time to     18 hours       At 60° F.Shore A of 85                   (16° C.)            8 hours        At 80° F.                           (27° C.)Color            GreyMaximum Service  150° F. ContinuousTemperature      (66° C.)                           Use__________________________________________________________________________ 
    
     FIGS. 4 and 5 show a multiple wall tank assembly 310 having steel wall means defining an inner tank 311, intermediate tank 314, and outer tank 316. Tanks 311 and 314 are cylindrical and horizontally elongated, having a common axis 320. They have concentric side walls 311a and 314a, parallel vertical end walls 311b and 314b at one end, and parallel vertical end walls 311c and 314c at their opposite ends. The two tanks 311 and 314 are spaced apart at 315a, 315b and 315c. Metal struts 321 in lower extent of space 315a support the inner tank and its contents on the side wall 314a of the intermediate tank. 
     The outer tank 316 is rectangular, not cylindrical, but is horizontally elongated in the direction of axis 320. It has a bottom steel wall 316a, elongated upright side walls 316b and 316c, upright ends walls 316d and 316e, and to wall 316f is tapered from level 316g to level 316h. The three tanks serve the same purposes and functions, as referenced in FIGS. 1 and 2. However, the two cylindrical tanks 311 and 314 are assembled as a unit into outer tank 316, as by lowering onto a saddle 324 formed as by thermal barrier material 370 (corresponding to blocks 270 in FIGS. 1 and 2) previously filled into the outer tank, cured, and forming a concave upper surface 370a to match the convex curvature of diameter D, of tank wall 314a. See FIG. 5. Subsequently, thermal barrier material is filled into space 317 between tanks 314 and 316 to fill that space at the sides and top of tank 314. Such added thermal barrier material is indicated at 371 in FIGS. 4 and 5. Such barrier material corresponds to that at 221a, 221b and 221c in FIGS. 1 and 2. At the top of tank 314 the thermal barrier material is thickened due to top wall taper at 316f. Fire-resistant material is added in layers at 350a and 350b, corresponding to sub-shells 250a and 250b in FIG. 1. 
     Equipment located at the top of the tank assembly is as shown, and includes 
     primary tank work vent 380 and elongated duct 380a connecting to 383. 
     secondary tank work vent 381 with duct 381a 
     tank gauge unit 382 accessing inner space 312, via duct 382a 
     vapor recovery duct 383 accessing space 312, via duct 383a 
     fluid product fill duct 384 accessing 312 
     fluid product spill drain duct 385 
     fluid spill container 386 associated with 385 
     product dispenser 387, and associated suction line 388 nd vapor return duct 389; see also pipe 387a through tank walls, and pipe 377a&#39; 
     monitor port 390 via which fluid leaking into open (unfilled) space 315 may be monitored, i.e., detected, as by a sensor 363 
     a liquid product return line 381b. 
     Tank supports appear at 399. 
     Space 15 in FIG. 4 and space 215 in FIG. 8 may contain, or be filled, with a non-oxidizable inert gas, such as N 2  for enhanced protection in case of leakage of hydrocarbon into the space. Also, the space 317 may contain a barrier layer, such as silica, adjacent side walls of outer tank 316, and which does not foam or bubble when heated to 1,200° F., for example. The assembly, as described, provides protection for the hydrocarbon contents such that up to 2,000° F. flame applied for a considerable period of time (1 to 2 hours) to the fire resistant outer shell 300 on the assembly will not result in heating of the hydrocarbon contents in space 312 (or space 212 in FIG. 1) above about 10% of ambient temperature. 
     Elongated duct 380a is usable as an additional reservoir for heat expanded tank (in space 302) if needed. 
     The thermal barrier material (in space 217, 220, 371, and 321) may for example consist of the following: Insta-Foam Products, Inc. two components (&#34;A&#34; - activator and &#34;B&#34; - resin) combinable system, further identified as follows: 
     
         ______________________________________IDENTIFICATION (A COMPONENT)Product:      &#34;A&#34; components for froth refill.Chemical Family:         Aromatic isocyanate with         halogenated hydrocarbonChemical Name:         Product is a mixture of polymeric         diphenylmethane diisocyanate (MDI),         dichlorodifluoromethane (R-12) and         nitrogen.Synonyms:     Urethane &#34;A&#34; component, iso,         isocyanate, activatorDOT Class:    Compressed gas N.O.S., non-         flammable gas UN 1956INGREDIENTS:             %4,4&#39; Diphenylmethane Diisocyanate (MDI)                    &lt;50CAS #101-68-8Higher oligomers of MDI  &lt;50CAS #9016-87-9Dichlorodifluoromethane (R-12)                    &lt;20CAS #75-71-8PHYSICAL DATA:Appearance:       Liquid and gasses under             pressure - frothy liquid upon             release from the tank.Color:            Dark brown to amber.Odor:             Mild fluorocarbon odor.Boiling Point:    R-12 is present as a liquified             gas and at one atmosphere             boils at -21.6° F. or -30° C.             MDI is present as a viscous             liquid and boils at 406° F.             (208° C.) at 5 mm Hg.Vapor Pressure:   Before the addition of             nitrogen, the vapor pressure             of the mixture is about 2700             mm Hg.Vapor Density (Air = 1):             8.5 (MDI)Solubility in Water:             Reacts slowly with water to             liberate carbon dioxide.Specific Gravity  1.3(Water = 1):% Volatile by Weight:             Less than 20%.IDENTIFICATION (B COMPONENT)Product:       &#34;B&#34; Components for froth          refill (densities 1.5 pcf          through 4.0 pcf)Chemical Family:          Urethane ResinChemical Name: Product is a mixture of          polyols, urethane catalysts,          silicone surfactant,          fluorocarbons (R-11 and R-12),          flame retardants, and          nitrogen.Synonyms:      Urethane &#34;B&#34; Component, ResinDOT Class:     Compressed gas N.O.S., non-          flammable gas UN 1956.INGREDIENTS:          %Polyol                &lt;70Silicone Surfactant    &lt;2Flame Retardants      &lt;30Catalyst              &lt;10Trichlorofluoromethane (R-11)                 &lt;30(CAS #73-69-4)Dichlorodifluoromethane (R-12)                 &lt;15(CAS #75-71-8)PHYSICAL DATA:Appearance:      Liquid and gasses under            pressure - frothy liquid upon            release from the tank.Color:           Brown to light yellow.Odor:            Mild fluorocarbon odor.Boiling Point:   R-12 is present as a liquified            gas and at one atmosphere            boils at -21.6° F. or -30° C.Vapor Pressure:  Before the addition of            nitrogen, the vapor pressure            of the mixture is about 2500            mm Hg.Vapor density (Air = 1):            Greater than 1 (fluorocarbon).Solubility in Water:            Partly soluble; does not            react.Specific Gravity 1.2(Water = 1):% Volatile by Weight:            Less than 35.______________________________________