Note: Descriptions are shown in the official language in which they were submitted.
11365-3CA/C7
STORAGE VAULT AND METHOD
There is a continuing interest in the safe
containment of liquids, particularly gasoline and other
fuels, because of the vast amount of fuel presently
stored throughout the country. It has become increas-
ingly apparent that underground storage tanks can anddo leak, thus causing serious ~hort-term and long-term
problems. Therefore~ many localities have chosen to
examine all underground tanks, mostly fuel storage tanks,
to determine if the tanks are leaking. It is an expen-
sive process to inspect the tanks and test the earthsurrounding the tanks for indications of leakage. Repair
or replacement of tanks which are shown to be leaking
increases the cost a great deal further.
To aid the detection and prevention of leaks,
double wall (dual containment) tanks have been used for
both underground and above ground storage. The space
between the two walls of the tanks is monitored for
leakage. When used underground, monitors can be used
to sense both water seepage in and stored liguid seepage
out. If a leak iæ detected, the tank can be drained
and abandoned, dug up and removed, or repaired in place.
These options are all quite expensive. If the contami-
nated soil surrounding the leaking tank must be removed,
the expense increases dramatically. However, conventional
double wall tanks are quite expensive and are not pres-
ently able to meet fire code standards for above-ground
storage of flammable liquids. Therefore, even when
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dual containment tanks are used, flammable llquid is most
often stored in below-ground tanks.
Creating a concrete encased hollow tank is not
without problems. One conventional method of doing
so is to form an open-top hollow shell, place the tank within
the hollow shell and then pour the top. However, this
process creates cold joints which are possible sources of
leaks and weak points in the structure. Therefore, a
homogenous concrete shell, which would eliminate cold joints,
would be preferable. Entombing a hollow tank in fluid
concrete is hindered, if not prevented by the fact that the
hollow tank has a tendency to bob up or float within the
fluid concrete. Although the tank could be filled with water
to give it neutral buoyancy, this solution causes other
problems, including difficulties arising from trying to
remove all the water from the tank after the concrete has
set.
The present invention is directed to a trans-
portable, earthquake-resistant storage vault suitable for
storing flammable liquid above ground while providing dual
containment and the ability to monitor leakage through the
primary (inner) containment vessel.
The present invention provides a dual containment
liquid storage vault comprising:
an inner tank for containing the liquid;
a liquid impervious outer tank containing the inner
tank and including a bottom and a space between the outer and
inner tanks, the space including a collection region; and
a spacer layer in the space between the outer and
inner tanks, the spacer layer being liquefiable upon contact
with the liquid so that any leak of the liquid through the
inner tank will allow the liquid to collect at the collection
region to permit monitoring for leaks.
The present invention also provides a method for
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making a liquid storaqe vault for containing a liquid
hydrocarbon comprising the following steps:
choosing a spacer material which liquifies upon
contact with the liquid hydrocarbon;
covering at least a substantial portion of an inner
container with the spacer material; and
totally encasing the inner container and spacer
material within a concrete outer container, the outer
container including a liquid barrier.
In one embodiment the storage vault is created by
wrapping the combination inner tank and spacer layer with a
large sheet of polyethvlene. The edges of the liner are
gathered at the top of the tank so that any leaks from the
inner tank are contained by the liner. The spacer layer
encased, polyethylene llner wrapped, inner tank is then
entombed within a layer of concrete, preferably reinforced
concrete.
The outer tank preferably includes bottom supports.
The bottom supports lift the tank a few inches above the
support surface on which the tank rests to provide a visual
inspection region between the bottom of the outer tank and
the support surface so the user can visually monitor for
leaks from the vault.
The spacer layer may be chosen so that if the
liquid stored within the inner tank contacts the spacer
layer. the spacer layer dissolves or "melts" thus permitting
the leaked liquid to gather within a liquid collection region
between the inner tank and the liner. A leak detection tube
is used between the inner tank and liner to permit monitoring
of the liquid collection
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region between the tube. This arrangement provides for
maximum thermal insulation without sacrificing the abil-
ity to monitor for leaks. The spacer layer, being a
good thermal insulator, provides further protection for
the contents of the inner tank during fires. The added
insulation also helps moderate the temperature swings
of the liquid within the inner tank which aids the con-
trol of atmosphere pollution, as well as reducing safety
risks., Since no air space needs to be provided between
the inner and outer tanks for leak detection, pouring
the concrete around the combination of the inner tank,
spacer layer and liner is much simpler.
The use of reinforced concrete as the outer
tank provides several advantages. The concrete provides
a protective physical barrier for the inner tank, to
protect the inner tank from physical damage, at a reason-
able cost. The concrete outer tank also serves as an
effective thermal barrier. By using an Underwriters
Laboratories approved inner tank and the reinforced
concrete outer tank, an above-ground storage vault suit-
able for use with flammable liquids is achieved.
The invention is transportable and can be
used above ground to store flammable liquids. This
allows the storage vault to be especially suited for
temporary use at construction sites. The costs associ-
ated with burying tanks underground are also eliminated
with the present invention.
If desired, multiple storage vaults can be
used and connected in parallel or in series according
to the use requirements. Also, two or more inner tanks
can be placed within a single outer tank.
Preferably the storage vault has a flat bottom.
Unlike many prior art storage containers. which are
spherical or cylindrical and must be supported on a
stand, the invention needs no separate support stand.
The invention is extremely stable and thus is quite
resistant to damage from earthquakes.
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With the present invention A flamm~ble liquid
can be stored safely above ground. This removes the
tank from local regulations and codes dealing with mon-
itoring below-ground storage tanks. The present inven-
tion still permits the user to effectively monitor forleaks before any contamination to the surrounding earth
occurs. The ability to monitor the region between the
primary and secondary containment vessels and the pro-
vision of skids or supports on the bottom of the storage
vault so that the region beneath the outer tank can be
visually inspected, provides a double measure of protec-
tion against damage to the environment.
The invention permits a user to store flamma-
ble fuels above ground while meeting environmental and
safety requirements at a cost much less than comparable
buried storage tanks.
Other features and advantages of the invention
will appear from the following description in which the
preferred embodiments have been set forth in detail in
conjunction with the accompanied drawings.
Fig. 1 is a side cross-sectional view showing
a vault made according to the present invention.
Fig. 2 is an exploded cross-sectional view
taken along line 2-2 of Fig. 1.
Fig. 3 is a schematic illustration showing a
method for making the vault of Fig. 1.
Fig. 4 shows the inner tank of Figs. 1-3 within
the form assembly of Fig. 3.
Fig. 5 illustrates the internal reinforcing
members of the inner tank of Fig. 4 allowing the tank
to be used as a pressure vessel.
Referring now to Figs 1 and 2, a vault 2 is
shown to include a steel inner tank 4 surrounded by a
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spacer layer 6 of polystyrene. Inner tank 4 and spacer
layer 6 are entombed or encased within an outer tank 8.
Outer tank 8 includes a concrete layer 10 strengthened
by rebar 12, and a liquid impervious liner 14, prefera-
bly by a sheet of polyurethane film. Conventional filland vent pipes 16 extend from inner tank 4. A leak
detector tube 20 is positioned between inner tank 4 and
liner 14 and terminates at a liquid collection region
22. T~lbe 20 permits leaks from inner tank 4 to be mon-
itored as the leaking liquid collects within region 22.
Spacer layer 6 performs a dual function.Spacer layer 6 is a good thermal insulator so to insulate
the contents of inner tank 4 from external heat sources,
such as forest fires. In addition, spacer layer 6 helps
keep the contents of inner tank 4 at a more uniform
temperature than would otherwise exist. This helps
reduce vapor pressures within inner tank 4 making the
storage of liquids safer and reducing the potential for
vapor leaks to the atmosphere. In addition, spacer
layer 6 is chosen so that it melts or liquifies when
the liquid within inner tank 4 contacts the material of
the spacer layer. Typically, inner tank 4 will hold a
liquid hydrocarbon fuel, such as gasoline or diesel
fuel. By choosing a spacer layer 6 made of polystyrene,
if the liquid within tank 4 leaks through and contacts
spacer layer 6, polystyrene spacer layer 6 melts or
dissolves thus creating an open region between inner
tank 4 and outer tank 8 permitting the leaked hydrocarbon
to collect at liquid collection region 22. This permits
the leak to be quickly noticed througll leak detector
tube 20 using conventional methods.
As a further aid to detection of leaks, outer
tank 8 includes bottom supports 24 which raise the bottom
26 of vault 2 above the support surface 28 to create an
inspection region 30 between bottom 26 and support sur-
face 28. If desired support sllrface 28 can be covered
with a sheet or layer to aid visual inspection of leaks.
Turning now also to Fig. 3~ a simplified view
of the method for making vault 2 is shown. First, an
appropriate inner tank 4 is selected and has a number
of polystyrene panels 32 secured to the outer surface
34 of ilmer tank 4, typically by an adhesive. A large
sheet 36 of a liquid impervious material, such as poly-
ethylene film, is wrapped around the spacer layer encased
inner tank. The edges 38 of sheet 36 are gathered over
the top 40 of inner tank 4 so to create a second liquid
barrier.
A concrete form assembly 42 is used to entomb
the inner tank 4, spacer layer 6, liner 14 combination.
Form assembly 42 includes a base plate 44, having a
pair of openings 46, used to form bottom supports 24,
and two L-shaped wall forms 48, 50. Wall forms 48, 50
constitute a sidewall form 51. After assembly of base
plate 44 and wall forms 48, 50, a rebar cage 52 is placed
within an enclosure 54 defined by wall forms 48, 50 and
base plate 44. A layer 56 of concrete is then poured
within enclosure 54 to cover base plate 44. The combi-
nation 58 of inner tank 4, spacer layer 6 and sheet 36,
which creates liner 14, is then positioned within en-
closure 54 on top of the still wet layer 56 of concrete.
Additional concrete is then placed within the region
60, see Fig. 4, ~etween combination 58 and wall forms
48, 50 sufficient to cover combination 50 and be gen-
erally level with top edge 62 of sidewall form 51. The
specific construction of form assembly 42 will now be
discussed with reference -to Fig. 4, in particular the
structure for keeping combination 58 from bobbing up
out of the fluid concrete.
Form assembly 42, in addition to wall forms
48, 50 and base plate 44, includes a pair of form clamp
assemblies 64 at opposite corners 66, 68 of sidewall
form 51, a lateral positioning assembly 70 adjacent
base plate 44 and a pair of hold-down assemblies 72
which keep inner tank 4 from floating within the con-
crete while it is fluid.
Clamp assemblies 64 each include an L--bracket
73~ welded to sidewall form 51, and a chain 74, secured
at one end to L-bracket 73 by an adjustment bolt 76.
Chain 74 has a hook 78 at the other end which engages
the corner of the adjacent wall form 48 or 50. Chain
74 is tightened using a chain binder 80 which allows
the user to easily apply a strong clamping load on the
two wall forms 48, 50. Adjustmellt bolt 76 can be used
to pro~ide any necessary fine adjustment to the tension
in chain 74. It has been found that use of two L-shaped
wall forms 48, 50 and four form clamp assemblies 64
allow wall form 50 to be easily but securely fastened
together while ensuring the proper, in this rectangular.
shape is maintained.
Lateral positioning assemblies 70 each include
a jack block 82 welded to base plate 44 at a position
spaced apart from wall forms 48, 50. A hydraulic jack
84 is mounted between each jack block 82 and the oppos-
ing side of wall forms 48, 50. Applying sufficient
20 force on wall forms 48, 50 through the use of jacks 84
positions sidewall form 51 on base plate 44 and keeps
the lower ends of sidewall form 51 from moving laterally
outwardly due to the pressure of the concrete while it
is still fluid.
~ach hold-down assembly 72 includes an elongate
hold-down bar 86 having chamfered ends 88 guided between
vertical guide plates 90. Guide plates 90 are mounted
to wall forms 48, 50 and extend above top edge 62.
Hold-down bar 86 has a pair of downwardly extending
hold-down tubes 92 depending from its bottom surface 94
and a strong bacX 96 mounted centrally above the top
surface 102 of hold-down bar 86. Strong back 96 has an
arcuate guide surface 98 and a pair of vertical guide
plates 100. Hold-down assembly 72 includes a chain 104
having each end 106 secured to an anchor point 108 on
jack block 82. Chain 104 passes from the jack block 82
on one side of form assembly 42, between vertical ~uides
90~ across chamered ends 88, over curved surface 98 of
strong back 96 and down past the chamfered ends of hold-
down bar 86 on the other si.de. Hold-down assembly 72,
also includes a chain ratchet 110. Chain ratchet 110
is used to shorten the effective of length of chain 104
thus forcing tubes 92 against the top 112 of inner tank
4.
Guide rings 114, each having an internal di-
ameter slightly larger than the external diameter of
tubes 92~ are welded to top 112 at positions chosen to
engage the lower ends of tubes 92. Once so engaged,
lateral, as well as upward, movement of inner tank 4
within enclosure 54 is substantially eliminated.
Strong back 96 is used to strengthen hold-down
assembly 72. Strong back 96 keeps hold-down bar 86
from bowing upwardly due to the upward force on the
hold-down bar caused by tank 4 attempting to float when
surrounded by fluid concrete.
Turning now to Fig. 5, an inner tank 4 is
shown to include U-channel reinforcing members 130 welded
to the inside surface 132 of inner tank 4 so that inner
tank 4 may be used as a pressure vessel. Reinforcing
members 130 form a number of hoops 134 circumscribing
the interior of tank 4 . The ends 136 of inner tank 4
have vertically extending reinforcing members 130 mounted
along their interior surfaces as well. Pairs of reinforc-
ing members 130 are placed back -to back at positions
138 along top 112 of inner tank 4 and at positions 140
along the bottom 142 of inner tank 4 . This provides
extra strength along the central portion of tank 4 . A
pair of lifting brackets 144 are welded to top 112 of
tank 4 adjacent positions 138 to facilitate moving
tank 4 .
A vault 2 made with an inner tank 4 can be
used as a vacuum storage vessel to safely handle waste
motor oil or crank case motor oil. The vault incorpo-
rating reinforced inner tank 4 could have a vacuum
continuously applied to the inner interior of inner
tank 4 . A hose (not shown) would then be used to con-
nect inner tank 4 to the oil, or other liquid, to be
disposed of. The waste oil .so collected could then
periodically be removed from the vault through the use
of, for example, a mobile vacuum tank truck which can
suck the waste oil directly out of the inner tank 4
and into the mobile tank. This would permit gasoline
servic~ stations~ auto dealers, lube and oil change
centers, among others, to safely and conveniently store
the waste oil and grease in a safe, cost-effective man-
ner. Even without creating a vacuum in the interior of
a vault 2, vault 2 would still be useful for safely and
inexpensively storing such waste oil, waste grease and
other flammable materials, by pumping or pouring the
waste material directly into the vault.
To use form assembly 42, base plate 44 is
positioned on a, preferably, level support surface.
Wall forms 48, 50 are positioned on base plate 44 and
are fastened to one another by form clamp assemblies 64
at each corner 66, 68. Hydraulic jacks 84 are then
operated to properly position sidewall form 51 on base
plate 44 and keep the bottom of the sidewalls from kick-
ing out due to the pressure of the fluid concrete.
~5 Rebar cage 52 is then placed within enclosure 54 and a
layer 56 of concrete is poured into enclosure 54 to
create bottom 26 of outer tank 8. Combination 58, see
Fig. 3, is then lowered into enclosure 54 until it rests
on layer 56 of concrete.
Hold-down bars 86 are then positioned over
enclosure 54 and lower ends of tubes 92 are positioned
within rings 114. Chains 104 are then placed over hold-
down bar 86 and fastened to jack blocks 82 at anchor
points 108. C~lain ratchets 110 are used to tighten
chains 104 sufficiently to place an appropriate force
on hold-down bars 86. Concrete is then poured into
enclosure 54 to entomb combination 58, with the exception
of various f i ll and vent pipes 16 extending up through
concrete outer tank 8. Note that layer 56 of concrete
is still wet when the subsequent pour of concrete is
made. This ensures a homogenous concrete layer 10 with
no cold joints. Sidewall form 51 is then vibrated to
settle the aggregate in the concrete. The top surface
120 of outer tank 8 is smoothed. Shear pins 122 can be
used to keep hold-down bars 86 from moving upwardly
past u~per holes 124 in vertical guides 90.
Once the concrete has set sufficiently, chain
ratchets 110 are actuated to loosen chains 104, shear
pins 122 are removed from holes 124 and hold-down bars
86 are lifted upwardly to remove tubes 92 from the layer
of concrete covering top 112 of inner tank 4. The holes
left by removal of tubes 92 are filled with fresh con-
crete. After the concrete has cured sufficiently, side-
wall form 51 is removed from vault 2 and vault 2 is
separated from base plate 44.
Modification and variation can be made to the
disclosed embodiments without departing from the subject
of the invention as defined by the following claims.
If desired, non-flammable liquids can be stored in vault
2. Although it is preferred to include rebar cage 52
as a part of outer tank 8, one need not necessarily do
so. Inner tank 4, although in the preferred embodiment
made of steel, could be made of other suitable material
according to the particular liquid being contained and
the environment. It is preferred that vault 2 have a
flat bottom for stability. However, other shapes are
also possible. Vertical force can be applied to inner
tank 4 during curing of the concrete in ways not shown.
~or example, tubes 92 could be replaced by I-beams per-
manently mounted to inner tank 4 and left within con-
crete top 126. Also, by appropriately positioning fill
and vent pipes 16, the tops of these pipes may be used
to apply the necessary vertical force on inner tank 4
to keep the inner tank from floating before the concrete
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has set. One or both of chain binders 80 and chain
ratchets 110 may be replaced by other suitable ti~hten-
in~ devices, such as hydraulic push-pull jacks.
