U.S. patent number RE34,203 [Application Number 07/639,914] was granted by the patent office on 1993-03-30 for double wall storage tank and method of making same.
Invention is credited to David T. Palazzo.
United States Patent |
RE34,203 |
Palazzo |
March 30, 1993 |
Double wall storage tank and method of making same
Abstract
A double wall tank for the storage of liquids is manufactured
from a rigid single wall inner tank by applying to at least a
portion of the exterior surface of the inner tank a release agent
for preventing bonding of a curable synthetic resin to the inner
tank exterior surface, applying over the inner tank exterior
surface and the release agent a substantially rigid outer sheath of
a curable synthetic resin that, when cured, is substantially fluid
tight, and breaking engagement between the inner tank exterior
surface and outer sheath.
Inventors: |
Palazzo; David T. (Tampa,
FL) |
Family
ID: |
27093429 |
Appl.
No.: |
07/639,914 |
Filed: |
January 10, 1991 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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105881 |
Oct 7, 1987 |
4780946 |
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105890 |
Oct 7, 1987 |
4780947 |
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43634 |
Apr 28, 1987 |
4744137 |
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884481 |
Jul 11, 1986 |
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775140 |
Sep 12, 1985 |
4640439 |
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818258 |
Jan 18, 1986 |
4644627 |
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Reissue of: |
194387 |
May 16, 1988 |
04817817 |
Apr 4, 1989 |
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Current U.S.
Class: |
220/62.19;
220/565 |
Current CPC
Class: |
B65D
90/028 (20130101); B65D 90/503 (20130101); B65D
90/029 (20130101) |
Current International
Class: |
B65D
90/02 (20060101); B65D 90/00 (20060101); B65D
90/50 (20060101); B65D 025/18 (); B65D
087/24 () |
Field of
Search: |
;220/445,453,457,469,420,455 ;29/455.1 ;73/49.2T |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Garbe; Stephen P.
Assistant Examiner: Castellano; S.
Attorney, Agent or Firm: Pettis & McDonald
Parent Case Text
RELATED APPLICATION
This application is a continuation-in-part eof applications Ser.
No. 105,881, U.S. Pat. No. 4,780,946 and Ser. No. 105,890, U.S.
Pat. No. 4,780,947 filed Oct. 7, 1987, which applications are a
continuations-in-part of application Ser. No. 043,634, filed Apr.
28, 1987, U.S. Pat. No. 4,744,137, which application is a division
of application Ser. No. 884,481, filed July 11, 1986, now
abandoned, which application is a continuation-in-part of
application Ser. No. 775,140, filed Sept. 12, 1985, and issued as
U.S. Pat. No. 4,640,439 and of application Ser. No. 818,258, filed
Jan. 18, 1986 and issued as U.S. Pat. No. 4,644,627, both entitled
Double Wall Storage Tank and Method of Making Same and filed in the
name of David T. Palazzo.
Claims
What is claimed is:
1. A method of manufacturing a double wall tank from a .Iadd.rigid
.Iaddend.single wall inner tank for storage of liquids, said inner
tank including a generally cylindrical sidewall and pair of end
walls, said method comprising;
applying to at least a portion of the exterior surface of said
rigid inner tank a release agent for substantially preventing
bonding of a curable synthetic resin to said inner tank exterior
surface portion;
applying over said inner tank exterior surface and said release
agent a substantially rigid outer sheath of .[.a.]. .Iadd.said
.Iaddend.curable synthetic resin that, when cured, is substantially
fluid tight; and
breaking engagement between said inner tank exterior surface and
said outer sheath, whereby is formed a double wall tank in which
said inner tank defines an inner wall and said outer sheath defines
an outer wall.
2. The method of claim 1 in which said step of breaking engagement
includes the step of applying between said inner tank exterior
surface and said outer sheath a fluid under pressure that is
sufficient to break, at least temporarily, engagement between said
inner tank exterior surface and the outer sheath.
3. The method of claim 2 in which said step of applying a fluid
under pressure includes the steps of connecting a fluid conduit to
said double wall tank such that a discharge opening of said conduit
is disposed within said outer sheath but outside said inner tank
exterior surface, and introducing a pressurized fluid to said
conduit to apply a positive fluid pressure between said inner tank
exterior surface and said outer sheath.
4. The method of claim 1 wherein said sheath comprises at least one
layer of fibrous material coated with .[.a.]. .Iadd.said
.Iaddend.curable resin which, upon curing, provides a coating which
is resistant to the passage of water or hydrocarbon liquid.
5. The method of claim 1 wherein said release agent is applied to
substantially the entire exterior surface of said inner tank.
6. The method of claim 1 wherein said outer sheath has a
configuration generally of a cylinder with closed ends, and wherein
said release agent is applied to said cylindrical sidewall, whereby
the release agent will serve to prevent bonding between the outer
surface of the cylindrical sidewall of the inner tank and the outer
sheath.
7. The method of claim 6 wherein .[.the.]. cylindrical sidewall
portions of said outer sheath overlying said inner tank cylindrical
sidewall are formed separately from .[.the.]. end portions of said
sheath overlying .[.the.]. closed end portions of said inner tank,
and wherein said sheath end portions are sealingly joined to said
sheath cylindrical .[.wall.]. .Iadd.sidewall .Iaddend.portions,
whereby is formed a continuous outer sheath overlying said inner
tank.
8. The method of claim 1 further comprising the step of forming an
aperture through said sheath and through a portion of a wall of
said inner tank, whereby is provided access to the interior of said
inner tank. .[.9. A double wall tank for storage of liquids
manufactured in accordance with
the method of claim 1..]. 10. A tank for storage of liquids
comprising;
a substantially rigid inner tank having a generally cylindrical
sidewall and a pair of end walls;
a substantially rigid and substantially fluid tight outer sheath
enclosing said inner tank and formed of a resin impregnated fibrous
material that is substantially fluid tight;
a release agent interposed between at least said inner tank
cylindrical sidewall and said outer sheath to prevent bonding
between said outer sheath and said .[.release agent coated.].
sidewall of said inner tank; and
means for applying between the exterior surface of said inner tank
and said outer sheath a fluid under a pressure that is sufficient
to break engagement between said outer sheath and the exterior
surface of said inner tank, whereby is formed a double wall tank in
which said inner tank exterior surface defines an inner wall and
said outer sheath defines an
outer wall. 11. The tank of claim 10 in which said means for
applying pressure includes a fluid conduit that extends through
said outer sheath and has a discharge opening that communicates
with the exterior surface of said inner tank and the interior
surface of said outer sheath.
Description
FIELD OF THE INVENTION
This invention relates to a double wall tank for the storage of
liquids and an improved method of making such a double wall storage
tank.
BACKGROUND OF THE INVENTION
Tanks for the storage of liquids have been constructed in a variety
of ways from a variety of materials. In one common application, the
underground storage of hydrocarbons, such as gasoline and other
petroleum products, the tanks have conventionally been fabricated
out of steel or fiberglass, most commonly with a single rigid wall.
In many applications this construction has proved reasonably
satisfactory, with such tanks functioning properly for many years
before requiring repair or replacement. However, the increasing age
of many of the tanks currently in place is beginning to present
serious environmental dangers. Many of the older steel tanks buried
underground have rusted and are beginning to leak, thus releasing
the petroleum materials into the ground where they may seep into
and pollute underground water supplies. While rustproof, some
fiberglass tanks have also exhibited leakage, causing the same
problems.
One of the primary problems with leaking storage tanks has been the
difficulty or inability to ascertain when or if such leaks are
occurring from a given tank. Because the excavation and removal of
such a storage tank, which may contain thousands of gallons of
fuel, is an expensive and difficult undertaking, such an operation
is difficult to justify unless there is some evidence of actual
leakage.
Because of the increasing potential danger of leaking storage
tanks, particularly in communities that utilize ground water for
public consumption, many municipalities have implemented or plan to
implement ordinances requiring the use of double wall storage tanks
underground and requiring replacement of existing single wall
tanks. While the installation of a conventional double wall tank in
a new facility entails no great difficulty and a generally
manageable increase in cost over a single wall tank, the burden of
complying with such ordinances by replacing existing sound, single
wall tanks with double wall tanks can be heavy. This burden has
promoted the search for methods of fabricating relatively
inexpensive double wall tanks. This burden has also given impetus
to the search for a method of remanufacturing existing single wall
tanks into a double wall assembly with means for detecting the
presence of any leaks into the space between the two walls.
A number of techniques have been disclosed for converting single
wall tanks into double wall tanks and providing such tanks with the
means for detecting the presence of leaks. Such methods are shown
for example in my U.S. Pat. Nos. 4,640,439, 4,644,627 and 4,655,367
as well as my copending applications Ser. Nos. 046,634, 105,881 and
105,890. Although these techniques provide for quite acceptable
double wall tanks they require the employment of a perforated
spacing material such as mesh, or alternatively, a molded spacing
material that must be constructed and applied to the inner tank.
The labor and time involved in constructing and installing these
spacing materials can be significant, and the need exists to reduce
even further the cost of producing such double wall tanks.
SUMMARY OF THE INVENTION
In view of the foregoing it is an object of the present invention
to provide an improved economical method of manufacturing a double
wall storage tank from a single wall tank by providing an outer
sheath enclosing the single wall tank.
It is a further object of this invention to provide such a method
in which at least a portion of the outer sheath of the tank is free
of engagement with the outer surface of such inner tank.
To achieve these and other objects that will become readily
apparent to those skilled in the art, this invention provides a
method of manufacturing a double wall tank for storage of liquids
from a single wall inner tank. The method includes the step of
applying to at least a portion of the exterior surface of the rigid
inner tank a release agent for substantially preventing bonding to
that inner tank exterior surface, applying over that inner tank
exterior surface and that release agent a substantial rigid outer
sheath of a curable synthetic resin that, when cured, is
substantially liquid-tight, and then breaking engagement between
the inner tank exterior surface and the outer sheath, whereby is
formed a double wall tank in which the inner tank defines an inner
wall and the outer sheath defines an outer wall.
In a preferred embodiment, the engagement of adhesion between the
outer sheath and the inner tank is broken by applying a fluid under
pressure between the inner surface of the outer sheath and the
exterior surface of the inner tank. This invention further provides
a double wall tank apparatus that includes an outer sheath applied
over the inner tank and includes means for applying a fluid under
pressure between the inner tank exterior surface and the outer
sheath sufficient to break any adhesion between the outer sheath
and the inner tank.
BRIEF DESCRIPTION OF THE DRAWINGS
Particularly preferred embodiments of the method and apparatus of
this invention will be described in detail below in connection with
the drawings in which:
FIG. 1 is a side elevational view, partially in section, of a tank
according to the present invention, illustrating various steps in
the fabricating process;
FIG. 2 is a fragmentary side sectional view of a portion of the
tank according to this invention and of an apparatus and technique
for breaking adhesion between the outer sheath and the inner
tanks.
FIG. 3 is a partial side sectional view, similar to the right hand
portion of FIG. 1, illustrating a different embodiment of the end
structure of the tank of this invention.
DESCRIPTION OF PREFERRED EMBODIMENT
A preferred embodiment of the apparatus of this invention is
illustrated in FIGS. 1 and 2. FIG. 1 is a side elevational view
illustrating the manner of making the completed tank assembly by
the application of the various materials to the storage tank.
While various forms and shapes of tanks may be utilized in practice
of this invention, the most common shape utilized for underground
storage is that of a cylinder, generally a right circular cylinder,
having closed end portions. For simplicity of illustration this
configuration of tank is utilized for illustrating the preferred
embodiment of the invention. Also, while virtually any construction
of the rigid inner tank, whether of metal or fiberglass or other
material, may be utilized in practicing this invention, one
preferred and readily available type of structure is a tank formed
of welded steel, having an appropriate corrosion resistant coating
on the liquid contacting surfaces. For purposes of illustration
such a steel tank will be described. It is also to be understood
that the tank to be used could be a newly fabricated tank, which
may or may not have any manhole opening cut in it, or it may be a
previously used tank removed from it prior underground installation
and cleaned for reuse with this invention.
To prepare an uncoated or a previously used steel tank, it is
preferred, but not required, to simplify subsequent steps by
attaching a spindle, as by welding, to the center of each tank head
or end portion, generally collinear with the axis of the tank. As
shown in FIG. 1, the spindles 4 and thus the inner tank 2 may then
be supported off the ground on conventional uprights 6. This
provides for rotation of the tank by an appropriate and
conventional rotary drive 7 for purposes to be set forth below.
Then it is desirable that the exterior surface of the tank be
conventionally sandblasted and coated with a rust inhibitive
material 8. This coating material 8 preferably may be a
conventional polyester resin incorporating a known paraffin-based
tack free additive known to those skilled in the art.
In the next step of the present invention a release agent, such as
that known in the industry as Partall, is applied to at least a
portion and preferably to the entire exterior surface of the inner
tank 2. Release agent 10 is applied to the inner tank 2 by
conventional techniques such as brushing or spraying as the tank is
rotated to provide preferably a substantially uniform coating over
the entire exterior surface of the inner tank 2, including the end
portions 3 of that inner tank.
After the release agent 10 has dried, the outer sheath of the tank
is applied. This outer sheath 12 may be fabricated in a number of
different ways. In this preferred embodiment the rigid outer sheath
12, and particularly the cylindrical sidewall portions 14 thereof,
are formed by bonding resin impregnated glass fiber matting over
the release agent 10 in a conventional manner. It has been found
convenient to lay sections of such glass fiber matting over the
release agent coated inner tank and then apply suitable and
well-known resins to that matting, although matting that is
preimpregnated with resin could be used with equal facility.
Likewise the application of resin and chopped glass fibers through
the "chopper gun" technique may also be used. While the thickness
of the outer sheath 12 may vary according to the severity of
conditions anticipated, it should be of sufficient thickness to
provide a substantial rigid sheath. It has been found that
one-quarter inch thickness of the cured, resin impregnated glass
fiber matting generally provides sufficient strength and rigidity
for the sheath 12.
To form end portions 16 of the sheath, the resin impregnated glass
fiber mat may simply be laid and wrapped around the tank end
portions, forming a continuous structure with the cylinder
sidewalls. If this technique is used, the release agent 10
preferably is continued over those end portions. This continuous
application of glass fiber material may be effected with the tank
still supported with spindles 4, or with those spindles cut off. If
the spindles are retained, they may be cut off at a later time and
a patch of appropriate resin impregnated glass fiber matting placed
over the hole left by the spindle. This continuous lay-up method of
forming the end portions 16 of the sheath 12 is illustrated in the
partial sectional view at the right hand end of FIG. 1.
In this invention it is desirable to break, at least temporarily,
the engagement between the exterior surface of the inner tank 2 and
the outer sheath 12 to provide for passage of liquids between the
exterior of tank 2 and the outer sheath. Accordingly, as shown in
FIG. 2, a suitable fitting or other means are provided for
introduction of a pressurized fluid P between the exterior surface
of the inner tank 2 and the outer sheath 14. Preferably this may be
accomplished by inclusion of structures, such as the fitting 20,
which may conveniently include a flange on one end and a female
thread, such as a pipe thread, on the other end. This fitting 20
may conveniently be placed or loosely held against the release
agent coated exterior surface of inner tank 2 prior to application
of the resin and glass fiber material making up outer sheath 12.
Then, as that outer sheath material is applied over the inner tank
2 and its release agent 10 and around the fitting 20, that fitting
will be firmly bonded in place by the outer sheath 12, as shown in
FIG. 2. Upon completion of the application of the sheath material
and curing of the curable resin that comprises that outer sheath
12, the fitting 20 may be firmly bonded in place.
As shown in FIG. 1, the inner tank 2 may also be provided with a
tube 18 extending generally diametrically through both sides of the
tank, with the lower end extending to a point closely adjacent to
one cylindrical sidewall, shown as the lower portion in FIG. 1, and
the opposite end shown as the upper portion 22 extending
substantially above a generally diametrically opposed portion of
the inner tank 2. In fabricating the outer sheath 12, the sheath
may be bonded around the portion 22 in a manner generally similar
that described above with respect to fitting 20. Thus, in the
completed double wall tank the tube 18 extends from its portion 22
outside the sheath through the adjacent portion of the outer sheath
12 and the sidewall of the inner tank and the opposite sidewall of
the inner tank, with its open lower end terminating adjacent the
lower portion (FIG. 1) of the outer sheath 12.
To enable the double wall tank formed by the method of this
invention to provide for the protection against leaking of fluids
to be contained within it, another process step comprises breaking,
at least temporarily, any engagement between the inner tank
exterior surface and the inner surface of the outer sheath. This
step may be performed by application of a fluid under pressure P,
such as air, that is sufficient to break, at least temporarily,
engagement between the inner tank exterior surface and the outer
sheath. Because of the coating of the inner tank outer surface with
the release agent 10, distortion or expansion of the outer sheath
12 caused by application of that fluid P under pressure, suitably
through fitting 20, causes that outer sheath 12 to separate and
break free from engagement with inner tank 2. The pressure required
may be as little as 1 to 5 pounds per square inch over ambient, and
the movement of the sheath from the inner tank under the influence
of that pressure may be as small as 1/1,000 of an inch. It is only
necessary to break the outer sheath from any substantial bonding to
the inner tank in order to provide a path for flow of hydrocarbons
between the outer sheath and the inner tank, for purposes to be
described below.
As an alternate construction method, the end portions 16 of the
sheath 12 may be fabricated separately from the cylindrical
sidewall portion 14. Such a technique, illustrated in the
fragmentary sectional view of FIG. 3, provides substantially the
same end result as the continuous lay-up process shown in FIG. 1.
However, this method of forming the end portions 16 separately may
simplify the manufacture by permitting formation of those end caps
16 over a male mold plug, thus permitting the glass fiber material
to be laid substantially horizontally instead of vertically, as is
required in the continuous lay-up approach of FIG. 1.
As shown in FIG. 3 the tube 18 may, alternatively, be bonded into
one, or both, of the end portions 16, extending from a point
adjacent the lowermost portion of the interior of the outer sheath
12 through an aperture formed in the upper portion of outer sheath
12. In this embodiment the tube 18 extends between the inner
surface of the end portion 16 of the outer sheath 12 and the
exterior surface of the end wall of inner tank 2. The pressurized
fluid P described above could equally well be introduced through
this tube 18 in FIG. 3, or through the corresponding tube 18
illustrated in FIG. 1, instead of through fitting 20.
The remaining steps involved in the manufacture of the double wall
tank of this invention may be substantially the same as those
described in detail in my prior U.S. Pat. Nos. 4,640,439, 4,644,627
and 4,655,367, the teachings of which patents are incorporated
herein by reference.
By the foregoing construction there is thus provided a double wall
tank that can be manufactured economically from a conventional
steel wall tank, and even from a used tank that has previously been
removed from underground storage. This structure provides an outer
sheath, which may be formed from a material that is free of any
tendency to rust or corrode, and which is free from any bonding
with the inner tank to permit the collection within the space
between the inner tank and the outer sheath, and thus detection, of
any liquids leaking into that space, either from the tank or from
sources exterior to the sheath. Thus may be determined the
existence of any leakage of either the tank or the sheath by simply
detecting the presence and nature of any liquid present in that
space. Additionally, leakage may be detected by applying a positive
or negative pressure to the tank or to the space between the
exterior surface of inner tank 2 and the interior of outer sheath
12 and then observing to determine if that level of pressure is
maintained, all as is known in the prior art. By the use of a
relatively thick and rigid outer sheath, the strength of that
sheath is enhanced over similar structures that may use a flexible
outer covering. Furthermore, such a rigid external sheath permits
testing of the integrity of the sheath and tank at substantial
pressures, which could not be done with a flexible covering without
danger of rupture. As an additional desirable feature, the space
between the inner and outer tanks is formed without the need for
any substantially rigid spacer material, thereby saving both labor
and material costs.
While the foregoing describes in detail several preferred
embodiments of the tank of this invention, it is to be understood
that such description is illustrated only of the principles of the
invention and is not to be considered limitative thereof. Because
numerous variations and modifications of both the method of
manufacture and the resulting tank will readily occur to those
skilled in the art the scope of this invention is to be limited
solely by the claims appended hereto.
* * * * *