U.S. patent application number 09/803548 was filed with the patent office on 2002-07-11 for double wall storage tank.
Invention is credited to Roy, Paul.
Application Number | 20020088805 09/803548 |
Document ID | / |
Family ID | 4168045 |
Filed Date | 2002-07-11 |
United States Patent
Application |
20020088805 |
Kind Code |
A1 |
Roy, Paul |
July 11, 2002 |
Double wall storage tank
Abstract
A method of making a double wall tank for storing liquids
comprises providing an inner tank having substantially cylindrical
sidewalls and end walls; wrapping an impervious sheet material
around the cylindrical sidewalls; providing a spacer means on
exterior surfaces of the end walls; covering the wrapped inner tank
and spacer means with reinforced resinous material to form an outer
tank; and providing access to inspect an interstitial space between
the impervious sheet material and the inner tank.
Inventors: |
Roy, Paul; (Tisdale,
CA) |
Correspondence
Address: |
Craig J. Lervick, Esq.
Oppenheimer, Wolff & Donnelly LLP
3400 Plaza VII, 45 South Seventh Street
Minneapolis
MN
55402
US
|
Family ID: |
4168045 |
Appl. No.: |
09/803548 |
Filed: |
March 9, 2001 |
Current U.S.
Class: |
220/560.03 ;
220/62.22 |
Current CPC
Class: |
B65D 90/505 20130101;
B65D 90/022 20130101 |
Class at
Publication: |
220/560.03 ;
220/62.22 |
International
Class: |
B65D 001/40; B65D
003/22; B65D 006/14; B65D 008/04; B65D 090/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 5, 2001 |
CA |
2,330,357 |
Claims
I claim:
1. A method of making a double wall tank for storing liquids, the
method comprising: providing an inner tank having substantially
cylindrical sidewalls and transverse end walls; wrapping an
impervious sheet material around the cylindrical sidewalls;
providing a spacer means on exterior surfaces of the end walls;
covering the wrapped inner tank and spacer means with reinforced
resinous material to form an outer tank; and providing access to
inspect an interstitial space between the impervious sheet material
and the inner tank.
2. The method of claim 1 wherein the reinforced resinous material
comprises fiberglass.
3. The method of claim 1 wherein the impervious sheet material
comprises a plastic film.
4. The method of claim 1 wherein the impervious sheet material
comprises MYLAR.TM. film.
5. The method of claim 1 wherein the impervious sheet material
comprises polyethylene sheeting.
6. A double wall tank for storing liquids comprising an inner tank
having substantially cylindrical sidewalls and transverse end
walls; an impervious sheet material wrapped around the cylindrical
sidewalls; a spacer means covering exterior surfaces of the end
walls; a reinforced resinous material applied to the impervious
sheet material and spacer means to form an outer tank; and an
access port operatively connected to an interstitial space between
the impervious sheet material and the inner tank to enable leak
detection.
7. The tank of claim 6 wherein the reinforced resinous material
comprises fiberglass.
8. The tank of claim 6 wherein the impervious sheet material
comprises a plastic film.
9. The tank of one of claim 6 wherein the impervious sheet material
comprises MYLAR.TM. film.
10. The tank of claim 6 wherein the impervious sheet material
comprises polyethylene sheeting.
Description
[0001] This invention is in the field of storage tanks and in
particular such tanks with a double wall to contain leaks, and
facilitate detection of leaks.
BACKGROUND
[0002] Safety and environmental regulations generally require that
tanks for storage of petroleum and like hazardous liquids be double
wall tanks. These are essentially an inner tank completely enclosed
in an outer tank. During initial testing, in order to detect leaks
in the inner or outer tanks, a pressure differential is imposed on
the interstitial space between the two tanks. Most commonly a
vacuum is imposed and a visual indicator is connected to the
interstitial space. If the pressure increases in the interstitial
space, as indicated on the visual indicator, a leak is present in
one of the inner tanks or outer tanks, requiring repair. To detect
leakage from the inner tank after the tank is installed, a tube is
generally provided from the top of the tank to the interstitial
space at the bottom. Leaks are detected by visually inspecting, or
dripping, the bottom of the interstitial space, where leaking
liquid from the inner tank will migrate, drawn by gravity.
[0003] In order to satisfactorily detect leaks, fluid must be able
to flow to a leak location through the interstitial space. If the
leaking fluid is trapped at one location in the interstitial space,
that location is then necessarily not in communication with the
rest of the interstitial space and so the leak will not be
detected.
[0004] For underground installations, these double wall tanks have
conventionally been made by covering an inner tank with fibreglass,
molten thermoplastic, or similar materials that will resist
corrosion from the soil. Conventionally as well, great care is
expended to ensure that the inner and outer tanks were spaced
apart. U.S. Pat. Nos. 4,640,439 and 5,664,313, both to Palazzo,
include a spacing material, such as mesh, in the interstitial space
between the two tanks. Similarly in U.S. Pat. No. 4,655,367 to
Palazzo, a sheet with projections extending toward the inner tank
is wrapped around the inner tank before the outer tank sheath is
applied. The projections ensure that there is a space between
tanks.
[0005] In U.S. Pat. No. 4,780,946 to Palazzo a plurality of raised
beads is provided on the surface of the inner tank ensures the
spacing and in U.S. Pat. No. 4,780,947 to Palazzo a resin spacer
material is applied to the surface of the inner tank. Similarly in
U.S. Pat. No. 4,927,050 to Palazzo, the inner tank is formed with a
patterned surface to provide the interstitial space.
[0006] In a somewhat different approach, U.S. Pat. No. 4,744,137 to
Palazzo discloses a rigid outer sheath molded with inwardly
extending projections. The outer sheath is installed over the inner
tank and the projections ensure the spacing.
[0007] In yet another approach, U.S. Pat. No. RE34,203 to Palazzo
discloses applying a release agent to the inner tank surface, and
then applying a rigid outer sheath of fibreglass or the like, and
then breaking the engagement between the inner tank surface and
outer sheath by injecting fluid under pressure. The pressure may be
as low as 1-5 psi, and sheath movement can as little as 1/1000 of
as inch. Similarly in U.S. Pat. Nos. 5,045,263 and 5,129,540, both
to Palazzo, an internal lubricating agent is mixed with a curable
synthetic resin to form a rigid outer sheath that resists bonding
to the inner tank surface. Although not claimed as strictly
necessary, preferably in these as well a fluid is injected between
the tanks to break any engagement between them.
[0008] Again in U.S. Pat. Nos. 5,816,435 and 6,119,887, both to
Palazzo, an expanded selection of release agents is applied over
the inner tank surface prior to applying the outer sheath as a
resin or extruded molten thermoplastic material. The release agent
is stated to depend on the material selected for the outer sheath.
For example where the outer sheath is extruded as molten
thermoplastic material, the release agent may include a film of
generally smooth imperforate material having higher melting point
than the temperature of the molten thermoplastic when extruded. As
the heated outer sheath is applied over the film, the film wrinkles
so as to define a plurality of ridges or grooves generally
circumferentially about the tank. The ridges and grooves provide
for the free flow of liquids between the inner and outer tanks.
Polyester resin film such as MYLAR.TM. is stated to be
suitable.
[0009] U.S. Pat. Nos. 5,060,817 and 5,102,005, both to Trussler,
disclose a double wall tank where the outer sheath is formed
separately in pieces which are then joined together to enclose the
inner tank without bonding to the inner tank. Fluid migration may
be enhanced by texturing the adjacent surfaces.
[0010] U.S. Pat. No. 5,752.616 to Watkinson discloses a double wall
tank where the interstitial space is provided by a fluid pervious
layer, such as open celled foam. U.S. Pat. No. 5,720,404 to Berg et
al. discloses a roto-molded double wall tank with inner and outer
tanks joined together by ties to create an annular space which can
be monitored for leakage. U.S. Pat. No. 5,462,191 to Bart low et
al. discloses a double wall tank with ribs and a spacer filament to
provide for fluid migration through the interstitial space.
[0011] U.S. Pat. No. 4,869,386 to sharp discloses a double wall
tank with ribs and a fibrous material in some portions of the
interstitial space, and a separating material such as foam or
matting in other portions. In U.S. Pat. No. 5,152,859, also to
Sharp a separating agent, such as wax, is applied to the surface of
the inner tank to ensure that a subsequently applied fibrous
reinforcing material will not adhere to the inner tank or seal
closed the annular space between the tanks. The wax can later be
heated and removed from the annular space. Other suitable
separating agents include grease. As well porous foam or matting
can be applied to the inner tank and covered with a Mylar or
polyethylene film to prevent the porous material from becoming
saturated with a subsequently applied resinous material.
[0012] All of the considerable prior art is very concerned with
ensuring that there is a well defined interstitial space between
the inner and outer tanks, providing projections, channels, mesh,
porous material such as foam, and so forth.
SUMMARY OF THE INVENTION
[0013] It is the object of the present invention to provide a
double wall tank that is easily and more economically constructed
than prior art tanks, and that includes an interstitial space
between inner and outer tanks that allows a free flow of fluid so
that leak may be detected.
[0014] The invention provides, in one aspect, a method of making a
double wall tank for storing liquids. The method comprises
providing an inner tank having substantially cylindrical sidewalls
and end walls; wrapping an impervious sheet material around the
cylindrical sidewalls; providing a spacer means on exterior
surfaces of the end walls; covering the wrapped inner tank and
spacer means with reinforced resinous material to form an outer
tank; and providing access to inspect an interstitial space between
the impervious sheet material and the inner tank.
[0015] In a second aspect the invention provides a double wall tank
for storing liquids comprising an inner tank having substantially
cylindrical sidewalls and end walls; an impervious sheet material
wrapped around the cylindrical sidewalls; a spacer means covering
exterior surfaces of the end walls; a reinforced resinous material
applied to the impervious sheet material and spacer means to form
an outer tank; and an access port operatively connected to an
interstitial space between the impervious sheet material and the
inner tank to enable leak detection.
[0016] The present inventors have found that essentially any film
of impermeable material may be wrapped around the inner tank, and
the outer sheath of fiberglass or the like simply applied over top
in the conventional manner. For example MYLAR.TM. or a plastic film
such as the polyethylene film commonly used for vapor barrier may
be used. The film does not need to be wrinkled by heat, or include
bumps or projections. The interstitial space, though small, is
larger than the molecular size of a stored liquid, allowing
migration of the liquid as required for leak detection. An
interstitial space on the end walls, communicating with the
interstitial space between the film and the cylindrical wall, is
provided by any of the conventional spacer means.
DESCRIPTION OF THE DRAWINGS
[0017] While the invention is claimed in the concluding portions
hereof, preferred embodiments are provided in the accompanying
detailed description which may be best understood in conjunction
with the accompanying diagrams where like parts in each of the
several diagrams are labeled with like numbers, and where:
[0018] FIG. 1 is a perspective view of an inner tank of the
invention wrapped with impervious sheet material;
[0019] FIG. 2 is a cross-section view of the wall of the completed
double wall tank;
[0020] FIG. 3 is a side view of a completed double wall tank;
[0021] FIG. 4 is a cross-section view of the access port where same
pierces the inner tank wall at the bottom of the tank.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
[0022] A method of making a double wall tank 10 for storing liquids
is disclosed. The method comprises providing an inner tank I having
substantially cylindrical sidewalls 2 and transverse end walls 3.
An impervious sheet material 4 is wrapped around the cylindrical
sidewalls 2 with an overlap 7 as illustrated in FIG. 1 in order to
prevent the subsequent layer of fiber glass or similar material
from bonding to the inner tank 1. The impervious sheet material 4
can be MYLAR.TM., or a plastic film such as the polyethylene film
commonly used for vapor barrier.
[0023] A conventional spacer means 5, such as mesh protected by a
film, wax, or the like is provided on exterior surfaces of the end
walls 3. The wrapped inner tank 1 and spacer means 5 is covered
with reinforced resinous material, such as fiberglass, to form an
outer tank 6. This spacing on the end walls 3 and formation of the
outer tank 6 are well known in the prior art.
[0024] No attempt is made, as is emphasized in the prior art, to
ensure that there is a measurable interstitial space between the
inner tank 1 and the impervious sheet material 4. The interstitial
space that results using the method is very small, however will
readily allow liquid to migrate, and gather at the bottom of the
interstitial space
[0025] For a typical underground installation, access to inspect
the interstitial space between the impervious sheet material 4 and
the inner tank 1 is conveniently provided by an access port 8 which
extends through the inner tank 1. The access port 8 pierces the
wall of the inner tank 1 at the bottom end thereof, and is covered
by the impervious sheet material 4 as illustrated in FIG. 4.
Leaking liquid thus migrates to the bottom of the tank 10 and can
be detected by visually checking the port 8, or by dipping or other
detection means. Other locations and detection means could be used
depending on the installation, or other conditions of use.
[0026] The foregoing is considered as illustrative only of the
principles of the invention. Further, since numerous changes and
modifications will readily occur to those skilled in the art, it is
not desired to limit the invention to the exact construction and
operation shown and described, and accordingly, all such suitable
changes or modifications in structure or operation which may be
resorted to are intended to fall within the scope of the claimed
invention.
* * * * *