Note: Descriptions are shown in the official language in which they were submitted.
WO 93/20372 PCT/US93/02977
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SECONDARY CONTAINMENT FLEXIBLE UNDERGROUND PIPING SYSTEM
Field of the Invention:
The present invention relates to secondary
containment systems and especially, although not
exclusively to a piping construction and a method for
providing secondary containment systems for hydrocarbon
storage and delivery systems.
BACKGROUND OF THE INVENTION
A secondary containment system is one which
functions to collect and contain the fluids leaking out
of another and primary containment system. For example,
a primary containment system may store and delivery
gasoline at a filling station. A secondary containment
system would collect and contain the same gasoline if a
primary delivery pipe should rupture or otherwise spill
the gasoline. Secondary containment systems have been
developed to overcome the environmental problems that
have been encountered with respect to leakage of
hazardous fluids from tanks and pipe lines. As
indicated, this has been a particular problem with
respect to underground installations in which undetected
leakage of hazardous fluids into the surrounding terrain
over long periods of time has produced harmful conditions
and extensive pollution which are difficult and expensive
to clean.
Today there is great public concern because
chemicals are penetrating into underground water supplies
contaminating public drinking water and making some of
the food supply unusable, amongst other things. The
entire environment is being degraded to a serious level
which tends to cast doubt on the future availability of
safe water. Therefore, many government agencies have
enacted and continue to enact laws which require a
secondary containment system designed to capture and
contain the spilled gasoline or other liquid materials
thus preventing it from leaking into the surrounding
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earth. ~he capture gasoline or other liquid material may
then be pumped out of the secondary container for proper
disposal. This eliminates the possibility of gasoline
spillage to contaminate underground water supply.
Manufacturers of containment systems have
responded by developing and producing a variety of
secondary containment systems for conventional
underground piping which are designed to contain and
prevent any leakage from escaping into the environment.
Many of these systems have proven to be effective
containment systems but have found to be difficult and
costly to install.
One known approach to secondary containment
systems, and, in particular, the secondary containment of
underground conventional piping has been to line the
piping trench with an impervious flexible membrane liner
or semi-rigid trough. This technique can provide a
measure of secondary containment of leaky product but
such an approach does not allow for effective leaking
detection in that it does not permit the determination of
which pipe is leaking and the location of the leak in the
piping line when the same occurs. It is also difficult
to test such systems using air pressure testing devices.
Additionally, said secondary containment systems do not
provide 360° containment and therefore can fill with
water and become ineffective.
Another approach toward solving the problem of
underground leakage in such conventional piping systems
has been to install a large semi-conventional piping
system over the conventional underground piping as a
means for providing the secondary containment. With such
an arrangement, the outer secondary containment rigid
pipe is installed simultaneously with the product piping.
The outer secondary containment pipe by necessity has a
larger diameter than the supply pipe to enable secondary
containment pipe to slide over the smaller pipe. The
secondary containment pipe fittings are of a clam shell
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design adapted to fit over the supply pipe fitting and
connect to the secondary containment pipe. The clam
shell fitting is sealed to itself and the secondary
container pipe by a variety of sealing techniques.
Depending on the type of secondary containment system
used, these sealing techniques could include metal or
plastic fasteners used with a combination of adhesives,
sealants and the like. Such secondary systems are
generally expensive to install because of the cost of the
l0 components which are used and the time required to
assemble both the product and the secondary containment
piping systems.
Another known approach to solving the
aforementioned problems is to employ a semi-conventional
piping system over the conventional product piping. This
type of containment system differs from the first
described systems in that it is not an entirely rigid
straight pipe but rather a combination of rigid straight
pipe with a larger diameter convoluted plastic pipe over
it which produces a telescoping effect. The convoluted
section of telescopic containment pipe serves as a
fitting of containment of the product, 90° and 45°
fittings as well as unions, flexible connectors, swing
joints, should they be so attached. The convoluted pipe
is designed to be flexible and sized to be shifted around
any angles in the production piping system.
Another type of secondary containment piping
system has been developed which utilizes spaced access
chambers interconnected by a secondary containment pipe
to provide a sealed housing for a flexible fluid supply
pipe, the ends of which are disposed within the access
' chambers and have a connector element at each end forming
a section adapted to be interconnected to other fluid
' conduits. The diameter and bending radius of the fluid
supply pipe and the size of the access chamber are such
as to permit the fluid pipe, after uncoupling, to readily
be removed from the secondary containment pipe through
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one of the access chambers. Should a leak occur in the
piping, the secondary containment system allows the piping
to be removed and replaced.
It is very difficult and expensive to meet all of the many
different environmental and safety standards at a reasonably
acceptable cost particularly in light of the many state and
local governments writing individual laws that impose a wide
variety of standards which the manufacturers of such systems
must meet.
Accordingly, an object of an aspect of the
invention is to provide a new and improved secondary
containment system which will draw all spilled fluids that
may leak from a primary supply pipe to a preselected
collecting point which may be monitored.
Another object of an aspect of the invention is to
provide a practical secondary containment system which may
be manufactured in a factory, shipped and installed at a
reasonably low cost in a fully usable manner and yet one
which meets all requirements of the environment within which
they must be used.
It is a further object of an aspect of the present
invention to provide an economical, easily installed, highly
durable and environmentally secure flexible piping system.
According to an aspect of the invention, a
secondary containment piping system comprises:
an inner supply pipe, wherein said inner pipe is
comprised of a first, inner layer fabricated from nylon, a
second, intermediate layer comprising a nylon reinforced
wrap, a third, outer layer comprising a polyethylene
material, said nylon inner material, said nylon wrap and
said polyethylene outer layer being extruded simultaneously
to form said inner pipe; and
a flexible outer secondary containment pipe within which
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said inner supply pipe is carried, said outer pipe being
fabricated from a non-foamed, fuel impervious material and
having a plurality of radially projecting flanges disposed
between said inner supply pipe and said outer secondary
containment pipe, to provide a locking engagement of said
pipes with respect to each other and to provide for a flow
passage between said pipes when said pipes are buried;
wherein after said pipes are buried, the outer
secondary containment pipe deforms to a slightly elongate
cross sectional shape, which deformation forms at least one
flow path between said pipes, said flow path being adjacent
an area wherein at least one of the radially projecting
flanges is not abutting both the inner pipe and the outer
pipe.
According to another aspect of the invention, a
secondary containment piping system comprises:
an inner supply pipe;
a flexible outer secondary containment pipe within
which said inner supply pipe is carried, said outer pipe
being fabricated from a fuel impervious material and having
a plurality of radially inwardly projecting flanges adapted
to engage the outer surface of said inner supply pipe when
said pipes are buried to provide a locking engagement of
said pipes with respect to each other and to provide for a
flow passage between said pipes;
said system having spaced underground chambers
which are interconnected in a fluid type manner through the
walls thereof by said secondary containment pipe which
passes therethrough, said inner supply pipe having end
couplings attached to the ends thereof, said end couplings
being disposed within said chambers at a point beyond the
termination of said outer secondary containment pipe;
said inner pipe being comprised of a first, inner
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layer fabricated from nylon, a second, intermediate layer
comprising a nylon reinforced wrap, a third, outer layer
comprising a polyethylene material, said nylon inner
material, said nylon wrap and said polyethylene outer layer
being extruded simultaneously to form said inner pipe;
said flexible outer secondary containment pipe
being fabricated with an integral wall, the interior of
which has a plurality of equally spaced radially projecting
projections which define thereinbetween u-shaped openings, a
selected portion of which will abut said outer layer of said
inner supply pipe when buried, said u-shaped openings
providing minimum flow passage communicating any fluid that
may leak from said inner pipe to one of said spaced
chambers;
said flexible outer secondary containment pipe
being fabricated from an extruded material that is
chemically compatible with and impervious to the fluids to
be transmitted and the surrounding environment within which
it is buried; and
said inner pipe being disposed within said outer
pipe prior to placement within the ground and said inner
pipe not being removable from said outer pipe when said
pipes are buried;
wherein after said pipes are buried, the outer
secondary containment pipe deforms to a slightly elongate
cross sectional shape, which deformation forms at least one
flow path between said pipes, said flow path being adjacent
an area wherein at least one of the radially projecting
projections is not abutting said outer layer of said inner
supply pipe.
According to a further aspect of the invention, a
method for fabricating a secondarily contained piping
system, comprising the steps of:
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fabricating a flexible inner supply pipe, wherein
said inner pipe is comprised of a first, inner layer
fabricated from nylon, a second, intermediate layer
comprising a nylon reinforced wrap, a third, outer layer
comprising a polyethylene material, said nylon inner
material, said nylon wrap and said polyethylene outer layer
being extruded simultaneously to form said inner pipe;
fabricating a flexible outer secondary
containment pipe, said secondary pipe being extruded from a
non-foamed material with a plurality of internal projections
radially extending inwardly from the interior surface
thereof;
inserting said inner supply pipe within said
secondary containment pipe;
forming a trench extending from an underground
chamber;
extending said inner and outer pipe into said
chamber;
sealing the outer surface of said secondary pipe
and said chamber to seal said chamber;
terminating the length of said outer pipe at a
position short of the terminated end of said inner pipe;
attaching a coupling to the end of said inner
pipe;
burying said inner and outer pipes, the weight of
the earth on said pipes collapsing portions of said flexible
outer secondary containment pipe such that the inward
projections will engage and lock the interior inner pipe
against movement relative to said outer pipe and to provide
a flow path for carrying fluid which may leak from said
inner pipe through the space between said outer pipe and
said inner pipe to said chamber;
wherein after said pipes are buried, the outer
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secondary containment pipe deforms to a slightly elongate
cross sectional shape, which deformation forms at least one
flow path between said pipes, said flow path being adjacent
an area wherein at least one of the inward projections is
not engaging the inner pipe.
Other objects, advantages and applications of the
present invention will become apparent to those skilled in
the art of underground piping systems when one example of
the best mode of the present invention is read in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The specification herein makes reference to the
accompanying drawings wherein like reference numerals refer
to like parts throughout the several views and wherein:
Fig. 1 is a schematic layout of an exemplary
gasoline storage and delivery system;
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Fig. 2 is an enlarged side view of a portion of
the fuel dispensing system of Fig. 1 as seen generally
along line 2-2 thereof;
Fig. 3 is an enlarged view of a portion of the
5 system illustrated in Fig. 2;
Fig. 4 is an enlarged perspective view of the
inner and outer pipes utilized in the secondary
containment piping system of the present invention with
layers of the inner pipe removed for illustrative
purposes;
Fig. 4A is a fragmentary perspective view of
the outer secondary containment pipe illustrated in Fig.
4;
Fig. 5 is a cross sectional view taken
generally along line 5-5 prior to the backfilling of the
trench within which the pipes are located; and
Fig. 6 is a view similar to Fig. 5
illustrating, in a slightly exaggerated manner, the
secondary containment piping system after backfilling.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings, and, in
particular, to Figs. 1 and 2, wherein there is
illustrated an underground fuel storage and dispensing
system generally indicated at 10 comprising fuel tanks 12
from which a plurality of underground fuel supply pipes
14 extend for distribution of fuel to dispersion areas 16
in a conventional manner. The system includes one or
more access chambers 20 which are also disposed below the
surface dispensing station 16. The access chambers 20
and the fuel tanks 12 are interconnected by containment
pipe segments 22 while the access chambers are connected
' via pipe segments 24 to a conventional drip pan 26
beneath the dispenser 16 and is connected thereto through
' suitable elbow connectors 28. The access chamber 20 and
the pan 26 are interconnected in a fluid sealing manner
through their side walls just above the bases thereof by
means of the secondary containment pipe 24.
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As can best be seen in Fig. 3, the side wall 30
of the access chamber 20 has an opening 32 through which
the end of the pipe 24 extends. A conventional seal 34
surrounds the outer surface of the containment pipe 24
and provides a fluid tight seal for the interior of the
access chamber 20.
As will be described in greater detail
hereinafter, the secondary containment piping system
comprises a flexible inner supply pipe 40 which is
completely encased within a flexible outer containment
pipe 42. It should be noted by reference to Fig. 3, that
the outer containment pipe 42 extends into the access
chamber 20 a sufficient distance so that it clears the
interior of the wall 30 of the access chamber 20. During
fabrication this will permit the insertion on the
terminated end 39 of pipe 42 of a suitable air pressure
device to permit testing as will be explained
hereinafter. The inner pipe 40 extends past the
terminated end 39 of the outer pipe 42 a sufficient
distance to permit it to be coupled by suitable
conventional couplings 44 to another inner pipe 40 which,
in turn extends outwardly from the access chamber 20
through an outer containment pipe 42. At the drip pan
26, the pipe 40 exist therethrough and continues through
a containment pipe 42 on to the next island.
The access chamber 22 has a removable cover 70
to permit easy access thereto for removal of any fuel
that might be captured by the containment pipe 40. A
fluid sensor 72 is disposed in the bottom of the access
chamber 22 and is electrically connected to an
appropriate indicator or alarm 74. When there is an
accumulation of fluid, such as due to leakage from the
primary pipe 40, the fluid will actuate the alarm.
As can best be seen in Figs. 4 and 5, the inner
pipe 40 is made from a fuel impervious material and is
comprises of three layers of material which are extruded
together and comprise an interior layer 50, which is
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fabricated from a nylon 12 material; a intermediate layer
52 consisting of a nylon 6 yarn reinforcement wrap; and
an exterior outer material 54 which is preferably
fabricated from a polyethylene material. The inner layer
50 is .080" thick and the outer layer is preferably 060"
thick. In the preferred embodiment, the pipe 40 has an
inside diameter of 1.68" and an outside diameter of
1.960", a maximum operating pressure of 150 psi and a
minimum burst pressure of 750 psi. The material is
flexible and has a bend radius of 12" to 24".
The inner pipe 40 is completely encased in the
outer containment pipe 42 which, as can best be seen in
Figs. 4, 4A and 5, comprises integrally extruded member
having a wall 60, the interior of which is provided with
a plurality of angularly spaced, radially inwardly
extending ribs or projections 64 that define therein
between U-shaped cross sections 60. The projection
extends along the full length of the interior of the wall
60 (Fig. 4A). The outer pipe 42 is sized to permit the
inner pipe 40 to be inserted therein with little or no
resistance and is, preferably, assembled in the combined
arrangement at the factory, ready for positioning in the
pipe trenches when delivered onsite. The outer pipe 42
is very flexible and can bend as needed to accommodate
the bending of the primary inner pipe 40. The outer pipe
42 is made from a fuel impervious material such as a
nylon or polyethylene, clear acrylonitrile or clear
polyurethane material.
In practice, trenches are laid out and the
various lengths of piping are laid in the trenches and
connected to the various underground access chambers 20
' and drip pans 26 via the sealing members 34. Once
connected, a portion of the outer pipe 42 is cut and
' removed so that a sufficient amount of the inner pipe 40
extends past the termination end 39 of the outer pipe 42
to permit the inner pipe 40 to be attached to a suitable
coupling 44.
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Before a coupling 44 is attached to the inner
pipe 40, an appropriate seal may be placed over the
outside of the inner pipe 40 to sealingly engage the
outer pipe 42 whereby pressurized air may be communicated
to the annular space (Fig. 5) formed between the inner
and outer pipes 40 and 42 to test the same to be sure
that there are no leakage points in the containment
system. Obviously, the opposite ends of the pipe 42 of
each of the access chambers 22 and drip pans 26 must be
sealed in order to effectively perform such a test.
Likewise, the inner pipes 40 can be subjected to air
pressure to test their integrity. Once the installer is
satisfied that the containment piping system is able to
perform its function without concern for leakage, the
trenches within which the containment pipes 14 have been
laid are backfilled.
The weight of the earth on the flexible outer
pipe 42 deforms the pipe 42 in the manner similar to that
illustrated in Fig. 6 of the drawings, until the outer
ends of the projections 64 abut the outer wall o~ the
inner pipe 40. The abutment of the projections 64 with
the wall 40 provides a two-fold purpose. First, it
snugly and lockingly engages the pipe 40 and prevents
relative movement between the inner and outer pipes
providing for a more secure system, and secondly, the
space between U-shaped cross sectional areas and the
space between the inner and outer walls always insures a
flow path for any fuel that may leak into the annular
space between the inner and outer pipes. The view
illustrated in Fig. 6 is exemplatory of the condition
that may exist. However, it should be noted that the
outer tube 42 may be deformed in a variety of different
shapes. Suffice it to say, that a continuous flow path
will exist in the event there is a leakage from the
primary inner pipe 40. While it is preferred that the
primary pipe 40 and secondary containment pipe 42 be
assembled at a factory location there may be situations
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in which the pipes are assembled on site before burial.
The pipe 40 may be removed and either pipe may be
replaced if a leak is found during testing. Once buried,
the weight of the fill collapses appropriate portions of
the outer containment pipe 42 around the primary pipe 40
and the primary pipe 40 may no longer be removed after
burial.
While this invention has been described has
having a preferred design, it should be understood by
those skilled in the art of the forms of the invention
may be had all coming within the spirit of the invention
and the scope of the appended claims. What is claimed is
as follows.
