Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Flexible Tank for 40-foot Shipping Container
Background
Lengthy shipments of goods frequently involve multiple modes of transport,
such as ocean going
vessels, railroad cars and trucks. Standardized intermodal shipping containers
facilitate intermodal
transport as they allow a variety of goods to be easily moved from place to
place in ports and
warehouses, and between ships and railroad cars. Some organizations, such as
the International
Standards Organization (ISO), have developed and continue to maintain
standards for shipping
containers such as size, location of doors, and the use of specific corners or
fittings so that a container
can be securely gripped and moved by lifting equipment. The ability to use a
standardized shipping
container is an advantage because the container handling equipment and
logistics of making shipments
of special kinds of goods is simplified when a particular customized shipping
container is not necessary.
For example, a large quantity of liquid can be transported by placing the
liquid inside of a flexible tank in
a shipping container also usable for dry goods and then that container can
preferably be treated like any
other shipping container without regard to the nature of its contents.
There is specialized equipment used for transport by road, rail and ship of
bulk liquid products.
However, it is desirable to take advantage of standard container equipment to
realize cost savings.
Standardized shipping containers are prevalent in both domestic and
international trade lanes, and thus
cheaper to use. For example, 40' or 53' shipping containers are readily and
commonly available in North
America. The prevalence or ubiquity of such larger shipping containers in some
multimodal transport
routes is such that it can be economically beneficial to use a flexitank in
them with the same capacity as
used in smaller 20' shipping containers.
These larger containers have a much higher internal volume than smaller 20'
shipping
containers. Due to weight restrictions, it can be difficult to take full
advantage of the larger internal
volume. The liquids to be shipped can have vastly different specific gravity
(weight per gallon), and the
volume of the liquid that can be shipped within the weight restriction varies
accordingly. Conventional
flexitanks are typically mass produced and are of a single capacity. This is a
disadvantage for a larger
shipping container with high internal volume where it is somewhat more
possible to ship different
volumes of liquids while remaining within the weight restriction. There are
also other disadvantages to
larger shipping containers that must be solved when shipping liquids.
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For example, a 40 foot container may not always facilitate the use of a
bulkhead. Flexible tanks
designed for a 20 foot container with a bulkhead are typically longer than the
internal length of the
container so that the ends of the flexitank are supported by the front inside
wall of the container and a
bulkhead panel placed across the door opening at the rear wall. Therefore, the
flexitank for a 20 foot
shipping container may be, for example, 23 feet long. A 40 foot shipping
container may not facilitate
use of a bulkhead and the front wall, so the flexible tank must be
freestanding, without relying on the
availability of any end wall or bulkhead support.
The flexible tank should not deform any of the side or end walls of the
container in which it is
placed. Intermodal shipping containers are sometimes stacked or placed very
close together in cargo
holds of vessels or ports, with only a few inches of tolerance, and an
outwardly deformed wall may
interfere with or prevent placement of the container. The side walls of a 40-
foot container are generally
more susceptible to deformation than the side walls of a 20-foot container if
for no other reason that
they are longer and have no additional support. There is a limit to the amount
of force that should be
placed on the side wall of a 40-foot container by a flexible tank full of
liquid.
But the largest disadvantage associated with the use of flexible tanks inside
of larger shipping
containers is the increased possibility of leak or rupture if the flexible
tank for a 20-foot container is
simply "lengthened" or made larger for a 40-foot container. Sudden movement
can cause a rupture of a
flexitank (even if there is no manufacturing defect or "weakness" in the
flexitank). Sudden starts, stops
or impacts can result in large waves that produce enormous pressure on the
ends of the flexible tanks.
The danger of a flexible tank rupture or leak depends greatly on the volume of
the liquid inside of it and
the length of the flexible tank from end to end. The liquid dynamics are
dramatically different
depending on the shape, proportion and volume of a flexitank. In particular,
the flexitank for a 40'
container will typically have a lower profile (height) than the flexitank for
a 20' foot container. Figs. 3(a)-
3(c) show the sewn end seams in a prior art flexitank. These end seams are
susceptible to liquid
dynamics (shown by the arrow in Fig. 3(c)) that impact the end seams at the
intersection where they are
sewn together, forcing the two halves to separate apart and away from each
other.
So even when a larger shipping container is available, a larger version of a
known flexible tank
has historically not been practical due to the risk of rupture. For example,
in U.S. Patent Application
Publication No. 2017/0144833 filed by Environmental Packaging Technologies,
Inc., three different
flexible tanks are used in a 40-foot or 53-foot container rather than one
larger flexible tank. Such a
system has the disadvantages that each flexible tank has to be individually
loaded and unloaded, and
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the cost of the three flexible tanks is more than it would be if there were
but a single flexible tank. A
single larger flexible tank has historically not been possible in larger
shipping containers because of the
likelihood of rupture or leak.
This risk of leakage of flexible tank rupture is even greater for a multimodal
shipment where the
larger shipping container will be partly transported by railroad. Railroad
cars are large and heavy,
especially when loaded. Railroad cars are typically interconnected to each
other by running them into
each other to cause them to be hooked together in a process sometimes referred
to as shunting. Even
at a low speed, these collisions create very large and very sudden forces of
deceleration, such as 2G's,
that are similar to those experienced in a sudden and complete full stop. But
this problem has been
solved by the preferred embodiments of the invention. In particular, the
flexible tanks of the preferred
embodiments of the invention, although freestanding, disposable, and made
especially for use in 40-
foot shipping containers, will not leak or rupture even when repeatedly
subjected to the impacts of
railroad car collisions.
Brief Description of the Drawings
Fig. 1(a) shows a flexitank for a 40-foot shipping container, according to a
preferred
embodiment of the invention, when it is partially filled with liquid.
Fig. 1(b) shows an optional preferred embodiment utilizing capacity bands.
Fig. 2 is an illustration of a railroad car impact which the preferred
embodiment of the invention
undergoes without leaking, rupturing, or damaging the container in which it is
placed.
Figs. 3(a) ¨ 3(c) show the end seam of a prior art flexitank.
Fig. 4 shows an improved strength end closure of the preferred embodiments.
Fig. 5 shows is an illustration of the assembly of the end closure in Fig. 4.
Fig. 6 is an exploded view of the end closure in Fig. 4.
Figs. 7(a) - 7(e) show the steps of forming a flexitank according to the
preferred embodiment.
Fig. 8 is a perspective view of an end closure in the preferred embodiment of
the invention.
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Fig. 9 shows an optional preferred embodiment in which an end cap is used to
further
strengthen the end closures of the flexitank.
Fig. 10 shows an end view of an exemplary bulkhead used in conjunction with
the flexitank of
one of the preferred embodiments.
Fig. 11 shows a side view of an exemplary bulkhead used in conjunction with
the flexitank of one
of the preferred embodiments.
The Preferred Embodiments of the Invention
Of course, the actual impacts on a larger shipping container when it is on a
railroad car during
part of a particular multi-modal shipment cannot be known in advance with
certainty. However, they
can be predicted and simulated. The preferred embodiments of the invention are
believed to be the
first to satisfactorily survive these impacts without leak, rupture, buckling
of the bulkhead securement
bars, damage or deforming of the container walls. A typical simulated impact
test is shown in Fig. 2.
The railroad car with the shipping container and flexible tank is released on
an approximate
0.8% downgrade of railroad track toward a string of empty anvil cars with
standard draft gears and a
combined weight of 250,000 lbs (113.40 metric tons), with the airbrakes set on
all impact vehicles, and
the handbrakes set on the first and last cars. The predetermined location is
selected such that, at the
point of impact, the railroad car carrying the flexitank has a speed of
approximately 4-6 miles per hour
(mph).
Fig. 1(a) shows a preferred embodiment of a flexitank according to the
invention resting on the
floor of the shipping container (horizontal cut away view). The flexitank is
shorter than the internal
length of the shipping container and its ends fall short of the end walls of
the container. It consists of
three layers of low density polyethylene (preferably 125 x 2 microns thick)
plus an outer layer of woven
polypropylene outer sleeve or cover (preferably 550 x 2 microns thick). The
cover provides additional
strength along the length of the flexitank that will absorb and control the
internal liquid dynamics during
transport. The cover for the flexitank is constructed from one layer of a 610
gram per square meter
vinyl fabric on a base reinforcing scrim of either a 14 x 14 or 20 X 20 per
centimeter polyester thread.
Such a relatively high thread count of the scrim provides added strength for
the carriage of liquids with a
specific gravity higher than water. The diameter of the covering external
layers is dependent on the
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desired capacity of the flexitank. There may be a single fill/discharge port
on the top of the flexitank or
there may a top fill port and a discharge valve at an end of the flexitank.
The preferred dimensions of a flexitank for a 40-foot container according to
the preferred
embodiments of the invention is 40.5 feet in length and 9.6 feet wide, and
approximately 27 inches in
height when loaded so as to have a capacity of 5,812 US gallons (22,000
liters). When filled to capacity,
the top is somewhat dome-shaped, being higher in the middle than it is at its
ends and sides. See Fig.
1(a). Another important aspect of the preferred embodiments is that the
flexitank is not filled to
capacity. This is counter-intuitive given the known concern over waves causing
ruptures at the ends of
flexitanks. The prior thinking was that, if the flexitank was completely
filled such that was no empty air
space, waves could not form that would travel from end to end, potentially
causing ruptures. But the
inventors have surmised that liquid dynamics are still created by sudden
impacts that stress the ends. In
addition to the improved end closures, the preferred embodiments also take a
different approach with
respect to capacity. The flexitank is intentionally not filled to capacity.
For example, for a flexitank with
a capacity of 5,812 US gallons (22,000 liters), it is only partially filled,
preferably with 5,425 US gallons
(20,560 liters).
Capacity bands can optionally be used at various points along the length of
the flexitank to
adjust the capacity of the flexitank to, for example, permit the shipping of
liquids of different specific
gravities while remaining within the weight restriction. The lengths of the
bands are somewhat less
than the circumference of the flexitank when it is completely filled to
capacity. The bands thus
"squeeze" the flexitank imparting a sort of four hump camel shape to the
flexitank and affecting the
capacity of the flexitank as shown in Fig. 1(b). The number and length of the
bands affect the flexitank
capacity to different extents. The number of bands can be increased and/or the
bands can be made
shorter to reduce the capacity. The preferred connection length of the bands
for the dimensions
provided above accommodates a circumference of 122 inches. Preferably, the
bands are disposed in a
symmetrical fashion along the length of the flexitank so as to avoid any
disproportionate effect on the
liquid dynamics. There may be three bands with the middle band positioned at
the center. Or there
could be an even number of bands spaced proportionally along the length of the
flexitank.
An important aspect of the capacity of the bands is that they are a separate
piece from the main
part of the flexitank, and selected at the time of installation according to
the liquid to be shipped. This
allows the main part of the flexitank to be mass produced and the capacity
thereof optionally decreased
by selective use of bands. The capacity bands are not sewn into or otherwise
secured on the main part
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of the flexitank. They surround the exterior and act somewhat like a belt for
a person's waist, relying on
the squeezing to keep them in place. It is important that the bands to do not
have buckles, or other
items with edges, to set their length or keep them in place. Testing has shown
that there is significant
abrasion between the capacity bands and the flexitanks during shipment, and
care must be taken that
the capacity bands themselves do not cause a leak or puncture. Preferably, the
ends of the capacity
bands are sewn together to form a continuous loop. A suitable construction of
the capacity bands is a
two inch width fabric constructed from a mixture of polyester and nylon
materials.
Another key feature of the preferred embodiments are improved end closures
shown in Figs. 4-
8. They seal both ends of the tank and provide additional strength to the heat
sealed end seams of the
inner tank when compared to the prior art sewn ends shown in Figs. 3(a) to
3(c), preventing any bursting
of the of the seam when under pressure from the liquid forces placed upon it.
The result is a flexitank
that is overall much stronger on the ends than the conventional flexitank.
A process of forming a flexitank according to a preferred embodiment of the
invention is shown
in Figs. 7(a) ¨ 7(e).
In the first step, long and narrow fabric layers are welded together
longitudinally, preferably by
radio frequency (RF) welding, to form the top and bottom external layers. The
ends of the top and
bottom layers are welded back onto itself as shown in Fig. 7(a) to form a loop
sufficiently large to accept
a nylon rope.
In the second step, the end flap is welded to the inside of the bottom layer
about 30 to 36
inches from each end of the bottom layer. This end flap is preferably the same
fabric as the top and
bottom outer layers. The end flap has the same width as the top and bottom
layers and a length of
approximately 7 to 8 feet. At this point, the end flap extends past the end of
the bottom layer as shown
by dashed line A in Fig. 7(b). When manufacture of the bag is complete, the
end flap will be positioned
as shown by dashed line B in Fig. 7(b). It is to be understood that, although
not shown in the cross-
section view, the longitudinal sides of the top and bottom layer are welded to
each other so as to form
an open ended tube.
In the third step, the looped ends of the top and bottom layers are cut at the
same points to
form corresponding equal sized sections of the looped ends as shown in Fig.
7(c). Odd loops are
removed from one of the layers and even loops are removed from the other layer
so that the layers
have alternating interlaced loops in the manner of a door hinge. The number of
loops is dependent on
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the width and, preferably, each loop is 6 centimeters long. The loops are
positioned in such a way that
in a lay-flat position, the loops of the top and bottom external layers will
be adjacent to and alternating
with each other in an interlaced manner. See Figs. 4-6.
In the fourth step, a top mounted load/discharge valve is attached to the
inner liner through an
opening on the top external layer centrally placed widthwise and near one end
seam lengthwise,
preferably about 30 to 36 inches from the end seam. The valve is preferably
secured using a clamp. The
inner liner, with its 2-4 layers already formed and welded together at the
ends, is inserted through the
open end of the bag nearer the valve and positioned between the top and bottom
layers. Any "coupon"
of the inner liner at the closed end of the bag is tucked so that it lays flat
against the outer layers. Any
"coupon" of the inner liner at the open end of the bag is tucked and then the
additional layer of fabric is
moved from the position of dashed line A in Fig. 7(b), so as to cover the end
and the coupon of the inner
liner as shown in Fig. 7(d) and be positioned over the top of the inner liner.
In the final step, the nylon rope is threaded through the alternating
interlaced loops of the open
ends of the bag completely across the seams. The rope closes the seams and
secures the flexitank into
the cover. Alternatively, grommets may be used in place of the alternating
loops to lace it together.
When the bag is filled with liquid as shown in Fig. 7(e), the inner liner
expands pushing against the end
flap and against the end closures with the loops. It is to be noted that the
loops in the end closure are
not watertight and are not intended to be watertight. The end flap provides
some protection against
leakage but primarily provides additional strength to the end closure. The end
flap contains the inner
liner inside the external layers of the cover, stopping it from coming into
direct contact with the end
closure. As shown in Fig. 8, the loops do not remain in alignment and the rope
does not remain straight
when the flexitank is filled, but they do provide end-closures of significant
strength.
The closure provides an extremely high strength which is particularly useful
for the end closures
of flexitanks. However, the closure is limited in its use to the preferred
embodiments described herein.
It can also be used for the sides of a rectangular shaped flexitank, or
anywhere a higher strength
replacement for a sewn seam is desired. The end closures here are based on
those disclosed in PCT
International Application No. PCT/U52018/058530 filed on October 31, 2018, and
US Provisional Patent
Application 62/579,612 filed on October 31, 2017, those disclosures being
incorporated by reference
herein.
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An alternative preferred embodiment of the end closure is shown in Fig. 9. In
addition to the
inner and outer layers, and end flap C, of the preferred embodiment shown in
Figs. 7(a)-7(e), an
additional end cap C is secured to the end of the inner layer. End cap C is
formed from a layer of PVC
fabric in a rectangular shape that is, for a flexitank having the preferred
dimensions noted above, about
116" wide x 60" long. It is folded in half making it 116" wide x 30" overall.
The folded over material is
then welded on each of the 30" long sides making the product shaped like a
canoe if filled with water.
This additional layer at a critical point adds strength overall to the end
closure system. The end cap C
helps to form the shape of the flexitank and further strengthen it against the
large liquid dynamic forces
resulting from the sudden starts, stops and jolts of a railroad car.
In addition to the above features, where a container has a door recess channel
directly inside its
doors, a bulkhead system may be inserted into that recess channel. The
bulkhead system may be the
bulkhead system shown in the end view of Fig. 10 and the side view of Fig. 11.
There are multiple
square bars 5 of 3/16th steel tube stock that fit into the door post slots.
Although five bars are shown in
Figs. 10 and 11, there may be four or six such bars. A bottom telescopic bar 2
is preferably formed of a
steel tube and includes an inner telescopic steel tube 3. Two vertically
oriented short-straps 4 are
preferably steel flat bars that secure steel bars 5 and telescopic bar 2
together, such as with hexagonal
bolts at the overlap of the bars and each short-strap. The steel bars 5 and
telescopic bar 2 protrude
horizontally to secure the bulkhead into the recess channel and provide 2
inches of clearance from the
bulkhead to the door. A corrugated polypropylene fluted panel board 1 is
secured to each bulkhead bar
and telescopic bar 2 by passing zip ties through the corrugated board 1 and
around the respective bar.
The board is preferably thick, such as 10 - 12mm. The container walls are also
lined with single wall
corrugated paper, preferably without any additional side or wall
reinforcement.
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