Note: Descriptions are shown in the official language in which they were submitted.
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Cellular tanks for storage of fluid at low temperatures
The present invention relates to a tank for storing of fluid, preferably
fluids at low
temperatures, a sandwich structure for use in a tank and a method for
producing a
tank.
There is a need for storage of Liquefied Natural Gas (LNG) at cryogenic
temperature and near atinospheric pressure in all areas of the LNG value
chain:
a) Fixed and floating offshore production facilities (liquefaction facility)
b) Onshore production and storage facilities
c) Waterborne transportation on ships
d) Fixed and floating offshore import terminal and possible re-gasification
facilities
e) Onshore import terininals and re-gasification facilities
Offshore_production facilities and import terminals are representing new areas
in
the LNG chain and several projects and concepts are currently being
investigated.
For floating production facilities and import terminals the tanks will
experience
different degrees of filling rates which may represent a problem to some tank
systems. Due to the wave induced motions of the structure, waves and dynamic
motion of the fluid will develop inside a partially filled tank giving high
dynainic
pressures on the tank structure. This iinportant effect called sloshing may
represent
a structural problem to most of the existing tank concepts.
For offshore production facilities, the shape of the tank is important as the
tanks
normally would be located inside the structure with the processing equipment
located on the deck above the tanks. Prismatic tanks are preferred as they
give the
best utilisation of the volume available for the tanks. Another aspect which
is
important for the offshore production facilities is the fabrication and
installation of
the tanks. Prefabricated tanks which can be transported to the construction
site in
one piece or a low nuinber of pieces offers reduced overall construction time
and by
that reduced cost. A fully prefabricated tank can also be leakage tested prior
to the
installation. The construction of a meinbrane tank systems is complicated and
need
to be done on the construction site inside a finished structure giving a
construction
time of typi,cally 12 months, or more.
For waterborne transport on ships, two main tank systems are dominating the
market; the Moss spherical tank system and the membrane tank systems developed
by GTT (Gaz Transport et Technigaz, France). The self-supporting SPB tank
developed by IHI (Ishikawajima-Harima Heavy Industries Co., Ltd., Japan) is
yet
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another possible system. The inaxiinuin size of LNG ships delivered today are
in the
range 138 000 - 145 000 m3 while the market demands now ships in the range
200 000 - 250 000 in3. These ship sizes may represent a design challenge for
the
existing tank systems. Long construction time is one of the main problems for
the
existing tank systems. Typically construction time for a 145 000 in3 LNG ship
is
around 20 months or inore with the construction and testing of the tank
systems as
the dominating bottleneck. A new challenge for the tank systems is introduced
in
connection with planned offshore loading and unloading giving a need to design
the
tanks for partially filling and associated dynamic sloshing pressures.
The Moss spherical tank concept was initially developed during 1969 - 1972
using
aluminiuin as the cryogenic material. The design is an independent tank with a
partial secondary barrier. The insulation is normally plastic foain applied to
the
outer surface of the tank wall. For ships and offshore facilities the
spherical tank
concept has relative low utilising of a restricted volume and it is not suited
for
having the possibility to have a flat deck on offshore facilities.
The development of the membrane tank systems was started in 1962 and has been
further developed by Technigaz. Today the systems consists of a thin stainless
steel
or Invar steel primary barrier, an insulation layer of Perlite filled plywood
boxes or
plastic foam, an Invar steel or Triplex secondary barrier and finally a
secondary
layer of insulation. The stainless steel meinbranes are corrugated in order to
handle
the thermal contraction and expansion of the membrane while the Invar steel
membrane does not need any corrugation. With respect to construction, the
systein
is.rather coinplicated with a lot of specialized coinponent and a substantial
amount
of welding. The welding of the membranes and the corrugations give variations
in
stress concentrations and stress variations due to sloshing all with
associated
possible cracking due to fatigue, give a potential high risk for leakages.
Liquid
sloshing due to wave induced motions of the vessel for partially filled tanks
is a
limitation for these tanks; typically no fillings between 10% and 80% are
allowed in
seagoing conditions. Sloshing generally gives very high dynamic pressures on
the
interior tank walls, particular in corner areas, which may cause damage to the
membrane and underlying insulation. Another concern is that inspection of the
secondary barrier is not possible.
The SPB tank developed by IHI is an independent prismatic tank with a partial
secondary barrier designed as a traditional orthogonally stiffened plate and
frame
system. The system consists of plates and a stiffening system consisting of
stiffeners, fraines, girders, stringers and bulkheads as in a traditionally
designed
ship structure. Due to these structural elements, sloshing is not considered
to be a
problem. Fatigue may have been considered to be a problem for this tank system
due to the significant amount of details and local stress concentrations.
Insulation is
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attached to the outer surface of the tank and the tank rests on a system of
wooden
block supports.
Mobil Oil Corporation has developed a box-like polygonal tank for storing of
LNG
on land or on ground based structures, described in patent application
PCT/US99/2243 1. The tank is comprised of an internal, truss-braced, rigid
frame
having a cover on the frame for containing the stored liquid within the tank.
The
internal, truss-based fraine allows the interior of the tank to be contiguous
throughout to sustain the dynamic loads caused by the sloshing of stored
liquid
which is due to the short excitation caused by seismic activity. The tank is
prefabricated in sections and asseinbled on site. The tank structure has a
nuinber of
details and stress concentrations which is a consideration with respect to
fatigue
life.
For onshore import tenninals and re-gasification facilities, the market is
dominated
by cylindrical tanks constructed as single containinent, full contaimnent or
double
containment tanks. A single containment tank comprises an inner tank and an
outer
container. The inner tank is made of cryogenic material, usually 9% Ni steel,
and is
normally a cylindrical wall with flat bottom. Pre-stressed concrete and
aluininium
has also been used for the inner tanks. The outer container is generally made
of
carbon steel which only has the function of keeping the insulation in place
and does
not provide significant protection in the event of a failure of the inner
tank.
The majority of LNG storage tanks built recently around the world is designed
as
double or full containment tanks. In these designs, the outer tank is designed
to
contain the full amount of the inner tank in case of a failure of the inner
tank. For
full containment tanks, the outer tank or wall is normally constructed as a
25. prestressed concrete wall distanced 1 - 2 in from the inner tank with
insulation
material in the spacing. Traditionally built onshore LNG tanks are expensive,
have a
construction time of about 1 year and have to be built on the location
requiring
substantial local infrastructure.
Purpose
The main purpose of the present invention is to provide a new type of highly
efficient, self-carrying low temperature tank which may have a hexahedral or
prismatic shape and which is fully scalable; that is, the tank is in principle
extendable to any dimensions or size while being based on mainly a repetitive
structural principle. It is also an aim that the tank concept can withstand a
large
member of cycles of pressure and temperature variations during its lifetime.
A further purpose is to achieve a tank with a high volume efficiency; that is,
for the
tank volume to be able to fill out as much as possible of surrounding spaces
that
typically are seginented in hexahedral, rectangular or prismatic volumes (e.g.
cargo
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holds in ships, containment spaces on floating platforins, seginented spaces
at land-
based plants, etc.).
An additional feature and purpose is to provide a tank system which solves the
problem of internal fluid sloshing for tanks that are onboard ships or
floating
installations.
A further aim is to provide a thermally insulated self-carrying tank that can
be
prefabricated in parts or in total and that can be transported and positioned
into final
location and position.
Another aim is to provide a low teinperature tank that has enhanced
operational
capabilities in terms of iinproved fatigue performance, design life and ease
of
inspection.
A further aim is to develop a tank system that is economically and technically
competitive with current tank systems for similar use.
A further purpose of the current invention is to provide a self-contained
system of a
tank or a cell structure that can be prefabricated in one location and
transported and
placed in another location, e.g. onboard ships, floating terminals or sites on
land.
The tank can extensively be equipped for its operational purpose including
filling
and discharge system, monitoring systems etc.
General part
These aims are achieved with the invention as defined in the following claims.
The invention regards a prismatic or hexahedral tank or containment system for
storage of fluids at very low temperatures. The external tank comprising side
walls,
floor and roof, at least some of these elements comprise a plate structure
which
serves the purpose of being the structural element and provide leak tightness
for the
tank. In an embodiment the plate structure may also as well as provide
required
therinal insulation or part of the thermal insulation of the tank. The plate
structure
(plate) comprises a layered structure, which at least comprises a sandwich. By
sandwich one should in this application understand at least two layers bonded
or
connected to each other by a core and transferring loads between the layers.
One
special embodiment of such a sandwich comprising two layers with a core
between,
is one where an outer layer may be fonned with a multitude of throughgoing
recesses, which recesses further are covered by a membrane material.
The external plate structure in the walls are anchored by way of a self-
equilibrating,
norinally thin, internal cell structure wall system that effectively anchor
the external
walls against the static and dynamic loads to which they are exposed.
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In a preferred embodiment the layered plate structure comprises the sandwich
structure, which comprises at least two surface sheets of metal or other
material
with similar properties with a core material in between. The core of the
sandwich
may be a continuous material or a structure comprising of different shaped
webs,
5 forming cells with a direction mainly parallel with the sheets in between
the two
sheets. This internal structure may also be a honeycomb or other similar
structure
between the sheets. The main element is that the core of the sandwich,
transfer
loads between the two sheets in the sandwich. Additional insulation may be
provided at the outside and or inside of this sandwich structure. Having this
sandwich structure with two sheets and a core structure also gives the benefit
of the
possibility to have a gas detection arrangement in between the two sheets in
the
sandwich.
The tank may have different prismatic forms; however, the typical geometry is
a
hexahedral or "box-like" shape. The external side walls or side plates and the
bottom floor or plate are exposed to static and dynamic fluid pressures and
are
designed to withstand such loads. A metal sheet or plate in the sandwich
structure
provides the necessary bending strength in relation to the core, which may be
a
structure or a material that mainly serve the purpose of transferring shear
forces.
The core of the sandwich may provide a part of the insulation of the tank,
this may
for instance be due to having a material with very low thermal conductivity
forming
at least a part of the core material or structure. Sufficient strength and
stiffness of
the external plate may also be provided by way of extra stiffeners.
The external walls are effectively anchored at vertical intersection lines
with the
internal cell structure walls and must essentially transfer the loads in plate
action to
these supports. Similarly the bottom plate may comprise a layered structure,
preferably a sandwich structure, that is exposed to fluid pressure as well as
own
weight. The bottom plate or floor essentially transfers these loads to
suitably
located supporting means, for instance at grid points of the internal cell
structure
wall system. These support means, which provide for a relative thermal motion
in
relation to the foundation, will be described later. The internal cell
structure walls
are primarily stressed in their own plane in horizontal direction due to the
pressure
loads transferred from the external walls: In the case of tanks located on
land the
internal cell structure walls may be very thin plates dimensioned according to
the
principle of "fully stressed design". Very thin plates may be difficult to
handle, a
way of improving this wall will be explained later. In cases of tanks on
moving
foundation the internal cell structure walls will also have to be designed for
dynamic loads from the fluid stored.
In case of sandwich construction the core material in the external plate parts
of the
tank serves the dual function of partly thermal insulation and structural
stiffness; it
must have strength and thickness sufficiently large to serve these purposes.
In one
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einbodiinent most of the thennal insulation may be performed by the core of
the
sandwich structure.
In one einbodiinent where the core is in the fonn of a continuous material
layer
various types of materials may be applied for the core as long as they have
suitable
properties in terms of stiffness, strength, thermal conductivity and thennal
expansion (contraction) coefficient. Typically the material mix may consist of
fine
grain components and larger granular coinponents submerged in a matrix
material.
The fine grain coinponents may be various types of sand or various inorganic
or
organic materials. The larger components are typically porous grains that
provide
strength and insulation at low weight. Such aggregates may be expanded glass,
it
may be burnt and expanded clay, or it may be other types of geo-materials or
organic materials such as plastics. Some examples of commercial aggregate
materials are Perlite, Liaver, Liapor, Leca, etc. An alternative to light
weight
aggregates is introducing air or gas bubbles into the matrix material before
binding.
The binder or matrix material may be one or several of typical binder
materials such
as cement paste, silica, polymers, or any other material that would serve well
in the
current context. Special chemical components may also be added to the paste in
order to achieve special properties such as desired viscosity, shrinkage
reduction or
voluine control, right speed of hardening, fatigue performance etc. Metallic,
inorganic or organic fibres may also be added to the mix to achieve higher
strength,
particularly in tension.
The core layer may as said also be provided by a structure formed by webs
between
the two sheet layers forming different shaped cells between the sheets, which
cells
has a longitudinal direction mainly parallel with the sheets. There may be
webs
arranged mainly across in relation to the sheets, or at an angle other than 90
degrees
in relation to the sheets, or forming more like a honeycomb structure.
There are several methods for producing the sandwich structure in the external
plates of the tank according to the preferred embodiment. The core material
may in
the form of a continuous material either be placed in fluid form directly
between
sheets that make out the formwork for the casting the core. Alternatively the
core
material may in part be prefabricated as plates or blocks that are grouted or
glued to
the sheets and to each other. The core may consist of different layers of
glued plate
material through the thickness. The material may also vary from one part of
the
plates to the other.
In the other version of the sandwich structure it may be extruded as a whole
structure with both sheets and core in one, or the core element may be
extruded and
welded to the sheets of the sandwich structure. The core element may also be
forined by several separate elements welded together to fonn the core element.
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In another version of the current invention the core material and dimensions
primarily serve the purpose of necessary structural strength, and the
additional,
necessary therinal insulation is provided by a largely non-structural
insulation layer
at the outside of the "sandwich" structural part. In this case the core of the
sandwich
can be made of a relatively high strength material such as good quality
concrete or a
structure. In the example of a continuous core, the core material may for
instance be
a "high strength" concrete with compressive strength of 80MPa and weight 2400
kg
per m3. The additional insulation on the outside is then not exposed to forces
of
significance, and can be inexpensive insulation like rock-wool or glass-wool.
In this
case the sandwich part of the external barriers will be under nearly uniforin
temperature corresponding to the temperature of the internal fluid. This
sandwich
part of the wall will accordingly contract or expand in.a rather uniform way.
The
insulation layer on the outside will host the main part of the temperature
gradient,
but will have no problem with accommodating the thermal deformation of the
sandwich on the inside since it is a loose, non-structural material.
The inner skin of the sandwich layered structure of the external plates of the
tank is
typically made of a metal that has sufficient strength as well as resistance
to the
thermal and chemical environinent of the fluid stored in the tank. It may also
be
formed by non-metallic materials with similar properties. In the case of a
tank for
LNG containinent the material may be 9% Nickel steels or austenitic stainless
steels
like 304, 304L, 316, 316L, 321 or 347. Other types of metals, aluminium alloys
or
Invar steel, or coinposites may also be used. The outer skin is typically not
exposed
to the same harsh thermal and chemical environment as the inner skin, and it
may be
made of for instance a simpler type of carbon structural steel. For the inner
as well
as the outer skin applies that the material must be suitable for joining, such
as
welding, and have sufficiently good bonding properties to the core, be it a
structure
or a core material or to the binder of core blocks.
In the case of using a higher strength, but less insulating, core material the
outer
skin of the sandwich layer will also be exposed to nearly saine therinal
regime as
the inner skin. In such case the outer skin must be an alloy that can maintain
sufficient strength at the actual temperatu.re regime.
The sandwich structiure in the plates may comprise stiffeners, for improving
the
bonding between the elements in the sandwich and also for iinproving the
structural
strength of the sandwich. In one embodiment may the core material in itself
give
little structural strength to the sandwich structure, this may be achieved
through
stiffeners. The stiffeners may be of different forins but preferably they are
plate like
ineinbers having a width running from one surface sheet to the other surface
sheet
and a length running in the direction from e.g. the bottom to the top of the
tank
structure, preferably the whole way, or possibly as a grid structure. There
may be a
continuous material in between the grid structure or there may be voids and
the grid
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structure them forins the core structure in the sandwich. A special case is
that the
external wall is made as a stiffened plate structure or a box structure rather
than a
sandwich plate. In such case, the insulation within or on the outside is not
required
to have structural properties.
The main coinponents of the tank is the external plates,,coinprising side
walls, a
floor and a roof, that are insulated, layered plates, and a set of cellular
internal walls
that essentially are self-equilibrating support or anchor walls for the
external plates.
The internal anchoring cell walls that make out the internal cellular
structure inust
satisfy the saine requirements as the inner sheet described earlier, i.e. they
will
typically be made of the saine material. The internal anchoring cell walls may
be
formed in several ways, they may be plane sheets crossing each other forming
cells,
this cell structure may also be formed by corrugated sheets.
Another preferred embodiment is to form the cell structure by a plurality of
beam
elements stretching from one side wall to the opposite sidewall. The cell
structure is
build by arranging one beam transverse to the next beam positioned next to the
first
beam, where a third beam is positioned similar to the first beam transverse to
the
second beam and a fourth beam transverse to the third beam, and by this
forming a
lattice structure, which lattice structure comprises openings between the
beams
positioned above each other, i.e. the first, third, fifth beain and second
fourth and
sixth beam etc. Another way of explaining it would be to say that the beams
forin a
sort of "log cabin" structure, with gaps between the different logs in the
structure.
The beams would preferably also run from one external wall to the opposite
external wall of the tank.
The cell structure is in this embodiment formed such that in a plane A
transverse to
the side walls, all beains A are arranged with their longitudinal direction in
the
plane A and mainly parallel to each other. The beains arranged directly above
these
first beams A are all arranged in a second plane B where the beams have mainly
parallel longitudinal axis. These planes A and B are repeated in an ABABABAB
pattern until the necessary height of the cell structure is achieved. Other
patterns are
also possible, with for instance a third layer of beams.
The angle between the first and second beam my preferably be around 90 degrees
fonning rectangular or square cells, but it is also conceivable to have an
arrangement where a crossing of beams forin angles of 60/120 or other
configuration.
The contact points where beams in one layer is crossing beams in another layer
is
preferably arranged in a straight line forming a position for transferring
loads from
for instance roof to floor construction of the tank.
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The beams used in the beam arrangement may have several forins of their cross
section, for instance T-shaped, I-shaped or only a rectangular or tubular
shape. The
flanges of the T or I shaped beams gives additional effects to avoid sloshing
damages, by making turbulence in the flow of fluid as a consequence of
movement
of the tank. The flanges of the beains also support the cell structure by
giving larger
contact areas between the layers of beams the layered structure and gives
rigidity in
the contact position between the different layers of beams. These forms
mentioned
are standard forins for beams, other configurations of the cross section of a
beam
may also be possible, while achieving the saine effect of anchoring of side
walls,
minimizing sloshing effects and at the same time having communication between
the different cells in the structure
For strength and for reasons of ease of production the intersections of the
internal
cell walls may include a separate ineinber to which the wall seginents are
attached.
This may be used for both plane plate cell walls and also a beam structure
wall as
described in the chapters above. For instance, this meinber may be a vertical
beam
of tubular or square cross-section. Since the internal cell walls themselves
will be
very thin (only a few millimetres), especially in the case of plate formed
cell walls,
it may in cases of applications where dynamic motion occurs be necessary to
provide additional transverse strength. This may be done by attaching
unilateral or
two-sided horizontal stiffeners at suitable distance, or, alternatively, by
providing
lateral strength via horizontal corrugation of the thin internal wall plate.
Note also
that the mentioned tubular meinber at the intersections between inner wall
segments
essentially will have to carry the weight of the cell walls since these have
nearly no
vertical carrying capacity because of proneness to buckling due to high
slenderness.
The saine tubular members will also have to carry the weight of the roof
structure of
the tank itself.
The sloshing phenomenon is strongly dependent on the size of the free surface
area
of the fluid volume, which, in the current invention is segmented into smaller
areas
by way of the cellular internal wall system. For instance, by using internal
cells of
5 to 10 meters square the sloshing problem would, in most cases, be virtually
eliminated. The internal cell walls would in such cases be subject to moderate
fluid
dynainic forces and should be designed for such purpose, e.g. by having a
corrugation that provides required bending and shear force capacity, by having
flanges on the beains. Similarly, the external plates, which comprise layered
plates,
preferably as a sandwich structure, are designed for fluid pressure loads
which
easily also may include moderate dynamic sloshing load components. It is. a
particular feature of the current invention that the sloshing problem is
relatively
independent of the degree of filling in the tank; in fact, the total fluid
pressures will
be reduced with lower degrees of filling.
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Even though the internal voluine is divided into separate cells there will in
the case
.of plate cell walls be open holes at the bottom of the cell walls that
equalize the
fluid level in the cells and that give easy human access to all cells for
inspection
and repair purposes. For the beam structure cell walls, there are opening
between
5 the beams fonning the walls giving communication. There may if necessary in
addition be open holes close to the floor for human access. The iinportant
factor is
to give communication between all the cells in the cell structure. These
openings are
positioned by the bottom floor and may have strengthening meinbers associated
with the opening edges.
10 The cellular grid of internal cell walls can be fully and uniformly
exploited stress-
wise and will typically 'be for plate cell walls very thin (a few millimetres)
and for
beam structure wall not be heavy. This is important since the internal plating
often
will have to be made of high grade, expensive alloys that can sustain the low
teinperatures and chemical enviromnent of the internal fluid. Having very thin
plates in the cell structure walls may as earlier mentioned cause a problem in
handling the cell structure walls. The cell structure wall are therefore in
one
embodiment of the invention provided with cooperative end part elements at two
opposite sides of the cell wall, which sides will meet another cell wall side
at an
intersection in the cell structure. These end part elements forin together a
stiffening
member, stiffening the cell walls and also thereby the cell structure of the
tank. For
the beam cell-wall structure the beams may preferably be formed with flanges
for
stiffening of the beams.
This gives a reasonable production and assembly of the cell structure. The
layered
sandwich construction of the external plates; side walls, floor and roof,
serving both
as structural and partly insulating elements, is economically very effective.
Moreover, the internal as well as the external parts of the tank are fully
modular and
repetitive. This means that the tank leans itself to a very high degree of
automation
during its production. This in turn will also contribute toward favourable
economic
performance.
In one version of the invention the corners of the external walls may be
rounded.
One reason for introducing rounded corners is that one may obtain less
concentrated
structural moments in such case. Another reason may be to reduce somewhat
thermal stressing between the two sides of the external walls.
The production method of the tank is important for practical reasons as well
as for
the overall economy. Pre-production in modules or in total implies reduced
construction time and that tank production can go in parallel with
construction of
the rest of the vessel, platforin or site where the tank is finally going to
be located.
The cellular tank system lends itself to prefabrication and automated
production to
an exceptionally high degree. All internal cell wall segments are essentially
equal
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and can be mass produced "asseinbly line style". Their attachment to the
joining
stiffening members can also be done in a repetitive and automated fashion.
Highly
effective welding techniques, such as friction stir welding, laser or plasma
welding,
may be considered in some cases. Also the outer plates may be produced
seginent-
wise and joined together between themselves and with the internal cell walls.
A tank according to the inveintion will as described be able to be used for
storage of
different kind of fluid and will give good performance in the temperature
range of
+200 C to -200 C, and especially suitable for LNG. The tank may withstand to
have
some bar static over pressure within the tank. It may be positioned on a
floating unit
or at a land based site.
The tank may be positioned on a bearing system, where one has one anchoring
point
and a means to prevent the tank form rotation. The tank may as an alternate
also be
positioned directly on a sand base or other base with similar properties.
The invention will now be explained with preferred einbodiinents, with
reference to
the drawings where:
Fig. 1 shows a tank according to one overall embodiment of the invention with
the
roof and one side wall removed,
Fig. 2 shows a second overall embodiment of a tank according to the invention,
Fig. 3 shows a third overall einbodiment of a tank according to the invention,
Fig. 4A and 4B show a detail of a corner of the tank in fig. 1 with a first
embodiment of an internal cell structure in fig. 4A, and a second embodiment
of the
internal cell structure in fig. 4B,
Fig. 5A shows a detail of a tank with a third einbodiment of an internal cell
wall
structure attached to an external plate,
Fig. 5B-E show exainples of details of the connection of a second embodiment
of an
internal cell wall structure to an external plate,
Fig. 6A shows a cross section of one embodiment of a cell wall in the first
embodiment of cell structure,
Fig. 6B shows a cross section of an intersection of four cell walls according
to the
embodiment shown in fig. 6A,
Fig. 7A shows a cross section of another einbodiinent of a cell wall in the
first
embodiment of cell structure,
Fig. 7B shows a cross section of an intersection of four cell walls according
to the
embodiment shown in fig. 7A,
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Fig. 8A-D show different cross sections of different einbodiinents of an
external
plate of a tank according to the invention,
Fig. 9A-B show exainples of different elevated view of alternative corner
solutions
of the external wall of a tank according to the invention,
Fig. 10A-B show two perspective views of a tank according to the invention
with
the outer skin of the sandwich removed,
Fig. 11 shows a tank according to the invention with external stiffeners, with
the
roof and one side wall removed,
Fig. 12 shows a detail of a part of the tank in fig. S.
The tank 1 according to the invention comprises side walls, roof and floor in
the
form of external plates and an internal cell wall structure, whereof there in
fig. 1 is
shown three side plates 2, a bottom plate 4 and an internal cell wall
structure 5,
dividing the internal void of the tank 1 into smaller cells. It is possible to
envisage
several different structures fonning the walls, roof and floor and their
connecting
zones. These may all be of similar or different constructions. The internal
cell wall
structure may also be envisaged constructed in several ways. Different
einbodiments
of these elements will be described below.
The internal cell walls 20, forming the internal cell wall structure 5 in the
form of
plates with a smooth surface, have passage openings 6 at the level of the
bottom
plate 4 with possible edge beams, to give internal communication between all
the
different cells. This also gives access between the cells for inspection and
repair in
the case of a larger tank. The tank will also comprise an emptying and filling
system
and other detection and monitoring systems and support means which are not
shown
in the figure.
Fig. 2 shows a different embodiment of the tank 1 with side walls 2 and a cell
structure 5 comprising of cell walls 20, where the four corner cells outer
walls are
fully rounded in an arc in comparison with fig. 1 where they are shown as only
partly rounded with a straight part at each end as well. Fig. 3 shows an
alternative
tank 1 with side walls 2 and a cell structure 5 of internal cells wal120,
where the
corners of the side walls are right angled.
Fig. 4A shows a perspective view of a detail of the tank in fig. 1, showing an
embodiment where the outer plates 2 are formed as a sandwich structure with an
outer surface skin 8 and an inner surface skin 9 where between there is a core
material 10. The sandwich structure also comprises stiffeners 11. These
stiffeners
may have several fonns but preferably they stretch from one surface skin of
the
sandwich structure to the other surface skin of the sandwich structure. In the
preferred embodiment the stiffeners are plate like elements which width is
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13
substantially equal to the distance between the surface skins in the sandwich
structure and where the length of the plate element run in the vertical
direction of
the side wall, and preferably for the whole height of the side wall. In this
figure the
internal cell wall structure is shown as in a first einbodiinent of the cell
wall
structure, where the cell walls are forined with single plate walls 20, which
are
joined at intersections 21. The internal wall plates 20 are preferably
anchored to the
side wall at the point where the sandwich structure have plate like stiffeners
11, by
for instance welding between the wall plate 20 and the internal surface skin 9
of the
sandwich structure. This is favourable in relation to transferral of loads
between the
external walls and the internal cell structure. The plate walls '20 may also
be formed
with a pattern of through going holes (not shown in any figures).
In fig. 4B there is shown a second embodiment of an internal, cell wall
structure. In
this einbodiment the cell walls 20 are formed by a plurality of beam elements
28
arranged above each other forming a cell wal120. The beams 28 are arranged
with
one set of beams 28A in a first layer and a second layer of beains 28B above
this
first layer are arranged with their longitudinal axis across the beains 28A in
the first
layer. In a third layer the beams 28A are arranged mainly parallel with the
beams in
the first layer. This forins a lattice structure with several layers and with
beams with
different longitudinal axes in different layers. This gives a cell wall formed
by beam
elements with spaces between each beam element in cell wall. This gives the
necessary communication between the cells and at the same time the necessary
prevention against sloshing in a tank positioned on a moving vessel. At the
intersection 21 of the cell walls 20 the beain elements 28A, 28B are arranged
abutting one on top of the other beain element forining support for each layer
of
beam elements 28A, 28B and also a transferring point for eventual loads from
roof
to floor.
The beam elements 28A, 28B may be plane plates, or have a I of T or H formed
cross section. By having a cross section with end flanges as in a I, T or H
fonned or
even tubular rectangular or rectangular, cross section one also achieves a
more
stable construction of the internal cell wall structure since a beam in one
layer may
lay with its end flanges in abuttement against the end flanges of the beains
in the
next layer. The beains may also be welded or mechanically fixed to each other
to
fonn an even more stable construction of the internal cell wall structure. One
beam
element in the cell wall structure may reach from one external wall to the
opposite
external wall, i.e. the beam elements forin a part of several cell walls.
The cell walls 20 may be smooth plate elements as shown in the embodiment in
fig.
4A, plate elements with stiffening means (not shown in any figure), fonned by
a
plurality of beain eleinents or even plates 20 with corrugations 23 as shown
in fig.
5A. These plates 20 have corrugations 23 running in a mainly horizontal
direction.
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14
The internal cell structure coinprises cell walls 23 which meet at
intersections 21.
These intersections 21 inay in a preferred einbodiment comprise at least one
stiffening member 24. The stiffening meinber may be wholly or partly tubular
(circular, square) or comprising main elements positioned in a right angle
relative to
each other, and abutting the surface sides of two adjacent cell walls, as
shown in
fig. 5A. There may be stiffening ineinbers only in one corner of the
intersection of
the wall plates 20, or there may be stiffeners at more than one corner or all
the
corners.
According to the invention the internal cell structure is anchored to the
external
walls of the tank, this may be done in several ways. One is as shown in fig.
4A
where the cell walls 20 are joined with the inner surface skin of the sandwich
structure at the position of the stiffeners. This gives a transferral of loads
through
the sandwich structure and out to the outer skin of the sandwich structure.
Another
possibility is shown in fig. 5A where a fastening element 14 is arranged in
the
sandwich structure, this also gives a transferral of loads to the outer part
of the
sandwich structure in the external walls. Another possibility is just to weld
the cell
walls 20 to the inner skin of the sandwich structure (not shown).
Other einbodiments especially suitable for cell wall structure comprising beam
elements are shown in fig. 5B-E, these solutions will also be usable for
connection
of cell wall structures formed by smooth plates or corrugated plate.
In fig. 5B it is shown that the beam eleinents 28A, are attached to a flange
40'
which is attached to the external wall 2, and protruding into the void of the
tank in a
direction transverse to the external wall. The flange 40' is shaped with a
larger
protruding part by the connection to a beam element 28A, and a less protruding
part
between the beain elements 28A.
Iri fig. 5C-F where the cell wall are shown as formed by several beam elements
28A, these beain elements 28A are attached to an external wall 2, comprising
of two
elements 2A and 2B joined by a connection element 40. The connection eleinent
40
shown in fig. 5C-E is forined with a mainly U-shaped groove for insertion of a
element of the external wall 2.
The connection element 40 is further formed with a flange 45 extending into
the
void of the tank in a direction transverse to the external cell wall 2. The
internal cell
wall structure, by the beam elements 28A are attached to this flange 45 in
several
ways. One einbodiinent is shown in fig. 5C where the beam elements 28A are
welded to the flange 45. Another einbodiment is shown in fig. 5D where the
beain
elements 28A is attached to the flange 45 through a connection piece 41 with
two
U-shaped grooves for position of a part of the beain elements 28A and a part
of the
flange 45 and connected to these eleinents by through going bolts through bolt
holes
42. In fig. 5E the beam elements are formed with a U-shaped groove for
insertion of
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the flange 45, which forins a third einbodiment, and connected by for instance
welding.
Fig. 6A-B and 7A-B show two different embodiments of a cell wall 20 fonned
with
end part elements 25 which cooperate with other end part elements 25 to fonn a
5 stiffening ineinber 24, at an intersection in the cell structure.
In fig. 6A there is shown a cross section of a cell wall 20. There is to both
ends of
the cell wall attached end part elements 25 which is longitudinal and has a L-
shaped
cross section.
The end part element 25 is attached to the cell wall 20 at a point on the
raised part
10 26 of the L-shape and the lower part 27 is facing away from the cell wall.
As can be
seen from fig. 6a the lower parts 27, 27' of the two end part elements 25, 25'
are
preferably positioned on opposing sides of the cell wall 20.
Fig. 6B shows a cross section of an intersection of four cell walls 20, with
an
embodiment as described in relation to fig. 6a. The end part elements 25, with
a
15 L-shape forin with a raised part 26 and a lower part 27, of all four cell
walls interact
at the intersection and forms together a stiffening member 24. The raised part
26 of
one end part element 25 is connected to a lower part 27 of another end part
element
and all four together forms a rectangular element. The L-shaped elements may
be
connected by welding, screws, bolts, pop rivets or equal.
20 Fig. 7A-B show another embodiment, where in fig. 7A it is shown a cell wall
20'
with an end part element 25' with a V-shape, attached to both ends of the cell
wall
20'.
In fig. 7B it is shown a cross section of four cell wall similar to the one
shown in
fig. 7A, forming an intersection where the four end part elements 25' form a
25 stiffening member 24'.
The outer plates of the tank 1, the roof, side walls and floor comprises
according to
the invention preferably a sandwich structure comprising an outer surface skin
8
and an inner surface skin 9 with a core between them, the core being a
continuous
material as shown in fig. 8A or a structure as shown in fig. 8B-C. The core
provides
for at least partly the strength of the wall and the insulation of the tank.
The
sandwich structure may comprise a structure or stiffeners 11 between the outer
and
inner surface skin, 8 and 9 respectively. These may have different forms shown
in
the fig. 8A-C, wherein in fig. 8A they are straight transverse stiffeners,
straight
stiffeners arranged with an angle other then 90 with the surface skins in fig.
8B or a
solution where the surface sheets 8,9 and the stiffeners are extruded in one
piece.
There may of course also be a continuous material between the structure of
stiffeners as shown in fig. 8A.
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In another embodiment as shown in fig. 8D the sandwich structure may comprise
in
addition external stiffeners 12, protruding outward from the side, top or
bottom
plates and an outer insulation layer 13. The external stiffeners 12 may
protrude
partly through the outer insulation layer 13, as shown, or fully through the
outer
insulation layer. As shown in fig. 8D there may be a connection between the
plate
walls 20 in the internal cell structure, the stiffeners 11 in the sandwich
structure and
the external stiffeners 12, or the stiffeners 11 and the external stiffeners
12 may
fonn part of an elongation of the plate wall 20. The stiffeners may be
provided with
cut-outs, recesses or other insulating material element to reduce the heat
transfer
through the stiffeners.
Examples of corner solutions for joining the external walls 2 are shown in
fig. 9A-
B. In the solution shown in fig. 9A there is a corner eleinent 16, forined
with mainly
U-shaped grooves for insertion of external wall segments and welded to the
corner
element 16. In the solution shown in fig. 9B the outer sheets of the sandwich
structure of the external wall 2 is joined together by welding directly to
each other
fonning a sharp angle.
In fig. l0A and l OB there are shown perspective views of a tank according to
the
invention with the outer surface skin of the sandwich structure and core
material
removed, showing the inner surface skin 9 and the plate like stiffeners 11,
running
in a grid patter in the top 3 and bottom 4 plates and in a direction running
from the
bottom 4 to the top 3 in the side plates 2. There are also arranged support
means 30
at all the ends and intersection of the stiffeners 11 for the bottom plate 4.
These will
be explained in more detail later.
Fig. 11 shows a tank according to the invention with a side wall and the roof
removed, and fig. 12 a detail of the tank in fig. 10. The side walls 2 of the
tank
comprise in this einbodiment external stiffeners 12 running in a grid
structure, with
stiffeners 12 running in a mainly horizontal and vertical direction. One may
see
from these figures that the plate wall 20 of the internal cell structure 5 is
connected
to the side walls 2 along the position of an external stiffener 12, this gives
beneficial structural integrity of the tank. Provided the stiffener system is
designed
with sufficient strength this embodiment of the invention does not require
structural
strength in the insulation layer.
In one embodiment of the invention the external plates may be connected to and
supported by other existing, adjacently located, structural systems at one or
several
point or along line contact areas by way of elastic links, linear or nonlinear
mechanical devices,-or pneumatic and or hydraulic devices or coinbination
thereby.
This is not shown in any figure. One specific embodiment is to use the
previous
described support means to support a side wall of the tank, however there may
be
envisaged a lot of other einbodiinents, as indicated above. The beam structure
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fonning the cell walls may be fonned by closed profiles having a tubular or
rectangular cross section.
The invention has now been explained with different detailed einbodiinents.
However, it is possible to envisage a lot of alterations and modifications to
these
embodiments within the scope of the invention as defined in the following
claims.
The cell structure may have different geometries. The outer structure may be
laterally supported by surrounding structures as for instance a ship. There
may be
several layers of insulation with different quality and this may be varied for
the
different plates forining the tank. The support means may be positioned for
supporting the tank laterally, or the may be other outer lateral support as
for
example an outer structure as the hull of a ship.
