U.S. patent application number 10/065998 was filed with the patent office on 2004-06-10 for composite tank stabilizer.
Invention is credited to Bettinger, David S..
Application Number | 20040108319 10/065998 |
Document ID | / |
Family ID | 32467280 |
Filed Date | 2004-06-10 |
United States Patent
Application |
20040108319 |
Kind Code |
A1 |
Bettinger, David S. |
June 10, 2004 |
Composite Tank Stabilizer
Abstract
A composite tank stiffener reinforces a filament wound tank of
generally cylindrical and hemispherical headed shape, possessing
first and second inlet pipe members internally extended within and
with fluid communication with the tank and movable, connected by a
slideable expansion sleeve selected to resist lateral moment forces
sufficient to distort the shape of said tank and also selected to
compressively limit dimensional relative movement between the
members to resist fabrication and operational loadings.
Inventors: |
Bettinger, David S.; (Grosse
Ile, MI) |
Correspondence
Address: |
DAVID S. BETTINGER
8030 COVENTRY
GROSSE ILE
MI
48138
US
|
Family ID: |
32467280 |
Appl. No.: |
10/065998 |
Filed: |
December 9, 2002 |
Current U.S.
Class: |
220/651 |
Current CPC
Class: |
B65D 88/06 20130101;
B65D 90/029 20130101; B65D 90/00 20130101 |
Class at
Publication: |
220/651 |
International
Class: |
B65D 001/42; B65D
006/34; B65D 008/08 |
Claims
1. A composite tank stiffener comprising: at least one generally
cylindrical pipe and strut possessing at least one slip joint
selected to provide (1) compressive dimensional limit by abutting
slip joint surfaces and (2) telescoping moment restraint during
axial relative positional movement by congruent wall slip joint
surfaces, said generally cylindrical pipe and strut connecting the
two internal faces of two composite boss for a filament wound
tank.
2. The composite tank stiffener of claim 1 whereby said generally
cylindrical pipe and strut possesses at least one opening and inlet
for the transfer of fluids in common with fluid inlets of said
filament wound tank.
3. The composite tank stiffener of claim 2 whereby said generally
cylindrical pipe and strut also possesses openings in communication
with the internal volume and reservoir of said tank.
4. The composite tank stiffener of claim 1 whereby said internal
faces of two opposing composite boss are connected by multiple
units of said generally cylindrical pipe and strut.
5. The composite tank stiffener of claim 1 whereby said two
opposing composite boss are selected of a size, shape, and strength
to provide the supporting structure for the filament winding of the
composite body of said filament wound tank.
6. An expandable composite tank cylindrical wall form comprising: a
first and second domed head form and boss selected to provide size,
shape, and rigidity for the support of filament windings, connected
to opposing ends of a pipe and telescoping slip joint assembly
selected to provide limited compressive movement by abutting end
surfaces within said slip joint and moment restraint during
relative dimensional movement between said first and second head
forms.
Description
FEDERAL RESEARCH STATEMENT
[0001] Not applicable.
BACKGROUND OF INVENTION
[0002] 1. Field of Invention
[0003] This invention is directed to the field of fluid storage
tanks fabricated from polymer matrix composites and more
particularly to an apparatus for internally stabilizing and
stiffening a thin shell tank structure using one or more stiffener
struts possessing telescoping slip joints with limited compressive
travel.
[0004] 2. Prior Art
[0005] It is well known that polymer matrix composites (PMC) can be
used for the manufacture of light-weight, high-pressure tanks. Such
tanks may be used for the storage of cryogens such as LNG, LOX,
LH2, and LN2. In a PMC tank, the material functions primarily in
tension to contain the pressurized fluid. The tension results
because the container shape as a sphere, domed vessel, or
hemispherical headed cylinder tends to distribute internal
pressures evenly due to diaphragm action as one might observe in a
thin shell structure such as a balloon. Such thin shell structures
are highly effective in their use of material.
[0006] A common fabrication technique for PMC tanks is to filament
wind the primary tank structure upon a mold or liner frame mounted
on a mandrel. Various designs for molds and liners that are either
removable or become permanent liners are known in the prior art.
Sand molds are a common support for the wound filaments of prepreg
or tow. A problem with sand is its propensity to remain in the
completed tank despite energetic washing.
[0007] Current practice is to utilize a metal alloy inlet
connection for the tank. These inlet connections are often flanged
and designed for easy connection to alloy piping. This practice
requires a mating of the thin shell composite structure to the
metal inlet in a metal transitional end structure called a boss.
The alloy boss is welded to the inlet and makes a suitable support
for the sand mold as well as an easy connection to a metal mandrel
pipe or shaft used to hold and turn the boss and mold supporting
structure securely during filament winding. These metal boss
disrupt the smooth stress flow of the thin shell composite
structure. In addition, the coefficients of temperature expansion
are sufficiently different between alloys and composite materials
to create major stresses leading to delamination between the two
components when transitioned between ambient and autoclave
temperatures during cross linking, and between ambient and
cryogenic temperatures during operations. Currently, the weight of
PMC tanks that carry cryogenic gases and fluids is severely
handicapped by the addition of these heavy flanged metal end
fittings. The weight of the metal boss can exceed 40% of the total
tank weight.
[0008] With the introduction of Dynamic Polymer Composite (DPC)
connectors in U.S. Pat. No. 5,552,197, a flange-less method of
connecting composites became available. With the advent of U.S.
Pat. No. 6,325,108, Prestressed Composite Cryogenic Piping, the use
of alloy cryogenic piping was no longer mandatory. By these two
teachings the justification for a heavy metal inlet was removed
since PMC tanks can now be connected to PMC piping. Yet the prior
art provides no teaching on the use of a composite boss as a form
for filament winding to maintain precise dimensional tolerance
without a sand casting. The prior art also offers no teaching for
stiffening of a thin shell tank without creating stress
concentrations and stress reversals in a thin shell tensioned
membrane.
[0009] Removable mandrels are well known in the filament winding
art, both for tanks and pipe. When removed, such a mandrel leaves
the thin shell structure shape pliable. The tensioned membrane is
left vulnerable to stress concentrations due to external support
connections, or stress reversals due to shape distortion as a
partially filled fluid load shifts. The alternative with removable
mandrels is to increase the thickness of the shell to counter shape
distortion. This compromises the weight advantage of the
structure.
[0010] In the prior art Hoffmeister et. al. in U.S. Pat. No.
4,561,568 discloses a tank assembly where a supply pipe passes
through a first tank to an inner tank. In retrospect, this integral
pass-through pipe can be considered a fixed stiffener. The
resultant large increase in tank cross-section and weight at the
inlet and outlet connections of this fixed pipe where it is
connected to this small first tank are a vivid illustration within
Hoffmeister FIG. 1 of the problems in the prior art.
SUMMARY OF INVENTION
[0011] In order to overcome the deficiencies of the prior art the
current invention, briefly stated, is a storage reservoir tank
constructed by filament winding from polymer matrix composite
materials having an internal stiffener connected to a boss so that
the boss and the stiffener are compressively restrained during
filament winding and fabrication and yet are also free to expand
after fabrication during operation when the tank is pressurized
with a cryogenic fluid.
[0012] The current invention also is described as an expandable
composite tank cylindrical wall form comprising a first and second
domed head form and boss selected to provide size, shape, and
rigidity for the support of filament windings, connected to
opposing ends of a pipe and telescoping slip joint assembly
selected to provide limited compressive movement by abutting end
surfaces within said slip joint and moment restraint during
relative dimensional movement between said head forms.
OBJECTS
[0013] It is a general object of the current invention to provide a
light weight and stiffer PMC cryogenic tank.
[0014] It is another general object of the current invention to
reduce the cost of tank fabrication.
[0015] It is a general object of the current invention to create a
stable mandrel assembly incorporating the boss so that prepreg or
fiber tow can be directly wound on the assembly without the use of
a sand cast support for the filament winding.
[0016] It is an object of the current invention to provide a single
central stiffener for the support during filament winding of small
diameter as well as multiple stiffeners for the support of large
diameter boss that act as supporting forms.
[0017] It is an object of the current invention to provide that
composite boss can be stabilized with struts to maintain precise
dimensional tolerance as a form for filament winding using a
composite boss.
[0018] It is another general object of the current invention to
create a stable form for tanks that require a sand cast mandrel
upon which to filament wind prepreg or tow so that precise
dimensional tolerances are maintained during filament winding.
[0019] It is an object of the current invention to internally
stabilize a thin shell composite tank for moment loadings from
external connection to tank supports. Since the inlet pipe stub
must often bear large external loadings, it is advantageous to
carry these loads by an internal inlet pipe stiffener that
traverses the axial diameter of a tank instead of strengthening the
tank body over its entire surface to counter these loads. This is
particularly true when the loads would distort the shape of the
tank.
[0020] It is another object of the current invention to allow
substantial compressive loads to be transmitted through the tank to
the structural frame of a rocket or other system.
[0021] It is yet another object of the current invention to allow
reinforcement of the tank for compressive loads without violating
the nature of the thin shell composite tank structure by avoiding
stress concentrations and reversal due to tension communicated from
a fixed internal strut stiffener while the tank is under pressure.
Pressure within a tank should develop a nearly uniform membrane
tension over the entire tank surface. If a tank under internal
pressure has a fixed internal strut, the tension stress would be an
order of magnitude larger that the uniform membrane tension. Such
strut stiffener tension restraint would act at ninety degrees to
the membrane tension with the result that extreme stress
concentrations and failure would occur at the intersection of the
stiffener and the tank.
[0022] It will be understood by one skilled in the art that the
slip joints may be located at any point along the length of a strut
including the ends.
[0023] It will be recognized by one skilled in the art that the
boss for the forming of a full hemispherical headed tank without a
sand casting form component may require addition stiffness in the
form of ribs or other thickening of the cross-section.
BRIEF DESCRIPTION OF DRAWINGS
[0024] FIG. 1. is a center cross-section of a form to support
filament winding of a fluid storage tank.
[0025] FIG. 2. is a cutaway of an elevation of a composite dome
headed tank.
[0026] FIG. 3. is a cross-sectional view of two dome headed boss
connected by multiple struts.
DETAILED DESCRIPTION
[0027] FIG. 1. shows a composite tank stiffener after the teaching
of this invention comprising at least one generally cylindrical
pipe and strut 1 possessing at least one slip joint 2 integral with
the other member 21 of the strut selected to provide (1)
compressive dimensional limit 3,4 by abutting slip joint member
surfaces 5,6 and (2) telescoping moment restraint during axial
relative positional movement 8 due to congruent member slip joint
wall surfaces 19, to resist an external moment indicated by arrows
7, said generally cylindrical pipe and strut 1 connecting and
integral with the two internal faces 9,10 of two opposing composite
boss 11,12. This composite tank stiffener assembly is the mold
portion of the mandrel for a filament wound tank 30 shown in FIG.
2.
[0028] Also in FIG. 1. the generally cylindrical pipe and strut 1
possesses at least one opening and inlet 13,14 for the transfer of
fluids in common with fluid inlets 31,32 of said filament wound
tank shown in FIG. 2.
[0029] Also in FIG. 2. the internal pressure 35,36 is shown acting
upon the inside surfaces of the tank such as 40 to elastically
stress and deflect them outward. This deflection has carried the
two members 37,38 of the slip joint apart a measurable dimension
39. Yet members 37,38 maintain moment restraint because of
congruent slip joint surfaces 41 during this axial relative
positional slip joint member movement and at any position after
axial relative positional slip joint member movement.
[0030] Additionally in FIG. 1 the generally cylindrical pipe and
strut 1 also possesses openings 15,16,17,18. In FIG. 2 an
equivalent opening 33 is shown in communication with the internal
volume and reservoir 34 of said tank 30.
[0031] In FIG. 3. The internal faces 50,51 of two opposing boss
52,53 are connected at points 55-66 by multiple units of said
generally cylindrical pipe and strut 67-72.
[0032] Inlets 75,76 are integral with the boss 52, 53 and provide
fluid access to the finished tank 30 (See FIG. 2.) after
fabrication.
[0033] Such a composite tank stiffener consists of two opposing
composite boss 52,53 that are selected of a size, shape, and
strength to provide the supporting structure for the filament
winding of the composite body of said filament wound tank 30 (See
FIG. 2.).
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