TECHNICAL FIELD
The present disclosure relates to a light weight pressure vessel for a storage of fluid. More
particularly, the present disclosure relates to a composite light weight pressure vessel for a storage
of fluid at high pressure. Furthermore particularly, the present disclosure relates to a Type 4 cylinder
for the storage of fluid specifically any gas, more specifically Compressed Natural Gas (CNG) at
high pressure of up to 800 bar.
BACKGROUND OF DISCLOSURE
Natural gas usage in transportation sector helps in reducing the atmospheric pollution. Therefore,
there is a merit in increasing the usage of natural gas as fuel. Natural gas is stored at a pressure of
200 bar as CNG for use in the transportation sector. At present, metal or composite cylinders are
being used to store CNG. Such cylinders are heavy and put a drag on the vehicle, reducing its fuel
efficiency. This results in an inefficient use of natural gas, which is a scarce commodity. A typical
CNG cylinder of 65 litres volume weighs more than 60 kg. A reduction in weight of the cylinder
would help to increase fuel efficiency of the vehicle and reduce atmospheric pollution. Such lightweight
cylinders would also be more acceptable to the consumers and helping penetration of CNG
The manufacturing of light weight Type 4 cylinder described in prior arts have challenges in its
commercial production. Also, the Type 4 cylinder described in prior arts are expensive. Type 4
cylinders are described in the standard, ISO 11439 and IS 15935.Type 4 cylinders are fully wrapped
with composite liner with no metal liner.
The paper “Study on the development of composite CNG pressure vessels” by B.S. Kim, B.H. Kim,
J.B. Kim and C.R. Joe describes the use of HDPE (high density polyethylene) liner with carbon fibres
as filament winding in the development of compressed natural gas pressure vessels. Operating and
burst pressure of the vessel used in this paper are 25 and 56 bars respectively.
US Patent No. 3508677 discloses a vessel for storing gases under extreme pressures for relatively
long periods comprising of a nylon liner with an intermediate diaphragm bonded to and completely
enclosing the liner and filament wounded wrapping made of resin impregnated fibre glass strands.
The diaphragm provides the necessary structural strength for withstanding the high interior vessel
pressures.
US Patent No. 4927038 mentions procedure for manufacture of container for high pressure gases
hydrogen and oxygen gases. The said container comprises a hollow shell of thermoplastic material
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having an inner surface and an outer surface. One of the surface is covered with a layer comprising
a metallized film of plastics material; and an outer layer comprising fibrous windings bound together
with resin. The choice of thermoplastic liner is medium density polyethylene and two types of fibres
carbon and aramid were used as reinforcement with polar winding.
EP Patent No. EP2628994 discusses merely about plastic liner with fixing elements for pressurised
containers wherein, the cylindrical pressure container comprises an inner plastic liner which is made
by at least one thermoplastic material that can be polyamide, and outer reinforcement layer is made
by fiber-reinforced material, that can be carbon fiber or glass fiber.
Accordingly, there remains a need for a light weight pressure vessel and a method for by which a
light weight pressure vessel could be commercially manufactured in a more economic manner while
satisfying all the standard provided in ISO 11439, IS15935. Consequently, there is a need to have
some innovation in this field.
The present disclosure addresses this need by innovating a light weight pressure vessel for a storage
of fluid. The present disclosure also discloses a method of manufacturing the said light weight
pressure vessel.
SUMMARY OF THE DISCLOSURE
The present disclosure discloses a light weight pressure vessel for a storage of fluid comprising a
composite made of fiber reinforced polymeric matrix wrapped over a polyamide based plastic liner.
The said composite having combination of hoop layer and helical layer that are provided in
predetermined order; wherein, hoop layer is wrapped over only a cylindrical part of the liner of the
pressure vessel and helical layer over both the cylindrical part and a dome part o f the liner of the
pressure vessel. The disclosed pressure vessel is having 30% to 50% light weight and is capable to
sustain internal pressure of fluid up to 800 bar. The present disclosure also discloses a method for
manufacturing light weight pressure vessel for storage of gas comprising i) applying a composite
hoop layer with continuous filament winding operation over a cylindrical part of the liner of the
pressure vessel and helical layer over both the cylindrical part and a dome part o f the liner of the
pressure vessel, curing the composite overwrap in two sequential stages and optionally applying
exterior coating on the top of composite overwrap. More particularly, the present disclosure relates
to a light weight composite pressure vessel for a storage of compressed natural gas and method of
manufacturing of the said pressure vessel. Further, more particularly, the present disclosure relates
4
to a light weight composite Type 4 pressure vessel/cylinder for a storage of compressed natural gas
and method of manufacturing of the said pressure vessel/cylinder.
BRIEF DESCRIPTION OF FIGURES
The disclosure itself, however, as well as a preferred mode of use, further objectives and advantages
thereof, will best be understood by reference to the following detailed description of an illustrative
embodiment when read in conjunction with the accompanying figures and tables. One or more
embodiments are now described, by way of example only, with reference to the accompanying
figures and tables in which:
Figure 1: represents a liner geometry of Type 4 cylinder;
Figure 2: represents complete geometry of finished Type 4 cylinder;
Figure 3: represents layup sequence of Type 4 cylinder;
Figure 4: indicates Von Mises stress distribution in Type 4 cylinder at 0 bar;
Figure 5: indicates Von Mises stress distribution in Type 4 cylinder at 200 bar;
Figure 6: indicates Von Mises stress distribution in Type 4 cylinder at 300 bar;
Figure 7: indicates Von Mises stress distribution in Type 4 cylinder at 470 bar;
Figure 8: indicates Von Mises stress distribution in Type 4 cylinder at 693 bar.
BRIEF DESCRIPTION OF TABLES
Table 1: Service conditions adopted for the development of Type 4 cylinder along with the
requirement specified by the standard, ISO 11439;
Table 2: Design parameters adopted for development of Type 4 cylinder along with the
requirement specified by the standard, ISO 11439;
Table 3: Winding sequence of Type 4 cylinder;
Table 4: Properties of carbon/epoxy composite used for stress analysis;
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Table 5: Process variables during cylinder manufacturing using filament winding;
DETAILED DESCRIPTION OF PRESENT DISCLOSURE
While the present disclosure is subject to various modifications and alternative forms, specific
embodiment thereof has been shown by way of example in the figures and will be described below.
It should be understood, however that it is not intended to limit the present disclosure to the particular
forms disclosed, but on the contrary, the present disclosure is to cover all modifications, equivalents,
and alternatives falling within the scope of the present disclosure.
It is to be noted that a person skilled in the art can be motivated from the present disclosure and can
perform various modifications. However, such modifications should be construed within the scope
of the present disclosure.
Accordingly, the drawings are showing only those specific details that are pertinent to understanding
the embodiments of the present disclosure so as not to obscure the disclosure with details that will
be readily apparent to those of ordinary skill in the art having benefit of the description herein.
The terms “comprises”, “comprising”, or any other variations thereof, are intended to cover a nonexclusive
inclusion, such that an assembly, setup, system, device that comprises a list of components
does not include only those components but may include other components not expressly listed or
inherent to such system or device or setup or method. In other words, one or more elements in the
system or apparatus or device proceeded by “comprises a” does not, without more constraints,
preclude the existence of other elements or additional elements in the assembly or system or
apparatus. The following paragraphs explain present disclosure. The invention in respect of the same
may be deduced accordingly.
Accordingly, the present disclosure relates a light weight pressure vessel for a storage of fluid
comprising a composite made of fiber reinforced polymeric matrix wrapped over a polyamide based
plastic liner; wherein, the said plastic liner is provided at inner surface of the pressure vessel and the
said liner is connected to a metal boss; wherein the said composite having combination of hoop layer
and helical layer that are provided in predetermined order; wherein, hoop layer is wrapped over only
a cylindrical part of the liner of the pressure vessel and helical layer over both the cylindrical part
and a dome part of the liner of the pressure vessel, characterized such that helical layer windings in
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the dome part of the pressure vessel having a helical angle between 7 o to 45o and the said pressure
vessel having 30% to 50% light weight and is capable to sustain internal pressure of fluid up to 800
bar.
In another embodiment of the present disclosure the pressure vessel has an opening at one of the
hemispherical heads and the plastic liner is connected to the metal boss through the said opening.
In another embodiment of the present disclosure the metal is aluminium.
In another embodiment of the present disclosure the pressure vessel is cylinder.
In another embodiment of the present disclosure the pressure vessel is cylindrical and attached to
hemispherical dome.
In yet another embodiment of the present disclosure the fluid is liquid or gas.
In yet another embodiment of the present disclosure the gas is natural gas, hydrogen gas, LPG or
mixture thereof.
In yet another embodiment of the present disclosure the gas is natural gas is compressed.
In another embodiment of the present disclosure the composite overwrap consisting of polymer
matrix reinforced with fiber.
In another embodiment of the present disclosure the reinforcing fibers are selected from glass,
aramid, carbon or combination thereof.
In a yet another embodiment of the present disclosure the polymeric matrix is thermoplastic resin or
thermosetting resin.
In a yet another embodiment of the present disclosure the thermoplastic resin is selected from
polyethylene or polyamide.
In a further embodiment of the present disclosure the thermosetting resin is selected from epoxy,
modified epoxy, polyester or polyvinyl ester.
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In a further embodiment of the present disclosure the number of hoop layer is in the range of 4 to 20,
more preferably 8 to 15.
In a further embodiment of the present disclosure the number of helical layer is in the range of 15 to
35, more preferably 20 to 30
In a further embodiment of the present disclosure the thickness of hoop layer is in the range of 1.0
mm to 10 mm, more preferably in the range of 4.0mm to 7.5mm.
In a yet another embodiment of the present disclosure the thickness of helical layer is in the range of
7.5 mm to 17 mm, more preferably in the range of 10 mm to 15.0 mm.
In a yet another embodiment of the present disclosure there is one or more helical and hoop layers.
In a further embodiment of the present disclosure the pressure vessel withstands the internal pressure
of the fluid up to 500 bar.
In a further embodiment of the present disclosure the weight of the pressure vessel is 30 to 50%
lighter than the conventional pressure vessel.
In a further embodiment of the present disclosure the composite overwrap further consisting of
exterior coating on the top of composite overwrap.
In another aspect of the disclosure it relates to a method for manufacturing light weight pressure
vessel for storing fluid comprising the steps: i) applying a composite hoop layer with continuous
filament winding operation over a cylindrical part of the liner of the pressure vessel and helical layer
over both the cylindrical part and a dome part of the liner of the pressure vessel, characterized such
that helical layer windings in the dome part of the pressure vessel having a helical angle between
7.0o to 45o; ii) curing the composite overwrap in two sequential stages: (a) 12 to 20 hours at room
temperature; (b) 3 to 8 hours at 40 to 100 0C and at both the stages allowing to rotate the pressure
vessel at a speed of 1-2 rpm; iii) optionally applying exterior coating on the top of composite
overwrap thus producing light weight pressure vessel for storing fluid and the said pressure vessel
having 30% to 50% light weight and is capable to sustain pressure of fluid up to 800 bar.
8
In another embodiment, the composite overwrap is cured at room temperature for 14 to 18 hours
sequentially followed by 60 to 80°C for 4 to 6 hours while rotating the cylinder at a speed of 1-2
rpm.
In another embodiment, the pressure vessel has an opening at one of the hemispherical heads and
the plastic liner is connected to the metal boss through the said opening
In a yet another embodiment the thickness of hoop layers is in the range 1.0 mm to 10 mm, more
preferably in the range of 4.0 mm to 7.5mm.
In a yet another embodiment the thickness of helical layers is in the range of 7.5 mm to 17 mm, more
preferably in the range of 10 mm to 15.0 mm.
In a yet another embodiment the number of hoop layers is in the range of 4 to 20, more preferably 8
to 15.
In a yet another embodiment the number of helical layers is in the range of 15 to 35, more preferably
20 to 30.
In a yet another embodiment the pressure vessel withstands at least the internal pressure of 470 bar.
In a yet another embodiment the weight of the pressure vessel thus produced is 30 to 50% lighter
than the conventional pressure vessel.
In yet another embodiment the hoop windings are replaced with higher helical angle windings to
provide better coverage in the corner of the dome part of the Type 4 cylinder.
In yet another embodiment aluminum boss is connected to the opening of the cylinder during the
manufacturing of the liner making it an integral part of the liner.
In yet another embodiment polyamide liner is used in the liner development of the Type 4 cylinder
which is a unique material for this case due to its excellent fatigue resistant properties and lower
permeability.
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MATERIALS USED IN PRESSURE VESSEL
The pressure vessel or Type 4 cylinders mainly comprise of a plastic liner and a filament wound
composite wrap over the entire cylinder.
The plastic liner is made up of a polymer material selected from but not limited to polyamide. The
plastic liner has an opening in one of the hemispherical heads and connected with metal end at boss.
The centerline of the openings coincides with the longitudinal axes of the cylinder.
A composite overwrap on the cylindrical part as well as on the dome part of the cylinder is made
of suitable polymeric matrix material and the fiber reinforcements are selected for the composite
overwrap. The polymeric matrix material i.e. resin is either a thermoset or thermoplastic material.
Thermoset materials selected from but not limited to epoxy, modified epoxy, polyester resin and
vinyl ester resin. For the current development of Type 4 cylinder, a couple of epoxy resins are
identified and tested. Epoxy resins tested include Araldite LY 556, manufactured by Huntsman
Chemicals, USA and Voraforce TW 103, manufactured by Dow Chemicals, USA. Considering
the results of the initial screening test, ease of curing and the ease of availability in India, the
epoxy resin, Araldite LY 556, manufactured by Huntsman Chemicals, USA is selected for the
development. A suitable curing agent (Hardener), Araldite XY 54, manufactured by Huntsman
Chemicals, USA is used for curing.
The reinforcement materials are selected from but not limited to glass or aramid or carbon fiber.
Preferably, carbon fiber is suitably coated with a coating to make it compatible with the epoxy
resin.
The cylinder with carbon fiber embedded in the epoxy resin used for composite overwrap. Further,
optionally a transparent gel coat such as but not limited to Kane Ace MX-11 is applied for the
purpose of improving aesthetics.
DESIGN AND STRESS ANALYSIS
Following is the description of the design of the pressure vessel, service conditions (Table 1),
design basis (Table 2), design calculations, stress analysis and other design considerations
adopted for the current technology to develop a Type 4 pressure vessel/cylinder.
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DESIGN OF THE PRESSURE VESSEL
Figure 1 representing the liner geometry of type 4 cylinder has two parts viz. curved cylindrical part
and dome part. The top and below of the said cylindrical part is closed by dome part respectively as
evident from figure 1. The thickness of the whole liner geometry i.e. a is 5 mm. Further, the height
hc of the cylindrical part is 706 mm and the diameter of the cylindrical part of liner (with thickness)
dl is in the range of 334 mm – 340 mm. The shortest distance between the center of the dome to its
sides R1 is 102 mm and the longest distance R2 coincides with the radius of the cylindrical part as in
figure 1. There is chamfer (opening) present in one end of the dome and its opening diameter dc
(along with the thickness of the liner geometry) is 48 mm. The total length of the liner geometry from
the mouth of the chamfer to the end of dome is Tl 956 mm.
Figure 2 represents complete geometry of finished Type 4 cylinder. The complete geometry
incorporates the liner geometry as described in Figure 1, with the windings around it. The thickness
b of the windings is 17.55 mm throughout liner geometry, expect at the ends of dome where the
thickness be being 22 mm. Further, the diameter of the cylindrical part of liner dl is fixed at 337 mm.
The metal adapter of the complete geometry has the diameter dc (with thickness) is 55 mm. The
thickness of the metal adapter c is 12.5 mm. The total length of the complete geometry from the
mouth of the metal adapter to the end of dome is Tc 978 mm.
Table 1: Service conditions adopted for the development of Type 4 cylinder along with the
requirement specified by the standard, ISO 11439
Service conditions Requirements adopted for the development
Service life
The minimum service life is targeted as 20 years (Confirmed by the
pressure cycling test)
Working pressure 200 bar
Max. filling pressure 260 bar
Gas composition Compatible with the requirement and as per the standard
External surfaces Compatible with the requirement and as per the standard
Settled temperature range of
gas in cylinder
- 40 0C to + 65 0C
Settled temperature range of
materials of cylinder
- 40 0C to + 82 0C
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Table 2: Design parameters adopted for development of Type 4 cylinder along with the
requirement specified by the standard, ISO 11439
Design Basis Adopted for the development
Minimum test pressure 300 bar
Minimum burst pressure 470 bar since carbon fiber is used
Stress analysis ANSYS 13.0 Mechanical APDL, SHELL 8 node 281 Element is
used.
Stress analysis of composite
cylinders
Carried out at 0 bar, 200 bar, 300 bar and design burst
pressure
Openings An opening is provided in one of the domes of the cylinder through
the connection of end boss
The design calculation methodology to determine the hoop layer and helical layer thickness.is
based on Netting analysis and reference can be made to Madhavi et al. [2009].
The desired number of helical and hoop layers can be determined by dividing the total helical and
the hoop thickness with the thickness of individual helical and hoop layer respectively. The
thickness of helical and hoop layer depends on the thickness of the resin impregnated fiber rovings.
The thickness of the resin impregnated carbon fiber roving used for the development of Type 4
cylinder is 0.3 mm to 1.0 mm, more preferably in the range of 0.5 to 0.7 mm.
At least two hoop layers and twelve hoop layers are suitable as per the netting analysis.
More helical and hoop layers is added to meet the criteria as per standard, ISO 11439. Therefore,
different winding angles are tried during designing of cylinder to determine the angle of winding
where no slippage will occur. From the trials 7° 15°, 25°, 35° and 45°angles are obtained as the
non-slipping angles of winding. Helical and hoop layers are arranged in such a way that the weight
of the cylinder is minimum while maintaining the desired properties. The number and thickness of
the helical and hoop layers can be varied depending upon the requirement and desired properties.
Various other permutation and combinations having these layers will also falls within the purview
of present disclosure. An example is summarized herein below for illustration. Based on the above
discussion the winding sequence for example is given in Table 3 and the winding or layup sequence
is presented schematically in Figure 3.
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Table 3: Winding sequence of Type 4 cylinder
Layer no. Type of winding Winding angle ( º )
1 Hoop 90
2 Helical 7.5
3 Helical 15
4,5 Hoop 90
6 Helical 15
7 Helical 25
8 Helical 15
9,10 Hoop 90
11 Helical 15
12,13 Hoop 90
14 Helical 25
15,16 Hoop 90
17 Helical 15
18,19 Hoop 90
20 Helical 15
21 Helical 7.5
22 Helical 7.5
23 Hoop 90
24 Helical 7.5
25 Helical 7.5
26 Hoop 90
27 Helical 7.5
28 Helical 7.5
29,30 Hoop 90
31 Helical 25
32 Helical 35
33 Helical 45
34 Helical 25
35,36 Hoop 90
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Stress Analysis
As per the standard ISO 11439, the stress analysis is to be carried out at 0 bar, 200 bar, test
pressure and design burst pressure. The values of the material properties required for the stress
analysis are given in Table 4.
Table 4: Properties of carbon/epoxy composite used for stress analysis
Property Value
Young’s moduli (MPa)
E1 1.17E+05
E2 1.00E+04
E3 1.00E+04
Shear moduli (MPa)
G12 5.00E+03
G23 3.90E+03
G31 3.90E+03
Poisson’s ratio
v12 2.70E-01
v23 2.70E-01
v31 2.70E-01
The stresses generated for the pressure of 0 bar, 200 bar (working pressure), 300 bar (test
pressure), 470 bar (design burst pressure) and 693 bar (higher than the specified burst pressure)
are presented in Figure 4, 5, 6, 7 and 8 respectively. Von Mises yield criteria is used for the stress
analysis. Von Mises stress is the resultant stress of the stresses in tangential direction and in X
and Y directions. Von Mises yield criteria is mostly used to predict if a specific design can
withstand a certain load by comparing the Von Mises stress with the design stress of the materials.
According to this criterion, the Von Mises stress induced in the material should be less than the
design strength of the material for the vessel to withstand the load. If the Von Mises stress
exceeds the design stress, then the vessel will burst.
As an example, the design strength of the composite materials used for the Type 4 cylinder
obtained using the design calculation is found to be 1839.3 MPa. Figure 4, represents the stress
analysis at 0 bar when no load is applied indicates no residual stress. However, when the pressure
is increased to 200 bar, the Von Mises stress is developed which is indicated in the Figure 5. The
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stress analysis of the cylinder at higher pressures such as 300 bar and 470 bar are presented
in Figure 6 and Figure 7 indicates that the Von Mises stress increases as the internal pressure
increases. The Von Mises stress at 470 bar which developed at the dome portion is 1248.81 MPa
which is less than the design strength. It indicates that cylinder will be able to withstand the
internal pressure of 470 bar. The stress analysis of the cylinder subjected to an internal pressure
of 693 bar which is above the the design burst pressure is presented in Figure 8 and the maximum
stress developed in the dome is 1841.33 bar which is higher than the design strength of 1839.3
MPa.
MANUFACTURING TECHNOLOGY
The key aspects for the manufacturing Type 4 cylinders comprising: Equipment configuration; Key
process parameters; Filament winding process description; Curing of the cylinder; and Exterior
coating for environmental protection/aesthetics.
Equipment configuration
The Type 4 cylinder is manufactured by applying a composite hoop layer with continuous filament
winding operation over the cylindrical part of the liner and helical layer over both the cylindrical
part and a dome part of the liner of the pressure vessel. Determining the effective equipment
configuration with a suitable control unit which is capable of winding the filament continuously in
different orientations as demanded by the design, without slippage, providing a good resin delivery
system and proper fiber bandwidth, delivering a good amount of surface tension which is critical
for obtaining a good fiber volume fraction and operating at a desired winding speed.
Key Process Parameters
The values and tolerances of the key process parameters such as winding angles, band width, fiber
tension, temperature of resin bath, and winding speed are determined by conducting several process
trials. A description of these key process parameters and the values for these process parameters
are provided in the section below. A summary of the values of these key process parameters used
for the development are presented in Table 6.
a. Winding angle
Winding angle is the angle between the fiber and the axis which is parallel to the mandrel. Winding
angle plays an important role in the manufacturing process as it decides the final product
15
performance and avoid slippage on the mandrel surface. In Type 4 cylinders, the feasible angles of
winding where no slip occurs on the mandrel surface are obtained as 7.5 ° 15°, 25°, 35° and 45°.
b. Bandwidth
The fiber bands are to be distributed equally without any excessive overlapping. Otherwise, there
will be excessive stacking of fiber, which will increase the production time as well the wastage of
material. The bandwidth is selected in the range 9 mm to 15 mm and more preferably 10-13 mm
for carbon fiber.
c. Winding speed
Proper speed of winding is important as it affects the fiber tension. If winding speed is too high
there will be chances of jamming of the machine and also resin will not impregnate properly onto
the fibers. Winding speed chosen for dome portion is in the range of 2200 to 2700 mm/min, more
preferably 2400 to 2500 mm/min and for cylinder portion in the range of 16000 to 22000 mm/min
more preferably, 18000 to 20000 mm/min.
d. Fiber tension
Fiber tension affects the fiber volume fraction and void content, which influences the strength and
stiffness of the composite. A tension of 2.73 N was measured for a single carbon fiber roving.
e. Resin bath temperature:
The temperature of the resin bath is maintained at ambient temperature.
Table 5: Process variables during cylinder manufacturing using filament winding
Process variables Data obtained
Fiber type and sizing Carbon fiber coated compatible with epoxy resin
Manner of impregnation Dip type resin bath
Winding tension 2.73 N for a single fiber
Winding speed for dome 2200 – 2700 mm/min
Winding speed for cylinder 20000 – 22000 mm/min
Number of rovings 4 to 10
Band width 9 to 15 mm
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Type of resin and composition Epoxy: Araldite LY 556 and
Temperature of the resin 25 ° C (ambient temperature)
Temperature of the liner 25 ° C (ambient temperature)
Winding angle As per design
Filament Winding Process Steps
Manufacturing the Type 4 cylinder using filament winding process comprises following steps:
1. Mounting carbon fiber on a fiber delivery system or a fiber stand. About 4 to 8 spools
are placed in the fiber stand, more preferably six spools are placed in the fiber stand;
2. Mounting a liner by using a headstock and a tailstock thereafter checking alignment of the
liner;
3. Curing a resin (such as but not limited to Araldite) wherein, the resin and curing agent is mixed
in 3:1 weight ratio. Pouring the resin in a dip type resin bath;
4. A single roving from each spool is threaded through guides onto the resin bath;
5. The resin impregnated thread is guided through a series of guides and rollers to wound on a
mandrel;
6. Creating a program for hoop and helical winding in the computer which is connected to a
CNC control panel. Data such as cylinder dimensions, winding angle, fiber bandwidth are
provided and a program is generated to operate the machine as per the requirement;
7. Sending subsequent program to the CNC control panel where the filament winding machine
is controlled. The winding is done as per the program instruction provided to the control
panel;
8. Pouring resin in small amount in several batches during the winding process;
9. Rotating the mandrel at a very low speed of 1-2 rpm in ambient condition for some time to
spread the resin uniformly on the mandrel.
Curing of Cylinder
After winding, the composite overwrap is sequentially cured. The composite overwrap is cured for
12 to 20 hours, preferably for 14 to 18 hours at room temperature which is followed by 3 to 8
hours, preferably 4 to 6 hours at 40 to 100 °C, preferably at 60 to 80°C. The pressure vessel
requires continuous rotation during cure at a speed of 1 to 2 rpm to prevent the accumulation of
the resin at the bottom of the cylinder due to gravitational force while being cured.
Exterior Coating for Environmental Protection/Aesthetics
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An exterior coating is further applied on the top of the composite overwrap improving the
aesthetics and protection from the environment. It is applied after the curing of the cylinder.
Gel coat of about 30 g is mixed with about 1000 g of araldite resin and is applied to the
cylinder using a gel coat sprayer. The acid environment test is carried out successfully using the
cylinder with this coat.
Accordingly, prototypes for Type 4 cylinder were manufactured for testing. The total weight
measured for the said cylinder is found in the range of 30 to 35 kg. The Type 4 prototype
pressure vessel leads to the reduction of weight of about 30 to 54 % as compared with
conventional cylinders as available in the market.
TESTING
The testing was carried out as per the International Standard, ISO 11439/Indian standard IS 15935.
DESCRIPTION OF TESTS PERFORMED AND RESULTS
1. Hydrostatic pressure burst test
Hydrostatic pressure burst test is carried out using the prototype of Type 4 cylinder manufactured.
as per the standard ISO 11439. The cylinder is pressurized hydrostatically at a rate of 3 bar/s
throughout the testing. Water at ambient temperature is used to build the hydrostatic pressure. The
cylinder is tested up to a pressure of 500 bar without any failure, which is above the recommended
pressure as per the standard (i.e. 470 bar).
2. Ambient temperature pressure cycling test
This test is carried out using the prototypes of Type 4 cylinder manufactured. The cylinder is
filled with water as a non-corrosive liquid and pressure cycled between 20 to 260 bar at a rate of
0.7 cycles/min. The cylinder is tested for 36000 cycles without failure, which is above the
recommended cycles as per the standard (i.e. 20000 cycles).
3. Leak- Before- Break (LBB) test
Leak Before Break test is carried out at ambient temperature pressure cycling test. The cylinder
filled with water as non-corrosive liquid is pressure cycled at a rate of 0.7 cycles/min between 20
to 260 bar. The cylinder has passed 36000, cycles and as recommended by the standard.
4. Bonfire test
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For carrying out the test, the cylinder is filled with compressed air and is pressurized at 50 bar.
The cylinder is placed horizontally at a height of 100 mm above the fire source. A uniform flame
source is placed to provide heat uniformly to the cylinder using LPG as fuel. Three thermo
couples were placed at the bottom of the cylinder. After ignition, the temperatures at three locations
indicated by the thermocouples are noted and the temperature reached more than 800 °C.
5. Acid environment test
Acid Environment test is carried out using a cylinder without gel coat and another cylinder with
gel coat as per the standard, ISO 11439. The cylinder is pressurized at 260 bar pressure and then
the outer surface of the cylinders are exposed to 30% sulfuric acid solution for 100 hours on
cylinder area of 150 mm diameter under pressurized condition. After the exposure of the surface
to the acid solution under pressurized condition, the cylinders are subjected to hydrostatic burst
pressure test. Cylinders are tested without burst up to a pressure of 460 bar which is more than
the 85 % of the minimum design burst pressure.
6. Resin shear strength
A sample of a composite overwrap is tested in accordance with the standard, ISO 14130. The
sample had the shear strength of about 15 MPa. After boiling in water for 24 h, its value exceeded
the standard requirement.
7. Softening temperature of plastics
The liner material is tested in accordance to standard, ISO 306. The softening temperature of the
plastic liner sample is found to be 171 °C which is greater than 100 °C as per the standard.
8. Drop test
In drop test, a cylinder is dropped horizontally, vertically and at 45° angle from either end, at a
height 1.8 m above the centre of gravity of the vessel. This cylinder is pressure cycled between 20
to 260 bar and it successfully met the ISO 11439 requirement of 3000 cycles. It failed at 12000
cycles which is much above the standard i.e. 3000 cycles.
9. Boss torque test
For boss torque test a torque of 495 N is applied to the end boss of the cylinder, first in the screw
tightening direction, then in the untightening direction and finally again in the tightening direction.
Finally, the cylinder is subjected to leak test as per the standard. No leakage was observed.
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10. Permeation test
This test is performed by using compressed air at 50 bar pressures.
ADVANTAGE
The light weight pressure vessel is 30 to 50% lighter than the conventional pressure vessels. The
disclosed pressure vessel withstands the internal pressure up to 500 bar. The said pressure vessel is
used for a storage of fluid under high pressure. The light pressure vessels are mainly for mid-size
vehicles and due to its light weight, it will lead to better fuel efficiency and less load on the vehicle.
The disclosed light weight pressure vessel is manufactured by a method which is commercially
feasible and is more economic while satisfying all the requirements provided in ISO 11439.

WE CLAIM:
1. A light weight pressure vessel for a storage of fluid comprising:
a composite made of fiber reinforced polymeric matrix wrapped over a polyamide based
plastic liner;
wherein, the said plastic liner is provided at inner surface of the pressure vessel and
the said liner is connected to a metal boss;
wherein the said composite having combination of hoop layer and helical layer that
are provided in predetermined order;
wherein, hoop layer is wrapped over only a cylindrical part of the liner of the
pressure vessel and helical layer over both the cylindrical part and a dome part o f t he liner
of the pressure vessel, characterized such that helical layer windings in the dome part of the
pressure vessel having a helical angle between 7 o to 45o and the said pressure vessel having
30% to 50% light weight and is capable to sustain internal pressure of fluid up to 800 bar.
2. The light weight pressure vessel as claimed in claim 1, wherein the pressure vessel has an
opening at one of the hemispherical heads and the plastic liner is connected to the metal boss
through the said opening.
3. The light weight pressure vessel as claimed in claim 1 or 2, wherein the metal is aluminum.
4. The light weight pressure vessel as claimed in claim 1, wherein the pressure vessel is cylinder.
5. The light weight pressure vessel as claimed in claim 1, wherein the pressure vessel is
cylindrical and attached to hemispherical dome.
6. The light weight pressure vessel as claimed in claim 1, wherein fluid is liquid or gas.
7. The light weight pressure vessel as claimed in claim 1, wherein gas is natural gas, hydrogen
gas, LPG or mixture thereof.
8. The light weight pressure vessel as claimed in claim 7, wherein natural gas is compressed
natural gas.
9. The light weight pressure vessel as claimed in claim 1, wherein reinforcing fibers are selected
from glass, aramid, carbon or combination thereof.
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10. The light weight pressure vessel as claimed in claim 1, wherein polymeric matrix is
thermoplastic resin or thermosetting resin.
11. The light weight pressure vessel as claimed in claim 10, wherein thermoplastic resin is
selected from polyethylene or polyamide.
12. The light weight pressure vessel as claimed in claim10, wherein thermosetting resin is
selected from epoxy, modified epoxy, polyester or polyvinyl ester.
13. The light weight pressure vessel as claimed in claim 1, wherein number of hoop layer is in
the range of 4 to 20, more preferably 8 to 15.
14. The light weight pressure vessel as claimed in claim 1, wherein number of helical layer is in
the range of 15 to 35, more preferably 20 to 30.
15. The light weight pressure vessel as claimed in claim 1, wherein the thickness of hoop layers
is in the range of 1.0 mm to 10 mm, more preferably in the range of 4.0 mm to 7.5 mm.
16. The light weight pressure vessel as claimed in claim 1, wherein the thickness of helicals layer
is in the range of 7.5 mm to 17 mm, more preferably in the range of 10 mm 15.0 mm.
17. The light weight pressure vessel as claimed in claim 1, wherein the pressure vessel withstands
the internal pressure of fluid up to 500 bar.
18. The light weight pressure vessel as claimed in claim 1, wherein the weight of the pressure
vessel is 30 to 50% lighter than the conventional pressure vessel.
19. The light weight pressure vessel as claimed in claim 1, wherein composite overwrap further
consisting of exterior coating on the top of composite overwrap.
20. A method for manufacturing light weight pressure vessel for storing fluid comprising the
steps:
i) applying a composite hoop layer with continuous filament winding operation
over a cylindrical part of the liner of the pressure vessel and helical layer over both the
cylindrical part and a dome part o f the liner of the pressure vessel, characterized such that
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helical layer windings in the dome part of the pressure vessel having a helical angle between
7.0o to 45o;
ii) curing the composite overwrap in two sequential stages:
(a) 12 to 20 hours at room temperature;
(b) 3 to 8 hours at 40 to 100 °C
and at both the stages allowing to rotate the pressure vessel at a speed of 1-2 rpm;
iii) optionally applying exterior coating on the top of composite overwrap thus
producing light weight pressure vessel for storing fluid and the said pressure vessel having
30% to 50% light weight and is capable to sustain pressure of fluid up to 800 bar.
.
21. The method as claimed in claim 20, wherein the composite overwrap is cured at room
temperature for 14 to 18 hours sequentially followed by 60 to 80 °C for 4 to 6 hours while
rotating the cylinder at a speed of 1-2 rpm.
22. The method as claimed in claim 20, wherein the pressure vessel has an opening at one of the
hemispherical heads and the plastic liner is connected to the metal boss through the said
opening.
23. The method as claimed in claim 20 and 22, wherein the metal is aluminum.
24. The method as claimed in claim 20, wherein the thickness of hoop layers is in the range 1.0
mm to 10 mm, more preferably in the range of 4.0 mm to 7.5mm.
25. The method as claimed in claim 20, wherein the thickness of helical layers is in the range of
7.5 mm to 17 mm, more preferably in the range of 10 mm to 15.0 mm.
26. The light weight pressure vessel as claimed in claim 20, wherein number of hoop layers is in
the range of 4 to 20, more preferably 8 to 15.
27. The light weight pressure vessel as claimed in claim 20, wherein number of helical layers is
in the range of 15 to 35, more preferably 20 to 30.
28. The method as claimed in claim 20, wherein the pressure vessel withstands the internal
pressure of fluid up to 500 bar.
29. The method as claimed in claim 20, wherein the weight of the pressure vessel thus produced
is 30 to 50% lighter than the conventional pressure vessel.