Pressure vessel for storing fluid

Abstract

To disclose a pressure vessel for storing fluid.SOLUTION: A pressure vessel includes a metal liner having a cylinder part and a pair of elliptical domes arranged at both ends of the cylinder part. Also, the pressure vessel includes a complex material for covering and surrounding the cylinder part and a pair of the elliptical domes. The complex material is formed of a polymer matrix which is reinforced by fibers, and the complex material includes a combination of a hoop layer and a helical layer which are arranged in a prescribed order with respect to each other. The hoop layer is wound around the cylinder part of the metal liner of the pressure vessel, and the helical layer is wound on both the cylinder part and a pair of the elliptical domes. The helical layer is wound around each of a pair of the elliptical domes so that a helical angle is defined in a position in which the cylinder part and a pair of the elliptical domes intersect with each other.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to pressure vessels, and more particularly, to lightweight pressure vessels for storing fluids at high pressure.

Background Art

[0002] Hydrogen is preferred over conventional energy sources due to its clean emissions and high efficiency. When supplied to a fuel cell, hydrogen produces three times more energy with water than an internal combustion engine. Therefore, there is an advantage in increasing the use of hydrogen gas as a fuel. Hydrogen gas is stored in the pressure range of 350 - 700 bar for on-vehicle storage in the automotive sector. Worldwide, metal or composite cylinders are considered the most primitive solution for storing pressurized hydrogen gas. Metal cylinders are easy to manufacture but are heavy, imposing a burden on the vehicle and reducing fuel efficiency. A typical Type 1 metal cylinder is approximately three times heavier than a Type 3 cylinder. The lightweight Type 3 cylinders described in the prior art have problems in terms of commercial production and cost. A Type 3 cylinder (referred to as Type-3 in the ISO 15869 standard) is a metal liner wrapped with resin-impregnated continuous filaments.

[0003] U.S. Patent Application Publication No. 20150219277 discloses a process for manufacturing a cylindrical container overlapped with resin-impregnated fiber strands, the process including manufacturing a metal liner and overlapping it with the fibers. Further, the prior art discloses rotating the liner around which the fibers are overlapped to prevent non-uniform deposition of the resin. However, the prior art does not disclose other aspects outlined in the important features of the proposed invention.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

SUMMARY OF THE INVENTION

MEANS FOR SOLVING THE PROBLEM

[0005] This summary is provided to introduce a selection of concepts in a simplified form that are further described in the detailed description of the invention. This summary is not intended to identify key or essential inventive concepts of the present invention, nor is it intended to determine the scope of the present invention.

[0006] In one embodiment of the present disclosure, a pressure vessel for storing a fluid is disclosed. The pressure vessel includes a metal liner including a cylindrical portion and a pair of elliptical domes disposed at both ends of the cylindrical portion. Further, the pressure vessel includes a composite material covering and wrapping the cylindrical portion and the pair of elliptical domes. The composite material is formed from a polymer matrix reinforced with fibers, and the composite material includes a combination of a hoop layer and a helical layer arranged in a predetermined order with respect to each other. The hoop layer is wound around the cylindrical portion of the metal liner of the pressure vessel, and the helical layer is wound over both the cylindrical portion and the pair of elliptical domes. The helical layer is wound around each of the pair of elliptical domes such that a helical angle is defined at a position where the cylindrical portion and the pair of elliptical domes intersect.

[0007] In another embodiment of the present disclosure, a method for manufacturing a pressure vessel for storing a fluid is disclosed. The method comprises applying a composite material over a metal liner of the pressure vessel. A hoop layer of the composite material is wound around a cylindrical portion of the metal liner of the pressure vessel by a continuous filament winding operation, and a helical layer of the composite material is wound around both the cylindrical portion of the pressure vessel and a pair of elliptical domes of the metal liner. The helical layer is wound around each of the pair of elliptical domes such that a helical angle is defined at a position where the cylindrical portion intersects the pair of elliptical domes. Further, the method includes curing the overlap of the composite material in a series of steps: (i) for 24 to 35 hours at room temperature, (ii) for 4 to 15 hours at a temperature in the range of 60°C to 100°C. During both curing steps, the pressure vessel is rotated at a speed in the range of 1 to 2 rpm.

[0008] To further clarify the advantages and features of the present invention, a more specific description of the present invention will be given with reference to specific embodiments shown in the accompanying drawings. It should be understood that these drawings show only typical embodiments of the present invention and should not be considered as limiting the scope thereof. The present invention will be described and explained more specifically and in detail with the use of the accompanying drawings.

Brief Description of the Drawings

[0009] These and other features, aspects, and advantages of the present invention will be better understood when the following detailed description is read with reference to the accompanying drawings.

[0010]

Figure 1

Figure 2a

Figure 2b

Figure 3a

Figure 3b

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

[0011] Furthermore, those skilled in the art will understand that the elements in the drawings are illustrated for simplicity and may not necessarily be drawn to scale. For example, the flowchart shows a method for the most prominent steps relevant to assist in understanding the aspects of the present invention. Further, regarding the structure of the device, one or more components of the device may be represented in the drawings by conventional symbols, and the drawings may show only specific details relevant to understanding the embodiments of the present invention so as not to obscure the drawings in detail, which will be readily apparent to those skilled in the art who benefit from the description herein.

DETAILED DESCRIPTION OF THE INVENTION

[0012] For the purpose of facilitating understanding of the principles of the present invention, from here on, reference will be made to the embodiments shown in the drawings and it will be described using specific terms. Nevertheless, it is not intended to limit the scope of the present invention thereby, and such changes and further modifications in the illustrated system, as well as such further applications of the principles of the present invention illustrated therein, will be understood to be commonly contemplated by those skilled in the art related to the present invention. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The systems, methods, and examples provided here are for illustrative purposes only and are not intended to be limiting.

[0013] As used herein, the term "a" is defined as "none, or one, or more than one, or all". Thus, the terms "none", "one", "a plurality", "a plurality but not all", or "all" all fall within the definition of "a". The term "an embodiment" may refer to "no embodiment, or one embodiment, or some embodiments, or all embodiments". Thus, the term "an embodiment" is defined to mean "no embodiment, or one embodiment, or more than one embodiment, or all embodiments".

[0014] The terms and structures used herein are for the purpose of describing, teaching, and clarifying an embodiment and its specific features and elements, and are not intended to limit, reduce, or narrow the spirit and scope of the claims or their equivalents.

[0015] More specifically, terms used in this specification such as, but not limited to, "include", "comprise", "have", "consist of", and their grammatical variations, are not intended to specify strict limitations or exclusions, and unless otherwise specified, do not exclude the possibility of adding one or more functions or elements. Further, unless otherwise stated in a limiting phrase such as "needs to comprise" or "needs to include", it should not be considered to exclude the possibility of deleting one or more of the listed functions and elements.

[0016] Regardless of whether a particular function or element is limited to being used only once, in any case, it may be referred to as "one or more functions" or "one or more elements" or "at least one function" or "at least one element". Further, the use of the terms "one or more" or "at least one" function or element does not exclude the absence of any of those functions or elements unless otherwise specified by limiting words such as "there needs to be one or more..." or "one or more elements are required".

[0017] Unless otherwise defined, all terms used in this specification, especially technical and / or scientific terms, may be construed to have the same meaning as commonly understood by those skilled in the art.

[0018] In this specification, reference is made to a "particular embodiment". It should be understood that it is an example of a possible implementation of any feature and / or element presented in the appended claims. A particular embodiment is described for the purpose of clarifying one or more potential ways in which the specific features and / or elements of the appended claims meet the requirements of distinctiveness, utility, and non-obviousness.

[0019] The use of phrases and / or terms such as "First Embodiment", "Further Embodiments", "Alternative Embodiments", "One Embodiment", "An Embodiment", "Plural Embodiments", "Certain Embodiments", "Other Embodiments", "Another Embodiment", "Further Embodiments", "Additional Embodiments", or variations thereof, but not limited thereto, does not necessarily refer to the same embodiment. Unless otherwise specified, one or more specific features and / or elements described in relation to one or more embodiments may be found in one embodiment, in two or more embodiments, in all embodiments, or in none of the embodiments. One or more features and / or elements may be described herein in the context of a single embodiment only, or alternatively in the context of plural embodiments, or further alternatively in the context of all embodiments, but the functions and / or elements may be provided separately, or alternatively in any suitable combination, or not provided at all. Conversely, any feature and / or element described in the context of separate embodiments may be realized alternatively as being present together in the context of a single embodiment.

[0020] All specific details described herein are used in the context of certain embodiments and, therefore, should not necessarily be construed as limiting factors with respect to the appended claims. The appended claims and their legal equivalents may be realized in the context of embodiments other than those exemplified in the following description.

[0021] One embodiment of the present disclosure discloses a lightweight pressure vessel for storing fluids, comprising a composite material made of a fiber-reinforced polymer matrix covering an aluminum alloy-based metal liner. The composite material has a combination of hoop layers and helical layers provided in a predetermined order, where the hoop layers are wound only around the cylindrical portion of the liner of the pressure vessel, and the helical layers are wound around both the cylindrical portion and the dome portion of the liner of the pressure vessel. The shape of the liner is reconfigured so that the fibers do not slip when winding at a larger angle. Due to the bundling effect of the fibers at a higher winding angle, the thickness of the composite layer increases at the region where the thickness of the liner is thin, i.e., at the position where the dome portion and the cylindrical portion intersect. This improves the strength of the cylinder, but the amount of additional composite material wound around the cylinder is relatively small. It further terminates the crack growth from the cylindrical portion to the dome portion as observed in the fracture analysis. This prevents the failure of the pressure relief device before rupture. This controls the cracks in the cylindrical portion itself and prevents the explosion of the container during leakage or accidents. In this regard, the safety of the container is significantly improved.

[0022] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0023] Figures 1a and 1b show different plan views of a pressure vessel 100 for storing fluids according to an embodiment of the present disclosure. Figure 1c shows a part of the pressure vessel shown in Figure 1a according to an embodiment of the present disclosure. In one embodiment, the pressure vessel 100 can be used to store fluids including, but not limited to, liquids and gases without departing from the scope of the present disclosure. The gas can be embodied as one of compressed natural gas, hydrogen gas, LPG, and mixtures thereof. In one embodiment, the pressure vessel 100 can withstand an internal pressure of up to 800 bar of fluid without departing from the scope of the present disclosure. The pressure vessel 100 mainly comprises a metal liner and a filament wound composite covering and enclosing the entire metal liner. Details of the structure and manufacture of the pressure vessel 100 will be described in subsequent sections of the present disclosure.

[0024] Referring to FIGS. 1a and 1b, in the illustrated embodiment, the pressure vessel 100 may include, but is not limited to, a metal liner 102 and a composite material 104 covering the metal liner 102. The metal liner 102 may include a cylindrical portion 106 and a pair of elliptical domes 108 disposed at both ends of the cylindrical portion 106. The pair of elliptical domes 108 may be individually referred to as a first elliptical dome 108-1 and a second elliptical dome 108-2. Further, the pair of elliptical domes 108 may be interchangeably referred to as elliptical domes 108-1, 108-2 without departing from the scope of the present disclosure.

[0025] The metal liner 102 may be disposed on the inner surface of the pressure vessel 100. In one embodiment, the metal line 102 may be manufactured using a spin forming process. The metal liner 102 may be T6 treated and O conditioned. Further, the metal liner 102 may be surrounded by elliptical domes 108-1, 108-2 connected to the intermediate cylindrical portion 106. The metal liner 102 may have a uniform thickness across the cylindrical portion 106 and may have different thicknesses across each of the elliptical domes 108-1, 108-2.

[0026] In one embodiment, the thickness of the metal liner 102 may be thinner at the location where the elliptical domes 108-1, 108-2 intersect the cylindrical portion 106. The thickness of the metal liner 102 near the pair of openings 202-1, 202-2 of the elliptical domes 108-1, 108-2 may be four times the thickness of the metal liner 102 in the cylindrical portion 106. In one embodiment, the metal liner 102 may be composed of an aluminum alloy-based material without departing from the scope of the present disclosure.

[0027] In the illustrated embodiment, the pressure vessel 100 may include a pair of openings 202 in the elliptical domes 108-1, 108-2. The pair of openings 202 can be individually referred to as a first opening 202-1 and a second opening 202-2. The first opening 202-1 may be formed at an end of the first elliptical dome 108-1. Similarly, the second opening 202-2 may be formed at an end of the second elliptical dome 108-2. Further, in one embodiment, without departing from the scope of the present disclosure, the pair of openings 202 can be interchangeably referred to as openings 202-1, 202-2. The centerlines of the openings 202-1, 202-2 coincide with the longitudinal axis of the cylindrical portion 106.

[0028] Figures 1a and 1b show exemplary dimensional characteristics of the pressure vessel 100. It should be understood that the dimensions shown are exemplary and should not be construed as limiting. Referring to Figures 2a and 2b, in one example, the thickness "a" and height "h" of the cylindrical portion 106 of the metal liner 102 c are 4.8 mm and 1050 mm, respectively. Also, the diameter "d" of the cylindrical portion 106 is in the range of 325 mm to 375 mm. The shortest distance "R1" between the centers of the elliptical domes 108-1 is 140 mm. The longest distance "R2" coincides with the radius of the cylindrical portion. The diameter "d" of each of the pair of openings c is 50 mm in combination with the thickness of the cylindrical portion. The overall length of the pressure vessel between the pair of openings of the elliptical domes is 1390 mm.

[0029] In one embodiment, the cylindrical portion 106 of the pressure vessel 100 may be connected to at least one control valve and at least one pressure relief device through the openings 202-1, 202-2. In particular, the at least one control valve and the at least one pressure relief device may be disposed at the openings 202-1, 202-2 of the pressure vessel 100 without departing from the scope of the present disclosure.

[0030] The composite material 104 may be wound over the cylindrical portion 106 and the elliptical domes 108-1, 108-2. The composite material 104 may alternatively be referred to as a composite overlap 104. In one embodiment, the composite material 104 may be formed from a fiber-reinforced polymer matrix without departing from the scope of the present disclosure. The fibers reinforcing the polymer matrix may be embodied as glass, aramid, carbon, and combinations thereof. Preferably, the carbon fibers are suitably coated with a coating that is mixable with an epoxy resin. Further, the polymer matrix may be embodied as one of a thermoplastic resin and a thermosetting resin. In one embodiment, the thermoplastic resin may be embodied as one of polyethylene and polyamide. The thermosetting resin may be embodied as one of epoxy, modified epoxy, polyester, and polyvinyl ester.

[0031] The composite material 104 may include a combination of hoop layers and helical layers arranged in a predetermined order relative to each other. In one embodiment, the hoop layer may be wound over the cylindrical portion 106 of the metal liner 102 of the pressure vessel 100. In one embodiment, the number of hoop layers may range from 10 to 30, more preferably from 15 to 26. The thickness of the hoop layer may range from 0.11 mm to 0.66 mm, more preferably from 0.22 mm to 0.44 mm.

[0032] Furthermore, the helical layer may be wound around both the cylindrical portion 106 and the elliptical domes 108-1, 108-2. The helical layer may be wound around each of the elliptical domes 108-1, 108-2 such that a helical angle is defined at the position where the cylindrical portion 106 and the elliptical domes 108-1, 108-2 intersect. In one embodiment, the helical angle may be in the range of 10° to 45° without departing from the scope of the present disclosure. The helical angle may be larger at the position where the elliptical domes 108-1, 108-2 and the cylindrical portion 106 intersect. In particular, the helical angle may be larger at the position where the first elliptical dome 108-1 and the cylindrical portion 106 intersect. Similarly, the helical angle may be larger at the position where the second elliptical dome 108-2 and the cylindrical portion 106 intersect.

[0033] In one embodiment, the number of helical layers may be in the range of 25 to 45, more preferably 29 to 40. The thickness of the helical layer may be in the range of 0.44 mm to 5 mm, more preferably 0.47 mm to 2.5 mm. The thickness of the helical layer may be uniform in the cylindrical portion 106. The thickness of the helical layer of the elliptical domes 108-1, 108-2 may be derived using the following formula.

[0034]

Number

[0035] Here, H dome is the thickness of the layer at a certain position, H cylinder is the thickness of the layer in the cylindrical region, R cylinder is the equatorial radius, R opening is the polar radius, B φ is the fiber bandwidth for winding at that angle, R location is the radius at that position.

[0036] In one embodiment, the thickness of the helical layer in the elliptical domes 108-1, 108-2 may be greater compared to the thickness of the helical layer in the cylindrical portion 106. The thickness of the helical layer is maximum near the respective orbits of the elliptical domes 108-1, 108-2, and the helical layer may cover the pressure vessel up to that point. In one embodiment, the length-to-diameter ratio of the cylindrical portion 106 may be in the range of 2.5 to 3. Further, each of the elliptical domes 108-1, 108-2 may have a radius-to-height ratio in the range of 1.25 to 1.30.

[0037] Referring to FIG. 1b, the winding thickness “b” is 20.25 mm throughout the cylindrical portion of the pressure vessel, except at both ends of the elliptical dome having a thickness of 25 mm. The intermediate thickness of the elliptical dome is determined using the obtained equation and is in the range of 22 to 27 mm. Also, the diameter “d1” of the cylindrical portion of the metal liner is fixed at 350 mm. The metal adapter of the pressure vessel may have a diameter “d c ” (including thickness) of 51 mm. As shown in FIG. 1c, the thickness “c” of the metal adapter is 10.2 mm. The total length of the complete shape from the mouth of the metal adapter to the end of the dome is Tc and is 1390 mm.

[0038] (Design and Stress Analysis) In the subsequent sections of the present disclosure, exemplary design parameters, operating conditions, stress analysis, and other exemplary design considerations implemented to design the pressure vessel 100 will be described.

[0039] Table 1 shows various operating conditions adopted for the development of the pressure vessel, along with the requirements specified by the ISO 15869 standard, according to one embodiment of the present disclosure. Those skilled in the art should understand that Table 1 is included to provide a better understanding of the present disclosure and should not, therefore, be construed as limiting.

[0040] (Table 1)

Table 1

[0041] Table 2 shows various design parameters adopted for the development of the pressure vessel 100, along with the requirements specified by the ISO 15869 standard, according to an embodiment of the present disclosure. Those skilled in the art should understand that Table 2 is included to provide a better understanding of the present disclosure and should not, therefore, be construed as limiting.

[0042] (Table 2)

Table 2

[0043] (Design of Pressure Vessel) The design calculation method for determining the thickness of the hoop layer and the helical layer is an extension of the methodical netting analysis after incorporating the thickness change in the shape of the metal liner 102, together with the thickness calculation of the composite material at the elliptical domes 108-1, 108-2.

[0044] The desired number of helical and hoop layers within the cylindrical portion 106 can be determined by dividing the total thickness of the helical and hoop layers by the respective thicknesses of the individual helical and hoop layers. The thickness of the helical and hoop layers depends on the thickness of the resin-impregnated fiber roving. The thickness of the resin-impregnated carbon fiber roving used in the development of the pressure vessel 100 depends on the manufacturing characteristics discussed in a later section of the present disclosure. The thickness of the resin-impregnated carbon fiber roving may be in the range of 0.1 mm to 3.0 mm, more preferably in the range of 0.22 to 1.5 mm. The desired number of helical layers in the elliptical domes 108-1, 108-2 is calculated after considering the load-bearing characteristics of the metal liner 102. In one example, at least 20 hoop layers and 21 hoop layers are appropriate according to the netting analysis. To meet the criteria of the ISO 15869 standard, additional helical and hoop layers are further added. Therefore, during the design of the pressure vessel 100, different winding angles are attempted to determine the non-slip winding angle and range.

[0045] Figure 3a shows an exemplary winding sequence of a pressure vessel according to an embodiment of the present disclosure. Trial angles of 10°, 15°, 25°, 35°, and 45° are obtained as smooth winding angles. The helical layer and the hoop layer are arranged such that the weight of the cylinder is minimized while maintaining the desired properties. Further emphasis is placed on adding a 45° angle to the winding pattern to reinforce the coating at the location where the cylindrical portion 106 intersects the elliptical domes 108-1, 108-2. The number and thickness of the helical layer and the hoop layer can be varied according to requirements and desired properties. Various other permutations and combinations with these layers are also within the scope of the present disclosure. For purposes of illustration, one example is summarized below. Based on the above discussion, the winding sequence is shown, for example, in Figure 3a.

[0046] Table 3 shows exemplary parameters such as winding angle, hoop thickness, and helical thickness calculated for different positions within the elliptical domes 108-1, 108-2 and the cylindrical portion 106 according to an embodiment of the present disclosure. Those skilled in the art should understand that Table 3 is included to provide a better understanding of the present disclosure and should therefore not be construed as limiting.

[0047] (Table 3)

Table 3

[0048] Here, X(R) represents the radius of the elliptical domes 108-1, 108-2 of the metal liner 102 along the X-axis, and the Y-axis represents the longitudinal direction or the respective lengths of the elliptical domes 108-1, 108-2 along the Y-axis.

[0049] Figure 3b shows the exemplary thickness of the composite material in one of the elliptical domes 108-1, 108-2 according to an embodiment of the present disclosure at different helical angles. By way of example, five helical angles are considered, such as 10°, 15°, 25°, 35°, and 45°. Thus, different helical winding angles are obtained in the elliptical domes 108-1, 108-2 for each helical winding angle at the cylindrical portion 106. The contours of the elliptical domes 108-1, 108-2 gradually taper from the cylindrical portion 106 towards the openings 202-1, 202-2. In Figure 3b, R g is the inner equatorial radius of the dome portions 108-1, 108-2. Also, R f is the outer equatorial radius of the domes 108-1, 108-2. Further, t0 is the thickness of the liner at the cylindrical portion 106. The coordinates (x i , y i ) and (x i i , y i ) are the outer and inner dome coordinates of the domes 108-1, 108-2. The inner dome coordinates of 108-1, 108-2 are calculated from the inner liner curve traced using ultrasonic waves as shown in Figure 2a. θ i is a coefficient for converting the coordinates of the liner at a given dome height from the XY coordinate system to the radial coordinate system.

[0050] Thus, the winding angle and helical thickness of the elliptical domes 108-1, 108-2 can vary axially along different portions of the elliptical domes 108-1, 108-2. The helical thickness of a single layer is considered to be 0.44 mm without departing from the scope of the present disclosure. The thickness of the hoop layer is calculated assuming a single fiber layer of 0.22 mm.

[0051] (Stress Analysis) In accordance with the ISO 15869 standard, the stress analysis is performed at the design burst pressure, and the details of the developed FEA model are as follows.

[0052] The metal liner 102 and the composite material 104 each function as body-1 and body-2. The SHELL181 element was used for these CAD bodies (body-1 and body-2) and they were meshed with an element size of 5 mm. Three other types of elements were created at the FE level. SURF154 was used to define the internal pressure load acting on the inner surface of the liner, i.e., body-1. It provides an additional layer of elements for applying surface loads such as pressure. The contact between the outer surface of the liner and the inner surface of the composite overlap 104 is defined by the contact pair (body-1 and body-2) between the two bodies. The CONTACT174 elements of body-1 and the TARGET170 elements of body-2 provide a layer of surface elements for detecting the contact between these two bodies. The modeling priority was defined in the ACP Pre module. Next, the shape was transferred to the Static Structural module to define the boundary conditions and calculate the burst pressure. The model was post-processed in the ACP Post module to predict the failure of the container. The engineering data was determined experimentally using coupon laminate tests in accordance with ISO 527-4. The test results of a carbon epoxy laminate with a fiber weight fraction of 0.56 are summarized in Table 4 below.

[0053] Table 4 shows exemplary properties of a carbon / epoxy composite used for stress analysis according to an embodiment of the present disclosure. Those skilled in the art should understand that Table 4 is included to provide a better understanding of the present disclosure and should not, therefore, be construed as limiting.

[0054] (Table 4)

Table 4

[0055] The stress analysis results of this static structure module were used to predict the theoretical bursting pressure of the container. The Von Mises yield criterion was used for this stress analysis. The Von Mises stress is the combined stress of the tangential stress and the stresses in the X and Y directions. The Von Mises yield criterion is mainly used to predict whether a specific design can withstand a specific load by comparing the Von Mises stress with the design stress of the material.

[0056] According to this condition, for the container to withstand the load, the Von Mises stress induced in the material must be less than the design strength of the material. When the Von Mises stress exceeds the design stress, the pressure vessel 100 will burst.

[0057] As an example, it was found that the hoop strength of the composite material 104 used in the pressure vessel 100 obtained by design calculation is 1982.7 MPa. The Von Mises stress at a given pressure is determined by the results of the stress analysis, and the corresponding bursting pressure of 1982.7 MPa is calculated therefrom. This indicates that the pressure vessel 100 can withstand the internal pressure up to a pressure below the bursting pressure and then fails when the load is increased. The stress analysis of the pressure vessel 100 subjected to an internal pressure of 712 bar exceeding the design bursting pressure is the simulated bursting pressure, and the Von Mises stress generated in the cylindrical portion 106 at this load is 1983 MPa, which is higher than the design strength of 1982.7 MPa. Since the Von Mises stress at the design bursting pressure of 712 bar is higher than the design strength, the pressure vessel 100 will be able to withstand up to the design bursting pressure.

[0058] To predict the failure characteristics of the composite overlap 104, various failure theories were used. The results are shown in FIG. 4, where 4(A, (B), (C), (D), (E), and (F) respectively show the failure characteristics predicted using the Tsai-Wu, Tsai-Hill, Hoffmann, Puck, maximum strain, and maximum stress criteria. The red zones (black in grayscale) are the most likely to fail during rupture, i.e., they are the locations where cracks may occur before rupture.

[0059] FIG. 5 shows a flowchart illustrating a method 500 for manufacturing a pressure vessel 100 for storing a fluid according to an embodiment of the present disclosure. For the sake of brevity, the features of the pressure vessel 100 that have already been described in detail in the descriptions of FIGS. 1a, 1b, 2a, 2b, 3a, 3b, and 4 are not described in detail in the description of FIG. 5.

[0060] The method 500 includes, at block 502, applying a composite material 104 over a metal liner 102 of the pressure vessel 100. In one embodiment, the hoop layer of the composite material 104 may be wound over the cylindrical portion 106 of the metal liner 102 of the pressure vessel 100 by a continuous filament winding operation. The helical layer of the composite material 104 may be wound over both the cylindrical portion 106 of the metal liner 102 of the pressure vessel 100 and a pair of elliptical domes 108-1, 108-2. Further, the helical layer may be wound around each of the pair of elliptical domes 108-1, 108-2 such that a helical angle is defined at the location where the cylindrical portion 106 intersects the pair of elliptical domes 108-1, 108-2.

[0061] Method 500 includes, at block 504, curing a composite overlap in a series of steps. In a first curing step, the method includes curing the composite overlap at room temperature for 24 to 35 hours. Thereafter, in a second curing step, the method includes curing the composite overlap at a temperature in the range of 60°C to 100°C for 4 to 15 hours. In both curing steps, pressure vessel 100 may be rotated at a speed in the range of 1 to 2 rpm without departing from the scope of the present disclosure. An exemplary manufacturing process of pressure vessel 100 is further detailed in subsequent sections of the present disclosure.

[0062] (Manufacture of Pressure Vessel) The spin-formed metal liner 102 is used as a mandrel, and the composite material 104 is wound onto the metal liner 102. A four-axis filament winding machine is used to wind the composite material 104. The winding parameters are set to avoid the possibilities of fiber slippage and breakage, delamination, large gaps between fiber spools due to inappropriate bandwidth, and insufficient performance of the composite material due to low fiber volume fraction. Automation of the winding process further reduces the possibility of defects caused by human intervention.

[0063] FIG. 6 shows a common fiber winding path for a four-axis filament winding machine implemented in the manufacture of pressure vessel 100 according to an embodiment of the present disclosure. The present disclosure discloses a process that facilitates the manufacturing process of a type-3 cylinder for storing compressed hydrogen gas. As previously explained, pressure vessel 100 includes a metal liner 102 and a carbon-epoxy composite overlap 104. The process of developing pressure vessel 100 depends on various parameters as described in subsequent sections of the present disclosure.

[0064] The profile of the liner plays an important role in determining the winding parameters. In research to optimize the winding parameters, it has been shown that an elliptical dome head with a length-to-diameter ratio between 1.25 and 1.30 is used to facilitate the use of large values of the winding angle during winding. The positions where the elliptical domes 108-1, 108-2 intersect the cylindrical part 106 provide proper coverage, thereby enhancing the safety of the pressure vessel 100.

[0065] A seamless aluminum alloy liner such as the metal liner 102 is manufactured using a spin forming process and is T6 heat treated and O conditioned to improve the ductility of the metal liner 106 and reduce the defect size. This reduces the susceptibility to hydrogen embrittlement in the material of the metal liner 102.

[0066] The winding pattern derived using netting analysis is wound around the metal liner 102 using filament winding technology. The carbon fiber functions as an epoxy matrix-based reinforcement. The volume fraction of the fiber plays an important role in determining the strength of the composite material 104. An electronic tensioner is used as the tension mechanism during winding.

[0067] The fiber path from the spool to the mandrel must be smooth and appropriate to prevent fiber breakage, improve the bandwidth, and ensure proper placement of the fiber on the mandrel. The number of placement pulleys at the payout eye is calculated as a function of the fiber tensioning ability and the system requirements to increase the volume fraction of the fiber without fiber breakage during winding. The appropriate value of the tension helps to squeeze out excess resin while winding the composite material. Excessive tension leads to delamination of the layers. The tension required as a function of the thickness of all composite material layers is determined for proper winding.

[0068] The resin bath plays an important role in wetting the fibers before winding. Irregular wetting of the fibers hinders load transfer between the reinforcements as the matrix transfers the load. Excessive wetting of the fibers reduces the volume fraction of the fibers. To function properly, the doctor blade needs to be attached at the required angle. A temperature controller is added to the resin bath system to prevent curing of the resin during winding. Delamination occurs when the resin cures in the middle of the winding.

[0069] Excess resin extruded onto the mandrel by the tensioned fibers of the subsequent layer is automatically collected using a movable doctor blade added as an add-on to the payout eye. Its contact angle varies according to a function that depends on the winding position. The fibers are arranged across a geodesic fiber path so as not to slip. The geodesic fiber path is determined as a function of the cylinder radius, the non-slip opening radius, and the dome height.

[0070] The winding parameters are mainly the bandwidth, winding speed, offset of the payout eye, and fiber tension, and they vary depending on the winding angle, number of layers, non-slip opening radius, fiber bundling required near the poles, and the capabilities of the machine. The fiber path for changing from a hoop layer to a helical layer or vice versa during winding is determined to assist in the automation of the process.

[0071] The thickness distribution of the individual composite material layers within the elliptical domes 108-1, 108-2 depends on the winding parameters. The correlation between layer thickness, non-slip opening radius, dome position, cylinder radius, and layer thickness in the cylindrical region is derived using the results of manufacturing trials. Various parameters related to the winding of the composite material onto the metal liner are described in subsequent sections of this disclosure.

[0072] (Process Parameters) a) Fiber tension mechanism: The fiber spool is first tensioned using a 105005 Dynaspede electric tensoner, which can apply a torque of 5 Kg. The value of its controller is initially set to apply a torque of 1.75 Kg to the dry fiber exiting the fiber spool and entering the tension pulley.

[0073] b) Tension mechanism: Various pulleys are arranged at regular intervals. The increase in tension by the tension pulley depends on the contact area between the fiber tow and the pulley, the material of the pulley, and the friction coefficient between the fiber tow and the material of the pulley. In this case, Teflon pulleys are used, and sandblasting treatment increases the friction coefficient of these pulleys.

[0074] c) Pay-off eye: The pay-off eye plays an important role in arranging the fiber spools together to form a bandwidth. A bandwidth without gaps between adjacent fiber tows and without overlap between fiber tows is considered an efficient bandwidth. This results in a better coating of the composite material in one winding cycle, reduces the influence of fiber bundling near the extreme parts, improves the load transfer between the reinforcing materials, and shortens the winding time.

[0075] d) Resin bath: The impregnation of resin plays an important role in determining the properties of the composite material. When the resin fraction in the composite material is high, the strength of the composite material decreases. Therefore, a resin with a low viscosity is used for impregnation. Two additional doctor blades added to squeeze out the excess resin provide a composite material with a high fiber volume fraction and excellent ultimate tensile strength and mechanical properties. The gelation time of the resin is 50 minutes and can be extended by attaching a temperature regulator to the resin bath. The resin bath is maintained at a temperature of 15°C, which increases the gelation time by 2 hours. When the previously wound composite material partially cures during winding, delamination may occur, and attaching a temperature controller is a solution to this problem that is allowed.

[0076] e) Winding mechanism: The composite material is wound across the geodesic fiber path using a 4-axis filament winding machine. The winding speed affects the accuracy of fiber placement during winding by influencing the slippage characteristics of the fibers. The geodesic fiber path is determined by CADFIL software, which depends on the winding angle, opening radius, coefficient of friction, offset, bandwidth, mandrel profile, and dome curvature. These winding parameters are optimized according to the required winding pattern. The mandrel chuck changes as the winding progresses with changes in the parameters. Table 6 shows the estimated values of the winding parameters with the lowest likelihood of manufacturing defects.

[0077] Table 6 shows exemplary winding parameters for winding the composite material onto the elliptical domes 108-1, 108-2 and the cylindrical portion 106 according to one embodiment of the present disclosure. Those skilled in the art should understand that Table 6 is included to provide a better understanding of the present disclosure and should therefore not be construed as limiting.

[0078] (Table 6)

Table 6

[0079] (Integration of composite overlap) a) Reduction of resin content: A doctor blade is added to the payout eye to automate the process of wiping off excess resin. The contact angle varies between 30° and 60°. This improves the fiber volume fraction of the cylinder by wiping off the excess resin extruded after the integration of the composite layer.

[0080] b) Curing: The manufactured prototype rotates axially until curing is complete to avoid non-uniform deposition of resin in the composite overlap. The resin shrinks during curing, and proper rotation of the container ensures uniform shrinkage as the matrix is uniformly dispersed throughout the composite material and the load is properly transmitted.

[0081] Therefore, the pressure vessel 100 is manufactured for testing. The total weight measured for the pressure vessel 100 was found to be in the range of 30 to 35 kg. The pressure vessel 100 results in a weight reduction of about 30 to 54% compared to conventional cylinders available in the prior art.

[0082] (Test) This test was carried out in accordance with the international standard ISO 15869.

[0083] An explanation and the results of the exemplary tests performed are described below.

[0084] 1. Hydrostatic burst test The hydrostatic burst test is carried out using the pressure vessel 100 in accordance with the ISO 15869 standard. The pressure vessel 100 is hydrostatically pressurized to 50 MPa at a rate of 0.48 MPa / s, after which the pressurization rate decreases to 0.37 MPa / s. As shown in Figure 7, when maintained by the control unit at 70 MPa, i.e., the minimum burst pressure, for 10 seconds, the pressure vessel 100 burst at a pressure of 812 bar. This pressure exceeds the standard recommended pressure, i.e., 700 bar.

[0085] 2. Failure analysis To verify the design model, the results of the finite element analysis were compared with the experimentally obtained results. The theoretically predicted burst pressure of the pressure vessel was 71 MPa, but its actual value was determined to be 81 MPa. Therefore, this design has a safety factor of 10 MPa and can be used in the design of the pressure vessel by predicting the burst pressure. The theoretically predicted failure characteristics of the pressure vessel according to various failure criteria shown in Figure 4 were compared with the failure characteristics obtained as shown in Figures 8(A) and (B). The Tsai-Wu failure criterion was found to be a reliable criterion for predicting failure. The comparison between the theoretical and actual failures is shown in Figure 8(C).

[0086] The above-described pressure vessel 100 and the method of manufacturing the pressure vessel 100 provide the following advantages.

[0087] The present disclosure provides a lightweight pressure vessel 100 for storing fluids. The present disclosure also discloses a method of manufacturing the lightweight pressure vessel 100 in a practical approach that results in better performance in terms of the weight, cost, and safety of the vessel.

[0088] The pressure vessel 100 is 30 - 50% lighter than conventional pressure vessels. The pressure vessel 100 can withstand an internal pressure up to 710 bar. The pressure vessel 100 is used for storing fluids under high pressure. The pressure vessel 100 is mainly for medium-sized vehicles and, being lightweight, improves fuel efficiency and reduces the load on the vehicle.

[0089] In the present disclosure, after reshaping the metal liner 102, it is possible to include larger winding angles in the winding pattern and avoid slippage of the fibers during these windings with larger angles. The fiber bundling effect with larger winding angles increases the thickness of the composite material layer in regions where the thickness of the liner is thin, i.e., at the positions where the elliptical domes 108-1, 108-2 intersect with the cylindrical portion 106. This improves the strength of the pressure vessel 100 while the amount of additional composite material wound around the metal liner 102 of the pressure vessel 100 is relatively small. Further, as observed from the fracture analysis results, the growth of cracks from the cylindrical portion 106 to the elliptical dome 108-1, 108-2 portions is stopped, thereby preventing the failure of the pressure relief device before rupture. This prevents the explosion of the pressure vessel 100 during leakage or accidents by controlling the cracks in the cylindrical portion 106 itself. Thereby, the safety of the pressure vessel 100 is significantly improved without affecting the cost of the pressure vessel 100.

[0090] The pressure vessel 100 is manufactured in a commercially viable and more economical way while meeting all safety standards defined in ISO 15869. The pressure vessel 100 is wound neatly to avoid gaps between consecutive layers of the composite material 104 and can maintain an internal pressure of the fluid up to 800 bar. The present disclosure also discloses a method of manufacturing the pressure vessel 100 for storing fluids.

[0091] As described above, this method involves alternately applying, on both the cylindrical part and the dome part of the liner of a pressure vessel, helical layers that partially cover the dome part with the maximum and minimum fiber bundling effects of possible winding angles, and applying them to a composite hoop layer by a continuous filament winding operation on the cylindrical part of the liner of the pressure vessel. More specifically, the present disclosure relates to a lightweight composite pressure vessel for storing compressed hydrogen gas, and a method for manufacturing the pressure vessel 100 that provides better weight performance. More specifically, the present disclosure relates to a lightweight composite Type 3 pressure vessel / cylinder such as the pressure vessel 100 for storing compressed hydrogen gas, and a design and manufacturing method of the pressure vessel 100.

[0092] Specific words are used to describe this subject, but the resulting limitations are not intended. As will be apparent to those skilled in the art, various operational changes can be made to the method to implement the inventive concept taught herein. The drawings and the foregoing description provide examples of embodiments. Those skilled in the art will understand that one or more of the described elements may be combined into a single functional element. Alternatively, a particular element may be divided into multiple functional elements. Elements of one embodiment may be added to other embodiments.

[0093] (Appendix) (Appendix 1) A pressure vessel for storing a fluid, a metal liner comprising a cylindrical part and a pair of elliptical domes disposed at both ends of the cylindrical part, a composite material that covers and wraps the cylindrical part and the pair of elliptical domes, the composite material being formed from a fiber-reinforced polymer matrix and comprising a combination of hoop layers and helical layers arranged in a predetermined order with respect to each other, comprising, the hoop layer is wound around the cylindrical part of the metal liner of the pressure vessel, the helical layer is wound around both the cylindrical part and the pair of elliptical domes, The helical layer is wound around each of the pair of elliptical domes such that a helical angle is defined at a position where the cylindrical portion and the pair of elliptical domes intersect. Pressure vessel.

[0094] (Appendix 2) The helical angle is in the range of 10° to 45°. The pressure vessel according to Appendix 1.

[0095] (Appendix 3) The pressure vessel includes a pair of openings in the pair of elliptical domes. The cylindrical portion of the pressure vessel is connected to at least one control valve and at least one pressure relief device through the pair of openings. The pressure vessel according to Appendix 1.

[0096] (Appendix 4) The fluid is embodied as one of a liquid and a gas. The pressure vessel according to Appendix 1.

[0097] (Appendix 5) The gas is embodied as one of compressed natural gas, hydrogen gas, LPG, and mixtures thereof. The pressure vessel according to Appendix 4.

[0098] (Appendix 6) The fibers reinforcing the polymer matrix are embodied as glass, aramid, carbon, and combinations thereof. The pressure vessel according to Appendix 1.

[0099] (Appendix 7) The polymer matrix is embodied as one of a thermoplastic resin and a thermosetting resin. The pressure vessel according to Appendix 1.

[0100] (Appendix 8) The thermoplastic resin is embodied as one of polyethylene and polyamide. The pressure vessel described in Supplementary Note 7.

[0101] (Supplementary Note 9) The thermosetting resin is embodied as one of epoxy, modified epoxy, polyester, and polyvinyl ester. The pressure vessel described in Supplementary Note 7.

[0102] (Supplementary Note 10) The metal liner is disposed on the inner surface of the pressure vessel, manufactured using a spin forming process, and the metal liner is T6 treated and O adjusted. The pressure vessel described in Supplementary Note 1.

[0103] (Supplementary Note 11) The metal liner is surrounded by the pair of elliptical domes connected to the cylindrical portion therebetween, the metal liner has a uniform thickness across the cylindrical portion, and has different thicknesses across each of the pair of elliptical domes. The pressure vessel described in Supplementary Note 1.

[0104] (Supplementary Note 12) The number of hoop layers is in the range of 10 to 30, more preferably 15 to 26. The pressure vessel described in Supplementary Note 1.

[0105] (Supplementary Note 13) The number of helical layers is in the range of 25 to 45, more preferably 29 to 40. The pressure vessel described in Supplementary Note 1.

[0106] (Supplementary Note 14) The thickness of the hoop layer is in the range of 0.11 mm to 0.66 mm, more preferably 0.22 mm to 0.44 mm. The pressure vessel described in Supplementary Note 12.

[0107] (Supplementary Note 15) The thickness of the helical layer is in the range of 0.44 mm to 5 mm, more preferably 0.47 mm to 2.5 mm. The pressure vessel described in Supplementary Note 13.

[0108] (Supplementary Note 16) The thickness of the helical layer is uniform in the cylindrical portion, The following formula is given to determine the thickness of the helical layer in the pair of elliptical domes, [Number] Here, H dome is the thickness of the layer at a certain position, and H cylinder is the thickness of the layer in the cylindrical region, R cylinder is the equatorial radius, and R opening is the polar radius, B φ is the fiber bandwidth for winding at that angle, and R location is the radius at that position, The pressure vessel described in Supplementary Note 15.

[0109] (Supplementary Note 17) The thickness of the helical layer is larger in the pair of elliptical domes compared to the thickness of the helical layer in the cylindrical portion, The thickness of the helical layer is maximum near the respective trajectories of the pair of elliptical domes, and the helical layer covers the pressure vessel up to that point. The pressure vessel described in Supplementary Note 16.

[0110] (Supplementary Note 18) The ratio of the length to the diameter of the cylindrical portion is in the range of 2.5 to 3, and each of the pair of elliptical domes has a ratio of the radius to the height in the range of 1.25 to 1.30. The pressure vessel described in Supplementary Note 1.

[0111] (Supplementary Note 19) The helical angle is larger at the position where the elliptical dome and the cylindrical portion intersect, and the thickness of the metal liner is smaller at the position where the elliptical dome and the cylindrical portion intersect. The pressure vessel described in Supplementary Note 1 or 3.

[0112] (Supplementary Note 20) The thickness of the metal liner near the pair of openings of the elliptical dome is 4 times the thickness of the metal liner in the cylindrical portion. The pressure vessel according to Supplementary Note 19.

[0113] (Supplementary Note 21) The pressure vessel withstands an internal pressure of fluid up to 800 bar. The pressure vessel according to Supplementary Note 1.

[0114] (Supplementary Note 22) A method for manufacturing a pressure vessel for storing fluid, comprising: applying a composite material onto the metal liner of the pressure vessel, wherein a hoop layer of the composite material is wound around the cylindrical portion of the metal liner of the pressure vessel by a continuous filament winding operation, a helical layer of the composite material is wound around both the cylindrical portion of the metal liner of the pressure vessel and a pair of elliptical domes, and the helical layer is wound around each of the pair of elliptical domes such that a helical angle is defined at a position where the cylindrical portion and the pair of elliptical domes intersect; overlapping the composite material (i) at room temperature for 24 to 35 hours, (ii) at a temperature in the range of 60°C to 100°C for 4 to 15 hours and curing the composite material in a series of steps, and rotating the pressure vessel at a speed in the range of 1 to 2 rpm during both curing steps; and a method for manufacturing a pressure vessel.

[0115] (Supplementary Note 23) The helical angle is in the range of 10° to 45°. The method according to Supplementary Note 22.

[0116] (Supplementary Note 24) The number of hoop layers is in the range of 10 to 30, more preferably 15 to 26. The method according to Supplementary Note 22.

[0117] (Supplementary Note 25) The number of helical layers ranges from 25 to 45, more preferably from 29 to 40, by the method described in Supplementary Note 22.

[0118] (Supplementary Note 26) The thickness of the hoop layer ranges from 0.11 mm to 0.66 mm, more preferably from 0.22 mm to 0.44 mm, by the method described in Supplementary Note 24.

[0119] (Supplementary Note 27) The thickness of the helical layer ranges from 0.44 mm to 5 mm, more preferably from 0.47 mm to 2.5 mm, by the method described in Supplementary Note 25.

[0120] (Supplementary Note 28) The thickness of the helical layer is uniform in the cylindrical portion, and the following formula is given to determine the thickness of the helical layer in the pair of elliptical domes, [Number] Here, H dome is the thickness of the layer at a certain position, H cylinder is the thickness of the layer in the cylindrical region, R cylinder is the equatorial radius, R opening is the polar radius, B φ is the fiber bandwidth for winding at that angle, R location is the radius at that position, by the method described in Supplementary Note 27.

[0121] (Supplementary Note 29) The thickness of the helical layer is larger in the pair of elliptical domes compared to the thickness of the helical layer in the cylindrical portion, The thickness of the helical layer is maximum near the respective orbits of the pair of elliptical domes, and up to that point the helical layer covers the pressure vessel, by the method described in Supplementary Note 28.

[0122] (Supplementary Note 30) The ratio of the length to the diameter of the cylindrical portion is in the range of 2.5 to 3, and each of the pair of elliptical domes has a radius-to-height ratio in the range of 1.25 to 1.30. The method according to Supplementary Note 22.

[0123] (Supplementary Note 31) The helical angle is larger at the position where the elliptical dome and the cylindrical portion intersect, and the thickness of the metal liner is smaller at the position where the elliptical dome and the cylindrical portion intersect. The method according to Supplementary Note 22.

Claims

1. A pressure vessel for storing a fluid, comprising a cylindrical portion, a pair of elliptical domes disposed at both ends of the cylindrical portion, and a metal liner having a pair of openings in the pair of elliptical domes, a composite material covering and wrapping the cylindrical portion and the pair of elliptical domes, the composite material being formed from a polymer matrix reinforced with fibers and comprising a combination of a hoop layer and a helical layer arranged in a predetermined order with respect to each other, comprising, the hoop layer being wound around the cylindrical portion of the metal liner of the pressure vessel, the helical layer being wound around both the cylindrical portion and the pair of elliptical domes, the helical layer being wound around each of the pair of elliptical domes such that a helical angle is defined at a position where the cylindrical portion and the pair of elliptical domes intersect, the helical angle being larger at a position where the pair of elliptical domes and the cylindrical portion intersect, and the thickness of the metal liner being smaller at a position where the pair of elliptical domes and the cylindrical portion intersect, the metal liner having different thicknesses across each of the pair of elliptical domes, and the thickness of the metal liner near the pair of openings of the elliptical domes being four times the thickness of the metal liner in the cylindrical portion, a pressure vessel.

2. wherein the helical angle is in the range of 10° to 45°, the pressure vessel according to Claim 1.

3. The cylindrical portion of the pressure vessel is connected to at least one control valve and at least one pressure relief device through the pair of openings, the pressure vessel according to Claim 1.

4. wherein the fluid is embodied as one of a liquid and a gas, the pressure vessel according to Claim 1.

5. wherein the gas is embodied as one of compressed natural gas, hydrogen gas, LPG, and mixtures thereof, the pressure vessel according to Claim 4.

6. wherein the fibers reinforcing the polymer matrix are embodied as glass, aramid, carbon, and combinations thereof, the pressure vessel according to Claim 1.

7. wherein the polymer matrix is embodied as one of a thermoplastic resin and a thermosetting resin, the pressure vessel according to Claim 1.

8. wherein the thermoplastic resin is embodied as one of polyethylene and polyamide, the pressure vessel according to Claim 7.

9. The thermosetting resin is embodied as one of epoxy, modified epoxy, polyester, and polyvinyl ester. The pressure vessel according to claim 7.

10. The metal liner is disposed on the inner surface of the pressure vessel, manufactured using a spin forming process, and the metal liner is T6 treated and O adjusted. The pressure vessel according to claim 1.

11. The metal liner is surrounded by the pair of elliptical domes connected to the cylindrical portion therebetween, and the metal liner has a uniform thickness across the cylindrical portion. The pressure vessel according to claim 1.

12. The number of hoop layers is in the range of 10 to 30. The pressure vessel according to claim 1.

13. The number of helical layers is in the range of 25 to 45. The pressure vessel according to claim 1.

14. The thickness of the hoop layer is in the range of 0.11 mm to 0.66 mm. The pressure vessel according to claim 12.

15. The thickness of the helical layer is in the range of 0.44 mm to 5 mm. The pressure vessel according to claim 13.

16. The thickness of the helical layer is uniform in the cylindrical portion, and the following formula is given to determine the thickness of the helical layer in the pair of elliptical domes. The thickness of the helical layer is uniform in the cylindrical portion, and the following formula is given to determine the thickness of the helical layer in the pair of elliptical domes. 【Number 1】 Here, H ｄｏｍｅ is the thickness of the layer at a certain position, and H ｃｙｌｉｎｄｅｒ is the thickness of the layer in the cylindrical region, R ｃｙｌｉｎｄｅｒ is the equatorial radius, and R ｏｐｅｎｉｎｇ is the polar radius, B φ is the fiber bandwidth for winding at that helical angle, R ｌｏｃａｔｉｏｎ is the radius at that position, The pressure vessel according to claim 15.

17. The thickness of the helical layer is larger in the pair of elliptical domes compared to the thickness of the helical layer in the cylindrical portion. The pressure vessel according to claim 16.

18. The ratio of the length to the diameter of the cylindrical portion is in the range of 2.5 to 3, and each of the pair of elliptical domes has a ratio of radius to height in the range of 1.25 to 1.

30. The pressure vessel according to claim 1.

19. The pressure vessel withstands an internal pressure of fluid up to 80000000 pascal. The pressure vessel according to claim 1.

20. A method for manufacturing a pressure vessel for storing fluid, Applying a composite material onto the metal liner of the pressure vessel, wherein the hoop layer of the composite material is wound around the cylindrical portion of the metal liner of the pressure vessel by a continuous filament winding operation, the helical layer of the composite material is wound around both the cylindrical portion of the metal liner of the pressure vessel and a pair of elliptical domes, and the helical layer is wound around each of the pair of elliptical domes such that a helical angle is defined at the position where the cylindrical portion and the pair of elliptical domes intersect; Overlapping the composite material (i) at room temperature for 24 to 35 hours, (ii) at a temperature in the range of 60°C to 100°C for 4 to 15 hours Curing in a series of steps, and rotating the pressure vessel at a speed in the range of 1 to 2 rpm during both curing steps; Comprising The helical angle is larger at the position where the pair of elliptical domes and the cylindrical portion intersect, and the thickness of the metal liner is smaller at the position where the pair of elliptical domes and the cylindrical portion intersect; The metal liner having a pair of openings in the pair of elliptical domes has different thicknesses across each of the pair of elliptical domes, and the thickness of the metal liner near the pair of openings of the elliptical domes is 4 times the thickness of the metal liner in the cylindrical portion; A method for manufacturing a pressure vessel.

21. The helical angle is in the range of 10° to 45°; The method according to claim 20.

22. The number of hoop layers is in the range of 10 to 30; The method according to claim 20.

23. The number of helical layers is in the range of 25 to 45; The method according to claim 20.

24. The thickness of the hoop layer is in the range of 0.11 mm to 0.66 mm; The method according to claim 22.

25. The thickness of the helical layer is in the range of 0.44 mm to 5 mm; The method according to claim 23.

26. The thickness of the helical layer is uniform in the cylindrical portion, and the following formula is provided to determine the thickness of the helical layer in the pair of elliptical domes; 【Number 2】 Here, H ｄｏｍｅ is the thickness of the layer at a certain position, and H ｃｙｌｉｎｄｅｒ is the thickness of the layer in the cylindrical region, R ｃｙｌｉｎｄｅｒ is the equatorial radius, and R ｏｐｅｎｉｎｇ is the polar radius, B φ is the fiber bandwidth for winding at that helical angle, R ｌｏｃａｔｉｏｎ is the radius at that position, The method according to claim 25.

27. The thickness of the helical layer is larger in the pair of elliptical domes compared to the thickness of the helical layer in the cylindrical portion, and the thickness of the helical layer is maximum near the trajectory of each of the pair of elliptical domes, and the helical layer covers the pressure vessel up to that point. ​ The method according to claim 26.

28. The ratio of the length to the diameter of the cylindrical portion is in the range of 2.5 to 3, and each of the pair of elliptical domes has a ratio of radius to height in the range of 1.25 to 1.

30. The method according to claim 20.

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