Description:The present invention relates to high-pressure storage vessels used for storing compressed gases such as Compressed Natural Gas (CNG) and Hydrogen (H₂). More particularly, it pertains to Type IV Composite Overwrapped Pressure Vessels (COPVs) that employ a polymeric liner and composite overwrap materials, resulting in a lightweight, non-corrosive, and durable storage solution.

BACKGROUND OF THE INVENTION:
Conventional Technologies:
Traditional pressure cylinders made of steel or aluminum alloys are widely used for the storage of high-pressure gases. However, these metal cylinders are inherently heavy and prone to corrosion due to continuous exposure to gases and environmental conditions. These drawbacks increase transportation costs, reduce fuel efficiency in vehicular applications, and require periodic maintenance and inspection.
To address these issues, composite pressure vessels, particularly Type III and Type IV cylinders, have emerged. Type III cylinders still use a metallic liner wrapped with composite fibers. In contrast, Type IV COPVs eliminate the metal liner entirely, replacing it with a polymeric liner, offering substantial advantages in terms of weight reduction and corrosion resistance.

PRIOR ART SEARCH
Patent References:
1. US8215504B2 – “Type IV pressure vessel with composite overwrap and polymer liner.”
o Teaches use of plastic liner and composite wrap but doesn’t focus on optimal material pairing for both weight and corrosion performance.
2. US20120145698A1 – “Lightweight pressure vessel.”
o Discusses lightweight design using composites, yet doesn't explore full polymer liner configurations with integrated non-corrosion benefits.
3. EP2633893A1 – “Pressure vessel with improved corrosion resistance.”
o Focus on external corrosion protection, rather than full internal non-corrosive liner exposure.
4. CN106755269A – “Composite gas cylinder with polymer liner.”
o Presents a similar liner but lacks specific application towards service life optimization and fuel efficiency in mobile applications.
Non-Patent Literature (NPL):
• Journal of Pressure Vessel Technology (ASME), 2020 – Study comparing Type III vs. Type IV COPVs showing weight savings and corrosion resistance benefits of polymer liners.
• Composite Structures, Elsevier, 2021 – Analysis of carbon fiber and resin performance under internal gas pressure in hydrogen storage.

ADVANTAGES OVER PRIOR ART:
• Fully non-corrosive design with zero metallic contact to gas.
• Use of high-performance lightweight polymeric liners with optimized overwrap for structural integrity.
• Design tailored to automotive, aerospace, and marine sectors where weight and safety are critical.
• Enhanced recyclability of materials compared to traditional all-metal designs.

SUMMARY OF THE INVENTION:
The invention provides an improved Type IV COPV that is:
• Lightweight due to the low-density polymeric liner and high-strength composite overwrap;
• Non-corrosive because no metallic component is in direct contact with the stored fluid;
• Structurally sound to withstand internal pressures exceeding 250 bar;
• Capable of maintaining integrity and shape over extended service periods under cyclic and static pressure loads.
The design incorporates:
• A polymeric liner (e.g., HDPE, PA6, PA12, or PET) that contacts the gas;
• An epoxy resin matrix embedded with carbon and/or glass fiber;
• A dome and cylindrical structure that optimizes strength-to-weight ratio;
• Optional barrier layers or liners to further enhance gas impermeability.

OBJECTS OF THE INVENTION:
1. To develop a pressure vessel that is lighter in weight than metal-based equivalents.
2. To ensure the non-corrosive interface between the vessel and stored gas.
3. To improve storage efficiency, especially in vehicular and aerospace applications.
4. To ensure mechanical integrity and pressure retention across the operational life.

DRAWINGS:
• Figure 1: Cross-sectional schematic of Type IV cylinder with labeled components
• Figure 2: Detail of polymeric liner geometry
• Figure 3: Exploded view of fiber winding sequence
• Figure 4: Stress distribution simulation under internal pressure
• Figure 5: Comparative weight chart between metallic and composite cylinders

DETAILED DESCRIPTION OF THE INVENTION:
The proposed invention is a Type IV Composite Pressure Vessel (COPV) comprising the following:
1. Polymeric Liner:
o Material: HDPE, PA6, PA12, or PET
o Function: To act as a gas barrier and maintain the shape during winding and operation.
o Properties: Chemically inert, lightweight, corrosion-resistant, and thermally stable.
2. Dome and Cylinder Geometry:
o The liner is blow-molded into a dome-ended cylindrical body to optimize internal volume and pressure distribution.
3. Overwrap System:
o Fiber: High-strength carbon fiber (T700 or similar) optionally mixed with glass fiber for cost optimization.
o Matrix: Toughened epoxy resin for load transfer and environmental resistance.
4. Manufacturing Process:
o Step 1: Fabrication of liner through blow molding or rotational molding.
o Step 2: Winding of dry fibers via filament winding in helical and hoop patterns.
o Step 3: Resin infusion and curing to consolidate the composite shell.
o Step 4: End fitting/boss integration using metallic or composite bosses bonded or threaded into the liner necks.
5. Performance Characteristics:
o Burst pressure >3× working pressure
o Weight reduction >60% compared to equivalent metallic cylinders
o No corrosion or chemical degradation of liner over standard life cycle
The present invention relates to a lightweight, non-corrosive composite overwrapped pressure vessel (COPV), specifically a Type IV cylinder used for storing compressed gases such as compressed natural gas (CNG) or hydrogen. The pressure vessel is designed with a focus on weight reduction, corrosion resistance, and structural reliability, using a fully non-metallic polymeric liner as the fluid-contacting element and a fiber-reinforced resin composite overwrap for mechanical strength.
The primary structural element is the polymeric liner, which serves both as a gas barrier and a structural form for filament winding. The liner is typically fabricated through blow molding or rotational molding from materials such as high-density polyethylene (HDPE), polyamide 6 (PA6), polyamide 12 (PA12), or polyethylene terephthalate (PET). These materials are selected for their excellent chemical resistance, dimensional stability, and low gas permeability. The liner includes a central cylindrical section with a uniform diameter to maximize internal volume, and integrated dome-shaped ends that transition smoothly into neck regions for boss attachment. The geometry of the dome is critically designed to avoid abrupt curvature transitions, thereby minimizing stress concentration zones and enabling uniform fiber placement during overwrapping.
Encasing the liner is the composite overwrap, which is applied through an automated filament winding process. The overwrap consists of continuous fibers—primarily carbon fibers, with the optional addition of glass fibers for cost optimization—impregnated with a thermosetting epoxy resin. Filament winding is performed using a precisely controlled winding head that deposits fibers in both hoop and helical orientations. The hoop windings (generally around 90° to the axis) provide radial strength to resist internal gas pressure, while the helical windings (typically in the 15–25° range) provide axial reinforcement and burst strength. After winding, the composite structure undergoes curing under controlled temperature and pressure to solidify the resin matrix and ensure proper bonding of all fibers.
At each end of the vessel, the neck region of the liner is fitted with a metallic or composite boss, which allows for the attachment of valves or regulators. These bosses are either co-molded into the liner during fabrication or bonded later using thermal and mechanical means. Importantly, the internal surfaces of the bosses are carefully sealed against gas leakage, and no metallic component is in direct contact with the stored gas, ensuring zero internal corrosion. The boss design also includes sealing grooves for O-rings or gaskets to ensure leak-proof operation under high pressure.
This novel construction results in a significant reduction in total weight—often exceeding 60% compared to conventional steel cylinders—while retaining sufficient strength to withstand operating pressures of 200–350 bar and burst pressures exceeding 600 bar. Additionally, the non-metallic liner ensures complete resistance to corrosion, eliminating one of the major degradation mechanisms in metal cylinders, particularly in hydrogen storage where metal embrittlement is a concern.
The cylinder design also offers extended service life, with the liner and composite structure capable of withstanding long-term cyclic and static loading without mechanical or chemical degradation. This makes the vessel ideal for automotive applications, where weight reduction contributes directly to improved vehicle efficiency and range. It is equally suitable for aerospace, marine, portable, and stationary gas storage systems, especially where durability and long life are critical.
In summary, the invention provides a Type IV pressure vessel that combines a corrosion-resistant polymer liner, a high-strength fiber-reinforced composite shell, and precisely designed dome and boss regions to achieve an optimal balance of performance, weight, and durability, addressing the critical limitations of traditional all-metal cylinders.

, Claims:. A lightweight, non-corrosive Type IV composite pressure vessel comprising:
• a polymeric liner having a cylindrical body with dome-shaped ends;
• a composite overwrap including reinforcing fibers embedded in a resin matrix applied over the liner;
• wherein the polymeric liner is in full contact with the stored pressurized gas and provides corrosion resistance due to its non-metallic composition.
2. The vessel of claim 1, wherein the polymeric liner is made of high-density polyethylene (HDPE), polyamide-6 (PA6), polyamide-12 (PA12), polyethylene terephthalate (PET), or combinations thereof.
3. The vessel of claim 1, wherein the dome ends of the liner are geometrically contoured with a smooth continuous radius to reduce stress concentration and optimize filament winding.
4. The vessel of claim 1, wherein the overwrap comprises carbon fibers, glass fibers, or a hybrid thereof, impregnated with a thermosetting epoxy resin.
5. The vessel of claim 1, wherein the composite overwrap is applied through a filament winding process with a combination of hoop and helical wind angles.
6. The vessel of claim 1, wherein a metallic or composite boss is bonded to the neck region of the liner and sealed against gas leakage.
7. The vessel of claim 1, wherein the vessel exhibits a weight reduction of at least 60% compared to a steel cylinder of equal water capacity.
8. The vessel of claim 1, wherein the polymeric liner resists internal chemical degradation and gas permeation over at least 15 years of operational use.
9. The vessel of claim 1, wherein no metallic component is in direct contact with the internal gas environment, thereby eliminating internal corrosion.
10. The vessel of claim 1, wherein the vessel is configured for storage of compressed natural gas (CNG), hydrogen (H₂), or other pressurized gases in automotive, aerospace, marine, or stationary storage systems.