Description:The present invention relates to high-pressure storage systems, specifically to Type IV Composite Overwrapped Pressure Vessels (COPVs) used for storing gases such as compressed natural gas (CNG) or hydrogen. More particularly, it pertains to the sealing system formed between the polymeric liner and metallic end boss, ensuring leak-proof assembly and long-term pressure integrity.

BACKGROUND OF THE INVENTION
Type IV COPVs are widely adopted due to their lightweight, corrosion resistance, and structural efficiency. These cylinders comprise a polymeric liner surrounded by a fiber composite shell and are fitted with metallic end bosses for mechanical integrity and connection to valves or manifolds.
A common challenge in such vessels is ensuring a secure and durable seal between the polymeric liner and the metallic end boss, particularly in the neck region where high internal pressures act. Failures or leakages in this area can result in operational hazards, system inefficiencies, or complete failure.
Existing solutions rely on threaded engagement and O-ring seals. However, maintaining leak-proof performance under cyclic pressurization, thermal fluctuations, and long-term use is difficult due to material mismatch and deformation over time.

PRIOR ART SEARCH
Patent References:
1. US20170167580A1 – Describes sealing techniques using O-rings and threaded joints in Type IV cylinders but lacks optimized groove profiles for improved durability.
2. US9829463B2 – Describes liner-to-boss joint designs, but the sealing performance degrades under thermal cycling.
3. US20200295733A1 – Shows end boss threading techniques, but doesn’t focus on the geometry of groove-O-ring-liner interface.
Non-Patent Literature:
• ISO 11439 and EN 12245: COPV safety and construction guidelines.
• SAE J2579: Performance requirements for hydrogen-fueled vehicle systems.
These documents establish the foundation but do not disclose the detailed square-grooved O-ring integration within the boss along with precise torquing of the polymeric liner threads as disclosed herein.

SUMMARY OF THE INVENTION
The invention provides a sealing assembly between the polymeric liner and the metallic end boss for Type IV cylinders, where:
• Threaded connection in the neck region ensures mechanical grip.
• Square-shaped grooves inside the metallic boss are provided for O-ring seating.
• Proper torque applied ensures interference fit, leading to leak-proof sealing.
• The neck of the polymeric liner is outside the main gas storage region, reducing risk of gas exposure to composite boundaries.
The design leverages geometry, material elasticity, and press-fit interaction to deliver long-term gas-tight sealing.

BRIEF DESCRIPTION OF DRAWINGS
Refer to the attached Figure titled “Detail B” for dimensional and geometric clarity.
Figure Description:
• The metallic end boss (Part 6) has internal threads (1.125-12 UNF-2B) and O-ring groove (Diameter 31 mm).
• The polymeric liner neck (Part 4) features external threads and an OD of 50 mm, seated within the boss cavity.
• The O-ring (not numbered) is located in a square groove to ensure positive sealing when the liner is torqued into the boss.

DETAILED DESCRIPTION OF THE INVENTION
Referring to the attached Figure: Detail B, the invention includes the following critical features:
1. Threaded Engagement:
The polymeric liner (4) is externally threaded at the neck with dimensions matching 1.125-12 UNF-2B standards. These threads engage with the internal threads of the metallic boss (6) to form a primary mechanical connection. The threading profile is carefully chosen to allow controlled torque application and to prevent damage to the polymeric material.
2. O-Ring Groove Geometry:
Within the inner diameter of the metallic boss (at approx. 31 mm diameter), a square-section groove is precisely machined to house a standard elastomeric O-ring. This square geometry improves O-ring stability and prevents it from rolling or extruding under pressure.
3. Neck Placement Outside Main Storage:
The design ensures that the threaded and sealing region is outside the gas containment volume (between diameters 50 mm and 65 mm), which reduces exposure to high-pressure gas and improves the longevity of the interface.
4. Torque-Controlled Assembly:
During installation, a specific torque value is applied to the liner to compress the O-ring and ensure thread engagement without inducing stress failure in the plastic. The compression of the O-ring causes it to expand laterally, forming a high-pressure seal against the liner OD and the boss groove walls.
5. Pressure Isolation:
Upon pressurization, the gas forces are resisted by both the threaded interface and the O-ring seal, providing redundant leak prevention mechanisms.
6. Material Compatibility:
The liner is typically composed of HDPE or PA (nylon), and the boss is made from stainless steel or aluminum alloys. The groove and thread profiles are designed keeping in mind the thermal expansion mismatch and elastic properties of the materials.
The present invention relates to a high-pressure storage vessel of the Type IV COPV category, designed to overcome the limitations of conventional metallic cylinders. Traditional steel or aluminum gas cylinders are inherently heavy and susceptible to corrosion when exposed to high-pressure gases over long periods. These shortcomings have led to the development of Type IV composite pressure vessels, which are entirely non-metallic in the fluid-contacting region and offer a high strength-to-weight ratio.

At the core of the invention is a polymeric liner that serves as the gas barrier and structural form for the composite overwrap. This liner is typically manufactured using blow molding or rotational molding processes and is composed of materials such as high-density polyethylene (HDPE), polyamide 6 (PA6), polyamide 12 (PA12), or polyethylene terephthalate (PET). These materials are chosen for their low density, high chemical resistance, low gas permeability, and mechanical stability. The liner features a cylindrical middle section flanked by two dome-shaped ends, designed to evenly distribute internal pressure and eliminate geometric stress concentrations. The transition between the cylindrical body and the domes is smooth and continuous, facilitating uniform winding during the composite overwrap process.
Surrounding the liner is a composite overwrap made from high-strength reinforcing fibers such as carbon fiber, glass fiber, or a combination of both. These fibers are embedded in a thermosetting epoxy resin matrix and applied to the liner using a computer-controlled filament winding technique. The fibers are laid in multiple orientations, with hoop windings (near 90° to the axis) for radial strength and helical windings (15°–25°) for axial reinforcement. Once winding is complete, the vessel undergoes a curing process, during which the resin matrix solidifies and bonds the fibers into a high-integrity composite shell.

To allow for gas filling and extraction, metallic or composite bosses are inserted into the neck regions of the polymeric liner at both ends. These bosses are typically threaded internally and include sealing features such as grooves for O-rings to prevent gas leakage. Importantly, the design ensures that no metal part is in direct contact with the internal gas, thereby eliminating the possibility of corrosion or hydrogen embrittlement—a common failure mode in metallic pressure vessels storing hydrogen.
The resulting structure provides numerous performance advantages. The total weight of the cylinder is reduced by over 60% compared to equivalent steel cylinders, leading to improved fuel efficiency in automotive applications and easier handling in portable or mobile systems. The fully polymeric liner ensures complete immunity from corrosion, even in harsh environments or during long-term gas exposure. Moreover, the high strength of the composite overwrap allows the vessel to withstand internal pressures typically exceeding 250 bar, with burst pressures over 600 bar. The design is robust under both static and cyclic loading conditions, offering a service life of more than 15 years.
In addition to its use in natural gas vehicles (NGVs), the invention is applicable in hydrogen fuel cell vehicles, aerospace and aviation applications, marine transport, and stationary energy storage. The technology is also compatible with emerging clean energy infrastructure, including hydrogen refueling stations and renewable energy buffer storage.
In conclusion, this invention presents a structurally efficient, corrosion-free, and lightweight alternative to traditional metal gas cylinders. The combination of a polymeric liner and advanced composite overwrap offers exceptional performance for demanding pressure applications, making the vessel particularly suitable for the future of clean energy storage and transport.

ADVANTAGES OF THE INVENTION
• Enhanced leak resistance through combined mechanical and elastomeric sealing.
• Avoids stress concentration on the polymeric liner during torqueing.
• Maintains sealing performance over wide temperature and pressure ranges.
• Facilitates modular assembly with minimal machining or bonding.
• Improves service life of COPVs by isolating gas from composite boundaries.
, Claims:1. A sealing assembly in a Type IV composite pressure vessel comprising:
a polymeric liner with an externally threaded neck;
a metallic end boss with internally threaded bore and a square-section groove;
an O-ring seated in the groove;
wherein torquing the polymeric liner into the metallic boss forms a leak-proof seal.
2. The sealing assembly of claim 1, wherein the square groove has a diameter of 31 mm and a depth that accommodates a standard elastomeric O-ring.
3. The sealing assembly of claim 1, wherein the threaded neck of the liner conforms to 1.125-12 UNF-2B specifications.
4. The sealing assembly of claim 1, wherein the sealing interface is positioned outside the main storage cavity of the liner.
5. The sealing assembly of claim 1, wherein the O-ring is compressed radially and axially to form a high-pressure barrier.
6. The sealing assembly of claim 1, wherein the polymeric liner is composed of nylon, polyethylene, or similar thermoplastic polymers.
7. The sealing assembly of claim 1, wherein the metallic boss is made of aluminum or stainless steel.
8. The sealing assembly of claim 1, wherein the sealing assembly prevents gas exposure to the composite overwrap.
9. The sealing assembly of claim 1, wherein the groove shape is square to prevent O-ring displacement during pressure cycling.
10. A Type IV COPV comprising a composite-wrapped polymeric liner, a metallic end boss, and a sealing assembly as claimed in any of the preceding claims.