NAS1612-5 - O-ring

NAS1612-5 – Nickel Alloy (Inconel X-750) Metallic Boss Seal

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The NAS1612-5 is a high-performance, metallic boss gasket engineered in strict accordance with National Aerospace Standard (NAS) 1612 for extreme temperature and pressure applications where conventional elastomeric O-rings would fail catastrophically. While its annular shape may lead to the colloquial term "O-ring," it is critical to identify this component as a precision-machined metallic seal. It is fabricated from age-hardened 825 Nickel Alloy, a superalloy commonly known as Inconel X-750, which is selected for its unparalleled strength and oxidation resistance at elevated temperatures.

This component provides a critical static seal for straight thread tube fittings, preventing leakage in high-energy systems. Its primary role is in pneumatic bleed air, anti-ice ducting, and firewall-forward hydraulic and fuel lines, where both temperatures and pressures far exceed the operational limits of any elastomer. The integrity of these systems is paramount for flight safety, making the use of the correct, specification-compliant NAS1612-5 seal a non-negotiable requirement for airworthiness.

Key Features

• Manufactured to National Aerospace Standard (NAS1612): Guarantees strict adherence to material composition, dimensional tolerances, and quality control for aerospace applications.

• Inconel X-750 Superalloy Construction: Provides superior strength, and resistance to corrosion, oxidation, and material creep at continuous service temperatures up to 1300°F (700°C).

• High-Pressure Crush Seal Design: Engineered to be plastically deformed upon installation, creating a positive, coined metal-to-metal seal capable of containing extremely high-pressure gases and fluids.

• Silver-Plated Finish: Coated with a thin layer of silver per aerospace specifications (e.g., AMS2410), which acts as a solid lubricant at high temperatures to prevent galling between mating threads and ensure proper sealing upon torquing.

• Single-Use Component: Designed to be replaced every time the fitting is disassembled to guarantee the integrity of the seal.

Technical Specifications

• Part Number / Specification: NAS1612-5

• Component Type: Metallic Boss Seal / Gasket

• Material: Nickel Alloy, Inconel X-750 (per AMS 5667 or similar).

• Finish: Silver Plated (per AMS 2410 or similar).

• Size Designator: -5, for use with 5/16 inch (0.3125 in) outside diameter tube fittings.

• Application: Provides a static seal for AS5202 / MS33649 straight thread bosses.

• Governing Specifications: NAS1612 (Seal Standard), AMS 5667/5671 (Material), AMS 2410 (Plating).

Aircraft Compatibility

The NAS1612-5 is a standard hardware component utilized on a vast range of military, commercial, and general aviation aircraft, particularly any turbine-powered platform with high-temperature bleed air systems. It is commonly found on, but not limited to, aircraft manufactured by Textron Aviation (Cessna/Beechcraft), Gulfstream, Bombardier, and Boeing.

Crucial Note: Verification against the specific aircraft's current Illustrated Parts Catalog (IPC) and maintenance manual is mandatory to ensure correct part number applicability for the specific location.

Applications

The NAS1612-5 is exclusively specified for high-temperature and/or high-pressure fluid and pneumatic connections where elastomeric seals are not viable. Primary applications include:

• Bleed Air Systems: Sealing fittings on ducting, pressure regulators, shutoff valves, and air cycle machines (ACMs).

• Anti-Ice Systems: Sealing connections for wing and engine cowl anti-ice piccolo tubes and valves.

• Firewall Forward: Sealing high-pressure hydraulic, fuel, and oil lines located in the high-temperature environment of the engine nacelle or pylon.

• APU Systems: Connections for bleed air ducting and high-temperature sensing lines.

Why Choose NAS1612-5?

The use of a genuine NAS1612-5 metallic seal is a flight-critical requirement. Mistaking this component for a standard elastomeric O-ring and making an improper substitution would result in an immediate, catastrophic failure in a hot bleed air system, potentially leading to an uncontrolled leak of high-temperature, high-pressure air, component damage, or an in-flight fire. The NAS1612 specification is the only guarantee that the seal possesses the required material composition, heat treatment, and plating to withstand these extreme conditions. Adherence to this standard ensures the joint's integrity, preventing system failures and preserving the safety of the aircraft.

The exceptional high-temperature performance of the NAS1612-5 seal is a direct result of the material science of its Inconel X-750 superalloy. This is a precipitation-strengthened, austenitic nickel-chromium alloy. Its remarkable strength at elevated temperatures is derived from the controlled formation of coherent, sub-microscopic gamma prime (γ′) precipitates—specifically Ni3​(Al,Ti)—within the metallic grain structure during a precise age-hardening heat treatment process. These gamma prime precipitates act as powerful obstacles to dislocation motion, the primary mechanism of plastic deformation in metals. This severely restricts material creep and maintains high tensile strength at temperatures where conventional steels would fail. The specified silver plating (AMS2410) functions as a solid-state lubricant, preventing the high-friction nickel alloy from galling or seizing against steel or titanium fittings during the high-torque assembly required to coin the seal and achieve a leak-proof metal-to-metal interface.

Note: The NAS1612-5 is a single-use, crush-type seal and must be replaced any time the associated fitting is loosened or disassembled. Re-using a previously torqued seal will result in a guaranteed system leak. Proper installation requires adherence to the specific torque values in the aircraft maintenance manual to ensure the seal is correctly deformed ("coined") to create a perfect seal. Installation must be performed by a certified A&P mechanic.

Documentation

The definitive technical requirements for this component are detailed in National Aerospace Standard NAS1612, which is maintained by the Aerospace Industries Association (AIA). This proprietary document must be sourced directly for complete engineering specifications.