NAS1612-5 - Textron Aviation OEM O-ring

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

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The NAS1612-5 is a high-performance, metallic boss gasket engineered for extreme temperature and pressure applications where conventional elastomeric O-rings would experience instantaneous failure. While often colloquially referred to as an "O-ring" due to its shape, it is critical to understand that this component is a precision-machined metallic seal manufactured in strict accordance with National Aerospace Standard (NAS) 1612. It is fabricated from age-hardened 825 Nickel Alloy, commonly known as Inconel X-750, a superalloy renowned for its exceptional strength and oxidation resistance at extreme temperatures.

As a specified component on numerous Textron Aviation platforms, including Cessna Citation and Beechcraft King Air models, the NAS1612-5 provides a critical static seal for straight thread tube fittings. Its primary function is to prevent leakage in high-energy systems such as pneumatic bleed air, anti-ice ducting, and firewall-forward hydraulic and fuel lines. The integrity of these systems is paramount for flight safety, and the use of the correct, specification-compliant metallic seal is non-negotiable.

Key Features

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

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

• High-Pressure Integrity: Designed as a crush-type seal to create a positive metal-to-metal seal capable of containing extremely high-pressure gases and fluids.

• Silver-Plated Finish: Typically coated with a thin layer of silver per AMS2410, which acts as a solid lubricant at high temperatures to prevent galling and ensure proper sealing upon torquing.

• Single-Use Design: Engineered to be deformed upon installation to perfectly coin and seal the mating surfaces, making it a critical single-use component for maximum reliability.

Technical Specifications

• Part Number / Specification: NAS1612-5

• Component Type: Metallic Boss Seal / Gasket

• OEM Manufacturer: Textron Aviation (as an OEM user/distributor of this NAS standard part)

• 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: 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 business aircraft, with significant application in the Textron Aviation fleet. Examples include, but are not limited to:

• Textron Aviation (Cessna): Most Citation series aircraft (525, 560XL, 680, 750, etc.) in bleed air and anti-ice systems.

• Textron Aviation (Beechcraft): King Air series (200, 300, 350), Premier, and Hawker jets.

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

Applications

The NAS1612-5 is exclusively used in high-temperature and/or high-pressure environments where elastomeric seals are not viable. Primary applications include:

• Bleed Air Systems: Sealing fittings on ducting, pressure regulators, and shutoff valves.

• 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.

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

Why Choose NAS1612-5?

The use of the correct NAS1612-5 metallic seal is a flight-critical requirement. Substituting this component with a standard elastomeric O-ring in a bleed air application would lead to an immediate and catastrophic failure, potentially resulting in an uncontrolled high-temperature air leak, component damage, or an in-flight fire. The NAS1612 specification ensures that the seal possesses the required material composition, heat treatment, and plating to withstand extreme conditions. Adherence to this standard guarantees the joint's integrity, preventing catastrophic system failures and ensuring the safety of the aircraft and its occupants.

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.