Double Ferrule Instrumentation Tube Fittings are precision-engineered components used to create reliable, leak-proof connections in tubing systems, particularly in high-pressure and high-temperature environments such as instrumentation, process control, and chemical processing systems.

These fittings consist of four primary components:

Fitting Body – The main housing that connects to the system tubing.

Nut – Used to tighten and secure the ferrules in place.

Front Ferrule – Provides the primary seal by gripping the tubing and swaging against the fitting body.

Back Ferrule – Provides a strong mechanical hold by gripping the tubing as the nut is tightened, preventing tube blowout.

• Leak-Proof Performance: Dual-ferrule design ensures a secure, gas-tight seal under high pressure and temperature without sealants.
• Torque-Free Assembly: Prevents stress on tubing, preserving connection integrity.
• Vibration Resistance: Back ferrule provides strong grip, ideal for dynamic and high-vibration environments.
• Easy Installation & Reusability: Simple to install, with consistent sealing even after multiple assemblies.
• Durable Materials: Made from stainless steel, brass, and other corrosion-resistant alloys for long service life.
• Versatile Configurations: Offered in various sizes, end connections (NPT, BSP, welded), and styles (elbows, tees, crosses) to fit diverse system needs.

Double ferrule tube fittings deliver reliable, maintenance-friendly, and leak-free connections for demanding instrumentation and control applications.

Twin/double ferrule fittings are widely used across various industries, including:

• Shipbuilding
• Chemical Processing
• Oil and Gas Applications
• Power Generation
• Pharmaceutical
• Semiconductors
• Vacuum Applications

Allowable working pressures are calculated using an S value of 20,000 psi (1378 bar) for ASTM A269 tubing at temperatures from −20 to 100°F (−28 to 37°C), in accordance with the ASME B31.3 Process Piping Code and ASME B31.1 Power Piping Code.

Table 1: Fractional Seamless Stainless Steel Tubing
Working pressure are shown in PSI.

Table 2: Metric Seamless Stainless Steel Tubing

Working pressure are shown in PSI.

Twin ferrule compression tube fittings temperature ratings vary in accordance to the body material as per below:

Body Material Temperature Rating
The nominal pressure (PN) may be reduced due to elevated fluid or ambient temperatures. Refer to the table below for specific derating factors.

Seal Material Temperature Consideration
When selecting seal materials, the seal’s temperature rating may become the limiting factor for the overall temperature rating of the fitting. Please refer to the temperature ratings provided below.

1. Cut the Tube
   Use a proper tube cutter to cut the tubing square. Do not use a saw or abrasive wheel. Ensure the cut is clean and straight.
2. Deburr and Clean
   Remove all burrs from both the inside and outside of the tube using a deburring tool. Wipe the tube end clean to remove any dirt, oil, or particles.
3. Insert the Tube
   Fully insert the tube into the fitting body until it bottoms out against the shoulder. The tube must rest firmly against the internal shoulder of the fitting.
4. Finger-Tighten the Nut
   Tighten the nut by hand until you feel resistance, ensuring the tube remains fully inserted.
5. Wrench-Tighten the Nut
   While holding the fitting body steady with a backup wrench, tighten the nut with a wrench:
   For initial installation, tighten the nut 1¼ turns from the finger-tight position (use 1½ turns for stainless steel tubing).
6. Inspect the Assembly
   Loosen the nut to verify proper ferrule engagement. The front ferrule should leave a clear ring mark on the tube, indicating proper bite. Reassemble by tightening the nut until snug; do not retighten 1¼ turns again.