Double Ring Compression Tube Fittings Overview

Redfluid provides a wide range of double ferrule compression fittings designed for leak-proof connections in gas, fluid, and vacuum systems. These fittings comprise four precision components: body, front ferrule, back ferrule, and tightening nut. They are engineered to handle high pressures, temperatures, vacuum, and vibrations, while allowing easy installation without twisting the tube.

Design and Construction

The fittings transmit axial load to the tube to avoid localized stress. The front ferrule forms the primary seal against the fitting body and tube exterior, while the back ferrule grips mechanically and resists vibration by pushing axially on the front ferrule. Nut threads are silver-plated to prevent galling and ease assembly/disassembly.

Size Range and Compatibility

• Imperial tubing: 1/16" (1.58 mm) to 1" (25.4 mm)
• Metric tubing: 2 mm to 25 mm
• Mixed adaptors for gas pipes: 1/8" (10.3 mm) to 1" (33.7 mm)

Applications

Suitable for instrumentation, process, and control systems in chemical, chromatography, petroleum, power generation, desalination, pulp and paper industries, and other demanding environments.

Materials

• Standard: 316/316L Stainless Steel (stainless tubing), Brass (copper tubing), Nylon ferrules (plastic tubing)
• Available on request: Carbon steel, Morel, Hastelloy, duplex, superduplex, Incorel

Working Principle

The front ferrule swages onto the tube and fitting body creating a pressure-tight seal; the back ferrule deforms inward to grip the tube mechanically. Tight nut-body tolerances ensure accurate tube alignment, low tightening torque, and prevent tube distortion or twisting during installation.

Working Pressures

Service pressure ratings match those of the connected tubing (assuming standard wall thickness and no external stresses). The fitting’s burst pressure exceeds that of the tube.

Tubing Selection Recommendations

• Use annealed seamless tubes with hardness lower than ferrules for optimal sealing.
• Tubes must have smooth, defect-free surfaces (no burrs or scratches).
• For welded stainless steel tubing, comply with EN ISO 1127 tolerances (D4/T3) and apply a 0.8 derating factor per ASME B31.3.
• Reject oval or deformed tubes that do not pass easily through fitting components.

Quality and Traceability

Redfluid fittings undergo rigorous testing and quality control. Each fitting has a unique traceability code; full material certification tracing to raw material melt is available on request.

Tube Wall Thickness and Dimensions

Specifications cover tube wall thicknesses from 0.8 mm to 4.5 mm (0.012" to 0.188") with corresponding outer diameters and working pressures in bar and Kpsi, guiding correct fitting selection.

Ordering Procedure

Each fitting and valve has a unique reference code indicating tube size and thread type. Orders must specify the reference plus material prefix: Stainless Steel (SS), Carbon Steel (AC), or Brass (L).

Material and Temperature Ratings

316 Stainless Steel fittings operate reliably from cryogenic (-196°C) to high temperatures (+649°C). Working pressure varies with temperature and must be adjusted using provided temperature correction factors (e.g., 1.00 at 100°C down to 0.30 at 1200°C).

• Max/min operating temperatures vary by material, e.g., Stainless Steel 316 (-196°C to 649°C), Carbon Steel (-53°C to 426°C), Copper (-40°C to 205°C), Titanium (-195°C to 315°C), Teflon (-17°C to 65°C).

Fitting Types and Thread Standards

Fittings include male connectors, adapters, elbows, tees, unions, reducers, valves, nuts, caps, plugs, ferrules, and tube inserts. Thread standards supported are NPT, BSPT, and BSPP, with detailed tables correlating tube diameters, thread sizes, and reference codes. Dimensions A and B (in mm) are provided for installation planning.

Technical Summary of Pipe Fittings and Connectors

The document catalogs pipe fittings by type and thread standard, including tees, connectors, elbows, unions, bulkhead connectors, and adapters. Thread sizes range from 1/8" to 1" with metric equivalents. Reference codes and dimensional data ensure precise ordering and compatibility.

Key Recommendations

• Match thread types carefully to avoid leaks or failures.
• Use reference codes for accurate ordering.
• Double ring compression fittings are recommended for high-pressure, leak-proof tube connections.
• Bulkhead connectors enable secure panel mounting.
• Verify dimensional data (A and B) against installation space.

Assembly Instructions for Double Ring Compression Fittings

1. Preparation: Cut tube squarely (avoid tube cutter tools that cause burrs), deburr inside and outside, clean, and lubricate fitting threads and nut with Wolfracoat C silicone-free grease.
2. Pre-Assembly: Slide nut and ferrules onto tube; insert tube into fitting body; hand-tighten nut; then tighten with wrench:
   • 1.5 turns for tubes ≤18 mm OD
   • 1.25 turns for tubes ≥20 mm OD
   Mark tube to monitor turns.
3. Final Assembly: Tighten nut until resistance increases, then an additional 1/6 turn for secure sealing.
4. Disassembly: Unscrew nut fully and remove fitting body; ferrules remain on tube.
5. Reassembly: Insert tube fully, hand-tighten nut, then wrench-tighten to original position plus 1/4 turn.

Additional Notes

• Use Wolfracoat C grease without silicone.
• Marking tube before tightening ensures correct torque.
• Tightening turns vary by tube diameter to prevent damage and ensure sealing.

Contact Information

REDFLUID - Pol. Indal. “Els Bellots” - C/ del Foc, 5 Nave 5 - 08227 TERRASSA - Barcelona, Spain
Tel: +34 93 785 75 66 | Fax: +34 93 785 31 97
Email: [email protected]
Website: www.redfluid.es

Summary of Critical Information

• Tube wall thickness and outer diameter specifications are essential for correct fitting selection.
• Material choice significantly impacts temperature and pressure ratings.
• Apply temperature correction factors to working pressures for accurate design.
• Thread type and fitting reference codes are critical for ordering and compatibility.
• Wide variety of fitting types support diverse piping configurations.
• Follow assembly instructions carefully to ensure leak-free, durable connections.

Additional Product Information

The document also covers dielectric fittings for electrical isolation (rated 200 bar at 20°C, -40°C to 100°C temperature range, electrical resistance 1x10^8 Ω), minor series needle valves for panel mounting with fine flow control, and accessories such as tube inserts, nuts, ferrules, and plugs. Thread standards include NPT, BSPT, and BSPP, with materials ranging from carbon steel to stainless steel and brass.

Extensive dimensional tables and reference codes facilitate precise product selection, ensuring system integrity and performance in instrumentation and piping applications.