316 SS Instrumentation Compression Fittings

316 Stainless Steel Double Ferrule Compression Tube Fittings

PVFPro's instrumentation division supplies 316L stainless steel double ferrule compression tube fittings engineered for high-pressure, high-purity, and critical-seal applications. Our fittings are precision-machined to industry standards and rated for pressures up to 6,000 PSI with a service temperature range of -65°F to 1200°F. Available in Tube Union, Union Elbow, Union Tee, Male Connector, and Female Connector configurations across 1/4", 3/8", 1/2", and 3/4" tube OD sizes.

What Are Double Ferrule Compression Tube Fittings?

Double ferrule compression tube fittings are mechanical connectors that create a leak-tight seal on metal tubing without welding, brazing, or flaring. The fitting consists of four components: a body, a front ferrule, a back ferrule, and a compression nut. When the nut is tightened, the two ferrules compress onto the tube outer diameter, creating a metal-to-metal seal that is both gas-tight and vibration-resistant.

The front ferrule forms the primary seal between the tube and the fitting body, while the back ferrule grips the tube to resist vibration, shock, and pull-out forces. This two-stage design is what distinguishes double ferrule fittings from single ferrule designs, which rely on a single compression point for both sealing and gripping.

Double ferrule fittings are the industry standard for instrumentation, process control, hydraulic, and pneumatic systems where leak integrity is critical. They are reusable — the fitting can be disconnected and remade multiple times without replacing components, making them ideal for maintenance-intensive environments.

How Double Ferrule Fittings Work

Installation follows a simple two-step process:

Step 1 — Insert and hand-tighten: Insert the tube fully into the fitting until it bottoms out against the body shoulder. Hand-tighten the compression nut.

Step 2 — Wrench-tighten: While holding the fitting body steady with a backup wrench, tighten the nut an additional 1-1/4 turns for 1/4" through 1/2" sizes, or 1 turn for 3/4" and larger. This action drives the ferrules onto the tube, creating the permanent seal and grip.

To disassemble, simply loosen the nut. The ferrules remain swaged onto the tube and will re-seal when reassembled in the same fitting body. Reusability is a key advantage over single-use compression sleeves or welded connections.

Double Ferrule vs Single Ferrule — Key Differences

Feature	Double Ferrule	Single Ferrule
Seal Mechanism	Front ferrule seals, back ferrule grips	Single ferrule does both
Vibration Resistance	Excellent	Limited
Reusability	Multiple reconnections	Limited to single use
Pressure Rating	Up to 6,000 PSI	Up to 3,000 PSI
Typical Application	Instrumentation, process, high-purity	General plumbing, low-pressure

Why 316L Stainless Steel

316L stainless steel is the preferred material for instrumentation and process fittings in demanding environments. The addition of molybdenum (2-3%) provides superior resistance to pitting and crevice corrosion compared to 304 stainless, particularly in chloride-containing environments. The "L" designation indicates low carbon content (max 0.035%), which minimizes carbide precipitation during welding or thermal cycling, preserving corrosion resistance across the fitting's service life.

316L is compatible with a wide range of media including chemicals, steam, gases, hydraulic fluids, and pharmaceutical process fluids. It maintains mechanical strength across the full -65°F to 1200°F temperature range and meets ASTM A276, ASME SA479, and AMS 5648 material standards.

Applications

Chemical Processing: Process lines, sample lines, and analyzer connections requiring corrosion resistance and leak-tight integrity
Oil & Gas: Instrumentation lines, hydraulic control systems, and offshore platform service exposed to harsh environments
Pharmaceutical & Biotech: High-purity process lines, WFI (water for injection) systems, and clean-utility distribution
Water Treatment: Analytical instrumentation, chemical dosing lines, and reverse osmosis systems
Power Generation: Steam sampling, hydraulic control, and turbine instrumentation lines
Food & Beverage: Process lines requiring sanitary-grade connections and CIP compatibility
Laboratories & Research: Gas delivery lines, analytical equipment connections, and high-vacuum systems
OEM Equipment: Hydraulic and pneumatic manifolds, test stands, and skid-mounted process equipment

How to Choose the Right Compression Fitting

1. Match tube OD to fitting size. Double ferrule fittings are sized by the outer diameter of the tubing they accept, not by thread size. A 1/4" fitting is designed for 1/4" OD tubing.

2. Select the correct body style. Tube Unions join two tubes of the same OD. Male and Female Connectors join tube to threaded ports. Union Tees and Elbows create branch and directional changes in a tubing run.

3. Verify pressure and temperature requirements. Our 316L fittings are rated to 6,000 PSI for 1/4" through 1/2" sizes and 5,000 PSI for 3/4". Confirm your system operating pressure includes a safety margin.

4. Confirm material compatibility. 316L SS is suitable for most chemical, hydraulic, and instrumentation applications. For extreme corrosion environments (high chloride, acidic), consider 316L with passivated surfaces or exotic alloys.

Frequently Asked Questions

Are these fittings compatible with Swagelok, Parker, or Hy-Lok tubing?
Yes. Our 316L double ferrule compression fittings are dimensionally compatible with standard instrumentation-grade tubing manufactured to ASTM A269 or A213 specifications. Tube OD is the critical dimension — as long as the tube OD matches the fitting size, the fitting will seal properly regardless of tubing manufacturer.

What is the pressure rating?
Rated to 6,000 PSI working pressure for 1/4", 3/8", and 1/2" sizes. 3/4" fittings are rated to 5,000 PSI. These ratings are for stainless steel tubing at ambient temperature. Pressure ratings decrease at elevated temperatures.

Can the fittings be reused?
Yes. Double ferrule fittings can be disconnected and reassembled multiple times. The ferrules remain swaged onto the tube and will re-seal when reinserted into the same fitting body. For critical applications, ferrule replacement is recommended after 5-6 reassembly cycles.

What tubing material is compatible?
316L stainless steel fittings are designed for use with stainless steel tubing (304, 316, 316L). They can also be used with hard copper, brass, and Monel tubing in lower-pressure applications. Soft tubing (annealed copper, PTFE) is not recommended for double ferrule fittings.

Do I need any special tools for installation?
No. Installation requires only two wrenches — one to hold the fitting body and one to tighten the nut. The standard tightening procedure is hand-tight plus 1-1/4 turns for sizes up to 1/2", and 1 turn for 3/4" and larger.

Why Buy From PVFPro

In-stock and ready to ship from multiple U.S. warehouses
Competitive pricing on 316L instrumentation fittings — save up to 60% vs. name brands
Expert technical support — our team understands instrumentation and process systems
Bulk and contract pricing available for OEMs and volume buyers
Full documentation — material certificates, pressure ratings, and dimensional data available on request