Stainless Steel & Alloy Instrumentation Tube Fittings

A stainless steel tube fitting is a mechanical-grip (compression) fitting that joins and seals instrument tubing by advancing a nut that drives one or two ferrules onto the tube outside diameter, forming a leak-tight metal seal and a strong tube grip without brazing, flaring, or threading the tube itself. Crestflo manufactures instrumentation tube fittings in 316/316L, high-nickel alloy, and titanium, with end connections up to 2" (50 mm) OD, single or double ferrule, imperial and metric, engineered as ASTM F1387-qualified drop-in replacements and delivered on a 6-8 week lead time.

These are instrumentation fittings for process, analytical, and hydraulic instrument lines, instrumentation-grade stainless and alloy compression tube fittings, not copper or plumbing compression fittings, and not pipe fittings. Ready stock for standard items, made-to-order for specials, 6-8 week delivery. Request a quote or request a sample.

Across catalogs and datasheets these components are specified under many names. The same part is called a tube fitting, a compression fitting, a compression tube fitting, a double-ferrule, two-ferrule, or twin-ferrule fitting, a single-ferrule or ferrule fitting, an instrument tube fitting, a tube coupling or tube union coupling, a tube connector, or simply a stainless tube fitting, an SS tube fitting, or a stainless-steel tube fitting; distributors and specifiers list the same SS tube fittings and stainless tube fittings interchangeably. Buyers searching for a "tube to pipe fitting" are looking for a tube-end by pipe-thread adapter, which is a threaded connector within the same family. Standards designations that travel with the product include ASTM F1387 (mechanically-attached fitting performance), ASTM A269/A213 (the instrument tubing they connect), ISO 8434-1 (24° cone), and DIN 2353 (bite-type). Crestflo supplies the full range under all of these designations.

What Is an Instrumentation Tube Fitting? Working Principle & Tube vs Pipe

An instrumentation tube fitting seals by mechanical grip. As the nut is tightened, it drives the ferrule (or a back-and-front ferrule pair) radially inward onto the tube OD; the ferrule bites into and springs back against the tube to grip it, while its leading edge coins a circumferential metal-to-metal seal against the fitting body. No heat, flame, flux, flare, or tube threading is involved, so the tube wall and its corrosion resistance stay intact. This is what distinguishes a compression, double-ferrule, twin-ferrule, or mechanical-grip fitting from welded, brazed, or flared connections.

Tube and pipe are specified differently, which matters when selecting fittings. Tube is called out by its actual outside diameter and wall thickness (for example per ASTM A269 or A213) and is used for instrument sensing, sampling, and hydraulic lines; pipe is called out by nominal size and schedule. These are fittings for tube. Where a run must transition to pipe, a threaded connector (NPT or BSPP) makes the tube-to-pipe adapter.

Compression Tube Fittings: Where They Are Used

Compression tube fittings (also written tube compression fittings) are the default make-and-break connection for instrument tubing because they are reliable, re-makeable, and require only a wrench and a gap-gauge check to install. They dominate analyzer and sampling systems, transmitter and gauge hook-ups, instrument-air and pneumatic lines, hydraulic control circuits, and process tie-ins where a welded joint is impractical. Crestflo offers both single-ferrule and double-ferrule compression designs, in hardened or non-hardened ferrules to suit the tubing hardness and service.

Double-Ferrule (Twin-Ferrule) Design & Vibration Resistance

The double-ferrule, or twin-ferrule, design separates the two jobs the connection must do. The back ferrule hinges and collets onto the tube to provide the grip and act as a spring-loaded vibration damper, while the front ferrule advances to form the primary seal against the body and the tube. Splitting grip from seal improves performance under vibration, pressure cycling, and thermal cycling, which is why twin-ferrule fittings are specified on rotating equipment, compressors, and thermally active lines. Crestflo double-ferrule fittings are qualified per ASTM F1387 and are offered with hardened or non-hardened ferrules. For single-ferrule, ferrule-less, and DIN 2353 bite-type variants, and for standalone ferrule sets, see the single-ferrule, ferrule-less, DIN 2353, and ferrules pages.

Tube Fitting Types & Shapes: Union, Tee, Elbow, Connector, Reducer

Crestflo builds every shape in the instrumentation tube-fitting family. Select the configuration your run needs and open its page for specifics.

End Connections & Threads: NPT, BSPP, JIC 37°, Socket-Weld & Tube-to-Pipe

Threaded and welded ends carry standard published thread forms; values are per the applicable standard and customizable to requirement. A tube-to-pipe fitting is simply a tube-OD end paired with a pipe thread.

Tube Fitting Sizes: Imperial (1/8"-1") & Metric (6-12 mm) to 2" OD

Every fitting is available in both imperial and metric tube sizes, with end connections up to 2" (50 mm) OD. Working-pressure capability is OD-, wall-, and alloy-dependent; use the published tube working-pressure tables for the selected tube per the applicable standard, customizable to requirement, see the size chart.

Tube Fitting Materials: 316 Stainless Steel Tube Fittings, Duplex, 6Mo & Nickel Alloys

Crestflo leads with 316/316L stainless steel and extends through duplex, super-austenitic, high-nickel, and titanium corrosion-resistant alloys (CRA), the exotic-alloy depth most catalog suppliers omit. Grades are offered NACE MR0175 / ISO 15156 compliant where the alloy qualifies. These pages educate the grade and link the instrumentation forms in which Crestflo supplies it.

Compositions and mechanicals are per the applicable ASTM/UNS standard, customizable to requirement. The US material scope is stainless and alloy, no brass. Material finish, electropolish, passivation, silver anti-galling plating, and oxygen cleaning per ASTM G93 are available.

Drop-In Interchange with Swagelok, Parker & Other Brands

Crestflo tube fittings are engineered as dimensional interchange, drop-in equivalents for the major instrumentation brands, Swagelok®, Parker®, Hoke®, Hy-Lok®, Fitok®, and others, with interchange backed by ASTM F1387 performance qualification, which few alternatives can show. We use interchange and equivalent language only; Crestflo parts are not represented as compatible with or genuine to any brand, and all trademarks belong to their respective owners. Crestflo is an independent manufacturer and is not affiliated with these companies. Rather than publishing a part-number table, our engineers will build the exact interchange for your bill of material. Request your Swagelok® or Parker® cross-reference from the engineering team, or see the Swagelok cross-reference and Parker A-Lok cross-reference pages.

Certifications, Testing & Traceability: ASTM F1387, NACE & EN 10204 MTC

Crestflo is ISO 9001 / 14001 / 45001 and PED certified, and holds the standard approvals applicable to compression tube fittings. Fittings are qualified to ASTM F1387 and offered NACE MR0175 / ISO 15156 compliant in the appropriate alloys.

In-house NDT is standard; destructive testing is performed at ISO/IEC 17025-accredited laboratories, and third-party inspection is available on request. Certificate copies are held in the quality section; material traceability accompanies every part. Datasheets and CAD are available to customers on request.

Why Crestflo for Tube Fittings: Manufacturer, Fast Lead Time, US-Served

Crestflo is the instrumentation division of a four-decade-old, Government-of-India-recognized export house with an established Middle-East delivery track record, now serving the US market. As a US-served tube fittings manufacturer with in-house CNC, VMC, EDM, and milling, not a trader, Crestflo controls quality from bar stock to finished fitting. The buyer advantages: a 6-8 week lead time versus the 20-plus weeks typical of the majors; ASTM F1387 drop-in interchange; imperial and metric on every fitting; small MOQ and private-label and OEM / made-to-print programs; and heat-number marking with EN 10204 MTC on every part. Indian origin; US / European melt available on request, with full material traceability. We Engineer Confidence.

Applications & Industries: Oil & Gas, Semiconductor, Hydrogen, Hydraulics

Crestflo instrumentation tube fittings serve process and analytical lines across oil and gas, refining and petrochemical, offshore and subsea, hydrogen, LNG and cryogenic, semiconductor, power generation, analytical and sampling systems, instrument air, hydraulics, and steam tracing. Hydraulic tube fittings and gas tube fittings for these lines are covered by the DIN 2353 bite-type and JIC 37° ranges above.

How to Order Tube Fittings: Request a Quote

There is no cart and no list pricing; Crestflo runs an RFQ model. Send the shape, end connection, tube size, material grade, quantity, and any specification, and the engineering team returns a quote. Ready stock for standard items, made-to-order for specials, 6-8 week delivery. Request a quote, request a sample, or contact us about OEM, private-label, and distributor programs. US contact: sales@crestflousa.com · +1 346 594 9005 · Houston, TX.

Tube Fittings FAQ

Related Pages

Explore the tree: tube union, male connector, NPT tube fittings, and metric tube fittings; the size chart; 316/316L and other materials; matching instrumentation tubing and instrumentation valves; the cross-reference library; and standards ASTM F1387, NACE MR0175, and EN 10204 MTC.

Reviewed by the Crestflo Engineering Team