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Technical Library > PIPE FITTINGS > FORGED FITTINGS & TUBE FITTINGS > Tube Fittings Overview
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TUBE FITTINGS


In this article, we define tube fittings (compression type) and show the available configurations (single and double ferrule), shapes (elbows, straight, unions, etc), material grades, pressure ratings.  The two major manufacturers of compression and precision fittings for tubes and tubing are Swagelok and Parker.


FERRULE FITTINGS

Compression fittings, otherwise called “ferrule fittings”, are used to connect tubing for instrumentation systems.

A ferrule fitting consists of an outer nut, two deformable ferrules (back/front) in soft alloy or non-ferrous metals and, a body. When the nut is screwed on the fitting, the ferrule is deformed, compressed and clamped around the tube creating a very tight seal able to withstand high pressures. The front ferrule creates a seal against the fitting body and on the tubing outside diameter. As the nut is turned, the back ferrule axially advances the front ferrule and radially applies an effective grip on the tube.

 

ferrule fitting

A joint made with a ferrule fitting can be disassembled for maintenance or retrofit work on the instrumentation system (spare ferrules and nuts are available and can replace the dismantled ones). Ferrule fittings do not, therefore, require any welding activity and are rather quick to install.

During installation, a correct force shall be applied when screwing the nut, otherwise, the fitting may get damaged and the connection might leak. It is recommended to tighten the nut manually at first and then use an appropriate wrench.

These tube fittings are available in single or double ferrule type, in metric-to-fractional and fractional-to-fractional sizes and multiple material grades (the most used is stainless steel 304/304L and 316/316L)

Video explains how to assemble ferrule fittings below 1 inch (source: Swagelok)

TYPES OF FERRULE FITTINGS

Ferrule fittings can be grouped into the following key types:

  • Connectors (male connector, female connector, bulkhead male connector, bulkhead female connector, butt weld pipe connector, socket weld tube connectors)
  • Male and female elbows
  • End closures (tube, fitting)
  • Reducers
  • Tees (male run tee, female-run tee, male branch tees, female branch tees)
  • Unions

types of compression fittingstypes of compression fittings2

TUBE FITTINGS PRESSURE RATINGS

Compression fittings are available in standard (up to 11 KPSIG), medium (11 to 20kpsig) and high-pressure (up to 60kpsig) ratings:

STANDARD TUBE FITTINGS

Pressure Ratings Up to 11.000 PSIG (760 bar)
Materials Stainless steel
End Connections NPT, ISO/BP, SAE/MS, AN, weld ends, port connectors, sanitary flanges, tube adapters
 Dimensional Range 1/16 to 2 inches (imperial); 2 to 50 mm (metric)
Configurations Straights, elbows, tees, crosses, caps, plugs, nuts and ferrules Chromatograph and Column End

MEDIUM PRESSURE TUBE FITTINGS

Pressure Ratings Up to 20.000 PSIG (1378 bar)
Temperature Ratings Up to 1000°F (537°C)
Materials 316 Stainless Steel or Alloy 625
End Connections Unions, NPT, medium-pressure cone and thread adapters, male SAE/MS, reducers, port connectors, tube adapters, caps, plugs
Dimensional Range 1/4, 3/8, 1/2, 9/16, 3/4 in.; 6, 10, 12 mm
Configurations Straights, elbow, tees, cross
Other medium-pressure products available Medium-pressure ball valves, medium-pressure tubing

CONE AND THREAD TUBE FITTINGS (MEDIUM PRESSURE)

Cone and thread connection types are suited for medium and high-pressure performance and can be equipped with antivibration components. They can meet NACE MR0175/ISO 15156.

Pressure Ratings Up to 20.000 PSIG (1378 bar)
Temperature Ratings Up to 1000°F (537°C)
Materials 316 Stainless Steel
Alloy 2507
Alloy 625
End Connections
 
1/4 to 1-1/2 in.
Configurations Straights, elbow, tees

CONE AND THREAD TUBE FITTINGS (HIGH PRESSURE)

Pressure Ratings Up to 60.000 PSIG (4134 bar)
Temperature Ratings Up to 1000°F (537°C)
Materials 316 Stainless Steel
Alloy 2507
Alloy 625
End Connections 1/4 to 9/16 in.
Configurations Straights, elbow, tees

For more information about tube fittings, we suggest the Swagelok Essential Guide.

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