Single / twin ferrule fittings are widely used for instrumentation systems within the petrochemical industry.

Ferrule fittings are used to join tubing without welding activities. They consists of an outer nut, two ferrules (back / front) generally in brass or copper material or alloys and, of course, a fittings body. When the nut is tightened, the ferrules get compressed and clamped around the tube (the middle of the ferrule inclines away from the pipe, thus making the ferrule thicker). Once serrated, the ferrule seal the space between the tubing, the nut and fitting creating a very tight joint among these elements even in case of high pressure. 

Ferrule fittings: front and back ferrule

Ferrule fittings are installed where occasional disassembly or partial removal for maintenance are necessary (as they can be opened and closed several times).

Compression fittings are available in the single or double configuration, and supplied in the metric-to-fractional and fractional-to-fractional sizes. It is critical to apply a correct force on the nut and avoid that it gets over tightned. If this happens, the excessive defomration of the ferrule would impact the integrity of the seal and the connection might leak. A good approach is to tighten the nut at first manually and then tighten it an additional one half-turn with an appropriate wrench for ferrule fittings.


Twin ferrule fittings can be grouped into the following key categories:

  • 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 ferrule fittings instrumentation



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Useful links: ANSI | ASME | ASTM | API | MSS | BS | DIN | ISO