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Hydraulic ferrule and Weld type Fittings

Design Principle

Hi-Line Flareless Bite type pipe fittings embody a unique three-piece design comprising a body, special case hardened ferrule and nut. Unlike ordinary compression joints, when the nut is screwed on to the body, the ferrule grips the pipe in position and the perceptibly “bite” into the pipe. When fully tightened, the case-hardened ferrule is bowed slightly in the middle and acts as a spring. This spring action of the ferrule maintains a continuous tension between the body and nut, and prevents the nut from loosening under vibration and strain.

The unique function of the ferrule is the result of careful selection of the right materials, precision machining and case-hardening to give it a hard exterior and a soft core. The ferrule thus not only “bite” into the pipe readily and superficially without causing surface cracks, but also maintains its spring action for repeated use with out loss of strength or seal qualities.

The fitting can then be dismantled and reassembled as often as necessary for the maintenance purpose, without weakening the joint or reducing the effectiveness of the seal in any way.
The benefit: an unmatched degree of safety and reliability in oil hydraulics, pneumatics, instrumentation systems, high-pressure fluid systems and various other applications


Hi-Line Flareless Bite Type fittings are available for the following types of pipes:

  • Metric size Outside Diameter pipes to DIN 2391/C or equivalent standards
  • Inch size Outside Diameter pipes to B.S. 3601/3602/3605 or equivalent standards
  • Inch size Nominal Bore pipes to B.S. 1387-1975 or equivalent standards.
For Oil Hydraulic service

Our Hydraulic Carbon steel fittings are available with ‘Parkerizing’ finish. The ‘Parkerizing’ process creates a fine, corrosion – resistant skin with sealant oil entrapped within. This combination not only prolongs the life of the finish against rusting and atmospheric corrosion; more, the presence of the entrapped oil lubricates the individual parts when the fitting is assembled on the pipe

For service in corrosive atmospheres

Where carbon steel is not attacked by the atmosphere or by the fluid to be handled, the use of our standard carbon steel fittings with ‘Parkerized’ finish is recommended. Where, however, the presence of the entrapped oil is likely to damage the fluid to be handled, galvanized or cadmium-plated finish can be provided. Cadmium plating, besides being superior finish, has the added advantage of “lubricating” the individual parts during assembly because of its softness. Galvanizing on the other hand has the advantage of lower cost.

Where carbon steel is attacked by the fluids to be handled or by the atmosphere, brass or stainless steel fittings are preferred. Brass fittings are generally restricted to pneumatic and low-pressure applications and are available in natural, nickel-plated or cadmium plated finish. Brass fittings are not suitable for use in atmosphere, which contains ammonia. Special Brass and Stainless Steel fittings with carbon steel ferrules can offered for high-pressure applications (e.g. in argon gas plants).

Materials of fittings and surface protection

End usage largely determines the choice of materials from which Hi-Line fittings and components are made. The fittings offered are made of the following construction.

Carbon Steel fittings
Brass fittings
Stainless steel fittings

Carbon and carbon manganese free cutting steels are used for making our carbon steel fittings. Carbon steel fittings are supplied with ‘Parkerized” (Manganese-based Phosphatizing) as standard. The ferrule is plated.

Brass fittings are made from free cutting brass for the body, ferrule and nuts. The ferrule is usually of brass for low-pressure applications, and of carbon steel for higher pressures. Brass fittings are supplied with passivated finish as standard. Nickle-plated finish for special applications in Urea plants etc is also available at extra cost.

Stainless steel fittings are generally available in AISI: 304 grade stainless steel, but can also be offered in AISI: 316 grade stainless steel where the application and line fluids warrant it.

A word about stainless steel ferrules. Stainless steel is not an ideal material for ferrules. Being non-hardening, the primary requirement of a hard outer casing and a soft core is not achievable. So where stainless steel fittings can be used with carbon steel ferrules,

excellent results will be obtained. Stainless steel fittings with stainless steel ferrules may, however, be necessary where line fluids are highly corrosive. In such cases, the recommended operating pressure has to be suitably reduced.