Hidroser New Wave F37 Non Welded Flange Technology Sails

A non-welded flange connection joins hydraulic tube to a flanged interface by clamping, swaging or a split flange instead of fusion. In marine hydraulics that single change removes hot work permits, weld distortion and joints that cannot be dismantled, and it moves attention to surface preparation, controlled torque and the flange gaskets used at bolted faces.

What Non-Welded Flange Technology Means

The term covers several families of mechanical pipe connection. A clamped collar grips the tube and seals against an elastomeric O-ring. A compression ring is swaged onto the tube as the nut is tightened. A split flange clamps a flange head that was formed or machined onto the tube end. What all three share is a joint made by deformation and clamping rather than by fusion: no heat, no filler metal and no weld inspection.

The best-known marine example is the F37 class of fittings, specified where thin-wall hydraulic tube runs through confined spaces. The hardware is proprietary, but the principle is general: keep the tube intact and seal it mechanically.

• No hot work permit, no fire watch and no gas-freeing procedure on tankers and gas carriers.
• No heat-affected zone, no scale in the bore and no local destruction of the stainless passive layer.
• A joint that opens with hand tools, so a repair does not mean cutting the line out.
• A critical requirement that moves from weld quality to surface preparation and controlled torque, both inspectable and repeatable.

Why Shipyards Are Moving Away from Welding

Welding a flange onto a hydraulic line aboard a vessel is not just a fabrication task. It requires a hot work permit, a fire watch, isolation of adjacent systems and, on tankers and gas carriers, compliance with gas-freeing procedures. The thin-wall hydraulic tube then distorts under weld heat, scale forms inside the bore and must be removed, and the passive layer of stainless is destroyed locally.

Table 1. Typical comparison for marine hydraulic lines; the pressure and size ceiling follows the fitting manufacturer and the classification requirement.

The maintenance consequence is the decisive one. A welded flange cannot be removed without cutting it out, which means draining the system and another hot work job in the same confined space. Non-welded connections avoid all three costs.

Sealing, Materials and Installation Discipline

These systems use two sealing philosophies. The first compresses an elastomeric O-ring or seal, with the metal parts positioning it and carrying the pressure load. The second wedges metal against metal, so tightening deforms a ring or ferrule against the tube surface. In both cases the seal depends on controlled compression, and the assembly is only as good as the torque applied, so a calibrated torque wrench is not optional equipment.

• Tube end cut square, deburred inside and out and cleaned of cutting fluid; a burr at the seal interface cuts the O-ring or stops the ferrule seating.
• Torque taken from the fitting manufacturer and applied with a calibrated wrench: under-torque leaks, over-torque deforms the tube and may crush the ferrule past its sealing range.
• Tube support spaced to the manufacturer and the classification requirement; a vibrating tube frets at the fitting, and fretting at a seal interface becomes a progressive leak.
• Pressure test after assembly: a joint that holds at working pressure but weeps at test pressure points to wrong torque or poor tube preparation.

Fittings are commonly supplied in 316 stainless for marine service, with duplex grades where chloride exposure is severe. Because there is no weld, there is no heat-affected zone to re-passivate, so the risk moves to the tube surface, where a scratch or embedded debris becomes the initiation point. Galvanic coupling still applies: a stainless fitting bolted to carbon steel pipe flanges or to an aluminium structure leaves the stainless part cathodic and the surrounding metal corrodes, so insulating washers or a compatible transition piece break the circuit.

FAQ

What is a non-welded flange connection?

It is a mechanical pipe connection that joins tube to a flanged interface by clamping, swaging or a split flange instead of by welding. The seal is made by an elastomer or a metal ferrule under controlled compression.

Why avoid welding for hydraulic lines on board?

Welding requires hot work permits, fire watch and system isolation, distorts thin-wall tube, leaves scale inside the bore and destroys the stainless passive layer locally. The welded joint also cannot be dismantled without cutting it out.

How is the joint checked if there is no weld to inspect?

You verify the installation procedure, the tube surface condition and the applied torque, then pressure-test. A joint that holds at working pressure but weeps at test pressure signals wrong torque or poor tube preparation.

Where does welding still win over a mechanical joint?

At very high pressure, at large diameter and under severe vibration or cyclic loading, in buried or inaccessible runs, and in services where classification or flag-state rules require welded connections.