What Is a Swivel Flange?

Quick Answer

A swivel flange is a two-piece flange assembly consisting of a welded hub and a separate rotating ring. The hub is welded to the pipe, while the ring spins freely around it, allowing bolt holes to be aligned with a mating flange without rotating the entire pipe spool. Swivel flanges are widely used in offshore pipelines, subsea tie-ins, and any application where spool rotation is impossible or impractical.

How It Works

The hub (also called the “weld neck hub” or “forged hub”) is butt-welded to the pipe end. The flanged ring sits behind the hub shoulder and rotates 360 degrees. During bolt-up, the ring is turned until the bolt holes align with the mating flange. The gasket seats on the hub face, not the ring.

Property	Detail
Components	Forged hub + rotating flange ring
Standard	ASME B16.5 dimensions; hub per project spec
Size range	NPS 2 to NPS 36 (common offshore range)
Pressure classes	150 through 2500
Materials	A105 (CS), A182 F316 (SS), duplex (A182 F51)
Face types	RF, RTJ
Gasket seating	On the hub face
Ring rotation	Full 360 degrees

Swivel Flange vs Lap Joint Flange

Both use a rotating ring, but the designs differ:

Feature	Swivel Flange	Lap Joint Flange
Hub type	Forged weld neck hub	Stub end
Hub-to-pipe connection	Butt weld	Butt weld (stub end to pipe)
Ring type	Heavy-duty forged ring	Standard lap joint ring
Pressure capability	High (Class 600+)	Moderate (typically Class 150-300)
Typical service	Offshore pipelines, subsea	Low-pressure utility, corrosion-resistant piping
Cost	High	Low to moderate
Standard	Project-specific / ASME B16.5	ASME B16.5

Common Mistake

Swivel flanges are not interchangeable with standard weld neck flanges even when dimensions match. The hub profile and ring retention detail are specific to the swivel design. Verify the hub OD, ring ID, and retention groove dimensions against the manufacturer drawing before ordering.

Where Swivel Flanges Are Used

• Subsea pipeline tie-ins: Spool pieces on the seabed cannot be rotated for alignment
• Offshore topsides: Connecting pre-fabricated spools to fixed equipment
• Pipeline repair: Field joints where pipe rotation is constrained
• Riser connections: Flowline-to-riser tie-ins on FPSOs and platforms

Pro Tip

Swivel flanges for sour service must comply with NACE MR0175 for both the hub and the ring. Specify hardness testing (HRC 22 max for carbon steel) on the purchase order to avoid rejection during inspection.

Read the full guide to flanges