What Is Flange Facing?

Quick Answer

Flange facing is the machined surface on a flange where the gasket seats to create a pressure-tight seal. The facing type determines the gasket style, sealing mechanism, and bolt loading requirements. ASME B16.5 defines five standard facing types: raised face (RF), flat face (FF), ring type joint (RTJ), tongue and groove (T&G), and male and female (M&F). RF is the default for steel pipe flanges; RTJ is used for high-pressure service.

ASME B16.5 Flange Facing Types

Facing Type	Abbreviation	Gasket Type	Typical Pressure Class
Raised face	RF	Spiral wound, ring, sheet	150-600 (standard default)
Flat face	FF	Full-face sheet or rubber	150 (cast iron mating)
Ring type joint	RTJ	Metal ring (R, RX, BX)	600-2500
Tongue and groove	T&G	Ring or sheet (confined)	Special applications
Male and female	M&F	Ring or sheet (confined)	Special applications

Raised Face (RF) Details

Parameter	Class 150/300	Class 400-2500
RF height	1.6 mm (1/16 in)	6.4 mm (1/4 in)
Surface finish	3.2-6.3 micrometers Ra (concentric or spiral serrated)
Gasket OD	Within RF diameter
ASME B16.5 default	Yes	Yes

Common Mistake

For Classes 150 and 300, the RF height (1.6 mm) is NOT included in the listed flange thickness. For Class 400 and above, the RF height (6.4 mm) IS included in the listed thickness. This distinction affects face-to-face calculations in piping isometrics.

Ring Type Joint (RTJ) Details

Parameter	Detail
Groove depth	Precision-machined to ASME B16.5 Table E-1
Groove profile	R-type (for oval/octagonal rings), RX, or BX
Flange face gap	Flanges must NOT touch after bolt-up (ring fills groove)
Ring material	Softer than groove material (soft iron, 304 SS, 316 SS, Inconel)
Groove finish	1.6 micrometers Ra (smoother than RF)

Facing Types Compared

Feature	RF	FF	RTJ	T&G	M&F
Gasket confinement	Partial (RF edge)	None	Full (groove)	Full (groove)	Full (recess)
Self-centering	No	No	Yes (ring in groove)	Yes	Yes
Ease of assembly	Easy	Easy	Moderate (ring alignment)	Difficult (alignment critical)	Difficult
Seal reliability	Good	Adequate (low P)	Excellent	Excellent	Excellent
Standard use	Most process piping	Cast iron equipment	HP/HT piping	Heat exchangers, special	Rare

EN 1092-1 Facing Forms

EN 1092-1 uses a different designation system:

EN Form	Description	ASME Equivalent
Form A	Flat face	FF
Form B1	Raised face (standard)	RF
Form B2	Raised face (recessed for ring gasket)	Modified RF
Form C	Tongue and groove	T&G
Form D	Tongue	T (half of T&G pair)
Form E	Groove	G (half of T&G pair)

Pro Tip

Always specify the facing type on purchase orders and MTOs. If no facing is specified, manufacturers will supply RF as the ASME B16.5 default for steel flanges. Converting from RF to RTJ requires re-machining the flange face and is possible only if sufficient material exists in the flange ring—this is standard practice for Class 600 and above.

Read the full guide to flanges