Gasket seat

SOP (slip-on welding, plate flange)Nominal pressure 5K, 10K, 10K thinThe pipe is slipped in and fillet welded. It is a flat plate with no hub and is the cheapest type. It is used for general low-pressure piping.SOH (slip-on welding, hub flange)Nominal pressure 5K, 10K, 10K thin, 16K, 20K, 30KA plate flange with a hub added to lower the stress at the root. Choose it where SOP does not stand the pressure or the repeated loading.SW (socket welding flange)Nominal pressure 5K, 10K, 16K, 20KThe pipe is pushed to the bottom of the socket and welded on the outside only. It is used for small-bore piping, 10A to 80A.WN (welding neck flange)All nominal pressures 5K to 63KIt is butt welded to the pipe. The joint is the strongest of all, and it is used for piping under high pressure, high temperature or repeated loading.LJ (lapped flange)Nominal pressure 5K, 10K, 16K, 20KIt is not fixed to the pipe but bears on the collar of a stub end. The flange turns freely, so lining up the holes is easy, and it can be a different material from the pipe.TR (threaded flange)Nominal pressure 5K, 10K, 16K, 20KThe pipe is screwed in with a taper pipe thread. It is used on sites where welding is not possible, and on lines where welding is unwanted. Only 10A to 150A are covered.IT (integral flange)Nominal pressure 5K, 10K, 16K, 20K, 30KA flange made in one piece with the body of a valve or a machine. It is not a separate part, so the table is consulted to match the joint dimensions to the mating side.BL (blind flange)All nominal pressures 5K to 63KA plate with no bore that closes the pipe end. It is used to stop a line off for testing, or for a branch to be added later.

Dimensions of the seating surface for the gasket on the mating face. There are three forms: raised face (RF), male and female (MF) and tongue and groove (TG). Which one is available depends on the nominal pressure and the flange type (Table 8).

Raised face (RF)

Nominal diameter [A]	5K		10K		16K		20K		30K		40K		63K
Nominal diameter [A]	g	f	g	f	g	f	g	f	g	f	g	f	g	f

Male and female (MF) / tongue and groove (TG)

Nominal diameter [A]	Male face / tongue face		Female face / groove face		Tongue face	Groove face
Nominal diameter [A]	c₃ [mm]	f₃ [mm]	c₄ [mm]	f₄ [mm]	c₁ [mm]	c₂ [mm]

Notes

References
- JIS B 2220:2012 Steel pipe flanges (Tables 3, 8 and 13)
The male and female form (MF) pairs a male face with a female face; the tongue and groove form (TG) pairs a tongue face with a groove face. Each set is one raised half and one recessed half.
The male and female and the tongue and groove dimensions do not depend on the nominal pressure. Values in brackets are for nominal pressure 10K, and only 150A and 300A take a different value.
The full face (FF) does not appear in this table. It has no raised height; the flange face itself is the gasket seating surface.
The lapped flange (LJ) has no gasket seat. The gasket bears on the face of the stub end lap.