LJ (lapped)

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.

A flange that is not fixed to the pipe. It hooks over the lap of a stub end welded to the pipe end and is drawn up with bolts. Because the flange turns freely, lining up the bolt holes is easy, and the flange can be a different material from the pipe. Available in nominal pressures 5K, 10K, 16K and 20K.

Lapped flange dimensions

Nominal pressure	Nominal diameter [A]	Joint dimensions					d₀ [mm]	t [mm]	Hub diameter		T [mm]	r [mm]	c [mm]
Nominal pressure	Nominal diameter [A]	D [mm]	C [mm]	h [mm]	Quantity	Thread designation	d₀ [mm]	t [mm]	a [mm]	b [mm]	T [mm]	r [mm]	c [mm]

Notes

References
- JIS B 2220:2012 steel pipe flanges (Table 14, Table 15, Table 17, Table 18, Annex F)
The source has one table per nominal pressure. Here they are combined into a single table, with a rule where the nominal pressure changes. A dash means the dimension is not specified for that pressure. Selecting a single nominal pressure above drops the columns that do not apply, giving the same column layout as the source.
The chain double-dashed line in the drawing is the mating part, the stub end lap. It is outside the scope of this standard and its dimensions are not given here. The lap sits in the flange bore d₀ and, being larger than it, cannot pull through.
There is no gasket seat (see the note to Table 8). The gasket bears on the face of the stub end lap, and that is why the raised face g and f are absent from the flange.
Chamfer c is the relief at the mouth of the bore. It clears the fillet at the root of the lap.
The smallest nominal size covered is 15A. There is no 10A.
The calculated mass is for reference. It assumes a steel density of 7.85 g/cm³.