CFR /  Title 46  /  Part 154  /  Sec. 154.528 Piping joints: Flange type.

(a) A flange must be one of the following types:

(1) Welding neck.

(2) Slip-on.

(3) Socket weld.

(b) If the piping is designed for a temperature between -10 [deg]C (14 [deg]F) and -55 [deg]C (-67 [deg]F), the pipe flange may be a:

(1) Slip-on type, if the nominal pipe size is 100 mm (4 in.) or less;

(2) Socket weld, if the nominal pipe size is 50 mm (2 in.) or less; or

(3) Welding neck.

(c) If the piping is designed for a temperature lower than -55 [deg]C (-67 [deg]F), the pipe flange must be a welding neck type.