154.528—Piping joints: Flange type.
(a)
A flange must be one of the following types:
(b)
If the piping is designed for a temperature between −10 °C (14 °F) and −55 °C (−67 °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
(c)
If the piping is designed for a temperature lower than −55 °C (−67 °F), the pipe flange must be a welding neck type.