A weld neck flange
consists of a circular fitting with a protruding rim around the circumference which is generally machined from a forging, these flanges are typically butt welded to a pipe. The rim has a series of drilled holes that permit the flange to be affixed to another flange with bolts. Such flanges are suitable for use in hostile environments that have extremes of temperature, pressure or other sources of stress.
Weld neck pipe flanges are typically provided with a raised face, flat face, or RTJ facing. When a raised face is necessary for weld neck pipe flanges, the standard height is 1/16 inch for weld neck pipe flanges fewer than 400#. For weld neck pipe flanges of 400# and up, the standard weld neck pipe flange raised face height is 1/4 inch.