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.

http://www.sxzwflange.com/