A flange is a forged or cast steel ring used to link sections of pipe or to unite pipe to a pressure vessel, pump, or other integrated flange assembly. Flanges are bolted together and welded or threaded into the piping system. Flanges are classified into the following types: stainless steel flanges (SS flanges), alloy steel flanges, carbon steel flanges, slip-on, blind, weld neck, threaded, socket weld, lap joint, and orifice.
Flanges are designed for pressure ratings of 150 lb, 300 lb, 400 lb, 600 lb, 900 lb, 1500 lb, and 2500 lb.

The most popular facings machined on flanges are:

(a) Raised face: 1/16 inch for 150lb to 300lb, ¼ inch for 400lb and above.

(b) Flat face, for 150 lb and 300 lb only; others may