Bolt two flat-surface flanges or two raised-surface flanges of the same size together with a gasket (sold separately) to create an access point in a pipe line.
Butt-weld flanges are also known as weld-neck flanges; the flange neck has a beveled end that, when flush to pipe, creates a trough for a strong weld. Forged flanges have better strength than cast flanges. 304 stainless steel flanges offer very good corrosion resistance, and 316 stainless steel flanges have excellent corrosion resistance.