Metal flanges are commonly used for industrial, commercial, and institutional application. Steel pipe flanges are available in variety of styles and pressure classes. Metal flanges are classified from 150 to 2500# rating.
The material of a flange, is basically set during the choice of the pipe, in most cases, a flange is of the same material as the pipe.
All flanges, discussed on this website fall under the ASME en ASTM standards, unless otherwise indicated. ASME B16.5 describes dimensions, dimensional tolerances etc. and ASTM the different material qualities.
Each flange ASME B16.5 has a number of standard dimensions. If a draftsman in Japan or a work preparer in Canada or a pipefitter in Australia is speaking about a Welding Neck flange NPS 6, Class 150, Schedule 40 ASME B16.5, then it goes over the flange which in the image here below is shown.
If the flange is ordered, the supplier want to know the material quality. For example ASTM A105 is a forged carbon steel flange, while A182 is a forged stainless steel flange.