All flanges should be stamped for identification on the outside diameter of the base for easy identification with:
- Manufacturer's name.
- Nominal pipe size (NPS).
- Pressure rating (150 lb., 300 lb., etc.)
- Face designation - the machined gasket surface.
- Bore - the nominal pipe size (NPS).
- Material designation
- Ring gasket number - used for ring joint flange.
- Heat number of code - the batch number used when forged and tested
Normally, a flange should be hard stamped but in some cases the stamping may not be legible or completely visible for observation. In that case it may have to be visually observed and physically measured. Check the number of bolts and bolt size, measure the flange and pipe size. Then compare these measurements with flange data.
Note: This practice also extends to pipe fittings where the size, schedule and material should be hard stamped on every fitting.