The grade and technical requirements of the butt welding flange should comply with the corresponding requirements of JB4726-4728.

1. Carbon steel and Austenitic stainless steel forgings with nominal pressure PN ranging from 0.25MP to 1.0MPa are permitted to use Grade I forgings.

2. In addition to the following stipulations, forgings with nominal pressure PN ranging from 1.6MPa to 6.3MPa should meet the requirements of Grade II or higher forging grade.

3. Shall meet one of the following conditions and shall comply with the requirements for Grade III and forgings:

Forge work for flanges with nominal pressure PN ≥ 10.0 MPa

(2) Forged parts made of chrome-molybdenum steel with nominal pressure PN greater than 4.0 MPa.

(3) Ferritic steel forgings with nominal pressure PN > 1.6 MPa and working temperature ≤ -20°C.