Relevant provisions in the national flange standard “GB/T9124-2010 Technical Conditions for Steel Pipe Flanges”:

3.2.1 For flanges with nominal pressures of PN2.5-PN16 Class150, low carbon steel, and austenitic stainless steel forgings are allowed to be Class I forgings (the hardness is tested piece by piece).

3.2.2 If the following conditions are met, the forgings for flanges shall meet the requirements of Class III or above forgings (sampling tensile inspection and ultrasonic testing one by one):

1. Forgings for flanges with nominal pressures ≥PN100 and ≥Class600;

2. Chromium-molybdenum steel forgings for flanges with nominal pressures ≥PN63 and ≥Class300;

3. Ferrite forgings for flanges with nominal pressure ≥ PN25 and Class ≥ 300 and operating temperature ≤ -20°C.

3.2.3 Other flange forgings should comply with the requirements for Grade II or above forgings (spot inspection and drawing).