1. Carbon steel and austenitic stainless steel forgings with a nominal pressure PN of 0.25MP-1.0MPa are allowed to use Grade I forgings.
2. Except for the following regulations, forgings with a nominal pressure PN of 1.6MPa-6.3MPa shall meet the requirements of Grade II or higher forging grades. 3. Those who meet one of the following conditions shall comply with the requirements of III and forgings:
(1) Chromium molybdenum steel forgings with nominal pressure PN>4.0MPa;
(2) Ferritic steel forgings with nominal pressure PN>1.6MPa and working temperature ≤ -20 degrees Celsius;
(3) Forged parts for flanges with nominal pressure PN ≥ 10.0MPa.
2、 Neck butt welding, neck flat welding, socket welding, and threaded flanges are generally made using forging or rolling processes. When using steel plates or sections for manufacturing, the following requirements must be met:
1. The steel plate should undergo ultrasonic testing and have no delamination defects;
2. It should be cut into strips along the direction of steel rolling, bent and welded into a circular ring, and the surface of the steel should form a cylindrical ring. Steel plates shall not be directly machined into necked flanges;
3. The butt weld of the circular ring should be a full penetration weld;
4. The butt welds of the circular ring should undergo post weld heat treatment and undergo 100% radiographic or ultrasonic testing, with radiographic testing meeting the Level II requirements of JB4730 and ultrasonic testing meeting the Level I requirements of JB4730.