Representation of large flanges

1. Use international chemical element symbols and national symbols to indicate chemical components, and use Arabic letters to indicate component content: such as: China, Russia 12CrNi3A
2. Use fixed-digit numbers to represent steel series or numbers; such as: the United States, Japan, 300 series, 400 series, 200 series;
3. The serial number is composed of Latin letters and sequences, only to indicate the purpose.