This standard specifies the type, size, technical requirements and marking of steel pipe flange covers marked with PN and Class for nominal pressure. This standard is applicable to steel pipe flange covers with nominal pressure PN 2.5 to PN 160 and Class 150 to Class 2500.
GB/T 9123-2010 Referenced Document
GB/T 9112 Types and parameters for steel pipe flanges
GB/T 9124 Specifications for steel pipe flanges*, 2011-10-01 Update