This standard specifies the type and size of steel pipe flange covers with concave and convex surfaces with nominal pressure PN of 1.6, 2.5, 4.0, 6.3, 10.0, 16.0MPa and nominal pressure PN of 5.0, 11.0, 15.0, 26.0MPa. This standard is applicable to steel pipe flange covers with concave and convex surfaces of nominal pressure PN1.6~PN26.0MPa.