SO Flange Slip-On flanges or SO flanges GOST 12820-80  PN 1.6 Mpa are commonly lower in price than weld-neck flanges, and to this effect are a popular choice for our customers. Standard:GOST 12820-80, ASME B16.5 Type: Plate Flange, SOP Flange (Raised Face) Pressure: PN1.6Mpa Sealing face of the slip on flange: RF and FF Size: