... public diameter: 6 ~ 4000mm c, Flange structure type: welding, socket welding, threaded connection, loose, butt weld and blind flange d ... face, male and female, tongue and groove, metal rings connected surface 3, Chinese steel pipe flanges National Standards ... Integral flange Unit flange a, threaded flange b, welding flange, welding neck flange, welding neck flange, socket weld flange with neck , ...