High quality carbon steel, cold drawn, bright heat treatment, no oxidation (NBK status), non-destructive testing, wall honing and internal smoothness.

quality carbon steel-- cold drawn--heat treatment without oxidization(NBK status)--nondestructive testing -- flushing the internal hole with special equipment under the high pressure--dealing with antirust oil on surface-- plastic capping on both ends.

Cold drawn and bright NBK seamlee steel tube is used as the tube to be phosphated.
The phosphated is realized with the imported chemical fluid to form a black film. 
The antirust oil is absorbed by means of the micro pore on the film to prevent from the rust. The caps are covered at two ends of tube to prevent from the dust

DIN high precision cold drawn bright seamless steel tube is used as the tube to be galvanized on the outer surface, caps are covered at two ends of tube to prevent from the dust.