Hot galvanized pipe is produced by the react of molten metal and the iron matrix alloy layer, to combine matrix and coating. HDG has advantages of a well-distributed coating, strong adhesion, long using life and others. Steel matrix and the molten bath arise complicated physical & chemical react to form iron alloy layer which is Zinc with corrosion resisting and tight structure. Alloy layer, Zinc layer and pipe matrix melt into one. So it is good at corrosion resisting.