It's outer layer is welding galvanized steel pipe,which is manufactured according to State Standard" GB/T3091 for low pressure liquid delivery" and whose wall thickness should conform to the grade of Normal Steel Pipe.It's inner lining is OCr19Ni9 Type welding stainless steel pipe, which is manufactured according to State Standard" GB/T12271-1991 for liquid delivery". The welding galvanized steel pipe are shapde into the composite steel pipe under pressure.Composite steel pipe with stainless steel lining and PE coating is also available. It is honored as "Popularized Item of Scientific and Technologic Products in Ministry of Construction" and "Shanghai New Hi-Tech Products converted Item".