A pre-galvanized steel tube is a steel tube that is galvanized a steel sheet before it is formed and welded into a tube. Steel tubes that are formed and galvanized afterwards are sometimes referred to as post-galvanized steel tubes, but hot-dipped steel tubes is a more commonly used expression.
However, since the zinc applied to the steel sheet is removed by the heat upon welding the pre-galvanized steel tube, re-sealing the exposed steel on the outside surface with zinc thermal spray is a required post-treatment process. This also means that the welding seam on the inside of the steel tube is not galvanized. The sacrificial anode properties of zinc allow for leaving the inner welding seam exposed without reducing the corrosion resistance and longevity of the product.