Apparatus for manufacturing steel tube and method for manufacturing the same

An apparatus for manufacturing a steel tube, comprising:

• a tube-forming device for forming a steel plate into a steel tube;
• a heat treatment device connected in-line to the tube-forming device to heat the steel tube to a high temperature;
• a pre-treatment device including a dual tube including an inner tube surrounding the steel tube, and an outer tube disposed around the periphery of the inner tube, a gas injection device supplying a mixed gas of nitrogen and hydrogen into the inner tube, and a cooling water supply device supplying cooling water between the inner tube and the outer tube to slowly cool down and anneal the steel tube and to form a reduction atmosphere;
• and
• a plating device including a pot for storing a corrosion-resistant alloy composed of 55 wt % aluminum and 43.4 to 44.9 wt % zinc in a molten state, a level block selectively inserted into the molten alloy to adjust a level of the molten alloy, a plating part into which the molten alloy flows in response to insertion of the level block and through which the steel tube passes substantially vertically, and a partition installed in the pot to divide an upper space of the pot and preventing waves in the molten alloy around the plating part during vertical movement of the level block.