The gases used for blasting and wiping the unsolidified zinc liquid on the inner wall of galvanized steel pipes mainly include superheated steam, compressed air, pressurized hot air, and saturated steam, among which superheated steam is more commonly used. This is because superheated steam can be heated above the zinc solidification point under the specified process pressure and contains very little moisture. When used to blast and wipe the zinc liquid on the inner wall of galvanized steel pipes, it does not cool down the zinc liquid; instead, it slightly increases its temperature. This is beneficial for blasting and wiping the zinc liquid on the inner bore wall to achieve a smooth surface. Additionally, the equipment for generating superheated steam is relatively simple and can be easily implemented in most factories. In contrast, saturated steam contains more moisture and has a lower temperature, which can absorb heat from the zinc liquid and accelerate its solidification. Compressed air, despite having less moisture, can also accelerate the solidification of the zinc liquid, increasing the resistance of compressed air passing through the inner bore of galvanized steel pipes and hindering the blasting and wiping process. The use of pressurized hot air for internal blasting and wiping of zinc is less common due to the difficulties in achieving the required high temperature, pressure, and flow rate, as well as the higher equipment costs and energy consumption.
If compressed air is first used for external blasting and wiping, it is even more necessary to adopt superheated steam (or pressurized hot air) at a higher temperature and pressure for internal blasting and wiping of zinc.
