Why does the greenhouse pipe have a problem of missed galvanizing?

The issue of missing galvanization on galvanized greenhouse pipes can generally be considered from five perspectives:

  Firstly, there is grease on the outer wall of the base pipe, which increases the surface tension. The acid pickling step before galvanizing cannot remove the surface grease. When the base pipe rusts, sometimes the electroplating agent cannot adhere, and a protective salt deposit forms.

  In the high-temperature molten zinc pool, the steel pipe undergoes rapid oxidation, preventing any chemical or physical reaction between the zinc and the substrate. After the steel pipe is removed from the zinc pool, the zinc will flow and accumulate unevenly under the influence of gravity. Therefore, black putty can still be found in the thinner zinc layer.

  Secondly, the outer surface of the alloy-based tube has been severely corroded. Despite attempts to clean the steel tube's outer surface, iron oxide still remains. Although the auxiliary plating agent can adhere to it, when the base tube is immersed in molten zinc, the zinc cannot directly contact the steel wire, and no reaction occurs. After the steel tube is separated from the zinc bath, the exposed side is relatively clean, resulting in pitting corrosion on the surface of the galvanized greenhouse tube.

  III. The wall of the base pipe is coated with thick grease and stubborn stains, which inevitably leads to missed plating. Additionally, processing becomes quite inconvenient as the steel pipe needs to be thoroughly cleaned from end to end. The wall of the base pipe bears stains the size of mung beans. During baking, the zinc liquid at the mouth of the steel pipe adheres tightly to its surface, resembling a rusted steel pipe. All missed plating layers are identical, but the occurrences of such missed plating are less continuous and the edges are relatively smoother.