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Causes and solutions for the leakage of seamless pipe hot-dip galvanizing

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Causes and solutions for the leakage of seamless steel pipe hot-dip galvanizing


1. The surface of the plated parts is not clean

⑴The surface of the plated parts contains paint, grease, and welding iron; it can be polished or prepared with related solvents for scrubbing.

⑵Iron oxide; lack of pickling; continue pickling.


2. Pickling and operation:

⑴ Under and over pickling. Under-pickling leaves iron oxides (rust spots) on the surface of the plated parts; over-pickling causes the surface structure of the steel substrate to be destroyed. The Si and a small amount of active metal refractory oxides are attached to the surface of the plated parts. Prevent the combination of iron and zinc. Or due to acid washing, the plating parts absorb hydrogen. During galvanizing, the hydrogen gas expands and escapes due to heat and the plating leaks. Solution: Strictly control pickling and grasp the pickling time.

⑵ During pickling, the plating parts are superimposed and overstocked, resulting in missing washing, or due to the structural reasons of the plating parts, they are neglected to turn and cause vortex and leak washing. Solution: Open the pickling as much as possible and flip it frequently.


3. The plating process

⑴ The concentration of the auxiliary agent is too low, and the plating assist effect is not ideal; Solution: adjust the concentration of the appropriate auxiliary agent.

⑵Improper proportion of additives and high zinc salt content makes the salt film of the additives easy to absorb water and deliquesce, and the hydroxide decomposes into gas and explodes zinc, resulting in leakage plating. Solution: adjust the ratio of additives.


4. Zinc liquid composition and pot operation:

⑴The aluminum content in the zinc liquid is too high, causing the leakage of the plating; the solution: add zinc or use ammonium chloride consumption and other methods to reduce the aluminum content;

⑵The speed of the plated parts is too slow, and the auxiliary agent is decomposed and failed due to heat, causing the plating to leak. Adjust the pot speed appropriately.

⑶ The zinc immersion time is too short so that the iron-zinc reaction can be carried out in the future.

⑷The zinc ash on the zinc liquid surface is not cleaned when the plating parts are put out of the pot so that the overheated zinc ash burns the auxiliary agent and the plating is missed.

⑸When the plated parts are placed in the pot, due to the process hole or structure, when the high-temperature gas in the plated parts escapes due to heat, the auxiliary agent will be burnt to cause the plating to leak. Solution: Sprinkle some ammonium chloride in an appropriate amount. 


5. Material of plating parts

⑴ The surface of the steel contains refractory oxides of elements such as silicon and aluminum, which prevents the iron-zinc reaction.

⑵The steel matrix contains too much carbon, or too much iron carbide is produced during the refining process of the steel, which makes the combination of iron and zinc difficult and causes leakage of plating.

⑶ The material processing and forming defects of the plated parts cause the material to rot and crack, and the acid, water, and additives enter, causing the plating to leak. At present, there is no good solution other than ammonium chloride.