Causes and Solutions for Incomplete Hot-Dip Galvanizing of Seamless Steel Pipes:

1. Unclean Surface of the Seamless Steel Pipe:
(a) The surface of the seamless steel pipe contains paint, grease, or welding residue; this can be addressed by grinding or using a suitable solvent for cleaning.
(b) Iron oxides; insufficient pickling; continue pickling.

2. Inadequate Pickling and Operation of Seamless Steel Pipes:
(a) Insufficient or Excessive Pickling. Insufficient pickling leaves iron oxides (rust spots) on the surface of the seamless steel pipe; excessive pickling damages the surface structure of the steel substrate, causing the Si and small amounts of refractory oxides of active metals to adhere to the surface, preventing the bonding of iron and zinc. Alternatively, excessive pickling may cause the workpiece to absorb hydrogen; during galvanizing, the hydrogen expands due to heat and escapes, resulting in incomplete galvanizing.
Solution: Strictly control pickling and ensure proper pickling time.
(2) Stacking and compaction of workpieces during pickling can cause missed pickling or insufficient agitation during pickling, due to the structure of the seamless steel pipe workpieces, which can lead to vortex formation and missed pickling.
Solution: Spread out the workpieces during pickling as much as possible and agitate them frequently.

3. Fluxing of Seamless Steel Pipes
(1) Low flux concentration results in an unsatisfactory fluxing effect.
Solution: Adjust the flux concentration appropriately.
(2) Improper flux ratio, high zinc salt content, makes the flux salt film easily absorb water and deliquesce, causing hydroxides to decompose into gas and explode, resulting in missed plating.
Solution: Adjust the flux ratio.

4. Zinc Bath Composition and Boiler Operation of Seamless Steel Pipes:
(1) High aluminum content in the zinc bath causes missed plating.
Solution: Reduce the aluminum content by adding zinc or using ammonium chloride to consume it.
(2) Slow loading speed of the seamless steel pipe workpieces into the pot causes the flux to decompose and become ineffective due to heat, resulting in missed plating.
Solution: Adjust the loading speed appropriately.
(3) Insufficient zinc immersion time prevents the iron-zinc reaction from proceeding properly.
(4) Failure to clean zinc ash from the zinc bath surface before placing the seamless steel pipe parts into the molten zinc bath causes the overheated ash to burn the additives, resulting in incomplete plating.
(5) During the plating process, due to process holes or structural issues, high-temperature gases escaping from the seamless steel pipe parts can burn the additives, causing incomplete plating.
Solution: Sprinkle an appropriate amount of ammonium chloride.

5. Material of Seamless Steel Pipe Parts
(1) The surface of the seamless steel pipe contains refractory oxides of elements such as silicon and aluminum, which inhibit the iron-zinc reaction.
(2) The seamless steel pipe matrix contains excessive carbon, or excessive iron carbide is produced during the steel refining process, making iron-zinc bonding difficult and causing incomplete plating.
(3) Defects in the processing and forming of the seamless steel pipe parts cause material cracking, allowing acid, moisture, and additives to enter, leading to incomplete plating. Currently, there is no good solution other than using ammonium chloride.