From the section on the composition of zinc ash, it can be seen that besides zinc oxide as the main component, zinc ash also contains other oxides such as aluminum oxide, antimony oxide, chlorides, iron, and acid-insoluble impurities. Therefore, the presence of these substances can cause many detrimental effects on galvanized steel pipes. These effects manifest as follows:
(1) Zinc ash at a higher temperature sits on the surface of the molten zinc. Steel pipes begin to immerse in the molten zinc after passing through the zinc ash. Therefore, the solvent may be burned off, leading to uncoated areas.
(2) Zinc ash can entrap solvent residues and other impurities. If these residues adhere to the steel pipes to be galvanized, not only will they fail to receive a zinc coating, but they will also be encapsulated within the pure zinc layer. When the galvanized steel pipes absorb moisture from the air, the chlorides in these residues react with water to form corrosive media, accelerating the corrosion of the pure zinc layer and causing it to drip off in tear-like streaks, resulting in damage. When the galvanized steel pipes emerge from the molten zinc, solvent (flux) residues may also adhere to the outer surface of the pipes, causing corrosion at these locations after absorbing moisture from the air.
(3) Zinc ash may contain carbon particles brought over from the pickling process of steel pipes, as well as carbon particles resulting from the dissolution of galvanizing pots and steel pipes. This can lead to apparent uncoated areas on the galvanized layer's surface. Although an iron-zinc alloy layer still exists internally, it is thinner than the surrounding pure zinc layer, affecting service life.
(4) The presence of a large amount of zinc ash can degrade the quality of the molten zinc, especially making the top layer of molten zinc thicker.
(5) When zinc ash accumulates excessively on the surface of the molten zinc, a considerable amount of zinc ash may adhere to the surface of the steel pipes as they exit the galvanizing pot. If not promptly blown off and wiped away internally and externally, solidified yellow spots or patches will appear on the surface. If the steel pipes are immediately conveyed out by the roller conveyor upon exiting the galvanizing pot, the weight of the steel pipes will press the zinc ash into the pure zinc layer. Additionally, as the galvanized steel pipes advance in a jumping manner on the roller conveyor, linear distributions of dotted yellow zinc ash spots will appear on the surface. If these zinc ash spots are not removed, the chlorides and other acidic impurities contained within them will corrode the galvanized layer after absorbing moisture from the air. Once the zinc ash at these spots is removed, pits will appear, and the pure zinc layer will be thinner or even absent, significantly shortening service life.
(6) Since zinc ash also contains a certain amount of iron, if it mixes into the pure zinc layer on the surface of the molten zinc, yellow rust spots may appear under certain wetting conditions, and false endpoints may occur during testing, affecting galvanizing quality.
