As seen in the section on the composition of zinc ash, besides the primary component of zinc oxide, there are also other oxides present, such as aluminum oxide, antimony oxide, chlorides, iron, and acid-insoluble impurities. The presence of these substances can cause numerous detrimental effects to galvanized steel pipes. These effects are manifested as follows:
(1) Zinc ash with a higher temperature sits on the surface of the zinc bath. The steel pipe begins to immerse in the zinc bath after passing through the zinc ash. As a result, the flux may be burned away, leading to ungalvanized areas.
(2) Zinc ash can entrain and conceal flux residue and other impurities. If these residues adhere to the steel pipe to be galvanized, not only will it fail to receive a zinc layer, but it will also be encapsulated within the pure zinc layer. When the galvanized steel pipe absorbs moisture from the air, the chlorides within the residue combine with water to form corrosive media, accelerating the corrosion of the pure zinc layer, which then drips off in tear-like streaks, causing damage. When the galvanized steel pipe exits the zinc bath, flux residue may also adhere to its outer surface, leading to corrosion upon absorbing moisture from the air.
(3) Since zinc ash may contain carbon particles brought over from the steel pipe pickling process and carbon particles resulting from the dissolution of galvanizing pots and steel pipes, false ungalvanized areas may appear on the surface of the galvanized layer. Although an iron-zinc alloy layer still exists internally, it is thinner than the surrounding pure zinc layer, affecting service life.
(4) The large presence of zinc ash can deteriorate the quality of the zinc bath, especially making the top layer of zinc thicker.
(5) When zinc ash accumulates excessively on the surface of the zinc bath, a considerable amount of zinc ash may adhere to the surface of the steel pipe as it exits the galvanizing pot. If not promptly blown off and wiped clean both inside and outside, yellow spots will appear in patches or dots after solidification. If the steel pipe is immediately conveyed out of the galvanizing pot by the roller conveyor, the weight of the steel pipe may press the zinc ash into the pure zinc layer. Additionally, since the galvanized steel pipe advances in a jumping manner on the roller conveyor, straight-line distributed dotted yellow zinc ash spots may appear on the surface. If these zinc ashes are not removed, the chlorides and other acidic impurities they contain 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 zinc bath, yellow rust spots may appear under certain moist conditions, and false endpoints may occur during testing, affecting galvanizing quality.
