First: Causes of anti-alkali (white rust, black spots)
1. The formation principle of white rust: When galvanized products are tightly packed and placed in humid air since there is no free-flowing air on the surface of the product, electrochemical corrosion will occur on the surface of the zinc layer, forming white rust. When the condensed water attached to the surface of the zinc layer combines with oxygen, carbon dioxide, hydrogen sulfide, sulfur dioxide, oxides, and other chemical gases, a corrosive aqueous solution will be produced and adhere to the surface of the zinc layer to form an electrolyte. This electrolyte and the zinc layer produce electrochemical corrosion, resulting in the white dot-like powdery substance (zinc oxide) visible to the naked eye. The secondary and tertiary oxidation products of white rust form a local black appearance, which is collectively called the anti-alkali phenomenon.
2. The impact of white rust: Because the volume of metallic zinc increases 3 to 5 times when it is transformed into zinc oxide or zinc hydroxide, the volume of white rust formed is larger, making the degree of white rust corrosion appear to be much more serious than the actual situation. , seriously affecting the appearance of the zinc layer, but they only cause a small loss of zinc on the surface.
3. Treatment of white rust: A large amount of white rust may appear on the surface of galvanized products, but the actual corrosion on the zinc layer is relatively slight. In most cases, the appearance of white rust does not indicate that the zinc layer has been seriously damaged. After white rust occurs, galvanized products should be spread out to allow their surfaces to dry quickly.
In summary, as mentioned above, due to factors such as weather, transportation, and storage, the anti-alkali phenomenon is common in galvanized products in summer. As long as the corroded zinc layer is higher than the standard value, it will not have any impact on the service life of the product.
Second: Things to note
1. All galvanized products will produce white rust in humid, high temperatures, poor air circulation, and corrosive environments. Products that are highly prone to white rust: angle steel, flat iron, square and rectangular tubes, round tubes, and other tightly packaged and sealed products have water accumulated in them. If the weather is hot and humid, the accumulated water will reverse moisture, and galvanized products are prone to alkali reversion.
2. After arriving at the destination, galvanized products should be stored in a well-ventilated warehouse and should not be stacked in places with a lot of harmful gases and dust.
3. If slight white rust or spots appear on the surface, it should be disassembled and dried immediately, ventilated until the white rust turns into powder, and then brushed off in time with a brush.
4. In humid and hot environments, store indoors as much as possible to keep them ventilated and dry, and avoid direct contact with moist soil when stacking.
5. Galvanized products are not afraid of high temperatures, humidity, or concentrated stacking, but they are afraid of having all three at the same time, that is, concentrated stacking in humid and hot conditions. Only passivated galvanized steel pipes are good steel pipes.
Post time: May-14-2024