1.In coastal areas, what are the coating structures and protective properties of hot-dip galvanized pipes?
The coating of hot-dip galvanized pipes is formed by the reaction of high-temperature molten zinc liquid with the substrate, and is composed of a zinc-iron alloy layer (inner layer) and a pure zinc layer (outer layer). This structure allows the coating to be tightly bonded to the steel pipe substrate, forming an integrated protective layer. Even if it is partially damaged, the zinc layer can continue to protect the substrate by corroding itself first through the principle of cathodic protection. On the other hand, the electro-galvanized pipe forms a pure zinc layer through electrolytic deposition, and is only bonded to the substrate through physical adsorption. When mechanical stress or corrosive medium penetrates, the coating is prone to peeling, resulting in exposure of the substrate, and the protective performance is relatively weak.
2.In coastal areas, what is the coating thickness and corrosion resistance of hot-dip galvanized pipes?
The thickness of the hot-dip galvanized layer is usually thicker than the electro-galvanized layer. Generally, the thickness of the hot-dip galvanized layer is ≥55μm. In the neutral salt spray test, it can reach more than 1000 hours, and the heavy-duty anti-corrosion coating can even exceed 5000 hours. The thickness of the electro-galvanized layer is usually 5-20μm. Without passivation treatment, the salt spray test is only 24-36 hours. After blue-white passivation, it can be increased to about 72 hours, which is much lower than the hot-dip galvanized pipe. In the humid and salty air in coastal areas, the thicker coating of hot-dip galvanized pipes can provide longer-term protection and stronger resistance to corrosion.
3.What is the environmental adaptability of hot-dip galvanized pipes in coastal areas?
Hot-dip galvanized pipes are suitable for harsh environments such as high humidity, high salt, acid and alkali. In soils with a pH value of 4-10, the corrosion rate is only 0.001mm/year. The air in coastal areas is humid and contains salt. Hot-dip galvanized pipes can adapt to this environment better and effectively resist the erosion of moisture and salt spray. In contrast, electro-galvanized pipes are more suitable for dry indoor environments. In environments with humidity > 60% or containing chloride ions, their corrosion rate will increase significantly, and they are prone to rust problems when used in coastal areas.
4.What is the maintenance cost of hot-dip galvanized pipes in coastal areas?
Hot-dip galvanized pipes have a long maintenance-free period, and the maintenance cost in a 20-year period is only 1/3 of that of electro-galvanized pipes. Due to its good corrosion resistance, it does not require frequent inspection and repair when used in coastal areas. Electro-galvanized pipes, on the other hand, require regular inspections. Once damage to the coating is found, it needs to be repaired in time with zinc-rich paint, etc. Otherwise, rust will spread rapidly, increasing maintenance costs and workload.
5.What is the industry trend of hot-dip galvanized pipe?
Hot-dip galvanizing is further improving corrosion resistance through chromium-free passivation technology (such as silicone modified coating), and the salt spray test can reach more than 2000 hours.