1.What is the difference between coating structure and protection mechanism?
Hot-dip galvanized pipes form a composite structure of zinc-iron alloy layer (inner layer) + pure zinc layer (outer layer) through the reaction of high-temperature molten zinc liquid and substrate. This metallurgically bonded alloy layer can be up to 30-60μm thick, forming a tight integrated protective layer with the steel pipe substrate. Even if it is partially damaged, the zinc layer can continue to protect the substrate through the principle of cathodic protection (zinc as an anode corrodes first).
Electrogalvanized pipes form a pure zinc layer through electrolytic deposition, which is usually 5-20μm thick, and the coating is only bonded to the substrate through physical adsorption. This structure is prone to coating peeling when mechanical stress or corrosive medium penetration occurs, resulting in direct exposure of the substrate.
2.What are the differences in salt spray test performance?
Hot-dip galvanized pipe: When the coating thickness is ≥55μm, the neutral salt spray test time can reach more than 1000 hours, and heavy-duty anti-corrosion (such as Z450 coating) can even exceed 5000 hours.
Electro-galvanized pipe: Without passivation treatment, the salt spray test is only 24-36 hours, which can be increased to 72 hours after blue-white passivation, but it is still much lower than hot-dip galvanizing.
3.What is the difference in actual service life?
Hot-dip galvanized pipe: The service life can reach 20-50 years in normal environment, and can still maintain more than 50 years in marine environment.
Electro-galvanized pipe: The service life is about 5-10 years in indoor dry environment, and only 2-3 years in humid or industrial environment.
4.What is the difference in environmental adaptability?
Hot-dip galvanized pipe: suitable for harsh environments such as high humidity, high salt, acid and alkali.
Electro-galvanized pipe: only suitable for dry indoor environments (such as building threading pipes), the corrosion rate increases significantly in humidity > 60% or chloride ion-containing environments.
5.What is the difference in maintenance costs?
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.
Electro-galvanized pipes need to be inspected and repaired regularly, especially after mechanical damage, they need to be repaired immediately with zinc-rich paint, otherwise rust will spread rapidly.