1. What is the main drawback of using galvanized coils in saline-alkali environments?
The main drawback is a drastically accelerated corrosion rate, leading to a significantly shortened service life. Saline-alkali soils contain high concentrations of soluble salts, such as chlorides (Cl⁻ ions) and sulfates. These ions damage the passivation film on the surface of the galvanized layer, accelerating zinc dissolution. Studies have shown that in high-salinity environments such as coastal saline soils, the corrosion rate of the galvanized layer can be accelerated by 1.5 to 2 times. Therefore, galvanized coils that could last 15 to 20 years in normal environments may have their lifespan reduced to about 5 years in highly saline-alkali areas.
2. What is the mechanism of galvanized coil failure in saline-alkali environments?
A: Galvanized coil protects steel using the "sacrificial anode" principle, where the more reactive zinc layer preferentially corrodes to protect the steel substrate. However, saline-alkali environments disrupt this mechanism through two pathways:
Direct chemical attack: Salts in the soil, especially chloride ions, continuously consume the zinc layer. As the zinc layer thins, eventually exposing the steel substrate, the corrosion products change from white (zinc corrosion products) to reddish-brown (rust), indicating complete protection failure.
Accelerated electrochemical corrosion: Salt increases the electrical conductivity of the soil, making the corrosion cell reactions more active and complete, thus significantly increasing the corrosion rate.
3.In saline-alkali environments, what factors further exacerbate the corrosion of galvanized coils?
Answer: Besides the fundamental factor of high soil salinity, the following environmental factors work together to create more severe corrosion conditions:
High humidity: A humid environment provides electrolytes for the corrosion reaction, a key condition for accelerating corrosion. In saline-alkali soil, salt absorbs moisture from the air, keeping the material surface constantly moist.
pH value: Whether acidic (some areas are acidic, such as pH < 4) or alkaline (such as heavily alkaline soils with pH > 9), saline-alkali environments accelerate the dissolution of the galvanized layer.
Temperature: High temperatures will exponentially accelerate the chemical reaction rate of corrosion, making the problem even more severe.
4. In which specific application scenarios are ordinary galvanized coils commonly used in saline-alkali land? What problems might be encountered?
A: Saline-alkali land is commonly found in coastal mudflats, inland saline agricultural areas, or heavily salted industrial areas. In these regions, galvanized coils are often used for the grounding of agricultural greenhouses, photovoltaic power station supports, fence wire mesh, and power transmission tower foundations. However, in these scenarios, ordinary galvanized materials face severe challenges:
Agricultural Greenhouses: Pipes buried in saline-alkali soil for extended periods are prone to corrosion, leading to a decrease in structural strength. Using low-quality "cold-galvanized" pipes can result in them becoming heavily rusted within months.
Power Grounding: In highly saline-alkali soil, galvanized grounding electrodes will experience severe corrosion, leading to a reduction in cross-sectional area and an increase in resistance, posing safety hazards.
Fence Wire Mesh: Salt will rapidly degrade the galvanized layer, causing the fence to lose its function prematurely.
5. For saline-alkali environments, are there better alternatives or improved solutions than ordinary galvanized steel coils?
A: Yes, there are several ways to significantly improve corrosion resistance:
Use superior coating materials: Aluminized zinc coils (such as double-sided AZ150 grade) contain aluminum, making their corrosion resistance 2 to 6 times that of ordinary hot-dip galvanized sheets, and extending their salt spray life from 5 years to 25 years.
Add an extra protective layer: Epoxy, polyurethane, or other anti-corrosion coatings can be sprayed over the galvanized layer. For photovoltaic facilities and similar applications, using "hot-dip galvanizing + fluorocarbon spraying" can achieve long-lasting dual protection.