1. How long can galvanized coils be stored without oxidation under protective measures?
Long-term storage of galvanized coils is not recommended. The industry consensus is that galvanized coils should not be stored for more than 3 months and should be used within 3 months.
For galvanized coils that have only undergone passivation treatment but not oiling, it is recommended to use them within 2 months.
For galvanized coils with both passivation and oiling protection, the shelf life can be extended to approximately 3 months.
2. Why does galvanized coil oxidize? What is its fundamental mechanism?
Oxidation of galvanized coil mainly manifests as "white rust," and its fundamental mechanism is electrochemical corrosion. When the surface of a damp galvanized coil is tightly packed or the packaging is too tight, preventing air circulation, a fine water film creates uneven oxygen concentration on the metal surface, forming an "oxygen concentration cell."
At this point, the area with lower oxygen concentration becomes the anode and is corroded, beginning to consume the zinc layer; the area with higher concentration becomes the cathode, eventually forming a white powdery corrosion product on the surface, which is "white rust."
3. What is the function of the passivation film on the surface of galvanized coils? Does it prevent oxidation during long-term storage?
The passivation film on the surface of galvanized coils is a crucial "protective layer."
This film primarily functions to: ① Physically isolate the zinc layer, effectively preventing oxygen and moisture from directly contacting it; ② Enhance corrosion resistance, significantly improving the product's oxidation resistance and weather resistance, which is essential for delaying oxidation caused by long-term storage. Some colored passivation films also possess "self-healing" capabilities, capable of repairing minor scratches to some extent.
4. How fast will the oxidation rate of galvanized coils be if the warehouse humidity is high?
Humidity has a significant impact on the oxidation rate. When the relative humidity in the air remains above 60%, especially in poorly ventilated warehouses, a continuous water film easily forms on the surface of the galvanized coils. If the relative humidity reaches 85% to 95%, the corrosion reaction will be very severe.
5. What special measures should be taken for galvanized coils that need to be stored for more than 6 months or even a year?
For long-term storage exceeding six months, in addition to the usual measures of drying, ventilation, moisture prevention, and protection from direct sunlight (ideal storage temperature range: 10℃ ~ 30℃, relative humidity ≤ 70%), the following effective enhanced measures should be taken:
Elevation for Moisture Prevention: Wooden or rubber blocks at least 15 cm high must be used to separate the galvanized coils from the ground.
Environmental Control: The warehouse should be equipped with dehumidifiers or air conditioners to ensure a stable environment.
Regular Inspection: It is recommended to establish a testing and record system, schedule weekly inspections and cleaning, and monitor the process using equipment such as zinc coating thickness gauges.
Enhanced Packaging: For special components stored for more than one year, vacuum packaging and nitrogen protection are strongly recommended. This is one of the most effective methods to prevent oxidation.