How to store aluminum coils to avoid oxidation

1. Warehouse environment requirements

1. Humidity & temperature control
   • Keep relative humidity ≤60% RH, temperature range 10–30°C.
   • Avoid dew point phenomenon: the surface temperature of aluminum coil must always be above the dew point of ambient air. Large temperature difference between aluminum stock and air is the primary cause of condensation. Do not move cold coils directly into a warm humid warehouse.
   • No water leakage, rain seepage, ground water ponding in the storage area. Ground should be concrete with moisture-proof layer.
2. Atmosphere cleanliness
   • Keep away from corrosive media: chlorides, acid vapor, alkaline dust, sulfur-containing gas (from chemical workshops, sewage areas, coastal salt spray).
   • Coastal storage needs extra anti-salt fog protection.
   • Do not store together with steel, cast iron, electrolytic materials, chemical reagents which may release corrosive substances.

2. Stacking & placement rules

1. Rack / pallet support
   • Aluminum coils shall be placed on dry wooden pallets or steel racks with isolation pads, not directly on the floor. The bottom clearance ≥100 mm to isolate ground moisture.
   • Use non-conductive, non-contaminating isolation materials (dry kraft paper, PE film, HDPE sheet). Avoid carbon steel contact without insulation to prevent galvanic corrosion.
2. Stacking specification
   • Horizontal storage for aluminum coils (coil axis horizontal). Never stand thin aluminum coils, which risks coil deformation and local stress concentration.
   • Limit stacking height: do not overload the bottom coil; prevent edge damage and compression of waterproof packaging.
   • Leave spacing between stacks for air circulation and inspection; avoid dead air pockets.
3. Classification management
   • Separate different alloys, tempers, surface finishes (mirror, bright, mill finish).
   • Separate new incoming coils and finished coils; mark production date for first-in first-out (FIFO).

3. Packaging & sealing protection

1. Original packaging integrity
   • The factory waterproof wrapping (waterproof kraft paper + PE moisture barrier film + desiccant bag) should be kept intact. Any torn packaging must be repaired or re-packaged immediately.
   • Desiccants have limited service life. Inspect and replace desiccant periodically for long-term stock.
2. Re-packaging for long storage
   • For long-term storage (>3 months): fully wrap coil with heat-shrink PE film or VCI anti-corrosion film. VCI film releases volatile corrosion inhibitor suitable for aluminum, blocking electrochemical corrosion.
   • Seal the coil eye and coil edges completely, prevent humid air from entering the inner layers of the coil.

Note: Do not use chlorine-containing plastic films.

4. Handling & daily management

1. Handling control
   • Forklift / crane operation: use soft sling; avoid scratching surface, breaking packaging. Damaged coating is a starting point for oxidation.
   • Do not unpack unless the coil is ready for use. Once unpacked, process it as soon as possible.
2. Regular inspection
   • Check packaging integrity, coil surface, RH & temperature log weekly.
   • Early warning signs: water stains, white spots, foggy surface. Isolate suspect coils immediately.
3. Seasonal special measures
   • High-rainy / plum season: increase dehumidifier running time, check desiccant more frequently.
   • Winter: prevent cold coils from being brought into warm workshop directly; hold coils in transition area for temperature equalization to avoid condensation.

5. Common mistakes to avoid

• ❌ Store aluminum coils outdoors even with tarpaulin (tarpaulin cannot stop condensation under temperature cycling)
• ❌ Stack coils on wet concrete
• ❌ Mix storage with steel, fertilizer, acid/alkali chemicals
• ❌ Ignore small packaging damage, leave it unrepaired
• ❌ Use chloride-containing wrapping materials

6. Supplementary note

The native Al₂O₃ passive film cannot resist long-term immersion and ionic pollution. Storage protection aims to cut off the electrolyte (water + ions) required for corrosion reaction. If white oxidation spots have already formed, it cannot be removed by simple wiping; the coil surface will be permanently impaired for painting, anodizing or lamination processes.