1.What are the main risks associated with storing cold-rolled coils during winter?
Rust-preventive oil fluidity deteriorates – at low temperatures, the viscosity of rust-preventive oil increases, leading to uneven coating and even "cold flow," with potential omissions at edges and ends;
Frosting and condensation – when cold-rolled coils are moved from outdoor low-temperature environments to indoor environments or shipping containers, frost or condensation occurs when the surface temperature is below the dew point. If not fully warmed before packaging, moisture is trapped between layers, causing corrosion;
Packaging material embrittlement – plastic films and moisture-proof paper lose toughness at low temperatures, making them prone to damage during handling or stacking;
Fluctuating storage temperature – large diurnal temperature differences or intermittent heating in warehouses cause repeated condensation on the surface of the steel coils, accelerating corrosion.
2.What are the special requirements for the selection and application of rust-preventive oil in winter?
Selection Requirements – Prioritize displacement-type rust-preventive oils with low pour points (≤-10℃) and good low-temperature fluidity to ensure uniform coating even below 5℃; some suppliers offer "winter-specific" formulations.
Preheating Treatment – If the viscosity of the rust-preventive oil is too high at low temperatures, preheat the oil (20-30℃) or the steel coil before coating to prevent uneven coating caused by cold coil contact with cold oil.
Oil Application Control – In winter, the oil application amount can be increased by 10%-15% to compensate for the reduced oil film spreadability at low temperatures, but care must be taken to avoid excessive accumulation at the edges.
Coating Timing – Oil must be applied when the steel coil is dry and the temperature is above the dew point. It is strictly forbidden to directly apply rust-preventive oil when there is frost or condensation on the surface, otherwise moisture will be sealed under the film.
3.Do packaging materials and usage methods need to be adjusted for winter?
Packaging Material Selection – In winter, use low-temperature resistant plastic films (such as LLDPE or PE films with added antifreeze) to avoid the brittleness of ordinary PVC films at low temperatures; moisture-proof paper should be stored in a warm, dry place to prevent it from absorbing moisture and freezing, thus becoming brittle.
Warm-up Before Packaging – If the steel coil is stored outdoors or transported at a temperature below 0°C, it should be allowed to warm up indoors for 12–24 hours until the temperature rises above the dew point and there is no frost on the surface before packaging.
Enhanced Sealing – At low temperatures, the adhesive strength of tape decreases; it is recommended to use low-temperature tape or use heat sealing to seal the overlaps of the plastic film. A waterproof plastic film should be placed between the bottom of the steel coil and the pallet to prevent condensation from ground cold radiation.
Vapor Phase Corrosion Inhibitor Paper – At low temperatures, the evaporation rate of the corrosion inhibitor in vapor phase corrosion inhibitor paper decreases. If the storage period is long, the dosage can be increased appropriately or combined with vapor phase corrosion inhibitor powder packets to enhance protection.
4.How should the warehouse environment be managed in winter?
Stable warehouse temperature – Avoid intermittent, large-scale temperature increases in the warehouse (such as heating during the day and stopping it at night). Otherwise, the surface of the steel coils will repeatedly experience a cycle of "heating up – cooling down – condensation," making them highly susceptible to corrosion. It is recommended to maintain a relatively constant warehouse temperature, or to allow the steel coils to fully warm up before placing them in the warehouse.
Avoid alternating hot and cold temperatures – Steel coils should not be frequently moved between low outdoor temperatures and high indoor temperatures. If movement is necessary, a buffer zone should be set up in the transition area to allow the steel coils to gradually adapt to the temperature difference.
Ground moisture prevention – In winter, the ground temperature is low, and warm, humid air easily condenses on the cold ground. Moisture-proof trays or wooden blocks must be used under the steel coils, and the ground should be checked regularly for condensation.
Ventilation strategy – When the outdoor air is dry in winter, ventilation can be used to remove moisture as needed. However, in rainy or snowy weather, or when the outdoor humidity is higher than 80%, warehouse doors and windows should be closed to prevent moisture intrusion.
5.What are the key points for inspection and maintenance during winter storage?
Condensation Inspection – Regularly inspect the inside of the packaging for water vapor or ice crystals, especially on the ends of the steel coils and the inner wall of the plastic film. If condensation is found, the packaging should be opened in a dry environment, re-dried, and then oiled.
Packaging Damage – Inspect the plastic film for low-temperature brittleness and check for detached sealing tape, paying particular attention to the edges of the steel coils and lifting contact points. Damaged areas should be repaired promptly with low-temperature resistant tape or covered with a waterproof cover.
End Face Corrosion – In winter, edge corrosion often occurs in hard-to-detect locations inside the packaging. Wipe the edges of the steel coil ends with a white cloth to check for yellow rust. Regular random checks and unpacking are also recommended.
Snow and Meltwater – If the steel coils are stored in sheds or in the open air, promptly remove snow from the top after snowfall to prevent meltwater from seeping into the packaging. Check that drainage around the warehouse is unobstructed to prevent meltwater backflow.
Temperature and Humidity Recording – It is recommended to install a thermometer and hygrometer in the warehouse to record daily minimum temperature and relative humidity changes. This will help trace the cause of corrosion and adjust protection strategies.