1.What are the main risks associated with storing cold-rolled coils along the coast?
Salt spray corrosion-Chloride ions (Cl⁻) carried by sea breezes can damage the passivation film on metal surfaces. Even trace amounts penetrating into the packaging can cause pitting corrosion on the steel coil surface, with a corrosion rate 3 to 5 times faster than in humid inland environments.
Sustained high humidity-The average annual relative humidity in coastal areas is often above 80%. Diurnal temperature variations easily lead to frequent condensation. Moisture and salt combine to form a strong electrolyte solution, accelerating electrochemical corrosion.
Strong winds carrying salt-During typhoons or strong winds, salt-laden air can penetrate ordinary packaging gaps, directly corroding the ends and edges of the steel coil.
Temperature differences and condensation-Large diurnal temperature variations in maritime climates cause repeated condensation on the surface of the steel coil and inside the packaging, creating alternating wet and dry conditions that accelerate corrosion.
Typhoons and torrential rains-Frequent typhoons in coastal areas, accompanied by heavy rainfall and storm surges, can lead to flooding of warehouses, packaging damage, and even immersion of steel coils.
2.What are the special requirements for the selection and application of rust-preventive oil when storing goods in coastal areas?
Selection Requirements-
A displacement-type rust inhibitor that has passed a neutral salt spray (NSS) test for ≥72 hours (or even ≥120 hours) must be selected. Ordinary rust inhibitors may have their rust protection period shortened by more than 70% under salt spray conditions.
The oil should possess resistance to chloride ion penetration, forming a dense barrier on the metal surface to prevent salt from contacting the substrate.
High flash point, low volatility heavy-duty rust inhibitors are recommended to ensure long-term oil film stability under high temperature and high humidity conditions.
Coating Coverage Requirements-The coating coverage in coastal environments should be 30%–50% higher than inland (e.g., The coating strength should be increased from the standard 1.5 g/m² to 2.0–2.5 g/m², ensuring full coverage of weak areas such as edges, end faces, and welds.
Coating Process – A double-coating process is recommended (apply a second coating after the first one has partially dried) to ensure a continuous and dense oil film. Before coating, the steel coil surface must be absolutely dry and free of salt residue (if salt stains are present, they must be cleaned first).
Quality Inspection – After coating, a film thickness gauge should be used for random sampling to ensure the oil film is uniform and meets the thickness standard. It is recommended to conduct salt spray tests on each batch to verify the protective effect.
3.What special reinforcement measures should be taken for packaging when storing goods in coastal areas?
Packaging Structure Upgrade-
Inner Layer: Vapor phase corrosion inhibitor paper is tightly adhered to the steel coil surface, releasing corrosion inhibitors to fill tiny gaps;
Middle Layer: A high-barrier moisture-proof film (such as VCI anti-rust film or aluminum-plastic composite film) is used, providing excellent moisture resistance and salt spray barrier capabilities;
Outer Layer: Metal protective rings and end face plates are added to prevent the plastic film from being punctured by strong winds or during handling;
Bottom: A fully enclosed waterproof base or plastic pallet with a waterproof membrane is used to prevent ground water and salt intrusion;
Sealing is essential. Required –
Packaging must be completely heat-sealed or sealed with weather-resistant sealing tape, eliminating any gaps;
The overlap between the end face protective plates and the plastic film at both ends of the steel coil should be double-sealed (inner seal + outer cover);
An airtightness test (such as a pressure test) should be performed after packaging to ensure there are no leaks;
Enhanced Vapor Phase Protection –
Additionally place vapor phase corrosion inhibitor packets (50% more than inland) inside the core and end face packaging of the steel coil to compensate for the accelerated consumption of corrosion inhibitors in high temperature and high humidity environments;
4.How should coastal warehousing environments be selected and managed?
Warehouse Site Selection and Construction-
Prioritize indoor warehouses located at least 5 kilometers from the coastline, away from areas directly exposed to sea breezes;
Warehouses should have sealed doors and windows, and be equipped with a salt spray filtration ventilation system (with salt spray filters at the air inlets);
The floor must be made of high-strength, impermeable concrete and coated with epoxy flooring to prevent moisture buildup from salt;
Temperature and Humidity Control-
The relative humidity inside the warehouse must be controlled below 60%; if it exceeds this level, a dehumidifier should be activated;
The warehouse temperature should be kept stable to avoid excessive day-night temperature differences that could cause condensation;
A temperature and humidity recorder should be installed to monitor and store data for future reference;
Salt Spray Isolation-
Warehouse windows should be sealed to reduce the intrusion of external salt spray;
A salt spray-resistant green belt or windbreak wall can be planted around the warehouse to reduce salt spray concentration;
5.What are the key points for inspection and maintenance during coastal storage?
Salt Spray Deposition Inspection-
Set up salt spray detection strips (copper or zinc) in the warehouse and regularly observe corrosion to assess the degree of salt spray intrusion;
Inspect the outer surface of the packaging for white salt deposits. If found, clean them immediately and check the packaging seal;
Packaging Integrity Inspection-
Focus on checking for damage to the plastic film, cracks at the heat seal, and displacement of the end face panels;
A comprehensive inspection must be conducted after a typhoon or strong wind. If any damage is found, immediately repackage in a dry environment (do not simply repair);
Internal Condition Monitoring –
Monthly random inspection of 1-2 steel coils, unpacking and checking for rust on the ends and edges, integrity of the oil film, and discoloration of the vapor phase rust inhibitor paper due to moisture;
If internal condensation or thinning of the oil film is found, a wider inspection of the same batch of steel coils is required, and protective measures should be adjusted;
Early Rust Treatment –
When minor rust spots are found, they should be removed immediately in a dry environment, the oil should be reapplied, and the packaging replaced;
Simply do not "touch up" rusted steel coils inside the packaging, otherwise the residual salt will continue to corrode;