1.How long does the rust prevention period of cold-rolled coils typically last?
Short-term protection (several days to 1 month): Use water-based rust inhibitor and store indoors temporarily;
Medium-term protection (1-6 months): Apply a thin layer of rust-preventive oil, wrap with moisture-proof paper, and store indoors;
Long-term protection (6 months to 2 years): Use displacement-type rust-preventive oil or rust-preventive wax, combined with vapor phase rust-preventive paper and composite packaging, and store in a dry warehouse;
Very long-term protection (over 2 years): Use peelable rust-preventive coatings or sealed packaging, and control ambient humidity.
2.What is the most critical factor affecting the rust prevention period of cold-rolled coils?
Surface cleanliness – If residual moisture, sweat, rolling fluid, or rust sources remain on the surface of the cold-rolled coil, the rust prevention period will be significantly shortened even after oiling.
Packaging airtightness – Using composite packaging consisting of vapor phase rust inhibitor paper, plastic film, and metal protective rings can significantly extend the rust prevention period; if simply oiled and then exposed, the rust prevention period may be shortened to one-third or even less of the original.
3.How long can cold-rolled coils typically guarantee rust protection when using displacement-type rust inhibitors?
Indoor storage: 6–12 months (normal industrial environment);
Export sea freight: 3–6 months (salt spray, high temperature and humidity, and container condensation must be considered);
Outdoor temporary storage: Not recommended; even with oiling, protection only lasts 1–2 months and is extremely risky.
Specific warranty periods must be based on salt spray test data (e.g., ASTM B117) provided by the supplier and verified under actual operating conditions.
4.How can we compare the rust prevention periods of different rust prevention solutions?
Water-based rust inhibitor (unpackaged) Several days to 2 weeks
Ordinary rust-preventive oil (outer storage) 1-3 months
Replacement rust inhibitor + moisture-proof paper: 3-6 months
5.How to determine if the rust prevention period of cold-rolled coils has reached the expected level?
Accelerated Corrosion Testing – A third party will conduct salt spray (neutral salt spray, NSS) and damp heat tests. The actual rust prevention period will be estimated based on the test hours (empirical formula: 1 hour of salt spray ≈ 1-3 days in indoor environment, but this is greatly affected by environmental fluctuations);
Simulated Storage Testing – Samples coated with rust-preventive oil and packaged will be placed in an actual warehouse or temperature and humidity alternating chamber, and the rust condition will be observed regularly;
Process Control – Establish systems for oil application quantity detection, packaging integrity inspection, and storage temperature and humidity monitoring to ensure that rust prevention measures are implemented effectively, thus ensuring the repeatability of the rust prevention period.