Stainless steel is not absolutely rust-free. Common causes:

1) Iron powder adhering to the surface: mixed storage with carbon steel, shared lifting gear or grinding wheels; iron powder contamination leads to localized rust. 2) Chloride environment: high humidity and salt-laden air in coastal areas can destroy the passive film. 3) Water accumulation inside packaging: wooden crates or paper packaging absorb moisture, and long-term enclosure leads to pitting corrosion. 4) Incomplete pickling: residual oxidation color on welds becomes the starting point for corrosion.

Prevention: store by zone, use dedicated lifting gear, dry dunnage, ensure ventilation, and cover with rainproof tarpaulins when necessary but do not seal.