Failure mode
Water Staining & White Rust in Transit
The container opens and the sheet or coil face carries white blotches or dried water marks that do not wipe off. It is cosmetic on some products and rejectable on others, and it always raises the question of who owns it.
What it actually is
The container opens and the sheet or coil face carries white blotches or dried water marks that do not wipe off. It is cosmetic on some products and rejectable on others, and it always raises the question of who owns it.
Mechanism
Why it happens
Four causes account for most of it. They are not equally common, and they are not equally within the mill's control.
Condensation inside the packing
Temperature swings over a long sea leg pull moisture out of the air inside a sealed package. This is the dominant cause and it happens after the mill has done everything right.
Residual moisture at packing
If the surface is not dry when it is wrapped, the moisture is sealed in with the metal.
Insufficient desiccant
Desiccant is sized to the package volume and the voyage length. Undersized desiccant is exhausted before arrival.
Container not sealed against humidity
A container without internal drying capacity leaves the packing doing all the work.
Verification
How it is measured
Inspect and photograph within the claim window — typically inside 48 hours to 14 days of arrival depending on the contract. Distinguish water staining from mechanical damage and from mill-origin surface defects; they have different causes and different responsible parties.
Specification
How to specify around it
Most of these cost nothing to write into an order and are difficult to enforce afterwards. This is the part worth copying into your next RFQ.
1
Describe the packing
Kraft and PE film, edge protectors, steel-strapped wooden pallet, desiccant, fumigation certificate. Name the components rather than writing "export packing".
2
Require a dry surface at packing
Say it. It is cheap to comply with and expensive to argue about later.
3
Size the desiccant to the voyage
Long or high-humidity routes justify VCI paper and container desiccant in addition to the in-package sachets.
4
Agree the claim window in advance
A stated number of days from arrival protects both sides. Unstated, it becomes a negotiation.
Packing is photographed before the container is sealed, and desiccant quantity is set against the voyage rather than against a fixed count. Our claim window is stated in the FAQ and in the quotation terms so it is settled before it is needed, not after.
We do not claim this never happens. Metal is rolled, shipped across an ocean and unloaded by someone else. What we do is ask the question before the order runs, put the answer in writing, and be the single party that answers for it afterwards.
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