Packing is the quietest clause in a steel contract and the one that decides who pays when a container is opened. A buyer who has spent a week arguing over coating mass will often accept "standard export packing" without a second look, then discover at the port that the coils arrived with white rust along the outer wraps, or that the load could not be lifted because the eye was vertical on a box with no headroom for a spreader. Most of those outcomes come down to four numbers: coil weight, inside diameter, eye orientation, and legal payload.

Start from the coil, not the container

Coil weight on coated stock is normally quoted in the 3 to 5 tonne band, as the Z275 galvanized steel coil data sheet states, though heavier programmes run higher: the DX51D+Z galvanized coil listing gives 3 to 8 tonnes, prepainted programmes reach 3 to 20 tonnes per coil on the PPGL prepainted galvalume coil page, and the 304 and 304L stainless steel coil range quotes 3 to 10 tonnes. Inside diameter is 508 mm or 610 mm.

Those figures drive the lashing plan. A 3 tonne coil can be handled with a C-hook or a coil ram on a heavy forklift; a 20 tonne prepainted coil needs a lifter, a spreader beam and a dunnaged floor. Splitting the tonnage into lighter coils eases handling but wastes cube, since each coil carries its own eye void and clearance. Eye orientation then decides the rest: eye-to-sky coils stack on their flat faces and brace well against each other but cannot be lifted without a boom, while eye-to-horizontal gives a cleaner lifting path through the bore at the cost of floor area per tonne.

Four layers, and what each one is doing

The inner wrap is a moisture barrier: waterproof or anti-rust paper, and on some programmes VCI paper that releases a vapour-phase corrosion inhibitor, sits directly against the coil face. The outer wrap is mechanical protection. The hot dipped galvanized steel coils and SECC electro-galvanized coil pages state "standard export package" without detail, but the PPGL coil specification spells the build-up out: waterproof paper inner, galvanized or coated steel sheet outer, side guard plates, then seven steel belts. The steel outer skin does real work: it takes the strap tension and the knocks instead of the coating.

Belts and pallet come next. Strapping should align with the guard plates rather than bite into the coil face, and the number of bands should scale with coil width. The galvanized coil listing offers horizontal packing on a wooden pallet, packing without a pallet, or vertical packing on a pallet, and those are genuinely different products in transit. A pallet keeps the coil off a wet container floor and lets a forklift lift the whole unit without touching the steel; a pallet-free coil saves cube but depends on the floor staying dry.

Weight first, then cube

Container selection for coil is almost always a weight decision. A 20 ft general purpose box measures 5898 by 2352 by 2393 mm and a 40 ft GP measures 12032 by 2352 by 2393 mm, with a 40 ft high cube adding roughly 300 mm at 2698 mm, as listed on the stainless steel coil page. Usable volume is quoted there as 24 to 26 CBM for the 20 ft, 54 CBM for the 40 ft GP and 68 CBM for the high cube.

Coil shipments fill by mass long before they fill by space. With a payload around 25 to 28 tonnes, a 20 ft box takes roughly six to eight coils in the 3 to 5 tonne band, which is why the 25 tonne minimum order quoted as one 20 ft FCL on the galvanized steel plate and galvanized processing product pages exists. Heavier coils reduce the count and worsen cube utilisation. Where the order is plate or cut sheet, the constraint flips back to volume and pallet height becomes the limiting dimension.

Moisture is the mechanism behind most arrival claims

White rust on galvanized or galvalume surfaces is not usually a torn wrap. It is a condensation cycle. A container loaded in a warm, humid yard and shipped through cooler nights will breathe: moisture condenses on the coldest surface, which is the steel. The zinc surface forms an oxide that converts to zinc carbonate in the presence of carbon dioxide, and the pale chalky staining that results ends up as a claim against the galvalume steel coil or galvanized steel order at destination.

The countermeasures are simple. Do not pack a coil still warm from the line, because the trapped moisture has nowhere to go. Use breathing paper rather than a fully sealed plastic envelope on long sea voyages; a film that keeps rain out also keeps condensation in, and desiccant should be sized to the number of air exchanges. Where the product is oiled, confirm the oil was applied before packing, since the ST02Z galvanized coil and duplex stainless steel coil options list oiled and non-oiled surfaces as separate specifications, and drying in transit is normal.

Sheet, plate and corrugated packs

Flat products fail differently. The galvalume steel roofing sheet listing describes a plastic film and cardboard cover over the stack, on wooden pallets with iron strapping, loaded in containers, which is the standard pattern. The weakness of a sheet stack is edge damage: strapping tightened onto a square corner creases the outer sheets, and on prepainted stock that crease is a paint defect. Edge protectors along the strap line cost very little and remove the most common sheet claim.

Corrugated panels add a second variable, nesting. Nested profiled sheets do not stack to their nominal thickness, and the real height of a pack depends on the profile pitch, so loaded height should be checked against the container internal height rather than estimated from the sheet count. Programmes such as the TDC51D+Z prepainted galvanized coil and the cold rolled aluzinc galvalume coil ranges are where this arithmetic goes wrong most often, because the parent coil and the finished profile are ordered in different units.

What to write into the purchase order

A packing clause that protects a buyer is short. State the coil weight band and the inside diameter, because those control handling. State the eye orientation. Require an inner moisture barrier and a steel or coated outer skin, with a stated number of bands keyed to coil width. Require palletised or non-palletised packing explicitly. Require the shipping mark stencilled on the outer wrap rather than printed on a label that will not survive the voyage. Where the order includes cut-to-length or profiled material, extend the same clauses to the finished packs, which the custom processing and steel plate shear services produce in a different physical form from the parent coil, and which the hot rolled steel coil range ships to the same rules.

None of this adds significant cost. All of it determines whether the container that leaves the mill is the container that arrives on the buyer's floor, and whether the dispute that follows is about the steel or about the packing. The second kind is much easier to avoid than to win.