What it is
Galvanized coil (GI) is flat steel hot-dip coated with zinc for corrosion resistance, used in roofing, cladding, ducting, and framing. The zinc coating weight determines both corrosion life and price, and because it is invisibly thin it is the single most defrauded spec in flat steel.
Grades & standards buyers order
| Grade | Standard | Notes |
|---|---|---|
| DX51D / DX52D | EN 10346 | Standard hot-dip galvanized forming grades. |
| SGCC | JIS G3302 | Commercial galvanized grade. |
| Coating: Z275, Z180, Z120 | EN 10346 | Zinc grams per m² both sides — the number you must verify. |
How it's sold: Sold by metric ton in coils, thickness ~0.2mm–2mm, coating class in g/m². Confirm coating weight, spangle, and passivation/oiling.
What drives the price
- Base steel cost plus zinc (zinc price is volatile)
- Coating weight — Z275 costs materially more than Z120
- Thickness and width
- Surface treatment (chromated, oiled, spangle)
Lock these into the contract before you pay
Coating weight in g/m² both sides
The whole price difference lives here; specify Z275 (or your class) and require testing.
Test method for coating
Name magnetic gauge or strip test and require sampling across the coil, not one point.
Base metal thickness (excl. coating)
Some quotes include coating in thickness to inflate the number.
Scams most common to gi coil
Coating-Weight & Galvanizing Fraud
Z120 or lighter coating shipped and invoiced as Z275 — the flagship galvanized fraud.
Forged Mill Test Certificates (MTC / EN 10204 3.1)
A certificate stating the ordered coating weight the coil does not actually carry.
Bait-and-Switch Quality
A correctly coated sample followed by under-coated production coils.
Red flags in a quote or sample
- Price too low for the quoted coating class
- Coating weight quoted vaguely ("heavy zinc") with no g/m² figure
- Thickness that appears to include the zinc layer
Already paid and something's wrong?
If you received off-spec gi coil, a certificate that doesn't match, or your supplier has gone quiet after a deposit, move quickly. Recovery odds drop with every day that passes on a wire transfer.
Buying gi coil from China: FAQ
What grades of gi coil can I buy from China?
The most commonly ordered grades are DX51D / DX52D, SGCC, Coating: Z275, Z180, Z120. Always pair the grade with its standard on the purchase order so the mill test certificate can be matched to what you actually receive.
What is the most common scam when buying gi coil from China?
Coating-Weight & Galvanizing Fraud. For this product specifically: Z120 or lighter coating shipped and invoiced as Z275 — the flagship galvanized fraud. The defense is to specify the exact grade and standard, require a verifiable mill test certificate, and commission independent pre-shipment inspection.
What should I check before paying for gi coil?
Lock down coating weight in g/m² both sides, test method for coating, base metal thickness (excl. coating) in the contract, verify the supplier is a real manufacturer, and never release the balance until an independent inspection confirms the goods.
I already paid a Chinese supplier for gi coil — what now?
Act fast: contact your bank about a recall on the wire, gather all contracts and communications, report the pattern so others are warned, and review the documented cases to understand your options. The sooner you act on a redirected or disappeared payment, the better the odds.
Related product guides
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HR coil
The base flat product for tubes, plate, and re-rolling. Grade substitution and thickness/gauge shortfall are the primary risks.