Cold rolled or hot rolled steel strip passed continuously through a bath of molten zinc, which leaves a metallurgically bonded zinc coating on both sides. Galvanized iron (GI) is the most used coated steel in the Middle East: roofing and wall sheet, ducting, purlins, light-gauge framing and the substrate for pre-painted coil are all made from it.
Also called
GI
GI coil
Galvanized sheet
HDG coil
Zinc coated steel
Galvanised steel
DX51D+Z
SGCC
Z275
G90
AR
لفائف وألواح الصلب المجلفن بالغمس الساخن
ZH
热镀锌卷板和镀锌板
DE
Feuerverzinktes Band und Blech
FR
Bobines et tôles galvanisées à chaud
ES
Bobinas y chapas galvanizadas en caliente
IT
Coils e lamiere zincati a caldo
TR
Sıcak daldırma galvanizli rulo ve sac
RU
Горячеоцинкованный рулонный и листовой прокат
Main formsCoils, cut sheets, slit coil, corrugated and profiled sheet; regular, minimised or zero spangle
Typical sizesThickness 0.12–4.0 mm (0.25–2.0 mm most traded); width 600–1,850 mm; coating Z60–Z600
Main standardsEN 10346, EN 10143, ASTM A653 / A924, JIS G3302, GB/T 2518, IS 277, AS 1397
Typical usesRoofing and cladding, HVAC ducts, purlins and framing, cable trays, appliances, pre-painted coil substrate
Overview
On a continuous galvanizing line the steel strip — usually full-hard cold rolled coil, or pickled hot rolled coil for thicker gauges — is cleaned, annealed in a reducing atmosphere and dipped in a zinc bath at about 450–460 °C containing a small amount of aluminium. Air knives above the bath wipe the coating to the ordered mass, and the strip is then cooled, skin-passed, passivated or oiled, and recoiled. The zinc forms an alloy layer with the steel, so the coating does not flake off when the sheet is bent or roll-formed.
Zinc protects steel in two ways: as a barrier, and sacrificially, corroding in preference to the steel at scratches and cut edges. Life is roughly proportional to coating mass, which is why the coating class matters as much as the steel grade. Z275 (275 g/m² total on both sides, about 20 µm per side), the same as G90 in ASTM terms, is the usual specification for building products in the GCC; lighter coatings are used indoors and under paint. Coastal and industrial atmospheres in the Gulf are aggressive, and for long exposed life aluminium-zinc coated Aluzinc / Galvalume or a painted system is often chosen instead.
The coating crystallises as it solidifies into a visible pattern — the spangle. Regular spangle is normal for unpainted building sheet; minimised or zero spangle, with a smoother surface, is preferred for painting. The surface is protected against white rust (storage stain) by chemical passivation (now usually chromium-free), by oiling or by both, and must be kept dry in transit.
Steel grades follow the substrate's purpose: DX51D to DX57D in EN 10346 for forming, and S220GD to S550GD for structural uses such as purlins, decking and light-gauge framing, where full-hard G550 / S550GD is common. The GCC has galvanizing lines in Saudi Arabia, the UAE and other countries, many of them fed with imported cold rolled coil, alongside large imports of GI from China, India, Korea and Turkey. MESteel publishes monthly prices for galvanized coil on HR base, 2 mm and on CR base, 1 mm.
Forms & sizes
GI is ordered by base metal thickness × width, coating class and spangle. Thickness may be quoted as base metal thickness (BMT) or total coated thickness (TCT), which includes the zinc — state which one is meant. Corrugated and trapezoidal roofing sheet is roll-formed from GI coil — see corrugated sheets.
Coils
0.12–4.0 mm thick, 600–1,850 mm wide; coil weight 3–25 t; inside diameter 508 or 610 mm
Sheets
Cut to length, commonly 1000 × 2000, 1220 × 2440 and 1250 × 2500 mm
Coating
Z60 to Z600 in EN terms (G30–G235 in ASTM); Z275 / G90 standard for building, Z100–Z180 for indoor parts and painting
Spangle
Regular, minimised or zero spangle; skin-passed for painting
Surface treatment
Chemical passivation (chromium-free in most markets), oiled, passivated and oiled, or anti-fingerprint
TSI METAL INDUSTRIES LLCAESteel Mills - Agents & Traders · Tube Manufacturer · Stockist - Distributor · Dubai
Gold
SellsCold Rolled, Hot Rolled, Hot Rolled Plates, Beams & Sections +8 BuysCold Rolled, Stainless HR Coils, Hot Rolled, Chemicals for descaling and pickling +8
TSI METAL INDUSTRIES LLCAESteel Mills - Agents & Traders · Tube Manufacturer · Stockist - Distributor · Dubai
Gold
SellsCold Rolled, Hot Rolled, Hot Rolled Plates, Beams & Sections +8 BuysCold Rolled, Stainless HR Coils, Hot Rolled, Chemicals for descaling and pickling +8
Steel Mills - Agents & Traders · Stockist - Distributor · Base Materials · Dubai
