The atmospheric gases — oxygen, nitrogen and argon — separated from air, plus carbon dioxide, hydrogen and fuel gases, used throughout steelmaking, heat treatment, cutting and welding. A modern EAF plant uses tens of cubic metres of oxygen per tonne of steel, which is why large steel plants have their own air separation units beside the melt shop.
Oxygen, nitrogen and argon are produced by cryogenic air separation: air is compressed, cleaned, cooled until it liquefies and distilled, and each component draws off at its own boiling point. Small and medium users take gas in high-pressure cylinders or liquid in insulated tanks; steel plants and other large consumers have air separation units on or beside the site, run by a gas company under a long-term supply contract and delivering by pipeline. Vacuum and pressure swing adsorption units supply lower-purity oxygen and nitrogen more cheaply on site.
In steelmaking oxygen is the main tonnage gas: it is blown into BOF converters, injected through lances and burners in electric arc furnaces to refine the steel and add chemical energy, and used to cut and scarf. Argon stirs steel in the ladle, shrouds it in casting and decarburises stainless steel in AOD converters, where nitrogen is also used; nitrogen and hydrogen make the protective atmospheres of annealing furnaces and continuous galvanizing lines.
In fabrication the gases are shielding gases and fuel gases. ISO 14175 classifies shielding gases by composition — I1 is pure argon, C1 pure CO₂, M21 an argon mix with 15–25% CO₂, the most common MAG welding gas for carbon steel — and welding procedures name the classification. Oxygen with acetylene, propane or LPG cuts steel; nitrogen and compressed air are used for plasma and laser cutting.
Industrial gases in the GCC are supplied by international and regional gas companies that run air separation plants serving the steel, petrochemical, glass and fabrication industries, with cylinder filling stations in every country. The larger DRI-EAF plants are served by dedicated on-site ASUs.
| Region | Standard | What it covers |
|---|---|---|
| International | ISO 14175 ISO |
Welding consumables — gases and gas mixtures for fusion welding and allied processes (classification I1, C1, M21 …) |
| USA | AWS A5.32/A5.32M AWS |
Welding consumables — gases and gas mixtures for fusion welding (an adoption of ISO 14175) |
| International | ISO 9809-1 ISO |
Gas cylinders — refillable seamless steel gas cylinders — quenched and tempered steel |
| Europe | EN 1089-3 CEN-CENELEC |
Transportable gas cylinders — gas cylinder identification — colour coding |
| International | ISO 7225 ISO |
Gas cylinders — precautionary labels |
| International | ISO 2503 ISO |
Gas welding equipment — pressure regulators for gas cylinders |
Grade equivalents and the standards bodies: Steel grades & standards
Fabrication · Contractors · Other Steel Users · Mathra
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