CO₂ grades and purity
Carbon dioxide (CO₂) behaves differently from the other industrial gases, and it catches buyers out. In a cylinder it is not a compressed gas at all — it is a liquid under its own vapour pressure, roughly 57 kg/cm² at room temperature. That single fact explains most of what is unusual about handling it.
Grade matters more here than in almost any other gas, because CO₂ goes into food and drink. Food-grade CO₂ is a different product from welding CO₂, with different purity control and traceability, and the two are not interchangeable.
| Grade | Typical purity | Where it is used |
|---|---|---|
| Industrial CO₂ | 99.5%+ | General process use, pH control, inerting, fire suppression |
| Welding-grade CO₂ | 99.5%+, low moisture | MIG/MAG welding of carbon and low-alloy steel; moisture control is critical to avoid weld porosity |
| Food-grade / beverage CO₂ | To food-contact requirement | Carbonation, modified-atmosphere packaging, brewing, cellar gas |
| High-purity CO₂ | 99.99%+ | Laboratory, incubators, analytical and specialty applications |
CO₂ specification in India is commonly cited against IS 307. Confirm the revision your inspection authority requires before order and we will certify against it. For food and beverage use, specify food grade explicitly — never assume industrial CO₂ will be accepted.
What carbon dioxide is used for
- ✓MIG/MAG welding of carbon and low-alloy steel — as pure CO₂ or in argon-CO₂ mixtures
- ✓Beverage carbonation, draught dispense and cellar gas
- ✓Modified-atmosphere packaging (MAP) to extend shelf life of meat, bakery and fresh produce
- ✓Brewing, winemaking and beverage-line purging
- ✓pH control and neutralisation in water and effluent treatment — cleaner and safer to handle than mineral acid
- ✓Inerting and blanketing where an inert, heavier-than-air gas is wanted
- ✓Fire suppression systems and portable extinguishers
- ✓Greenhouse enrichment and controlled-atmosphere storage
- ✓Dry-ice production for cold chain and cleaning
CO₂ in welding: what actually matters
Pure CO₂ gives deep penetration and costs less than argon-based mixtures, which is why it remains popular for structural steel. The trade-off is a harsher arc and noticeably more spatter than an argon-CO₂ blend.
The failure that costs shops the most is moisture. CO₂ is supplied as a liquid, and gas drawn off carries whatever moisture the cylinder holds; wet CO₂ produces hydrogen porosity in the weld. If you are seeing porosity on clean steel with sound technique, check the gas and the cylinder before anything else.
| Shielding gas | Penetration | Spatter | Typical use |
|---|---|---|---|
| Pure CO₂ | Deepest | Highest | Structural and heavy carbon steel, cost-driven work |
| Argon-CO₂ 80:20 | Good | Low | General fabrication, thin to medium carbon steel |
| Argon-CO₂ 82:18 | Good | Low | Spray-transfer MIG on carbon and low-alloy steel |
How CO₂ is supplied, and how to draw it
Because the cylinder contains liquid CO₂, it is charged and sold by weight, not by volume — a point that surprises buyers used to ordering nitrogen or argon by cubic metres. A standard industrial cylinder typically holds around 30 kg of liquid CO₂.
Withdrawal rate is the other practical constraint. Every kilogram of CO₂ that vaporises absorbs heat from the cylinder, so drawing gas too fast chills the cylinder, drops the vapour pressure and can freeze the regulator solid. Where a high continuous flow is needed, the answer is a manifolded bank drawing from several cylinders at once, or a heated vaporiser — not a bigger regulator.
| Packaging | Typical content | Suits |
|---|---|---|
| High-pressure cylinder | ~30 kg liquid CO₂ | Welding shops, beverage dispense, laboratory use |
| Cylinder bank / quad | Multiples of cylinder weight | Production welding, bottling lines, continuous draw |
| Manifolded bank with changeover | Continuous | Applications that cannot tolerate a supply break or regulator freeze-up |
| Siphon (dip-tube) cylinders | ~30 kg liquid CO₂ | Where liquid CO₂ is required rather than gas — dry ice, some fire systems |
Siphon cylinders draw liquid rather than gas and are identified separately. Fitting one to a gas application, or a gas cylinder to a liquid application, will not work and can be dangerous — tell us which you need.
Cylinder identification and safety
Under IS 4379, carbon dioxide cylinders have a black body with a white neck band. This is worth flagging on any mixed site: oxygen cylinders are also black, and the white band is the distinguishing mark. Always read the label as well as the colour.
CO₂ is non-flammable, but unlike nitrogen and argon it is not simply an asphyxiant — it is physiologically active. At around 5% in air it causes headache and laboured breathing; higher concentrations cause rapid unconsciousness. It is also markedly denser than air and collects in cellars, pits and basements, which is why beverage cellars and bottling plants are the classic incident sites.
- ✓Fit CO₂ monitoring and alarms in cellars, basements and any enclosed area where CO₂ is stored or used
- ✓Ventilate low-lying spaces; never enter a cellar showing an alarm condition
- ✓Secure cylinders upright with valve caps fitted; a dropped CO₂ cylinder holds a great deal of stored energy
- ✓Do not warm a cylinder with a flame to raise pressure — use a bank or a proper vaporiser
- ✓Protect skin and eyes from liquid CO₂ and dry ice — contact causes cold burns
- ✓Use only regulators rated for CO₂ service pressure, with the correct connection
Why buy CO₂ from IIGAS
IIGAS has supplied industrial gases since 1947 and sits on the BIS committees CHD 6 (Industrial Gases) and MED 16 (Gas Cylinders). CO₂ is supplied with documented purity, grade-appropriate handling, and correct identification — with food grade treated as the distinct product it is, not as industrial gas with a different label.
Tell us the application rather than a purity number, and we will specify the grade, packaging and draw arrangement that actually suits it.
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